TY  - JOUR
A1  - Botcharnikov, Roman E.
A1  - Koepke, J.
A1  - Holtz, Francois
A1  - McCammon, C.
A1  - Wilke, Max
T1  - The effect of water activity on the oxidation and structural state of Fe in a ferro-basaltic melt
N2  - Experimental investigations have been performed at T = 1200 degrees C, P = 200 MPa and fH(2) corresponding to H2O-MnO-Mn3O4 and H2O-QFM redox buffers to study the effect of H2O activity on the oxidation and structural state of Fe in an iron-rich basaltic melt. The analysis of Mossbauer and Fe K-edge X-ray absorption nearedge structure (XANES) spectra of the quenched hydrous ferrobasaltic glasses shows that the Fe3+/Sigma Fe ratio of the glass is directly related to aH(2)O in a H-2-buffered system and, consequently, to the prevailing oxygen fugacity (through the reaction of water dissociation H2O <-> H-2 + 1/2 O-2). However, water as a chemical component of the silicate melt has an indistinguishable effect on the redox state of iron at studied conditions. The experimentally obtained relationship between fO(2) and Fe3+/Fe2+ in the hydrous ferrobasaltic melt can be adequately predicted in the investigated range by the existing empiric and thermodynamic models. The ratio of ferric and ferrous Fe is proportional to the oxygen fugacity to the power of similar to 0.25 which agrees with the theoretical value from the stoichiometry of the Fe redox reaction (FeO + 1/4 O-2 = FeO1.5). The mean centre shifts for Fe2+ and Fe3+ absorption doublets in Mossbauer spectra show little change with increasing Fe3+/Sigma Fe, suggesting no significant change in the type of iron coordination. Similarly, XANES preedge spectra indicate a mixed (C3h, Td, and Oh, i.e., 5-, 4-, and sixfold) coordination of Fe in hydrous basaltic glasses. Copyright (c) 2005 Elsevier Ltd
Y1  - 2005
SN  - 0016-7037
ER  - 
TY  - JOUR
A1  - Botcharnikov, Roman E.
A1  - Koepke, J.
A1  - Holtz, Francois
A1  - McCammon, C.
A1  - Wilke, Max
T1  - The oxidation and structural state of Fe in hydrous ferrobasaltic melt
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Richet, Pascal
A1  - Whittington, Alan
A1  - Holtz, Francois
A1  - Behrens, Harald
A1  - Ohlhorst, Susanne
A1  - Wilke, Max
T1  - Water and the density of silicate glasses
Y1  - 2000
ER  -