Effect of Si content on H sub(2) production using Al-Si alloy powders

The effect of Si content in Al-Si alloy powder with NaOH on H sub(2) production was investigated. The total amount of H sub(2) produced decreased as Si content increased, which is inconsistent with the results predicted by the chemical reaction. Si caused a delay in the rate of H sub(2) production. Energy dispersive spectrometry showed that a large amount of unreacted Si remained in the matrix, and the unreacted fraction increased as the Si content increased. As the evolution reaction of Al and Al-Si alloys is exothermic, the temperature of all the specimens increased. Si addition reduced the hydroxide removal rate, which decreased the average H sub(2) production rate. The initiation time for H sub(2) evolution depends on the elimination rate of the oxide film formed during production of the powder. On increasing the Si content, SiO sub(2) was formed, which is harder to eliminate than Al sub(2)O sub(3); this delayed the initiation.