Experimental Study on the Phase Relations of the SiO2-MgO-TiO2 System in Air at 1500°C

We investigated the phase relations of the SiO2-MgO-TiO2 system in air at 1500°C using the high-temperature isothermal equilibration/quenching technique, followed by x-ray diffraction measurements and direct phase analysis using scanning electron microscopy coupled with x-ray energy dispersive spectrometry. One single liquid phase domain, five two-phase domains (liquid-TiO2, liquid-cristobalite, liquid-MgO·SiO2, liquid-2MgO·SiO2, and liquid-MgO·2TiO2), and five three-phase regions (liquid-TiO2-MgO·2TiO2, liquid-MgO·SiO2-cristobalite, liquid-TiO2-cristobalite, liquid-MgO·SiO2-2MgO·SiO2 and liquid-2MgO·SiO2-MgO·2TiO2) were observed. We constructed a 1500°C isothermal phase diagram based on the experimentally measured liquid compositions. We compared simulations using MTDATA and FactSage thermodynamic software and their databases with the experimental results obtained in this study. These results can be used to provide guidelines for updating the MTDATA and FactSage titania-bearing thermodynamic databases by reassessing the thermodynamic properties of the phase with new experimental data.

Phase Stabilities in Some B2 Type Ordered Ni-Al-X Alloys

The difference in developing of solubility lobe (s.l.) of B2 phase from the B2 NiAl point on each isothermal phase diagram of Ni-Al-Co, Ni-Al-Fe and Ni-Al-Mn is expected to be explained in terms of the pattern of free energy minimum (f.e.m.) line in the B2 phase region of these phase diagrams. To calculate such the f.e.m. line, a simple way has been proposed based on the tetrahedron approximation of the cluster variation method (CVM) making use of a relationship to correlate the conventional chemical potential of a species with some kinds of the CVM variables. The calculated results show that the f.e.m. line well reflects the solubility lobe developing of the B2 phase for both Ni-Al-Fe and Ni-Al-Co while some disagreement arises with Ni-Al-Mn. The results also show a theoretical possibility of transition from the high ordered state B2 to a low ordered one under a relatively low temperature regime so far as the present free energy model are concerned.

Thermodynamic rationalization of molten-salt clectrodeposition in oxide-based systems

Electrodeposition from molten-salt systems has been studied extensively as a method of producing both polycrystalline and single-crystalline materials. In this work, the thermodynamic aspects of the electrodeposition process are examined in a number of cases in which the molten-salt system behaves effectively as an oxygen-transporting medium, with particular reference to the thermodynamic properties of the melt. It is demonstrated how information gained from the construction of the appropriate isothermal phase diagram may be used to control and/or rationalize the behavior found in a given melt system on electrolysis.

Low- to medium-grade metamorphism in silicate iron-formations of the Cape Smith Belt, New Quebec

Four different assemblages of iron-rich silicates from the silicate iron-formation of the Cape Smith belt in New Quebec have been investigated. These rocks all contain quartz, magnetite, some calcite, and are composed mostly of two or more of the following silicates: stilpnomelane, minnesotaite, iron chlorite, grunerite, almandite, and biotite.From eight chemical analyses and petrographic examination, using a method developed by J. B. Thompson, an isothermal phase diagram of the system Al2O3–Fe2O3–FeO–MgO–SiO2–H2O has been constructed for the upper part of the greenschist facies of metamorphism.Speculation based on this diagram and on available experimental data is offered on the sequence of reactions leading to the assemblages observed, and on the possibility of finding mineral assemblages representing invariant points in metamorphosed iron-formations.