Kinetic modelling of solid state magnesium aluminate spinel formation and its validation.

The kinetic pathway for magnesia-excess magnesium aluminate spinel (MgAl 2 O 4 ) formation is determined from the dilation behaviour of MgO–Al 2 O 3 (34:66 w/w) oxide compacts during reaction sintering under dynamic heating regime at different constant heating rates ( β ). It is calculated from expansion values at different β , analysed through model-free and model-based kinetic methods to arrive at the most suitable and unambiguous kinetic pathway, where spinelisation is best described ( r 2 =0.986) with Avrami model with exponent n =0.65 and activation energy ( E a ) 409 kJ mol −1 . To validate the kinetic model, an isothermal heat treatment of the oxide compact was done and % spinelisation was determined by Rietveld refinement of the XRD data. The results matched the predicted values very closely and validate our kinetic model. This method can be extended to several industrially important thermally activated solid state reactions which require thermal treatment in order to minimise the energy requirement by optimising the heating protocol. [ABSTRACT FROM AUTHOR]