Obscurant Material Drying Processes

Applied Separations has significant experience in drying metal flakes in supercritical carbon dioxide (scCO2) for obscuration. We have shown reduced agglomeration and better aerosolization of scCO2 dried particles and flakes vs those dried by thermal and freeze-drying methods. Dried metal flakes from organic solvent suspensions have been prepared in multi-kg quantities. Two drying approaches with scCO2 are proposed: (a) dry commercial graphite and brass flakes to reduce particle agglomeration, (b) prepare free-flowing metal flakes from organic solvent suspensions. Different sized graphite and brass flakes have been selected for drying. Dried flakes will be tested individually and as mixtures for aerosolization, flow under shear and obscuration. PVD process prepared metal flakes are available as organic solvent suspensions. Aluminum flake suspensions (with desired particle size) and varying amounts of silica coating (“passivation” of aluminum) and flakes with prismatic structure will be dried to free-flowing powders. Based on refractive index, chromium flakes should have larger extinction coefficient versus brass and aluminum; chromium flake suspension will be dried for evaluation. Packaging for large quantities of dried flakes will be designed. US Army has current contract with Halide Group Inc; Excet: Project 201149.1.3.1: Drying of Aluminum Flakes (Start May, 2019); joint work with Applied Separations.