Thermal and devitrification behavior of (2.5− x)CaO·( x/3)In 2O 3·2SiO 2 glasses

Abstract

A study of the influence of the substitution of In 2O 3 for CaO at constant O/Si ratio on thermal properties and non-isothermal devitrification of 2.5CaO·2SiO 2 is reported. Differential thermal analysis (DTA) and X-ray diffraction analysis were used. The X-ray diffraction pattern of the crystallized In 2O 3 base glass shows that the α-CaO·SiO 2, 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 In 2O 3 rich phase. The glass transformation temperature T g results can be explained on the basis of the increased structural rigidity when Ca 2+ ions are substituted by In 3+ with the formation of stronger bond to the oxygen, while crystal growth activation energy ( E c) values can be explained considering the increasing of the crystallization temperature T p. Devitrification involves a mechanism of surface nucleation; surface nuclei behaving as bulk nuclei in samples that soften and sinter before devitryfing.