Corrosion inhibitors

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CHEMISTRY RESEARCH AND APPLICATIONS

CORROSION INHIBITORS PRINCIPLES, MECHANISMS AND APPLICATIONS

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CHEMISTRY RESEARCH AND APPLICATIONS

CORROSION INHIBITORS PRINCIPLES, MECHANISMS AND APPLICATIONS

ESTHER HART EDITOR

New York

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NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

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Published by Nova Science Publishers, Inc. † New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

vii Organic Corrosion Inhibitors and Industrial Applications Gözde Tansuğ and Tunç Tüken Application of Polymer Composites and Nanocomposites as Corrosion Inhibitors Saviour A. Umoren and Moses M. Solomon Uses of Environmentally Friendly Corrosion Inhibitors in Amine-Based CO2 Absorption Processes Amornvadee Veawab, Sureshkumar Srinivasan and Adisorn Aroonwilas The Effectiveness of Copaiba Oil Loaded into a Microemulsion System as a Green Corrosion Inhibitor Denise P. Emerenciano, Ana Carla C. Andrade, Melyssa L. de Medeiros, Maria de Fátima V. de Moura and Maria Aparecida M. Maciel Corrosion Mechanism and Inhibitors for Al Based Particulate Metal Matrix Composite (APMMCs) Ajay Singh Verma, Sumankant and N. M. Suri

1

27

59

79

105

vi Chapter 6

Index

Contents Electrochemical Study of 1,3,4-Triazolium-2-Thiol as a Corrosion Inhibitor of Mild Steel in Saline Medium Jardel D. Cunha, Cátia G. F. T. Rossi, Djalma R. Silva, Ewerton R. F. Teixeira, Aurea Echevarria and Maria Aparecida M. Maciel

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PREFACE This book discusses principles, mechanisms and applications of corrosion inhibitors. Chapter One focuses on organic corrosion inhibitors and their industrial applications. Chapter Two explores the application of polymer composites and nanocomposites as corrosion inhibitors for different metal substrates in different corrosive media. Chapter Three provides a review of corrosion inhibitors and a progress towards use of environmentally friendly corrosion inhibitors in the amine-based CO2 absorption process for acid gas treatment and carbon capture. Chapter Four studies the effectiveness of copaiba oil loaded on microemulsion systems as green corrosion inhibitors. Chapter Five addresses the mechanism of corrosion for APMMCs, and discusses different methods of inhibition to corrosion for APMMCs. Chapter Six focuses on the electrochemical study of 1,3,4-triazolium-2-thiol as a corrosion inhibitor of mild steel in saline medium. Chapter 1 – Organic corrosion inhibitors have been frequently studied, since they offer simple solution for protection of metals against corrosion in aqueous environment. Thus, there are many commercialized corrosion inhibitors for industrial applications like; cooling systems, pipelines, oil and gas production units, boilers and pickling process etc. The largest amount of inhibitor is demanded by cooling water systems and it is the fact that inorganic inhibitors (phosphates, tungstate, molybdate etc.) are still widely used in this area. For such engineering purposes, the required inhibitor is anticipated to assemble chemisorbed film (preferably monolayer), either by direct adsorption on metal surface or forming insoluble complex with metal ions existing at the interface. For copper and its alloys, there have been numerous chemical formulations based on organic inhibitors. However, steel has been the most widely used material, and there is a need for further development in the

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application of organic inhibitors for protection of steel against corrosion. On the other hand, there has been an increasing concern about the use of “green” chemicals for such purposes and this consideration also urges the investigations subjecting the organic corrosion inhibitors. For this purpose, molecular design and synthesis of novel organic inhibitors have been pronounced as a promising way, for tailoring one compound equipped with multitasking. On the other hand, it is necessary to develop new approaches (methods) for the assessment of corrosion inhibitor performance, in practical application conditions. Because, there are many parameters (temperature, pH, composition of corrosive media, etc.) that should be evaluated carefully for success of the application, in order to avoid excess chemical use or insufficient protection. Possible interference between the critical parameters should also be taken into account, for convenient application. For this reason, statistical evaluations should be carried out with data obtained from various routes employed to determine the corrosion rate. Generally, the preferred method is based on electrochemical techniques, and utilizes Tafel and Stern-Geary methods. Solution assay analysis, weight loss measurements have also been widely employed, since they offer simplicity for quantification of corrosion rate. This paper focuses on the interpretations of these addressed issues, with the theory and review of recently published studies in relevant field. Chapter 2 – Corrosion commonly defined as the deterioration of a material (usually a metal) or its properties because of a reaction with its environment is a global problem. NACE International, The Corrosion Society, estimates that global corrosion costs can be about 3–5% of GDP or GNP. Methods commonly adopted to combat corrosion include coatings and linings, cathodic protection, materials selection and corrosion inhibitors. Corrosion inhibitors are chemicals that, when present in very low concentrations, retard corrosion. Corrosion inhibitors form a layer over the metallic substrate and protect the metal from corrosion, thereby enhancing the life of the metal. Polymers, both naturally occurring and synthetic have been tested for metal corrosion inhibitors as replacement for the toxic inorganic and organic corrosion inhibitors. Interest in polymers stems from their availability, cost effectiveness, and eco-friendliness in addition to the inherent stability and multiple adsorption centers. However, it is found that most polymer materials studied are moderate corrosion inhibitors. Several attempts such as copolymerizing, addition of substances that exert synergistic effect, cross linking, blending, and most recently incorporation of inorganic substances in nano size into the polymer matrix have been made to improve the inhibition ability of polymers. Composites are materials consisting of two or more

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chemically distinct constituents on a minute-scale, having a distinct interface separating them, and with properties which cannot be obtained by any constituent working individually. The production of composite materials is either by ex-situ or in-situ formation through chemical synthesis although electrochemical method had been used recently. The application of polymer composites and nanocomposites as anticorrosion materials have shown promising results and are believed to form metal chelate which could barricade metal surfaces from corrosive agents. In this chapter, the application of polymer composites and nanocomposites as corrosion inhibitors for different metal substrates in different corrosive media is explored. Chapter 3 – Corrosion is a severe operational problem in the carbon dioxide (CO2) absorption process using aqueous solutions of amines, when carbon steel is used for plant construction. Past experiences with these plants have provided practitioners with a number of recommendations to keep corrosion under acceptable levels. Among these, the application of corrosion inhibitors is the most widespread because it is economical and requires small or no process modifications to existing plants. Various corrosion inhibitors have been developed, patented and commercialized by many major chemical companies for uses in amine treating plants. The patented organic inhibitors include thiourea and salicyclic acid, while inorganic inhibitors are vanadium, antimony, copper, cobalt, tin and sulfur compounds. The inorganic inhibitors are in practice more favored than the organic compounds because of their superior inhibition performance. Vanadium compounds, particularly sodium metavanadate (NaVO3), are the most extensively and successfully used in amine treating plants. Despite the successful use of the inorganic corrosion inhibitors, concerns about impacts of their toxicity on human health and the environment have increased in past decades. To respond to the environmental concerns on the use and disposal of harmful chemicals, a number of initiatives were taken around the world. In Canada, usage of toxic substances is regulated by the Canadian Environmental Protection Act (CEPA). Inorganic arsenic and cadmium inhibitors are classified as carcinogenic and considered toxic. As a result, their usage was banned. In the US, the Environmental Protection Agency (EPA) regulates the usage of chemicals through Clean Water Act (CWA) and Clean Air Act (CAA). In Europe, an environmental regulatory mechanism OSPAR was established by fifteen Northeast Atlantic nations to protect the marine environment which was later broadened to cover land based sources and offshore industry. Based on the OSPAR guidelines, most corrosion inhibitors that are used, tested and patented for amine-based CO2 absorption processes are non-environmental friendly. Hence, to respond to the

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environmental concerns and reduce the cost of waste disposal as well as prepare for more stringent regulations for chemical uses, application of effective and environmentally friendly corrosion inhibitors is necessary. The objective of this book chapter is to provide a review of corrosion inhibitors and a progress towards use of environmentally friendly corrosion inhibitors in the amine-based CO2 absorption process for acid gas treatment and carbon capture. The chapter is divided into four sections. Section 1 provides background information of the amine-based CO2 absorption process, including process description and type of amine used. Section 2 describes typical corrosion problems taking place in the process and provides historical corrosion cases in actual plant operations. Section 3 provides a compiled list of corrosion inhibitors that have been patented, tested and applied in this plant operation, discusses the use of environmentally friendly corrosion inhibitors and provides an update on research related to environmentally friendly corrosion inhibitors in the amine-based CO2 absorption process. Chapter 4 – Corrosion inhibitors have been applied on protection of steel structures and their alloys in industry. In this sense, natural inhibitors become as an important alternative to sustainable technological development. As advantage, natural corrosion inhibitors reduce the toxic effects observed for synthetic organic compounds, and depending on their formulation could range from lower toxicity to nontoxic commercial products. Additionally, green inhibitors are attractive in function of the low cost procedures, inhibition performances are closely related to plant extracts, fractions, oil, and even, isolated compounds. In this present work a commercial copaiba oil sample (CO) belonging to the vegetal species Copaifera L., was loaded into a O/W self-microemulsion system (SMEDDS colloidal-type) composed with CO (1.0% as oil phase), Tween® 80 (10.0% as surfactant) and water (89.0%), affording the green sample SME-CO. The SME-CO formulation was applied as a natural corrosion inhibitor measured at different concentrations (ranging from 5 ppm to 150 ppm), in a saline corrosive medium (3.5% of sodium chloride). The best SME-CO corrosion inhibition efficiencies (77.15%) was observed at 100 ppm by electrochemical method of linear polarization curves with Tafel extrapolation, and obeys Langmuir model isotherm. The greatest inhibitory effect of the tested green sample (SME-CO) could be correlated with the SMEDDS adsorption phenomena on the metal surface (steel AISI 1018), being herein considered as a eco-friendly corrosion inhibitor. In the other hand, CO-corrosion efficiency could be correlated with the synergistic effect of its phytocompounds of which diterpenes and sesquiterpenes with

Preface

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different functional groups are adsorbed on the metal surface, forming a stable plant source-metal complex, reducing metal damage. Chapter 5 – Corrosion in metals is gradual degradation by oxidation in hostile environment. APMMCs are the materials which developed by combining two distinguish parts namely matrix and reinforcement phases fabricated by different casting techniques. Corrosion in APMMCs happens due to pitting initiation at the interface of the fabricated APMMCs and crevices on the surface of the fabricated APMMCs. Corrosion mechanism in APMMCs is due to galvanic reaction between the matrix phase and its reinforcement phase. Formation of new compounds at the interface of the APMMCs is also a reason of selective corrosion. Pitting action occurs in APMMCs as localize corrosion. Potential gradient elevate the oxidation of metal in hostile environment results in pitting phenomenon. Generally APMMCs are more susceptible to corrosion as compare to its base alloys but superior in strength in terms of mechanical properties. Cognition behind this is reinforcement is hurdle for preserve the passive film which is on the surface of aluminum. Aluminum having strong thin passive film on the surface which brakes, it recovers itself. In APMMCs reinforcements shatter the oxide film, allowing pitting and crevice corrosion. Hence, inhibition of corrosion becomes necessary to protect the APMMCs from the hostile environment and to increase the life of fabricated APMMCs. Polymer coating, anodizing, surface modification and chemical passivity are the inhibitor process for the fabricated APMMCs. Among these inhibitors anodizing is the best method to protect APMMCs from corrosion in hostile environment. This chapter addresses the mechanism of corrosion for APMMCs. Different methods of inhibition to corrosion for APMMCs are also discussed. Chapter 6 – The mesoionic compound 1,3,4-triazolium-2-thiol (MI) was solubilized in an oil-in-water microemulsion (OCS-ME) containing saponified coconut oil (OCS) as surfactant, butan-1-ol as cosurfactant, kerosene as oil phase and saline solution as aqueous medium. The MI-loaded system (OCSME-MI) was evaluated as corrosion inhibitor at lower concentrations (ranging from 12.5 ppm to 100 ppm) using the electrochemical and gravimetric methods, Linear Polarization Resistance (LPR) and Mass Loss (ML), respectively. The corrosion inhibition of OCS-ME-MI was evidenced on the AISI 1018 steel, in saline solution (NaCl 1%) showing higher inhibitory effect, such as 92.60%, at 75 ppm of OCS-ME-MI sample by LPR technique, and 92.68% at 75 ppm of OCS-ME-MI sample by ML technique. According to the electrochemical method applied, linear polarization curves with Tafel extrapolation, OCS-ME-MI obeys Frumkin adsorptions isotherm.

In: Corrosion Inhibitors Editor: Esther Hart

ISBN: 978-1-63485-791-8 © 2017 Nova Science Publishers, Inc.

Chapter 1

ORGANIC CORROSION INHIBITORS AND INDUSTRIAL APPLICATIONS Gözde Tansuğ1 and Tunç Tüken2, 1

Cukurova University, Ceyhan Engineering Faculty, Chemical Engineering, Adana, Turkey 2 Cukurova University, Sciences and Letters Faculty, Chemistry Department, Adana, Turkey

ABSTRACT Organic corrosion inhibitors have been frequently studied, since they offer simple solution for protection of metals against corrosion in aqueous environment. Thus, there are many commercialized corrosion inhibitors for industrial applications like; cooling systems, pipelines, oil and gas production units, boilers and pickling process etc. The largest amount of inhibitor is demanded by cooling water systems and it is the fact that inorganic inhibitors (phosphates, tungstate, molybdate etc.) are still widely used in this area. For such engineering purposes, the required inhibitor is anticipated to assemble chemisorbed film (preferably monolayer), either by direct adsorption on metal surface or forming insoluble complex with metal ions existing at the interface. For copper and its alloys, there have been numerous chemical formulations based on organic inhibitors. However, steel has been the most widely used material, and there is a need for further development in the application of 

Corresponding Author address E-mail: [email protected].

2

Gözde Tansuğ and Tunç Tüken organic inhibitors for protection of steel against corrosion. On the other hand, there has been an increasing concern about the use of “green” chemicals for such purposes and this consideration also urges the investigations subjecting the organic corrosion inhibitors. For this purpose, molecular design and synthesis of novel organic inhibitors have been pronounced as a promising way, for tailoring one compound equipped with multitasking. On the other hand, it is necessary to develop new approaches (methods) for the assessment of corrosion inhibitor performance, in practical application conditions. Because, there are many parameters (temperature, pH, composition of corrosive media, etc.) that should be evaluated carefully for success of the application, in order to avoid excess chemical use or insufficient protection. Possible interference between the critical parameters should also be taken into account, for convenient application. For this reason, statistical evaluations should be carried out with data obtained from various routes employed to determine the corrosion rate. Generally, the preferred method is based on electrochemical techniques, and utilizes Tafel and Stern-Geary methods. Solution assay analysis, weight loss measurements have also been widely employed, since they offer simplicity for quantification of corrosion rate. This paper focuses on the interpretations of these addressed issues, with the theory and review of recently published studies in relevant field.

Keywords: organic inhibitors, corrosion, cooling water systems, green chemistry

1. INTRODUCTION The corrosion inhibitors have widespread application in various industries (oil & gas, steel industry, general cooling water systems etc.), and the global market was reported to be 5.20 billion US$ and forecasted to reach 7.4 billion by the end of 2019 [1]. Within this market, the application of corrosion inhibitors in cooling water system takes noteworthy part, because of the variety of industries involving such cooling water systems. In these systems, widely used commercial products are chemical formulations based on inorganic corrosion inhibitors. These formulations also include some coadditives (biocides, dispersant agents etc.), because ground/lake/sea water is necessarily used in cooling water systems for various chief industries. In all cases, the cooling water is subjected to various pretreatments, but still should be considered as a matrix including various inorganic/organic species within.

Organic Corrosion Inhibitors and Industrial Applications

3

For cooling water systems, chromates and nitrates have long been utilized as efficient inhibitors, until their use have been restricted due to environmental concerns. Then, the silicates, molybdates, phosphates have been widely used in commercialized formulations, since they offer remarkable efficiency and they are friendly against the environment [2]. Of course, the cost of chemicals is another important issue for designing such inhibitor formulations. For this reason, molybdate and tungstate like chemicals have been frequently employed for closed water cooling systems, since these kinds of systems that require less chemicals. It is noted that well-conditioned water with efficient corrosion inhibitor could be used for a long time in such systems, over and over again. However, in open cooling water systems, there is water loss due to evaporation in each cycle, as well as contamination (suspended solids, grease etc.). Therefore, there is necessity for feeding the chemicals to tune the water quality, after each cycle. Thus, inhibitor formulations using cheaper chemicals like phosphate derivatives are widely commercialized with the aid of coadditives like dispersive agents, biocides etc. In the following sections, the application of organic inhibitors will be discussed, in the aspects of potential for commercialization, requirements of industrial cooling water systems, and recent developments.

2. INHIBITORS IN INDUSTRIAL APPLICATIONS Inhibitor application is simply based on the fact that the surface of substrate should be shielded with stable and compact thin films, in order to hinder the attack of corrosive environment. For this purpose, molybdate and silicate anions directly react with the metal ions of corroding metal/alloy, which are released at the interface due to corrosion of material itself. On the other hand, phosphate derivatives are not easy to form protective films with dissolved Fe (II, III) ions, since they require remarkably high pH values for direct deposition of stable complex between phosphate and iron ions. Highly alkaline conditions bring the risk of intense scale deposition on steel. The solution has been found with chemical deposition of zinc phosphate (Zn3(PO4)2) on steel surface, this compound has extremely low solubility product, 9.0×10–33. The use of phosphate derivatives (sodium salts of hexametaphosphate and tripolyphosphates, Figure 1) offer versatility, low cost and good efficiency under circulating water conditions. However, phosphate based chemical formulations involve high dosages and well-adjusted water parameters. In order to avoid bulk scale deposition on the surface, especially in

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heat exchangers or hydrothermal plants, water hardness and ionic species (hydroxide and carbonate) should be carefully managed for success of inhibitor application. Abd-El-Khalek and Abd-El-Nabey studied on evaluation of sodium hexametaphosphate (SHMP) as scale and corrosion inhibitor in cooling water, by using electrochemical techniques and comparing with polyacrylic acid. SHMP is more efficient as antiscalant than polyacrylic acid, SHMP delays nucleation period and thus hinder scale formation. A critical concentration of 4 ppm SHMP was required to obtain 81% of scale inhibition. In presence of 2 ppm of polyacrylic acid and SHMP, the scale inhibition efficiencies were 30.1% for polyacrylic acid and 55.9% for SHMP [3]. Moudgil et al. investigated synergistic effect of antiscalants: 1-hydroxyethane-1,1diphosphonic acid (HEDP), sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP) and trisodium phosphate (TSP) in different combinations for carbon steel in industrial cooling water system. When HEDP was mixed with other antiscalants, the corrosion inhibition increased with the following order; HEDP/SHMP (97.6%) >HEDP/STPP (91.4%) >HEDP/TSP (59.8%) [4]. In another research, inhibition efficiencies of hydroxyl carboxylate-based corrosion inhibitors (e.g., gluconate, citrate, tartarate) and zinc sulfate heptahydrate have been studied in the pipeline of reclaimed water supplies and in downstream recirculating cooling water system. It was reported that the appropriate combination of phosphate and zinc ions reduce the cost and environmental risk of excess phosphorus release. With 2.0 mg/L phosphate concentration and 0.5 mg/L zinc ions, the corrosion rate was lower than 0.1 mm/year. In the same study, a non-phosphorus formulation was also reported, using hydroxyl carboxylates as the main corrosion inhibitors, zinc ions as additive, PESA as anti-scaling and LN-104B as dispersant. The corrosion rate decreased down to below 0.075 mm/year, with hydroxyl carboxylate dosage in range of 4-8 mg/L, PESA and LN-104B dosages were 6-10 mg/L [5]. In another work, the influence of inhibitors and biocides were investigated for mild steel and copper-nickel alloys in a power plant cooling water system with help of electrochemical and weight loss measurements. The formulation included sodium hypochlorite, 1-hydroxyethylidene-1,1-diphosphonate, maleic anhydride homopolymer, 2-phosphonobutane-1,2,4-tricarboxylic acid as scaling inhibitors, and zinc ions, 2-mercaptobenzothiazole as corrosion inhibitors. The results showed that corrosion rate of carbon steel was 3.88 mpy (mil per year) and 0.76 mpy was reported for copper-nickel, in presence of inhibitor formulation [6].

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Figure 1. Structures of the mostly used commercial phosphate compounds.

Figure 2. Structures of the mostly used commercial phosphonic acids.

The good performance of phosphate compounds is simply related to their superior functional group which is capable of complexing many metal ions, so similar compounds have been researched frequently. Moreover, phosphonates and various anionic polymers have found application in commercial chemical formulations. For instance, 1-hydroxyethane-1,1-diphosphonic acid (HEDP) has partaken in formulation of various commercial corrosion inhibitor products (Figure 2). Mohammedi et al., [7] investigated the inhibition efficiency of a mixture formulation based on HEDP and sodium metasilicate, on carbon steel in industrial hard water. They showed that HEDP and calcium ions synergistically support passivity of the metal, reported inhibition efficiency is 94% at pH 7. This kind of compounds have grabbed much

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attention due to their rare properties like; stability, strong adsorption on metal surface, complexing many metal ions and dispersant activity. Phosphonates are good chelating agents, thanks to their ability to bind strongly to di- and trivalent metal ions. In the case that the molecule tailored with an amine group, the chelating capability increases. Examples for such compounds are amino (trimethylene phosphonic acid), ethylene diamine tetra (methylphosphonic acid) (Figure 2). Sodium salt of polyaspartic acid (PASP) and amino trimethylene phosphonic acid (ATMP) were investigated as scale inhibitors in circulating cooling water system for stainless steel. The reported corrosion inhibition efficiency is 83%–89%, up to 20 mg/L concentration range ATMP. It was also reported that scale inhibition efficiency of PASP was three times greater than ATMP [8]. Jin et al. [9] reported a new water treatment formulation for carbon steel surface in a pilot-scale cooling system with reclaimed wastewater as the makeup water. The optimized composition of scale and corrosion inhibitor was 12.5% 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), 21.8% ZnSO4, 18.7% polyaspartic acid (PASP), 9.4% 2-hydroxyl phosphonoacetic acid (HPAA), 18.8% acetic acid (AA) - amino trimethylene phosphonic acid (ATMP) - 2-hydroxyl phosphonoacetate (HPA) polymer, and 18.8% hydrolyzed polymaleicanhydride (HPMA). For this formulation, the reported inhibition efficiencies against scale deposition and corrosion were 93.3 and 94.4%, respectively. Of course, the stability of metal complexes increases with increasing number of phosphonic acid groups. These types of species are well known with their scale prevention effect, when they are used in cooling water with notable hardness. However, the chemistry of these phosphonate based metal complexes does not allow forming compact and reasonably thin protective films on steel surface. Therefore, the dosage should be high, in order to utilize this type chemicals for achieving both scale prevention and inhibition. The corrosion inhibition mechanism is explained with strong adsorptive interaction with the surface, in the case that metal surface is not occupied by other species like; scale, corrosion products etc. The inhibition efficiency of such compounds is highly sensitive against the pH and composition of corrosive aqueous environment. They are very successful on bare metal surface, i.e., when the pH is low enough for prevention of deposits like quasi-stable (nonprotective) corrosion products on the surface. Another consideration is the presence of diverse anions like Cl- or OH-. In this case, the competitive adsorption between these anions and inhibitor molecules generally limits the

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success of corrosion inhibition. As a conclusion, the chelating performance and scale prevention capability of phosphonates step forward, when they are utilized in corrosion inhibitor formulations to be used in cooling water systems.

3. ORGANIC INHIBITORS 3.1. Why Organic Inhibitors? The reason that there is gradually increasing concern about the use of environmentally friendly chemicals, there is a necessity for developing new “organic” inhibitors with better efficiency. Of course, the versatility, cost and efficiency should be taken into account. Even though there have been some effort about development of inorganic corrosion inhibitors, for example there have been many studies focused on Schiff base compounds, organic inhibitors are easy to functionalize with multitasks and they offer “green” solutions. The corrosion inhibitor must be “green” (biodegradable and harmless for the environment), because sooner or later these chemicals are released to environment, one way or another. It is not surprising that almost all organic compounds exhibit inhibition efficiency against corrosion in aqueous media, especially when they possess heteroatoms like; nitrogen, sulphur, phosphorous and oxygen. The organic molecules simply adsorb on the metal surface by displacing water molecules. So, the forces involved in this process can be summarized as; organic molecule-electrode forces and lateral interactions (i.e., intermolecular forces between the adsorbed organic molecules). Then inhibition efficiency arises due to one or more of the following routes: preferential adsorption on anodic or cathodic sites and blocking the reaction, assembling a protective barrier film on the surface. According to inhibition mechanism, the inhibitors are classified as anodic, cathodic or mix-type. Various electrochemical experimental studies should be realized carefully, and collected data should also be evaluated properly for defining the type of inhibitor. This is not within the targeted topic of this paper; however an example will be discussed briefly in the section titled assessment of corrosion inhibition efficiency.

Gözde Tansuğ and Tunç Tüken

8

O

OH

A

SH N

B

OH

C

Figure 3. Molecular structures for (A) hydroxybenzene, (B) benzenethiol, (C) nicotinic acid.

Going back to adsorptive interaction of organic inhibitors with the surface, availability of lone pair electrons and/or π-bonding electrons in the molecule enables formation of coordinate covalent bond involving electron transfer from inhibitor to the metal. In this case, the adsorption type shifts from physisorption to chemisorption, soon, and the adsorption strength depends on the electron density on the donor atom of the functional group and the polarizability of the group. To conclude, structure, size and orientation of the organic molecule are the essential factors influencing the adsorption type and strength. For example, linear (or branched) hydrocarbon chains can exhibit weak interaction with water molecules and electrode surface. Aromatic compounds are generally anticipated to interact strongly with the metal surface and neighboring adsorbed molecules (lateral interactions), due to their πelectrons. The type of molecule and functional groups alter greatly the orientation of organic molecule at the interface. As an example, hydroxybenzene (phenol) molecule (Figure 3A) is preferentially held to the surface in a flat orientation, because of strong attraction between delocalized π-bonding system and the surface, rather than –OH group. On contrary, benzenethiol (phenyl mercaptan) molecules (Figure 3B) attach to the surface through the sulphur atoms, and then the benzene rings are aligned towards the solution side of the interface [10]. In the latter case, the benzene rings also interact with each other and provide extra stability and hydrophobic surface. Therefore, it is not surprising to obtain higher inhibition efficiencies with organic molecules tailored with mercaptan groups. It should also be noted that the orientation (with respect to surface) of organic molecules may change depending on the surface charge of metal. A typical example is nicotinic acid (Figure 3C), which could interact with negatively charged surface through its nitrogen atom; the adsorption happens through aromatic nitrogen and carboxylate groups, at positively charged surface. For such interpretations, quantum chemical methods and molecular modeling techniques could also be

Organic Corrosion Inhibitors and Industrial Applications

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useful for characterizing the orientation, and binding properties of inhibitor molecules [11]. However, the details of these methods are not within the scope of this work.

3.2. Organic Inhibitors in Cooling Water Systems There is necessity for novel organic corrosion inhibitors to be employed in chemical formulations to protect steel against corrosion, in nearly neutral conditions. Adapting an organic inhibitor to cooling water systems is a great challenge, since the cooling water is a matrix with points of considerations like; hardness, suspended solid materials, grease etc. Therefore, lab-scale experimental results may indicate to excellent inhibition efficiency, but the inhibitor may not work in a real circulating cooling water system. Scale deposition is the major problem to be handled, because the organic inhibitors are generally successful on bare metal surfaces. This is also the reason that most of the studies reporting outstanding protection efficiency with organic inhibitor are mostly in acidic environments. At this point, it should be noted that the greatest demand for corrosion inhibitors is for cooling water systems, where the pH value is generally in between 6.5-8.5. One may ask the question: why the pH value should be in this range? Scale deposition is directly related with the pH and ionic composition of water (hardness). Generally, it is easy to adjust the parameters for prevention of scale deposition; taking into account the Langelier Saturation index (LSI). This value is an equilibrium model which could be simply given with the following equation. LSI = pH - pHs

(1)

As can be seen, this index is related with the degree of saturation of water with respect to calcium carbonate. In this equation; pH is the measured value and pHs is the value at which saturation of calcium carbonate is reached in that water sample. The value pHs could be directly determined with help of a simple experiment with water samples or calculated theoretically, with help of water parameters [12]. Mostly, the operators try to adjust the water parameters in such a way that the LSI index value is < 0, then there is no risk for scale deposition. In this case, the risk of corrosion increases (for mostly used material: steel) and therefore it is generally preferred to keep the index in slightly greater than

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zero, this is also frequently recommended by suppliers and also in the Literature [13-15]. However, this route could only be achieved by tuning the pH of cooling water and is not so easy in practice, since the parameters are quite changeable, especially in open water cooling systems. For this reason, various dispersive agents are added to chemical mixture formulation of corrosion inhibitor. Biocides are also inevitably necessary for controlling the microbial activities, because microorganisms (bacteria, fungi and algae) may lead to formation biofilms on the surface, in presence of organic compounds. The metabolism of these species could produce corrosive compounds (acids or aggressive species) then the result is generally severe corrosion under the biofilm. So the organic inhibitor should also be compatible with such co-additives [6, 16-18].

3.3. Plant Extracts Plant extracts are generally considered as green corrosion inhibitors and the extract includes a part of phytochemicals, depending on the extraction procedure parameters (solvent type, pretreatments, temperature etc.). The chemical compounds that occur naturally in plants are named as phytochemicals. The said phytochemicals are of course related with the type of plant, but generally they are phenolic compounds, organic acids, esters, alkaloids, flavonoids, tannic acids etc. It is generally assumed that plant extracts are biocompatible due to their biological origin, i.e., green corrosion inhibitors. However, the studies aiming to research green inhibitors should be better accomplished with detailed analysis of degradability of organic inhibitors in the nature. Because the biodegradation is a complicated process occurring under influence of microbial activity, water, UV-visible light etc. The organic compound itself may be green, however the intermediates of degradation mechanism could be unsafe for the environment. El Hamdani et al. investigated alkaloids extract of Retama monosperma (L.) Boiss seeds used as novel eco-friendly inhibitor for carbon steel corrosion in 1 M HCl solution. They reported 94.4% inhibition efficiency for 400 mg/L concentration [19]. Gerengi worked on mimosa extract for AA6060 alloy in acid rain solution, the inhibition efficiency is 45% at 2750 ppm [20]. Al-Otaibi et al. [21] studied on alcoholic extract of eight different plants and examined their corrosion efficiencies on mild steel. The extracts (0.01g/100 ml) of Artemisia sieberi and Tripleurospermum auriculatum exhibited about 91% efficiency in 0.5 M HCl. The protection efficiency of the Calligonum

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comosum (CC) extract was investigated on Cu corrosion in 2 M HCl solution. The polarization studies showed that maximum efficiency is 80%, with 0.8g/L CC extract [22]. The aqueous extract of Coriandrum sativum L. (CSE) seeds was studied as an eco-friendly green inhibitor for corrosion control of aluminium in 1 M phosphoric acid solution. 500 ppm CC showed the highest inhibition efficiency (71.51%), at 30oC [23]. As a conclusion, there are hundred thousands of plant species on the earth and each one of them could be studied as potential green corrosion inhibitor. It is difficult to say that all of them should necessarily be investigated. Because most of these plant extracts have shown to be effective corrosion inhibitor under acidic conditions, then these could be useful for pickling or chemical cleansing processes involve utilization of high acid concentrations. It should be noted that the chemistry of plant extracts are not customary. Also, there is a problem for commercialization of such plant extracts as commodity material to be used in inhibitor formulations. The fact that most of the corrosion inhibitors are demanded by cooling water systems, it is very difficult to employ these plant extracts in such systems. These extracts generally exhibit mixed type inhibitor behavior, through physisorption on the metal surface. Industrial cooling water systems involve circulation of water with a constant flow rate. The efficiency of such inhibitors could be very limited in such circumstances, since the weakly adsorbed inhibitor molecules could easily detach from the surface, due to the drifting effect of running water. Increasing the inhibitor concentration is not a reasonable way for enhancing the efficiency, because one can’t go through this way easily in a practical application. For this reason, the most appropriate choice still appears to be design and synthesis of specific organic molecules, for the purpose of cooling water systems.

3.4. Molecular Designing and Synthesis Designing an organic inhibitors molecule is challenging task because of the variety and complexity of corrosive environment. Steel and copper are mostly used metals for engineering purposes; pipelines, heat exchangers etc. Azole and thiolate containing organic compounds have been designed, synthesized and studied frequently; finally some of them have found application in commercial formulations. This is due to their ability for chemisorption and film assembling on the surface, via coordination with unfilled d orbitals of metal. Generally, sulphur and nitrogen containing functional groups exhibit strong metal-chelating (electron donor) capability,

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thus they are highly compatible with vacant d-orbitals of many metals. For this reason, various organic compounds tailored with these atoms have been studied frequently; of course the efficiency varies with the orientation and bond type within the molecular structure (Figure 4). The presence of an aromatic ring improves remarkably the stability of adsorption layer and the molecule itself. Based on these facts innumerous derivative compounds with these functional groups have been synthesized and investigated, since it was recognized that chemisorption is possible via these centers. Especially for copper, nitrogen atoms (with free electron pairs) of azole compounds constitute active center for bonding with copper (I), thus longlasting polymeric Cu(I) complex film is formed on the surface. This film is highly protective, inert and insoluble in a wide pH range. Since it is chemically adsorbed on the surface and compatible with cuprous/cupric oxide, good protection efficiency is guaranteed even under elevated temperature. Typical example is benzotriazole which consisted of benzene and triazole ring, the triazole ring enables chemical bonding with copper (I) and responsible for inhibitory effect of BTA [24-45].

Figure 4. Functional groups of mostly used for designing corrosion inhibitors.

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Following the physisorption of molecule on copper surface via electrostatic attraction, Cu(I)BTA complex is formed in the first step copper dissolution mechanism. It was reported that the pH increase favors complex formation on the surface. Cu(s) + BTAH(aq) → Cu:BTAH(ads) + H +(aq)

(2)

Cu:BTAH(ads) → Cu(I)BTA(s) + H +(aq) + e

(3)

Self-assembled monolayers (SAM) of a series of thiol compounds with benzene ring have been investigated for copper protection. Because the mercapto group (-SH) has strong affinity for copper and the inhibitor molecules attach to copper surface via the thiolate bond. The formation of protective chemisorbed film occurs via Cu(I)-thiolate complex, the mechanism is analogous with that discussed for azole compounds [46-60]. Innumerous organic compounds have been synthesized and investigated for protection of copper, under illumination of previously mentioned discussions. Methyl 3-((2-mercaptophenyl)imino)butanoate, a newly synthesized compound, exhibited very high inhibition efficiency against copper corrosion in acidic chloride environment [61]. The inhibition mechanism was explained with complex formation between the inhibitor and Cu(I) ions at the interface. The molecule is functionalized with both azole and thiol groups. These groups generate strong adsorptive interaction with metals/alloys, especially in acidic environment. The thiol group of the molecule improves the adsorptive interaction with the copper surface. Also, the carboxylate end group has significant dipole character and results with important intermolecular interaction between the adsorbed inhibitor molecules. Once the adsorbed molecules interact with each other along the carboxylate tails, a film like adsorption layer could be formed on the surface. The protection efficiency increased with increasing inhibitor concentration, and 99.30% efficiency of 10 mM concentration. The durability of protective film was found to be good against temperature increase; the efficiency was 92.70% at 55oC. The protection efficiency was also good for extending periods, 96.60% efficiency was determined, after 7 days exposure to 10 mM inhibitor containing test solution. Also, the SEM results proved that the inhibitor could successfully protect the copper surface for considerably 7 days exposure period. In the literature, 90.80% inhibition efficiency was reported for 10 mM benzotriazole (BTA) in 0.1 M HCl acid solution [24]. Higher efficiency values were reported when a thiol group is also attached to inhibitor molecule, for

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example 4-amino-4H-1,2,4-triazole-3-thiol exhibits 91.38%, in acidic chloride solution [25]. In another study, the efficiency of 5-methyl benzotriazole was reported to be 97.87% [24]. The inhibition efficiency of MMBP is quite well, when compared to others reported in the literature. Also, it was shown that the efficiency of MMBP was not to diminish with extending exposure periods. In another study, the inhibition efficiency of 2-aminoethanethiol (2-AEE) was reported as effective inhibitor against steel corrosion [62]. The molecule possesses -SH and -NH2 functional groups that offer strong adsorption behavior on steel surface (Figure 5). The inhibition efficiency increased regularly with concentration and 93% value reported for 10 mM 2-AEE.

Figure 5. The schematic illustration for 2-AEE adsorption on steel/0.1 M HCl interface.

Also, methyl 3-((2-mercaptophenyl)imino)butanoate (MMPB) compound was synthesized and studied as corrosion inhibitor for steel and 97% efficiency was reported for 10 mM inhibitor concentration [63]. The intermolecular attraction forces between carboxylate tail groups are also important for efficiency, as well as major azole and thiol groups. The said attractions between the tail groups consolidate the stability of adsorbed inhibitor molecules on the surface. The sulfur atom with unshared electrons can easily coordinate with vacant d orbitals of iron atoms aligned through the bare surface. The best auxiliary groups are those can modify the solution side of organic layer, in order to obtain less hydrophobic and/or permeable nature. In the case that the auxiliary groups increase intermolecular attraction between the adsorbed molecules, a polymer like layer could be obtained on the surface. In the literature, 97.9% and 97.2% inhibition efficiencies were reported for 10 mM 2,5-bis (4-dimethylaminophenyl)-1,3,4-thiadiazole and 2,5-bis (4-

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dimethylaminophenyl)-1,3,4-oxadiazole in 1 M HCl acid solutions [64]. Also lower efficiency values were reported for 20 mM (2,5-bis (2-pyridyl)-1,3,4thiadiazole [65] and 20 mM (2,5-bis (3-pyridyl)-1,3,4-thiadiazole [66] in 1 M HCl solutions as 84.4% and 94.5% respectively. Considering similar inhibitors reported recently, the synthesized MMPB has good inhibition efficiency and its molecular design offers good stability, too. 2,5-dimercapto-1,3,4-thiazole (DMTD) was studied against copper corrosion in 0.5 M HCl solution . The inhibition efficiency reached to the highest value at 7.5 mM DMTD-ethanol solution by self-assembling for 10 h. From molecular simulation, it was shown that DMTD molecule tends to be adsorbed on copper surface in a closely parallel by virtue of the interaction between three S atoms of DMTD and Cu+ or Cu+2 to form coordinate bonds [67]. Rochdi et al. studied corrosion inhibition of oxadiazole derivatives using electrochemical techniques on low carbon steel in simulated cooling water system. Mixture of 2,5-bis(n-methylphenyl)-1,3,4-oxadiazole (n=2,3,4) compounds and cetyltrimethylammonium bromide exhibited better inhibition efficiency (99.8%) than each product solely. The addition of biocide in oxadiazole mixture formed the most protective film against corrosion [68]. A new imidazole derivative named {[(benzimidazol-2-ylmethyl)imino] bis(methylene)} was synthesized by insertion of phosphonate functional groups into structure as an environmental friendly corrosion and scale inhibitor. It was showed that the performance of this organic compound was comparable to sodium tungstate, against carbon steel corrosion in simulated cooling tower water [69]. Singh et al. investigated non-toxic quinolone derivatives as corrosion inhibitors for mild steel in 1 M HCl. The inhibition efficiency varied in between 90-98%, depending on concentration. Electrochemical measurements revealed that inhibitor functioned via physisorption with pre-adsorbed chloride ions and chemisorption with vacant d-orbital of iron atoms, surface analysis proved the formation of a protective film on the metal surface [70]. Dithiocarbamate compounds (DTCs) are good chelating agents against variety of metal ions, due to presence of –C = S and -C-S – sites [71-74]. Their polymeric complexes with different metal ions are highly stable and sparingly soluble in water [75]. As a class of nontoxic material, diethyldithiocarbamate (DDTC) offer favorable alternative for designing green corrosion inhibitors for copper alloys [76]. Moreover, DDTC has been reported as efficient inhibitor against steel corrosion [77]. Liao et al. studied the inhibition behavior of DDTC for inhibition of copper [78] and brass corrosion [79] in 3% NaCl. It was reported that both anodic and cathodic processes are controlled by

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strongly adsorbed DDTC molecules. Li et al. have reported the use of diethyldithiocarbamate as corrosion inhibitor for cold rolled steel in 0.5 M HCl corrosive solution [80]. In another study, sodium phenylcarbamodithioate (PDTC) was designed and synthesized, from aniline and carbondisulfide starting materials. Electrochemical studies showed that this compound is an efficient adsorption type inhibitor. This good efficiency was explained with capability of both physisorption and chemisorption on steel surface. The phenyl group also presents a hydrophobic surface, when the molecule is adsorbed via its thiocarbamate end. It was shown that the inhibitor molecules were chemically bonded to surface, in the form of monomolecular layer. The inhibition efficiency was shown to increase slightly with the temperature, 98.65% at 55oC. Also, the inhibition efficiency was shown to remain stable with extending exposure time, it was 85.93%, three days later than employing single dose (500 ppm) inhibitor. This was an important result for the purpose of practical applications [81].

3.5. Polymeric Inhibitors Water soluble polymers have also been investigated as corrosion inhibitors, natural or synthetic in the origin. It is easy to modify the polymer backbone with appropriate functional groups, in order to enhance chelating capability against metal ions and adsorption on metal surfaces. The size of macromolecules may appear as a disadvantage for adsorption strength on the surface, but the number and type of functional groups could easily be adjusted in order to improve the stability of adsorption layer. For application of polymers in practice, the molecular weight and chain length are also crucial parameters, as well as solubility. The solubility of natural polymers could easily be improved via further modification of backbone with appropriate hydrophilic functional groups like; -OH, -NH2, -COOH, -SO3 etc. Since these macromolecules cover a large surface area, thus blocking the surface and hinder the attack of corrosive environment. For this purpose natural polymeric materials have long been studied by many authors. Guar Gam was reported as an effective corrosion inhibitor for C-steel in 1 M sulphuric acid environment, 1500 ppm compound showed 93% inhibition efficiency [82]. Some sulfated water-soluble natural polymer (carrageenan) compounds on the corrosion of iron in 1 M HCl possess 80% inhibition efficiency for 500 ppm concentration [83]. Umoren investigated corrosion protection efficiency on mild steel and aluminum exposed to sulphuric acid

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solution of a natural polymer named Gum arabic. Gum Arabic controlled the corrosion more effectively on aluminum (inhibition efficiency is 76.69%) rather than mild steel (inhibition efficiency is 37.88%) [84]. Polyethylene glycol methyl ether was reported to exhibit remarkable inhibition efficiency (84.2% at 298 K for 10-3 M) for mild steel corrosion in acidic medium with respect to gum Arabic [85]. The effect of naturally occurring exudate gum (from Raphia hookeri) on the corrosion of mild steel in H2SO4 was investigated. The inhibition efficiency reached a maximum of 71.9% at 0.5 g/L exudate concentration, at 30oC [86]. The inhibition efficiencies of kraft lignin and soda lignin were studied against corrosion of mild steel in 3.5% (w/v) sodium chloride. Kraft lignin exhibited maximum inhibition efficiency of 95% and 92% at pH 6 and 8, respectively, whereas soda lignin had 97% and 95% efficiencies [87].

4. ASSESMENT OF CORROSION INHIBITON The conventional corrosion rate measurement methods (electrochemical and non-electrochemical) are employed for the assessment of inhibition efficiency. Thereby, the same methods are necessarily utilized for illuminating the corrosion inhibition mechanism and defining the type of inhibitor (anodic, cathodic or mix-type). At this moment, surface examinations with various spectroscopic techniques are also necessarily used, for example FT-IR, XPS, XRD, Raman, SEM-EDX etc. Spectroscopic analyses are generally regarded as complementary methods which provide additional data and corroborate the electrochemical testing results. These spectroscopy techniques are very useful for identification of the composition of corrosion products and adsorption layer, type of adsorption, orientations of inhibitor molecules with respect to the surface or synergistic effect between the inhibitor other species present on the surface. Solution assay analysis also involves spectroscopy devices (AAS or ICP), which based on the quantitative analysis of corrosion products in test solution. This method frequently appears in publications subjecting corrosion inhibitors and it should be noted that it could only give meaningful results in the lab-scale. Therefore, this method has not found application in in-situ corrosion rate measurement in industrial water systems. On the other hand, “ellipsometry” has been recently shown to be a direct method for evaluation of corrosion rate, where the corroding metal is convenient for the formation of stable corrosion products (oxides, sulfides, insoluble salts etc.) accumulating on the surface. Of course, the studied

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corrosive environment is also important for success of this method. In such cases, the thickness of surface film is directly proportional with the amount of metal ions released due to corrosion, thus the protective film should be consisted of an insoluble compound of these ions [88]. For uniform corrosion, weight loss/gain measurement has still been the most prevalent method, at which the collected data average the loss/gain over the exposure period. The test is simply performed by immersing coupons in test solution either in laboratory or in-situ industrial water system. Laboratory tests should necessarily simulate the water chemistry and operating conditions of real process, for acquisition of meaningful data. In-situ testing is conducted in pilot plants for monitoring the success of water treatment, regarding the effect of operating parameters. Metal coupons are mounted in pipe plugs and exposed to water flowing in metal piping, and then the corrosion averages the specimens’ corrosion rate over its surface. It should be noted that meaningful data may require a couple of months, depending on the test specimen and corrosive environment. Many details should necessarily be taken into account when conducting coupon test; required pretreatments for coupons, placement, supports, exposure time and cleaning. In order to eliminate the possible errors and enhance the accuracy a standard method should be followed. For this purpose, ASTM G1 standard describes each point of consideration, in details. Electrochemical testing methods give the opportunity for measuring instant corrosion rate; linear polarization resistance measurement, potentiodynamic measurements, impedance spectroscopy and noise measurements. Even though, it is still very difficult to employ one of these methods under in-situ conditions, this route provides fast and reliable data for assessment of corrosion rate. For accuracy of data collected by this route, the measurement conditions/parameters should be carefully handled. Linear polarization resistance and potentiodynamic measurements are regularly used with Tafel equation and famous Stern-Geary equation, in order to quantify corrosion rate. However, the parameters employed during these measurements have vital effect on accuracy of collected data and requires great attention. For this purpose, ASTM G52 defines the standard method for conducting linear polarization resistance measurement and ASTM G5-14 explains the requirements for potentiodynamic anodic polarization. Finally, ASTM G102 standard describes the calculation of corrosion rate with help data collected from electrochemical measurements, including Tafel extrapolation and linear polarization resistance [89]. Potentiodynamic measurements are widely used for interpretation of corrosion inhibition mechanism, in order to define its type; anodic, cathodic or

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mixed type. Simply, the shift of corrosion potential (Ecorr) and alteration of anodic/cathodic current values are compared for the absence and presence of inhibitor. Therefore, the scan rate and initial-final potential values have great importance. For the assessment of corrosion rate, generally, the scan measurement is performed by polarizing the specimen about 300-500 mV anodically (positive with respect to the Ecorr) and cathodically (negative with respect to the Ecorr). For each branch, the initial point should be better chosen as the measured Ecorr value. Thus the cathodic and anodic branches are obtained in two separate measurements with the same specimen. However, it is frequently seen that the measurement is conducted in single experiment, where the scan starts from a cathodic initial value and terminated in anodic domain. Does it make a difference with the collected data and relevant interpretations about corrosion inhibition efficiency and mechanism? The answer is absolutely yes. A specimen at its Ecorr has both anodic and cathodic currents present on its surface, so the anodic and cathodic reactions occur simultaneously. Since these currents are exactly equal in magnitude, there is no net current to be measured. During polarization towards slightly more positive than Ecorr, the anodic process (thus anodic current) predominates at the expense of the cathodic event, and vice versa. When potentiodynamic measurement starts from cathodic initial value (about 300-500 mV negative to Ecorr), it will take considerable time to reach the measured Ecorr value, since quite low scan rates (< 1 mV/s) are necessarily involved. During this period only cathodic reaction (hydrogen evolution or oxygen reduction etc.) will take place on the surface. So the surface may change dramatically, and the data collected for anodic region will include significant error. For example, adsorbed inhibitor (or metal ion-inhibitor complex film) may detach from the surface during cathodic polarization. Then, immediately taken anodic measurement gives misleading current values which cannot be relied on for assessing the inhibitor interaction with surface, considering spontaneous corrosion conditions natural corrosion. To conclude, it is strongly recommended that two or more methods should be utilized for determination of corrosion inhibition efficiency and the collected data should be evaluated comparatively. At this point, it is also important to use statistical evaluations for ensuring that the measured difference is meaningful, between inhibited and un-inhibited conditions. For this purpose, chi-square, T and F testing methods could be realized and such approximations would certainly improve the significance and impact of the results. The statistical approach could also be used for development of mathematical model between the corrosion inhibitor efficiency and effective

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independent variables (pH, temperature, water composition etc.) of system. It is also possible to establish an equation between the corrosion rate and varying conditions (flow rate, inhibitor concentration, suspended solids etc.) of system. This allows making trustworthy predictions for practical applications and the model includes a mathematical equation between the output (efficiency) and variables of system. Actually it could be named as a fitting model for inhibition efficiency; the success of model could also be tested with basic statistical arguments, residual and variance analysis, T and F tests, and R2 value. For engineering applications of corrosion inhibitors, such a fitting model will certainly help to avoid from excess chemical use or insufficient protection [90-94]. Thus optimization of industrial inhibitor applications becomes possible.

Figure 6. Efficiency versus pH and concentration (C) diagram.

As an example, 2-aminoethanethiol (2-AEE) was reported to have efficiency against steel corrosion in a pH range between 1 and 3.5. Response surface methodology (RSM) was employed to explain the relation between pH, inhibitor concentration and the efficiency. The regression analysis was realized for development of an equation between independent variables and the output. In this study, inhibitor concentration (0.5 – 10mM) and pH (1-3.5) were independent variables and the percent inhibition efficiency (φ) was the dependent output. The success of fitting model was tested with basic statistical

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arguments, residual and variance analysis, T and F tests, R2 value. It was shown that this equation could successfully explain the experimental data, in a 95% confidence level. The statistical evaluations showed that the obtained polynomial equation can be successfully used for optimization of applications involving the use of 2-AEE as inhibitor. This method could also provide important information for realization of any application from lab scale to industrial processes [62].

CONCLUSION Even though they have been widely pronounced as green inhibitors, due to their biological origin, the plant extracts are still not adaptable for development of commercial corrosion inhibitor products. The fact that most of the corrosion inhibitors are demanded by industrial cooling water systems, and most effort should be paid for green organic inhibitors for these applications. For such purposes, inhibitors are required to produce highly stable chemisorbed films on metal surface, which cannot be succeeded with physically adsorbed non-selective organics. For copper systems, there have already developed products including organic inhibitors, while there is still a need for developing eco-friendly high performance inhibitors to be used for steel. Increasing the inhibitor concentration is not a reasonable way for enhancing the efficiency, because one can’t go through this way easily in a practical application. For this reason, the most appropriate choice still appears to design and synthesize specific organic molecules, with minimum toxicity and good efficiency. An inhibitor could not be considered as 100% green, just because it is biological source, like phytochemical. More detailed investigations are needed for “green” inhibitor studies, including the analysis of degradation in environmental conditions. The organic compound itself may be green, however the intermediates of degradation mechanism could be unsafe for the environment. The statistical approach could also be used for development of mathematical model between the corrosion inhibitor efficiency and effective independent variables (pH, temperature, water composition etc.) of system. It is also possible to establish an equation (fitting model) between the corrosion rate and varying conditions (flow rate, inhibitor concentration, suspended solids etc.) of system. This allows making trustworthy predictions for practical

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applications and the fitting model will certainly help to avoid from excess chemical use or insufficient protection, thus optimization could be succeeded.

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[44] Curkovic, H. O.; Stupnisek-Lisac, E.; Takenouti, H. Corros Sci. 2009, 51, 2342-2348. [45] El-Sayed M. S.; Erasmus, R. M.; Comins, J. D. Corros Sci. 2008, 50, 3439-3445. [46] Tuken, T.; Kicir, N.; Elalan, N. T.; Sigircik, G.; Erbil, M. Appl Surf Sci. 2012, 258, 6793-6799. [47] Antonijevic, M. M.; Milic, S. M.; Petrovic, M. B. Corros Sci. 2009, 51, 1228-1237. [48] Rao, B. V. A.; Iqbal, M. Y.; Sreedhar, B. Corros Sci. 2009, 51, 14411452. [49] Tan, Y. S.; Srinivasan, M. P.; Pehkonen, S. O.; Chooi, S. Y. M. Corros Sci. 2006, 48, 840-862. [50] Li, C.; Li, L.; Wang, C.; Zhu, Y.; Zhang, W. Corros Sci. 2014, 80, 511516. [51] Cui, F. Y.; Guo, L.; Zhang, S. T. Mater Corros. 2014, 65, 1194-1201. [52] Benabdellah, M.; Tounsi, A.; Khaled, K. F.; Hammouti, B. Arab J Chem. 2011, 4, 17-24. [53] Tian, H.; Li, W.; Cao, K.; Hou, B. Corros Sci. 2013, 73, 281-291. [54] Ye, X. R.; Xin, X. Q.; Zhu, J. J.; Xue, Z. L. Appl Surf Sci. 1998, 135, 307-317. [55] Qin, T. T.; Li, J.; Luo, H. Q.; Li, M.; Li, N. B. Corros Sci. 2011, 53, 1072-1078. [56] Sherif, E. M.; Park, S. M. Electrochim Acta 2006, 51, 6556-6562. [57] Finšgar, M. Corros Sci. 2013, 72, 90-98. [58] Finšgar, M.; Merl, D. K. Corros Sci. 2014, 80, 82-95. [59] Finšgar, M. Corros Sci. 2013, 72, 82-89. [60] Zhang, D.; Gao, L.; Zhou, G. Corros Sci. 2004, 46, 3031-3040. [61] Tansug, G.; Tuken, T.; Giray, E. S.; Findikkiran, G.; Sigircik,, G.; Demirkol, O.; Erbil, M. Corros Sci. 2014, 84, 21–29. [62] Tansug, G.; Tuken, T.; Kicir, N.; Erbil, M. Ionics 2014, 20, 237-294. [63] Tansug, G.; Tuken, T.; Sigircik, G.; Findikkiran, G.; Giray, E. S.; Erbil, M. Ionics 2015, 21, 1461-1475. [64] Bentiss, F.; Traisnel, M.; Vezin, H.; Hildebrand, H. F.; Lagrenée, M. Corros Sci. 2004, 46, 2781-2792. [65] El Azhar, M.; Mernari, B.; Traisnel, M.; Bentiss, F.; Lagrenée, M. Corros Sci. 2001, 43, 2229-2238. [66] Bentiss, F.; Lebrini, M.; Vezin, H.; Lagrenée, M. Mater Chem Phys. 2004, 87, 18-23.

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[67] Qin, T. T.; Li, J.; Luo, H.; Li, Q.; Li, M. N. B. Corros Sci. 2011, 53, 1072-1078. [68] Rochdi, A.; Touir, R.; El Bakri, M.; Ebn Touhami, M.; Bakkali, S.; Mernari, B. J. Env Chem Eng. 2015, 3, 232-242. [69] Borghei, S.; Dehghanian, C.; Yaghoubi R.; Yari, S. Res Chem Intermed. 2016, 42, 4551-4568. [70] Singh, P.; Srivastava, V.; Quraishi, M. A. J Mol Liq. 2016, 216, 164173. [71] Kanchi, S.; Singh, P.; Bisetty, K. Arab J Chem. 2014, 7, 11-25. [72] Faraglia, G.; Sitran, S.; Montagner, D. Inorg Chim Acta 2005, 358, 971980. [73] Amin, E.; Saboury, A. A.; Mansouri-Torshizi, H.; Zolghadri, S.; Bordbar, A. K. Biochim Pol. 2010, 57, 277-283. [74] Kicir, N.; Tansug, G.; Erbil, M.; Tuken, T. Corros Sci. 2016, 105, 88-99. [75] Singh, A. K.; Puri, B. K.; Rawley, R. K. Indian J Chem. 1988, 27, 430433. [76] Aljinovic, L. J.; Gudic, S.; Smith, M. J Appl Electrochem. 2000, 30, 973-979. [77] Hong-bo, F.; Hui-long, W.; Xing-peng, G.; Fia-shen, Z. Anti-Corros Method M. 2002, 49, 270-276. [78] Liao, Q. Q.; Yue, Z. W.; Yang, D.; Wang, Z. H.; Li, Z. H.; Ge, H. H.; Li, Y. J. Corros Sci. 2011, 53, 1999-2005. [79] Liao, Q. Q.; Yue, Z. W.; Li, Y. J.; Ge, H. H. Corrosion 2010, 66, 125002-125006. [80] Li, L.; Qu, Q.; Bai, W.; Yang, F.; Chen, Y.; Zhang, S.; Ding, Z. Corros Sci. 2012, 59, 249-257. [81] Tansug, G.; Kicir, N.; Demirkol, O.; Giray, E. S.; Tuken, T. J Adh Sci Tech. 2016, 30, 1984-2000. [82] Abdallah, M. Port Electrochim Acta 2004, 22, 161–175. [83] Zaafarany, I. Curr World Environ. 2006, 1, 101–108. [84] Umoren, S. A. Cellulose 2008, 155, 751–761. [85] Umoren, S. A. Open Corros J. 2009, 2, 175–188. [86] Umoren, S. A.; Obot, I. B.; Obi-Egbedi, N. O. J. Mater Sci. 2009, 44, 274–279. [87] Akbarzadeh, E.; Ibrahim, M. M.; Rahim, A. A. Int J Electrochem Sci. 2011, 6, 5396–5416. [88] Goller, K. (2011) Spectroscopic ellipsometry study on the oxide films formed on nickel-base alloys in simulated boiling water reactor environments. Determination of oxide film thickness. https://www.

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[89]

[90] [91] [92] [93] [94]

Gözde Tansuğ and Tunç Tüken kth.se/polopoly_fs/1.469671!/Spectroscopic%20ellipsometry%20study %20on%20the%20oxide%20films%20formed%20on%20nickel-base% 20alloys%20in%20simulated%20boiling%20water%20reactor.pdf/. Baboian, R. Corrosion Tests and Standards: Application and Interpretation (2nd Edition): ASTM International, West Conshohocken, PA, 2005; 107-340. Oraon, B.; Majumdar, G.; Ghosh, B. Mater Des. 2006, 27, 1035–1045. Zhao, X.; Jiang, R.; Zu, Y.; Wang, Y.; Zhao, Q.; Zu, B.; Zhao, D.; Wang, M.; Sun, Z. Appl Surf Sci. 2012, 258, 2000-2005. Guo, R.; Ren, X.; Ren, H. J Hazard Mater. 2012, 237, 270-276. Baş, D.; Boyacı, I. H. J Food Eng. 2007, 78, 836-845. Perfetti, G.; van der Meer, D. E. C.; Wildeboer, W. J.; Meesters, G. M. H. Adv Powder Technol. 2012, 23, 64-70.

In: Corrosion Inhibitors Editor: Esther Hart

ISBN: 978-1-63485-791-8 © 2017 Nova Science Publishers, Inc.

Chapter 2

APPLICATION OF POLYMER COMPOSITES AND NANOCOMPOSITES AS CORROSION INHIBITORS Saviour A. Umoren1,* and Moses M. Solomon2 1

Centre of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia 2 Corrosion Research Laboratory, Kaynasli Vocational College, Duzce University, Kaynasli, Duzce, Turkey

ABSTRACT Corrosion commonly defined as the deterioration of a material (usually a metal) or its properties because of a reaction with its environment is a global problem. NACE International, The Corrosion Society, estimates that global corrosion costs can be about 3–5% of GDP or GNP. Methods commonly adopted to combat corrosion include coatings and linings, cathodic protection, materials selection and corrosion inhibitors. Corrosion inhibitors are chemicals that, when present in very low concentrations, retard corrosion. Corrosion inhibitors form a layer over the metallic substrate and protect the metal from corrosion, thereby enhancing the life of the metal. Polymers, both naturally occurring and synthetic have been tested for metal corrosion *

Corresponding author: [email protected] (S.A. Umoren).

28

Saviour A. Umoren and Moses M. Solomon inhibitors as replacement for the toxic inorganic and organic corrosion inhibitors. Interest in polymers stems from their availability, cost effectiveness, and eco-friendliness in addition to the inherent stability and multiple adsorption centers. However, it is found that most polymer materials studied are moderate corrosion inhibitors. Several attempts such as copolymerizing, addition of substances that exert synergistic effect, cross linking, blending, and most recently incorporation of inorganic substances in nano size into the polymer matrix have been made to improve the inhibition ability of polymers. Composites are materials consisting of two or more chemically distinct constituents on a minutescale, having a distinct interface separating them, and with properties which cannot be obtained by any constituent working individually. The production of composite materials is either by ex-situ or in-situ formation through chemical synthesis although electrochemical method had been used recently. The application of polymer composites and nanocomposites as anticorrosion materials have shown promising results and are believed to form metal chelate which could barricade metal surfaces from corrosive agents. In this chapter, the application of polymer composites and nanocomposites as corrosion inhibitors for different metal substrates in different corrosive media is explored.

Keywords: polymers, composites, nanocomposites, corrosion inhibitor

1. INTRODUCTION In industries, particularly oil and gas industry, acid solutions are commonly employed in practices like acid pickling, oil-well acidizing, industrial cleaning, acid descaling, etc. This exercise usually promotes the corrosion of metals deployed in service in the environment. As a preventive measure, anti-corrosive agents (inhibitor) are always added to the acid solutions to lower the metal’s corrosion rate and reduce acid consumption. A metal corrosion inhibitor is a substance that, even at low concentration in a corrosive environment can interrupt and slow down corrosion reactions. Substances, both organic and inorganic origins have used to accomplish this task of suppressing metal dissolution in aggressive corrosive environments but the mode of action differs, hence inhibitors are classed into different groups as shown in Figure 1. However, mere suppression of the rate of metal dissolution in an aggressive environment does not qualify a substance to be used as an inhibitor. Other requirements abound and this include: (i) availability and cost effectiveness – the substance has to be readily available and inexpensive; (ii)

Application of Polymer Composites and Nanocomposites …

29

durability – should be able to protect the metal surface for a reasonable length of time; and (iii) toxicity – should be safe in handling and non-toxic to the natural environment. Although inorganic compounds like chromates, silicates, phosphates, molybdates, and nitrates as well as organic compounds containing heteroatoms (N, O, and S) and/or π-electrons in their molecules have enjoyed high patronage as metal corrosion inhibitor for decades [1-4], the adverse effect of inorganic compounds on the ecosystem and the exorbitant prices of the organic counterparts have come under severe criticism particularly in the 21st century. A cursory search on corrosion literature revealed that the corrosion scientists are now focusing attention on exploring plant extract and polymers as possible replacement for inorganic and organic corrosion inhibitors. Interest in polymers essentially arose from their availability, cost effectiveness, and eco-friendliness added to their inherent stability and multiple adsorption centers. However, it is found that most polymer materials studied are moderate corrosion inhibitor and tends to be unstable at elevated temperatures [5-7]. Abandoning this material and engaging in a search for alternative materials might not be a profitable venture; as such, corrosion scientists have resorted to modifying polymers so as to enhance their inhibitive ability and stability at higher temperature. Approaches employed in recent times include; copolymerizing [8, 9], addition of substances that exert synergistic effect [10, 11], cross linking [12], blending [13], and most recently incorporation of inorganic substances in nano size into the polymer matrix [14, 15]. Composite is a term used to describe a material that contains two or more chemically distinct constituents on a minute-scale, separated by distinct interface, and having properties which are different from the properties of the components working individually.

2. GLOBAL DEMAND OF CORROSION INHIBITORS In the present age, corrosion inhibitors are accorded top priority during project design and implementation particularly in areas where metals are used. The reason is simple; they can help elongate the lifespan of a material and by so doing maximize profit. The corrosion inhibitors’ market has thus witnessed an increase in demand. Corrosion inhibitors’ market is grouped based on application, functionality, and geography. The application segment include: power generation, pulp and paper, oil and gas industries, metal and mining, chemical processing, and the others. By functionality, corrosion inhibitors’

30

Saviour A. Umoren and Moses M. Solomon

market is divided into organic and inorganic inhibitors. Geographically, the market is segmented into North America, Europe, Asia-Pacific, and the rest of the world. According to the report of Transparency Market Research (www.transparencymarketresearch.com/corrosion-inhibitors), corrosion inhibitors demand globally stood at 4,425.9 kilo in 2012 with the cost pinned at US$ 5.20 billion. Of this amount, power generation had 29.1%, pulp and paper 12.3%, chemical processing 6.1%, oil and gas 19.4%, metal and mining 10.9%, and others 22.1% (Figure 2). The organic corrosion inhibitors led the market by almost 70% and Asia-Pacific held the largest share (>35%) in terms of demand while the North American and European corrosion inhibitors markets jointly held more than 50%. In 2013, inhibitors demand increased to 4,659.8 kilo and is predicted that the global inhibitors’ market would grow at 5% during 2015-2022 market year with the cost estimated to be US$9.2 billion by 2022 (www.grandviewresearch.com/industry-analysis/corrosion-inhibitorsmarket).

3. POLYMER COMPOSITES AND NANOCOMPOSITES 3.1. Methods of Preparation There are several methods of synthesizing polymer composites and nanocomposites. They can be grouped into two broad groups: in-situ and exsitu methods. The in-situ technique is simple, effective and involves one-step fabrication and as such enjoyed higher patronage than ex-situ method. In this method, one of the components (mostly the inorganic) is generated in-situ from corresponding precursors and are grown inside the polymer matrix. The merit of this technique is that it prevents particle agglomeration while maintaining a good spatial distribution in the polymer backbone. However, the major shortcoming of this method is that the un-reacted educts of the in-situ reaction might affect the properties of the composite formed. Some metal/polymer composites reported to have been prepared by in-situ approach include poly(methacrylic acid)/silver nanoparticles (PMAA/AgNPs) composite [14, 16], polypropylene glycol/silver (PPG/AgNPs) nanoparticles composite [17, 18], nanocomposites of aniline and CeO2 nanoparticles [19], etc. Ex-situ method, on the other hand, involves the dispersion of pre-made particles directly into polymer to form composites. The ex-situ synthesis technique is more suitable for large-scale industrial productions. This method

Application of Polymer Composites and Nanocomposites …

31

allows for precise control of the size, shape, and density of the inorganic particles that are used to form composites. However, the major challenge of this method is the difficulty in preparing inorganic components that possess higher dispersibility in the polymer backbone and have long-term stability against aggregation. Guo et al. [20] reported that this challenge can be overcome by using sonication methods in the dispersion process. Classification of Inhibitors

Interface Inhibitors: These are

Scavengers (Environmental Conditioners): These are inhibitors

inhibitors in which inhibition is caused by specific adsorption forming two-dimensional (2-D) layers on the corroding metal surface. They perform the task of inhibition by either geometric blocking, deactivation of active sites or reactive 2-D coverages

Vapour Phase

that inhibit by removing the corrosive agents from the medium

Liquid Phase

Anodic: This class of inhibitors

Cathodic: This category of

Mixed Adsorption: This class

acts by forming a protective oxide layer on metal surface causing the corrosion potential to shift significantly in anodic direction; forcing the metal surface into the passivation region. Examples are Chromates, nitrates, tungstate, molybdates, etc.

inhibitors performs by either suppressing the cathodic reactions or selectively precipitating on cathodic areas to obstruct the diffusion of corrosive species to the surface. Sulphite and bisulphate are typical examples

inhibits by reducing both the cathodic and anodic reactions. Silicates and phosphates are the common examples

Poison

Precipitators

Figure Classification ofof corrosion inhibitors Figure 1. 1:Classification corrosion inhibitors.

Physical: This

Chemical:

involves electrostatic interaction between charged molecules and a charged metal surface. Increase in temperature decreases the inhibitive power

involves electron sharing or transfer from the inhibitor molecules to the metal surface to form a coordinate type of bond. Increase in temperature increases inhibition efficiency

Film forming

32

Saviour A. Umoren and Moses M. Solomon

(Source: Goldman, Sachs, Virtus Global Partners, Delloite, ICS, EPA, Primary Interviews, Transparency Market Research) Figure 2. Global corrosion inhibitors’ market volume share, by end-use, 2012.

3.2. Application of Polymer Composites as Corrosion Inhibitors The primary feature that makes polymers to be investigated for anticorrosive effect is the present of heteroatom(s) and/or unsaturated bond(s) in their molecule. Organic compounds generally inhibit metal corrosion by adsorption onto the surface and heteroatom and/or π-bond is accepted [10, 21] to serve as the adsorption site. Polymers are macromolecules consisting of multiple repetitions of one or more atoms or groups linked to each other in sufficient amount capable of providing the molecule a set of properties. They have been extensively studied as metals corrosion inhibitor in various aggressive environments [22, 23] because of the numerous advantages mentioned in the introductory section. However, as mentioned before, they are moderate inhibitors and some authors [10] have attributed this to the influence of methylene group which characterized them on their solubility. Compositing is one of the many approaches employed by corrosion scientists to improve the inhibition efficiency of polymers and tremendous successes have been recorded. For instance, Zhu et al. [24] reported that perfluorinated lubricant/polypyrrole composite coated on low alloy steel can afford 99.8978% protection to the metal surface in 3.5% NaCl solution. It was demonstrated by Zou et al. [25] that bridged cyclodextrin (β-CD-PEG)

Application of Polymer Composites and Nanocomposites …

33

synthesized by the reaction of cyclodextrin and polyethylene glycol possessed better inhibiting ability for Q235 steel in HCl environment than cyclodextrin and polyethylene glycol due to its excellent solubility in water. Experimental results showed that 110 mg/L β-CD-PEG afforded 97% protection to the metal surface and scanning electron microscope (SEM) and energy dispersive x-ray (EDX) indicated that the high inhibition efficiency was due to the adsorption of inhibitor molecules and protective film formation on the metal surface (Figure 3). Syed et al. [26] prepared water-soluble polyaniline−poly(acrylic acid) (PANI−PAA) composites by a one-step in-situ polymerization technique and found that PAA did not only enhanced the solubility of PANI in water but also prevented the formation of macroscopic PANI clusters. The corrosioninhibition performance of PANI−PAA composites tested for 316 stainless steel (316SS) in 0.5 M HCl by electrochemical measurements revealed that PANI−PAA acted as a mixed-type inhibitor, and its inhibition efficiency increased with inhibitor concentration. The optimum concentration (200 ppm) showed a marked inhibition efficiency of 91.68%. The authors attributed the enhanced efficiency to an insulating interfacial layer formed by the adsorption of PANI−PAA, which obstructs the corrosion reaction at the interface. In Table 1 is presented polymer composites reported as metals’ corrosion inhibitors.

Figure 3. SEM images and EDX spectra of Q235 carbon steel exposed to 0.5 M HCl solution (a) without and with (b) bridged -CD-PEG (Adapted from Zou et al. [25]).

34

Saviour A. Umoren and Moses M. Solomon Table 1. Polymer composites reported as metals corrosion inhibitors

S/N

Composite

Metal/Alloy Protected

Environment Used

1

Aminothiourea-modified chitosan Chitosan salicyadehyde Schiff base Polyaniline/silver/cerium nitrate ternary

304 steel

2 3

4 5 6 7 8 9 10 11 12 13

Poly(vinyl alcohol-omethoxy aniline) Poly(vinyl alcohol- aniline) Poly (vinyl alcoholsulphanilic acid) Poly(vinyl alcohol-histidine) Poly(vinyl alcohol-leucine) Polyaniline/polyacrylic acid Pectin-g-polyacrylamide; Pectin-g-polyacrylic acid β-cyclodextrin-polyethylene glycol Perfluorinated lubricant/polypyrrole Pyrrole/2-amino-4phenylthiazole

Reference

Acetic acid

Highest Reported Percentage Protection 92

Mild steel

HCl

75.35

[28]

Coating material for metals Mild steel

H2SO4

68.08

[22]

HCl

72.99

[29]

Mild steel Mild steel

HCl HCl

92 84

[30] [15]

Mild steel Mild steel 316 stainless steel Mild steel

HCl HCl HCl

95 95 91.68

[31] [32] [26]

NaCl

85

[12]

Q235 carbon steel Low alloy steel Mild steel

HCl

94

[25]

NaCl

99.93

[24]

HCl

75

[33]

[27]

Outstandingly, three factors are identified from reports to have influence on the efficiency of composites when used as metals corrosion inhibitor. These are: concentration of inhibitor; exposure time; and temperature of the system. Increasing the concentration of inhibitor is found to cause an increase in the inhibitive ability of the composites and the reverse is true for decreasing the concentration of composites. For instance, Menaka and Subhashini [28] noted that, in 1 M HCl solution, 1500 ppm of a natural biopolymer chitosan modified into its Schiff base derivative with salicylaldehyde (CHSA) inhibits mild steel corrosion maximally but behaved poorly (43.30%) at a concentration of 100 ppm. Karthikaiselvi and Subhashini [29] reported that the optimum concentration of a water soluble composite, poly(vinyl alcohol-omethoxy aniline) (PVAMOA) required to achieve inhibition efficiency of 86.91% at 323 K for mild steel in 1 M HCl is 2000 ppm. Karthikaiselvi et al. [30] observed that 100 ppm of poly (vinyl alcohol-aniline) (PVAA) composite could only protect the surface of mild steel immersed in 1 M HCl solution by 37.67% but could be stepped-up to 92.00% if the concentration is raised to

Application of Polymer Composites and Nanocomposites …

35

2000 ppm. Also, an optimum concentration of 0.6% of poly (vinyl alcoholhistidine) and poly (vinyl alcohol-leucine) composites respectively is needed to achieve protection of more than 95% to mild steel surface deploy in service in 1 M HCl environment [31, 32]. Syed et al. [26] recently documented that, for a water-soluble polyaniline-poly(acrylic acid) composite to effectively extend the life span of 316SS steel utilized in 0.5 M HCl environment by 91.68%, 200 ppm of the inhibitor is required. This is in agreement with the findings of Geethanjali et al. [12] on the use of pectin-grafted polyacrylamide and pectin-grafted polyacrylic acid respectively for the protection of mild steel in 3.5% NaCl medium. This effect of composite concentration on its inhibition efficiency (IE) might not be far from the availability of the inhibitor molecules for adsorption. Metals corrosion inhibition by organic inhibitor is initiated by the displacement of adsorbed water molecules by the inhibitor species resulting in specific adsorption of the inhibitor molecules on the metal surface [34]. By increasing inhibitor concentration, higher number of water molecules is substituted and larger area of the metal surface covered and the effect is high inhibition. The length of time upon which metal is exposed to a corrosive medium containing inhibitor is another factor identified to affect inhibition efficiency. Menaka and Subhashini [28] studied the influence of immersion time on the performance of chitosan Schiff base as inhibitor for mild steel in 1 M HCl and found that IE varies directly as immersion time and reached a maximum value of 91% at 24 h of immersion time (Figure 4(a)). Karthikaiselvi and Subhashini [29] noticed that IE of PVAMOA increased at first instance and reached a maximum value of 97.21% at 3 h immersion but thereafter decreased to 92.02% at 24 h of exposure time. Karthikaiselvi et al. [30] equally found that, for any concentration of PVAA studied, IE increased with time and maximum inhibition was obtained at 12 h of immersion time (Figure 4(b)). In the work of Srimathi et al. [15] on polyvinyl alcohol–sulphanilic acid (PVASA) composite as corrosion inhibitor for mild steel in 1 M HCl medium, the authors noticed that IE increased during the first one hour and reached the highest value of 90.5% for 6000 ppm of PVASA but thereafter decreased steadily to 79.9% at 24 h and finally 63.0% at 48 h of exposure to the investigated corrosive environment (Figure 4(c)). As earlier stated, inhibition of metal corrosion by organic inhibitor is an adsorption process whereby inhibitor species replaced adsorbed water molecules on the metal surface. However, the effectiveness of an adsorbed inhibitor layer in protecting metal surface from aggressive agents present in an environment depends to a large extent on the thickness, stability, and rigidity of the adsorbed layer. It is deduced from the reports that, adsorbed

36

Saviour A. Umoren and Moses M. Solomon

composite films, at prolonged exposure to corrosive environment become relatively unstable and gradually loses its efficacy as efficient metals corrosion inhibitor.

Figure 4. Variation of inhibition efficiency of different composites with immersion time (Re-plotted with permission from (a) Karthikaiselvi and Subhashini [28] (b) Karthikaiselvi et al. [30] and (c) Srimathi et al. [15]).

Application of Polymer Composites and Nanocomposites …

37

Figure 5. Variation of inhibition efficiency of different composites with temperature (Adapted from (a) Karthikaiselvi and Subhashini [29], (b) Menaka and Subhashini [28] and (c) Karthikaiselvi et al. [30].

38

Saviour A. Umoren and Moses M. Solomon

In inhibited corrosive environment, many changes such as rapid etching, desorption and decomposition of inhibitor, etc. take place on metal surface as temperature of the environment changes. Research findings have shown that temperature change has serious influence on the inhibition efficiency of inhibitors. The study on the influence of temperature on the performance of PVAMOA [29] and PVAA [30] on mild steel exposed to 1 M HCl environment revealed that IE increased with rise in temperature up to 323 K and then decreased beyond this temperature (Figure 5 (a and c)). Srimathi et al. [15] found that PVASA behaved in like manner as PVAMOA and PVAA when the temperature of the PVASA inhibited acid system was raised. Menaka and Subhashini [28] however observed that the inhibition efficiency of CHSA varies directly with temperature up to 333 K before decreasing thereafter (Figure 5(b)). The structural orientation of these polymers would have a lot to do with this observation. As noted by Solomon et al. [34], polymers are mostly extended (rod-like) at low temperatures but at elevated temperatures, the molecules overlap and coil up and then, entangle to become a thermoreversible gel. This means that, at lower temperatures the adsorbed inhibitor molecules on the metal surface appreciably cover the surface but at higher temperatures, the thermoreversible gel which could also dissolve from the surface expose some areas to corrosive agent and the resultant effect is the reported lesser IE at elevated temperatures (Figure 5).

3.3. Application of Polymer Nanocomposites as Corrosion Inhibitors Recently, nanocomposites have gain global attention due to the fact that their properties (optical, electrical, magnetic, etc.) uniquely differ from those of the conventional composites. By definition, nanocomposites are those composites in which the diameter of one of the constituents is below micron dimension (generally less than 0.1 µm i.e., 100 nm). The endearing feature of nanocomposites is the dependency of their properties on the size of the nanoparticle. Decrease in the particle size increases the ratio of surface-tovolume and the effect is good surface properties. Metals/polymer nanocomposites are of special interest because they have excellent flexibility, high compatibility, and strong adhesive power than other forms of nanocomposites [35, 36]. Corrosion scientists have noted that nanocomposites possess excellent inhibiting ability for metals in different media than their corresponding polymers and should be utilized in full scale

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39

for commercial purposes. Solomon and Umoren [17] and Solomon et al. [18] reported that polypropylene glycol/silver nanoparticles (PPG/AgNPs) composite has the efficacy to effectively inhibit the corrosion of mild steel and aluminium in sulphuric acid environment. According to the reports, PPG/AgNPs could protect mild steel surface in sulphuric acid solution by 94% at temperature as high as 333K and Al surface by 85.6% at 303 K. Figure 6 illustrates the synthetic step of PPG/AgNPs and its effectiveness as inhibitor for mild steel in acid solution. Solomon et al. [14, 16] documented that poly (methacrylic acid)/silver nanoparticles (PMAA/AgNPs) composites prepared in-situ using natural honey as the reducing and capping agent can be used for safeguarding the life of mild steel and Al in acid medium. It was noted that PMAA/AgNPs interrupted both anodic and cathodic corrosion reactions and can offer protection of more than 80% to the metal surfaces in the aggressive environment. Atta et al. [37] and [38] reported that poly (ethylene glycol) thiol, poly (vinyl pyrrolidone) self-assembled monolayer Ag nanoparticles and Ag/2-acrylamide-2-methylpropane/N-isopropylacryamide nanocomposite respectively were effective corrosion inhibitor for steel in HCl environment. Also, polyaniline-α-Fe2O3 nanoparticle composite [39], polypyrrole-clay nanocomposite [40], chitosan/ZnO nanoparticle composite [41], and polyaniline/CeO2 nanocomposite [19] had been reported to have inhibitive ability towards the corrosion of 316LN steel, cold rolled steel, and mild steel in NaCl and HCl media respectively. Recently, Hefni et al. [42] advocated for the use of chitosan grafted poly (ethylene glycol) assembled on silver nanoparticles (ch-g-PEG/AgNPs) for the corrosion inhibition of carbon steel in HCl medium. The authors stated that inhibition efficiency of 92.75% can be achieved at 298 K with 3 mM ch-g-PEG/AgNPs. Table 2 summarized polymer nanoparticles composites reported as efficient corrosion inhibitor for metals in different corrosive environments.

3.4. Mechanism of Corrosion Inhibition by Composites and Nanocomposites The effectiveness and interaction of an organic inhibitor with a metal surface depend to a large extent on the adsorption ability of the inhibitor molecules [43]. However, certain factors namely, concentration of electrolyte, nature of inhibitor, and the charge on the metal surface influence the adsorption as well as efficiency of inhibitor molecules [44]. Depending on the concentration of the electrolyte, organic inhibitors exist as charged species,

40

Saviour A. Umoren and Moses M. Solomon

neutral species, or both and adsorption is a function of metal surface charge. The metal surface charge is defined by the position of corrosion potential (Ecorr) with respect to the potential of zero charge (PZC) Eq = 0. When the difference (ψ) between Ecorr and Eq = 0 is negative, the metal surface acquires a net negative charge and adsorption of positively charged inhibitor species are favored but adsorption of negatively charged inhibitor species is favored if Ecorr minus Eq = 0 is positive [45]. Table 2. Polymer nanocomposites reported as metals corrosion inhibitors S/N Composite

Metal/Alloy Protected

1

2

3 4 5 6

7

8

9 10 11

Poly (methacrylic acid)/silver Nanocomposite Poly (methacrylic acid)/silver nanocomposite Polypropylene glycolsilver nanoparticle Polypropylene glycolsilver nanoparticle Polyaniline/CeO2 nanocomposite Poly(ethylene glycol) thiol and poly(vinyl pyrrolidone) self assembled monolayer silver nanocomposite 2-acrylamido-2methylpropane/Nisopropylacrylamine silver nanocomposite Polyaniline-α-Fe2O3 nanocomposite Polypyrrole-clay nanocomposite Chitosan/ZnO nanocomposite Chitosan-g-Polyethylene glycol assembled silver nanocomposite

Reference

Al

Environment Highest Used Reported Percentage Protection H2SO4 85.6

Mild steel

H2SO4

81.8

[16]

Mild steel

H2SO4

94

[17]

Al

H2SO4

85.6

[18]

Mild steel

HCl

69.25

[19]

Carbon steel HCl

90.95

[37]

Steel

HCl

81.46

[38]

316LN stainless steel Cold rolled steel Mild steel

NaCl

–

[39]

NaCl

–

[40]

HCl

73.80

[41]

Carbon steel HCl

92.75

[42]

[14]

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41

Figure 6. Synthesis route and characterization of PPG/AgNPs and its effectiveness as mild steel corrosion inhibitor in sulphuric acid solution (Solomon and Umoren [17]).

Generally, the adsorption of organic inhibitor onto metal surface is a quasi-substitution process whereby inhibitor molecules in the solution (Inhsol) replace adsorbed water molecules (H2Oads) on metal according to Equation 1 [45]:

Inh sol  xH 2 O ads  Inh ads  xH 2 Osol

(1)

where Inhads is the adsorbed inhibitor on the metal surface and 𝑥 is the number of water molecules replaced by the inhibitor molecules. There are therefore three possible ways in which composite molecules can substitute adsorbed water molecules: (i) by sharing of electrons between their heteroatoms and the metal surface, (ii) through π-electron interaction between unsaturated bonds and metal surface, and (iii) through electrostatic attraction between charged inhibitor species and charged metal surface. Menaka and Subhashini [28] explained that the mechanism of adsorption of chitosan Schiff base onto mild steel surface in acid environment was through both electrostatic interaction and chemical electron sharing according to Figure 7. However, the

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Saviour A. Umoren and Moses M. Solomon

mechanism of metals corrosion inhibition by inorganic nanocomposite is more complex than that of organic composite as corrosion scientists believed that the inorganic nanoparticles play significant role in the adsorption and inhibition process. According to Solomon and Umoren [17], metal nanoparticles can be chemisorbed on metal surface and decrease the hydrophilicity of metal surface and as effect promotes the adsorption of organic component of the composite. Hefni et al. [42] explained in their work on ch-g-PEG/AgNPs as inhibitor for steel in HCl solution that when iron is immersed in ch-g-PEG/AgNPs inhibited acid solution, adsorption of the nanocomposite molecules happened in two ways: (i) by monomethylated PEG and (ii) through adsorption of AgNPs directly on the metal surface which is possible because of the active properties of the nanoparticles. Sasikumar et al. [19] equally opined that the mechanism of corrosion inhibition of mild steel in acid environment by PANI/CeO2 nanocomposite occurred by the formation of inhibitor film due to redox reaction of iron and PANI and also by secondary reaction of formation of cerium-iron complex. According to the authors, the protection of the metal surface takes place through the reduction of polyaniline emeraldine salt to polyaniline leucoemeraldine salt with the concomitant release of cerium ions which formed iron-cerium complex along with the passive film formed by PANI.

3.5. Challenges on the Use of Composites and Nanocomposites as Metals Corrosion Inhibitors Two issues are most likely to hamper the commercial utilization of polymer composites and polymer-nanoparticles composites. These are: (i) difficulty in dispersing added component uniformly in polymer matrix and (ii) the cost of production on a commercial scale. Composites and nanocomposites in which the added component is well dispersed in the polymer matrix perform better. However, the fact that the added particles particularly inorganic particles have the tendency to agglomerate always poses difficulty during synthesis. The cost of production is another issue; at present, the price of synthetic polymers depends on the price of crude oil. Utilizing synthetic polymers on large scale production of composites and nanocomposites for commercial application as metal corrosion inhibitor might not be cost effective. Also, already there are expressions of fear over petroleum-based products since crude oil is non-renewable resource. Scientists [28, 34] are

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43

advocating for the use of naturally occurring polymers but availability in a commercial scale is still in doubt.

Figure 7: Schematic representationofofplausible plausible interaction Schiff basebase withwith mild Figure 7. Schematic representation interactionofofchitosan chitosan Schiff steel surface in acid medium (Menaka and Subhashini, [28]) mild steel surface in acid medium (Menaka and Subhashini, [28]).

CONCLUSION This chapter focused on the application of polymer composites and nanocomposites as metal corrosion inhibitors in various aggressive environments. It is evident from reports that polymer composites and nanocomposites can effectively protect metal surface deployed in service in a corrosive environment. However, the extent of protection depends principally on the concentration of the inhibitor, exposure duration, and temperature of the environment. Nevertheless, the utilization of polymer composites and nanocomposites on an industrial scale might be hampered by the difficulty involved in producing a well and uniformly dispersed composites and nanocomposites and the financial implication of large scale production.

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Li, X; Deng, S; Fu, H; Mu, G. Synergistic inhibition effect of rare earth cerium(IV) ion and 3,4-dihydroxybenzaldehye on the corrosion of cold rolled steel in H2SO4 solution, Corros. Sci., 51, (2009), 2639–2651.

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Li, X; Deng, S; Fu, H; Mu, G. Synergistic inhibition effect of rare earth cerium(IV) ion and anionic surfactant on the corrosion of cold rolled steel in H2SO4 solution, Corros. Sci., 50, (2008), 2635–2645. [3] Gunasekaran, G; Palniswamy, N; Apparao, BV; Muralidharan, VS. Enhanced synergistic inhibition by calcium gluconate in low chloride media. Part 1: kinetics of corrosion, Proc. Indian Acad. Sci (Chem. Sci.), 108, (1996), 399 – 405. [4] Qu, Q; Hao, Z; Jiang, S; Li, L; Bai, W. Synergistic inhibition between dodecylamine and potassium iodide on the corrosion of cold rolled steel in 0.1 M phosphoric acid, Mater. Corros., 59(11), (2008), 883-888. [5] Bayol, E; Gurten, AA; Dursun, M; Kayakirilmaz, K. Adsorption behavior and inhibition corrosion effect of sodium carboxylmethyl cellulose on mild steel in acidic medium, Acta Physco-Chim. Sin., 24, (2008), 2236. [6] Arukalam, IO; Nleme, KI; Anyanwu, AE. Comparative inhibitive effect of hydroxyethylcellulose on mild steel and aluminium corrosion in 0.5 M HCl solution, Academic Res. Int., 1(3), (2011), 492-498. [7] Rajeswari, V; Kesavan, D; Gopiraman, M; Viswanathamurthi, P. Physicochemical studies of glucose, gellan gum, andhydroxypropyl cellulose - inhibition of cast iron corrosion, Carbohyd. Polym., 95, (2013), 288-294. [8] Govindaraju, KM; Gopi, D; Anver, K. Basha, Synthesis, characterization, and electrochemical evaluation of anti-corrosive performance of poly((N-Methacryloyloxymethyl) benzotriazole-coNVinylpyrrolidone) coatings, J. Appl. Electrochem., 43, (2013), 1043– 1054. [9] Xu, Y; Zhang, B; Zhao, L; Cui, Y. Synthesis of polyaspartic acid/5aminoorotic acid graft copolymer and evaluation of its scale inhibition and corrosion inhibition performance, Desalination, 311, (2013), 156– 161. [10] Umoren, SA; Solomon, MM. Effect of halide ions on the corrosion inhibition efficiency of different organic species - A review, J. Ind. Eng. Chem., 21, (2014), 81 – 100. [11] Jeyaprabha, C; Sathiyanarayanan, S; Venkatachari, G. Influence of halide ions on the adsorption of diphenylamine on iron in 0.5 M H2SO4 solution, Electrochim. Acta, 51, (2006), 4080–4088. [12] Geethanjali, R; Ali Fathima Sabirneeza, A; Subhashini, S. Water-soluble and biodegradable pectin-grafted polyacrylamide and pectin-grafted polyacrylic acid: electrochemical investigation of corrosion-inhibition

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behaviour on mild steel in 3.5% NaCl media, Ind. J. Mater. Sci., 2014, (2014), 1-9. Umoren, SA; Eduok, UM; Solomon, MM. Effect of polyvinylpyrrolidone – polyethylene glycol blends on the corrosion inhibition of aluminium in HCl solution, Pigm. Resin Technol., 43 (5), (2014), 299–313. Solomon, MM; Umoren, SA. Performance assessmentof poly (methacrylic acid)/silver nanoparticles composite as corrosion inhibitor for aluminiumin acidic environment, J. Adhes. Sci. Technol., 29(21), 2311-2333. Srimathi, M; Rajalakshmi, R; Subhashini, S. Polyvinyl alcohol– sulphanilic acid water soluble composite as corrosion inhibitor for mild steel in hydrochloric acid medium, Arab. J. Chem., 7, (2014), 647–656. Solomon, MM; Umoren, SA; Abai, EJ. Preparation and evaluation of the surface protective performance of poly (methacrylic acid)/silver nanoparticles composites (PMAA/AgNPs) on mild steel in acidic environment. J. Mol. Liq., 212, (2015), 340–351. Solomon, MM; Umoren, SA. In-situ preparation, characterisation, and anticorrosion property of polypropylene glycol/silver nanoparticles composite for mild steel corrosion in acid solution. J. Coll. Interf. Sci., 462, (2016), 29–41. Solomon, MM; Umoren, SA; Israel, AU; Ebenso, EE. Polypropylene glycol - silver nanoparticles composites prepared in-situ as corrosion inhibitor for aluminium in acidic environment, J. Mater. Eng. Perform., 24, (2015), 4206 - 4218. Sasikumar, V; Madhan Kumar, A; Gasem, ZM; Ebenso, EE. Hybrid nanocomposite from aniline and CeO2nanoparticles: Surface protective performance on mild steel in acidic environment, Appl. Surf. Sci., 330, (2015), 207–215. Guo 1, Q; Ghadiri, R; Weigel, T; Aumann, A; Gurevich, EL; Esen, C; Medenbach, O; Cheng, W; Chichkov, B; Ostendorf, A. comparison of in situ and ex situ methods for synthesis of two-photon polymerization polymer nanocomposites, Polymers, 6, (2014), 2037-2050. Umoren, SA; Solomon, MM. Recent developments on the use of polymers as corrosion inhibitors-A review, The Open Mater. Sci. J., 8, (2014), 30 – 45. Li, Y; Li, Z; Zheng, F. Polyaniline/silver/cerium nitrate ternary composite: synthesis, characterization and enhanced electrochemical properties, J. Appl. Polym. Sci., 2015, DOI: 10.1002/APP.42785.

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[23] Mobin, M; Khan, MA; Parveen, M. Inhibition of mild steel corrosion in acidic medium using starch and surfactants additives, J. Appl. Polym. Sci., 121, (2011), 1558–1565. [24] Zhu, H; Hou, J; Qiu, R; Zhao, J; Xu, J. Perfluorinated lubricant/polypyrrole composite material: preparation and corrosion inhibition, J. Appl. Polym. Sci., 131(9), (2014), 1-7. [25] Zou, C; Liu, Y; Yan, X; Qin, Y; Wang, M; Zhou, L. Synthesis of bridged β-cyclodextrin-polyethylene glycol and evaluation of its inhibition performance in oilfield wastewater, Mater. Chem. Phys., 147, (2014), 521-527. [26] Syed, JA; Tang, S; Lu, H; Meng, X. Water-soluble polyaniline−polyacrylic acid composites as efficient corrosion inhibitors for 316SS, Ind. Eng. Chem. Res., 54, (2015), 2950−2959. [27] Li, M; Xu, J; Li, R; Wang, D; Li, T; Yuan, M; Wang, J. Simple preparation of aminothiourea-modified chitosan as corrosion inhibitor and heavy metal ion adsorbent, J. Coll. Interf. Sci., 417, (2014), 131– 136. [28] Menaka, R; Subhashini, S. Chitosan Schiff base as eco-friendly inhibitor for mild steel corrosion in 1 M HCl, J. Adhes. Sci. Technol., 30, (2016), 1622 – 1630. [29] Karthikaiselvi, R; Subhashini, S. Study of adsorption properties and inhibition of mild steel corrosion in hydrochloric acid media by water soluble composite poly (vinyl alcohol-o-methoxy aniline), J. Assoc. Arab Univer. Basic Appl. Sci., 16, (2014), 74-82. [30] Karthikaiselvi, R; Subhashini, S; Rajalakshmi, R. Poly (vinyl alcohol – aniline) water soluble composite as corrosion inhibitor for mild steel in 1 M HCl, Arab. J. Chem., 5, (2012), 517–522. [31] Sabirneeza, AAF; Subhashini, S. A novel water-soluble, conducting polymer composite for mild steel acid corrosion inhibition, J. Appl. Polym. Sci., 127, (2013), 3084–3092. [32] Sabirneeza, AAF; Subhashini, S; Rajalakshmi, R. Water soluble conducting polymer composite of polyvinyl alcohol and leucine: An effective acid corrosion inhibitor for mild steel. Mater. Corros., 64 (1), (2013), 74-82. [33] Sayyah, SM; El-Deeb, MM. Electrocopolymerization of a binary mixture of pyrrole and 2-amino-4-phenylthiazole: kinetic studies, copolymer structure, and applications as corrosion protection for mild steel in acid medium, J. Appl. Polym. Sci., 103, (2007), 4047–4058.

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[34] Solomon, MM; Umoren, SA; Udousoro, II; Udoh, AP. Inhibitive and adsorption behavior of carboxymethyl cellulose on mild steel corrosion in sulphuric acid solution, Corros. Sci., 52, (2010), 1317 – 1325. [35] Taryba, M; Lamaka, SV; Snihirova, D; Ferreira, MGS; Montemor, MF; Wijting, WK; Towes, S; Grundineier, G. The combined use of scanning vibrating electrode technique and micro-potentiometry to assess the selfrepair processes in defects on ‘smart’ coatings applied to galvanized steel, Electrochim. Acta, 56, (2011), 4475–4488. [36] Ramezanzadeh, B; Attar, MM. An evaluation of the corrosion resistance and adhesion properties of an epoxy-nanocomposite on a hot-dip galvanized steel (hdg) treated by different kinds of conversion coatings, Surf. Coat. Technol., 205, (2011), 4649–4657. [37] Atta, AM; Allohedan, HA; El-Mahdy, GA; Ezzat, ARO. Application of stabilized silver nanoparticles as thin films as corrosion inhibitors for carbon steel alloy in 1M hydrochloric acid, J. Nanomater., 2013, (2013), 1-8. [38] Atta, AM; El-Mahdy, GA; Al-Lohedan, HA; Ezzat, AO. Synthesis and application of hybrid polymer composites based on silver nanoparticles as corrosion protection for line pipe steel, Molecules, 19, (2014), 62466262. [39] Umare, SS; Shambharkar, BH. Synthesis, characterization, and corrosion inhibition study of polyaniline-a-Fe2O3 nanocomposite, J. Appl. Polym. Sci., 127, (2013), 3349–3355. [40] Yeh, JM; Chin, CP; Chang, S. Enhanced corrosion protection coatings prepared from soluble electronically conductive polypyrrole-clay nanocomposite materials, J. Appl. Polym. Sci., 88, (2003), 3264–3272. [41] John, S; Joseph, A; Jose, AJ; Narayana, B. Enhancement of corrosion protection of mild steel by chitosan/ZnO nanoparticle composite membranes, Prog. Organic Coat., 84, (2015), 28–34. [42] Hefni, HHH; Azzam, EM; Badr, EA; Hussein, M; Tawfik, SM. Synthesis, characterization and anticorrosion potentials of chitosan-gPEG assembled on silver nanoparticles, Int. J. Bio. Macromol., 83, (2016), 297–305. [43] Doner, A; Solmaz, R; Ozcan, M; Kardas, G. Experimental and theoretical studies of thiazoles as corrosion inhibitors for mild steel in sulphuric acid solution, Corros. Sci., 53, (2011), 2902−2913. [44] Badr, GE. The role of some thiosemicarbazide derivatives as corrosion inhibitors for C-steel in acidic media, Corros. Sci., 51, (2009), 2529−2536.

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[45] Gerengi, H; Ugras, HI; Solomon, MM; Umoren, SA; Kurtay, M; Atar, N. Synergistic corrosion inhibition effect of 1-ethyl-1methylpyrrolidinium tetrafluoroborate and iodide ions for low carbon steel in HCl solution, J. Adhes. Sci. Technol., DOI: 10.1080/ 01694243.2016.1183407.

BIOGRAPHICAL SKETCH Name: SOLOMON, Moses Monday Affiliation: Corrosion Research Laboratory, Department of Mechanical Engineering, Duzce University, Turkey Education: PhD (Polymer Chemistry) Research and Professional Experience: Research is focused on polymer synthesis, characterization, modification, and extensively on investigating materials corrosion and corrosion inhibition mechanisms on conventional polycrystalline as well as nanocrystalline surfaces. Professional Appointments: Postdoctoral Research Fellow, Department of Mechanical Engineering, Duzce University, Turkey (TUBITAK 21514107115.02-56312), 13th May, 2016 to 13th May, 2017 Publications Last 3 Years: (A) Journals 1. Gerengi, H., Ugras, H. I., Solomon, M. M., Umoren, S. A., Kurtay, M. and Atar, N. (2016). Synergistic corrosion inhibition effect of 1ethyl-1- methylpyrrolidinium tetrafluoroborate and iodide ions for low carbon steel in HCl solution. J. Adhes. Sci. Technol., 30 (21):23832403 2. Solomon, M. M. and Umoren, S. A. (2016). In-situ preparation, characterisation, and anticorrosion property of polypropylene glycol/silver nanoparticles composite for mild steel corrosion in acid solution. Journal of Colloid and Interface Science, 462: 29–41 3. Solomon, M. M., Umoren, S. A., Israel, A. U., and Etim, I. G. (2015). Synergistic inhibition of aluminium corrosion in 0.5 M H2SO4 solution by polypropylene glycol in the presence of iodide ions. Pigment Resin Technology, DOI:10.1108/PRT-01-2015-0010 4. Solomon, M. M., Umoren, S. A. and Abai, E. J. (2015). Preparation and evaluation of the surface protective performance of poly (methacrylic acid)/silver nanoparticles composites (PMAA/AgNPs)

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5.

6.

7.

8.

9.

10.

11.

12.

13.

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on mild steel in acidic environment. Journal of Molecular Liquids, 212: 340–351 Solomon, M. M., Umoren, S. A., Israel, A. U., and Ebenso, E. E, (2015). Polypropylene glycol - silver nanoparticles composites prepared in-situ as corrosion inhibitor for aluminium in acidic environment. Journal of Materials Engineering & Performance, 24: 4206 - 4218 Solomon, M. M. and Umoren, S. A. (2015). Electrochemical and gravimetric measurements of inhibition of aluminium corrosion by poly (methacrylic acid) in H2SO4 solution and synergistic effect of iodide ions. Measurement, 76: 104 - 116 Umoren, S. A., Solomon, M. M. Israel, A. U., Eduok, U. M. and Jonah, A. E. (2015). Comparative study of the corrosion inhibition efficacy of polypropylene glycol and poly (methacrylic acid) for mild steel in acid solution. Journal of Dispersion Science and Technology, 36(12): 1721-1735 Jonah, A. E., Solomon, M. M. and Ano, A. O. (2015). Assessment of the physico-chemical properties and heavy metal status of water samples from Ohii Miri river in Abia State, Nigeria. Merit Research Journal of Environmental Science and Toxicology, 3(1): 001 – 011 Solomon, M. M. and Umoren, S. A. (2015). Performance evaluation of poly (methacrylic acid) as corrosion inhibitor in the presence of iodide ions for mild steel in H2SO4 solution. Journal of Adhesion Science and Technology, 29 (11): 1060 – 1080 Jonah, A. E., Solomon, M. M., Ikpe, D. I., and Etim I. G. (2015). Macro nutrients determination and bacteriological status assessment of water and sediment samples from Ohii Miri River in Abia State, Nigeria. International Journal of Engineering Innovation & Research, 4(3): 383 – 389 Solomon, M. M. and Umoren, S. A. (2015). Enhanced corrosion inhibition of mild steel by polypropylene glycol in the presence of iodide ions in acid solutions. Journal of Environmental Chemical Engineering, 3: 1812–1826 Solomon, M. M. and Umoren, S. A. (2015). Performance assessment of poly (methacrylic acid)/silver nanoparticles composite as corrosion inhibitor for aluminium in acidic environment. Journal Adhesion Science and Technology, 29: 21, 2311-2333 Osu, S. R., Solomon, M. M., Abai, E. J. and Etim, I. G. (2015). Human health risk assessment of heavy metals intake via cassava

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Saviour A. Umoren and Moses M. Solomon consumption from crude oil impacted soils with and without palm bunch ash additive. International Journal of Technical Research and Applications, 3 (4): 140-148 14. Umoren, S. A., Solomon, M. M., Eduok, U. B., Obot, I. B. and Israel, A. U. (2014). Inhibition of mild steel corrosion in H2SO4 solution by coconut coir dust extract obtained from different solvent systems and synergistic effect of iodide ions: Ethanol and acetone extracts. Journal of Environmental Chemical Engineering, 2: 1040 – 1060 15. Umoren, S. A. and Solomon, M. M. (2014). Recent developments on the use of polymers as corrosion inhibitors-A review. The Open Material Science Journal, 8: 30 – 45 16. Jonah, A. E., Solomon, M. M. and Ano, A. O. (2014). Study on the physicochemical properties and heavy metal status of sediment samples from Ohii Miri River in Abia State, Nigeria. Fountain Journal of Natural and Applied Science, 3 (1): 29 – 49 17. Umoren, S. A., Eduok, U. B. and Solomon, M. M. (2014). Effect of polyvinylpyrrolidone-polyethylene glycol blends on the corrosion inhibition of aluminium in HCl solution. Pigment and Resin Technology, 43(5): 299 – 313 18. Umoren, S. A. and Solomon, M. M. (2014). Effect of halide ions on the corrosion inhibition efficiency of different organic species - A review. Journal of Industrial Engineering Chemistry, 21: 81 – 100 19. Umoren, S. A., Obot, I. B., Isreal, A. U., Asuquo, P. O., Solomon, M. M., Eduok, U. M. and Udoh, A. P. (2014). Inhibition of mild steel corrosion in acidic medium using coconut coir dust extracted from water and methanol as solvents. Journal of Industrial Engineering Chemistry, 20: 3612 – 3622 (B) Book/Book Chapter: 1. Umoren, S. A., Solomon, M. M. “Polymer Characterization: Polymer Molecular Weight Determination” In: Polymer Science: Research Advances, Practical Applications and Education Aspects (A. MéndezVilas, A. Solano-Martin (Eds)), Formatex Research Centre, Badajoz, Spain (To be published in summer 2016) 2. Umoren, S. A., Solomon, M. M. “Polypropylene (PP)/Starch Based Biocomposites and Bionanocomposites” In: Propylene Based Composites and Bionanocomposites (P. M. Visakh, Matheus Poletto (Eds), (To be published by Wiley and Sons, USA).

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3. Abasiekong, B. O. and Solomon, M. M. (2015). Rudiments of Chemistry, Ikot Ekpene: Gift Printers (Nig.). Name: Dr. Saviour A. Umoren Affiliation: King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia Education: PhD (Polymer Science) Research and Professional Experience: (a)Research Experience: Research Interests        

Electrochemical investigation of corrosion phenomena in different aqueous aggressive environments. Development of environmentally friendly corrosion inhibitors for oil and gas industry Development of corrosion inhibitors for high temperature applications. Interface characterization, including adsorption and biosorption studies. Polymer synthesis and characterization/additives in polymer. Organic coatings (Alkyd resins) Nanotechnology Development of polymer-nanoparticles composites for corrosion protection.

Research Grants 1. Studies On Corrosion Inhibition Potential of Extracts of Coconut Coir Dust Obtained from Different Solvent Systems for Mild Steel in Different Environments. (Project #: 10−107RG/CHE/AF/AC-G; Value: $23,860; Role: PI) Grant for Research Units from TWAS, the Academy of Sciences for the Developing World, May, 2011. 2. Development of Environmentally Friendly Corrosion and Scale Inhibitors from Indigenous Plants of Saudi Arabia (Project #: 14ADV2452-04; Value: $533,213.33; Role PI) (Grant from NSTIP, Saudi Arabia)

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Saviour A. Umoren and Moses M. Solomon 3. Computer-Aided Design of Ecofriendly Organic Inhibitors for Steel Corrosion (Project #: 14-ADV2448-04; Value: $406,314.67; Role: Co-I) (Grant from NSTIP, Saudi Arabia)

Postgraduate Supervision: Supervised and graduated 11 MSc and 1 PhD students (b) Professional Experience: (i) University of Uyo, Uyo, Nigeria (a) Assistant Lecturer, Department of Chemical/Petroleum Engineering, University of Uyo, March 1998 – October 1998. (b) Assistant Lecturer, Department of Chemistry, University of Uyo, Oct. 1998- September 2002 (c) Lecturer II, Department of Chemistry, University of Uyo, October1, 2002 –September 2004. (d) Lecturer I, Department of Chemistry, University of Uyo, October 1, 2005 - September 2007. (e) Senior Lecturer, Department of Chemistry, University of Uyo, Oct. 1, 2008 – September, 2011 (f) Associate Professor, Department of Chemistry, University of Uyo, October 1, 2011 – Date. (ii) King Fahd University of Petroleum and Minerals (KFUPM), Saudi Arabia (a) Research Scientist II (Associate Professor), December 2012 Date University Administration Head of Department, Department of Chemistry, UNIUYO (2010 – 2012) Journal Review: I have served as a reviewer to more than 70 international journals which include Corrosion Science, Carbohydrate Polymers, Journal of Solid State Electrochemistry, Industrial and Engineering Chemistry Research, International Journal of Biological Macromolecules, Journal of Applied Electrochemistry, Green Chemistry Letters and Reviews, Journal of Molecular Liquids, Research on Chemical Intermediates, Pigment and Resin Technology, Anti Corrosion Methods and Materials, Ionics, Materials Chemistry and Physics, Arabian Journal of Chemistry, Cellulose, Journal of Industrial and

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Engineering Chemistry, Journal of Polymer Technology, Journal of Environmental Chemical Engineering amongst others. Professional Appointments: Membership of Journal Editorial Board (a) American Journal of Chemistry (Scientific and Academic Publishing), USA (b) International Scholarly Research Notices (ISRN) (Materials Science), USA. (c) Journal of Materials and Environmental Science, Morocco. (d) International Journal of Environment and Bioenergy, Florida, USA (e) Journal of Composites and Biodegradable Polymers (f) Physical Chemistry Communications (g) Innovations in Corrosion and Materials Science (h) Journal of Adhesion Science and Technology (Taylor and Francis) (i) Recent Patents on Materials Science Journal Honors:       

TWAS-UNESCO Associateship appointment (2011 – 2013) CAS-TWAS Postdoctoral Fellowship (2009 - 2010) Akwa Ibom State Government of Nigeria Postgraduate Scholar (2002, 2005) Federal Government of Nigeria Postgraduate Scholar (1992) Akwa Ibom State Government of Nigeria Scholar (1988 - 1990) Mary Lot’s Prize for the best Science Student in Year II, Faculty of Natural Sciences, University of Jos (1989) University of Jos Award for the best Year II Chemistry Student (1988)

Publications Last 3 Years: 2016 1. Solomon, M. M., Umoren, S. A. (2016). In-situ preparation, characterization and anticorrosion property of polypropylene glycol/silver nanoparticles composite for mild steel corrosion in acid solution, Journal of Colloid and Interface Science 462: 29 – 41.

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Saviour A. Umoren and Moses M. Solomon 2. Ahovan, M., Nasr-Esfahani, M., Umoren, S. A. (2016). Inhibitive effect of 1-[(2-hydroxyethyl) amino]-2-(salicylideneamino) ethane towards corrosion of carbon steel in CO2 saturated 3.0% NaCl solution, Journal of Adhesion Science and Technology 30 (1): 89 – 103. 3. Umoren, S. A., Eduok, U. M. (2016). Application of carbohydrate polymers as corrosion inhibitors for metal substrates in different media: A review, Carbohydrate Polymers 140: 314 – 341. 4. Inam, E. I., Etim, U. J., Akpabio, E. G., Umoren, S. A. (2016). Simultaneous adsorption of lead (II) and 3,7-bis(Dimethylamino)phenothiazin-5-ium chloride from aqueous solution by activated carbon prepared from plantain peels, Desalination and Water Treatment, 57 (14): 6540-6553. 5. Essien, E. E., Umoren, S. A., Effiong, E. E. (2016). Synthesis and characterization of luffa cylindrica fatty acids-based alkyd resins, Research on Chemical Intermediates 42(3): 2177-2189. 6. Umoren, S. A. (2016). Polypropylene glycol: A novel corrosion inhibitor for X60 pipeline steel in 15% HCl solution, Journal of Molecular Liquids 219: 946 – 958. 7. Umoren, S. A. (2016). Biomaterials for Corrosion Protection: Evaluation of Mustard Seed Extract as Eco-friendly Corrosion Inhibitor for X60 Steel in Acid Media, Journal of Adhesion Science and Technology 30 (17): 1858-1879. 8. Umoren, S. A., Essien, E. E., Effiong, E. E. (2016). The utilization of Lagenaria breviflorus seed oil in the synthesis of alkyd resins, Journal of Materials and Environmental Science 7 (6): 1846-1855. 9. Gerengi, H., Ugras, H. I., Solomon, M. M., Umoren, S. A., Kurtay, M., Atar, N. (2016). Synergistic corrosion inhibition effect of 1-Ethyl1-methylpyrrolidinium tetrafluoroborate and iodide ions for low carbon steel in HCl solution, Journal of Adhesion Science and Technology 30 (21): 2383–2403 10. Inam, E. I., Etim, U. J., Akpabio, E. G., Umoren, S. A. (2016). Process optimization for Plantain peels carbon application in dye abstraction. Journal of Taibah University for Science, http:// dx.doi.org/ 10.1016/ j.jtusci. 2016.01.003 11. Solomon, M. M., Umoren, S. A., Israel, A. U., Etim, I. G. (2016). Synergistic inhibition of aluminium corrosion in H2SO4 solution by polypropylene glycol in the presence of iodide ions, Pigment and Resin Technology doi: 10.1108/PRT-01-2015-0010

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2015 12. Solomon, M. M., Umoren, S. A., Abai, E. J. (2015). Poly(methacrylic acid)/silver nanoparticles composites: In-situ preparation, characterization and anticorrosion property for mild steel in H2SO4 solution. Journal of Molecular Liquids 212: 340 – 351. 13. Umoren, S.A, Inam, E.I, Udoidong, A. A., Obot, I. B., Ubong, U. M, Kim, K. W. (2015). Humic acid from live stocks dung: ecofriendly corrosion inhibitor for 3sr aluminium alloy in alkaline medium. Chemical Engineering Communications. 202 (3): 206 – 216. 14. Solomon, M. M., Umoren, S. A., Israel, A. U., Ebenso, E. E. (2015). Polypropylene glycol - silver nanoparticle composites: A novel anticorrosion material for aluminium in acid medium. Journal of Materials Engineering and Performance 24 (11): 4206 – 4218. 15. Solomon, M. M., Umoren, S. A. (2015). Electrochemical and gravimetric measurements of inhibition of aluminium corrosion by poly (methacrylic acid) in H2SO4 solution and synergistic effect of iodide ions, Measurement 76: 104 – 116. 16. Salimi, S., Nasr-Esfahani, M., Umoren, S. A., Saebnoori, E. (2015). Complexes of imidazole with poly(ethylene glycol) as corrosion inhibitor for carbon steel in sulphuric acid, Journal of Materials Engineering and Performance 24 (12): 4696 – 4709. 17. Umoren, S. A., Solomon, M. M. (2015). Effect of halide ions on the corrosion inhibition efficiency of different organic species – A Review. Journal of Industrial and Engineering Chemistry 21(1): 81 – 100. 18. Odewunmi, N. A., Umoren, S. A., Gasem, Z. M. (2015). Utilization of watermelon rind extract as a green corrosion inhibitor for mild steel in acidic media. Journal of Industrial and Engineering Chemistry 21(1): 239 – 246. 19. Umoren, S. A., Obot, I. B., Madhankumar, A., Gasem, Z. M. (2015). Effect of degree of hydrolysis of polyvinyl alcohol on the corrosion inhibition of steel: theoretical and experimental studies. Journal of Adhesion Science and Technology 29 (4): 271 – 295. 20. Umoren, S. A., Obot, I. B., Gasem, Z. M., Odewunmi, N. A. (2015). Experimental and theoretical studies of red apple fruit extract as green corrosion inhibitor for mild steel in HCl solution, Journal of Dispersion Science and Technology 36 (6): 789 – 802.

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Saviour A. Umoren and Moses M. Solomon 21. Odewunmi, N. A., Umoren, S. A., Gasem, Z. M. (2015). Watermelon waste products as green corrosion inhibitors for mild steel 2 in HCl solution. Journal of Environmental Chemical Engineering 3(1): 286 – 296. 22. Umoren, S. A., Gasem, Z. M. Obot, I. B., (2015). Date palm (Phoenix dactylifera) leaf extract as eco-friendly corrosion inhibitor for mild steel in 1 M hydrochloric acid solution, Anticorrosion Methods and Materials 62(1): 19 – 28. 23. Obot, I. B., Umoren, S. A., Gasem, Z. M., Suleiman, R., Ali, B. (2015). Theoretical prediction and electrochemical evaluation of vinylimidazole and allylimidazole as corrosion inhibitors for mild steel in 1M HCl, Journal of Industrial and Engineering Chemistry 21 (1): 1238 – 1339. 24. Solomon, M. M., Umoren, S. A. (2015). Performance evaluation of poly (methacrylic acid) as corrosion inhibitor in the presence of iodide ions for mild steel in H2SO4 solution, Journal of Adhesion Science and Technology 29 (11): 1060 -1080. 25. Umoren, S. A., Solomon, M. M., Israel, A. U., Eduok, U. M., Jonah, A. E. (2015). Comparative study of the corrosion inhibition efficacy of polypropylene glycol and poly (methacrylic acid) for mild steel in acid solution, Journal of Dispersion Science and Technology 36 (12): 1721 – 1735. 26. Solomon, M. M., Umoren, S. A. (2015). Enhanced corrosion inhibition effect of polypropylene glycol in the presence of iodide ions at mild steel/sulphuric acid interface, Journal of Environmental Chemical Engineering 3 (2015) 1812–1826 27. Solomon, M. M., Umoren, S. A. (2015). Performance assessment of poly (methacrylic acid)/silver nanoparticles composite as corrosion inhibitor for aluminium in acidic environment, Journal of Adhesion Science and Technology 29 (21): 2311 – 2333. 28. Obot, I. B., Madhankumar, A., Umoren, S. A., Gasem, Z. M. (2015). Surface protection of mild steel using benzimidazole derivatives: experimental and theoretical approach, Journal of Adhesion Science and Technology 29 (19): 2130–2152 29. Umoren, S. A., Obot, I. B., Gasem, Z. M. (2015). Adsorption and corrosion inhibition characteristics of strawberry fruit extract at steel/acids interfaces: experimental and theoretical approaches. Ionics 21 (4): 1171 – 1186.

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30. Odewunmi, N. A., Umoren, S. A., Gasem, Z. M., Ganiyu, S. A., Muhammad, Q. (2015). L-Citrulline: an active corrosion inhibitor component of watermelon rind extract for mild steel in HCl medium, Journal of Taiwan Institute of Chemical Engineers 51: 177 – 185. 31. Umoren, S. A., Obot, I. B., Madhankumar, A., Gasem, Z. M. (2015). Performance evaluation of pectin as ecofriendly corrosion inhibitor for X60 pipeline steel in acid medium: Experimental and theoretical approaches, Carbohydrate Polymers 124: 280 – 291. 2014 32. Umoren, S. A., Pan, C., Li, Y., Wang, F. H. (2014). Elucidation of mechanism of corrosion inhibition by polyacrylic acid and synergistic action with iodide ions by in-situ AFM. Journal of Adhesion Science and Technology 28 (1): 31 – 37. 33. Obot, I. B., Gasem, Z. M. Umoren, S. A. (2014). Molecular Level understanding of the mechanism of Aloes leaves extract inhibition of low carbon steel corrosion: A DFT approach. International Journal of Electrochemical Science 9 (2): 510 – 522. 34. Obot, I. B., Gasem, Z. M., Umoren, S. A. (2014). Understanding the mechanism of 2-mercaptobenzimidazole adsorption on Fe (110), Cu (111) and Al (111) surfaces: DFT and Molecular dynamics simulations approaches, International Journal of Electrochemical Science 9(5): 2367 – 2378. 35. Umoren, S. A., Solomon, M. M., Eduok, U. M., Obot, I. B., Israel, A. U., (2014). Inhibition of mild steel corrosion in H2SO4 solution by coconut coir Dust extract obtained from different solvent systems and synergistic effect of iodide ions: Ethanol and acetone extracts. Journal of Environmental Chemical Engineering 2(2): 1048 – 1060. 36. Umoren, S. A., Obot, I. B., Gasem, Z. M. (2014). Green synthesis and characterization of silver nanoparticles using red apple (Malus domestica) fruit extract at room temperature. Journal of Materials and Environmental Science 5(3): 906 – 914. 37. Umoren, S. A., Obot, I. B., Israel, A. U., Asuquo, P. O., Solomon, M. M., Eduok, U. M., Udoh, A. P. (2014). Inhibition of mild steel corrosion in acidic medium using coconut coir dust extracted from water and methanol as solvents. Journal of Industrial and Engineering Chemistry, 20 (5): 3612 – 3622.

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Saviour A. Umoren and Moses M. Solomon 38. Umoren, S. A., Obot, I. B (2014). Synergistic inhibition between 1octadecanethiol and iodide ions on X60 pipeline steel for corrosion protection, Journal of Adhesion Science and Technology 28 (20): 2054 – 2064. 39. Umoren, S. A., Gasem, Z. M. (2014). Influence of molecular weight on mild steel corrosion inhibition effect by polyvinyl alcohol in hydrochloric acid solution. Journal of Dispersion Science and Technology, 35 (8): 1181 – 1190. 40. Umoren, S. A., Solomon, M. M. (2014). Recent developments on the use of polymers as corrosion inhibitors: A Review. Open Materials Science Journal 8: 39 – 54. 41. Umoren, S. A., Eduok, U. M., Solomon, M. M. (2014). Effect of polyvinylpyrrolidone ̶ polyethylene glycol blends on the corrosion inhibition of aluminium in HCl solution, Pigment & Resin Technology 43 (5): 299 – 313. Publication: Book Chapters 1. Umoren, S. A., Solomon, M. M. “Polymer Characterization: Polymer Molecular Weight Determination” In: Polymer Science: Research Advances, Practical Applications and Education Aspects (A. MéndezVilas, A. Solano-Martin (Eds)), Formatex Research Centre, Badajoz, Spain (To be published in summer 2016) 2. Obot, I. B., Eduok, U. M., Umoren, S. A. “Natural Polymer: Corrosion Protection”; In “Encyclopedia of Polymeric Applications: (Munmaya Mishra (Ed.)), (To be published by Taylor and Francis, New York, USA) 3. Umoren, S. A., Solomon, M. M. “Polypropylene (PP)/Starch Based Biocomposites and Bionanocomposites” In: Propylene Based Composites and Bionanocomposites (P. M. Visakh, Matheus Poletto (Eds), (To be published by Wiley and Sons, USA).

In: Corrosion Inhibitors Editor: Esther Hart

ISBN: 978-1-63485-791-8 © 2017 Nova Science Publishers, Inc.

Chapter 3

USES OF ENVIRONMENTALLY FRIENDLY CORROSION INHIBITORS IN AMINE-BASED CO2 ABSORPTION PROCESSES Amornvadee Veawab*, Sureshkumar Srinivasan and Adisorn Aroonwilas Energy Technology Laboratory, Faculty of Engineering and Applied Science, University of Regina, Regina, SK, Canada

ABSTRACT Corrosion is a severe operational problem in the carbon dioxide (CO2) absorption process using aqueous solutions of amines, when carbon steel is used for plant construction. Past experiences with these plants have provided practitioners with a number of recommendations to keep corrosion under acceptable levels. Among these, the application of corrosion inhibitors is the most widespread because it is economical and requires small or no process modifications to existing plants. Various corrosion inhibitors have been developed, patented and commercialized by many major chemical companies for uses in amine treating plants. The patented organic inhibitors include thiourea and salicyclic acid, while inorganic inhibitors are vanadium, antimony, copper, cobalt, tin and sulfur compounds. The inorganic inhibitors are in practice more favored *

Corresponding author: Amornvadee Veawab. Address: 3737 Wascana Parkway, Regina, Saskatchewan, Canada S4S 0A2. Tel: 1-306-585-5665, fax: 1-306-585-4855, email: [email protected].

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A. Veawab, S. Srinivasan and A. Aroonwilas than the organic compounds because of their superior inhibition performance. Vanadium compounds, particularly sodium metavanadate (NaVO3), are the most extensively and successfully used in amine treating plants. Despite the successful use of the inorganic corrosion inhibitors, concerns about impacts of their toxicity on human health and the environment have increased in past decades. To respond to the environmental concerns on the use and disposal of harmful chemicals, a number of initiatives were taken around the world. In Canada, usage of toxic substances is regulated by the Canadian Environmental Protection Act (CEPA). Inorganic arsenic and cadmium inhibitors are classified as carcinogenic and considered toxic. As a result, their usage was banned. In the US, the Environmental Protection Agency (EPA) regulates the usage of chemicals through Clean Water Act (CWA) and Clean Air Act (CAA). In Europe, an environmental regulatory mechanism OSPAR was established by fifteen Northeast Atlantic nations to protect the marine environment which was later broadened to cover land based sources and offshore industry. Based on the OSPAR guidelines, most corrosion inhibitors that are used, tested and patented for amine-based CO2 absorption processes are non-environmental friendly. Hence, to respond to the environmental concerns and reduce the cost of waste disposal as well as prepare for more stringent regulations for chemical uses, application of effective and environmentally friendly corrosion inhibitors is necessary. The objective of this book chapter is to provide a review of corrosion inhibitors and a progress towards use of environmentally friendly corrosion inhibitors in the amine-based CO2 absorption process for acid gas treatment and carbon capture. The chapter is divided into four sections. Section 1 provides background information of the amine-based CO2 absorption process, including process description and type of amine used. Section 2 describes typical corrosion problems taking place in the process and provides historical corrosion cases in actual plant operations. Section 3 provides a compiled list of corrosion inhibitors that have been patented, tested and applied in this plant operation, discusses the use of environmentally friendly corrosion inhibitors and provides an update on research related to environmentally friendly corrosion inhibitors in the amine-based CO2 absorption process.

Keywords: corrosion, corrosion inhibitor, carbon capture, CO2 absorption, gas treating

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CARBON CAPTURE FROM INDUSTRIAL WASTE GAS The Intergovernmental Panel for Climatic Change (IPCC) has reported that between 1995 and 2006, eleven out of twelve years were the warmest in the instrumental record of global surface temperature (IPCC1, 2007). Melting of glaciers and continual increases in sea level are the direct effects of global warming. This is mainly attributed to the increase in the atmospheric concentrations of greenhouse gases (GHGs) in recent times, which is evident from the fact that GHG emissions now are 70% higher than their values in the 1970s (IPCC1, 2007). Particularly, carbon dioxide (CO2) is the most significant greenhouse gas as its emissions have increased by 80% in the same time frame, and CO2 represented 77% of the total anthropogenic GHG emissions in 2004 (IPCC1, 2007). Coal-fired power plants, natural gas processing plants, and manufacturing industries such as cement, ammonia, and steel plants are some of the major sources of CO2 emissions (IPCC2, 2005). Among the above, coal-fired power plants assume specific importance as they typically contribute to approximately 30% of the total CO2 emissions (Aaron and Tsouris, 2005). Carbon capture and storage (CCS) is a technology used to remove CO2 from industrial flue gas especially from power plants where it can effect a gross reduction of CO2 emissions by approximately 85-95% (IPCC2, 2005). The CO2 removal can be accomplished by a number of processes such as membrane separation, adsorption onto solids, and absorption into liquids. However, the latter is most commonly used for gas treating applications (Astarita et al., 1983). The industrial separation of CO2 for natural gas processing and ammonia manufacture by absorption into liquid is a mature technology and has been successfully used for many decades. However, adaptation of this technology for flue gas treatment began only in the 1980s (Kittel et al., 2009). For example, IMC Global Inc (previously North American chemicals), in Trona, US, features a CO2 capture unit that is used to sequester CO2 from flue gas from a coal-fired power generation plant that started operation in 1978 and is still functioning. Similarly, Indo-Gulf Corporation, a fertilizer industry in India, features CO2 capture from flue gas of the ammonia reformer unit that has been operational since 1988 capturing 150 tonnes CO2/day. Bellingham Cogeneration facility, Massachusetts, US, produces food grade CO2 by treating 300 tonnes/day of CO2 from flue gas emitted from an electricity generation plant since 1991. Sumitomo Chemicals, Japan, treats flue gas generated from onsite boilers and coal/oil boilers since 1994 with a capacity of 150 tonnes CO2/day. As illustrated by the above examples of

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A. Veawab, S. Srinivasan and A. Aroonwilas

successful and continuous adaptation of this technology for the past three decades, it is clearly discernible that the flue gas treatment using absorption into liquid is viewed as a promising technology. In a typical CO2 absorption process as illustrated in Figure 1, a flue gas stream containing CO2 enters the absorber from the bottom and interacts counter-currently with down-flowing chemical solvent entering from the top. CO2 reacts with the solvent and is absorbed, rendering the gas stream with permissible levels of CO2, and the treated gas leaves the absorber top. The CO2 loaded rich solvent leaving the bottom of the absorber passes through the rich-lean heat exchanger where it is preheated and then enters the regenerator from the top where, on application of heat in the form of steam, the solvent is stripped of CO2, and the lean solvent is recycled back into the absorber after being cooled down to the required operating temperature. A portion of lean solvent is withdrawn at the reclaimer where it is heated and the vapour mixture containing amine and CO2 are reintroduced into the regenerator. From the bottom of the reclaimer, a sludge containing insoluble salts and other chemicals are obtained and removed for waste handling. The vapor mixture containing CO2 and water vapor leaves the regenerator and enters the overhead condenser where most of the water vapor is condensed and recycled back to the regenerator, and the concentrated CO2 leaves the overhead condenser (Aroonwilas, 1996). CO2 OVERHEAD CONDENSER

TREATED GAS

COOLER REFLUX PUMP

REGENERATOR

ABSORBER

RICH-LEAN HEAT EXCHANGER

FLUE GAS

STEAM REBOILER

CONDENSATE RECLAIMER

SLUDGE DISPOSAL

Figure 1. Process flow diagram for the amine-based CO2 absorption process.

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A wide range of absorption solvents have been used for CO2 absorption processes, among which, aqueous alkanolomine-based solvents are the most widely used absorbents. Alkanolamines can be classified into three categories, namely, primary, secondary, and tertiary amines. Monoethanolamine (MEA) and diglycolamine (DGA) belong to the primary type whereas diethanolamine (DEA) and diisopropanolamine (DIPA) are the secondary type. Methyldiethanolamine (MDEA) and triethanolamine (TEA) are examples of tertiary amines. In general, primary amines have high reaction rates with CO2, followed by secondary amines and tertiary amines, respectively (Veawab, 2000). Since, for flue gas applications, CO2 partial pressures are low and the gas flow rate is extremely high compared to natural gas processing, the absorption rate has to be correspondingly faster. With this consideration, MEA shows promise and could well be the first available solvent absorbent for this application (Kittel et al., 2009; Kittel et al., 2010).

CORROSION AND ITS IMPACTS A typical CO2 absorption process has a number of factors that can cause operational difficulties, but corrosion is the chief influencing factor from an economic perspective (Kohl and Nielson, 1997). Corrosion can greatly influence both economics and safety associated with the CO2 absorption process. The economic losses are caused by unplanned downtime, production losses, and reduced equipment life or safety issues such as injury or death of plant personnel (Dupart et al., 1993). A summary of plant experiences on corrosion in the CO2 absorption process is given in Table 1. From Table 1, it can be observed that the absorber bottom, regenerator, heat exchanger, and associated piping and valves are the areas susceptible to severe corrosion. Both general (uniform) and localized corrosion were observed in the CO2 absorption plants. Localized corrosion such as erosion corrosion due to the presence of foreign particles in the circulating solution and pitting corrosion were reported to occur in addition to galvanic corrosion, stress corrosion cracking (SCC), and intergranular corrosion. Acid gas flashing on walls, high lean loading, high solution velocities, the presence of particulate contaminants, coupling of dissimilar alloys, and improper metal stress treatment are some of the reported causes of corrosion. Corrosion mitigation measures include use of corrosion inhibitors, design measures to reduce acid gas flashing, and replacement of carbon steel with corrosion resistant alloys in the heat exchanger and regenerator areas (trays and valves) in some cases.

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USE OF CORROSION INHIBITORS There are many alternative approaches to mitigating corrosion in CO2 absorption plants, such as proper equipment and process design, use of corrosion resistant materials, side stream removal of particulate matters from amine solution, and use of corrosion inhibitors. Among these, the use of corrosion inhibitors is considered the most economical, mainly because it requires no major process modification (Kohl and Nielson, 1997; Dupart et al., 1993; Veawab, 2000). From the plant experiences detailed in Table 1, it can be seen that despite the usage of corrosion inhibitors, corrosion can still occur due to certain design problems such as coupling of dissimilar metals and acid gas flashing in selected areas (Dupart et al., 1993). Hence, corrosion inhibitors in combination with one or all of the above approaches have to be deployed for effective corrosion reduction. This chapter focuses mainly on use of corrosion inhibitors. A corrosion inhibitor is defined as a chemical substance that, when added in small concentrations to the fluid phase of a corroding environment, are capable of retarding corrosion by interacting either with the metal surface or the environment (Sastri, 2001). A wide array of corrosion inhibitors were tested and patented for gas treating applications over the past fifty years (Table 2), but the most effective ones are heavy metal based chemicals such as arsenic and vanadium (Dupart et al., 1993). For a period of around two decades, beginning in 1957, several heavy metal inhibitors such as lead-, antimony-, bismuth-, arsenic-, vanadium-, and tin-based compounds were tested and patented. Disposal of toxic chemicals has resulted in significant damage to human health and environment and, based on those experiences, environmental awareness has been tremendous growth in the last few decades. As a result, a number of initiatives were taken across the world. For instance, in the United States, for a period of over 100 years, since the late 1800s, only 20 environmental laws were passed. However, in the few decades that followed, over 120 environmental regulatory laws were set in place. Consequently, the cost of compliance with those environmental regulations through waste treatment, control, and disposal were high and has been estimated to be in the range of 100-150 billion USD per year for the affected industries (Anastas and Williamson, 1998; Doble and Kruthiventi, 2007). In Canada, usage of toxic substances is regulated by the Canadian Environmental Protection Act (CEPA). For example, inorganic arsenic and cadmium compounds are classified as carcinogenic and considered toxic and were listed as CEPA 1999

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Schedule-I compounds, and as a result, their usage was banned. In the US, the Environmental Protection Agency (EPA) regulates the usage of chemicals through the Clean Water Act (CWA) and Clean Air Act (CAA). In Europe, an environmental regulatory mechanism OSPAR was established by fifteen Northeast Atlantic nations by unifying their policies in the 1972 Oslo convention against waste dumping to protect the marine environment. This was later broadened to cover land-based pollutant sources and offshore industries in the Paris Convention of 1974 (OSPAR, 2011). As per the guidelines set by OSPAR for environmentally-friendly chemicals, for a chemical to be listed in PLONOR (poses little or no risk), two out of three of the following requirements has to be satisfied with its biodegradability being superior to 20% in 28 days: a) Biodegradability (>60% in 28 days), b) Toxicity (Lethal concentration (LC50) or Effective concentration (EC50) > 1 mg/L for inorganic species, and LC50 or EC50 > 10 mg/L for organic species, where LC50 or EC50 is the dose large enough to kill 50% of sample animals under test); and c) Bioaccumulation (logpow < 3 where pow is the partition in octanol/ water). Based on the above OSPAR guidelines, it can be observed from Table 3 that most corrosion inhibitors that are used, tested, and patented are nonenvironmentally friendly. For instance, Antimony (III) oxide, arsenic oxide, cobalt acetate, thiourea, aniline, pyridine, and vanadium compounds are toxic and carcinogenic. Hence, there is a need to develop an environmentallyfriendly corrosion inhibitor that can replace the present highly toxic inhibitors and also provide comparable inhibition efficiencies. Many works have attempted to search for effective and environmentally friendly corrosion inhibitors for absorption-based gas treating plants. New corrosion inhibitors were relatively less toxic than previous ones. Davidson and Friedli (1978) registered a patent for the claim of copper and sulfur-based chemical compounds as corrosion inhibitors that were less toxic than heavy metal corrosion inhibitors. Copper carbonate in combination or alone has been suggested as a potential corrosion inhibitor since 1979 (Asperger et al., 1979; Pearsce, 1984; Trevino, 1987; Soosaiprakasam and Veawab, 2009). Many organic compounds such as pyridinium-based, piperazine-based, thiophenoland thiol-based, and amine and carboxylic acid-based compounds were also reported with comparable inhibition efficiencies of around 90%. Inorganic inhibitors were generally used in the concentration range of 20-2000 ppm whereas organic inhibitors were in the range of 100-20000 ppm.

Table 1. Summary of plant experience on corrosion in absorption-based gas treating plants Reference

Plant type

Solvent

Acid gas Corrosion problem

Dingman et al. (1966)

Sour gas treating plant

MEA

CO2 H2S

Smith and Twenty-four Sour DEA Younger (1972) gas treating plants in western Canada

CO2 H2s

Heisler and Weiss (1975)

Natural gas treating plant, Aderklaa, Austria

MEA

CO2 H2S

Schmeal et al. (1978)

Sour gas treating plant

CO2 H2S

Asperger et al. (1979)

Refinery

Sulfinol (DIPA + sulfolane) MEA (17-19%)

Hall and Barron Ram river gas plant (1981)

DEA

Gerus (1981)

N/A

Natural gas treating plant

CO2 H2S COS N/A

CO2 H2S

 Rich-lean heat exchanger, solution letdown valve, piping downstream letdown valve, upper portion of regenerator  Erosion corrosion  Erosion corrosion at: Rich lean heat exchanger Regenerator Reboiler-vapor line and letdown Rich solution piping  Stress corrosion cracking at: Stainless steel heat exchanger  Tray type regenerator including wall internal, downcomer, circumferential joint, weld seam and joint, and tray  Uniform, pitting, erosion  Absorber below 5th tray  Pitting

Cause of corrosion    



Flashing of acid gas from hot surface High solution velocity Change in direction of fluid flow Contamination with solids such as iron oxide, iron sulfide, mill scale and sand Contamination of foreign particles in circulating solution High solution velocity (5.5 ft/s) Insufficient liquid level over tight tube spacing in reboiler and heat exchanger Chloride ion evolved from gasket material used between plates Cavity in vapor flash



Acid gas flashing

   

 Mild steel/Reboiler outlet and cross N/A exchange  General corrosion (1.89 and 2.43 mmpy)  Reboiler bundle N/A  Rich lean heat exchanger (upper most tubes)  Hot side of cooler  Pitting and erosion corrosion N/A

Corrosion mitigation N/A

N/A

N/A

N/A

Corrosion inhibitor (Cu based) N/A

N/A

Reference

Plant type

Solvent

Acid Corrosion problem gas CO2  Carbon steel  Hot rich amine circuit  General corrosion (18.8 mmpy) CO2  Carbon steel  Hot lean circuit  General corrosion (1.52 mmpy) CO2  Carbon steel and Stainless steel  General corrosion (1.78 and 0.38 mmpy) CO2  Carbon steel H2S  Liquid level control valve in absorber bottom to flash drum line  Pitting and erosion corrosion

Krawczyk Gas et al. (1984) conditioning

MEA (18%)

Krawczyk Natural gas et al. (1984) purification

MEA (30%)

Krawczyk Hydrogen et al. (1984) purification

MEA (16-27%)

Dupart et al. (1993)

Gas treatment (Fuel gas production)

Formulated MDEA

Dupart et al. (1993)

Ammonia plant (Synthesis gas treatment)

Formulated MDEA

CO2

 

Dupart et al. (1993)

Ammonia plant (Synthesis gas treatment)

25% MEA (with CO2 heavy metal corrosion inhibitor)

 

  Dupart et al. (1993)

Natural gas treatment

Formulated MDEA

CO2



Cause of corrosion

Corrosion mitigation

 N/A

 Corrosion inhibitor (Ammonium thiocyanate)

 N/A

 Corrosion inhibitor (Ammonium thiocyanate)

 N/A

 Corrosion inhibitor (Arsenic based)

 Pitting - Wet CO2 flashing  Erosion - Cavitation by bubble collapse  High velocity impingement points Absorber wall (Bottom)  Turbulent interaction between the inlet gas and Erosion liquid surface which prevents the formation of normal passivation layer Carbon steel  Penetration of passive iron carbonate film in vapor Absorber bottom (vapor area between region due to reaction with liquid level and first tray), bottom oxygen. three tray downcomers, Vapor region between bottom five trays  Galvanic action between resulting active area due to Uniform/ galvanic corrosion previous action and passive Corroded to max. allowance in regions. absorber bottom Regenerator at carbon steel tray and  CO2 flashing in heat 304 stainless steel (SS) valve opening, exchanger due to excessive heat exchanger tube at shell side, pressure drop booster pump impeller and case, 304  High lean CO2 loading due SS valve coupled with carbon steel to plugging by carbon and deck insufficient stripping

 Piping material in flashing zone was replaced with 304 SS. Piping velocity was limited to 5 ft/s.  Farthest inlet distributor holes were closed  Cleaned eroded areas and filled with metal impregnated epoxy  Direct contact between the inlet gas and susceptible areas was avoided by removing bottom five trays, turning the inlet gas distributor upside down and maintaining the liquid level over it.  Replaced stripper internals with 316 SS trays and valves  Replaced carbon steel with SS 316 in heat exchanger bundle

Table 1. (Continued) Reference

Plant type

Solvent

Acid gas CO2

Corrosion problem

Cause of corrosion

Corrosion mitigation

 Pitting, erosion, galvanic

 Carbon solids circulation

   

 Coupling of SS valves with carbon steel decks  Sensitization of stainless steel from fabrication techniques or metallurgy used in vessel  Excessive vibration from disengaging gases and non-flooded top tubes

 Installed a full flow mechanical filter at the downstream of filters  Use sufficient reflux ratio for the stripper  Correct weld procedure to maintain corrosion resistance of 304 SS and affected welds repaired  N/A

Dupart et al. Natural gas (1993) treatment

Formulated MDEA

Dupart et al. Natural gas (1993) treatment Dupart et al. Ammonia plant (1993)

Formulated MDEA Formulated MDEA

CO2

Litschewski Treating H2S from MEA (with (1996) FCC unit corrosion inhibitor)

H2S

Dehart et al. CO2 recovery (1999) plant

MEA (30%)

CO2

CO2

Rodriguez Natural gas DEA-MDEA and Edwards processing, UPR blend (40%) (1999) gas plant complex, TX

CO2 H2S (Trace)

Rampin (2000) Sutopo and Safruddin. (2000)

Refinery

MEA

CO2

Liquified natural gas unit

MDEA

CO2

    

General corrosion (0.89 mmpy) 304 SS/intergranular Heat affected shell (longitudinal/circumferential welds) Regenerator areas between 304 SS trays and carbon steel wall, reboiler bundle Non-stress relieved pipe weld Galvanic and SCC Striper, bottom of absorber Uniform, galvanic corrosion

 Carbon steel  Rich amine line (from Heat exchanger)  General corrosion (1.27-1.52 mmpy)  Regenerator, amine exchanger  Erosion and general corrosion  Absorber, regenerator, Erosion

 Carbonic acid attack accelerated by O2, reduction of copper ion to metal  N/A

 N/A

 Presence of mixed phases

 N/A

 N/A

 N/A

 Corrosion inhibitor (Sulfur based-Non toxic)

Table 2. Summary of corrosion inhibitors in gas treating plants Reference

Plant type

Solvent

Material

Inhibitor type

Inhibitor

Fischer (1957) Union Oil Company

Natural gas treatment

10-30% MEA

Mild steel

Heavy metal, Organometallic

Fischer (1959) Union oil Company

Natural gas treatment

25% MEA

Mild steel

Heavy metal Organometallic

Negra et al. (1963) Chemical Construction Corporation Mago and West, (1974) Union Carbide Corporation

Synthesis gas production

Hot potassium carbonate

Mild steel

Heavy metal, Inorganic

Mixture of lead naphthenate with linseed oil and two commercially available products Armeen and Ninol Mixture of tartaric acid, Antimony 0.05-0.5% N/A trichloride, sodium hydroxine and alkyl pyridines or quinolines Trivalent oxides of Arsenic, Antimony and 0.1-0.5% Corrosion rate of Bismuth 11 mpy

Ammonia plant - 15% MEA, 30% MEA and Hydrogen 15% HEED [N-(2purification hydroxyethyl) ethylene diamine] Mago and West (1975) Ammonia plant - 15% MEA, 30% MEA and Union Carbide Hydrogen 15% HEED Corporation purification Mago (1976) Lab scale acid Hot potassium carbonate Union Carbide gas treatment (with 5% bicarbonate) Corporation

Mild steel

Heavy metal, Inorganic

Vanadium - Antimony compounds (e.g., Sodium meta vanadate - Antimony tartrate)

0.05-0.1% 90-95%

Mild steel

Organic

Nitroterephthalic acid mixed with sodium 4-nitro benzoate

0.01 to 2%

>90% and 87% on heat transfer plate

Mild steel (Cold rolled)

Heavy metal, Inorganic

a) Vanadium compounds b) Antimony compounds c) Combination of above

0.01-2%

Mago and West (1976) Union Carbide Corporation Davidson et al. (1978) Dow Chemical Company

30% MEA, 30% 1:1 MEA:HEED

Mild steel

Heavy metal, Inorganic

Stannous tartarate

0.01-2%

a) -400% (aggravated corrosion) b) -70% (aggravated corrosion) c) 84-90% 80-95%

30% MEA

Mild steel

Inorganic

Reaction product of copper and sulfur yielding compounds with monoethanolamine

0.002-2% N/A

30% MEA

Mild steel

Organic

Tetradecyl polyalkylpyridinium bromide with polyethylene polyamine

100 ppm

Asperger and Clouse (1978) Dow chemical company

Ammonia plant Hydrogen purification Natural or synthesis gas treatment (pilot plant) Natural or synthesis gas treatment

Inhibitor Inhibition dosage efficiency 0.05-0.5% N/A

91%

Table 2. (Continued) Reference Clouse and Asperger (1978) Dow Chemical Company Clouse and Asperger (1978) Dow Chemical Company Asperger et al. (1979) Nieh (1983) Texaco Inc

Plant type Lab scale Acid gas treatment

Solvent Material 30% MEA Mild steel

Inhibitor type Inhibitor Organic + Tetradecyl polyalkylpyridinium bromide Inorganic with thio urea and cobalt acetate

Inhibitor dosage 50 ppm (with 10-50 ppm cobalt acetate)

Inhibition efficiency 96%

Lab scale Acid gas treatment

30% MEA Mild steel

Organic

50 ppm

a) 77% b) 91% c) 92%

30% DEA

Inorganic

Refinery offgas stripping Lab scale Acid gas treatment Nieh (1983) Texaco Lab scale Inc acid gas treatment

Krawczyk et al. (1984) Dow Chemical Company Pearsce (1984) Dow Chemical Company

Mild steel

Tetradecyl polyalkylpyridinium with a) Thio urea b) Thiocyanate or c) Thionicotinamide Copper carbonate mixed with sulfur

500 ppm CuCO3 with 55% 100 ppm sulfur 100 ppm Corrosion rate of 1 (96 h) oxide (rainbow trout) Bismuth (III) 5000 oxide Cobalt (II) 503 acetate

EC50 Biodegradability (water flea) mg/L 5 (48 h) Biotic/Aerobic 75% readily biodegradable

Bioaccumulation

Ecological effect

Regulatory and Toxicological information

BCF: 13.6 for Oryzias latipes

-

Highly toxic. Carcinogenic

10.1 (48 h)

-

-

1000 (48 h)

-

-

-

-

-

8.23 (24 h)

-

-

-

Bioconcentration factor (BCF): 236 for Lepomis cyanellus -

-

-

-

Cobalt (II) nitrate (hexa hydrate) Copper (II) carbonate

Toxic to aquatic organisms and may cause long term adverse effect s in aquatic environment Very toxic material causing other toxic effects. Carcinogenic Very toxic to aquatic life with Toxic material causing long lasting effects immediate and serious effects Very toxic material causing immediate and serious toxic effects. Carcinogenic Toxic material causing other toxic effects Very toxic material causing other toxic effects. Carcinogenic Very toxic to aquatic life Toxic material causing immediate and serious effects. Carcinogenic Toxic material causing other toxic effects

691

-

-

-

-

1350

-

-

-

-

Inhibitor

LD50 (oral LD50 (fish) rat) mg/kg mg/L

Bioaccumulation

Ecological effect

Copper (II) oxide

470

-

Nickel (II) acetate (tetra hydrate)

350

EC50 Biodegradability (water flea) mg/L 25.4 (96 h) 0.011(rainbow trout) 0.039 (48 h) -

Very toxic to aquatic life with long lasting effects -

Pyridine

891

-

-

Pyridine-2carboxylic acid Sodium metavanadate

750

93.8 (96 h) (Fath ad minnow) -

-

-

-

98

-

-

-

-

Thio urea

1750

10 (96 h) (zebra fish)

5.6-18 (48 Biotic/Aerobic