Details
| Original language | English |
|---|---|
| Pages (from-to) | 65-74 |
| Number of pages | 10 |
| Journal | Journal of Non-Crystalline Solids |
| Volume | 478 |
| Early online date | 2 Oct 2017 |
| Publication status | Published - 15 Dec 2017 |
Abstract
Reduction experiments were conducted to study the structural role (redox state and coordination) of iron in peralkaline rhyolitic glasses as a function of oxygen fugacity and alkali atomic ratio ([Na/(Na+K)] = 0.0, 0.69 and 1.0). The glasses investigated, analogues of natural pantellerites of the Kenya Rift Valley, have been synthesized at ambient pressure, 1250 °C and equilibrated under controlled redox conditions. Oxygen fugacities, ranging from NNO + 7 to NNO- 6.8 (relative to Ni/NiO assemblage buffer), were adjusted by different gases and/or gas mixtures (air, O2, CO2, Ar/H2/H2O, Ar/H2) in a horizontal gas-mixing furnace. Iron oxidation state and coordination geometry have been inferred by Fe K-edge X-ray Absorption Near-Edge Structure (XANES) spectroscopy, which suggested the presence of Fe3 + in four-fold coordination and Fe2 + having an average coordination number intermediate between four- and five-fold in all the glasses. A colorimetric method has been employed to determine the Fe2 +/Fetot ratios for all the samples. We verified in the samples a continuous increase of divalent iron for more reducing conditions (e.g. Fe2 +/Fetot ranging from 0.09 in air to 0.93 in Ar/H2 atmosphere) but a non-linear relation between [Na/(Na+K)] molar ratio and iron redox was observed. The weak dependence of log (Fe3 +/Fe2 +) on log (fO2/bar) indicates a strong deviation from ideal mixing of iron species in pantelleritic compositions which suggests a different behaviour of alkali dominated peralkaline melts compared to other aluminosilicate melts in terms of fO2 and alkalis effects.
Keywords
- Alkali ratio, Fe-coordination, Fe-oxidation state, Oxygen fugacity, Pantelleritic glasses, XANES
ASJC Scopus subject areas
- Materials Science(all)
- Electronic, Optical and Magnetic Materials
- Materials Science(all)
- Ceramics and Composites
- Physics and Astronomy(all)
- Condensed Matter Physics
- Materials Science(all)
- Materials Chemistry
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In: Journal of Non-Crystalline Solids, Vol. 478, 15.12.2017, p. 65-74.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The effect of oxygen fugacity and Na/(Na+K) ratio on iron speciation in pantelleritic glasses
AU - Stabile, Paola
AU - Giuli, Gabriele
AU - Cicconi, Maria Rita
AU - Paris, Eleonora
AU - Trapananti, Angela
AU - Behrens, Harald
N1 - Funding Information: We acknowledge the Italian CRG beamline BM08 and the European Synchrotron Radiation Facility for provision of beamtime. We thank Anika Husen and Marius Stranghoner from Institute for Mineralogy (Hannover) for wet chemistry analyses of the iron redox state. The authors thank Michael R. Carroll for useful suggestions. This work was supported by grants from FIRB to G.G. (grant n. RBFR082WRU ) and DAAD and Erasmus grants to P.S. We thank the editor and the reviewers for constructive comments. Publisher Copyright: © 2017 Elsevier B.V. Copyright: Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2017/12/15
Y1 - 2017/12/15
N2 - Reduction experiments were conducted to study the structural role (redox state and coordination) of iron in peralkaline rhyolitic glasses as a function of oxygen fugacity and alkali atomic ratio ([Na/(Na+K)] = 0.0, 0.69 and 1.0). The glasses investigated, analogues of natural pantellerites of the Kenya Rift Valley, have been synthesized at ambient pressure, 1250 °C and equilibrated under controlled redox conditions. Oxygen fugacities, ranging from NNO + 7 to NNO- 6.8 (relative to Ni/NiO assemblage buffer), were adjusted by different gases and/or gas mixtures (air, O2, CO2, Ar/H2/H2O, Ar/H2) in a horizontal gas-mixing furnace. Iron oxidation state and coordination geometry have been inferred by Fe K-edge X-ray Absorption Near-Edge Structure (XANES) spectroscopy, which suggested the presence of Fe3 + in four-fold coordination and Fe2 + having an average coordination number intermediate between four- and five-fold in all the glasses. A colorimetric method has been employed to determine the Fe2 +/Fetot ratios for all the samples. We verified in the samples a continuous increase of divalent iron for more reducing conditions (e.g. Fe2 +/Fetot ranging from 0.09 in air to 0.93 in Ar/H2 atmosphere) but a non-linear relation between [Na/(Na+K)] molar ratio and iron redox was observed. The weak dependence of log (Fe3 +/Fe2 +) on log (fO2/bar) indicates a strong deviation from ideal mixing of iron species in pantelleritic compositions which suggests a different behaviour of alkali dominated peralkaline melts compared to other aluminosilicate melts in terms of fO2 and alkalis effects.
AB - Reduction experiments were conducted to study the structural role (redox state and coordination) of iron in peralkaline rhyolitic glasses as a function of oxygen fugacity and alkali atomic ratio ([Na/(Na+K)] = 0.0, 0.69 and 1.0). The glasses investigated, analogues of natural pantellerites of the Kenya Rift Valley, have been synthesized at ambient pressure, 1250 °C and equilibrated under controlled redox conditions. Oxygen fugacities, ranging from NNO + 7 to NNO- 6.8 (relative to Ni/NiO assemblage buffer), were adjusted by different gases and/or gas mixtures (air, O2, CO2, Ar/H2/H2O, Ar/H2) in a horizontal gas-mixing furnace. Iron oxidation state and coordination geometry have been inferred by Fe K-edge X-ray Absorption Near-Edge Structure (XANES) spectroscopy, which suggested the presence of Fe3 + in four-fold coordination and Fe2 + having an average coordination number intermediate between four- and five-fold in all the glasses. A colorimetric method has been employed to determine the Fe2 +/Fetot ratios for all the samples. We verified in the samples a continuous increase of divalent iron for more reducing conditions (e.g. Fe2 +/Fetot ranging from 0.09 in air to 0.93 in Ar/H2 atmosphere) but a non-linear relation between [Na/(Na+K)] molar ratio and iron redox was observed. The weak dependence of log (Fe3 +/Fe2 +) on log (fO2/bar) indicates a strong deviation from ideal mixing of iron species in pantelleritic compositions which suggests a different behaviour of alkali dominated peralkaline melts compared to other aluminosilicate melts in terms of fO2 and alkalis effects.
KW - Alkali ratio
KW - Fe-coordination
KW - Fe-oxidation state
KW - Oxygen fugacity
KW - Pantelleritic glasses
KW - XANES
UR - http://www.scopus.com/inward/record.url?scp=85030265580&partnerID=8YFLogxK
U2 - 10.1016/j.jnoncrysol.2017.09.051
DO - 10.1016/j.jnoncrysol.2017.09.051
M3 - Article
AN - SCOPUS:85030265580
VL - 478
SP - 65
EP - 74
JO - Journal of Non-Crystalline Solids
JF - Journal of Non-Crystalline Solids
SN - 0022-3093
ER -