One of my friends here has been having some issues getting a clean, reliable start on a motor, so I suggested using a thermite igniter to get things moving quickly. Seeking some evidence to use for convincing the higher-ups, we did some high speed videos of a couple thermite igniters to see what goes on. We fired a standard copper thermite compound, as well as one based on manganese dioxide and aluminum. Each shot was 5 grams of material. The CuO igniter was filmed at 2000 frames per second, and the MnO₂ at 10,000 frames per second. I also sped up the MnO₂ video and stuck the shots next to each other, to allow easier comparison between the two types.
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One of the best ways to get really high burning rates with propellants is to introduce a much finer oxidizer particle into the binder matrix. Finer AP particles also help out tremendously with combustion, breaking down large fuel molecules much more effectively than coarse AP particles do. The end result is a propellant that burns smoother, produces a cleaner flame, and is nice and fast, to boot.

While I had the 200 micron AP under the microscope, I also pulled out some ground 20 micron to photograph, just for fun. This 20 micron AP is just above the limiting particle size for posting on the list of explosives. AP is a monopropellant, and can also undergo deflagration-to-detonation transition (DDT); these problems are exacerbated when the particles are extremely fine and in the neat state. Any milling operation involving energetics should be treated with the utmost of caution. But the end results are totally worth it. For preparing the ultimate in multimodal propellants, 20 mic can’t be beat.