FORMATION OF CRYSTALLINE PHASES IN GLASS-CERAMICS BASED ON SIO2-AL2O3-ALPO4-CAF2-AIF3-NAF

The crystal structures formed in a system of ion-leachable glass-ceram ics based on SiO2-Al2O3-AlPO4-CaF2-AlF3-NaF, with optional additions o f CaO and LiO, were identified by x-ray diffraction. The occurrence of crystalline phases was indicated by the observation of varying degree s of opacity after the heat treatment of previously transparent quench ed samples. In six-component glasses with high concentrations of Ca, c ompared to (Si and Al), the principal crystalline phase was Ca2Al2SiO7 , with a lesser amount of (Ca,Na)(Si,Al)4O8 and a relatively smaller a mount of Ca5F(PO4)3. When the Ca concentration was reduced relative to (Si and Al), (Ca,Na)(Si,Al)4O8 became the principal constituent with m inor amounts of Ca2Al2SiO7 and Ca5F(PO4)3. In eight-component glass-ce ramics containing additional Na, (Ca,Na)(Si,Al)4O8 was also the princi pal constituent, but the presence of a small amount of LiO had no obse rvable effect on the structures of the crystalline phases.