Phase Equilibrium Studies in the System CaO‐Cr ₂ O ₃ ‐SiO ₂

Results are presented of a study in air of mixtures in the system CaO‐Cr 2 O 3 ‐SiO 2 . The phase equilibrium diagram shows relations at liquidus temperatures for all but the high‐lime part of the system. In this omitted part chromium in the mixtures oxidizes in air to higher valence forms. The compound Ca 3 Cr 2 Si 3 O 12 (uvarovite) occurs at subsolidus temperatures, decomposing at 1370°C. to α‐CaSiO 3 and Cr 2 O 3 . The inhibiting action of chromium oxide on the inversion of high‐temperature forms of Ca 2 SiO 4 to the low‐temperature γ‐Ca 2 SiO 4 is discussed in the light of new data. Evidence is presented for the existence of a pentavalent chromium compound, Ca 3 (CrO 4 ) 2 , having solid‐solution relations with Ca 3 SiO 4 .