Phase Equilibrium Studies in the System Iron Oxide-Al2O3-Cr2O3

Subsolidus phase relations in the system iron oride-Al₂O₂-Cr₂O₃ in air and at 1 atm. O₂ pressure have been studied in the. temperature interval 1250° to 1500°C. At temperatures below 1318° C. only sesquioxides with hexagonal corundum structure are present as equilibrium phases. In the temperature interval 1318° to 1410°C. in air and 1318° to 1495° C. at 1 atm. O₂, pressure the monoclinic phase Fe₂O₃. Al₂O₃ with some Cr₂O₃ in solid solution is present in the phase assemblage of certain mixtures. At temperatures above 1380°C. in air and above 1445°C. at 1 atm. O₂ pressure a complex spinel solid solution is one of the phases present in appropriate composition areas of the system. X-ray data relating d- spacing to composition of solid solution phases are given.     

Phase Equilibrium Studies in the System Iron Oxide- A12O3 in Air and at 1 Atm. O2 Pressure

Phase equilibrium data, obtained by using the quenching technique, are presented for the system iron oxide-A1₂O₃ in air and at 1 atm. O₂ pressure in the temperature interval 1085° to 1725°C. Stability ranges of the various phases are delineated, and approximate compositions of crystalline and liquid phases are determined. Special attention is focused on the phase Fe₂O₃·A1₂O₃(ss) and its stability relationships.     

Phase Relations at Liquidus Temperatures in the System MgO-NiO-SiO2

The well-known "quenching technique" has been used to determine liquidus and solidus phase relations in the system MgO-NiO-SiO₂. Oxide mixtures were heated at selected temperatures for sufficient lengths of time for attainment of equilibrium, followed by quenching to room temperature, and phase identification by optical microscopy (transmitted-and reflected-light examination) and X-ray diffraction. Two ternary liquidus invariant points are present in the system. One is characterized by the coexistence of pyroxene (Mg-SiO₃-NiSiO₃ solid solution), olivine (Mg₂SiO₄-Ni₂SiO₄ solid solution), silica (cristobalite), and liquid at 1547°C. The other eutectic is at 1633°C and is characterized by the coexistence of olivine, oxide (MgO-NiO solid solution), silica, and liquid. There is a temperature maximum on the olivine-silica liquidus boundary curve at 1639°C. Reversals in the distribution ratios of magnesium and nickel between solid and liquid phases coexisting in equilibrium during crystallization of melts in this system may occur, depending on the compositions of the mixtures.     

Reactions Between Iron Oxides and Alumina-Silica Refractories

Phase equilibrium data for the system FeO– Fe₂O₃–Al₂O₃–SiO₂ are used to evaluate the attack of iron oxides on alumina-silica refractories under various idealized conditions which approach those occurring in practice. The extent of attack and the nature of the reactions at various levels of O₂ pressure are discussed.     

Phase Relations in the System FeO-Fe2O3-ZrO2-SiO2

Phase equilibrium relations in the liquidus-temperature region of the system iron oxide-ZrO₂-SiO₂ in air were delineated by the quenching technique. Additional equilibration runs were made at other controlled oxygen pressures as well as in sealed containers. The results of all runs have been combined with literature data for the system in contact with metallic iron to locate approximately the quaternary liquidus invariant points within the system FeO-Fe₂O₃-ZrO₂-SiO₂.     

Melting Relations of CaO-Manganese Oxide and MgO-Manganese Oxide Mixtures in Air

Melting relations in the systems CaO-manganese oxide and MgO-manganese oxide in air have been determined at temperatures up to 1705°C. In the system CaO-manganese oxide four crystalline phases have stable existence in equilibrium with liquids: lime (approximate composition CaO-MnO), spinel (approximate composition Mn₃O₄-CaMn₂O₄), and two ternary solid solution phases in which Ca/Mn ratios as well as oxygen contents vary over considerable ranges. One of these ternary solid solution phases may for the sake of simplicity be represented approximately by the formula CaMnO₃ and the other by the formula CaMn₂O₄. Three isobaric invariant situations exist, with temperatures and phase assemblages as follows: At 1588°± 10°C the two crystalline phases lime and CaMnO₃ coexist in equilibrium with liquid (40 wt% CaO, 60 wt% manganese oxide) in a peritectic situation. Another peritectic at 1455°± 5°C is characterized by the equilibrium coexistence of CaMnO₃, CaMn₂O₄, and liquid (25 wt% CaO, 75 wt% manganese oxide). A eutectic situation exists at 1439°± 5°C with CaMn₂O₄, spinel, and liquid (18 wt% CaO, 82 wt% manganese oxide) present together in equilibrium. In the system MgO-manganese oxide in air periclase-manganosite solid solution (approximate composition MgO-MnO) and spinel (approximate composition Mn₃O₄-MgMn₂O₄) are the only crystalline phases present in equilibrium with liquids. Liquidus and solidus temperatures increase with increasing MgO content. A peritectic situation exists at 1587°± 10°C, with the two crystalline phases coexisting in equilibrium with liquid (1 wt% MgO, 99 wt% manganese oxide).     

Phase Equilibria in the System MnO-"FeO"-ZrO2-SiO2

Phase equilibrium relations in the liquidus temperature region of the system MnO-"FeO"-ZrO₂-SiO₂ and of its bounding systems MnO-ZrO₂, MnO-ZrO₂-SiO₂, and MnO-"FeO"-ZrO₂ were determined by the quenching technique. The equilibrations were carried out at sufficiently low O₂ pressures to keep most of the Mn and Fe in divalent states. The results obtained were combined with literature data for the other bounding binary and ternary systems to present phase diagrams showing liquidus surfaces and interrelations between coexisting liquid and solid-solution phases. Applications of the data to refractory problems are discussed.     

The System Manganese Oxide–Alumina in Air

The quenching technique has been used to determine equilibrium relations among the various phases in the system manganese oxide-alumina in air in the temperature range 800° to 1765°C. Three isobaric invariant situations have been determined, as follows: Tetragonal Mn₂O₃ solid solution, Mn203 solid solution, corundum, and gas (PO₂= 0.21 atm) coexist in equilibrium at 881°± 5°C. Tetragonal Mn₃O₄ solid solution, spinel solid solution, corundum, and gas are the phases present together in equilibrium at 990°± 5°C. Spinel solid solution, corundum, liquid, and gas coexist in equilibrium at 1740°± 10°C.     

Phase Equilibria in the System CaO-MgO-Iron Oxide at 1500°C

Phase relations in the system CaO-MgO-iron oxide were determined at 1500°C at two levels of oxygen pressure, 10^–9 atm and 0.2 atm (air). Particular attention was directed toward de termining the maximum amount of iron oxide which may be tolerated in CaO-MgO-iron oxide bodies before a liquid phase forms under equilib rium conditions at the two chosen oxygen pres sures. Inferences are made regarding the possible bearing of the results on the perform ance of tar-bonded dolomite brick used in steel making furnaces.     

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.