Silicate melts oxidation states

The drawbacks of a simplified relative fo approach become apparent in the case of the relative volumetric properties of EeO and Ec203 in sihcate melts even at relatively low pressures (Kress and Carmichael, 1991). There are two problems first, the pressure dependence of EeO-Ec203 equilibria is different from the pressure dependence of the nickel-nickel oxide (NNO) buffer such that use of NNO as a normalization for relative/oj can be misleading. The volume change of the FMQ buffer (0.17 log/o units per GPa) is much closer to the redox state of a silicate melt than is that of the NNO buffer (0.51 log/o units per GPa). Second, the compressibilities of FeO and Fe203 are much different, so that even pressures of 1-2 GPa will have a large effect on their partial molar volumes. Any calculation of relative /o should include an assessment of the volumetric properties of both the buffer phases, and the phases involved in the redox reaction. 

Capobianco C. J., Dr e M. J., and DeAro J. A. (1999) Siderophile geochemistry of Ga, Ge and Sn cationic oxidation states in silicate melts and the effect of composition in iron-nickel alloys. Geochim. Cosmochim. Acta 63, 2667-2677. 

Paul a Douglas (1965) studied the Fe - Fe equilibrium in alkali silicate melts containing 0.4% Fe203, iii air atmosphere. Attainment of the equilibrium was very slow, as shown by Fig. 64 the final value of the Fe /Fe ratio was the same for the steady state reached from both the lower and the higher oxidation state. The equilibrium is shifted towards Fe with increasing R2O content and in the order of Li20 — Na O — K2O. 

Sender E, Martinelli JR, Zulu RA, Weeks RA (1987) The use of ion beam analysis for measrrring ion transport in oxides. Cryst Latt Def Amorph Mater 15 277-282 Staschewski D (1969) Kinetik des mit Bicarbonat katalysierten Sauerstuff-Austausches zwischen Kohlendioxid und Wasser. Chemie-Ing-Techn 41 1111-1118 Stanton TR (1990) High pressure isotopic studies of the water diffusion mecharusm in sihcate melts and glasses. PhD Dissertation, Arizona State University, Tempe, Arizona Stebbins J (1995) Dynamics and stmcture of silicate and oxide melts Nuclear magnetic resonance studies. In Stebbins J, McMillan P, Dingwell D (eds) Stiucture Dynamics and Properties of Sihcate Melts, Rev Mineral 32... 

Oxidation states of transition metal ions in silicate melts... 

Although in crystalline phases determination of the enthalpy of formation from the constituent elements (or from constituent oxides) may be carried out directly through calorimetric measurements, this is not possible for molten components. If we adopt as standard state the condition of pure component at T = 298.15 K and P = bar , it is obvious that this condition is purely hypothetical and not directly measurable. If we adopt the standard state of pure component at P and T of interest , the measurement is equally difficult, because of the high melting temperature of silicates. 

Electrolytic conductance, a property of the so called conductors of the second class, is encountered mainly in the case of salts in dissolved, melted and solid state. Among these compounds are sulphates, halides, nitrates, silicates, also many oxides, hydroxides, sulphides and so on. The same group includes also the potential electrolytes, i. e. the substances from which ions are formed only in mutual reaction with a solvent (solutions of acids in basic solvents, solution of bases in acid solvents, further amines and different chlorine derivatives of organic compounds in liquid sulphur dioxide, nitro-compounds in liquid amines etc.). Finally also numerous colloidal solutions (such as proteins and soaps) conduct the current like electrolytes. 

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