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

Abstract

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 ∼10 nm width and 98% TD for the LaPO4–10 wt% ZrO2 composition upon sintering at 1600 °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.