Kinetic analysis of the formation of magnesium aluminate spinel (MgAl2O4) from α-Al2O3 and MgO nanopowders

This work reports on the formation kinetics of magnesium aluminate spinel (MAS), from α-Al2O3 and MgO nanopowders. A non-isothermal kinetic analysis was performed by the thermodilatometric analysis (TDA) for the first time. The measurements were carried out using a dilatometer on compact samples with heating rates from 3 to 11 °C min–1. Phases formed during the spinelisation process, in specimens heat-treated in both the dilatometer and furnace, were characterized by X-ray diffraction (XRD). The use of pure nano-oxide powders to produce spinel reduced the formation temperature and activation energy. MAS started to form, in the furnace heat-treated specimens, at 1000 °C and its formation was complete at 1400 °C. For specimens heated in the dilatometer, MAS formation temperature increased from 1002 to 1061 °C with the increase in heating rate from 3 to 11 °C min−1. The activation energy for spinelisation, under non-isothermal conditions, was calculated by linear reaction models (Integral isoconversional methods) using Flynn–Wall–Ozawa (FWO) method. Boswell, and Kissinger equations. The average activation energy (Ea), correlation coefficient (R2), Avrami parameter (n), and dimensionality of crystal growth (m) were equal to 293.31 kJ mol−1, 0.99, 1.22, and 0.98, respectively. The Johnson–Mehl–Avrami (JMA) reaction model, following Ligero method (Differential isoconversional methods), was used to analyze spinelisation kinetics under non-isothermal conditions. The average activation energy (Ea), correlation coefficient (R2), Avrami parameter (n), and the frequency factor (k0) were found to be 283.90 kJ mol−1, 0.99, 1.2, and 4.17 × 108 s−1, respectively.