Phase relations and gibbs energies in the system Mn-Rh-O

Phase relations in the system Mn-Rh-O are established at 1273 K by equilibrating different compositions either in evacuated quartz ampules or in pure oxygen at a pressure of 1.01 × 10⁵ Pa. The quenched samples are examined by optical microscopy, X-ray diffraction, and energy-dispersive X-ray analysis (EDAX). The alloys and intermetallics in the binary Mn-Rh system are found to be in equilibrium with MnO. There is only one ternary compound, MnRh₂O₄, with normal spinel structure in the system. The compound Mn₃O₄ has a tetragonal structure at 1273 K. A solid solution is formed between MnRh₂O₄ and Mn₃O₄. The solid solution has the cubic structure over a large range of composition and coexists with metallic rhodium. The partial pressure of oxygen corresponding to this two-phase equilibrium is measured as a function of the composition of the spinel solid solution and temperature. A new solid-state cell, with three separate electrode compartments, is designed to measure accurately the chemical potential of oxygen in the two-phase mixture, Rh + Mn_3−2xRh_2xO₄, which has 1 degree of freedom at constant temperature. From the electromotive force (emf), thermodynamic mixing properties of the Mn₃O₄-MnRh₂O₄ solid solution and Gibbs energy of formation of MnRh₂O₄ are deduced. The activities exhibit negative deviations from Raoult’s law for most of the composition range, except near Mn₃O₄, where a two-phase region exists. In the cubic phase, the entropy of mixing of the two Rh³⁺ and Mn³⁺ ions on the octahedral site of the spinel is ideal, and the enthalpy of mixing is positive and symmetric with respect to composition. For the formation of the spinel (sp) from component oxides with rock salt (rs) and orthorhombic (orth) structures according to the reaction, MnO (rs) + Rh₂O₃ (orth) → MnRh₂O₄ (sp),ΔG° = -49,680 + 1.56T (±500)J mol⁻¹ The oxygen potentials corresponding to MnO + Mn₃O₄ and Rh + Rh₂O₃ equilibria are also obtained from potentiometric measurements on galvanic cells incorporating yttria-stabilized zirconia as the solid electrolyte. From these results, an oxygen potential diagram for the ternary system is developed.     

Phase equilibria in the system HfO2-Y2O3-La2O3 AT 1900°C

We have used x-ray phase analysis, electron-probe microanalysis, petrography, and electron microscopy on annealed specimens to study phase equilibria in the ternary system HfO₂-Y₂O₃-La₂O₃ at 1900 °C over the entire concentration range. We have plotted the isothermal cross section of the phase diagram for this system at the indicated temperature. We found 23 phase regions. A typical feature of the system is formation of solid solutions based on different crystal modifications of the starting components (A-and H-La₂O₃, C-Y₂O₃, T-and F-HfO₂) and also the compounds La₂Hf₂O₇, LaYO₃. We did not observe new phases in the system. The nature of the phase equilibria in the system is consistent with the high relative thermodynamic stability of lanthanum hafnate (ΔH °La₂Hf₂O₇ ≈ 100 kJ/mole) compared with LaYO₃. We established that adding a third component extends the thermal stability region for the ordered phase of LaYO₃ toward higher temperatures. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 73–87, January–February, 2006.     

Phase equilibria in the system Fe-Mo-Cl-H-O

Conclusions Under the conditions we dealt with, only wQstlte is stable in the system Fe-Mo-O while molybdenum is reduced and passes into the solution. Practically with all compositions of the solid solution iron is predominantly chlorinated, and it passes into the molybdenum. Therefore the alloy iron-molybdenum can be obtained through the chloride phase only by chlorination of pure molybdenum. Chlorination of iron oxides and molybdenum oxides in the presence of hydrogen is inefficient because it is difficult to ensure the necessary composition of the gas phase.The results of the present work can be used for working out technological regimes of alloying the surface of iron objects through the chloride phase and for obtaining powdered alloys Iron-molybdenum.Translated from Poroshkovaya Metallurgiya, No. 1(301), pp. 43–46, January, 1988.     

Phase equilibria in the system molybdenum-chromium-carbon

Summary The methods of x-ray diffraction and microstructural analyses were employed for studying the system Mo-Cr-C, and an isothermal section (1350°C) of the system was plotted. At high carbon contents, the alloys which have not been subjected to heat-treatment contain, the-phase, which has a cubic face-centered structure of the NaCl type (a = 4.24–4.27 A). The carbide Mo₂C dissolves up to 46 at.% Cr, and the carbide Cr₂₃C₆ up to 15 at.% Mo. It is shown that the Mo atoms dissolved in the carbide Cr₂₃C₆ are distributed in an ordered manner.     

Phase equilibria in the Co-P-B system

Translated from Poroshkovaya Metallurgiya, No. 5(329), pp. 56–59, May, 1990.     

Phase equilibria in the Al-Si-C system

The Al-C, Si-C, and Al-Si-C systems were investigated by metallography, X-ray diffraction, electron microprobe, and thermal analysis. Internally sealed liquidus crucibles were used to determine the solubility of C in Al and Si in the range 1700° to 2150 °C and isothermal sections for the ternary system at 2000° and 2150 °C. The isopleth Al₄C₃-SiC, determined in the range 1900° to 2300 °C, was found to contain the ternary intermediate phases 2A1₄C₃ · SiC and A1₄C₃ · SiC, which decompose incongruently at 2085° and 2080 °C, respectively. The incongruent decomposition temperature of A1₄C₃ (2156 °C) was confirmed. A phase reported by others with the stoichiometry Al₄C₃-2SiC was not confirmed. A partial liquidus surface was mapped from the carbon solubility and thermal analysis measurements.     

Phase equilibria in the system zirconium-chromium-carbon

Summary Phase equilibria in the system Zr-Cr-C at 1300°C were investigated by themethods of x-ray diffraction and microstructural analyses (Fig. 2). Zirconium carbide dissolves up to 6 at.% Cr, while chromium carbides dissolve negligible amounts of zirconium. In accordance with results of a thermodynamic calculation, zirconium carbide is in equilibrium with chromium carbides, chromium, and the compound ZrCr₂.     

Phase equilibria in the system Zr-W-C

Summary The system Zr-W-C was investigated by the methods of X-ray diffraction and microstructural analyses. Phase equilibria at 1500°C were determined for as-cast and annealed alloys. The carbide ZrC dissolves 34 mo%WC at 500°C; at l,950°C. the solubility ofWC increases to 40 mol.'yo. As-cast alloys contain the - phase, which has a cubic NaCl-type structure (a = 4.25–4.30 A), and is distributed along the 50 at.% C line at 2–10 at.% Zr. It is shown that the solubility of WC in ZrC may be even greater at temperature approaching the melting point of the alloys.     

Phase equilibria in the system Al-Rh

Methods of differential thermal analysis, x-ray diffraction, microstructural analysis and electron probe microanalysis are used to study alloys of the Al-Rh system over the whole concentration range. It is established that the phase of equiatomic composition AlRh melts congruently at 2060°C and it has an extended range of homogeneity (45.1–54.2 at.% Rh). The solubility of aluminum in rhodium reaches 9 at.%, decreasing to 6 at.% at 850°C. Coordinates are determined for the eutectic point l ⇆ AlRh + 〈Rh〉 as 70 at.% Rh and 1715°C. The existence of intermediate phases, their crystal structure, and also the method of forming phases in the field of composition rich in aluminum given in publications are confirmed. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 48–56, May–June, 2006.     

Phase equilibria in the titanium-oxygen system

Data in the literature on the Magneli oxides of titanium have been critically evaluated and equations have been developed from these data for the standard-state Gibbs energy of formation of the following oxides: Ti₄O₇, Ti₅O₉, Ti₆O₁₁, Ti₈O₁₅, and Ti₉O₁₇. Examination of those data yielded the following:

Phase equilibria in the lanthanum-tin system

Translated from Poroshkovaya Metallurgiya, No. 2(314), pp. 79–9O. February, 1989.     

Phase equilibria in the erbium-silicon system

The structure and phase composition have been examined by microstructure, x-ray phase, and differential thermal analysis for cast and annealed erbium–silicon alloys. The complete phase diagram for the erbium–silicon system has been compiled for the first time. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 24–30, January–February, 1997.     

Phase equilibria in the Fe-Ti-Cl-H-O system

Conclusions In the Fe-Ti-O system at 1373°K only Ti₂O₃ is stable, and iron is reduced from oxides and passes into solution. At practically all compositions of the solid solution preferential chlorination of titanium takes place, together with its transport to iron. During the chlorination of an iron-titanium alloy only gaseous chlorides are formed (T = 1373°K) because under these conditions equilibrium between the solid solution and liquid chlorides is not attained. Chlorination of titania in the presence of hydrogen as a reducing agent is impractical owing to difficulties in ensuring the required composition of the gaseous phase. The results obtained can be utilized for developing technological processes for the surface alloying of iron parts through a chloride phase and producing iron-titanium alloy powders.Translated from Poroshkovaya Metallurgiya, No. 1(265), pp. 52–55, January, 1985.