Phase Relations in the System Iron Oxide—Cr ₂ O ₃ in Air

The quenching method has been used to determine approximate phase relations in the system iron oxide‐Cr 2 O 3 in air. Only two crystalline phases, a sesquioxide solid solution (Fe 2 O 3 –Cr 2 O 3 ) with corundum structure and a spinel solid solution (approximately FeO ·Fe 2 O 3 –FeO – Cr 2 O 3 ), occur in this system at conditions of temperature and O 2 partial pressure (0.21 atm.) used in this investigation. Liquidus temperatures increase rapidly as Cr 2 O 3 is added to iron oxide, from 1591°C. for the pure iron oxide end member to a maximum of approximately 2265°C. for Cr 2 O 3 . Spinel(ss) is the primary crystalline phase in iron oxide‐rich mixtures and sesquioxide (ss) in Cr 2 O 3 –rich mixtures. These two crystalline phases are present together in equilibrium with a liquid and gas (po 2 = 0.21 atm.) at approximately 2075°C.