Very low thermal conductivity in lanthanum phosphate-zirconia ceramic nanocomposites processed using a precipitation-peptization synthetic approach

A wet chemical synthetic approach involving precipitation-peptization mechanisms was successfully adopted for the development of LaPO4-ZrO2 nanocomposites with the ZrO2 content varying in the 5-20 wt% range. Stoichiometric lanthanum phosphate, formed as nanofibrils during the precipitation reaction with orthophosphoric acid, was subsequently transformed into nanorods of similar to 10 nm width and <100 nm length upon peptization at pH 2. Zirconia dispersions were homogeneously incorporated as ultrafine particulates through zirconium oxychloride hydrolysis using ammonia. The nanocomposite precursor thus obtained could be densified to > 98% TD for the LaPO4-10 wt% ZrO2 composition upon sintering at 1600 degrees C. The addition of ZrO2 to LaPO4 impeded densification and grain growth inhibition of up to 50% was obtained for LaPO4-20 wt% ZrO2 nanocomposites. Furthermore, the nanocomposites indicated very low thermal conductivity values (1 W m(-1) K-1) compared to single phase LaPO4. The non-reactivity of LaPO4 and ZrO2 at high temperatures and the low thermal conductivity values of LaPO4-ZrO2 render them effective for high temperature thermal insulation applications.