Experimental study of ignition of mechanical alloy and pure metal powders

Mechanical alloys of Al Mg, AI Zr, Al Ti, Al Li, Al C, Al Mg H, B Mg, B Al, and B Ti were produced and tested for possible applications as high energy density additives to fuels, propellants, explosives, and incendiaries. These new materials are metastable, supersaturated, nanocrystalline solid solutions that include a base metal as a solvent and another component (metal or gas, e.g. hydrogen) as a solute. Phase changes occurring in such materials during ignition and combustion are expected to significantly affect both ignition and bum rates. This experimental program focused on the characterization of ignition kinetics of these alloys. An experimental setup is built around an electrically heated filament coated with the powder of a tested material. The filament is heated at a reproducible rate causing ignition of the powder. The temperature of the filament at the instant of ignition is measured using an optical pyrometer. The time of ignition and the filament heating rate are determined from the optical and electric signals recorded using a computerized data acquisition system. For alloys with higher ignition temperatures, video imaging and image processing technique was used. Experiments showed that the pyrometer technique is more accurate but a discrepancy between the video imaging and pyrometry is small. Each material is ignited at three different heating rates. Ignition temperatures are determined for aluminum and boron based alloys as a function of their elemental composition. It is observed that the ignition temperatures of a set of prepared aluminum based alloys are significantly lower than that of the pure aluminum. It was also found that the measured ignition temperatures increased with an increase of heating rate for all the investigated alloys