Bulk samples of lanthanum phosphates were synthesized in a hydrothermal hot pressing process. In this process, the pressing temperature, pressure, and the volume of water were varied to improve the density and various strengths. The strength of the bulk samples was estimated from drilling and ultrasonic treatments, and the residual ratio in hydrofluoric acid. Lanthanum phosphate formed the porous bulk samples with about 60% filling factor, which were calculated from the real and theoretical densities. By heating the lanthanum phosphate before the pressing, the maximum diameter became larger of the phosphate pellets without cracking. Lanthanum phosphate bulk samples gave a high residual ratio in hydrofluoric acid. The hydrothermal hot pressing process is a useful method to obtain the bulk samples of lanthanum phosphate.

Keywords: Lanthanum phosphate, Hydrothermal hot pressing process, Drilling, Resistance against hydrofluoric acid.