Calcium deoxidation and nitrogen distribution in liquid nickel equilibrated with CaO-Al 2 O 3 slags
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INTRODUCTION
F O R the improvement of product cleanliness in Ni-hase alloys, the compositional and morphological control of nonmetallic inclusions is of primary importance. Thermodynamic analysis for the refining reactions, such as deoxidation in ladle practices, requires a knowledge on the effect of alloying elements on the activity coefficients of nonmetallic solutes in liquid nickel. However, the reported values of interaction parameters in Ni-alloy systemstml are very limited compared with those in Fe-alloy systems. Particularly, to the authors knowledge no published data on the interaction parameter between Ca and O in liquid nickel are available. The present authors recently assessed the f'wst-order and second-order interaction parameters between Ca and O in liquid iron at 1873 K t3] by using the datat4-8] obtained in slag-metal equilibrium experiments. In this study, based on the reciprocal relationships with respect to the interaction parameters on mass percent, t3~ the first-order and second-order interaction parameters between Ca and O in liquid nickel were estimated at 1873 K by equilibrating liquid nickel with the CaO-AIzO3 slags in an A1203 or CaO crucible. Furthermore, the valD3/4/DI/2~. ues for nitride capacity, C(N){= (mass pct N) "-02/-N~ J, for the CaO-A1203 slags were obtained by using the present results for nitrogen distribution ratio, Lr~ {=(mass pct N)/[mass pct N]}, and the aA~2o3values reported by Rein and Chipman. t9j
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EXPERIMENTAL
A. Procedure The master slags were prepared by premelting the mixtures of reagent-grade CaCO3 and A1203 in a platinum crucible under a dry air atmosphere. A verticalresistance furnace with heating bars of LaCrO3 was used. Thirty grams of pure Ni (
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