Thermal and devitrification behavior of (2.5−x)CaO·(x/3)In2O3·2SiO2 glasses

A study of the influence of the substitution of In2O3 for CaO at constant O/Si ratio on thermal properties and non-isothermal devitrification of 2.5CaO·2SiO2 is reported. Differential thermal analysis (DTA) and X-ray diffraction analysis were used. The X-ray diffraction pattern of the crystallized In2O3 base glass shows that the α-CaO·SiO2, that should be stable only above 1125°C, forms in the temperature range 900–1000°C. A new ternary crystalline phase whose reflections are not reported in the JCPDS cards, was found to form during crystallization of the glass. As their intensity progressively increases with substitution, they should refer to a In2O3 rich phase. The glass transformation temperature Tg results can be explained on the basis of the increased structural rigidity when Ca2+ ions are substituted by In3+ with the formation of stronger bond to the oxygen, while crystal growth activation energy (Ec) values can be explained considering the increasing of the crystallization temperature Tp. Devitrification involves a mechanism of surface nucleation; surface nuclei behaving as bulk nuclei in samples that soften and sinter before devitryfing.