Activity coefficient of nickel oxide in BaO-based slags
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Table I.
Activity Coefficient of Nickel Oxide in BaO-Based Slags KENJI MATSUZAKI, TADASHI YAMAGUCHI, and KIMIHISA ITO BaO-based slag has lately attracted considerable attention because of its high refining ability for dephosphorization and desulfurization of steel. Determination of the thermodynamic property of nickel oxide in this slag system is valuable in view of the refinement of nickel-containing melts using the slag-metal reaction. In the present work, activity coefficients of nickel oxide in BaO-BaF2, BaO-BaCl2, and BaO-B2O3 slags were measured by a chemical equilibration technique. Slag samples were prepared by mixing reagent grade BaO, BaF2, BaCl2, and B2O3. The slag was equilibrated with a nickel crucible under a selected oxygen potential, which was controlled by a flowing CO-CO2 gas mixture (PO2 5 3.12 3 1029 atm). A SiC electric resistance furnace was used for the equilibrium experiments at 1573 K. The equilibration time was predetermined as 8 hours. After equilibrium was attained, the crucible was quenched in water. The slag sample was crushed, ground to powder, and analyzed. Nickel concentration in slags was determined by inductively coupled plasma (ICP) emission spectrometry. Since the solubility of nickel oxide is proportional to [1] P1/2 the equilibrium reaction among slag-metal-gas is exO2 , pressed as Eq. [1]. Its standard Gibbs free energy change and equilibrium constant are given in Eqs. [2] and [3], respectively. 1 Ni (s) 1 O2 (g) 5 NiO (s) 2
[1]
DG 71 5 2234,310 1 84.95T (J/mol)[2]
[2]
K1 5
aNiO g X 5 NiO 1/2NiO 1/2 aNiP O2 P O2
[3]
Since a pure nickel crucible was used, the activity of nickel, ai, was unity. The mole fraction of NiO, XNiO, was experimentally measured, and PO2 was calculated from the mixing ratio of CO/CO2. The Raoultian activity coefficient of nickel oxide, gNiO, was thus obtained, where pure solid NiO was taken as the standard state. The solubility of carbon dioxide in BaO-BaF2 and BaOBaCl2 slags was calculated using the available carbonate capacity.[3,4] All the dissolved CO2 was assumed to be barium carbonate. The calculated CO2 concentrations were alKENJI MATSUZAKI, Research Associate, and KIMIHISA ITO, Professor, are with the Department of Materials Science and Engineering, Waseda University, Tokyo 169-0072, Japan. TADASHI YAMAGUCHI, formerly Graduate Student, Department of Materials Science and Engineering, Waseda University, is Engineer with Hitachi Metals Ltd., Shimane 692-0011, Japan. Manuscript submitted July 6, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
Experimental Results of BaO-BaF2 Slag at 1573 K Slag Composition
Sample Number
XBaO
XBaCO3
XBaF2
XNiO 3 103
Log gNiO
1 2 3 4 5 6 7 8
0.026 0.039 0.052 0.064 0.077 0.089 0.101 0.124
0.086 0.128 0.170 0.211 0.251 0.290 0.330 0.406
0.886 0.831 0.776 0.722 0.668 0.616 0.564 0.464
1.03 1.62 2.18 3.02 4.18 5.00 4.51 6.33
2.08 1.88 1.75 1.61 1.47 1.39 1.44 1.29
Table II. Experimental Results of BaO-BaCl2 Slag at 1573 K Slag Composition
Sample Number
XBaO
XBaCO3
XBaC12
XNiO 3 103
Log gNiO
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