Papers by Keyword: Phase Equilibria

Abstract: Materials based on cerium oxides and REE are perspective for use in medicine, energy and mechanical engineering due to the uniqueness of their authorities. Stationary system diagrams are the physicochemical basis for the creation of such materials as solid electrolytes for fuel comics, oxygen gas sensors, catalyst carriers, protected coatings for alloys, etc. In this work, phase equilibria and structural transformations in the system CeO₂-La₂O₃-Yb₂O₃ at a temperature of 1500 oС in all international concentrations are investigated by the methods of microstistructural and X - ray phase analysis. It is established that in the triple system CeO₂-La₂O₃-Yb₂O₃ fields of solid solutions based on cubic (F) modification of the structure of the structure of fluorite CeO₂, monoclinic (B) and cubic (C) modification of Yb₂O₃ and hexagonal (A) modification of La₂O₃ (R) are used, which crystallizes in a Perovski-type structure with rhombic curvatures. It was found that the rarefaction of CeO₂ in the crystal lattice of the ordered phase with the structure of the perovskite type LaYbO₃ (R) is ~ 3 mol. %. Isothermal review of the state diagram of the systems CeO₂-La₂O₃-Yb₂O₃ at reveals the presence of two three-phase (F + C + R), (A + R + F) and five two-phase (A + F), (A + R), (R + C), (F + R), (F + C) regions.

Abstract: Interest in a comprehensive study of lead tungstate single crystals is due to its scintillation properties [1-5]. It was found that lead tungstate occupies an exceptional position in the family of tungstates with a scheelite structure. Lead tungstate single crystal is a scintillation material [1] used in the LHC electromagnetic calorimeter and photon detector in the ALICE experiment at CERN [1, 2]. Now it can be said unequivocally that lead tungstate is the most promising scintillation material in the next decade.

Abstract: Thermodynamic modeling of phase equilibria with the subsequent construction of the phase diagram of the SrO–Al₂O₃ system has been carried out. To calculate the activities of the oxide melt in the course of this work, we used the approximation of the theory of subregular ionic solutions, with the most optimal values of the energy parameters Q₁₁₁₂ = –104 349: Q₁₁₂₂ = –217 689; Q₁₂₂₂ = –104 436 J/mole. The results obtained for the liquidus line in this work are in good agreement with the literature experimental data. In the course of the calculation, the values of the equilibrium constants for the formation of strontium aluminates from the components of the oxide melt were estimated.

Abstract: Thermodynamic modeling of phase equilibria and further construction of a full projection of the liquidus surface in the FeO–Al₂O₃–Cr₂O₃ and MgO–Al₂O₃–Cr₂O₃ systems were carried out. Theories of sub-regular ionic solutions, regular ionic solutions and ideal ionic solutions were used for calculation. Values of energy parameters of the used thermodynamic models were obtained in the course of the research. These values might be applicable for further modeling of more complex oxide slag systems which are formed in the process of manufacture of chromic steels. Calculated phase diagrams for the FeO–Al₂O₃–Cr₂O₃ and MgO–Al₂O₃–Cr₂O₃ systems were compared with available data from literature sources.

Abstract: The differential scanning calorimetry and the method of cooling curves are used to obtain data on liquidus temperatures of oxide-chloride systems Gd₂O₃ – K Cl - GdCl₃. The solubility of gadolinium oxide in K Cl - GdCl₃ melts has been studied. This information can be used for a developing process of the reduction of solid rare-earth oxides into their metals in molten salts.

Abstract: Thermodynamic modeling of coordinates of phase diagrams’ liquidus lines of the FeO–MgO, FeO–Al₂O₃, MgO–Al₂O₃ systems and coordinates of phase diagram’s liquidus surface of the FeO–MgO–Al₂O₃ system has been carried out. In the course of work, a thermodynamic model which describes activity of oxide melt had been selected for each of the systems; energy parameters of the model have been determined. Regions of thermodynamic stability of solid phases which are at equilibrium with the oxide melt have been determined. Results of the modeling have been compared with experimental data existing in the literature. Modeling technique has also allowed evaluating enthalpies and entropies of FeAl₂O₄ and MgAl₂O₄ compounds’ formation out of components of the oxide melt. The obtained results are of interest for steelmaking industry processes when determining the melt temperature of a slag containing oxides of iron, magnesium and aluminum.

Abstract: Thermodynamic modeling of phase equilibria in a liquid metal of Fe–La–Ce–O system at 1600 °С, using the technique of constructing the solubility surfaces for the components of a metal, was carried out. The calculation technique allowed assessing the depth of liquid iron de-oxidation at a complex use of lanthanum and cerium as deoxidizing agents. Also, diagrams of de-oxidants’ consumption for one ton of liquid oxygen-containing iron were calculated in the course of the work. Carrying out a calculation of the solubility surfaces for the components of a metal required simulation of phase diagrams of the following oxide systems: FeO–La₂O₃–Ce₂O₃, FeO–CeO₂–La₂O₃, CeO₂–La₂O₃–Ce₂O₃. The obtained results might be of interest for optimization of the use of rare-earth metals in steelmaking technology.

Abstract: The isothermal section of the phase diagram of Tb–Fe–C system at 800 °C was studied in the full concentration range using powder X-ray phase and structure analyses, and energy-dispersive X-ray spectroscopy. Six ternary compounds Tb_1.88Fe₁₄C, Tb₁₃Fe₁₀C₁₃, TbFeC₂, Tb₁₅Fe₈C₂₅, Tb_5.64Fe₂C₉, Tb₂FeC₄ and a limited solid solubility of carbon in the crystal structure of the binary parent compound Tb₂Fe₁₇C_х (0≤ х ≤0.8) have been found to exist at 800 °C. The crystal structures of two new ternary carbides have been determined by means of powder X-ray diffraction: Tb₁₅Fe₈C₂₅ with structure type Er₁₅Fe₈C₂₅, space group P321, a = 11.9706(3) Å, c = 5.1733(2) Å, R_B(I) = 0.07, R_P = 0.06, R_Pw = 0.08, and Tb₁₃Fe₁₀C₁₃ with structure type Gd₁₃Fe₁₀C₁₃, space group P3₁21, a = 9.1800(9) Å, c = 23.703(5) Å, R_B(I) = 0.04, R_P = 0.16. Both compounds are representatives of the carbometalate class of complex carbides. Tb₁₅Fe₈C₂₅ displays an itinerant ferro-or ferrimagnetic ordering of the Fe 3d-moments below T_M ≈ 50 K while Tb 4f-moments remain essentially paramagnetic at least down to about 10 K.

Abstract: The thermodynamic modeling of phase equilibria in the liquid metal of the Cu–Na–O, Cu–K–O and Cu–Na–K–O systems in the temperature range of 1100–1300 °С was done. The calculations were performed using the methodology of constructing a surface of component solubility in the metal melt, which does not only allow us to calculate the isotherms of oxygen solubility in the molten metal, but also to link the changes in the composition of such molten metal with quality changes in the composition of the interaction products. The isotherms of the oxygen solubility in the liquid metal of the Cu–Na–O, Cu–K–O and Cu–Na–K–O systems were constructed.

Abstract: The diffusion of a B element into an A matrix was studied by the random walk theory. Considering that concentration of B element in the A matrix is very low, the jumps of diffusing atoms are independent of each other. The A matrix is a two-region material with different properties, such as a two-phase material, a single crystal with dislocations, or regions influenced by other solute and a polycrystalline material.It is assumed that material B has a penetration that allows it to cross each region of material A several times. This implies that jumps across the surface between those regions have an average frequency and, as a consequence, there is an interdiffusion coefficient between them. The interdiffusion coefficient between those regions is different than the coefficient of the diffusion in each region.Expressions were obtained that allow to delimit the ranges of validation with greater precision than the corrected Hart-Mortlock equation for solute diffusion. In addition, an original relationship was obtained between the segregation coefficient and parameters specific to the diffusion. New powerful tools were also found that can help to understand diffusion in nanocrystalline materials, diffusion in metals influenced by impurities and diffusion produced by different mechanisms.