The effect of impurities in coarse granules of aluminum on its hydrothermal oxidation for hydrogen production

Abstract

Abstract This study is devoted to hydrothermal oxidation of aluminum – the exothermic process in which hydrogen and aluminum oxide (or hydroxide) are produced. In this work, the influence of the chemical purity of aluminum on the conversion degree of coarse aluminum at hydrothermal oxidation was studied. Distilled water and coarse granules of aluminum with an average size of ~ 7–10 mm of three different aluminum purity of 99.7, 99.9 and 99.99% were used in the experiments. The oxidation experiments were carried out inside 5-litter autoclave in an isothermal mode at temperatures from 200 to 280°C with a step of 20°C. The holding time at the set temperature changes from 4 to 10 hours. Our results showed that with the increasing of temperature and holding time, the conversion degree increases. It was showed that chemical purity of aluminum influence considerably the oxidation kinetics. More chemically pure aluminum oxidizes much faster, e.g. at a temperature of 280°C and a holding time of 10 hours, the conversion degree of granules with the chemical purity of 99.9% and 99.7% was less than 2%, while 99.99% aluminum was almost fully oxidized.