CRYSTALLISATION OF APATITE STOICHIOMETRIC IONOMER GLASSES FOR MEDICAL APPLICATIONS AND OPTOELECTRONICS

摘要

Substitution of fluorine for oxygen strongly influences the crystallization of 4.5SiO_2-3Al_2O_3-1.5P_2O_5-(5-z)CaO-zCaF_2 glasses. A glass with z = 0 crystallized to whitlockite and anorthite. Introduction of F caused the formation of FAP instead of whitlockite, and inhibited anorthite formation. For z = 1, only FAP was formed. For z > 2, mullite also crystallized. The inhibition of anorthite favors mullite formation, probably due to the high Al:Si ratio of the glasses and, following FAP crystallization, the lack of charge balancing cations for maintaining the Al(Ⅳ) state. Al is mainly Al(Ⅳ) for z = 0, while F causes the formation of Al(Ⅴ) and Al(Ⅵ). These seem to disappear on heat treatment at Tpl and (Tp1+Tp2)/2, but new Al(Ⅴ) and Al(Ⅵ) species often appear on heating to Tp2. The F is present initially as F-Ca(n) and Al-F-Ca(n) species. The former appear to be used preferentially in forming FAP. The P in the glass is present initially as Al-O-PO_4~(3-) type species, but forms FAP and a small amount of AlPO_4. A small amount of P remains in the residual glass as PO_4 tetrahedra, coordinated primarily by Al.