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 alpha-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 degrees 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 degrees C and its formation was complete at 1400 degrees C. For specimens heated in the dilatometer, MAS formation temperature increased from 1002 to 1061 degrees C with the increase in heating rate from 3 to 11 degrees 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 (E-a), correlation coefficient (R-2), 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 (E-a), correlation coefficient (R-2), Avrami parameter (n), and the frequency factor (k(0)) were found to be 283.90 kJ mol(-1), 0.99, 1.2, and 4.17 x 10(8) s(-1), respectively.

Automated summary

This work investigates the formation kinetics of magnesium aluminate spinel from alpha-Al2O3 and MgO nanopowders, using thermodilatometric analysis and X-ray diffraction. The results show that the use of nano-oxide powders reduces the formation temperature and activation energy of spinel.