Oxidation state of iron in silicate glasses and melts: a thermochemical model (original) (raw)
Related papers
Redox viscometry of some Fe-bearing silicate melts
American Mineralogist, 1991
The dependence of shear viscosity on the oxidation state of six ferrosilicate melts has been measured using the concentric cylinder method and a gas mixing furnace. The measurements were performed under air, COr, and COr-CO mixtures at I atm and in a temperature range of 1345 to 1470"C. The experimental procedure involved a continuous measurement of viscosity during stepwise reduction of the melts. Melt chemistry was controlled by dip sampling the tiquids at each oxidation state. The resulting glassesw ere analyzed by electron microprobe, a volumetric FeO itration, and 57Fe Mdssbauer spectroscopy. The electron microprobe data indicate Fe loss for some of the most reduced samples.T he wet chemical (+ microprobe) and spectroscopicd eterminations of theseF erich samples yield oxidation states that are in excellent agreement. The viscosity of all melts investigated herein decreasesw ith melt reduction. The viscosity decrease is, in general, a nonlinear function of oxidation state e...
Experimental study of the influence of SiO2 on the solubility of cobalt and iron in silicate melts
Petrology, 2007
The solubility of cobalt and iron in silicate melts with variable SiO 2 content was experimentally determined under controlled oxygen fugacity. It was shown that, independent of temperature and oxygen fugacity, the solubility of the two metals reaches a maximum (minimum of CoO and FeO activity coefficients) in melts of intermediate compositions. The analysis of available published data demonstrated that the γ MeO values of at least four metals (Ni, Co, Fe, and Cr) dissolving in melts as divalent oxides show a minimum in melts with ≈ 57 ± 2 mol %. The position of the minimum is essentially independent of the element, melt temperature, and oxide concentration (from a few ppm to 13 wt %). The extremes of iron solubility ( γ FeO ) in Fe-rich MgOfree melts may shift toward significantly lower values, although this inference requires additional experimental verification. Using a numerical example, some problems were discussed in the use of experimental data obtained in different laboratories for the development of a general model for the γ MeO dependence on melt composition.
Thermodynamic Description of 'FeO'-MgO-SiO2 and 'FeO'-MnO-SiO2 Melts - a Model Approach
High Temperature Materials and Processes, 2000
Activities of the oxide components in the 'FeO'-Mg0-Si0 2 and 'Fe0'-Mn0-Si0 2 systems have been predicted based on the information of binary systems using a thermodynamic model. The model considers the ionic melt as an oxygen-ion matrix with the cations including Si 4+ distributed in it. The interactions between different cations in the presence of O 2 " are considered as functions of both composition and temperature. The activities predicted by the model are in good agreement with the experimental data available in the literature.
Journal of Non-Crystalline Solids, 2018
The analysis of iron, manganese and antimony in silicate glass is of great interest in chemistry, materials science, earth sciences and archaeological sciences. Yet, conclusions from different fields appear to be contradictory and many questions about redox reactions in glass remain. The purpose of this study is thus to discuss whether and how these multivalent elements interact in glass. Soda-lime silicate melts containing iron along with manganese and/or antimony have been analysed at different high temperatures under argon atmosphere. Using in-situ XANES at the Fe K-edge, redox thermodynamics, kinetics and diffusivities have been assessed for the different compositions. The data obtained show that antimony is more efficient at oxidising iron compared to manganese at all temperatures. The oxidising power trend would thus be Sb > Sb + Mn > Mn. Furthermore, hypotheses on the formation of Fe-Mn complexes are also reported in glasses with stoichiometric proportions of iron and manganese. Based on the determination of redox diffusivities, it appears that presence of other multivalent elements does not significantly affect the iron redox mechanisms and that diffusivity is essentially controlled by the mobility of calcium.
Polymerisation, basicity, oxidation state and their role in ionic modelling of silicate melts
Annals of Geophysics
In order to describe and quantify the reactivity of silicate melts, the ionic notation provided by the Temkin formalism has been historically accepted, giving rise to the study of melt chemical equilibria in terms of completely dissociated ionic species. Indeed, ionic modelling of melts works properly as long as the true extension of the anionic matrix is known. This information may be attained in the framework of the Toop-Samis (1962a,b) model, through a parameterisation of the acid-base properties of the dissolved oxides. Moreover, by combining the polymeric model of Toop and Samis with the «group basicity» concept of Duffy and Ingram (1973, 1974a,b, 1976) the bulk optical basicity (Duffy and Ingram, 1971; Duffy, 1992) of molten silicates and glasses can be split into two distinct contributions, i.e. the basicity of the dissolved basic oxides and the basicity of the polymeric units. Application to practical cases, such as the assessment of the oxidation state of iron, require bridging of the energetic gap between the standard state of completely dissociated component (Temkin standard state) and the standard state of pure melt component at P and T of interest. On this basis it is possible to set up a preliminary model for iron speciation in both anhydrous and hydrous aluminosilicate melts. In the case of hydrous melts, I introduce both acidic and basic dissociation of the water component, requiring the combined occurrence of H + cations, OH − free anions and, to a very minor extent, of T-OH groups. The amphoteric behaviour of water revealed by this study is therefore in line with the earlier prediction of Fraser (1975).
The Effect of Fe3+ Ions on the Anionic Structure of Iron-bearing Sodium Silicate Melts
ISIJ International, 2000
The effects of the coordination of iron ions on the anionic structure of molten iron bearing sodium silicate slags at 1 273 K have been investigated by Raman spectroscopy. The Raman spectra of Na 2 O-SiO 2-FeO-Fe 2 O 3 system equilibrated with various oxygen pressures (pO 2) have been measured. The effect of the concentration of iron oxide on the Raman spectra of these systems has also been studied. Under low pO 2 conditions (CO 2 /COϽ10), the Raman spectra of Na 2 O • 2SiO 2-FeO-Fe 2 O 3 are essentially the same as that of Na 2 O • 2SiO 2. However, under high pO 2 conditions (CO 2 /COϾ54), a new Raman band of around 900 cm Ϫ1 appears and its intensity increases with increase of pO 2 and iron oxide content. The scattering intensity at low frequency region (Ͻ550 cm Ϫ1) also becomes intense with increase of the iron oxide content. It is confirmed that the near 900 cm Ϫ1 band can be attributable to the network structure involving Fe 3ϩ ions. Fe 3ϩ ions in the metasilicate melts is found to conjugate the chain units and produce the sheet and monomer units. In the disilicate melts, it will conjugate the sheet units and produce the chain and three-dimensional network units.
Geochimica et Cosmochimica Acta, 1988
The densities of 12 melts in the Na20-FeO-FezOrSi02 system have been determined in equilibrium with air, in the temperature range of lOOO-15OO"C, using the double bob, Archimedean technique. Ferrous iron determinations of 100-200 mg samples, "dip" quenched from high temperature, indicate that all the melts investigated were highly oxidixed under these experimental conditions. "Fe Massbatter spectra of glasses obtained by drop quenching 80 mg melt samples from loop equilibration runs yield Fe3+/F$+ data equivalent to that for the densitometry (dip) sampies for all but the most viscous melt, and confirm that all but one melt equilibrated with air during the densitometry measunments. Melt densities range from 2.17 to 2.88 g/cm3 with a mean standard deviation (from replicate experiments) of 0.36%. Least squares regression of the density data at 1300, 1400 and 1 500°C, was calculated, both excluding and inciuding excess volume terms (herein named linear and nonlinear fits, respectively) and the root mean squared deviation (RMSD) of each regression was compared with the total experimental error. The partial molar volumes computed for linear fits for Na20 and Si02 are similar to those previously repotted for melts in the Na@-AlzOrSi02 system (STEIN et al., 1986). The partial molar volumes of Fe203 obtained in these linear fits are equal to those obtained by SHIRAIS~~I et al. (1978) in the FeO-Fe20s-SiO2 system but 5 to 10% lower than repotted by MO et al. (1982) in multicomponent melts. The partial molar volume exhibited by Fe'+ in this system is representative of the partial molar volume of tetrahedrally