Relaxation processes in inorganic melts and glasses: An elastic continuum model as a promising basis for the description of the viscosity and electrical conductivity

• Published in: Glass physics and chemistry Vol. 36; no. 3; pp. 253 - 285
• Main Author: Nemilov, S. V.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01-06-2010; Springer Nature B.V
• Subjects: Activation energy; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Continuums; Glass; Materials Science; Mathematical models; Melts; Natural Materials; Oxides; Physical Chemistry; Viscosity; Viscous flow; polymer glasses; viscosity; molecular glasses; ionic conductivity; relaxation; elastic moduli; oxide glasses
• ISSN: 1087-6596; 1608-313X
• DOI: 10.1134/S1087659610030028

A brief review is presented of the concepts regarding the nature of α and β relaxation processes in melts and glasses. Experimental data have been used to show that different types of relaxation in oxide systems can be interrelated to each other. The molecular mechanism of viscous flow in inorganic systems has been discussed in detail with the use of continuum theories (elasticity and hydrodynamics) developed in the works by the author in 1967–2007. A rigorous relationship between the volumes of atoms overcoming the activation barrier, the instantaneous shear modulus, and the barrier itself (free activation energy) has been derived. This relationship allows one to calculate the sizes of atoms involved in the viscous flow with a deviation that does not exceed 10% of the values determined by direct structural methods. In this case, empirically chosen constants are absent. Based on the results obtained by Anderson and Stewart (1954) and the author (1974), it has been established that the activation energy for ionic conduction can be calculated using similar notions. It has been demonstrated for the first time that the universal relation between the viscosity and conductivity over a wide range of temperatures (for alkali-containing oxide melts) i.e., the Littleton equation, finds a simple quantitative explanation in the framework of the same models, even though the mechanisms of both processes do not depend on each other.