Glass forming ability and crystalization in the system CaO.SiO2-Na2O.2CaO.3SiO2-Na2O.3CaO.6SiO2

Abstract

The system Na2O-CaO-SiO2 is of great importance for the manufacture of glass and glass-ceramics. It covers several glass applications, from window and packaging to biomaterials. In general, compositions containing relatively large proportions of SiO2 easily form glass. However, as the concentration of calcium and sodium increases, the glass forming ability deteriorates. From the point of view of glass-ceramic manufacturing, the interest lies in the understanding of the nature and proportion of the crystalline phases in the microstructure. It is important to know the process conditions to obtain the desired phases or minimization of deleterious phases. The variation of the proportion of the components can result in crystallization of different phases and their ratios, which in turn results in different properties. Also the phase morphology and distribution in the microstructure are important in determining the material properties. In particular, mechanical properties such as strength, toughness and hardness are important for all kinds of applications. The glass-ceramic process is interesting because it allows manufacturing polycrystalline ceramics with considerable control of microstructure. In this process, initially vitreous materials are obtained which are crystallized in subsequent thermal treatments. The control of microstructure is achieved from a detailed knowledge of the crystallization kinetics of the material. The resulting materials have a number of technological applications as biomaterials, integrated circuits and ceramic tiles, among others. To better understand the effect of the major components in the evolution of the microstructure of glass-ceramics in the system SiO2-CaO-Na2O, we planned to study the glass forming ability of compositions in this system and characterize the microstructure of the obtained materials after heat treatments for crystallization, focused on the nature, relative amount, distribution and morphology of the formed phases. In particular, we plan to study compositions in the compatibility triangle CaO.SiO2-Na2O.2CaO.3SiO2-Na2O.3CaO.6SiO2, in order to develop wollastonite (CaO.SiO2) glass-ceramics. (AU)