9 - Liquidus Temperatures in Calcium Ferrite Slags in...

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Liquidus Temperatures in Calcium Ferrite Slags in Equilibrium with Molten Copper A. ILYUSHECHKIN, P.C. HAYES, and E. JAK Experimental laboratory methods have been developed that enable phase-equilibria studies to be carried out on slags in the system Ca-Cu-Fe-O in equilibrium with metallic copper. These techniques involve equi- libration at temperature, rapid quenching, and chemical analysis of the phases using electron-probe X-ray microanalysis (EPMA). Equilibration experiments have been carried out in the temperature range of 1150 °C to 1250 °C (1423 to 1523 K) and in the composition range of 4 to 80 wt pct “Cu 2 O,” 0 to 25 wt pct CaO, and 20 to 75 wt pct “Fe 2 O 3 ” in equilibrium with metallic copper. Liquidus and solidus data are reported for the primary-phase fields of spinel (magnetite) and dicalcium ferrite. The resulting data have been used to construct liquidus isotherms of the CaO-“Cu 2 O”-“Fe 2 O 3 ” system at metallic copper saturation. I. INTRODUCTION C ALCIUM ferrite slags described by the Ca-Cu-Fe-O sys- tem are used in the copper-converting stage of the Mitsubishi process. These slags have a number of advantages over tradi- tional silica-based slags, such as reduced slag volume, reduced copper losses, high fluidity, and more efficient removal of impurities from molten copper. [1] Phase-equilibrium infor- mation on the Ca-Cu-Fe-O system is important for the control and development of these processes. The compositions of the calcium ferrite slags in the range CaO-Cu 2 O-FeO-Fe 2 O 3 (assuming all Cu is in Cu ± form) may be represented in the Ca-Cu-Fe-O compositional space as illus- trated in Figure 1. The limiting binary and ternary subsystems are represented by edges and surfaces of this composition tetra- hedron. The phase equilibria of Ca-Cu-O system have been examined in several studies, using high-temperature equili- bration and quenching followed by X-ray powder diffraction analysis; [2,3] thermogravitational analysis was used in another study. [4] The Cu-Fe-O system has been investigated using thermogravitational analysis [5] and differential thermal analy- sis. [6] The latter author [6] also quenched samples equilibrated in controlled gas atmospheres and measured the compositions of the slag and Pt crucible with bulk chemical analysis and electron-probe X-ray microanalysis (EPMA), respectively, to determine Cu 2 O activities. None of these studies investigated the phase equilibria in contact with metallic copper. The Ca-Fe-O system has been well characterized over a wide range of compositions, temperatures, and oxygen partial pressures. Phillips and Muan [7] investigated the Ca-Fe-O system in air and in pure oxygen using equilibration and quenching followed by microstructural (optical microscopy) and X-ray diffraction analyses. [7] Takeda et al. [8] investigated the Ca-Fe-O system using equilibration in controlled gas atmospheres and a quench- ing technique followed by bulk wet-chemical analysis. They determined that the liquid phase is stable at 1200 °C (1473 K)
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9 - Liquidus Temperatures in Calcium Ferrite Slags in...

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