GLASS-TRANSITION TEMPERATURE OF GLASSES IN THE SIO2-NA2O-CAO-P2O5-AL2O3-B2O3 SYSTEM

A total of 24 glasses in or near the bioactive region in the system SiO2-Na2O-CaO-P2O5-Al2O3-B2O3 were studied. By differential thermal analysis their glass transition temperatures, T(g), were determined. On basis of an experimental plan for 16 glasses, two phenomenological equations describing the relationship between T(g) and glass composition were developed. The equations describe T(g) within the compositional ranges: SiO2, 38.0-65.5; Na2O, 15.0-30.0; CaO, 10.0-25.0; P2O5, 0-8.0; B2O3, 0-3.0; Al2O3, 0-3.0 wt%. The glass transition temperature shows a linear dependence of the Na2O content. The higher the Na2O content, the lower the T(g). Compositional alterations not including Na2O influences T(g) little in comparison with changes in the Na2O content.