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Thermodynamic parameters of bonds in glassy materials from viscosity-temperature relationships

Ojovan, M.I., Travis, K.P. and Hand, R.J. (2007) Thermodynamic parameters of bonds in glassy materials from viscosity-temperature relationships. Journal of Physics: Condensed Matter, 19 (415107). ISSN 1361-648X

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Abstract

Doremus's model of viscosity assumes that viscous flow in amorphous materials is mediated by broken bonds (configurons). The resulting equation contains four coefficients, which are directly related to the entropies and enthalpies of formation and motion of the configurons. Thus by fitting this viscosity equation to experimental viscosity data these enthalpy and entropy terms can be obtained. The non-linear nature of the equation obtained means that the fitting process is non-trivial. A genetic algorithm based approach has been developed to fit the equation to experimental viscosity data for a number of glassy materials, including SiO2, GeO2, B2O3, anorthite, diopside, xNa2O–(1-x)SiO2, xPbO–(1-x)SiO2, soda-lime-silica glasses, salol, and α-phenyl-o-cresol. Excellent fits of the equation to the viscosity data were obtained over the entire temperature range. The fitting parameters were used to quantitatively determine the enthalpies and entropies of formation and motion of configurons in the analysed systems and the activation energies for flow at high and low temperatures as well as fragility ratios using the Doremus criterion for fragility. A direct anti-correlation between fragility ratio and configuron percolation threshold, which determines the glass transition temperature in the analysed materials, was found.

Item Type: Article
Copyright, Publisher and Additional Information: © 2007 Institute of Physics and IOP Publishing Limited. This is an author produced version of a paper published in Journal of Physics: Condensed Matter. Uploaded in accordance with the publisher's self-archiving policy.
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Materials Science and Engineering (Sheffield)
Depositing User: Sherpa Assistant
Date Deposited: 10 Jul 2008 09:28
Last Modified: 08 Feb 2013 16:56
Published Version: http://dx.doi.org/10.1088/0953-8984/19/41/415107
Status: Published
Publisher: Institute of Physics
Refereed: Yes
Identification Number: 10.1088/0953-8984/19/41/415107
URI: http://eprints.whiterose.ac.uk/id/eprint/4058

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