The effects of SiO2 and K2O on glass forming ability and structure of CaOsingle bondTiO2single bondP2O5 glass system

The effects of SiO2 and K2O were investigated on the glass forming ability (GFA) and structural characteristics of CaOsingle bondTiO2single bondP2O5 system. Differential thermal analyzer (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and 31P magic angle spinning NMR methods were applied for characterizations of the system. Unwanted crystallization in the initial three components base glass composition was observed by adding SiO2 and crystalline phases such as TiP2O7, rutile (TiO2) and cristobalite (SiO2) were formed in it. The results showed that K2O prevents crystallization of glasses and promotes the formation of glass. FT-IR and X-ray diffraction showed that the addition of K2O caused the formation of phosphate–silicate network as Psingle bondOsingle bondSi, and formation of isolated droplet phases (rich of Si and P) separated from the phosphate matrix. The optimum amounts of SiO2 and K2O in phosphate structure were respectively 6 and 2 wt.%, 0 in accordance with glass forming ability (GFA) parameters. Despite addition of SiO2 along with K2O; the 31P MAS NMR and infrared spectrums of glasses show that no Q2 sites were in the phosphate network. The Q1 and the pyrophosphate groups was the predominant structural unit in these glasses.