Kinetic processes in glasses and glass ceramics

Abstract

The general objective of this project is to contribute for the solution of several relevant problems in the international literature about the transport (diffusion) processes controlling crystal nucleation and growth, viscous flow, sintering, and ionic conductivity in glasses and glass-ceramics. The specific objectives of this proposal are divided into six subprojects, in basic (1-3) as well as technological (4-5) researches: 1. Difusional processes in oxide glasses: nucleation, crystal growth and viscous flow: from experimental determinations of the different processes (crystal nucleation, growth, viscous flow and ionic conductivity) we intend to compare the respective coefficients of effective diffusion with literature data for the self-diffusion coefficients of glass former and modifier elements of the glasses used to verify the diffusional mechanisms in wide temperature range, from the melting point (or liquidus) to the glass transition range. 2. Sintering with concurrent crystallization: we will study theoretically and experimentally the competition between sintering and the simultaneous crystallization of particulate glasses to define the conditions that favor one or another phenomenon. We will utilize spherical as well as irregular (jagged) glass particles specially produced for this purpose. The main idea is to perform a rigorous test of the Clusters model previously developed by our group. 3. Electric conductivity of glasss & glass-ceramics partially crystallized: we will carry out systematic studies to understand the ion transport dynamics in glasses and glass-ceramics as a function of volume fraction crystallized, thus contributing to the understanding of ionic conductivity processes in such systems. 4. Development of Li2O-Al2O3-SiO2 glass-ceramics by sintering: we will develop glass-ceramics with near zero thermal expansion coefficient by sintering of particulate glasses instead of the traditional way that induce the crystallization in the glass interior by nucleating agents. The techniques of sintering in electric oven as well as microwave oven will be tested. 5. Crystal nucleation and growth in photo-thermo-refractive glass: we will characterize the crystallization kinetics (crystal nucleation and growth) in photo-thermo-refractive glass (PTR), an advanced material capable of supporting volume holograms and diffraction gratings with revolutionary application in the photonics industry. 6. Other relevant problems: other relevant problems concerning diffusion as well as crystallization kinetics should occur as results of new advances or our own researches and could be analyzed. One or more of these six subprojects will probably be able to and should produce original discoveries. The integration between them is assured by the focus of the research (crystallization in glass and glass-ceramics), aiming to solve specific problems. (AU)