Computer Science
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59..895c&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 59, Issue 5, pp.895-907
Computer Science
1
Scientific paper
Liquidus phase relations in the system Si0 2 -TiO 2 have been determined at 3.0 GPa to investigate the effect of pressure on the partitioning of Si and Ti between coexisting immiscible liquids. Experiments on oxide mixtures containing 10, 50, 90, and 100 mol% TiO 2 were performed in multi-anvil and piston-cylinder apparatus at 2173-2740 K. At 1 atm, immiscible liquids form because the liquid structures are dissimilar: tetravalent cations occur in primarily fourfold (Si0 2 -rich liquid) vs. sixfold (TiO 2 -rich liquid) coordination by oxygen. At 3.0 GPa, immiscible liquids also coexist, but the phase relations and liquid compositions are significantly different. The eutectic liquid is now Ti0 2 -rich (78.4 vs. 8.1 mol% TiO 2 at 1 atm). Above the liquidus, the coexisting immiscible liquids are enriched in Si0 2 . The Si0 2 content of the TiO 2 -rich liquid has increased by more than a factor of 3, while the TiO2-content of the SiO 2 -rich liquid has decreased by 1/2. The persistence of a wide solvus implies that pressure does not cause liquid structure assimilation. The observed shift in immiscible liquid compositions indicated that pressure has raised the activity of TiO 2 in the liquid dominated by tetravalent cations in fourfold coordination and lowered the activity of SiO 2 in a liquid dominated by tetravalent cations in sixfold coordination. The decrease in TiO 2 content of the SiO 2 -rich liquid with pressure is probably related to the positive volume of mixing observed in 1 atm glasses in this composition range. The enhanced solubility of SiO 2 in the TiO 2 -rich liquid with pressure may be due to a pressure-induced increase in the coordination state of Si.
Agee Carl B.
Circone S.
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