Particle size and size distribution (PSD) play a major role in the properties of the explosive material. For instance, the shock sensitivity (ignition by pressure) increases as the particle size decreases for high density explosives. Also, the presence of defects within the structure affects its sensitivity. Pressed solid explosive formulations (explosive particles with a binder material) present defects (voids), which are mainly located outside the explosive particles, and increasing the number of defects increases the sensitivity.
Therefore, accurate, precise, consistent and reproducible measurement of particle properties is essential for the successful tailoring of explosive materials.
An explosive material is a highly reactive substance that contains a large amount of potential chemical energy, which can undergo rapid decomposition or combustion, producing an explosion. The decomposition or the combustion is often accompanied by the evolution of gaseous products, the emission of light and sound, and heat.
The production of gaseous products is what in fact produces the explosion. A given mass of gaseous molecules occupy a much larger volume than the equivalent mass in the liquid or solid states. The material’s rapid volume expansion produces a high pressure region that travels outwards, from the original explosion point, in the form of a pressure wave.
There are several classification systems for explosives, reflecting the different properties that are important for their correct functioning. For instance, they are classified as primary, secondary and tertiary according to the amount of heat or pressure required to initiate the ignition process. Primary explosives are very unstable and are often used in small amounts to initiate the reaction of secondary explosives (usually very stable under normal conditions). The properties of the explosive material depend not only of its chemical nature, but also on the physical format they are presented.
Nowadays, many explosive materials are produced in the form of particulate materials. By careful optimization of the production process, it is possible to consistently produce particulate explosive materials with well-defined properties. The solid explosive materials are usually produced from well-known solid formation processes, such as crystallization or precipitation from the synthesis solutions. The particle properties are then optimized from the crude material by different physical operations, including crushing, grinding, cutting, vibrating or atomization.
Despite their inherent instability and, therefore, danger of explosion, the explosive materials (secondary and tertiary explosives) are produced using particle production techniques that are also commonly found in other industries. Evidently, the production processes are adapted to safely avoid ever reaching the ignition conditions.
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