2013

Mutual interaction of redox pairs in silicate melts: a case study for Na₂Si₂O₅ melt

Borisov А.А.

 Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM),

Russian Academy of Sciences

aborisov@igem.ru.

Mutual interaction of redox pairs was considered in the light of the concept of intrinsic oxygen fugacity. A “rose of fO₂ trends” was proposed for the visualization of possible directions of mutual oxidation/reduction of redox pairs for a given melt composition (Borisov, 2013). Experimental data in Na₂Si₂O₅ (Johnston, 1964, 1965) were considered as an example. The influence of temperature at which the system is closed, minimum interaction temperature, and bulk proportions of redox pairs on the extent of interaction was quantified.

Missing thermodynamic data for the vanadium redox pairs in Na₂Si₂O₅ melt were estimated, and the V⁵⁺/V⁴⁺/V³⁺/V²⁺ tetrad was quantitatively characterized. It was shown that even in a melt devoid of other redox pairs, exchange reactions within the V tetrad result in the redistribution of vanadium valence states during melt quenching to a glass. The vanadium oxygen barometer of Sutton et al. (2005) was critically evaluated. It was shown that quenching of iron-bearing natural melts must be accompanied by a change in the effective valence of vanadium by ±0.2.

References:

Borisov A.A. (2013) Mutual interaction of redox pairs in silicate melts: V⁵⁺/V⁴⁺/V³⁺/V²⁺ tetrad and other equilibria. Petrology 21, 305-315.

Johnston W.D. (1964) Oxidation-reduction equilibria in iron-containing glass. Journal of the American Ceramic Society 47, 198-201.

Johnston W.D. (1965) Oxidation-reduction equilibria in molten Na₂O•2SiO₂ glass. Journal of the American Ceramic Society 48, 184-190.

Sutton S.R., Karner J., Papike J. , Delaney J.S., Shearer C., Newville M., Eng P., Rivers M., Dyar M.D. (2005) Vanadium K edge XANES of synthetic and natural basaltic glasses and application to microscale oxygen barometry. Geochimica et Cosmochimica Acta 69, 2333-2348.