High-temperature phase equilibria of Cu–O–Al2O3 system in air

Phase equilibria of Cu–O–Al₂O₃ system were experimentally investigated in a temperature range of 1100–1400°C under 0.21?atm oxygen pressure. The experiments were conducted employing a high-temperature equilibration and quenching method. Microstructures of the quenched samples were observed with scanning electron microscope. The phase compositions in the samples were analysed with electron probe microanalysis technique. Measured solubility of Al₂O₃ into the molten oxide ranged from 0.0 to 1.8?wt-%. A small solubility of Cu₂O into Al₂O₃ was also observed ranging from 1.20 to 1.58?wt-%.     

Thermodynamic activity of the liquid-phase components in the CaO · SiO2-CaO · Al2O3 · 2SiO2-CaO · TiO2 · SiO2 system with four-phase invariant equilibrium

The CaO · SiO₂-CaO · Al₂O₃ · 2SiO₂-CaO · TiO₂ · SiO₂ system is analyzed. Thermodynamic analysis of monovariant and invariant solidification shows that, for invariant equilibrium and for solidification along the boundary curve between the solidification fields of anorthite and sphene, peritectic processes are observed. The invariant-state parameters of the system are determined: t = 1513 K; a _CaO = 0.0407; $a_{SiO_2 } = 0.5268$ ; $a_{Al_2 O_3 } = 0.00003$ , $a_{TiO_2 } = 0.005$ ). A corrected phase diagram is presented.     

Modeling of γ/γ′ phase equilibrium in the nickel-aluminum system

A theoretical model is proposed for the determination of phase equilibrium in alloys taking into consideration dissimilar lattice parameters. Volume dependent pair interactions are introduced by means of phenomenological Lennard-Jones potentials and the configurational entropy of the system is treated in the tetrahedron approximation of the cluster variation method. The model is applied to the superalloy relevant nickel-rich, γ/γ′ phase region of the Ni-Al phase diagram. The model predicts reasonable values for the lattice parameters and the enthalpy of formation as a function of composition, and the calculated phase diagram closely approximates the experimental diagram.     

Experimental investigations and thermodynamic calculations of the structural and phase composition in the Ti–Si–C system

Thermodynamic calculations of the structural-phase equilibrium in the Ti–Si–C system at 1100–1400°C are performed using the CALPHAD method. Calculated phase diagrams of this system are presented. It is established that 100% of the Ti₃SiC₂ phase is formed with the stoichiometric component ratio. With the deviation of the carbon or silicon content, titanium carbide, titanium disilicide, or silicon carbide appear in the system. The temperature almost does not affect the phase composition in the studied temperature range. The calculated data are compared with the experimental determination of the phase composition of the samples of the mentioned system after the spark-plasma sintering of the mechanically activated powder composition. In practice, the process temperature and duration of high-temperature holding substantially affect the phase composition of the final product, which is associated with the limited rate of solid-phase reactions during the synthesis of compounds. The samples have a grain size of 1–5 μm and hardness of 4–15 GPa, depending the phase composition.     

Calculation of the equilibrium phase diagrams and the spinodally decomposed structures of the FeCuNi system

Thermodynamic stability of ternary systems with miscibility gaps is discussed and applied to the f.c.c. phase of FeCuNi alloys. The stability of the system with respect to infinitesimal composition fluctuation is described. The direction most likely for initial composition fluctuation is defined as the one with the largest negative curvature on the Gibbs energy surface. Along this direction, zero-time wavelength at initial stage of spinodally decomposed alloy structure may be calculated. The thermodynamic values of the f.c.c. FeCuNi alloys are obtained from limited amount of thermochemical and phase equilibrium data. It is found that the ternary interaction parameters for both the f.c.c. and liquid phases of FeCuNi may be approximated from the binary interaction parameters of the constituent binaries.     

Phase equilibria of the Na2O–SiO2 system between 1173 and 1873 K

Knowledge of phase equilibria in the Na₂O–SiO₂ system at elevated temperatures is important for mastering the metallurgical process and for the glass and ceramic industries. The phase diagram at metasilicate and silica saturations in the Na₂O–SiO₂ system between 1173 and 1873?K has been investigated by quenching and phase analyses. The experimental technique involved equilibration of high purity oxide mixtures at sub-liquidus temperatures, rapid quenching in cold water and followed by compositional measurement of the phases using electron probe X-ray microanalyser. The phases stable in the equilibrium assemblages have been characterised over a wide range of compositions and temperatures. The results were compared with previous experimental data and an optimised phase diagram.     

Experimental measurements and modelling of viscosity in CaO–Al2O3–MgO slag system

Abstract

The viscosity of the CaO–Al₂O₃–MgO slag system has been measured by the rotating cylinder method up to 1823 K. The MgO content was between 0·39 and 11·33 wt-%, and the mass ratio of CaO/Al₂O₃ was between 0·60 and 1·28. The results indicated that both the MgO content and the mass ratio of CaO/Al₂O₃ have an influence on the viscosity of the slag. The effect of the mass ratio of CaO/Al₂O₃ is larger than that of the MgO content. The viscosity decreased with increasing MgO content and then increased. The effect of the mass ratio of CaO/Al₂O₃ on the viscosity was similar. The main mineralogical compositions of the slag were determined by X-ray diffraction, and their effects on viscosity were investigated. The measured results were in good agreement with those given by the Iida model.     

Thermodynamic description of the interaction processes in the Cu–Ce–O system in the temperature range 1100–1300°C

A thermodynamic simulation and an experimental study of the interaction between cerium and oxygen in liquid copper have been performed. The thermodynamic analysis of the interaction processes in the Cu–Ce–O system is carried out using the technique of constructing the surface of solubility of components in a metal in the temperature range 1100–1300°C. As a result of simulation, data on changes in the Gibbs energy ΔG _T ° and the equilibrium constants of formation of cerium oxides Ce₂O₃ and CeO₂ from the components of a copper-based metallic melt are obtained. The first-order interaction parameters (according to Wagner) of cerium and oxygen dissolved in liquid copper, namely, e _Ce ^Ce, e _O ^Ce, and e _Ce ^O, are evaluated. Experimental studies of the Cu–Ce–O system have been performed. The morphological features, the size, and the composition of nonmetallic inclusions formed as a result of interaction in the Cu–Ce–O system are studied using scanning electron microscopy and electron-probe microanalysis.     

Solidus surface of the equilibrium diagram of the HfO2—Y2O3—La2O3 system

The phase equilibria on the solidus surface of the phase diagram of the HfO ₂−Y₂O₃−La₂O₃ system have been investigated using DTA in helium up to 2500°C, TA with solar energy in air up to 3000°C, X-ray phase analysis, petrography, and electron microscopy. Five solid solution fields based on hexagonal (H) and cubic (C) crystal modifications of Y₂O₃, cubic modifications of HfO₂ with fluorite structure (F), high-temperature cubic modifications of La₂O₃ (X), and crystallization field of the ordered phase La₂Hf₂O₇ with the pyrochlorine (Py) type structure have been found on the solidus surface. The ternary system has three quaternary novariant equilibria of the eutectic (1) and peritectic (2) type. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(407), pp. 56–65, May–June, 1999.     

Experimental studies of viscosities of some CaO–CaF2–SiO2 slags

Abstract

In the present work, the viscosities of some CaO–CaF₂–SiO₂ slags were measured using the rotating cylinder method. The effects of various volatile fluorine compounds on the change in slag composition are discussed on the basis of thermodynamic calculations. The kinetic factors concerning the escape of the volatile fluorides under the experimental conditions were also examined. It was found that the formation of gaseous species SiF₄ was the main source for compositional changes during the viscosity measurements. In the case of CaO–CaF₂–SiO₂slags, the formation of SiF₄ would be somewhat limited owing to the existence of CaO. The composition change during the measurements was only about ±1 wt-% for all components in most cases. Viscosity measurements are reported for slags, based on the post-measurement compositions. It was found that the addition of CaF₂ causes a significant decrease in viscosity.     

Effect of K2O on Phase Relation and Viscosity of the CaO–SiO2—ZnO—FeO–Al2O3 System Slags

Russian Journal of Non-Ferrous Metals - The effect of K2O on phase relation and viscosity of the CaO–SiO2–25 wt % “FeO”–12 wt % ZnO–3 wt % Al2O3 slags...     

Vanadium oxide solubility in CaO–SiO2–VOX system

The solubility of vanadium oxide in the SiO₂–CaO–VO_X system was investigated as a function of basicity (CaO/SiO₂) at a fixed temperature of 1600°C and oxygen partial pressure of 10^?10?atm. Formed phases and microstructures of saturated samples were identified with SEM–EDS analysis and XRD. Maximum solubility of vanadium oxide was between 15 and 20% independent of basicity. Pure karelianite (V₂O₃) was formed in all samples at saturation of vanadium oxide. The morphology of karelianite changed with the change in basicity in the slag, where needles or threads were formed for slags with basicity B2?=?0.54 and B2?=?0.67 and stars or dendritic patterns were formed with basicity B2?=?1.0 and B2?=?1.22. Wollastonite (CaSiO₃) was also formed in the slags with star or dendritic patterns.     

Properties of Na2O–SiO2 slags in Doré smelting

Solubilities of metals in sodium silicate slags have been studied at 1000–1300°C in oxygen pressures of P(O₂) = 10^?4 to 0.5 atm, in Doré alloy smelting of copper anode slimes. The boundary conditions for the slags were silica saturation, magnesia saturation with about 10 wt% and without BaO. The trace elements studied were copper, gold, palladium, rhodium, and tellurium. The analytical methods used in the phase composition analyses of equilibrated samples, quenched in brine, were electron probe X-ray microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. Thermodynamic features of the slags, trace element solubilities with the given constraints, and their oxidation mechanisms were determined. The data allow optimizing the anode slime-smelting for the metals’ maximum recovery in sodium silicate fluxing.     

The effect of elastic anisotropy on the migration of intergranular liquid films and the precipitation of a liquid phase in a CoCu alloy

When a Co20Cu (wt%) alloy prepared by liquid phase sintering at 1300°C is heat-treated at 1150°C, the intergranular liquid films and grain boundaries migrate, leaving behind a new solid solution with reduced Cu content. The phenomenon is identical to that observed previously in MoNi. The calculated driving force for the migration is almost equal to the coherency strain energy in the solute diffusion zone ahead of the migrating boundaries. The migrating liquid films show faceting with curved planes and edges. Their shape closely resembles the growth shapes predicted on the basis of the coherency strain energy with anisotropic elastic constants. During the heat-treatment, liquid precipitates form within grains and at grain boundaries, and they also show faceting, which is consistent with orientation dependent coherency strain energy in the diffusion zone around the precipitates.