Mechanical and dielectric properties of porous lanthanum orthophosphate materials with TiO2 addition via foam-gelcasting

Abstract

ABSTRACT Lanthanum orthophosphate (LaPO4) powder was prepared by a solid–liquid precipitation reaction of lanthanum carbonate powder with H3PO4 in order to fabricate porous LaPO4 materials. The phase transition and morphology evolution of the reaction products were found to be dependent mainly on the mass ratios of reactants and calcination temperatures. Porous materials using as-synthesized single-phase LaPO4 powders and TiO2 additives via direct foam-gelcasting exhibit large spherical-shaped cells without preferred orientation. The bulk density increases with the increase of sintering temperatures, as evidenced by bigger strut thickness, smaller cell and window sizes and lower inter-connectivity. Porous LaPO4 bulk ceramic with 5 wt% TiO2 addition sintered from 1100°C to 1500°C shows a porosity within 66.80–82.03% and a compressive strength from 4.0 to 17.2 MPa. The compressive strength dependence on the relative density follows a power-law relationship with an exponent value of ~2.45. While imaginary parts of dielectric permittivity of the porous LaPO4 materials measured over the X-band frequencies (8.2–12.4 GHz) depend weakly on the frequency and TiO2 addition, the real parts are affected strongly by TiO2 addition and sintering temperatures and fall within the range between 1.9 and 3.5 in this study.