Changes in the Surface Characteristics of Gas-atomized Pure Aluminum Powder during Vacuum Degassing

Vacuum degassing is essential in the preparation of RS P/M aluminum alloys to remove adsorbates and for the decomposition of hydrated-$Al_{2}O_3$ on the powder surface. Changes in the surface characteristics during vacuum degassing were investigated by X-ray photoelectron spectroscopy and temperature-programmed desorption measurement. Hydrated-$Al_{2}O_3$ decomposition to crystalline-$Al_{2}O_3$ and hydrogen desorption on the surface of argon gas-atomized aluminum powder occurred at 623 K and 725 K, respectively. This temperature difference suggests that the reaction converting hydrated-$Al_{2}O_3$ to crystalline-$Al_{2}O_3$ during vacuum degassing should be divided into the two reactions $"2Al+Al_{2}O_3{\cdot}3H_2O\;2Al_{2}O_3+6H_{surf}"and"6H_{surf}3H_2"$.