Not so crystal clear : Defects, hot spots and initiations in explosive crystals

Abstract

Nitroamine explosives are a crystalline material used in munitions, as a charge or propellant in powder form. These crystalline powders are compounded into formulations with other materials that can be tuned to fit requirements and their sensitiveness to insult is well understood. The larger part of these formulations are the crystalline explosives, which currently have less tunability. Researchers are aware that different crystal structures result in different materials properties. This is seen in nitramine explosives, such as RDX, where sensitivity can be reduced by manufacturing RDX particles to be more spherical and reducing the crystalline defects. They also know that hot spot formation, spots within the structure that heat up faster than surrounding areas, a contributing factor to initiation, is caused by defects within the crystal structures of the explosives. The types of defects, point, line, surface, substitutional, or interstitial, are not unique to energetic crystalline materials and a material could have any combination of these. A better understanding of how thse defects effect the formation of hot spots and the subsequent sensitivity will enable researchers to develop techniques that can produce highly tuned crystalline explosives. This thesis will focus on the nitroamine explosive, HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine. Large single crystals will be grown using temperature lowering methods and the subsequent defects will then be identified and mapped out using Xray topography. Once characterised, the single crystals will then be subject to a shockwave which will cause initiation. Correlations between this initiation and the mapped defects will be identified.