期刊
AMERICAN MINERALOGIST
卷 105, 期 9, 页码 1375-1384出版社
MINERALOGICAL SOC AMER
DOI: 10.2138/am-2020-7285
关键词
Mossbauer; Fe redox; Raman; glass transition; X-ray absorption
资金
- Department of Energy Waste Treatment and Immobilization Plant Federal Project Office [DE-EM002904, 89304017CEM000001]
- DOE OS [DE-SC0012704]
- Department for Business, Energy & Industrial Strategy [EP/T011424/1]
- Engineering and Physical Sciences Research Council (EPSRC) [EP/T011424/1]
- UK Engineering and Physical Sciences Research Council [EP/N017870/1, EP/S01019X/1]
- EPSRC [EP/N017870/1, EP/T011424/1, EP/S01019X/1] Funding Source: UKRI
The crystallization of iron-containing sodium silicate phases holds particular importance, both in the management of high-level nuclear wastes and in geosciences. Here, we study three as-quenched glasses and their heat-treated chemical analogs, NaFeSiO4, NaFeSi2O6, and NaFeSi3O8 (with nominal stoichiometries from feldspathoid, pyroxene, and feldspar mineral groups, i.e., Si/Fe = 1, 2, and 3, respectively) using various techniques. Phase analyses revealed that as-quenched NaFeSiO4 could not accommodate all Fe in the glass phase (some Fe crystallizes as Fe3O4), whereas as-quenched NaFeSi2O6 and NaFeSi3O8 form amorphous glasses. NaFeSi2O6 glass is the only composition that crystallizes into its respective isochemical crystalline polymorph, i.e., aegirine, upon isothermal heat-treatment. As revealed by Mossbauer spectroscopy, iron is predominantly present as fourfold-coordinated Fe3+ in all glasses, though it is present as sixfold-coordinated Fe3+ in the aegirine crystals (NaFeSi2O6), as expected from crystallography. Thus, Na-Fe silicate can form a crystalline phase in which it is octahedrally coordinated, even though it is mostly tetrahedrally coordinated in the parent glasses. Thermal behavior, magnetic properties, iron redox state (including Fe K-edge X-ray absorption), and vibrational properties (Raman spectra) of the above compositions are discussed.
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