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CaO-FeO-SiO 2 Fig. 09537 —System CaO-"FeO"-SiO2.  ( A ) Calculated liquidus surfaces for CaSiO3 (CS), Ca2SiO4 (C2S), and liquidus boundary between C2S and F2S (Fe2SiO4).  Dotted lines represent isotherms under the assumption that Fe2+ is in tetrahedral coordination in the melts.  ( B ) Portion of the liquidus surface in the system CaO-"FeO"-SiO2 from Ref. 1.  Psw = pseudowollastonite; Wo = wollastonite; Ra = rankinite; Ol = olivine; Trd = tridymite.
V. Danek, Chem. Zvesti , 38 [3] 379-386 (1984).
Liquidus surfaces in the system were calculated with the model of Ref. 2 to estimate the activity of the CS (CaSiO3) component.  The liquidus surface was then calculated from the LeChatelier-Shreder equation with the assumption of structural analogy between CaSiO3 in the crystalline and molten state.  Enthalpy of fusion data were from Refs. 3 and 4.
The calculated liquidus diagram closely reproduces the experimentally-produced diagram1 provided that Fe2+ is in octahedral coordination in the melts.  Independent spectroscopic evidence from six-fold coordination of ferrous iron in silicate melts can be found in Ref. 5.
1. A. Muan and E. F. Osborn; Phase Equilibria Among Oxides in Steelmaking, 236 pp. Addison-Wesley Publishing Company, Reading, Massachusetts, 1965.
2. R. Haase, Phys. Chem. , 1 , 293-365 (1971).
3. I. Barin and O. Knacke; Thermochemical Properties of Inorganic Substances, 921 pp. Springer-Verlag, Berlin, Germany, 1973.
4. Y. Bottinga and P. Richet, Earth Planet. Sci. Lett. , 40 [3] 382-400 (1982).
5. D. Virgo and B. O. Mysen, Phys. Chem. Miner. , 12 [2] 65-76 (1985).
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