The oxidation kinetic study of mechanically milled ultrafine iron powders by thermogravimetric analysis

The effect of mechanical milling on the oxidation kinetics of ultrafine iron powders was investigated by thermogravimetric (TG) analysis. The initial α-Fe powder with average particles size of 100 nm was made by the electric explosion of wire. The milling of iron powder was carried out by AGO-2S planetary ball mill using a rotation speed of 2220 rpm and the milling times of 15 and 40 min. According to the XRD data, the main content of α-Fe was observed in all samples. However, a certain amount (~ 20 mass%) of wustite phase (FeO) is formed after ball milling of ultrafine iron powders. From TG analysis, the powders milling leads to increase in the temperature of thermal oxidation onset and shifts the reaction to higher temperatures. A model-free isoconversional method of the Friedman analysis was employed only in a first qualitative approximation. More accurate kinetics parameters were obtained using the multivariate nonlinear regressions, where three-step reaction with branching set of n -order equations for each step was chosen.