Activity of titanium oxide was determined in CaO-SiO 2 -Ti 3 O 5 slags in the composition range 25-44% CaO, 30-46% SiO 2 , 10-39% TiO 1.67 at 1600 • C using electromotive force method.In the experiments, slags with different titanium oxide contents were equilibrated with liquid iron at 1873 K. Oxygen activity in the iron melt was measured and used with the titanium content in the metal to calculate titanium oxide activity in the slag. According to the results, it was concluded that the activity coefficient of titanium oxide (γ TiO 1.67 ) is in the range of 0.39 to 1.68 depending on the titanium oxide content and slag basicity. It was evident from the experiments that the activity coefficient increases with the increase in basicity and tends to decrease with increasing SiO 2 .

Oxidation state of titanium was determined in CaO‐SiO2‐TiOx slags in the composition range 25‐53 percent CaO, 27‐46 percent SiO2, 10‐55 percent TiOx at 1873K using gas equilibration method. In the experiments, slags with different titanium oxide contents were equilibrated with a known carbon monoxide and carbon dioxide ratio. The results were used to determine the Ti3+ and Ti4+ contents as well as the activity coefficient ratio of corresponding oxides in the slag. The dependence of the activity coefficient ratio as a function of oxygen partial pressure was determined.