Phase Relations in the System Cr₂O₃-MgO-TiO₂ in Air at 1400°C

Abstract

Phase relations and solid solubilities in the system Cr₂O₃-MgO-TiO₂ were determined in air at 1400°C. The results obtained were as follows: (1) In the binary MgO-TiO₂ system, TiO₂, MgTi₂O₅, MgTiO₃, Mg₂TiO₄ and MgO existed and no solid solubilities could be detected in their compounds, (2) in the system Cr₂O₃-MgO, Cr₂O₃ could be soluble up to 8wt% into MgO and MgO also soluble up to a few percents into Cr₂O₃. Cr₂O₃ and MgO could not enter into MgCr₂O₄ lattice to form solid solution, (3) the formation of the complete solid solution between MgCr₂O₄ and Mg₂TiO₄ was confirmed, (4) the solubility of TiO₂ into MgCr₂O₄ was 16wt%, (5) the solubility of MgO into Cr₂Ti₂O₇ was 2wt%, (6) a new ternary compound (referred to as A in the present work) was found in Cr₂O₃-MgO-TiO₂ system at the composition of Cr₂O₃:MgO:TiO₂=51.0:5.0:44.0 (in wt%) (3:1:5 in mole ratio), (7) the phase diagram of the system Cr₂O₃-MgO-TiO₂ at 1400°C in air was composed of seven regions; MgO-MgCr₂O₄⋅Mg₂TiO₄ spinel solid solution, MgCr₂O₄⋅Mg₂TiO₄ spinel solid solution-MgTi₂O₅, A-MgCr₂O₄ solid solution-MgTi₂O₅, A-MgCr₂O₄ solid solution-Cr₂O₃ solid solution, A-Cr₂O₃ solid solution-Cr₂Ti₂O₇ solid solution, A-Cr₂Ti₂O₇ solid solution-MgTi₂O₅, and Cr₂Ti₂O₇ solid solution-TiO₂ solid solution-MgTi₂O₅.