Ceramic Composites Based on Lanthanum Orthophosphate and Alumina: Preparation and Properties

An original approach to synthesis of nanosized (1 – x)LaPO4·nH2O–xAl(OH)3 precursor powders for (1 – x)LaPO4–xAl2O3 ceramic composites preparation was considered. Sol-gel synthesis was carried out separately using reverse flocculation of components. Thermal behavior of precursor powders was studied by DSC/TG. Ceramic composites with microhardness up to 30‒40 GPa were obtained by pre-heat treatment of powders and subsequent step wise sintering in the 1000–1600°C temperature range. The fracture surface of ceramic samples at different sintering temperatures was examined using electron microscopy. Ceramic samples exhibited low thermal conductivity at various temperatures and open porosity 3‒5%. Chemical stability of 0.8LaPO4–0.2Al2O3 sample was studied by leaching experiment in a solution of a mixture of NaCl and Na2SO4 salts. The resulting set of properties of (1 – x)LaPO4–xAl2O3 ceramic composites made it possible to offer these materials as heat barriers for rotors in high-speed micro gas turbines, and as ceramic matrices for immobilization of nuclear waste.