Synthesis and sintering of LaPO4 powder and its application

Lanthanum phosphate powders were synthesized by direct solid–liquid reaction of lanthanum oxide and phosphoric acid at the La:P ratio of 1:1. Phase-pure and fine grain size LaPO4 powders could be obtained by calcining the as-received powders at the temperature higher than 600 °C. It was demonstrated that the phase type, grain size and morphology of the LaPO4 powders were calcined at various temperatures. We have studied the microstructure of sintered LaPO4 ceramic and Al2O3/LaPO4 composite using the synthesized powders by SEM and TEM analysis. An interesting layered crystal structure and lots of dislocations inside LaPO4 grains and at the interface of Al2O3/LaPO4 composite were observed. Low hardness and multiple dislocations and dislocation networks indicated the layered LaPO4 ceramic could possess excellent machinability. As an example for engineering application, machinable Al2O3/LaPO4 composite with weak bonding was fabricated and characterized.