Thermodynamic observations of the molten FeS-FeO system and its vicinity at 1473 K
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INTRODUCTION
THE molten Fe-S-O system plays important roles in several disciplines of science and engineering, such as geological magma,[1] coal combustion,[2] iron metallurgy,[3] and matte smelting.[4–7] The literature prior to 1980 was summarized by Turkdogan in his classical monograph,[8] while the publications up to 1992 were reviewed by Zhong and Hepworth.[2] Although several mathematical models[1,2,9] were put forward to describe the thermodynamic properties of the Fe-S-O melts at matte-smelting temperatures (1400 to 1525 K), the fundamental data used in these models are primarily the experimental results produced by Nagamori and Kameda.[4] Experimentally, the activities of sulfur and oxygen in the Fe-S-O melts can be measured simultaneously by equilibrating a melt sample with a gas phase composed of H2-H2OH2S or CO-CO2-SO2. The so-obtained data can be treated by the Gibbs–Duhem integration to calculate iron activity and, subsequently, all the other thermodynamic properties of the melts. The experiments have to be planned and then executed in such a way that a systematic and elaborate network of S2 (g) and O2 (g) isobars covers a wide melt composition range including the Fe-S binary. Thus far, only two groups of researchers[4,5] were successful in covering the Fe-S-O melt with an isobaric network of S2 (g) and O2 (g) at matte-smelting temperatures. The current article presents new experimental results regarding the equilibration between the Fe-S-O melt and the CO-CO2-SO2 gas, exploring the melt composition range that was not investigated in the previous experiments. II. EXPERIMENTAL A. The CO-CO2-SO2 Gas The CO-CO2-SO2 system gas permits a simultaneous measurement of the partial pressure of S2 (g), Ps2 atm, and that of O2 (g), Po2 atm, over the Fe-S-O melt, where 1 atm ⫽ 101.3 kPa. The following symbols are employed in this article:
MEGURU NAGAMORI is a Thermochemistry Consultant, 300-800 Alain, Ste-Foy, PQ, Canada G1X 4E7. AKIRA YAZAWA, Professor Emeritus, is with IAMP, Tohoku University, Sendai, Miyagi 980, Japan. Manuscript submitted January 22, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
; Po ⫽ 106 Po1/2 Ps ⫽ Ps1/2 2 2
[1]
A pair of Ps and Po at 1473 K and the corresponding COCO2-SO2 gas composition at room temperature are shown in Table I. The thermodynamic method for calculating a gas composition for given Ps and Po was shown earlier.[4] The present experiments were carried out mostly under a constant S2 partial pressure of Ps ⫽ 0.02, while varying Po from 1 to 18.1. The isobar of Ps ⫽ 0.02 runs through both low-Fe and high-Fe sides of the FeS-FeO pseudobinary. The literature is reticent on the Fe-S-O melts in this range, probably because the SO2 (g) contents in the inlet CO-CO2-SO2 gases then become lower than 1 vol pct, being close to the limit of experimental feasibility with this gas system. B. Apparatus, Procedure, and Analyses The experimental apparatus employed was the same as described elsewhere.[4] About 2 g of a premelted Fe-S-O mixture of a known composition were charged in an alumin
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