Analysis of phase transformations of modified silicate xerogels during heat treatment

Abstract

The ways of obtaining glass for dental cements with low synthesis temperature were analyzed. The xerogels of the SiO2–CaO–P2O5 systems were synthesized by sol-gel technology from affordable raw materials. The physicochemical processes, temperature regions of phase transformations and intensity of their course, which occur during heat treatment of xerogels of two series of the system at the SiO2 content of 50 wt.% and 60 wt.% were investigated by the method of differential thermal analysis. Analysis of the obtained results allowed us to affirm that all regions of phase transformations in the xerogel powders with 50 wt.% SiO2 content shifted to the lower temperature range. It was established that an increase in the temperature during heat treatment of the xerogel powders with different compositions led to the phase transformations: from a loose powdered state through a sintered state to the formation of a glassy state. It was determined that all samples are X-ray amorphous up to the temperature of 6500C. It was shown that increasing the CaO content in the composition of xerogels up to 30 wt.%, and accordingly increasing the ratio CaO:P2O5 from 1 to 6, leads to the absence of glass phase. The optimal ratio CaO:P2O5 is 2. The influence of Li2O and BaO on a decrease in the glass formation temperature was substantiated and experimentally confirmed by thermal analysis.