Towards better understanding of fundamental dephosphorization slags of the FeO-CaO-SiO 2 -P 2 O 5 quaternary system, this study aimed at clarifying the thermochemical properties of iron oxide in Ca 2 SiO 4 -Ca 3 P 2 O 8 solid solutions. The solubility and activity of FeO in the solid solutions coexisting with CaSiO 3 at 1 573 K were determined by SEM-EDX analysis and a gas equilibrium method, respectively. Based on the present experimental results, the phase relationships could be explained that the solid solution of high FeO solubility coexists with CaSiO 3 and liquid slag of low FeO content, while the solid solution of low FeO solubility coexists with CaO and liquid slag of high FeO content.
The knowledge of Cr 2 O 3 activity in slag is necessary to decarburize chromium-containing special steel while minimizing the oxidation loss of chromium. In the present study, firstly, the phase relationship in the CaO-SiO 2 -Cr 2 O 3 system was determined at 1 573 K. Subsequently, the Cr 2 O 3 activities in two-and threephase coexisting slags at 1 573 K were measured by equilibrating molten copper with oxide phases under a stream of Ar + H 2 + CO 2 gas mixtures, and the Gibbs energy changes of the formations of CaCr 2 O 4 and Ca 3 Cr 2 Si 3 O 12 were derived. It was found that the present results were compatible with the phase diagram and the literature data reported at higher temperature than 1 573 K.
The knowledge of sulfur distribution ratios between FeO-containing slag and hot metal is necessary for better understanding resulfurization in hot metal pre-treatment. To measure sulfur distribution ratios at temperature below the melting point of pure iron, copper-iron liquid alloy has been suggested as a reference metal equilibrated with slag. In the present study, the Henrian activity coefficient of sulfur in copperiron liquid alloy was determined at 1 573 K and 1 673 K. The sulfur activity coefficient decreased with an increase in iron content; this result was not inconsistent with that reported by Alcock and Richardson. Negative logarithmic value for the sulfur activity coefficient indicated that the chemical affinity between iron and sulfur would be stronger than that between copper and sulfur.
where (i) slag denotes anion i in slag, K 1 represents the apparent equilibrium constant of Reaction (1), f S 2− and (%S 2 − ) are the activity coefficient and mass% concentration of S 2 − , respectively, and a O 2− is the activity of O 2 − . According to Eq. ( 3), the value for C S 2− increases in the conditions that slag basicity is high, i.e., a O 2− is high, and slag contains components with high chemical affinity for sulfur, i.e., f S 2−
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