Weiping Gong

Diffusion coefficients of some solutes in fcc and liquid Al: critical evaluation and correlation

The diffusion coefficients of several transition elements (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and a few non-transition elements (Mg, Si, Ga, and Ge) in fcc and liquid Al are critically reviewed and assessed by means of the least-squares method and semi-empirical correlations. Inconsistent experimental data are identified and ruled out. In the case of the elements, for which plentiful experimental data are available in the literature, the least-squares analysis gives rise to the activation energies and pre-exponential factors in an Arrhenius equation. For the elements with limited experimental data or no data at all, the diffusion parameters are estimated from two semi-empirical correlations. In one correlation, the logarithmic pre-exponential factors are plotted against the activation energies for various elements in Al. In the other correlation, the activation energies are shown as a function of valences relative to Al. The diffusion coefficients calculated by using the evaluated diffusion parameters agree reasonably with the reliable experimental data. The proposed semi-empirical correlations are used to predict the diffusion coefficients of a few elements in liquid Al. A satisfactory agreement between the predicted and measured diffusion coefficients is obtained.

Thermodynamic reassessment of the Al-V system

Abstract An optimized set of thermodynamic functions to describe the Al – V system has been obtained by a computer-operated least squares method applied to the experimental phase diagram and thermodynamic data available from the literature. Special attention is paid to the modeling of the intermediate phase Al8V5. Based on the crystal structure data, Al8V5 is described by a sublattice model Al6/13(Al, V)2/13 (Al, V)3/13 V2/13 in a final treatment. The boldface Al and V mean the normal atoms (i. e., major species) in the sublattices. In order to provide reasonable starting values for the final modeling, three treatments are performed. In the first treatment, Al8V5 is assumed to be a stoichiometric compound; in the second and third ones, it is described by sublattice models Al6/13(Al, V)2/13 V5/13 and Al8/13(Al, V)3/13 V2/13, respectively. This step-by-step modeling procedure provides reliable estimates and useful starting values for the parameters at each of the higher levels. The other phases (liquid, fcc...

Thermodynamic properties of the Al–Nb–Ni system

Abstract This paper provides a consistent thermodynamic data set for the whole Al–Nb–Ni ternary system via thermodynamic modeling. The order/disorder transitions between disordered bcc_A2 and ordered bcc_B2 phases as well as between disordered fcc_A1 and ordered L1 2 phases are treated using a two-sublattice model. The calculations indicate that the disordered and ordered phases can be described with a single equation. All of the experimental phase diagram data available from the literature are critically reviewed and assessed using thermodynamic models for the Gibbs energies of individual phases. Inconsistent experimental information is identified and ruled out. Optimal thermodynamic parameters are then obtained by considering reliable literature data. Comprehensive comparisons between the calculated and measured phase diagrams show that almost all the accurate experimental information is satisfactorily accounted for by the present thermodynamic description.

Thermodynamic investigation of ZrO2-BaO system

Thermodynamic description of ZrO2-BaO system was developed using the available experimental information. Special attention was paid to the modelling of the perovskite phase BaZrO3 by a temperature-dependent polynomial to fit the experimental thermodynamic properties. The liquid phases, C(subscript SS) (cubic ZrO2 solid solution) and T(subscript SS) (tetragonal ZrO2 solid solution) were modelled with Redlich-Kister formula. The compounds Ba2ZrO4 and Ba3Zr2O7 were treated as stoichiometric phases and the BaO(subscript SS) and M(subscript SS) (halite BaO and monoclinic ZrO2 solid solutions) were treated as pure compounds. Comparisons between the calculated and the measured phase diagram as well as the thermodynamic quantities indicate that the most reliable experimental information is satisfactorily accounted for by the present thermodynamic calculation.

Thermodynamic modelling and applications of Ce–La–O phase diagram

Abstract The Ce–La–O system was investigated via experiments and thermodynamic modeling. A series of CeO 2 –LaO 1.5 mixtures were prepared by co-precipitation technique and examined by X-ray diffraction. Mutual solubilities between LaO 1.5 and CeO 2 at 1273 K were determined. Using the new experimental data together with literature information, a set of self-consistent thermodynamic parameters for the CeO 2 –LaO 1.5 system were optimized. Combined with thermodynamic descriptions of Ce–O and La–O systems from literature, several property diagrams of Ce–La–O system were calculated and used to explain oxidation process of the Ce–La alloys. The fluorite phase is the unique oxidation products for most of the Ce–La alloys.

Thermodynamic investigation of Fe-Ti-Y ternary system

An extensive investigation on the Fe-Ti-Y system was performed via experimental measurement and thermodynamic calculation. The Fe-Ti-Y ternary couples at 1 273 K were prepared with a desire to provide accurate phase relationships needed for the refinement of this ternary phase diagram. And a tentative isothermal section of Fe-Ti-Y at 1 273 K was built based on the experimental information. In the thermodynamic modeling, the thermodynamic parameters for the Ti-Y binary system and the ternary phase in the Fe-Ti-Y system were evaluated. Those for the Fe-Ti and Fe-Y systems from literature were slightly modified for the compatibility. The isothermal sections of Fe-Ti-Y ternary system at 873 K and 1 273 K were calculated. The ternary compound Fe11TiY and Fe2(Ti, Y) solid solution formed from Fe2Ti and Fe2Y are detected, which is in good agreement with the literature information.

Experimentation and thermodynamic modelling on SrZrO3

Experimental data for the perovskite phase SrZrO3 were subjected to a critical thermodynamic assessment using the CALPHAD approach. Special attention was paid to the structural behavior of SrZrO3 to illustrate, how to select an appropriate thermodynamic model based on crystal structure and chemistry information, how to identify and resolve the inconsistency between various kinds of experimental data, and how to use thermodynamic modeling as a basic tool in the development and optimization of materials and process. Our assessment results in a Gibbs energy function covering the temperature range between 300 K and the melting point, which explains the experimental data within the experimental uncertainty.