Decomposition of Al2TiO5 and Al2(1-x)MgxTi(1+x)O-5 ceramics

The decomposition of Al2(1-x)MgxTi(1+x)O5 ceramics in air has been studied between 900° and 1175°C for 0 £ x £ 0.6. The decomposition temperature versus composition x predicted using a thermodynamic model based on the regular solution approach is in satisfactory agreement with the experimental results. The decomposition kinetics has been studied at 1100°C for x = 0, 0.1, and 0.2 and follows a nucleation and growth mechanism. Random nucleation of the reaction products is hindered by the high elastic stresses that result from the molar volume change related to decomposition because of the small chemical driving force available. Decomposition occurs only at a limited number of sites, probably associated with the presence of impurities and/or glassy phase. The decomposition products grow as nodules formed by an Al2O3 (+ MgAl2O4 for x > 0) core and a TiO2 shell. The growth is parabolic for x = 0 and linear for x = 0.1 and 0.2. The rate-controlling step in the decomposition mechanism of pure Al2TiO5 (x = 0) is the transport of Al3+ ions through the TiO2-rutile phase.