Glass-Ceramics: Concepts and Practical Aspects
- Pp. 39-65 (27)Maria Helena Vaz Fernandes and Ana Margarida Batista Silva
During the last century, new materials have been developed and improved envisaging specific properties in diverse applications, from the conventional ones to those in which high tech is imperative. Glass-ceramics are among those materials since they can exhibit attractive properties for usage in cookware or architectural components, for example, but also remarkable performances in advanced applications such as electronic devices, medical prosthesis, tissue engineering, etc. </p><p> Glass-ceramic materials are polycrystalline solids consisting of tiny crystals homogeneously dispersed in a residual glass phase, where the number of precipitated crystals, their growth rate and final size can be manipulated by suitable heat treatments. It is this controlled crystallization, generally induced by nucleating additives that yields an array of materials with interesting, sometimes unusual, combination of properties. </p><p> In this chapter a simple approach of the concept of glass-ceramic is made, based on practical aspects of its development. The methodologies for the production of a glass-ceramic and the typical heat-treatment cycles through which a parent glass is converted into a crystallized structure are presented. </p><p> The final microstructure and thus the properties of a glass-ceramic depend on the time-temperature schedule imposed to the base glass but are also affected by its composition and the additives that catalyze crystallization. The most common nucleating agents are presented and the ways through which they act as precipitation catalyzers are discussed. </p><p> Finally a very brief reference is made to a few experimental techniques, considered as essential tools for glass-ceramics study at the different development stages.