Oxidation of aluminum particles in mixed CO₂/H₂O atmospheres

Oxidation of spherical aluminum powder was investigated by thermogravimetric analysis in oxygen, CO₂, steam, and mixtures of these oxidizers. Heating rates ranged between 2 and 20 K/min, and the maximum temperatures were 1370 and 1770 K in atmospheres containing steam and in dry atmospheres, respectively. Qualitative differences in oxidation behaviors observed for oxygen, steam, carbon dioxide, and for mixed oxidizers are established and described. These differences primarily concern an oxidation step occurring on Al melting that is only observed in the presence of steam and that is shown to increase dramatically if CO₂ is added. Other differences in oxidation behavior are observed at higher temperature: in the presence of steam oxidation is complete at temperatures as low as 1250 K, whereas in dry O₂ and CO₂ oxidation continues while temperature increases to 1700 K. An explicit kinetic model is used to determine the activation energy as a function of reaction progress for each individual experiment. Results in mixed atmospheres involving all three components show results somewhat similar to the behavior observed in steam. Results are discussed and several hypotheses aimed to explain the observed oxidation behavior are introduced.