Ferric-ferrous equilibria in Na sub 2 O-FeO-Fe sub 2 O sub 3 -SiO sub 2 melts: Effects of analytical techniques on derived partial molar volumes

Journal Article · Fri Sep 01 04:00:00 EDT 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90343-8· OSTI ID:7024618

Lange, R A; Carmichael, I S.E. ^[1]

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1. Univ. of California, Berkeley (USA)

A published comparison between Moessbauer spectroscopy and wet chemistry applied to silicate glasses containing large concentrations of total iron (>14 wt% Fe{sub 2}O{sub 3}) indicates a large, systematic discrepancy in the determination of FeO between the two techniques, with Moessbauer results typically lower in the ferrous component. This may be accounted for by the common assumption that ferric and ferrous iron in silicate glasses have equivalent Moessbauer absorption efficiencies at room temperature, which has been shown to be invalid for several crystalline materials. Although this assumption has been demonstrated to be valid for glasses with low concentrations of total iron, the approximation breaks down when total iron concentrations approach 14 wt% Fe{sub 2}O{sub 3}. The authors have measured ferrous iron concentrations in 65 Na{sub 2}O-FeO-Fe{sub 2}O{sub 3}-SiO{sub 2} glasses quenched from melts equilibrated in air between 926 and 1,583{degree}C using a colorimetric wet chemical method. These data were used to derive a symmetric, regular solution model for ferric-ferrous equilibria which has a standard error of 0.36 (2{sigma}) in the prediction of wt% FeO. Additional liquids with initial compositions close to the stoichiometry of acmite (NaFe{sup 3+}Si{sub 2}O{sub 6}) but which crossed the perferruginous join due to sodium loss during high-temperature equilibration (1,420-1,540{degree}C) are significantly reduced relative to other Na{sub 2}O-FeO-Fe{sub 2}O{sub 3}-SiO{sub 2} liquids. A re-interpretation of the density data of Dingwell et al. (1988) based upon these wet chemical ferric-ferrous data demonstrates that the partial molar volume of Fe{sub 2}O{sub 3} is independent of composition in the Na{sub 2}O-FeO-Fe{sub 2}O{sub 3}-SiO{sub 2} system with a derived value of 41.78 {plus minus} 0.41 cc/mol at 1,400{degree}C.

• OSTI ID: 7024618
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 53:9; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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15 GEOTHERMAL ENERGY
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58 GEOSCIENCES
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ABUNDANCE
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CHEMISTRY
CONCENTRATION RATIO
ELEMENT ABUNDANCE
EQUILIBRIUM
GEOCHEMISTRY
IRON COMPOUNDS
MAGMA
MAGMATISM
MATHEMATICAL MODELS
MINERALS
PARTICLE MODELS
PHASE STUDIES
PHYSICAL PROPERTIES
QUANTITATIVE CHEMICAL ANALYSIS
REDOX REACTIONS
SILICATE MINERALS
SPECTROSCOPY
STATISTICAL MODELS
STOICHIOMETRY
THERMODYNAMIC ACTIVITY
THERMODYNAMIC MODEL
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS