Papers by Keyword: Phase Equilibria

Abstract: The Ni-aluminides are integral constituents of thermal barrier coatings applied over Ni-based superalloys. These aluminides provide oxidation-resistance by forming a protective α–Al₂O₃ surface layer. The Pt-modified β–NiAl bond coat has been developed with an impetus to increase the service-life of Ni-based superalloys. The Pt-modified β–NiAl bond coat significantly improves the oxidation-resistance of superalloys. An interdiffusion zone containing topologically closed packed phases develops at the bond coat/superalloy interface. This eventually leads to Al-lean γ′–Ni₃Al transformation, whose oxidation resistance is inferior to that of β–NiAl. The Pt-group metals Ir and Ru delay this transformation and impart creep-resistance to the bond coat. Recent investigations demonstrate that alloying with transition metals such as Cr, Mo and Fe enhance the mechanical strength. The functional stability of bond coat-superalloy assembly counts on the interfacial reaction and associated local structural variations which is a function of bond coat composition. This chapter elucidates the effect of various alloying elements on phase constitutions, crystallographic structural stability and thermodynamics of Ni-and Fe-aluminides to engineer a prospective bond coat.

Abstract: Using rare earth metals as deoxidizers is an efficient way of getting highly deoxidized copper melt required for certain bronzes production. Thermodynamic modeling of phase equilibria in the Cu–La–O system in the temperature range of 1100–1300 °С was performed to assess a possible depth of copper melt deoxidation with lanthanum, and also to determine the resulting oxide phases. During the experimental part of the work, Cu–La–O system metal samples were melted and then studied with the JEOL JSM 6460-LV scanning electron microscope equipped with the energy-dispersive spectrometer providing electron microprobe analysis to specify formed nonmetallic inclusion type.

Abstract: The thermodynamic characteristics of processes in the liquid metal system Fe–Y–Cr–C–O are considered as applied to low-carbon and low-alloy metal. The critical parameters for the state diagram of the oxide system Y₂O₃–Cr₂O₃ were established based on the values quoted in literature. The temperature dependence of the melting reaction constant Y₂O₃·Cr₂O₃ was determined. The coordinates of eutectic transformation points for the system Y₂O₃–Cr₂O₃ were calculated. In accordance with subregular solution theory, the energetic parameters which are necessary to calculate the activities Cr₂O₃ and Y₂O₃ of oxide melts in the system Y₂O₃–Cr₂O₃ were determined. The energetic parameters of subregular solution theories for the oxide system FeO–Cr₂O₃–Y₂O₃ were determined based on the values for the binary systems FeO–Y₂O₃, FeO–Cr₂O₃ and Y₂O₃–Cr₂O₃. The view of this diagram, as coupled with the existence domain of liquid metal within the framework of the quaternary system Fe–Y–Cr–O–С, suggests that low-carbon chromic liquid metal when injected with yttrium can form the following non-metallic inclusions: |Cr₂O₃|, |Y₂O₃|, |FeO·Cr₂O₃|, |Y₂O₃·Cr₂O₃| or oxide melt (FeO, Y₂O₃, Cr₂O₃). Oxide melt may contain up to 2 % of divalent chrome (Cr2+). The equilibrium constants for the main reactions of steel deoxidation with the formation of liquid, solid and gas products of chemical reactions were also established. The activity of components dissolved in metal was calculated using interaction parameters. The set of derived expressions for the activity of components and the dependences of equilibrium constants of chemical reactions and phase transformations allowed us to diagram the surface of component solubility in liquid metal (SCSM). SCSM diagrams show the compositions of liquid metal and indicate oxide phases which are in equilibrium with liquid metal.

Abstract: Thermodynamic modeling of phase equilibria in the copper-rich corner of the Cu–Ni–Si–Cr system is performed. The "FactSage" software was used for thermodynamic modeling. Isothermal sections of the Cu–Ni–Si–Cr phase diagram with phase existence areas depending on the concentrations of nickel, silicon and chrome are plotted. Reactions between nickel, silicon and chrome, dissolved in a copper melt, are studied experimentally. The samples after crystallization are investigated using scanning electron microscope and X-ray phase analysis. The conditions of silicide formation in as-cast condition are defined. The research results can be used for technology analysis in copper and copper-based alloys production.

Abstract: Phase equilibria of the BaO-SiO₂-Al₂O₃ ternary system was experimentally investigated using a quenching technique and analyzed by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Analysis (EDS) and X-ray Powder Diffraction (XRD). A ternary compound was confirmed in the present work. The liquidus composition in equilibrium with the ternary compound at 1500 °C were quantified. The isothermal sections of the BaO-SiO₂-Al₂O₃ ternary system at 1400 °C, 1500 °C, 1600 °C, and 1700 °C were calculated. Based on the data acquired, the isothermal section at 1500 °C was constructed.

Abstract: Fusibility curves of FeO–La₂O₃–Al₂O₃, FeO–Ce₂O₃–Al₂O₃, La₂O₃– Ce₂O₃–Al₂O₃ oxide systems are created based on the literature data and modern thermodynamic theories of oxide and metal melts. Admitting the oxide systems conjugation with the area of metal melts existence, we define oxide phases, which can maintain the equilibrium with metal melts of Fe–Ce–Al–O, Fe–La–Ce–Al–O systems. The surfaces of component solubility are created for above mentioned metal melts. For Fe–Ce–Al–O system it is established that the following phases can be at equilibrium with metal: Al₂O₃, Сe₂O₃, FeO∙Al₂O₃, Сe₂O₃∙11Al₂O₃, Сe₂O₃∙Al₂O₃, and the oxide melt (FeO, Al₂O₃, Сe₂O₃, СeO₂). For Fe–La–Ce–Al–O system the following oxide phases can be at equilibrium with the liquid metal: La₂O₃, Al₂O₃, Сe₂O₃, La₂O₃∙Al₂O₃, Сe₂O₃∙11Al₂O₃, Сe₂O₃∙Al₂O₃, and the oxide melt (FeO, La₂O₃, Al₂O₃, Сe₂O₃, СeO₂). Diagrams of active components consumption, which are used to establish the possibility of chosen equilibrium, are created for iron deoxidation with cerium and aluminium as well as with Ce and La at fixed Al content (0.01 wt. %).

Abstract: The results of the analysis of phase equilibria ordered phases in binary systems based on palladium Pd-Me (Me = Co, Rh, Ir, Cu, Ag, Au, Ni, Pt) are set out to search for correlations and crystal-chemical and crystal geometric factors. It is found that the packing factor in disordered solid solutions in binary systems based on Pd is close to the value of 0.74 on a background of a slight deviation from the atomic volumes Xena. It is revealed that increasing of the hydrogen permeability in Cu-Pd binary alloys correlates with significant reduction of the packing factor in B2 ordered phase in the range of 40 at.% Pd. It is found that various structural-phase states are formed in Pd-Me binary systems with certain combinations of temperature and size factors.

Abstract: A model for simulating mushy zone resolidification in a temperature gradient is presented. For describing macroscopic mass transport in the liquid phase in the mushy zone, an extended diffusion equation is solved numerically using the Finite Difference Method. Temperature dependent local equilibria at each position in the mushy zone are calculated using the thermodynamic software package ChemApp. The resolidification model treats multicomponent alloying systems and accounts for multiphase equilibria. Simulation results for peritectic Cu-40wt%Al and eutectic Al-5wt%Si-1wt%Mg alloys are compared with microstructures from temperature gradient annealing experiments. It is shown that the model is well suited to predict mushy zone resolidification in multicomponent and multiphase alloys. The predicted evolution of the liquid fraction is qualitatively in full agreement with the observed microstructures, including local remelting at the peritectic temperature prior to resolidification, an effect that was first predicted by the model and confirmed by the experiments.

Abstract: Phase equilibrium data for the hydrates formed in four three-component systems: CO₂ + glucose + water system, CO₂ + fructose + water system, C₃H₈ + glucose + water system, C₃H₈ + fructose + water system were measured in pressures range of (0.24 to 4.57 MPa) and temperatures range of (274.9 to 283.1 K) at 5% and 10% mass fraction of additives. The experimental data were determined using an isochoric pressure-search method. The effects of glucose (or fructose) on CO₂ and C₃H₈ hydrate formation condition were studied. The addition of glucose or fructose increase the equilibrium pressure of the CO₂ and C₃H₈ to form hydrate, and the presence of 10 mass% concentration of glucose (or fructose) showed more remarkable inhibition effect on CO₂ and C₃H₈ hydrate formation.

Abstract: A pyroprocessing technology has been developed to process spent nuclear fuels with decreased waste and increased proliferation resistance. A main process of the pyroprocessing is an electrorefining which requires a post-treatment for recovered uranium. A distillation approach is adopted to remove an electrolyte salt residue on the uranium. In this work, the vapor composition of the distillation process and the total pressure were estimated to obtain basic data for process design and integration. Six chlorides including KCl, LiCl, UCl₃, PuCl₃, CeCl₃, and YCl₃ were considered to understand the behavior of the representative components of actinides and lanthanides. It was found that small amount of the actinides and lanthanides would be accompanied by the electrolyte salts (KCl and LiCl) during the distillation under high vacuum.