Thermodynamics and kinetics of decomposition of Al2TiO5-base ceramics

The decomposition of MgxAl2(1-x)Ti(1+x)O5 solid solutions with x = 0 (Al2TiO5), 0.1 and 0.2 was studied at 1100°C. The kinetics follows the Avrami equation with a time exponent of 1.6 for x = 0 and 34÷3.5 for x = 0.1 and 0.2. Decomposition of materials with x > 0 is considerably delayed in comparison to pure Al2TiO5: the tune of half-transformation into parent oxides is increased by an order of magnitude. The micro structure of partially decomposed materials show the presence of nodules with a core composed of Al2O3 (and MgAl2O4 when x > 0) elongated crystal, surrounded by an irregular TiO2 shell. The nodules grow retaining their structure as decomposition proceeds. The decomposition kinetics is probably controlled by the nucleation of the reaction product at a limited number of "easy to nucleate" sites owing to the small chemical driving force available.