Composition of liquid-Saturated selenium vapor
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This work was supported by the Assistant Secretary of Conservation and Renewable Energy, Office of Energy Systems Research, Energy Storage Division of the United States Department o f Energy under Contract N u m b e r DE-AC03-76SF00098. REFERENCES 1. J. Szekely and K. Nakanishi: Metall. Trans. B, 1 9 7 5 , vol. 6B, p p . 245-56. 2 . E. D. Tarapore and J. W. Evans: ibid., 1976, vol. 7B, pp. 343-51. 3 . E.D. Tarapore, J.W. Evans, and J. Langfeldt: ibid., 1977, vol. 8B, p p . 179-84. 4 . J. Szekely and C.W. Chang: lronmaking and Steelmaking, 1977, vol. 3 , p p . 196-204. 5 . J. Szekely, C.W. Chang, and R.E. Ryan: Metall. Trans. B, 1977, vol. 8B, p p . 333-38. 6 . J. Szekely, C.W. Chang, and W.E. Johnson: ibid., 1977, vol. 8B, p p . 514-17. 7 . D.J. Moore and J. C. R. Hunt: Proc. 3rd Beer-Sheva Symposium on MHD Flows and Turbulence, Beer-Sheva, Israel, 1981. 8 . B.E. Launder and D. B. Spalding: C o m p . Meth. in Appl. Mech. and Eng., 1974, vol. 3 , p p . 269-89.
their compilation of vapor pressure relations for elements and compounds. These authors5remarkthat the vapor-phase in equilibrium with liquid selenium is mostly Se6 . Berkowitz and Chupka6 investigated the molecular composition ofselenium vapor in equilibrium with a-monoclinic (or hexagonal) selenium by a mass spectrometric technique. They6 reported finding eight different species--Se, Se2, Se3, Se4, S e s , Se6, SeT, and Se8-- in the vapor phase. For theseeight species, a listing of thermodynamic quantities AH~298, S~98, and Ce appears in a recent publication by Wiedemeier and co-workers.7 The vapor pressure measurements of Rau2'3 and Baker 4 have been found to be satisfactorily represented by the following three-term equation: 5337 1.563 × 105 log p~at(atm) = - "-7"-- + T2 + 5.4
[B]
which equation applies quite well over a temperature range o f 550 to 1650 K; it predicts a boiling point of 685 °C, a value fairly close to that reported by Brooks. The present analysis is concerned with the determination o f the vapor-phase composition under conditions of saturation with the liquid-phase; the mole fraction of each selenium species in the vapor-phase in equilibrium with liquid selenium at a given temperature will be computed. This will be accomplished by combining Eq. [B] with equilibrium constant data for the association equilibria occurring in the vapOr-phase. Since selenium in liquid state is known to be present in a state o f association, i.e., in dimeric form, the vaporization may be represented by the reaction Se2(I) = Se2(g)
[C]
The results of the present calculations will be used in the derivation o f a three-term free energy equation for the vaporization equilibrium represented by Eq. [C]. Such information is currently unavailable in the literature. The minimum set of independent reactions required to describe this system fully may be written as follows:
Composition of Liquid-Saturated Selenium Vapor Y. K. RAO The objective of this communication is to present a digital computer method for calculating the composition of the vapor-phase by combining
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