The role of bound water in the process of low-temperature oxidation of aluminum powders

The processes of oxidation of aluminum powders with various particles size (micron and submicron samples) when heated in air were studied using differential thermal analysis. It was found that decreasing of particle size leads to an increase in the content of bound water in the form of hydroxides in the aluminum particles shells. The (hydr)oxides decompose with the release of water vapor when heated, and there is a local loss of continuity of the protective shells of Al particles, which contributes to the initiation of the metal oxidation process. In the temperature range of 350-600 C, water vapor interacts with the surface of Al particles, resulting in the presence of hydrogen in the gas released from the thermal analyzer furnace. Based on a combination of data from thermal analysis, mass spectrometry and electron microscopy, it was shown that the main cause of the onset of oxidation of submicron Al particles was destruction of the (hydr)oxide shells due to intense gas formation at the metal core/shell interface due to the release of water vapor and hydrogen.