The effects of SiO_2 and K_2O on glass forming ability and structure of CaO-TiO_2-P_2O_5 glass system

摘要

The effects of SiO_2 and K_2O were investigated on the glass forming ability (GFA) and structural characteristics of CaO-TiO_2-P_2O_5 system. Differential thermal analyzer (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and ~(31)P 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 SiO_2 and crystalline phases such as TiP_2O_7, rutile (TiO_2) and cristobalite (SiO_2) were formed in it.The results showed that K_2O prevents crystallization of glasses and promotes the formation of glass. FT-IR and X-ray diffraction showed that the addition of K_2O caused the formation of phosphate-silicate network as P-O-Si, and formation of isolated droplet phases (rich of Si and P) separated from the phosphate matrix.The optimum amounts of SiO_2 and K_2O in phosphate structure were respectively 6 and 2 wt.%, 0 in accordance with glass forming ability (GFA) parameters. Despite addition of SiO_2 along with K_2O;;the ~(31)PMAS NMR and infrared spectrums of glasses show that no Q~2 sites were in the phosphate network. The Q~1 and the pyrophosphate groups was the predominant structural unit in these glasses.