Comparison of Thermal Behavior of Regular and Ultra-fine Aluminum Powders (Alex) Made from Plasma Explosion Process

Alex powder (an ultra-fine aluminum powder produced by the plasma-explosion process) has been shown to be a very effective burning rate enhancer for solid propellants and fuels. The objective of this research is to investigate the mechanisms responsible for the beneficial effect of Alex. A TGA and DTA were employed to examine the thermal bahavior of Alex and regular aluminum particles in different gases. An environmental scanning electron microscope (ESEM) was utilized to study the particle surface bahavior when samples were heated in air and nitrogen. A transmission electron microscope (TEM) was employed for examining the microstructure of Alex particles. Alex powder was demonstrated in TGA and DTA experiments to behave very differently from the regular aluminum in air, oxygen and nitrogen. Rapid weight gain of Alex particles in air and nitrogen environment occurred around 548°C and 700°C, respectively. The low-temperature reaction in air corresponds to an oxidation reaction. Comparing DTA traces of Alex and regular aluminum in air, it was found that oxidation of Alex particles occurs at a lower temperature with a higher degree of reaction. This is believed to be mainly due to the higher reactivity associated with greater surface area of the Alex particles. In the comparison of DTA traces of Alex and regular aluminum in nitrogen, the rapid nitridation reaction of Alex particles occurs at temperature around 680°C and proceeds to near completion.