Chemical Aging and Influence of Manufacture on High Explosives

Abstract

This study originated from a civil request from the Canadian National Railway (CNR) to the Department of National Defence (DND) for assistance to dispose of former US military munitions which were converted into civilian avalanche control use. They consisted of the 105 mm calibre recoilless munitions which were produced in 1954 and had been stored in ambient conditions. This study investigated the long-term ambient aging impacts and the influence from manufacturing on the 2,4,6-trinitrotoluene (TNT), Composition B (Comp B), and Composition A 3 (Comp A-3) using X-ray imaging, mechanical sensitivity tests, Electro-Static Discharge (ESD) sensitivity test, Scanning Electron Microscopy (SEM), and Thermal Gravimetry Analysis (TGA) - Differential Scanning Calorimetry (DSC) techniques. The TNT composition was further analysed by the Gas Chromatography – Mass Spectrometry (GC-MS). The Comp A-3 composition consisted of Research Department Explosive (RDX) and inert wax mix. It had shown minimal measurable changes with respect to the mechanical, ESD and thermal sensitivity of the material. The X-ray and SEM images also revealed no discernable changes. This study concluded that there is no safety impact with respect to long-term ambient aging of the Comp A-3. The TNT was found to have exhibited characteristics of thermally damaged materials on the surface level by SEM imaging. This resulted in the lowering of the friction resistance when compared to the known standards of the modern TNT. The cause of such reduction was attributed to the surface texture of the material which had an equivalent effect of increasing the surface area. The activation energy of the aged TNT was found to be 174 ± 31 kJ/mol with an R square value of 0.86 using the Kissinger method. However, this study noted that there were non-linear properties in the Kissinger kinetic plot which resulted in the low R square value. The non-linear properties could be attributed by the multi-mechanism degradation behaviour of TNT. The TNT GC-MS analysis revealed only three impurities with low quantity when compared to a list of known impurities in the literature. However, difficulties were noted in the employment of the GC-MS techniques during the study. Thus, this study concludes that the aged TNT had retained its purity level with noted reduction in friction resistance due to thermal exposure. The Comp B composition consisted of TNT and RDX. It was noted with similar defect as the aged TNT in its aging behaviour. There was a reduction in the friction resistance which was contributed by the aging of the TNT. The thermal sensitivity result revealed that the RDX was synthesized using the Bachmann process and was considered as the Type II RDX which contained a small quantity of His Majesty’s Explosive (HMX). Based on the results from the Comp A-3, this study concludes that the aging of TNT had a predominant effect on the aging behaviour of the Comp B while the RDX had negligible effect. In conclusion, the aging behaviours of the TNT, Comp B and Comp A-3 have been investigated using 71 years old samples which were stored in ambient conditions. The Comp A 3 was found to have no discernable changes with respect to aging while TNT was noted to have a reduction in friction resistances. The aging of Comp B was predominately affected by the aging of its TNT component while the RDX had negligible effects. No evidence was found to suggest the chemical stability of the explosives had been compromised. Thus, this study concluded that they can be safely stored and handled by the Canadian Armed Forces.