The Solubility of MgO-Cr
2O
3 in MgO-Al
2O
3-SiO
2-CaO Slag and the activilies of chromium oxide in the slags were measiredat 1 600°C under Reducing conditions. For MgO-SiO
2 melts which were saturated with 2MgO·SiO
2, the solubility of MgO·Cr
2O
3 increased with decreasing oxygen partial pressure, because of decrease in γ
CrO1.5.When CaO is added to the melts mentioned above, soluble total chromium content decreased because γ
CrO1.5 and γ
CrO increased with increasing CaO content in the melts.
Under a fixed oxygen partial pressure, activities of chromium oxides in the chromite MgO·(Cr
xAl
1-x)
2O
3 were also measured by equilibrating them with Ni-Cr alloys for which the activity coefficient γ°
Cr(at 1 600°C) was determined as 0.421 in this study. It was found that the free energy change of the reaction : MgO(s)+Cr
2O
3(s) = MgO·Cr
2O
3(s) is expressed by-126 800+47.3
T (J/mol) and that MgO·Cr
2O
3 and MgO·Al
2O
3 form a solid solution which exhibits negative deviation from ideal behavior at 1600°C.
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