Activity--Composition Relations of Chromium Oxide in Silicate Melts at 1500 deg C Under Strongly Reducing Conditions

The solubility and activity--composition relations of chromium oxide in melts of the systems CaO--CrO sub x --SiO sub 2 and CaO--Al sub 2 O sub 3 --CrO sub x --SiO sub 2 have been determined at 1500 deg C by equilibrating melts with Pt--Cr alloys at known oxygen pressures. It is shown that the increase in the concentration of divalent Cr ions, as the O pressure and the basicity of the melt decrease, results in a dramatic increase in the solubility of chromium oxide in the liquid phase. An increase in the Al sub 2 O sub 3 content of the melt leads to a decrease in the solubility of chromium oxide over the whole composition range studied. The activity coefficient of CrO has been found to increase with increasing melt basicity and decreasing O pressure, whereas the activity coefficient of CrO sub 1.5 decreases sharply with increasing melt basicity for siliceous melts but levels off at a basicity ratio (wt.% CaO/wt.% SiO sub 2 ) of approx 0.7. An increase in the Al sub 2 O sub 3 content of the melts results in an increase in the activity coefficient of CrO.