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Influence of Quenched Defects on Thermal Expansion and Glass Transition in Diopside (CaMgSi2O6)

Published online by Cambridge University Press:  25 February 2011

S. V. Raman
S. V. Raman*
Affiliation:
Brookhaven National Laboratory, Upton, N.Y. 11973
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Abstract

This study was conducted to investigate the possible occurrence of non-equilibrium defects and their influence on glass transition in a relatively depolymerized silicate structure. The glass of interest has an average bridging/non-bridging oxygen ratio of 1:2. It was prepared by fast quenching and was examined in the alumina pushrod dilatometer at heating rates of 5 and 15 ° C/min. The thermal expansion decreases with increase in the rate of heating although, the expansion coefficient is independent of heating rate at temperatures below the transition region. In the supercooled liquid region the expansion coefficient is higher at the higher heating rate. In the transition region it is both heating rate and temperature dependent. Three distinct temperatures are revealed in the transition region from temperature dependence of expansion rate. Their dependence on heating rate is described by a low activation energy of about 3Kcal/mol for transition. The single parameter fictive temperature is not in agreement with kinetics of relaxation due to a wide temperature interval of 600 to 750° C for the transition region. The transition kinetics is perhaps enhanced by the presence of defects whose annealing is impedded with increase in heating rate. Thus under the influence of higher defect concentration a spiked change in relaxation rate occurs and points to the presence of a critical temperature in the transition region. In the neighborhood of this temperature the relaxation rate of supercooled liquid is significantly lower than its solid analog. For short relaxation times in the supercooled liquid thermal expansion coefficient is relatively higher at the higher heating rate.

Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 61: Symposium P – Defects in Glasses , 1985 , 447
Copyright
Copyright © Materials Research Society 1986

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