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The influence of slag composition of FeO/TiO2 (=F/T) ratio, Al2O3/(SiO2+Al2O3) (=A/(S+A)) ratio and oxygen partial pressure (pO2=10−10to10−9atm) on the thermodynamic behavior of vanadium oxide in molten ilmenite smelting slag, i.e., FetO-TiO2-MgO-Al2O3-SiO2 system, was investigated at 1550 °C. The distribution ratio of vanadium (=LV) between molten iron and FetO-TiO2-MgO-Al2O3-SiO2 slag increases with increasing F/T ratio, while it decreases with increasing A/(S+A) ratio. In addition, logLV generally increases with increasing theoretical optical basicity of the slag (=Λslag). Vanadium oxide (VOx) is expected to behave as an acidic component in the present system. Vanadium in ilmenite smelting slags primarily consist of V3+, V4+, and V5+ ions, as determined by Gaussian deconvolution of X-ray photoelectron spectra. A linear relationship between log(wt%V4+/wt%V3+) and logpO2 is confirmed. Both (wt% V3+) and (wt% V5+) ions increase with increasing F/T ratio, whereas (wt% V4+) ions show the opposite behavior with increasing F/T ratio, irrespective of A/(S+A) ratio. Meanwhile, (wt% V3+) increase while (wt% V4+) and (wt% V5+) decrease with increasing A/(S+A) ratio. The linear relationship between log(wt%V3+/wt%V5+) and log(wt%V4+) has a slope of 1.8, which is good agreement with the theoretical slope of 2.0, which indicates that multi-valent vanadium ion species, i.e., V3+, V4+, and V5+, are thermodynamically balanced based on redox equilibria.

The pharmacokinetic and pharmacodynamic behaviour of drugs and the interacting biomolecules are highly influenced by their species-specific physico-chemical properties. The first of such bio-relevant, structure-dependent properties were the species-specific acid-base constants and the co-dependent concentrations, but the past decade brought significant advances to previously uncharted territories, including the experimental determination of species-specific partition coefficients, solubilities and redox equilibrium constants. This review gives an overview of the types and definitions of species-specific physico-chemical and analytical properties. We survey the pertinent literature, the fundamental relationships, and summarize some of our recent work that enabled the determination of species-specific partition coefficients for coexisting, inseparable protonation isomers and pH-independent, microscopic redox equilibrium constants. The thorough insight provided by these species-specific properties improves our understanding of the submolecular mechanism of pharmacokinetic processes. As a result, there are some pieces of clear-cut evidence of practical significance. A few of them are as follows: – passive diffusion into lipophilic media is not necessarily predominated by the non-charged species, contrary to the widespread misbelief. – the reactive microspecies in structure-controlled, highly specific biochemical reactions is not necessarily the major one. – a preventive defence system against oxidative stress can be based upon thiol-disulfide equilibria of custom-tailored redox potentials. [ABSTRACT FROM AUTHOR]

In this work we present a series of experiments that examine the relationship between oxygen fugacity and Cr valence ratio in olivine grown from a basaltic liquid. These experiments are specifically targeted for an olivine-rich martian basalt composition that was modeled after the bulk chemistry of the meteorite Yamato 980459 (i.e., Y-98). The chromium valence ratio in the olivine crystals was measured with X-ray absorption near edge spectroscopy (XANES) at the Advanced Photon Source, Argonne National Laboratory. Results from the XANES measurements indicate that the ratio of divalent to trivalent Cr in the olivine is not only systematically correlated with fO2, but is also reflective of the molar Cr3+/Cr2+ in the silicate liquid from which it grew. In this way, measurements of Cr valence in olivine phenocrysts can yield important information about the oxygen fugacity and molar Cr3+/Cr2+ of its parental liquid in the absence of a quenched melt phase. Although the results from the experiments presented in this work specifically apply to the Y-98 parental melt, the concepts and XANES analytical techniques discussed within the text present a novel, generalized methodology that may be applicable to any olivine-bearing basalt. Furthermore, the XANES-based measurements are made on a micrometer-scale, thus potential changes of the Cr3+/Cr2+ in the melt during crystallization could be examined with a great deal of spatial detail [ABSTRACT FROM AUTHOR]

Highlights: [•] The Generalized Electron Balance (GEB) is considered as a Law of Nature. [•] A new criterion distinguishing redox and non-redox systems is presented. [•] Two equivalent approaches to formulation of GEB are presented. [•] GEB is applicable for electrolytic redox systems of any degree of complexity. [ABSTRACT FROM AUTHOR]

Abstract: In a melt with the base mol% composition 25Na2O-15B2O3-60SiO2, doped with chromium and manganese, a redox reaction takes place during cooling the melt. This reaction was studied using high temperature UV–vis spectroscopy. Above 600°C, the reaction is in equilibrium and shifted during cooling to the Cr3+ and Mn3+ species. At temperatures between 500 and 600°C, the kinetics of the redox reaction is decisive and the cooling rate plays an important part. At temperatures<500°C, the reaction is frozen in. The smaller the cooling rate, the smaller is the Cr6+ concentration and the lower is the fictive redox temperature. The kinetics of the reaction was described by a differential equation assuming Arrhenian behaviour. The equation was numerically solved and fictive temperatures were calculated. These temperatures depended on cooling rate similar to Bartenev equation. Activation energies calculated hereof were around 38kJ∙mol−1 larger than those inserted into the kinetic equation. The experimentally determined activation energy is 565kJ∙mol−1, a value much larger than the activation energies of diffusion of the polyvalent elements. The rate determining step in the case of the Cr3+/Cr6+/Mn2+/Mn3+ system is the electron transfer reaction, because a notable structural rearrangement is necessary during the course of the electron transfer reaction (Cr3+ and Cr6+ occur in octahedral and tetrahedral coordination, respectively). The latter leads to a large inner reorganisation energy and to an activation energy similar to that of the viscous flow. In the case of the redox reaction between copper and arsenic, the activation energy is much smaller (210kJ∙mol−1), because here the coordination numbers do not change during the course of the redox reaction. [Copyright &y& Elsevier]

Abstract: Glass melts with the basic mol% composition 26 Na2O · x Al2O3 · (74− x) SiO2 (x =5, 10, 15 and 20); x Na2O · 10 CaO · 10 Al2O3 · (80− x) SiO2 (x =10, 15, 20 and 25) and x Na2O · 20 Al2O3 · (80− x) SiO2 (x =10, 15 and 20) doped with 1mol% CuO were studied by means of square-wave voltammetry in the temperature range from 800 to 1150°C. Each voltammogram shows two distinct maxima. The first maximum occurs at potentials in the range from −100 to +150mV and is caused by the Cu+/Cu2+-redox pair. The second maximum is observed at more negative potentials and is due to the Cu+/Cu0-redox transition. With decreasing temperature both peaks are shifted to more negative (or less positive) values. From the linear dependency of the peak potentials upon the temperature ΔH°, ΔS° and the Cu+/Cu2+-redox ratio at 1000°C were calculated. Furthermore the effect of the glass composition on the Cu+/Cu2+-redox equilibrium was discussed with respect to the melt structure and the incorporation of the copper ions into the alumosilicate network. [ABSTRACT FROM AUTHOR]

Abstract: The effect of pH and redox potential on the redox equilibria of iron oxides in aqueous-based magnetite dispersions was investigated. The ionic activities of each dissolved iron species in equilibrium with magnetite nanoparticles were determined and contoured within the –pH framework of a composite stability diagram. Both standard redox potentials and equilibrium constants for all major iron oxide redox equilibria in magnetite dispersions were found to differ from values reported for noncolloidal systems. The “triple point” position of redox equilibrium among Fe(II) ions, magnetite, and hematite shifted to a higher standard redox potential and an equilibrium constant which was several orders of magnitude higher. The predominant area of magnetite stability was enlarged to cover a wider range of both pH and redox potentials as compared to that of a noncolloidal magnetite system. [Copyright &y& Elsevier]

The early augite syenite unit in the 1·13-Ga-old Ilímaussaq intrusive complex, South Greenland, consists of a magmatic assemblage of ternary alkali feldspar + fayalitic olivine + augite + titanomagnetite + apatite + baddeleyite ± nepheline ± quartz ± ilmenite ± zircon. Feldspar, nepheline and QUILF thermometry yield T = 1000–700°C, at P = 1 kbar, which is derived from fluid inclusion data from other parts of the complex. Ternary feldspar was the first major liquidus phase. It crystallized at temperatures between 950 and 1000°C from a homogeneous magma with aSiO2 = 0·8 and fO2 about 1·5–2 log units below the fayalite–magnetite–quartz (FMQ) buffer. Later, closed system fractionation produced nepheline-bearing assemblages with aSiO2 = 0·4 and log fO2 = FMQ – 3 to FMQ – 5. Assimilation of wall rocks produced local variations of melt composition. Four traverses through the unit were sampled parallel to the assumed direction of crystallization. They exhibit significant differences in their mineral assemblages and compositions. The chemical zoning and calculated intensive parameters of four sample suites reflect both closed system fractional crystallization and local assimilation of wall rocks. [ABSTRACT FROM PUBLISHER]

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The formal potentials of the Hg/Hg, Hg/Hg and Hg/Hg redox couples and the apparent equilibrium constants of the reaction Hg + Hg ∝ Hg in conc. aqueous solutions of Mg(ClO) and Ca(ClO) have been determined from emf measurements performed using cells with liquid junction. Based on these data, the hydration numbers of the Hg and Hg ions were estimated. [ABSTRACT FROM AUTHOR]

The effects of composition on the iron redox equilibria and structural changes in the CaO Al 2 O 3 Fe t O melts have been investigated at 1823 K. The ferric to ferrous (Fe3+/Fe2+) ratio increases with increasing basicity and total iron oxide content when the activity of CaO (a CaO) is greater than 0.3. However, the Fe3+/Fe2+ ratios decrease with increasing iron oxide content in the case of the existence of octahedrally coordinated Fe3+ ions in a CaO =0.2 composition range. From Raman spectroscopic analysis, it was observed that the addition of iron oxide (up to 10 wt% T.Fe) to calcium aluminate melts modifies the aluminate networks. Furthermore, the non-bridging oxygen per tetrahedron (NBO/T) ratio in the CaO Al 2 O 3 Fe t O melts increases with increasing content of iron oxide because the [FeO 4 -tetrahedron ferrite networks substitutes for the [AlO 4 -tetrahedron aluminate networks. The activation energy for the viscous flow of the CaO Al 2 O 3 Fe t O melts has a good linear relationship with the relative concentration of polymerized [AlO 4 unit, i.e., ln Q Al 4. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to an article about environmental aspect of serum ɣ-glutamyltransferase to treat atherosclerosis.

The iron-oxygen system is the most important reference of rocks' redox state. Even as minor components, iron oxides can play a critical role in redox equilibria, which affect the speciation of the fluid phases chemical differentiation, melting, and physical properties. Until our recent finding of Fe4O5, iron oxides were assumed to comprise only the polymorphs of FeO, Fe3O4, and Fe2O3. Combining synthesis at high pressure and temperature with microdiffraction mapping, we have identified yet another distinct iron oxide, Fe5O6. The new compound, which has an orthorhombic structure, was obtained in the pressure range from 10 to 20 GPa upon laser heating mixtures of iron and hematite at ~2000 K, and is recoverable to ambient conditions. The high-pressure orthorhombic iron oxides Fe5O6, Fe4O5, and h-Fe3O4 display similar iron coordination geometries and structural arrangements, and indeed exhibit coherent systematic behavior of crystallographic parameters and compressibility. Fe5O6, along with FeO and Fe4O5, is a candidate key minor phase of planetary interiors; as such, it is of major petrological and geochemical importance. We are revealing an unforeseen complexity in the Fe-O system with four different compounds-FeO, Fe5O6, Fe4O5, and h-Fe3O4-in a narrow compositional range (0.75 < Fe/O < 1.0). New, finely spaced oxygen buffers at conditions of the Earth's mantle can be defined.