Sol-gel synthesis of precursors and preparation of ceramic composites based on LaPO4 with Y2O3 and ZrO2 additions

Nanosized powders as precursors have been synthesized via sol-gel technique to prepare ceramic composites in the LaPO4-Y2O3 and LaPO4-ZrO2 systems through normal sintering. Sol-gel technique was based on separate synthesis of LaPO4 center dot nH(2)O, Y(OH)(3), and ZrO(OH)(2) components as sol using "reverse precipitation" (or "reverse flocculation") technique, and further mixing them together to prepare (1-x)LaPO4 center dot nH(2)O-xY(OH)(3) and (1-x)LaPO4 center dot nH(2)O-xZrO(OH)(2) compositions as gels. During sol-gel synthesis, formation of hexagonal LaPO4 center dot nH(2)O and Y(OH)(3) or monoclinic ZrO(OH)(2) was observed. As-prepared precursors of nanosized powders were then calcined at 850 degrees C for dehydration of the components and decomposition of yttrium and zirconium hydroxides to obtain nanosized (1-x)LaPO4-xY(2)O(3) and (1-x)LaPO4-xZrO(2) compositions, where x did not exceed 0.20 mole fraction. Ceramic composites were prepared by sintering these compositions subsequently at 1000, 1200, and 1300 degrees C for 24 h. Vickers microhardness was found to depend on x and sintering temperature. The influence of yttria and zirconia additions on dispersion of powders, their thermal behavior, specific surface area and ceramic fracture surface of the composites, and their open porosity was discussed. Initial nanosized powders of 0.8LaPO(4)center dot nH(2)O-0.2Y(OH)(3) (left) and 0.8LaPO(4)center dot nH(2)O-0.2ZrO(OH)(2) (right) Fracture surfaces of 0.8LaPO(4)-0.2Y(2)O(3) (left) and 0.8LaPO(4)-0.2ZrO(2) (right) ceramic composites sintered at 1300 degrees C for 24 h.