The Synthesis of Thermochemically Stable Single Phase Lanthanum Titanium

Highlights 2  Single phase LaTi2Al9O19 (LTA) has been successfully synthesized by sol-gel method at relatively low temperature (1350 o C), something not previously investigated.  The sol-gel synthesized LTA shows good thermochemical stability up to 1500 o C.  Sol-gel synthesized LTA shows higher coefficients of thermal expansion than the solid state reaction synthesized LTA.  LTA is a face centre monoclinic material which has a very complicated crystal structure formed by AlO6 and TiO6 octahedra, connected through AlO4 tetrahedra and 12-fold-coordinated La 3+ cations. Abstract Lanthanum titanium aluminium oxide (LaTi2Al9O19, LTA) synthesized by solid state reaction has been proven to be a promising thermal barrier material. However, LTA synthesized via solid state reaction requires a high processing temperature of at least 1500 o C for 24h. In this paper, single phase LTA was synthesized by sol-gel at a lower temperature (1350 o C) and the process parameters, phase composition, and relative thermal properties were investigated. Two-step calcination was used to obtain fine LTA powders. According to X-ray diffraction, the best calcination temperature of sol-gel synthesized LTA is 1350 o C. XRD results also showed the thermochemical stability of sol-gel synthesized LTA, which does not react with Al2O3 up to 1500 o C, to be excellent. Compared to LTA synthesized by solid state reaction, sol-gel synthesized LTA has higher coefficients of thermal expansion (CTEs) which are circa 10.2×10-6 o C-1 at 950 o C, related to the size dependent characteristic of CTEs. Therefore, sol-gel synthesized LTA can be a promising candidate as a thermal barrier material on Ni-based superalloys.