The self-diffusion of silicon and oxygen in diopside (CaMgSi2O6) liquid upto 15 GPa

Citation
Je. Reid et al., The self-diffusion of silicon and oxygen in diopside (CaMgSi2O6) liquid upto 15 GPa, CHEM GEOL, 174(1-3), 2001, pp. 77-86
Citations number
22
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
CHEMICAL GEOLOGY
ISSN journal
0009-2541 → ACNP
Volume
174
Issue
1-3
Year of publication
2001
Pages
77 - 86
Database
ISI
SICI code
0009-2541(20010401)174:1-3<77:TSOSAO>2.0.ZU;2-X
Abstract
The self-diffusivities of silicon and oxygen in diopside (CaMgSi2O6) liquid have been measured at pressures and temperatures up to 15 GPa and 2300 deg reesC, using a 1200-tonne multianvil apparatus. Diffusion couples were prep ared using finely ground, diopside glass, half of which was enriched in tra cts isotopes O-18 (5%) and Si-30 (12%). Results indicate that silicon and o xygen self-diffusivities are coincident (within an accuracy range of 10% RS D, 1 sigma) up to 13 GPa and show an initial decrease with pressure up to 1 1 GPa(oxygen self-diffusivities are 9.8 X 10(-10) m2/s at 3 GPa and 3.9 X 1 0(-10) m2/s at 11 cpa) after which there is an increase with pressure up to 15 GPa(9.1 X 10(-10) m2/s) at 2000 degreesC. The activation energy of self -diffusion of both silicon and oxygen was calculated to be 267 kJ mol(-1), with no observable pressure effect up to 3 GPa. Self-diffusivity is inverse ly proportional to viscosity, the relationship between these properties bei ng well approximated by the Eyring equation using the diameter of an oxygen anion as the translation distance. The calculated viscosities are in good agreement with previous direct viscosity measurements at lower pressure alt hough the previously found high positive activation volumes were not reprod uced. (C) 2001 Elsevier Science B.V. All rights reserved.