The effect of composition on Cr2+/Cr3+ in silicate melts
作者： A. J. Berry , H. St.C. O'Neill , D. R. Scott , G. J. Foran , J.M.G. Shelley
DOI: 10.2138/AM.2006.2097
关键词:
摘要: Chromium K -edge X-ray absorption near-edge structure (XANES) spectra were recorded at room temperature for 27 CaO-MgO-Al 2 O 3 -SiO (CMAS) glass compositions quenched from melts equilibrated various oxygen fugacities ( f ) 1400 °C. Values of Cr 2+ /∑Cr determined the intensity a shoulder on main edge, attributed to 1s → 4s transition, which is characteristic in these glasses. For each composition, could be quantified as function , using theoretical expression, few three samples (Cr 0, 0.5, and 1). This allowed log ′, or reduction potential 3+/2+ half-reaction, hence relative change ratio γ melt 3+ 1.5 /γ composition. At constant log[Cr /Cr ] was found decrease linearly with increasing optical basicity. The variation ′ composition controlled by corresponding capacity stabilize both charge preferred solvation site . method then applied situ °C synthetic mid-ocean ridge basalt (MORB) allowing Fe-bearing first time. vary ~0.45 nickel-nickel oxide (NNO) buffer ~0.90 iron-wustite (IW). indicates that likely dominant oxidation state terrestrial basaltic melts.
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