Surface modifications of plasma treated aluminum particles and direct evidence for altered reactivity

Abstract

Aluminum particles (Al) inherently contain a natural oxide (Al2O3) coating that limits rates of diffusion-controlled energy release and can prevent complete conversion of the chemical energy available within an Al particle. Therefore, altering Al surface properties to reduce the oxide shell and/or transform shell chemistry are active areas of research. This study used atmospheric pressure plasmas to reduce the aluminum oxide shell, then examined the resulting changes in reactivity. Two plasma gas discharges were compared: argon (Ar) and helium (He). All plasma-treated particles were characterized using Powder X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). Results show Ar plasma treatment resulted in high concentrations of surface hydration, while He plasma treatment did not. Both plasma-treated Al particles show reduced oxidation barriers that result in increased reaction rate constants by an order of magnitude for oxidation reactions. The results further an understanding of the effects of surface modifications on reaction kinetics and energy release behavior of fuel particles.