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Structural relaxation of lead metasilicate and lithium disilicate glasses

Grant number: 19/15108-8
Support type:Scholarships in Brazil - Master
Effective date (Start): November 01, 2019
Effective date (End): February 28, 2021
Field of knowledge:Engineering - Materials and Metallurgical Engineering
Principal Investigator:Edgar Dutra Zanotto
Grantee:Ricardo Felipe Lancelotti
Home Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
Associated research grant:13/07793-6 - CEPIV - Center for Teaching, Research and Innovation in Glass, AP.CEPID

Abstract

Glasses are thermodynamically unstable and they spontaneously relax towards the supercooled liquid (SCL). The relaxation time varies from seconds at temperatures above the glass transition to geological times in temperatures well below it. Structural relaxation is a steady and spontaneous process, which depends on the study temperature and the chemical composition of glasses. Relaxation occurs because any unstable system tends to decrease the free energy towards the metastable state of the SCL, which will later crystallize. During the structural change the materials properties also changes, which allows to follow the process through some property measurement. The difference in the property value in relation to the unrelaxed state increases when the temperature decreases below the glass transition. In this project, the analyzed properties will be the refractive index, the glass transition temperature, and the viscosity of lead metasilicate and lithium disilicate glasses. We hope that the results will allow us to analyze whether the relaxation of some of these properties is most dependent on the isostructural or equilibrium viscosity. In addition, we will analyze if the Kohlrausch and MAP models are able to describe the experimental data as the temperature decreases below the glass transition. This project represents a significant extension and analysis data refinement obtained during the internship project (FAPESP 2015/20681-8) and should allow an advance on the understanding of structural relaxation.