Effect of microstructure on thermal and mechanical properties of solid solutions Al2TiO5 - MgTi2O5

Abstract

Aluminium titanate - tialite belongs to the compounds with pseudobrookite structure. The polycrystals made of tialite show valuable useful thermal properties: low thermal expansion, very low thermal conductivity and high resistance to thermal shock. These properties result from the cracks present in the microstructure, resulting from significant differences in the lattice coefficients of aluminium titanate. The basic disadvantage of tialite consist in a thermal decomposition occurring at the temperatures of about 750–1280 °C. This decomposition can be limited by structural and microstructural stabilization. The addition of cations, e.g. magnesium or iron, leads to the formation of stable solid solutions, while the addition of SiO2 or ZrO2 leads to the formation of secondary phases - diffusion barriers occurring at intergranular boundaries. Most often these additives are introduced simultaneously and at the reaction sintering stage. Stable solid solutions are usually produced by a classical solid phase reaction between the initial oxides: Al2O3, TiO2 and MgO. In this work, an innovative synthesis was applied to produce solid solutions, involving a heterogeneous isostructural nucleation with magnesium titanate. The polycrystals obtained in this way, at a much lower temperature, with a high content of solid solutions (95–96 %), high density, homogeneous microstructure with necessary microcracks were obtained. As a result, the obtained polycrystals exhibit the typical pseudobrookite structure behaviour as a function of temperature.