Free volume and energy barriers to equilibrium viscosity and ionic transport in alkali disilicates

Author(s)

Ferreira Nascimento, Marcio Luis ^[1] ; Martins Rodrigues, Ana Candida ^[2] ; Souquet, Jean-Louis ^[3]

Affiliation

^[1] Univ Fed Bahia, Inst Humanidades Artes & Ciencias, BR-40170115 Salvador, BA - Brazil

^[2] Univ Fed Sao Carlos, Dept Mat Engn, Lab Mat Vitreos, BR-13565905 Sao Carlos, SP - Brazil

^[3] PHELMA, Lab Electrochim & Physicochim Mat & Interfaces, F-38402 St Martin Dheres - France

• Document type: Journal article
• Source: PHYSICS AND CHEMISTRY OF GLASSES-EUROPEAN JOURNAL OF GLASS SCIENCE AND TECHNOLOGY PART B; v. 52, n. 4, p. 157-166, AUG 2011.
• Web of Science Citations: 0

Abstract

A microscopic interpretation is developed of the temperature dependence of viscosity above the glass transition range, validating the representation of experimental data by a ``hybrid{''} equation, which is a product of Arrhenius and Vogel-Fulcher-Tamman-Hesse (VFTH) exponential terms. By employing this hybrid equation to fit experimental viscosity data for lithium, sodium, and potassium disilicates, we found an activation energy of E(eta)(A)approximate to 1.2 eV for the Arrhenius term. We propose that this energy is representative of the exchange of nonbridging oxygen atoms between adjacent SiO(4) tetrahedra, allowing for consecutive relaxations of macromolecular silicate chains. Based on a free volume interpretation of the VFTH term, we also calculated the free volume required for chain movement, which, according to our results, is about 30% of the intrinsic volume of chain segments. This relatively low free volume may indicate the occurrence of limited rotational or translational displacements during viscous flow. These results are discussed and compared with the activation enthalpies and free volumes determined for ionic transport in the same alkali disilicate glasses considering a similar ``hybrid{''} equation for electrical conductivity. (AU)

• FAPESP's process: 10/08003-0 - Electrical transport mechanisms in glass and glass-ceramics
• Grantee: Ana Candida Martins Rodrigues
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• FAPESP's process: 07/08179-9 - Kinetic processes in glasses and glass ceramics
• Grantee: Edgar Dutra Zanotto
• Support Opportunities: Research Projects - Thematic Grants