Effects of transition metals on the kinetics of slag-refractory reactions
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INTRODUCTION
ALUMINA-BASED refractories are commonly used in secondary steelmaking processes. These refractories have high resistance to mechanical erosion and chemical corrosion by the liquid steel, but can suffer from severe chemical attack by the slag phase. Consequently, refractory wear at the “slag line” usually determines their service life. At BHP Steel’s Long Product Division in Whyalla some severe wear of the alumina-based refractory material used in the injection refining up temperature (IRUT) process was observed around the slag line. In this processing step, the temperature of the liquid steel is raised through aluminothermic reaction by submerged injection/oxidation of aluminum with oxygen. The degree of wear in the alumina snorkel was found to be variable and apparently related to the steel grade. It was found that the treatment of high carbon grades caused a greater degree of erosion of the snorkel than the low or medium carbon grades. Table I shows the typical composition of the slag for the three grades of steel. The major differences between the slag chemistries of the high carbon grades and those of low and medium carbon grades are the Al2O3 content, CaO/SiO2 ratios, and the concentrations of FeOx and MnOx. These differences are due to the deoxidation practices used, i.e., the high carbon grades are deoxidized by additions of ferromanganese and ferrosilicon, while the other grades are aluminum killed. Analysis of the slag chemistry, with respect to the thermodynamic driving force for dissolution of alumina, revealed that in all cases the magnitude of the driving force is similar and large enough to not cause any significant difference in the dissolution rate of the alumina refractory. Given that the rate of such reactions is also dependent on the transport and interfacial properties of the reactants, it MARK LEE, Senior Technologist, formerly with BHP Research is now with the Corus-Teesside Technology Centre, Grangetown, TS6 6UB, United Kingdom. SHOUYI SUN, Principal Research Scientist, STEVEN WRIGHT, Senior Experimental Scientist, and SHARIF JAHANSHAHI, Chief Research Scientist and Manager Base Metal Pyrometallurgy, are with CSIRO Minerals, Victoria 3169, Australia. Manuscript submitted April 25, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
was decided to investigate the dependence of the dissolution rate of alumina on slag chemistry. Previous work on the kinetics of dissolution of single[1] and polycrystalline alumina[2] in calcium aluminosilicate melts at temperatures up to 1550 ⬚C has shown that the rates obtained from single crystals of sapphire are not much different than those from polycrystalline alumina under stagnant or forced convection regimes. The measured rates are in good accord with the expected rate for diffusion/mass transfer in the slag phase. Furthermore, the effective diffusivities derived from these results are in good agreement with the relatively low value of tracer diffusivity (⬃5 ⫻ 10⫺7 cm2/s at 1550 ⬚C) in such slags.[3,4,5] Olsson et al.,[6] used a rotating disc o
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