Non-isothermal kinetic studies on the formation of Al2O3/Nb composite

The reaction mechanism and activation energy (Eα) of aluminothermic reaction between Al and Nb2O5 were investigated under non-isothermal conditions using X-ray diffractometry (XRD) and differential thermal analysis (DTA). It was found that the mechanically alloyed Al–Nb2O5 powder mixture was converted to Al2O3/Nb composite in three stages and during the reduction, intermediate Nb oxides (NbO2 and NbO) were formed. Four isoconversional methods, of Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Tang and Starink, were used to determine the value of E on a conversion fraction of α = 0.5 for these three exothermic reactions. The results showed that all methods lead to similar values of E and have a good agreement with one another. Also, the isoconversional method of Starink was used to determine the variation of the activation energy, Eα, for three exothermic reactions with degree of conversion (α). It was revealed that the Eα for the first and third reactions are independent from α while different behavior was observed for the second reaction, where a decrease of Eα occurred in the conversion range of 0.6 ≤ α ≤ 0.95.