The System SrO - "Chromium Oxide" in Air and Oxygen.

Phase relations in the system SrO-"chromium oxide" were determined in air and 1 atm O (1 atm = 1.013 × 10 N/m) and are shown as isobaric projections on the SrO-CrO pseudobinary. At both oxygen pressures, the system consists of three joins in the SrO-CrO-oxygen ternary, (1) SrO-SrCrO, (2) SrCrO-SrCrO, and (3) SrCrO-CrO. The former is binary from 1065 °C to liquidus temperatures in air and includes a eutectic near 79 mol percent SrO (in terms of SrO-CrO starting materials). SrCrO melts congruently at 1453 °C. Below 1065 °C in air, phase relations are complicated by reactions with atmospheric water vapor resulting in the formation of SrCrO (OH) which decomposes to SrO and SrCrO above 1065 °C. In air, below 775 °C, SrCrO reacts with water vapor and oxygen to form SrCrO (OH) and SrCrO. Water vapor reactions are restricted in 1 atm O. The SrCrO-SrCrO join contains a binary eutectic between 69-70 mol percent SrO but liquidus relations are ternary below 69 (air) and 68 (oxygen) mol percent SrO, as reduction of Cr occurs. Likewise, the SrCrO-CrO join is not binary at solidus and liquidus temperatures. In air, SrCrO melts at 1251 °C to CrO plus liquid with release of oxygen. In oxygen, the compound melts at 1283 °C with evolution of oxygen.