Partial Excess Gibbs Free Energy Research Articles

Electrochemical behavior and effective extraction of Er in fused LiCl-KCl eutectic

For the efficient electrolytic extraction of Er from spent nuclear fuel, a series of electrochemical methods was used to research the electrochemical behavior of Er(III) in the LiCl-KCl system on inert (Mo) electrode and on reactive (Ni) electrodes. On the inert Mo electrode, the reduction of Er(III) to Er(0) is a one-step with three-electron and quasi-reversible reaction process. Meanwhile, the apparent generation Gibbs free energy and activity coefficients of Er(III) on the inert electrode were determined. Thereafter, the electrochemical reduction of Er(III) on the Ni electrode was emphatically investigated. Er(III) is reduced at a corrected potential owing to the formation of Ni-Er alloys. In addition, thermodynamic parameters such as partial excess Gibbs free energy change of Er in Ni, activity and apparent generation Gibbs free energy of the Ni-Er alloys were determined by the electromotive force method. Finally, different Ni-Er alloys were produced using potentiostatic electrolysis on the Ni cathode by controlling different potentials. Moreover, electrolytic extraction was carried out on the Ni cathode at the potential of –2.0 V, and the separation efficiency of Er reaches 99.72%, which proves the practicability of separating Er from LiCl-KCl eutectic on the reactive Ni cathode.

Thermodynamic, structural and surface properties of rare earth metallic alloys: Au-La liquid system

A complete information related to the mixing behaviours of Au alloyed with rare earth metals or lanthanides is very scarce. Therefore, an attempt has been made in this work to compute and study the temperature and concentration dependent thermodynamic, structural and surface properties of Au-La liquid alloy using different theoretical approaches. The thermodynamic properties, such as excess Gibbs free energy of mixing, enthalpy of mixing, excess entropy of mixing and activity of the system were computed using available coefficients of interaction energy parameters in the framework of Redlich-Kister polynomial. Taking these as reference values, model parameters for quasi-lattice model were optimised at 1473 K. The model parameters were then determined at higher temperatures assuming them to be linear temperature-dependent. The thermodynamic and structural properties were then computed in the temperature range 1473 K-1773 K. The surface properties of the system were computed using Bulter’s model using determined values of partial excess Gibbs free energy of its components. Present investigations revealed that the compound forming tendency of the system gradually decreased with increase in temperature of the system.

Thermodynamic and surface properties of Al–Li–Mg liquid alloy

The thermodynamic database of excess Gibbs free energy of mixing was theoretically reproduced at temperatures 1000 K, 1073 K 1150 K, and 1250 K for liquid Al–Li–Mg ternary alloy on the basis of GSM, Toop and Kohler models. For this purpose, the linear as well exponential T-dependent interaction parameters of Redlich-Kister (R–K) polynomials were optimised. These parameters were used to compute the activities of the monomers of the binary sub-systems. The enthalpy of mixing of the ternary system was computed using exponential T-dependent parameters. The surface tensions of binary sub-systems were calculated employing Butler's equations and using the theoretically determined partial excess Gibbs free energy of constituent elements of the alloy. Further, the optimised coefficients of R–K polynomials were obtained for excess surface tensions of binary sub-systems. With the aid of these coefficients, the surface tension of the ternary system was computed in the frame work of models mentioned above.

Critical evaluation and thermodynamic optimization of Mg–Ga system and effect of low pressure on phase equilibria

A complete literature review and critical evaluation of the Mg–Ga binary system are presented. All stable phases known in this system were thermodynamically modeled in the framework of CALPHAD. Liquid phase was modeled using the Modified Quasichemical Model in the pair approximation which takes into account short-range ordering. α-(Mg) solid solution of hcp structure was modeled as a substitutional solution. All intermetallic phases Mg5Ga2, Mg2Ga, MgGa, MgGa2, Mg2Ga5, as well as Ga-rich phase, were treated as stoichiometric compounds. Gas phase was assumed to behave as an ideal solution. Thermodynamic optimization was carried out by evaluating enthalpic and entropic contributions to the Gibbs free energy of all phases independently. It showed that the optimized model parameters along with the model equations could reproduce the available and reliable experimental data in the Mg–Ga system. Representation of partial excess Gibbs free energy of Mg in Ga-rich liquid was improved compared to the previous thermodynamic modeling. Low pressure phase equilibria in this system were analyzed using the developed thermodynamic model, and it was compared with a recent observation of an Mg nanopillar fabricated by Ga+ ion beam in a focused ion beam (FIB), followed by in-situ heating in a transmission electron microscope (TEM). Reported surface melting of Mg nanopillar in the TEM column pressure (~10−10bar) is attributed to the fact that decreasing pressure enhanced sublimation of Mg from the Mg nanopillar significantly, leaving Ga-rich liquid.

On the three-factor models and the subregular approximation in phase diagram calculation

An algorithm for the systematic investigation of the values of the excess Gibbs free energy of a ternary system and the partial excess Gibbs free energies of its components as predicted by a large class of three-factor models in the subregular approximation is presented. The equations used in ternary phase diagram calculation are written in a form that emphasizes the three-factor model dependent part of each function.

Discussion of the decrease in the homologous retention increment on raising the polarity of a stationary phase in gas chromatography

The empirical observation that the retention ratio of two successive homologues decreases upon increasing the polarity of the stationary phase in gas chromatography is explained in terms of the thermodynamic properties of the sorption system. This retention ratio is proportional to the negative value of the sum of the standard Gibbs free energy change of condensation and the partial excess Gibbs free energy per mole of a CH 2 group of the solute. As the value of the Gibbs free energy of condensation is negative while the excess Gibbs free energy increases in the positive direction on increasing the polarity of the sorbent, the absolute value of the above sum must be the smaller, the higher the polarity of the sorbent.