I.S. Jha

Structural asymmetry in liquid Fe–Si alloys

The thermodynamic properties and microscopic structure of liquid Fe–Si alloys at 1873 K were studied by using the regular associated solution model. The model was utilized to determine the complex concentration in a regular associated solution of Fe, Si and Fe2Si. The complex concentration was then used to calculate the integral excess free energy of mixing, activity, concentration fluctuations in the long-wavelength limit, SCC (0), and the Warren–Cowley short-range parameter α 1. The analysis suggests that heterocoordination leading to the formation of complex Fe2Si is likely to exist in the liquid and is of a strongly interacting nature. The theoretical analysis reveals that the alloy is more ordered towards the Fe-rich region. The observed asymmetry in the properties of mixing of Fe–Si alloys in the molten state is successfully explained on the basis of the regular associated solution model.

Structural and energetic asymmetry in liquid Ag–Al alloys

The thermodynamic and microscopic structure of Ag–Al liquid alloy at 1273 K has been studied by using regular associated solution model. This model has been utilised to determine the complex concentration in a regular associated solution of Ag and Al. We have then used the complex concentration to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity and concentration fluctuations in long wavelength limit S CC(0) and the Warren–Cowley short-range parameter α 1. The analysis suggests that heterocoordination leading to the formation of complex Ag3Al is likely to exist in the liquid but is of a weakly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is more ordered towards Ag-rich region. The alloy behaves like a segregating system in Al-rich region.

Anomaly in mixing properties of lithium–magnesium liquid alloy

The concentration dependent asymmetry in mixing properties of LiMg liquid alloys at 1000 K has been investigated on the basis of regular associated solution model. The analysis suggests that heterocoordination leading to the formation of chemical complex Li2Mg is likely to exist in the melt.

Theoretical assessment on mixing properties of liquid Tl–Na alloys

Abstract Thermodynamic and structural properties of mixing of molten Tl–Na alloys at 673 K have been investigated using quasi-chemical model. To understand the mixing behaviour in more detail, emphasis is placed on the role of interaction energy term, and viscosity and surface tension of the alloys have also been analysed under statistical considerations. Our study shows negative deviation from the Raoultian behaviour in the properties of Tl–Na alloy thereby indicating hetero-coordination in the Tl–Na melt at 673 K in the full range of concentration. Theoretically, computed thermodynamic data at 673 K agree very well with the corresponding experimental data. The viscosities of the alloys computed from Kaptay equation show small negative deviation and those computed from Singh and Sommer’s formulation show small positive deviation from ideal values while the Budai-Benko-Kaptay equation predicts noticeable negative deviation in Na-rich end and positive deviation in Tl-rich end of the composition. The calculations of surface tension reveal that results obtained from layered structure approach and compound formation model are in good agreement in the Na-rich side and in reasonable agreement in Tl-rich side of the composition, while those computed from Butler equation show noticeable deviations in the intermediate compositions. Both the viscosity and surface tension of liquid Tl–Na alloys increase with addition of Tl-component, viscosity having approximately linear variation with concentration. The study shows that there is non-linear variation in surface composition with bulk concentration and for most of the compositions the surface of the alloy is enriched with Na-atoms which segregate to the surface.

Phase separation in Na–K liquid alloy

The quasi-chemical expression for weakly interacting binary alloy has been applied to obtain energy parameters and their temperature derivatives for Na–K liquid alloy at 384 K. These energy parameters have then been used to calculate thermodynamic functions, such as free energy of mixing, heat of mixing, entropy of mixing and microscopic functions, such as concentration fluctuation in long wavelength limit, Warren–Cowley short-range order parameter, ratio of mutual and self-diffusion coefficients. The analysis reveals that the energy parameters are temperature dependent and the Na–K liquid alloy at 384 K is a weakly interacting homocoordination system. The observed thermodynamic properties of Na–K alloy in molten state have successfully been explained by assuming Na2K complex on the basis of the quasi-chemical formalism for a weakly interacting system.

Prediction of thermodynamic and surface properties of Pb−Hg liquid alloys at different temperatures

Abstract The thermodynamic properties, such as free energy of mixing, heat of mixing, activity and structural properties, such as concentration fluctuation in long wavelength limit, short-range order parameter of Pb–Hg liquid alloy at 600 K have been calculated using theoretical modelling. It has then been correlated with modified Butler model to compute the surface tension of the alloys at different temperatures. The Pb–Hg system at 600 K is found to be ordering at higher concentration of Pb.

The segregating nature of Cd–Pb liquid binary alloys

The segregating nature of Cd–Pb liquid alloys has been reported using simple statistical theory of mixing. The energetics of mixing in liquid binary alloys has been analysed through the study of surface properties (surface tension and surface concentration), transport properties (viscosity and chemical diffusion) and various thermodynamic and structural functions. Positive deviation from Raoultian behaviour has been observed in the computed mixing parameters of the alloys. Our results are in good agreement with experimental data and support a weak demixing tendency in Cd–Pb liquid alloys.

Structural and energetic assessment in cadmium–indium liquid alloys

The mixing behaviour of liquid cadmium–indium alloys has been analysed on the basis of quasi-chemical approximation by computing thermodynamic parameters, such as free energy of mixing (G M), entropy of mixing (S M), heat of mixing (H M) and chemical activities (a i) and structural functions, such as concentration fluctuation in the long wavelength limit (S cc(0)), the Warren–Cowley short-range order parameter (α 1) and the ratio of diffusion coefficients (D m/D id) of the alloys at 800 K. The analysis suggests that there is a tendency of like atom pairing (Cd–Cd, In–In) in Cd–In alloy over entire concentrations and ordering energy is found to be temperature dependent. Cd–In alloy at 800 K in the molten state is slightly segregating in nature.

Theoretical investigations on thermodynamic properties and concentration fluctuations of Zn-Sn binary liquid alloys at different temperatures by optimization method

ABSTRACTThe concentration fluctuations in long wavelength limit and thermodynamic properties, i.e. free energy of mixing, heat of mixing, entropy of mixing and activity of the components involved in the Zn-Sn binary liquid alloy at a specified temperature, have been investigated using a familiar formalism in which the combined effect of size ratio, entropic and enthalpic effect is considered. These properties of Zn-Sn liquid alloys at 750 K have been computed by estimating the best fit value of order energy parameter (W) and size ratio () in the entire range of concentration in order to match their experimental and theoretical values. This value of W has been used to determine the values of W at different temperatures with the help of temperature derivative of W which are then used for the optimization procedure in order to calculate the corresponding values of excess free energy of mixing, partial excess free energy of mixing and activity of the components involved in the alloy at different temperatures....

Mixing behaviour of Au–Cu melt

The quasi-chemical expression for weakly interacting binary alloy has been applied to obtain energy parameters and their temperature derivative for Au–Cu liquid alloy at 1550 K. These energy parameters have then been used to calculate thermodynamic functions, such as free energy of mixing, heat of mixing, entropy of mixing, and activity and microscopic functions, such as concentration fluctuation in long wavelength limit and Warren–Cowely short-range order parameter. The analysis reveals that the energy parameters are temperature-dependent and the Au–Cu liquid alloy at 1550 K is moderately interacting hetero-coordinating system. The observed thermodynamic properties of Au–Cu alloy in molten state have successfully been explained by assuming Au3Cu complex on the basis of the quasi-chemical formalism for weakly interacting system.