Decomposition of Al ₂ TiO ₅ and Al _{2(1‐ <b> <i>x</i> </b> )} Mg _{<b> <i>x</i> </b>} Ti _{(1+ <b> <i>x</i> </b> )} O ₅ Ceramics

Abstract

The decomposition of Al 2(1‐ x ) Mg x Ti (1+ x ) O 5 ceramics in air has been studied between 900° and 1175°C for 0 lessthan equal to x lessthan equal to 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 Al 2 O 3 (+ MgAl 2 O 4 for x &gt; 0) core and a TiO 2 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 Al 2 TiO 5 ( x = 0) is the transport of Al 3+ ions through the TiO 2 ‐rutile phase.