2019 Volume 59 Issue 7 Pages 1205-1213
A study has been carried out to measure the solubility of oxygen in a molten Ni–Cr alloy contained in a MgO crucible in equilibrium with CaO–SiO2–MgO–Cr2O3 system slag. It was found that oxygen content increased with increasing Cr content in the range between 2 and 40 mass%.
According to SEM observation along with EDS analysis, the oxide phases in the slag consisted of MgO·Cr2O3 crystals and CaO–SiO2–MgO slicate phases. In the crucible close to the surface in contact with the molten alloy and the slag, almost pure MgO phases were observed in addition to the above two phases. Therefore, it was confirmed that soluble oxygen in the molten Ni–Cr alloy was supplied by decomposition of the MgO·Cr2O3 phase as MgO·Cr2O3(s) = MgO(s) + 2Cr + 3O. Consequently, thermodynamic analysis led to the interaction coefficient of = −0.162±0.012 (Cr: 2–5 mass% in reference to Ni) and −0.044±0.001 (Cr: 5–40 mass% in reference to Ni-5%Cr) available in molten Ni.