Silica Solubility and the Activity of MnO in MnO-SiO 2 Slags
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Nomenclature
Silica Solubility and the Activity of MnO in MnO-Si~ Slags
the slag. Also shown in Fig. 1 are points obtained in an earlier study by Turkdogan and Hancock' which again indicate a discontinuity at about 0.165 mole fraction of Si. The reason for the different behavior of the relation above 0.165 mole fraction of Si is probably due to approach to equilibrium from high Si contents of the alloy in the present study but from high Si02 contents of the slag in the study of Turkdogan and Hancock. The intersection of the three lines in Fig. 1 enables an accurate determination of the Si0 2 solubility at 1450°C of 0.56 mole fraction. The solubility is con-
W.J. RANKIN
The commonly accepted MnO-Si0 2 phase diagram of Glasser1 indicates a solubility of Si02 at 1450°C considerably lower than found by the author during a recent study of the equilibrium of Mn-Si-C (sat) alloys with MnO-Si0 2 slags. High purity Mn and Si were melted in graphite crucibles with MnO-Si0 2 slags at 1450°C under a pure carbon monoxide atmosphere as part of a study of the slag-metal equilibrium in high carbon ferromanganese production. Slag-metal equilibrium was attained in under 4 h and all runs were carried out for at least 5 h. As expected from the equation: 2 (MnO) + [Si]
Convective mass transfer coefficient. Diam of a reaching particle. Binary gas diffusion coefficient. Binary gas diffusion coefficient in a porous product layer. Effective binary gas diffusion coefficient in a porous product layer. Effective binary diffusion coefficient for H2/H20 gas mixtures in porous product iron. Radius of a reacting particle. Sherwood number (= ad/D). Parameter termed by Sohn as a modified Sherwood number (= aro/D e). Mass transfer resistance due to the diffusion of hydrogen in the porous iron.
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1. R. H. Spitzer, F. S. Manning, and W. O. Philbrook: Trans. TMS-AIME, 1966, vol. 236, p. 726. 2. A. W. D. Hills: Heat and Mass Transfer in Process Metallurgy, A. W. D. Hills, ed., pp. 39-77, London Inst. Min. Met., 1967. 3. E. T. Turkdogan and J. V. Winters: Met. Trans., 1971, vol. 2, pp. 3175-88. 4. A. W. D. Hills: Heterogeneous Kinetics at Elevated Temperatures, G. R. Belton and W. L. Worrell, eds., pp. 449-501, Plenum Press, 1970. 5. A. W. D. Hills: Chern. Eng. 1968, vol. 23, pp. 297-320. 6. F. Sadrehasherni: Ph.D. Thesis, London University, 1977. 7. A. G. Matyas and A. V. Bradshaw: IronmakingSteelmaking, 1974, vol. 1, pp. 180-87.
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= 2 [Mn] + (Si0 2 )
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the equilibrium Si0 2 content of the slag was found to increase as the Si content of the alloy was increased. The variation is shown in Fig. 1. For Si contents of metal greater than about 0.165 mole fraction the curve is horizontal indicating the saturation level of Si0 2 in W. J. RANKIN, formerly with the National Institute for Metallurgy, Johannesburg, is now Senior Lecturer in Extractive Metallurgy, University of Stellenbosch, Stellenbosch, 7600 South Africa. Manuscript submitted May 24, 1978.
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