Biggest Bang for Your Buck Particle Size Characterization of Secondary Explosives

Secondary explosives, such as trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX) and 1,3,5,7- tetranitro-1,3,5,7-tetrazocane (HMX), are frequently used for a variety of industrial applications such as mining, demolition and pyrotechnics. These explosives were developed in the 19th and early 20th century. Almost all industrially produced explosive compounds combine azo-, azido- and nitro-groups to create a thermodynamically unstable compound with a favorable nitrogen and oxygen balance. When ignited by primary explosives, heated to a certain temperature or subjected to a specific impact force, these compounds disintegrate rapidly, which releases a large amount of energy and gas volume in a very short time.
Secondary explosives (SEs) are commercially available in the form of fine powders, granulates, pellets and melt-casted blocks with a predefined size. Fine powders are often wetted, phlegmatized with wax or thermoplastic polymers to improve safety and simplify logistic operations. Granulates made from explosive compounds are frequently used for mining operations. Explosive charges, which can additionally contain reactive metal powders, oxidizers and polymer matrix, are usually produced by pressing and casting. Particle size and particle size distribution (PSD) of secondary explosives directly influence packing density and detonation parameters (velocity and pressure of detonation) of explosive charges [1, 2].
This means that the performance of explosive charges is dependent both on particle size and the PSD of ingredients. Particle size and PSD also have a significant impact on the production process of cast polymer-bonded explosives (PBX) by influencing the rheological properties of suspensions. Finally, the mechanical properties of plastic explosives and cured PBX are dependent on the particle size of SEs as well.
Due to the unstable nature, heat sensitivity and toxicity of explosive compounds, particle size measurements pose a significant challenge and often require a specialized setup. Wet sieving is the most commonly used method for measuring the particle size distribution of explosive powders. This method is highly time- and energy-consuming, and well-trained operators are required. Alternatively, fine explosive powders can be sized using light scattering [3] or laser diffraction [1, 4]. In this application report, we demonstrate a quick, easy and safe way to characterize the particle size of different explosive samples by laser diffraction with the PSA 1190LD.