Effects of Titanium Oxide on Equilibria Among Refractory Phases in the System CaO‐MgO‐Iron Oxide

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Abstract
The role of titanium oxide in some important refractory systems was elucidated by studying selected equilibria in the system CaO‐MgO‐iron oxide‐titanium oxide at O2 pressures of 0.21 atm (air) and 10−9 atm and under the extreme reducing conditions imposed by the presence of metallic Ti in contact with the oxide phases. Solidus relations were determined for the system CaO‐MgO‐TiO2 in air; 6 composition triangles were delineated, within each of which 3 crystalline phases coexist in equilibrium with liquid at a constant solidus temperature. The solidus temperatures range from 1407° to 1670°C. There is also a composition area within which MgO coexists with a Ca4Ti3O10‐Ca3Ti2O7 solid solution, with solidus temperatures varying continuously from 1659° to 1670°C. Studies of reactions between MgO and titanium oxide in contact with metallic Ti in a closed system indicate that the mutual solubility between MgO and TiO at 1400°C is very small. Addition of 5 wt% TiO2 to the system CaO‐MgO‐iron oxide at 1500°C in air and in 10−9 atm O2 decreases the amount of iron oxide which can be absorbed by a CaO‐MgO body without formation of a liquid phase; hence, titanium oxide has a strong deleterious effect on the refractoriness of such bodies.

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