Surface crystallisation behaviour of invert calcium phosphate glasses doped with V2O5

The crystallisation behaviour of calcium phosphate glasses with molar ratios of [CaO]\[P2O5]=1.2 and V2O5 contents of 5-13 mol% is investigated. The results indicate the complex crystallisation behaviour of these glasses, which depends on the V2O5 content. The crystallisation of these glasses was detected on DTA (differential thermal analysis) curves as one or two successive exothermal peaks in the temperature interval T=650-850degreesC The crystallisation temperature peak decreased with increasing V2O5 content. alpha-Ca2P2O7 was formed as the primary phase, while beta-Ca2P2O7 and VP2O7 were formed as the secondary phases. The content of beta-Ca2P2O5 decreased with increasing V2O5 content, while that of VP2O7 increased. From DTA analysis on powdered glasses and micrographs of fracture surfaces of heat treated bulk glasses it was confirmed these glasses crystallise via surface crystallisation.