Preparation of calcium doped LaCrO3 fine powders by hydrothermal method and its sintering

The synthesis of fine powders of LaCrO3 and its solid solutions doped with calcium under hydrothermal conditions and the sintering of these powders were investigated. Precursor alkaline coprecipitated lanthanum chromite gels with three different compositions: LaCrO3, La0.9Ca0.1CrO3 and La0.8Ca0.2CrO3, were processed under hydrothermal conditions at low temperatures (350–425 °C), for a reaction time between 30 and 120 min. Powders of a single phase with orthorhombic structure of LaCrO3, La0.9Ca0.1CrO3 and La0.8Ca0.2CrO3 were obtained at a temperature as low as 350, 400 and 425 °C, respectively, for a short reaction interval of 1 h. SEM and TEM micrographs showed that particles with an irregular morphology and an average particle size of 300 nm, were mainly obtained under hydrothermal conditions. The powders were pressed by cold isostatic pressing at 200 MPa, and then sintered in air at a temperature range of 1200–1500 °C for various intervals (1 to 5 h). A maximum apparent density of 97.7% was achieved on specimens with high calcium content, La0.8Ca0.2CrO3, at 1400 °C for 5 h. The average grain size measured on the sintered specimens was 6 μm.