Redox equilibria, structure, and properties of Fe-bearing aluminosilicate melts: Relationships among temperature, composition, and oxygen fugacity in the system Na sub 2 O-Al sub 2 O sub 3 -SiO sub 2 -Fe-O

Journal Article · · American Mineralogist; (USA)

OSTI ID:7127019

Mysen, B O; Virgo, D ^[1]

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1. Geophysical Laboratory, Washington, DC (USA)

Redox ratios of Fe and structural positions of Fe{sup 3+} and Fe{sup 2+} in melts in the system Na{sub 2}O-Al{sub 2}O{sub 3}-SiO{sub 2}-Fe-O have been determined with Moessbauer spectroscopy. The value of log(Fe{sup 2+}/Fe{sup 3+}) generally is linearly correlated with log f{sub O2} and 1/T (T in kelvins). The Fe{sup 2+}/Fe{sup 3+} ratio decreases linearly with increasing Al/(Al + Si) and, for NBO/T > 0.4, the Fe{sup 2+}/Fe{sup 3+} ratio decreases with increasing NBO/T of the melt (NBO/T = nonbridging oxygens per tetrahedrally coordinated cation). The inverse correlation of Fe{sup 2+}/Fe{sup 3+} with Al/(Al + Si) is more pronounced at higher temperatures and with f{sub O2} reduced below that of air. The free energy of reduction of Fe{sup 3+} to Fe{sup 2+} increases (becomes less negative) with decreasing Al/(Al + Si) and NBO/T. With Fe{sup 3+}/{Sigma}Fe > 0.6, Fe{sup 3+} is tetrahedrally coordinated, whereas for Fe{sup 3+}/{Sigma}Fe < 0.3, Fe{sup 3+} occurs in octahedral coordination. In the Fe{sup 3+}/{Sigma}Fe = 0.6-0.3 range, tetrahedral and octahedral Fe{sup 3+} coexist. The degree of polymerization of silicate liquids depends, therefore, on Fe{sup 3+}/{Sigma}Fe. For properties that depend on degree of melt polymerization, these properties will also be functions of Fe{sup 3+}/{Sigma}Fe. For melts in the system Na{sub 2}O-Al{sub 3}O{sub 3}-SiO{sub 2}-Fe-O with 5 wt% iron oxide added as Fe{sub 2}O{sub 3}, the viscosity decreases by more than 40% in the Fe{sup 3+}/{Sigma}Fe range between 1.0 and 0.0.

• OSTI ID: 7127019
• Journal Information: American Mineralogist; (USA), Vol. 74:1-2; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
MAGMA
THERMODYNAMIC PROPERTIES
MOLTEN SALTS
ALUMINIUM OXIDES
CHEMICAL COMPOSITION
CORRELATIONS
CRYSTAL STRUCTURE
IRON OXIDES
MOESSBAUER EFFECT
OXIDATION
OXYGEN
REDUCTION
RESERVOIR FLUIDS
RESERVOIR TEMPERATURE
SILICON OXIDES
SODIUM OXIDES
SPECTROSCOPY
TEMPERATURE DEPENDENCE
VISCOSITY
ALKALI METAL COMPOUNDS
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
FLUIDS
IRON COMPOUNDS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SALTS
SILICON COMPOUNDS
SODIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
152002* - Geothermal Data &amp; Theory- Properties of Minerals &amp; Rocks