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

Abstract

Lanthanum orthophosphate (LaPO 4 ) powder was prepared by a solid-liquid precipitation reaction of lanthanum carbonate powder with H 3 PO 4 in order to fabricate porous LaPO 4 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 LaPO 4 powders and TiO 2 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 LaPO 4 bulk ceramic with 5 wt% TiO 2 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 LaPO 4 materials measured over the X-band frequencies (8.2-12.4 GHz) depend weakly on the frequency and TiO 2 addition, the real parts are affected strongly by TiO 2 addition and sintering temperatures and fall within the range between 1.9 and 3.5 in this study. ARTICLE HISTORY