Apatite-mullite glass-ceramics

Two series of glasses based on (2-x)SiO2 . xP(2)O(5) . Al2O3 CaO . yCaF(2) were studied. The values of x and y were varied from 0 to 1. The nucleation and crystallisation processes that occurred in these glasses were measured. Glasses in which x = 0.5 and y was greater than 0.5 crystallised to fluorapatite and mullite. Crystallisation occurred by a bulk nucleation mechanism involving prior amorphous phase separation. The glass with x = 0.5 and y = 0.5 was converted to a ceramic to give a material consisting of elongated fluorapatite crystals that had high fracture toughness.