Devitrification behavior of calcium phosphate glasses containing AL(2)O(3)and SiO2 additives

The effects of Al2O3 and SiO2 additives on the crystallization of calcium p hosphate glasses were studied. When the Al2O3 content was higher than 7 mol %, surface devitrification occurred in the glasses. However, for glasses wi th Al2O3 contents higher than 10 mol%, bulk devitrification predominanted. For the glasses with SiO2, a surface devitrification mechanism predominante d. Non-isothermal DTA techniques were applied in order to establish the dev itrification mechanism, and the kinetic parameters of crystal growth were o btained. The parameter rn depends on the mechanism and morphology of devitr ification of calcium phosphate, glass containing SiO2 as additive, the valu es of m being lower than 1.2. These results indicate that the devitrificati on is controlled by the reaction at the glass-crystal interface, or occurs from surface nuclei.