The measurement of the thermodynamic properties of NiO−MnO solid solutions by a solid electrolyte cell technique

The activity of NiO in NiO?MnO solid solutions has been measured using the cell Ni, NiO |Zr_0.85 Ca_0.15 O_1.85|Ni, [NiO]_s.s. in the temperature range 900° to 1200°C for compositions between 0 and 80 mol pct NiO. The activity-composition relationships for MnO have been determined by integration of the Gibbs-Duhem equation, and the partial and integral thermodynamic quantities for the system have been calculated. The system exhibits a positive deviation from ideal behavior with a maximum heat of mixing of 850±150 cals per mole, and a positive excess entropy of mixing of 0.24±0.1 cal per mole °C was detected at the equimolar composition.     

The wetting transition in high and low energy grain boundaries in the Cu(In) system

Wetting of two symmetrical tilt grain boundaries, 77° 〈110〉 and 141° 〈110〉, in synthetic copper bicrystals with a Cu(In) melt was studied in the temperature range 690°990°C. The contact angle at the site of GB intersection with the solid-melt interface was measured. A wetting transition occurred at T_w = 960 ± 6°C for the 77° 〈110〉 grain boundary and at T_w = 930 ± 5°C for the 141° 〈110〉 grain boundary. The contact angle approached zero for this transition. The relative surface energies of the two boundaries were measured using the thermal grooving technique. The energy of the 77° 〈110〉 grain boundary is about 40% lower than that of the 141° 〈110〉 grain boundary. Therefore, it has been shown experimentally that the lower the grain boundary energy, the higher the wetting transition temperature. This is in agreement with the thermodynamic model of wetting transitions on grain boundaries.     

An unusual phenomenon in the formation of Li5B4 compound-alloy

In the course of scientific development, occasionally a phenomenon is encountered which challenges our understanding and defies a complete explanation. Such a phenomenon occurs in the formation of Li₅B₄ compound-alloy which is formed by heating (not cooling). The liquid metallic solution of Li and B which exists at low temperature (300 to 450°C) transforms to a metallic solid at high temperature (500 to 550°C). Following the transformation to solid, Li₅B₄ compound-alloy formation takes place at 550 ± 2°C, accompanied by a heat release of about 2.2 ± 0.3 kcal per gram of B. The compound-alloy thus formed is a totally metallic solid existing from room temperature to 1000°C. Above 1000°C, the compound-alloy sublimes (with Li vaporizing) leaving behind a blackish substance. While these observations are unusual in terms of the wide composition and temperature ranges in which they occur, they are by no means ‘strange’. They are not inconsistent with the thermodynamic principles of phase diagrams and can be interpreted once the whole process is fully characterized.     

Application of Computational Thermodynamics to the Design of a Co-Ni-Based γ′-Strengthened Superalloy

A currently available commercial Calphad thermodynamic database was utilized to investigate its applicability to alloy design in the new class of Co-Ni-based γ′-strengthened high-temperature alloys. A simple primary design criterion was chosen: maximize the γ′ solvus temperature in the six-component Co-Ni-Al-Ti-W-Ta system while ensuring no formation of secondary, potentially deleterious phases. Secondary design considerations included the effects of alloying elements on equilibrium γ′ volume fraction and on solidus and liquidus temperatures. The identified composition, Co-30Ni-9Al-3Ti-7W-2Ta-0.1B (expressed in mole percent), representing a conservative estimate of the maximum allowable concentrations of alloying additions Al, Ti, W, and Ta, was subsequently produced and characterized. The experimentally measured γ′ solvus temperature of the new alloy was 1491 ± 3 K (1218 ± 3 °C), about 35 K (35 °C) above any previously reported two-phase γ−γ′ Co-(Ni)-based alloy. No secondary phases were observed in the alloy after annealing at temperatures between 1173 K and 1473 K (900 °C and 1200 °C). Additional alloy compositions with experimentally measured γ′ solvus temperatures in excess of 1533 K (1260 °C) were also identified employing the same basic approach. The efficacy of currently available thermodynamic databases in their application to Co-based γ′-strengthened superalloy development is discussed, including expanding design efforts to include additional alloying elements, as well as specific areas for improvement of future databases.

     

Phase relations and thermodynamics of the system Fe-Cr-0 in the temperature range of 1600 °C to 1825 °C (1873 to 2098 K) under strongly reducing conditions

Equilibrium relations involving alloy and oxide phases in the system Fe-Cr-O were determined in the temperature range from 1600 °C to 1825 °C (1873 to 2087 K). Compositions of coexisting alloy and spinel phases were established as a function of oxygen pressure by equilibrating liquid Fe-Cr alloys with iron chromite (Fe_3-xCr_xO₄) solid solutions at 1600 °C and 1700 °C. Combinations of these experimental data and thermodynamic calculations were used to construct composition-oxygen pressure diagrams for the system at 1600 °C and 1700 °C. Additional runs for selected mixtures were made at still higher temperatures (1700 °C to 1825 °C), and thermodynamic parameters were derived for spinel-containing phase assemblages at temperatures up to 1865 °C. The spinel phases occurring in the present system are typically in the high-chromium range of the solid-solution series Fe₃O₄-Cr₃O₄,i.e., in the range between stoichiometric iron chromite (FeCr₂O₄) and Cr₃O₄. The activities of the various oxide components of the spinel solid solution at 1600 °C were calculated from experimentally determined parameters for coexisting alloy and spinel phases, as well as by statistical-mechanical modeling of the same spinel solid solution based on crystal-chemical considerations. The agreement between the two sets of results was excellent. Temperature variation of parameters characterizing the univariant equilibria spinel + Cr₂O₃ + alloy and spinel + alloy + liquid oxide was established. The univariant curves were found to display temperature maxima of 1715 °C ± 5 °C and approximately 1865 °C, respectively. In analogy with relations in the Cr-O system, the increase in divalent chromium of the liquid oxide phase with decreasing oxygen potential was identified as the main cause of the sharp decrease in liquidus temperatures of chromites in contact with Fe-Cr alloys of high Cr contents. Formerly Graduate Research Assistant, Department of Metallurgy, The Pennsylvania State University L.S. DARKEN and ARNULF MUAN, formerly Professors of Geochemistry and Materials Science, The Pennsylvania State University, University Park, PA 16802, are deceased.     

Thermodynamic Modeling of the Al-Ti-V Ternary System

The sub-binary systems Al-Ti, Ti-V, and Al-V are reviewed and adopted from the previous assessments, the thermodynamic analysis of the Al-Ti-V ternary system is performed by the CALPHAD approach, and a set of self-consistent thermodynamic parameters of the ternary system are obtained. Furthermore, the isothermal sections of this system at 1073 K, 1173 K, 1273 K, 1373 K, and 1473 K (800 °C, 900 °C, 1000 °C, 1100 °C, and 1200 °C) and the ternary invariant equilibria are calculated and compared with the corresponding experimental data, and all are in good agreement with most of the experimental results. Thus, the optimized thermodynamic parameters in this study may provide more accurate guidance to develop the new alloys involving it.     

The high temperature phase diagrams for zirconium-molybdenum and hafnium-molybdenum

The high temperature regions of the Zr−Mo and Hf−Mo binary phase diagrams have been constructured from temperature-composition data obtained by gravimetric and pyrometric methods. The liquidus curves were obtained directly from the measurements of saturation solubilities of molybdenum (single crystal) in liquid Zr and Hf. The solubility results are supported by electron microprobe analyses which identify the formation of thin (∼10 μm) layers of nearly stoichiometric compounds ZrMo₂ and HfMo₂ on the surface of the single crystal molybdenum below the respective peritectic temperatures 1918±5 and 2206±5°C. These thin layers and the negligible diffusion zones of Zr and Hf in single crystal molybdenum do not significantly affect the measured solubilities. The diffusion coefficient of Hf in Mo-single crystal at 2080°C is ∼5×10⁻¹² m² s⁻¹. The melting, solidus, liquidus, eutectic and peritectic temperatures were directly measured by pyrometrically observing the partial or complete destruction of “black-body” conditions inside an effusion cell with the appearance of a liquid phase that forms a highly reflecting mirror. The melting points of Zr and Hf metals, 1860±3 and 2228±3°C, respectively, are in good agreement with previously assessed values. The respective eutectic temperatures peratures and compositions 1551±2°C, 29.0±0.5 at. pct Mo and 1896±3°C, 40.5 at. pct Mo, are considerably more precise and only in fair agreement with previously measured or estimated values. The liquidus composition at the peritectic temperature for the Zr−Mo binary is precisely fixed at 54.0±1.0 at. pct Mo and that for the Hf−Mo binary is 61 ±3 at. pct Mo. The thermodynamic activities of molybdenum in the liquid Zr−Mo alloy indicate positive deviations from Raoult's Law. temporarily attached to the Chemistry Division, Argonne National Laboratory, Argonne IL 60439 This work was performed at Argonne National Laboratory under the auspices of the U.S. Energy Research and Development Administration     

A reinvestigation of phase equilibria in the system Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>-ZnO

The phase equilibria and liquidus temperatures in the binary SiO₂-ZnO system and in the ternary Al₂O₃-SiO₂-ZnO system at low Al₂O₃ concentrations have been experimentally determined using the equilibration and quenching technique followed by electron probe X-ray microanalysis. In the SiO₂-ZnO system, two binary eutectics involving the congruently melting willemite (Zn₂SiO₄) were found at 1448±5 °C and 0.52±0.01 mole fraction ZnO and at 1502±5 °C and 0.71±0.01 mole fraction ZnO, respectively. The two ternary eutectics involving willemite previously reported in the Al₂O₃-SiO₂-ZnO system were found to be at 1315±5 °C and 1425±25 °C, respectively. The compositions of the eutectics are 0.07, 0.52, and 0.41 and 0.05, 0.28, and 0.67 mole fraction Al₂O₃, SiO₂, and ZnO, respectively. The results of the present investigation are significantly different from the results of previous studies.     

Experimental Phase Equilibria Studies of the Pb-Fe-O System in Air,in Equilibrium with Metallic Lead and at Intermediate Oxygen Potentials

The phase equilibria information on the Pb-Fe-O system is of practical importance for the improvement of the existing thermodynamic database of lead-containing slag systems (Pb-Zn-Fe-Cu-Si-Ca-Al-Mg-O). Phase equilibria of the Pb-Fe-O system have been investigated: (a) in air at temperatures between 1053 K and 1373 K (780 °C and 1100 °C); (b) in equilibrium with metallic lead at temperatures between 1053 K and 1373 K (780 °C and 1100 °C); and (c) at intermediate oxidation conditions for the liquid slag in equilibrium with two solids (spinel + magnetoplumbite), at temperatures between 1093 K and 1373 K (820 °C and 1100 °C). The high-temperature equilibration/quenching/electron probe X-ray microanalysis technique has been used to accurately determine the compositions of the phases in equilibrium in the system. The Pb and Fe concentrations in the phases were determined directly; preliminary thermodynamic modeling with FactSage was used to estimate the ferrous-to-ferric ratios and to present the results in the ternary diagram.     

Desulfurization of CO:SO2 contaminated gases by manganous oxide

To contribute to the curtailment of anthropogenic emission of sulfurous compounds, the susceptibility of manganous oxide for sulfur under reducing atmospheres (C−O−S system) has been investigated over the temperature range 700 to 900°C (973 to 1173 K). A thermodynamic evaluation of the Mn−S−O system and the C−O−S system was undertaken and the basic, bivariant, and univariant equilibria in the Mn−S−O system over the temperature range 700 to 1100°C are listed. The kinetic investigation employed thermogravimetry and anin situ solid electrolyte oxygen probe to follow the sulfidization reaction of spherical MnO pellets under various experimental conditions. The kinetic evaluation was complemented by X-ray diffraction and krypton B.E.T. surface area analyses. Apparent activation energy of sulfidization of manganous oxide, under measured oxygen potentials in the C−O−S system, was determined to be 6.26 (±2.0) kcal/gmol (26.2 (±8.4) kJ/gmol), and a comparison with some alternative desulfurization agents in the H−O−S system is included.     

Electromotive Force Measurements in the Ternary System Bi-In-Zn

The thermodynamic properties of the ternary Bi-In-Zn system were determined with the electromotive force (EMF) method using a liquid electrolyte. Four different cross sections with constant In/Bi ratios of 1:2, 1:1, 2:1, and 9:1 were applied to measure the thermodynamic properties of the ternary system in the temperature range between the liquidus temperature of the alloys and 973 K (700 °C). Zinc was added in steps of 5 at. pct from 5 to 90 pct. The partial free energies of Zn in liquid Bi-In-Zn alloys were determined as a function of concentration and temperature. The integral Gibbs free energy and the integral enthalpy of the ternary system at 873 K (600 °C) were calculated by Gibbs–Duhem integration. The ternary interaction parameters were evaluated using the Redlich–Kister–Muggianu polynomials.     

Prediction Expressions of Component Activity Coefficients in Si-Based Melts

Prediction expressions of component activity coefficients of the molecular interaction volume model (MIVM) are suggested for making up for absence of Wagner interaction parameters in Si-based melts. Their effectiveness is verified in liquid Fe-Si-B system at 1823 K (1550 °C). In comparison with experimental data, all errors of ±22 to 56 pct and deviations of ±0.0132 to 0.0318 predicted by MIVM are smaller than those (±53 to 94 pct and ±0.0759 to 0.1010) by the unified interaction parameter formalism. This indicates that the former is better than the later in the system. Accordingly, some interested thermodynamic diagrams and parameters at 1687 K and 1823 K (1414 °C and 1550 °C) are predicted in liquid Si-Al-Fe system, for instance, $ \varepsilon_{\text{Al}}^{\text{Al}} = 2.318 $ , $ \varepsilon_{\text{Fe}}^{\text{Fe}} = 4.297 $ , and $ \varepsilon_{\text{Fe}}^{\text{Al}} = \varepsilon_{\text{Al}}^{\text{Fe}} = - 2.443 $ in the dilute solution at 1687 K (1414 °C). The method of MIVM is able to expand to Si-based multicomponent melt if its sub-binary activity data are available. The reliability of predicted results for the melt is closely dependent upon that of component activities or infinite dilute activity coefficients in its sub-binary systems.     

Phase equilibria of the Al-Li binary system

The solid + liquid phase equilibria between α-Al and β-AlLi were determined using differential thermal analysis (DTA), metallography, and chemical analysis. Boron nitride (BN), which was found to be inert to these alloys, was used as the container. These measurements were carried out in order to resolve the discrepancies reported in the literature. The α-Al+β-AlLi eutectic temperature and composition were determined to be 600 °C±1 °C and 25.8±0.5 at. pct Li. Using these data and data reported in the literature concerning the phase equilibria and thermodynamic properties, thermodynamic models for all the phases were obtained by optimization. The thermodynamic values obtained for the β-AlLi phase describe not only the phase equilibria, but also yield structural defect data in agreement with measured values. The assessed enthalpies of formation, excess entropies of formation, and entropies of melting for all the intermetallic phases obtained are compared with empirical correlations when experimental data are not available. In addition to the stable diagram, a metastable diagram involving the δ′-Al₃Li is also calculated from the thermodynamic models. The calculated diagram is in good agreement with the experimental data.     

Equilibrium phase relations and thermodynamics of the Cr-0 system in the temperature range of 1500 °C to 1825 °C

Phase relations and thermodynamic properties of the Cr-O system were studied at temperatures from 1500 °C to 1825 °C. In addition to Cr and Cr₂O₂, a third crystalline phase was found to be stable in the temperature range from 1650 °C to 1705 °C. The atomic ratio of oxygen to chromium of this phase, which decomposes upon cooling to form Cr and Cr₂O₃, was determined as 1.33 + 0.02, in good agreement with the formula Cr₃O₄. Temperatures and phase assem blages for invariant equilibria of the Cr-O system were determined as follows: Cr₂O₃ + Cr + Cr₃O₄, 1650 °C ± 2 °C; Cr₃O₄ + Cr + liquid oxide, 1665 °C ± 2 °C; and Cr₃O₄ + Cr₂O₃ + liquid oxide, 1705 °C ± 3 °C. The composition of the liquid oxide phase at the eutectic temperature of 1665 °C was found to be close to CrO. Relations between oxygen pressure and temperature for the univariant equilibria of the Cr-O system were established by equilibrating Cr and/or Cr₂O₃ starting materials in H₂-CO₂ mixtures of known oxygen potentials at temper atures from 1500 ΔC to 1825 °C. From this information, the standard free-energy changes (ΔGΔ) for various reactions were calculated as follows: 2Cr (s) + 3/2O₂ = Cr₂O₃ (s): ΔG ° = -1,092,442 + 237.94T Joules, 1773 to 1923 K; 3Cr (s) + 2O₂ = Cr₂O₄ (s): ΔG ° =-1,355,198 + 264.64T Joules, 1923 to 1938 K; and Cr (s) + l/2O₂ = CrO (1): ΔG ° =-334,218 + 63.81T Joules, 1938 to 2023 K. Formerly Graduate Research Assistant, The Pennsylvania State University Formerly Professor     

The chromium-platinum constitution diagram

The system Cr?Pt has been investigated over the entire composition range by metallography, X-ray diffraction, and electron microprobe studies. There is only one intermediate phase and it has a Cr₃Si(A15)-type crystal structure. The fcc platinum terminal solid solution extends to 71 at. pct Cr at 1530°C and forms a congruent melting maximum at about 1790°C. Atomic ordering within this solid solution range begins at about 17 at. pct Cr and there is a continuous change from the Cu₃Au-type structure to the CuAu-type structure with increasing chromium content. Two eutectic reactions at 1530°C±10°C and at 1500°C ±10°C were indicated and there is evidence of a syntectic reaction at 1580°C±10°C. Platinum is soluble in the bcc chromium terminal solid solution up to about 10 at pct Pt at 1500°C but the solubility decreases rapidly at lower temperatures.     

Interdiffusion, Intrinsic Diffusion, Atomic Mobility, and Vacancy Wind Effect in γ(bcc) Uranium-Molybdenum Alloy

U-Mo alloys are being developed as low enrichment uranium fuels under the Reduced Enrichment for Research and Test Reactor (RERTR) Program. In order to understand the fundamental diffusion behavior of this system, solid-to-solid pure U vs Mo diffusion couples were assembled and annealed at 923 K, 973 K, 1073 K, 1173 K, and 1273 K (650 °C, 700 °C, 800 °C, 900 °C, and 1000 °C) for various times. The interdiffusion microstructures and concentration profiles were examined via scanning electron microscopy and electron probe microanalysis, respectively. As the Mo concentration increased from 2 to 26 at. pct, the interdiffusion coefficient decreased, while the activation energy increased. A Kirkendall marker plane was clearly identified in each diffusion couple and utilized to determine intrinsic diffusion coefficients. Uranium intrinsically diffused 5-10 times faster than Mo. Molar excess Gibbs free energy of U-Mo alloy was applied to calculate the thermodynamic factor using ideal, regular, and subregular solution models. Based on the intrinsic diffusion coefficients and thermodynamic factors, Manning’s formalism was used to calculate the tracer diffusion coefficients, atomic mobilities, and vacancy wind parameters of U and Mo at the marker composition. The tracer diffusion coefficients and atomic mobilities of U were about five times larger than those of Mo, and the vacancy wind effect increased the intrinsic flux of U by approximately 30 pct.     

Experimental Investigation and Thermodynamic Calculation of the Co-Si-Zn System

Phase relations of the Co-Si-Zn ternary system were experimentally investigated and thermodynamically calculated. First, the isothermal sections of the Co-Si-Zn system at 1123 K and 1323 K (850 °C and 1050 °C) were investigated experimentally using scanning electron microscopy coupled with wave-dispersive X-ray spectroscopy and X-ray diffraction. Then the thermodynamic calculation for this system was carried out using the CALPHAD technique. The calculated results and the experimental data are reasonably self-consistent.     

The alpha-gamma phase boundaries and theT 0 line for Fe-Mn alloys

The iron-manganese phase diagram relevant to phase transformation in the 0 to 5 pct Mn (580° to 911 °C) range has been redetermined. Phase boundaries at 762° and 822 °C haye been measured. These data have been combined with other relevant experiments and thermodynamic data to generate an optimal phase diagram. The correspondingTo line, relevant to composition-invariant transformations, has also been evaluated.     

On the decomposition of solid solutions of magnesium in aluminum

A nonequilibrium version of measuring the electromotive force during a continuous decrease in the temperature at a rate of 5–7 °C/min is used to study the thermodynamic properties of solid solutions of magnesium in aluminum. The studies show that the abrupt change in the potential of an alloy containing 20–30 mol % Mg at 370–380°C reliably correlates with the decomposition of the solid solution formed at 450°C.