Explosive Performance Properties of Erythritol Tetranitrate (ETN)

Citation preview

Short Communication DOI: 10.1002/prep.201500066

Explosive Performance Properties of Erythritol Tetranitrate (ETN) Virginia W. Manner,*[a] Daniel N. Preston,*[a] Bryce C. Tappan,[a] V. Eric Sanders,[a] Geoff W. Brown,[a] Ernie Hartline,[a] and Brian Jensen[a]

Abstract: Erythritol tetranitrate (ETN) is a melt-castable explosive with impressive performance, similar to the wellknown related nitrate ester, pentaerythritol tetranitrate (PETN). Though ETN has been known since 1849, its properties have not been thoroughly investigated. We report here the first 1=2 ’’ copper cylinder tests of ETN, compared with

PETN. We discuss detonation and wall expansion velocity, along with diameter effect information in unconfined rate stick tests. The detonation velocity of ETN is 99 % that of PETN in the same test setup, showing that performance properties are very similar for the two nitrate esters.

Keywords: ETN · Erythritol tetranitrate · Explosive · Performance · Cylinder test

1 Introduction

2 Results and Discussion

Erythritol tetranitrate (ETN) (Figure 1) is an explosive first prepared in 1849 [1] with similar properties to pentaerythritol tetranitrate (PETN). ETN is melt-castable, has impressive performance, and is not difficult to prepare, which increases the necessity for understanding its properties from a homemade explosive threat determination perspective [2]. Due to its handling sensitivity, ETN has been involved in recent accidents [3] and should not be handled outside of a dedicated explosives facility. We have recently reported the first X-ray crystal structure of ETN [4], and discussed the influence of crystal packing on the sensitivity of the material, relative to PETN [5]. Another recent publication also discusses basic characterization of ETN [6]. We describe herein the first analysis of copper cylinder expansion tests with pressed ETN. We discuss the detonation behavior for the material, along with wall velocity and diameter effect information. All data is compared to PETN tested under similar conditions.

Figure 1. Erythritol tetranitrate (ETN).

460

2.1 Cylinder Tests

ETN has greater sensitivity than PETN, so it was important to evaluate its safety relative to the cylinder loading process. In addition to the standard small-scale safety testing [4], ETN was tested for friction sensitivity using a copper plate, and did not undergo any visible reaction at the highest input level. Pressed pellets were prepared of recently purified ETN at an average density of 1.74 œ 0.01 g cm¢3 (98 % TMD). However, over the course of approximately 20 d, the pellets expanded to an average density of 1.69 œ 0.03 g cm¢3 (95 % TMD). Copper 12.90 mm (1=2 ’’) cylinder tests were performed with the expanded pellets (the cylinders were honed from 12.70 mm to account for pellet expansion). Shorting switches and PDV (Photonic Doppler Velocimetry) measurements were used in a configuration that has been described in detail elsewhere [7]. Two cylinder tests were performed using ETN at slightly different densities, and one control cylinder test was performed with PETN. The data are summarized in Table 1. The ETN detonation velocity (Figure 2a) is 99 % that of PETN when corrected for density. Wall velocities are comparable between ETN and PETN (Figure 2b and Table 1).

[a] V. W. Manner, D. N. Preston, B. C. Tappan, V. E. Sanders, G. W. Brown, E. Hartline, B. Jensen Explosive Science and Shock Physics Los Alamos National Laboratory Los Alamos, NM 87545, USA *e-mail: [email protected] [email protected]

Ó 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Propellants Explos. Pyrotech. 2015, 40, 460 – 462

Explosive Performance Properties of Erythritol Tetranitrate (ETN) Table 1. ETN and PETN cylinder performance data. Material

Density [g cm¢3] [TMD/%]a)

Detonation velocityb)/mm ms¢1

Wall velocityc) [m s¢1]

Adjusted detonation velocityd) [mm ms¢1]

ETN 1 ETN 2 PETN

1.682 œ 0.019 [94.9] 1.704 œ 0.010 [96.1] 1.663 œ 0.006 [94.0]

7.887 œ 0.007 7.994 œ 0.022 7.926 œ 0.033

1775 œ 12 1807 œ 5 1794 œ 12

7.95 œ 0.02 7.99 œ 0.02 8.04 œ 0.03

a) ETN TMD = 1.773 g cm¢3, PETN TMD = 1.770 g cm¢3 (ref. [4]). b) The uncertainties are the twice the standard deviation of the velocity. c) Average and twice the standard deviation of the velocity values at 20 ms collected from 4 PDV probes (all within 10 m s¢1 of average final observed values). d) Detonation velocity after adjusting each shot density to 96 % TMD using D1 = D2 + 3(11¢12) (Ref. [8]).

2.3 Cheetah Thermochemical Code

Cheetah 6.0 thermochemical code calculations were performed on ETN at 96 % TMD [10], and give a detonation velocity of 8.113 mmms¢1. This is in good agreement with the average experimental detonation velocity of 7.97 œ 0.02 mm ms¢1 (at 96 % TMD), 1.7 % below the calculated value. In comparison, Cheetah calculates a PETN detonation velocity of 8.270 mm ms¢1 at 96 % TMD, which overestimates our experimental value by 2.8 %. Cheetah predicts that ETN forms (in mole fractions) predominantly CO2 (0.415), H2O (0.314), and N2 (0.168) gaseous products, along with smaller amounts of NO (0.0782) and O2 (0.0138). The PETN products are mostly CO2 (0.362), H2O (0.340), N2 (0.145), and CHNO (0.103), with some CO (0.0388). Overall, the predicted detonation velocities and product gases are very similar between the two nitrate esters. Cheetah JWL fit results give total energy of detonation of ¢10.11 kJ cm¢3 and ¢10.05 kJ cm¢3 for ETN and PETN, respectively, in very good agreement.

3 Experimental Section

Figure 2. (a) Shorting switch data used to determine detonation velocities. (b) PDV wall velocities for ETN and PETN cylinder shots. Each line is an average from 4 PDV probes.

2.2 Small Diameter Detonation Tests

Small scale, unconfined detonation rate sticks were tested at 3.00 œ 0.03 mm and 6.35 œ 0.03 mm pellet diameters. The ETN pellets were pressed to an initial average density of 1.74 œ 0.01 g cm¢3 (98 % TMD), and pellet expansion was not measured thereafter. These measurements gave a detonation velocity of 7.90 œ 0.13 and 8.03 œ 0.04 mm ms¢1 at 3.00 and 6.35 mm respectively, which are within uncertainty of the adjusted detonation velocities observed in the cylinder tests, given in Table 1. These velocity measurements demonstrate a critical diameter for ETN of < 3 mm, which is consistent with the PETN critical diameter of < 1 mm [9]. Propellants Explos. Pyrotech. 2015, 40, 460 – 462

CAUTION: Erythritol tetranitrate is a very sensitive and dangerous explosive that has been involved in several recent explosives accidents [3]. It should only be prepared and handled in an explosives facility. ETN should never be burned, as a small amount of confinement of even a small sample (ca. 10 mg) can sometimes lead to a violent explosion. ETN was prepared from nitric acid, sulfuric acid, and erythritol using literature procedures [4]. Batches were synthesized on a ‹ 30 g scale, and the solid product was dissolved in ethanol (ca. 700 mL), precipitated with water (ca. 1300 mL), and characterized by NMR spectroscopy [4]. ETN pellets were pressed at ambient temperature using a 15 ton pneumatic using an applied pressure of 3.9 Õ 108 Pa, with two intensifications of three minutes with a one minute rest between intensifications. Pressing was done slowly due to friction sensitivity. Expansion on diameters averaged 0.05 mm and height expansions averaged 0.20 mm during a 20 d measurement period (half of the observed expansion occurred in the first 4 d, and then slowed). During further pressing, material amounts were slightly decreased and pellets pressed shorter to allow for the pellet expansion to reach the final average size of 12.86 œ 0.29 mm (height) Õ 12.82 œ 0.03 mm (diameter). Re-

Ó 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.pep.wiley-vch.de

461

Short Communication

V. W. Manner et al.

explosives are within 1 %, and wall expansion velocities are within uncertainty of each other. Initial measurements indicate the critical diameter of ETN is < 3 mm, and is potentially well under 1 mm as with PETN. The predicted behavior from Cheetah 6.0 calculations also show close agreement between the two nitrate esters, with very similar predicted product gases and energies of detonation. Figure 3. (a) Friction testing of ETN on a copper surface, executed before loading the cylinder with ETN pellets. Unreacted ETN is visible at the edge of the distressed area. (b) Cross section of cylinder test setup showing ETN pellets.

sults showed that lower initial pressing pressures of 3.6 Õ 108 Pa resulted in larger expansion than the higher pressures used after the first 10 pellets. PETN (XTX grade) was pressed in 12.68 œ 0.05 mm (height) Õ 12.73 œ 0.02 mm (diameter) pellets using standard pressing procedures. ETN was tested for friction sensitivity using a half-hard oxygen-free, high conductivity (OFHC) C101 copper plate, in lieu of the typically used ceramic plates (which are harder than the copper tubes used in the cylinder tests). Eleven consecutive NOGOs (Figure 3a) were recorded at the highest energy level (360N). A half-scale cylinder test configuration was used for the shot series; tubes were 152 mm (6”) in length, with measured 12.90 œ 0.01 mm (1=2 ’’) ID and 1.25 œ 0.06 mm (0.05’’) wall thickness. Charges were initiated using a RP-1 EBW detonator. Detonation velocity was measured using formvarcoated magnet wire at 8 points along the copper tube, and wall velocity was measured with 4 PDV probes/fiber optic cables per shot, as described in detail elsewhere [7]. A novel design feature to the shot stand (Figure 3b) includes a scheme for loading pellets that dramatically reduces the possibility of entraining air at the joints of ETN pellets, which could cause jetting and premature cylinder break-up. Using a modification of a known procedure [11], a vacuum greasecoated Teflon plug is inserted into the cylinder, followed by vacuum grease-coated ETN pellets. Each new pellet is used to push the preceding pellet into the tube and air is allowed to vent through holes in the base where finally the plug rests in a void beneath the cylinder. This loading method nearly eliminates air in the system. High-speed video was taken of the cylinder expansion using a Phantom 12 camera (Vision Research) and indicated even expansion.

4 Conclusions Erythritol tetranitrate is a melt-castable, high-performance nitrate ester explosive that has recently become important due to its use in homemade explosives. We have investigated the detonation behavior of ETN using cylinder tests and small diameter unconfined rate sticks. Similar performance properties were observed between ETN and the closely related nitrate ester, PETN: detonation velocities for the two 462

www.pep.wiley-vch.de

Acknowledgments Los Alamos National Laboratory is operated by LANS, LLC, for the U. S. Department of Energy under contract DE-AC52–06NA25396.

References [1] J. Stenhouse J. Ueber die naheren Bestandtheile einiger Flechten, Justus Liebigs Ann. Chem. 1849, 70, 218 – 228. [2] J. C. Oxley, J. L. Smith, J. E. Brady IV, A. C. Brown, Characterization and Analysis of Tetranitrate Esters, Propellants Explos. Pyrotech. 2012, 37, 24 – 39. [3] The most recent accident occurred at Dugway Proving grounds in July 2013; a detonation occurred while a chemist was grinding the material. [4] V. W. Manner, B. C. Tappan, B. L. Scott, D. N. Preston, G. W. Brown, Crystal Structure, Packing Analysis, and Structural-Sensitivity Correlations of Erythritol Tetranitrate, Cryst. Growth Des. 2014, 14, 6154–6160. [5] E. A. Zhurova, A. I. Stash, V. G. Tsirelson, V. V. Zhurov, E. V. Bartashevich, V. A. Potemkin, A. A. Pinkerton, Atoms-in-Molecules Study of Intra- and Intermolecular Bonding in the Pentaerythritol Tetranitrate Crystal, J. Am. Chem. Soc. 2006, 128, 14728 – 14734. [6] R. Matyas, M. Kunzel, A. Ruzicka, P. Knotek, O. Vodochodsky, Characterization of Erythritol Tetranitrate Physical Properties, Propellants Explos. Pyrotech. 2015, 40, 185 – 188. [7] V. W. Manner, S. J. Pemberton, J. A. Gunderson, T. J. Herrera, J. M. Lloyd, P. J. Salazar, P. Rae, B. C. Tappan, The Role of Aluminum in the Detonation and Post-Detonation of Selected Cast HMX-based Explosives, Propellants Explos. Pyrotech. 2012, 37, 198 – 206. [8] P. W. Cooper, Explosives Engineering, Wiley-VCH, New York, 1996, p. 76. [9] A. S. Tappan, R. Knepper, R. R. Wixom, M. P. Marquez, J. P. Ball, J. C. Miller, Critical Detonation Thickness in Vapor-Deposited Pentaerythritol Tetranitrate (PETN) Films, in: AIP Conference Proceedings 1426. Shock Compression of Condensed Matter2011 (Eds.: M. L. Elert, W. T. Buttler, J. P. Borg, J. L. Jordan, T. J. Vogler), New York, American Institute of Physics, 2012, 677– 680. [10] ETN was added to the Cheetah 6.0 thermochemical code library using a theoretical maximum density density of 1.773 g cm¢3 (Ref. [4]), and a heat of formation value of 376 cal g¢1, obtained from: Encyclopedia of Explosives and Related Items (Eds.: B. T. Fedoroff, O. E. Sheffield), vol. 5, 1972, New Jersey, p. E124. [11] L. G. Hill, Is the Detonation “Dead Zone” Really Dead? Proc. Combust. Inst. 2015, 35, 2041 – 2049.

Ó 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Received: March 25, 2015 Revised: April 27, 2015 Published online: June 5, 2015

Propellants Explos. Pyrotech. 2015, 40, 460 – 462