Ceramic Composites Based on Nanosized Lanthanum Orthophosphate and Their Properties

The original approach was used to prepare (1 ‒ x)LaPO4·nH2O–xZrO(OH)2 and (1 ‒ x)LaPO4·nH2O–xY(OH)3 nanosized powders in wide concentration range as precursors via sol-gel technique. Ceramic composites based on LaPO4–Y2O3 and LaPO4–ZrO2 systems were obtained through normal stepwise sintering at 1000, 1200 and 1300°C for 24 and 1600°C for 1 h of the precursor powders preliminary calcined at 850°C. Vickers microhardness, thermal conductivity and chemical stability were investigated. For LaPO4–Y2O3 composites, the thermal conductivity values were presented for the first time. The influence of zirconia and yttria additions to LaPO4 and sintering temperature on these properties, as well as phase contents and ceramic fracture surfaces was discussed. These ceramic composites were shown to exhibit high microhardness, chemical and thermal stability, and low thermal conductivity, which allows them to be used not only as thermal barriers but as matrices for nuclear waste immobilization.