• PDF / 613,141 Bytes
• 8 Pages / 603.28 x 783.28 pts Page_size
• 75 Downloads / 222 Views

DOWNLOAD

REPORT

---

I.

INTRODUCTION

THE activity measurements for FexO in various slags and fluxes have successfully been conducted by the present authors by employing an electrochemical technique involving stabilized zirconia.t~-t~~The work has now been extended to the system CaO + A1203 + Fe~O. These slags would appear as refining agents for ladle metallurgy of molten steel, especially desulfurization, although their thermodynamic properties have not been reported in the literature. The electrochemical cell used in this study can be expressed as Mo/Mo +

MoO2/ZrO2(MgO)/Fe

+ (CaO + A1203 + Fe~O)~l.JAg/Fe

II.

EXPERIMENTAL ASPECTS

The experimental apparatus and procedures have been described elsewhere, l~ An iron crucible was charged with 20 to 30 g of the slag and about 35 g of pure silver and heated to 1673 K in a stream of purified argon inside a SiC resistance furnace. A disposable electrochemical oxygen probe, Mo/Mo + MoOz/ZrO2(MgO), consisted of a zirconia tube and a two-phase mixture of Mo + MOO2. A molybdenum rod was used as an electrical contact to the reference electrode, while the electrical contact to the outer electrode of the zirconia probe was made by the liquid silver and a steel rod soldered to the iron crucible. The use of dissimilar electrical connectors required a correction for thermal electromotive force (emf) of a steelmolybdenum couple. I~l The experimental procedure consisted of measuring the open-circuit emfs of the oxygen probes and subsequently sampling the slag. Cell potentials generated were measured by a strip chart recorder of 2 M ohm internal impedance with an accuracy of --_0.1 mV and more accurately read by a digital voltmeter of 100 M ohm input impedance with an accuracy of -+0.01 mV. Samples of 2 to 3 g were withdrawn from the slag by dipping a steel rod in the molten slag for 2 to 3 seconds. The compositions of the samples were determined by wet chemical analysis. V. ESPEJO, Research Student, Department of Metallurgy, and M. IWASE, Associate Professor, Department of Energy Science and Engineering, are with Kyoto University, Kyoto 600, Japan. Manuscript submitted April 18, 1994. METALLURGICALAND MATERIALSTRANSACTIONS B

The slag compositions investigated in this study are given by 11 straight lines drawn in the ternary field of Figure 1. All the lines pass through the FexO apex; during a single experimental run, the molar ratio, Xc~o/X~,~2o~, within the bulk of the slag was kept constant. Attention was focused on slags of Xcao/X^1203 > 1/2. Binary phase diagrams for the systems CaO + A1203, [16l CaO + FexO, H71and FexO + AlzO~t~s] are also given in Figure 1. In order to increase the Fe~O concentrations, pellets of iron oxide were added and stirred into the melt. Mixtures of appropriate double oxides between CaO and A1203, depending upon C a O / m l 2 0 3 mole ratios, were also used for lowering the FexO concentrations. The preparation of double oxides was based on mixing CaCO3 with A1203 at requisite CaO/AI203 mole ratios and firing at 1673 K for 48 hours. A single experimental run with a fixe