Summary of the Workshop on Structural Nanomaterials [1 ed.] 9780309580557

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Copyright © 2001. National Academies Press. All rights reserved.

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Summary of the Workshop on Structural Nanomaterials June 20–21, 2001

Washington, D.C.

Robert Dowding Delcie Durham NATIONAL MATERIALS ADVISORY BOARD NATIONAL RESEARCH COUNCIL

NATIONAL ACADEMY PRESS Washington, D.C.

Copyright © 2001. National Academies Press. All rights reserved.

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NOTICE: The workshop that is the subject of this summary was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The workshop was conducted by the National Materials Advisory Board under Grant No. DASC02-01-P-0038 from the U.S. Army National Ground Intelligence Center. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the organizations or agencies that provided support for the project. Available in limited supply from National Materials Advisory Board, 2101 Constitution Avenue NW, Washington, DC 20418; 202–334– 3505; [email protected]; http://www.nas.edu/nmab Cover: Illustration of a thermal spray gun courtesy of Stephen Ridder, National Institute of Standards and Technology. Copyright 2001 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Acade my has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Wm. A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. Wm. A. Wulf are chairman and vice chairman, respectively, of the National Research Council. www.national-academies.org

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NATIONAL MATERIALS ADVISORY BOARD EDGAR A.STARKE, University of Virginia, Charlottesville, Chair EDWARD C.DOWLING, Cleveland Cliffs, Inc., Cleveland, Ohio THOMAS EAGAR, Massachusetts Institute of Technology, Cambridge HAMISH FRASER, The Ohio State University, Columbus, Ohio ALASTAIR M.GLASS, Lucent Technologies, Murray Hill, New Jersey MARTIN E.GLICKSMAN, Rensselaer Polytechnic Institute, Troy, New York JOHN A.S.GREEN, The Aluminum Association, Washington, D.C. THOMAS HARTWICK, TRW (retired), Snohomish, Washington ALLAN J.JACOBSON, University of Houston, Houston, Texas MICHAEL JAFFE, New Jersey Center for Biomaterials and Medical Devices, Piscataway, New Jersey SYLVIA M.JOHNSON, NASA-Ames Research Center, Moffett Field, California FRANK E.KARASZ, University of Massachusetts, Amherst, Massachusetts SHEILA F.KIA, General Motors Research and Development, Warren, Michigan HARRY A.LIPSITT, Wright State University, Dayton, Ohio ALAN G.MILLER, Boeing Commercial Airplane Group, Seattle, Washington ROBERT C.PFAHL, Motorola, Schaumberg, Illinois JULIA PHILLIPS, Sandia National Laboratories, Albuquerque, New Mexico HENRY RACK, Clemson University, Clemson, South Carolina KENNETH L.REIFSNIDER, Virginia Polytechnic Institute and State University, Blacksburg, Virginia T.S.SUDARSHAN, Modification, Inc., Fairfax, Virginia JULIA WEERTMAN, Northwestern University, Evanston, Illinois Staff TONI MARECHAUX, Director ARUL MOZHI, Associate Director JULIUS C.CHANG, Program Officer JANICE PRISCO, Project Assistant

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PREFACE

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Preface

The Workshop on Structural Nanomaterials, planned and organized by the members and staff of the National Materials Advisory Board (NMAB) of the National Research Council (NRC), was conducted under a contract with the U.S. Army’s National Ground Intelligence Center (NGIC). NGIC sponsored the workshop to help its Advanced Materials and Manufacturing Technologies Working Group, under the auspices of the Scientific and Technical Intelligence Committee, identify the key enabling technologies, junctures, and “chokepoint” areas that are deemed critical to the scientific, technological, and commercial advancement of structural nanomaterials. NGIC intends to use the input gained from this workshop as a guide and reference in drafting a classified report on the technology status of nanomaterials, with an emphasis on structural nanomaterials. The workshop focused on nanomaterials having properties particularly suitable for structural applications. Appendix A lists the workshop participants and the agenda. The objectives of this workshop were as follows: • Develop a consistent definition of the terms used in the field, to include nanoscale, nanotechnology, nanoscience, nanophase, nanoparticle, nanotube, nanolayer, nanomaterial, nanostructure, and nanostructural material. • Identify the scientific and technological challenges and the commercial opportunities in the following areas: • • • •

Synthesis of nanomaterial building blocks, Assembly of nanomaterials from the building blocks, Characterization of nanomaterials, and Potential structural applications of nanomaterials.

• Discuss key examples of structural nanomaterials science and technology. For each example identify the current level of understanding of the system, particularly with respect to synthesis, assembly, and chemical and physical characterization. Identify interdisciplinary issues. • Determine the major barriers to scientific understanding and technological utility of structural nanomaterials. Identify the requirements to overcome the barriers. The NMAB staff would like to thank all those who attended the workshop (see Appendix B), and the following individuals, who prepared presentations: Chris Berndt, SUNY Stony Brook Thomas Gates, NASA Langley Research Center

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PREFACE

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Maurice Gell, University of Connecticut Terence Langdon, University of Southern California Evan Ma, Johns Hopkins University Sara Majetich, Carnegie Mellon University Geoffrey Malafsky, Technology Intelligence International Merrilea Mayo, Pennsylvania State University Walter Milligan, Michigan Technological University Joseph W.Piche, Eikos Inc. James Rawers, Albany Research Center, Department of Energy Stephen Ridder, National Institute of Standards and Technology Ganesh Skandan, Nanopowder Enterprises T.S.Sudarshan, Materials Modification Inc. Klaus Tomantschger, Integran Technologies Julia Weertman, Northwestern University Norman Wereley, University of Maryland Danny Xiao, Inframat Corporation Jackie Ying, Massachusetts Institute of Technology

NMAB thanks the session chairs: Julia Weertman, Northwestern University; T.S. Sudarshan, Materials Modification Inc.; Delcie Durham, National Science Foundation; Robert Dowding, Army Research Laboratory; Lawrence Kabacoff, Office of Naval Research, and Thomas Gates, NASA-Langley Research Center. It is particularly grateful to Dr. Dowding and Dr. Durham for acting as the workshop’s rapporteurs and for preparing the workshop summary. Dr. Sudarshan and Professor Weertman were invaluable as co-chairs of the workshop. This summary has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s (NRC’s) Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published summary as sound as possible and to ensure that the summary meets institutional standards for objectivity, evidence, and responsiveness to the workshop objectives. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their participation in the review of this summary: Mike Davey, NRC; Thomas Gates, NASA Langley Research Center; and Henry Rack, Clemson University. Although the reviewers listed above have provided many constructive comments and suggestions, they did not see the final draft of the summary before its release. The review of this summary was overseen by Ganesh Skandan, Nanopowder Enterprises. Appointed by the National Research Council, he was responsible for making certain that an independent examination of this summary was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this summary rests entirely with the rapporteurs and the institution. Comments and suggestions may be sent via e-mail to NMAB at [email protected] or by fax to (202) 334– 3718.

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CONTENTS vii

Contents

INTRODUCTION 1

SESSION 1: SYNTHESIS, ASSEMBLY, AND PROCESSING 3

SESSION 2: FABRICATION AND PRODUCTION 9

SESSION 3: APPLICATIONS 17

SESSION 4: STRUCTURE, PROPERTIES, AND CHARACTERIZATION 23

SESSION 5: MODELING AND SIMULATION 25

WORKSHOP WRAP-UP 29

APPENDIXES WORKSHOP PARTICIPANTS AND AGENDA LIST OF ATTENDEES 31 33 39

A B

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INTRODUCTION

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Introduction

Julia Weertman of Northwestern University opened the workshop by welcoming the participants on behalf of her co-chair, T.S.Sudarshan of Materials Modification Inc., National Materials Advisory Board (NMAB) project director Julius Chang, and the NMAB staff. Before describing the goals and hoped-for outcomes of the workshop, she briefly went through the many materials-related terms that involve the prefix “nano.” Most of these “nano-X” terms—e.g., nanoscale, nanophase, nanolayer, nanomaterial, nanostructure—indicate that at least one feature (X) has a length scale less than ~100 nm. Nanoscience is the science of the nano-Xs, while nanotechnology as used in the present context refers to the production and use of the nano-Xs. Professor Weertman listed the topics and goals to be addressed: • • • • •

Synthesis and assembly of nanomaterial building blocks; Characterization of nanomaterials; Examples of structural nanomaterials currently in use; Potential applications of nanomaterials; Gaps in understanding of synthesis, assembly, chemical, and physical characterization and the need for an interdisciplinary approach; and • Identification of the “showstoppers”—major barriers to utilization of nanomaterials. The workshop then moved on to the first session, on synthesis, assembly, and processing.

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INTRODUCTION 2

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SYNTHESIS, ASSEMBLY, AND PROCESSING

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Session 1: Synthesis, Assembly, and Processing

Five presentations were given in this session on topics related to the synthesis, assembly, and processing of nanostructured materials. A panel of presenters then fielded questions from one another and from other participants. The nanomaterials discussed included carbon nanotubes, metal nanopowders and particles, and ceramic powders. The processes ranged from nanomilling and mechanical alloying, to thermal spray, powder consolidation, and other additive processes, to the processing of nanocomposites. Joseph W.Piche of Eikos Inc. led off the session with his talk, “Nanoshield Composite Electromagnetic Shielding for Hardening to Electromagnetic Interference and Electrostatic Dissipation.” He gave an overview of what is currently being done or planned for the next 5 years in the processing of electromagnetic interference (EMI) shielding products. He reminded the participants that in industry, what is used is what is economical, such as the trays used to carry disks in semiconductor processing. While cost is a challenge, production rates of nanotubes are scaling up to meet the demand. Mr. Piche felt that the cost of carbon nanotubes at a quality level required for immediate application was not an issue. He quoted a current price of $29/lb in large quantity. The issue is producing high-quality carbon nanotubes for higher performance applications. Mr. Piche anticipated the production of multiwall carbon nanotube (MWCNT) products within 1 to 5 years. Carbon nanotube suppliers to Eikos are already producing tons-per-day quantities of material, although the nanotubes are of low grade. Piche cited several current applications for single-wall and MWCNTs, such as EMI shielding, electrostatic dissipation protection, and capacitor dielectrics. Mr. Piche identified the following opportunities, barriers, and future applications: • • • •

Enhancing EMI shielding by “postprocessing” the tubes, Improving optical clarity without affecting other properties, Improving the reproducibility of product, and Shielding for Army mobile shelters (future application).

Evan Ma of Johns Hopkins University presented a talk entitled “Structural Nanomaterials Prepared by Mechanical Milling/Alloying.” He focused on the production of nanomaterials, including nanocomposite powders, by milling and mechanical alloying. He indicated that this solid-state processing method produced grain sizes of a few to 30 nm and could be used for ceramics, metals, polymers, and composites. The challenge is to consolidate these powders while maintaining the nanograin size. Pressure-assisted

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SYNTHESIS, ASSEMBLY, AND PROCESSING

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processes such as hot isostatic pressing (HIPing) and rapid high-temperature sintering are being used to get centimeter-size samples. Professor Ma noted that nanoscale metals, including consolidated nanomaterials, exhibit small, uniform tensile elongations. He believes the reasons are (1) porosity/processing defects in the sample, especially for consolidated samples and, more importantly, (2) the lack of strain hardening and strain rate hardening in these high-strength metals. Without hardening, necking instability sets in early. Professor Ma stated that nanometals are very strong and have significant ductility in compression. But if tested in tension, usually the ductility appears low. One needs to identify/provide mechanisms for strain and strain rate hardening if large tensile elongation is desired. Professor Ma listed the following opportunities, barriers, and potential applications: • Processing requires high pressure and/or fast consolidation with process control. • Processing requires improved consolidation for better throughput and reduction of costs. • The deformation behavior of materials such as pure Fe is significantly different at smaller scales—the tensile behavior of the nanoscale material exhibits extremely low uniform elongation. • The fundamental mechanisms are not well understood. • Contamination can occur, pointing to the need for “seasoned” tooling and inert or reducing atmospheres. • Tank penetrators for Army applications are a potential application. Next, Klaus Tomantschger of Integran Technologies gave his presentation, “Electrosynthesis of Nanocrystalline Metals, Alloys, and Metal-Matrix Composites: Achievements and Future Challenges.” He concentrated on electrosynthesis methods for thermomechanical processing of materials with original grain sizes of less than 100 nm. He provided several examples of this electrodeposition process that occurs at room temperature, producing either dense coatings or freestanding forms such as foils of varying thickness. Dr. Tomantschger gave an example of the effect of grain size (10 nm, 100 nm, conventional) on mechanical properties such as yield, ultimate tensile strength, and modulus of elasticity that indicated that nanoscale materials could exhibit better wear or fatigue resistance than their conventional counterparts, contrary to some other findings for high cycle fatigue. Examples of current technologies include the creation of nanofoils by rotating a 2-foot-wide drum in the electrolyte and peeling off the resulting foil continuously, at a production rate of 4 to 5 tons/machine/year. Dr. Tomantschger presented multiple opportunities, barriers, and potential applications: • Developing process modification to further improve the hardness of wear-resistant materials by process control and postprocess annealing, • Gaining control over grain growth during processing, • Creating structures in magnetic materials that have both high saturation and low coercivity, and

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SYNTHESIS, ASSEMBLY, AND PROCESSING

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• Future applications: copper foil for high-density printed circuit boards, replacing hard Cr with nano Co, nanocoatings such as Ni-Mo that have reduced friction coefficient and increased hardness, nanocomposite coatings such as Ni-SiC with improved hardness and strength, metallization of plastic parts using nano Ni-Mo, and developing micromachines based on nanomaterials. Chris Berndt of SUNY Stony Brook spoke on his topic, “The Unique Mechanical Properties of Thermal Spray Coatings Interpreted from a Nanostructural Viewpoint.” Professor Berndt gave a thorough update on thermal spray that included processing of thermal barrier coatings, control of the process, including an understanding of defect generation, and effect upon performance. The basic need is to understand the relationship between the processes, the selection and optimized use of feedstock, and the resulting performance of the structures. The application of nanomaterials in a production environment will require more process modeling and control efforts. A fundamental challenge is to take advantage of nanophenomena, for example by creating a framework of cracks at the nanoscale to accommodate thermal gradients so that as the temperature increases, the material can accommodate the temperature change. Professor Berndt provided a list of his top six opportunities, barriers, and potential applications: • What is the vision for the next 5, 10, and 20 or more years? This has not been articulated. • A big barrier is the current belief that if it is not 100 percent nano, then there is no technical advantage. Existing R&D has proven this a fallacy. The scientific and engineering approaches should be adjusted to recognize that partial nano might be not only good, but also preferable in some applications. There needs to be a cultural adjustment in the nano-community to recognize this potential. Engineering applications will require the integration of materials at all length scales. • Block funding (i.e., centers and institutes) is not always the best approach. Such consolidation schemes have negative impacts on individual creativity, and the creation of large centers will not address core issues. • Database activities are needed. Use the resources of the National Institute of Standards and Technology (NIST). Sharing of such resources is vital for intelligent and efficient growth. • The current skepticism concerning the future of nanoscience needs to be addressed. Such cynicism is not really justified and must be negated. This is a major barrier within our conservative engineering culture that is impeding funding and progress. We need to focus on the positives, to address short-term versus long-term R&D. • The “picking of low-lying fruit” needs to be reconciled with the ability to take on really challenging problems. It is agreed that picking the sure winners is good for program longevity. However, there need to be some high-risk, “out of this world” tasks as well. Jackie Ying of the Massachusetts Institute of Technology wrapped up Session 1 with her presentation, “Synthesis and Application of Nanostructured Materials.” Professor Ying focused on the chemistry of nanostructured materials, specifically looking at applications that demanded a mix of chemical, physical, and biological properties. She presented

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SYNTHESIS, ASSEMBLY, AND PROCESSING

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numerous nanoscale applications where, again, the challenges are to keep the cost down and to improve the processing efficiency. Professor Ying first discussed hydroxyapatite (HAP)-biocompatible material (close resemblance to bone minerals). The challenge with conventional HAP is that it is difficult to sinter (it decomposes at temperatures greater than 1000 °C) and has poor mechanical properties. Nano-HAP and nano-HAP with 3 percent Zr (in the form of highly dispersed zirconia nanocrystals) have better bending and compressive strengths than conventional HAP. Nano-HAP also exhibits enhanced protein adsorption and cell attachment (increased osteoblast adhesion, proliferation, and mineralization). The second application presented dealt with catalytic combustion using nanoparticles. Burning light hydrocarbons such as methane and natural gas could reduce the impact of CO2 emissions on global warming. However, flame temperatures over 1300 °C also produce NOx emissions, which are a major component of smog. Catalytic combustion can lower the flame temperature, reduce NOx emissions, and provide the potential for burning ultralean mixtures. This requires a catalyst active from 400 °C to 1300 °C (for methane, light-off— defined as 10 percent conversion of the fuel stream—should ideally occur at about 400 °C). Professor Ying’s research group has synthesized nanocrystalline barium hexaaluminate (BHA) catalyst materials using a reverse-microemulsion-mediated sol-gel technique. In this approach, a reverse microemulsion is used to confine the hydrolysis and polycondensation reactions to nanometer-size aqueous domains. Normally, BHA is difficult to synthesize as nanocrystals owing to the different reactivity of barium and aluminum precursors. The nanocrystalline BHA provides superior catalytic conversion. Nanocrystallization occurs at 1100 ° C, with a surface area of 250 m2/g when calcined at 800 °C (10-nm grains). Methane light-off occurs at 590 °C. For nanocrystalline BHA plus a CeO2 coating, methane combustion can be sustained down to 400 °C. In contrast, conventional BHA shows substantial grain growth (15 m2/g surface area) and a methane light-off at 720 °C. Professor Ying’s third application was in the area of semiconductor gas sensors to detect toxic gases via changes in sensor resistivity. She presented results for a SnO2-In2O3nanocomposite semiconductor with ultrahigh sensitivity, high-temperature stability, and engineered gas selectivity. The nanocomposite showed improved surface area and reduced grain size. A 75:25 SnO2-In2O3 material showed suppressed grain growth to