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About activation energy of viscous flow of glasses and melts

Published online by Cambridge University Press:  09 February 2015

Michael I. Ojovan
Michael I. Ojovan*
Affiliation:
Department of Materials, Imperial College London, London SW7 2AZ, UK
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Abstract

Data on a viscous flow model based on network defects – broken bonds termed configurons – were analysed. An universal equation has been derived for the variable activation energy of viscous flow Q(T) of the generic Frenkel equation of viscosity η(T)=A∙exp(Q/RT) which is known to have two constant asymptotes – high QH at low temperatures and low QL at high temperatures. The defect model of flow used by e.g. Doremus, Mott, Nemilov, Sanditov states that higher the concentration of defects (e.g. configurons) the lower the viscosity. We have used the configuron percolation theory (CPT) which treats glass–liquid transition as a percolation-type phase transition. Additionally the CPT results in a continuous temperature relationship for viscosity valid for both glassy and liquid amorphous materials. We show that a particular result of CPT is the universal temperature relationship for the activation energy of viscous flow: Q(T)=QL+RT∙ln[1+exp(-Sd/R) exp((QH-QL)/RT)] which depends on asymptotic energies QL (for the liquid phase) and QH (for the glassy phase), and on entropy of configurons Sd. This equation has two asymptotes, namely Q(T<<Tg) = QH, and Q(T>>Tg) = QL. Moreover we demonstrate that the equation for Q(T) practically coincides in the transition range of temperatures with known Sanditov equation.

Keywords

amorphousliquiddefects
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1757: Symposium UU – Structure-Property Relations in Amorphous Solids , 2015 , mrsf14-1757-uu01-10
Copyright
Copyright © Materials Research Society 2015 

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