High Thermal Shock Resistant Aluminium Titanate Type Ceramics

Microstructure control is a critical issue facing manufacturers of advanced ceramics. Secondary phases, introduced to improve sintering, have become increasingly important in controlling the average grain size and grain-size distribution of the major phase. The effect of ZrO2 addition (1, 5, 10 % by weight) on tialite type, binary TiO2-Al2O3 compositions were investigated at 1550 o C. The influence of CeO2, MgO and Nd2O3 on the thermal shock resistance, mechanical strengths, open porosity, bulk density, and microstructure have been studied. Dilatometric analysis, Fourier Transform – Infrared analysis (FTIR), X-Ray Diffraction (XRD) analyses and Scanning Electron Microscopy (SEM) used to study both phase transformation and sintering processes. The addition of ZrO2 improves the thermal shock resistance of tialite compositions (> 40 reversals of heating at 900 o C followed by rapid cooling in water). Introduction Pure ceramic materials based on ZrO2 or TiO2 show a proper corrosion resistance against slag or slag/metal corrosive environment but are affected from thermal shock conditions [1]. Aluminium Titanate (tialite) represents a high useful refractory ceramic due to the low thermal expansion coefficient (0.1-1x10 -6 o C -1 ), low thermal conductivity (0.9-1.5 W/m o C) and excellent thermal shock resistance. These characteristics make it an attractive material for specialised applications. A limiting factor is the decomposition of tialite in the temperature range 700-1300 o C [2] with formation of Al2O3 and TiO2 (rutile). As a result of decomposition, the tialite (Al2TiO5) no longer exhibits a low coefficient of thermal expansion [3]. The thermal decomposition of Al2TiO5 can be controlled by adding different additives (oxideMgO, SiO2, Fe2O3, fluoride, glass, etc.) [4]. The melting point of tialite is above 1800 o C and the bulk coefficient of thermal expansion is very low and consequently developing an excellent thermal shock resistance [5]. On the other hand, the highly anisotropic materials like Al2TiO5, showing grain boundary microcracking in polycrystalline bodies have extremely low strength [6]. The strength can be improved by alloying with a material of high strength while the matrix maintains the low thermal expansion [7,8]. The aim of this work was to improve the mechanical characteristics of aluminium titanate ceramics, synthesised from equimolar amount of Al2O3 (corundum) and of TiO2 (anatase), by alloying with 5% and 10% (by weight) stabilised zirconia. The influence of some oxides, such as MgO, CeO2 and Nd2O3 on the tialite-zirconia composite thermal stability at the heating-cooling condition has been investigated also. Experimental Procedure