A Theory of the Specific Heat and Viscosity of Liquid SiO2 and BeF2
- Robert N. Schock
Published Online: 18 MAR 2013
Copyright 1985 by the American Geophysical Union.
Point Defects in Minerals
How to Cite
Brawer, S. A. (1985) A Theory of the Specific Heat and Viscosity of Liquid SiO2 and BeF2 , in Point Defects in Minerals (ed R. N. Schock), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM031p0036
- Published Online: 18 MAR 2013
- Published Print: 1 JAN 1985
Print ISBN: 9780875900568
Online ISBN: 9781118664070
- Mineralogical chemistry—Congresses;
A theory of the transport and thermal properties of the network fluids SiO2 and BeF2 is presented. The theory is based on molecular dynamics simulations of BeF2. It is observed in such simulations that a “diffusion event,” requiring the separation of a Be-F neighbors, occurs only when the F ion is 3-fold coordinated, and the Be usually S-fold coordinated. These high coordination number “defects” are thermally excited in the fluid, and their number is very small (less than 1%) below the melting point. Because application of pressure increases the average coordination number, and thus increases the number of ldquo;sitesrdquo; at which diffusion occurs, it is predicted that the viscosity will decrease with increasing pressure. (This has been observed experimentally in GeO2 and albite, but not yet in SiO2 or BeF2.) Further, because the number of defects is so small, their contribution to the specific heat is immeasurably small below the melting point. Therefore, the specific heat of these fluids is vibrational, and there is no break in specific heat at the glass transition.