『Abstracts
　A program has been developed for generating stability diagrams that combine the principles of the Pourbaix E-pH diagrams with a rigorous and predictive thermodynamic model for multicomponent, nonideal; aqueous solutions. Since the diagrams are based on a realistic model for the aqueous phase, they are referred to as real-solution stability diagrams. They are valid for solutions ranging from dilute to concentrated (up to 30 mol kg^-1) at temperatures up to 300℃ and pressures up to 1 kbar. The stability diagrams are used to predict the conditions that favor the stability of various iron sulfide species. For this purpose, the applicability of the diagrams is extended to include the prediction of both stable and metastable products. The diagrams indicate that the formation of iron monosulfide follows the FeHS⁺→amorphous FeS→mackinawite→pyrrhotite replacement sequence. It is predicted that a transformation of iron monosulfides to pyrite may occur through greigite and/or marcasite. Greigite is predicted to be absent in strictly reducing environments. The predictions are in agreement with experimental data on iron sulfide formation in solution and/or at the iron/solution interface.

Key Words: Iron sulfides; Thermodynamics; Speciation; Stability diagrams; H2S corrosion』

Introduction
Structure of the program
Results and discussion
Conclusions
References
Appendix
　Thermodynamic framework

• Anderko,A., Sanders,S.J. and Young,R.D.(1997): Real-solution stability diagrams. A thermodynamic tool for modeling corrosion in wide temperature and concentration ranges. Corrosion, 53(1), 43-53.
• Helgeson,H.C., Kirkham,D.H. and Flowers,G.C.(1981): Theoretical prediction of the thermodynamic behavior of aqueous electrolytes at high pressures and temperatures. IV. Calculation of activity coeffeicients, osmotic coefficients and apparent modal and standard and relative partial molal properties to 600℃ and 5 kb. American Journal of Science, 281(10), 1249-1516.
• Pourbaix,M.(1966): Atlas of Electrochemical Equilibria in Aqueous Solutions. Pergamon, New York, 644p.
• Rafal,M., Berthold,J.W., Scrivner,N.C. and Grise,S.L.(1995): Models foe electrolyte solutions. In: Sandler,S.I.(ed.), Models for Thermodynamic and Phase Equilibria Calculations, M. Dekker, New York, 601-670.
• Shock,E.L. and Helgeson,H.C.(1988): Calculation of the thermodynamic and transport properties of aqueous species at high pressure and temperature: correlation algorithms for ionic species and equation of state predictions to 5 kbar and 1000℃. Geochimica et Cosmochimica Acta, 52(8), 2009-2036.
• Shock,E.L. and Helgeson,H.C.(1990): Calculation of the thermodynamic and transport properties of aqueous species at high pressure and temperature: standard partial molal properties of organic species. Geochimica et Cosmochimica Acta, 54(4), 915-943.
• Sverjensky,D.A.(1987): Calculation of the thermodynamic properties of aqueous species and the solubilities of minerals in supercritical electrolyte solutions. Reviews in Mineralogy, 17, 177-209.
• Tanger,J.C. and Helgeson,H.C.,(1988): Calculation of the thermodynamic and transport properties of aqueous species at high pressures and temperatures: revised equation of state for the standard partial molal properties of ions and electrolytes. American Journal of Science, 288(1), 19-98.
• Zemaitis,J.F.,Jr., Clark,D.M., Rafal,M. and Scrivner,N.C.(1986): Handbook of Aqueous Electrolyte Thermodynamics. American Institute of Chemical Engineering, New York, 852p.