Solutions of CeO 2 in cryolite melts
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[1]
6CeO2 1 2AIF3 5 6CeOF 1 Al2O3 1 3/2O2
[2]
and From the equilibrium constants it follows that, at constant oxygen pressure and AlF3 content of the melt, the solubility as CeF3 should vary as (aAl2O3)21/2, while the solubility as CeOF should vary as (aAl2O3)21/6. Analysis of the experimental data for the solubility of CeO2 in Na3AlF6 at 1 atm pressure of oxygen in terms of the equation solubility 5 A (aAl2O3)21/2 1 B (aAl2O3)21/6
[3]
shows that the coefficient B is not only not statistically different from zero, but is negative. No physical meaning in terms of the existence of CeOF can be attached to it. Figure 1 shows a log-log plot of the solubility as a function of the alumina activity.[4] The least-squares slope is 20.523 5 0.064 (standard error of the estimate), which is not significantly different from 20.5, and a line of slope 20.5 is shown. The results as they now stand are completely consistent with the hypothesis that Eq. [1] is the only mechanism of solution, and there is no evidence for the existence of CeOF. The original article[1] also gave some data and discussion on the variation of the solubility with variation of the NaF/AlF3 ratio of the solvent at constant alumina content. The solubility was found to vary roughly as (aAlF3)1/3. It was postulated that CeF3 was complexed to Na2CeF5 in solution. That suggestion stands.
ERNEST W. DEWING, 648 Pimlico Pl., Kingston, ON K7M 5T8, Canada, is retired. JOMAR THONSTAD, Professor of Electrochemistry, is with the Norwegian University of Science and Technology, 7034 Trondheim, Norway. Manuscript submitted June 14, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
Fig. 1—Solubility of CeO2 in cryolite alumina melts at 1293 K (log-log plot). The abscissa is alumina activity derived from recent calculations.[4]
REFERENCES 1. E.W. Dewing, G.M. Haarberg, S. Rolseth, L. Rønne, J. Thonstad, and N. Aalberg: Metall. Mater. Trans. B., 1995, vol. 26B, pp. 81-86. 2. E.W. Dewing: Can. Met. Q., 1974, vol. 13, pp. 607-18. 3. E.W. Dewing: Can. Met. Q., 1991, vol. 30, pp. 153-61. 4. E.W. Dewing and J. Thonstad: Metall. Mater. Trans. B, 1997, vol. 28B, pp. 1089-93.
Dependence of Carbon Solubility on Oxygen Partial Pressure for 80 Mass Pct BaO-MnO and CaOsatd-B2O3 Slags MAMIKO MORI, KAZUKI MORITA, and NOBUO SANO As is well known[1–4] carbon is dissolved as carbonate ion, CO22 3 , at higher oxygen partial pressures, as shown by Eq. [1], and as carbide ion, C22 2 , at lower oxygen partial pressures, as shown in Eq. [2]. CO2 (g) 1 O22 (slag) 5 CO 22 (slag) 3 3C (s) 1 O22 (slag) 5 C 22 (slag) 1 CO (g) 2
[1] [2]
In the present work, carbon solubilities in 80 mass pct BaO-MnO melts and CaOsatd-B2O3 melts were measured over a wide range of oxygen partial pressures from carbide stable region to carbonate stable region, as found in the sulfide and sulfate[5] and phosphide and phosphate[6] equilibria in some slag systems. The equilibrium among MO, M0.5C, or MCO3 and gas may be written using Eqs. [3] through [5], where M is Ca or Ba.
MAMIKO MORI, Research Assistant, and KAZUKI
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