The System Manganese Oxide–Cr2O3 in Air

The quenching technique has been used to determine equilibrium relations in the system manganese oxide-Cr₂O₃ in air in the temperature range 600° to 1980°C. The following isobaric invariant situations have been determined: At 910°± 5°C tetragonal Mn₃O₄ solid solution, cubic Mn₃O₄ solid solution (=spinel), Mn₂O₃ solid solution, and gas coexist in equilibrium. Cubic Mn₃O₄ solid solution, Cr₂O₃ solid solution, liquid, and gas are present together in equilibrium at 1970°± 20°C. The invariant situation at which cubic Mn₃O₄ solid solution, Mn₂O₃ solid solution, Cr₂O₃ solid solution, and gas exist together in equilibrium is below 600°C.     

Phase Equilibria at Liquidus Temperatures in the System Iron Oxide–Al2O3–SiO3 in Air Atmosphere

Liquidus temperatures, obtained by the quenching technique, are presented for mixtures in the system iron oxide–Al₂O₃–SiO₂ in air atmosphere. Approximate compositions of crystalline phases in equilibrium with liquids have been determined, and paths of equilibrium crystallization are discussed briefly. Application of the phase diagram to refractories problems is indicated.     

Phase Equilibria at Liquidus Temperatures in the System MgO-FeO-Fe2O3-SiO2

Liquidus temperatures are presented for mixtures in the system MgO-FeO-Fe₂O₃-SiO₂. The standard quenching technique was modified for work under controlled atmospheres of varying O₂ pressures. Data were obtained for the temperature range 1159° to 1775°C., and with O₂ pressures ranging from 1 to 10^-8.⁹ atm. Approximate compositions of crystalline phases were determined, and paths of equilibrium crystallization were derived for selected mixtures under idealized conditions. Application of the phase diagrams to steel-plant refractories problems is indicated.     

Phase Equilibria in the System MgO—FeO—Fe2O2, in Temperature Range 1400° to 1800°C

Equilibrium relations in isothermal sections through the system MgO-FeO-Fe₂O₃ have been determined in the temperature range 1400° to 1800°C. Oxide mixtures prepared from reagent-grade chemicals were equilibrated and subsequently quenched to room temperature while sealed in 80Pt20Rh tubes. The data obtained for the isothermal sections are used to infer equilibrium relations existing along the liquidus surface of the system.     

Phase Equilibrium Relationships at Liquidus Temperatures in the System FeO–Fe2O3–Al2O3–SiO2

Phase equilibrium data at liquidus temperatures are presented for mixtures in the system FeO–Fe₂O₃–Al₂O₃–SiO₂. The volume located between the 1 and 0.2 atm. O₂ isobaric surfaces of the tetrahedron representing this system was studied in detail. Scattered data were obtained at lower O₂ pressures. Results obtained in the present investigation were combined with data in the literature to construct a phase equilibrium diagram, at liquidus temperatures, for the entire system FeO–Fe₂O₃–Al 2 O₃–SiO₂. Methods for interpretation of the diagram are explained.     

Activity-Composition Relations in Co2SiO4-Fe2SiO4 Solid Solutions at 1180°C

Activity-composition relations of cobalt orthosilicate in cobalt-iron-orthosilicate solid solutions were determined at 1180°C by studying the equilibrium between these solid solutions, silica, metallic cobalt, and a gas phase of known oxygen pressures. The solution shows a slight positive deviation from ideality.     

Melting Relations of Magnesium Oxide-Iron Oxide Mixtures in Air

The quenching technique has been used to investigate phase relations in the liquidus temperature region of a part of the system magnesium oxide-iron oxide. The study concerns primarily the nature of the melting behavior of the spinel phase magnesioferrite, "MgO-Fe₂O₃." This phase is shown to decompose at 1713°± 5°C. to a magnesiowüstite solid solution phase and liquid, under equilibrium conditions in air.     

Phase Diagrams for the Systems Si-O and Cr-O

Equilibrium studies in the systems Si-O and Cr-O at high temperatures indicate that no stable intermediate compounds exist between the metals and the oxides, SiO₂ or Cr₂ O₃, up to solidus temperatures. In both systems, there is a large concentration range of coexistence of two liquid phases above liquidus temperatures.     

Phase Equilibria in the System CaO-Iron Oxide-SiO2, in Air

Phase equilibrium relations in the liquidus temperature region of the system CaO-iron oxide-SiO₂ in air were determined, using the quenching technique. The results are illustrated by means of a projection of the liquidus surface onto the composition triangle CaO-Fe₂O₃-SiO₂. A supplementary diagram is presented in order to indicate true compositions of liquids at liquidus temperatures. Data obtained in the present investigation are combined with literature data to construct diagrams showing stability relations among crystalline phases at subsolidus temperatures. A diagram is also presented to show phase relations along the join CaO SiO₂-2CaO Fe₂O₃.     

Stability of Mullite as Derived from Equilibria in the System CoO-Al2O3-SiO2

The free energy of reaction for the formation of mullite from its oxide components was derived from equilibrium studies in the system CoO-Al₂O₃-SiO₂. Within this system there appears, at solidus temperature in a certain composition area, the phase assemblage mullite + silica + spinel (= cobalt aluminate) + liquid. Determination of the oxygen pressure of a gas phase at which metallic cobalt precipitates from this phase assemblage and from the phase assemblage spinel (= cobalt aluminate) + corundum in the system CoO-Al₂O₃ permits calculation of ΔG° for the reaction 3Al₂O₃+ 2SiO₂= Al₆Si₂O₁₃. The value obtained at 1422°C is -5.8 kcal.