Short Range Order Modeling in Alloys

The Short and Long Range Orders in alloys can be considered based on a new expression for the combinatorial factor. This expression is more convenient and intuitive than the traditionally used form and can be directly applied to reproduce the results of several good known statistical-thermodynamic models that usually are considered completely independent or even inconsistent.The short list includes quasichemical theory, associated solution model, surrounded atom model, cluster site approximation.As result, the formalism and interpretation of these models are significantly clarified, allowing simultaneously to identify and fix several long standing errors that otherwise could be left unnoticed.Multicomponent generalization of listed models is also critically simplified.For the systems experiencing a phase transition, the advanced version of theory provides a mechanism allowing to reproduce the correct critical temperature of conversion and at the same time to increase significantly the precision of thermodynamic functions.

Modelling thermodynamic properties of binary Cu–Eu and ternary Al–Cu–Eu melts

Model calculations of the whole set of thermodynamic properties of liquid alloys for the binary Cu–Eu and ternary Al–Cu–Eu systems have been performed. Authors used the ideal associated solution model (IAS model) for calculation of the entropies and excess Gibbs energies of mixing for these systems. The binaries were given as the Redlich-Kister polynomials. The thermodynamic properties for the ternary system are described using the Redlich-Kister-Muggianu formalism. A comparison of the surfaces of excess Gibbs energy and entropy of mixing for liquid Al–Cu–Eu alloys at 1350 K demonstrates that the ordering related to the formation of rather strong associates in the Al–Eu system significantly affects the concentration dependence of the excess Gibbs energy of mixing in the liquid phase at this temperature.

Chromous capacities of ferrochromium and matte smelting slags

Purpose: of this paper is to extend the slag capacity concept to sparingly soluble cationic species encountered for example in matte smelting and ferrochromium processing in terms of chromous capacities. Design/methodology/approach: In this context in order to develop the chromous capacity the experimental data on slag-metal equilibrium for ferrochromium smelting and on chromium distribution between slag and matte phases encountered in sulphide smelting of PGM (Platinum Group Metals) and chromium containing copper nickel concentrates were used. Findings: The calculated chromous capacities were in the 10-8 range for ferrochrome smelting slags and 10-4 range for matte smelting slags. These values indicate the very low and moderate chromous ion dissolving ability of ferrochromium smelting slags and matte smelting slags respectively. Research limitations/implications: Due to highly reducing conditions in ferrochromium smelting and the imposed low oxygen partial pressures in sulphide smelting of chromium and PGM containing concentrates chromium in the slag was assumed to be in its divalent state. The slag-metal/matte reaction for dissolution of chromium into the slag as a cation under reducing conditions -in contrast to reactions for dissolution of species such as sulphur and phosphorus into the slag as anions under oxidizing conditions – required the release of electrons. Thus to maintain charge neutrality the dissolution of chromium from the metal or the matte phases into the slag as Cr2+ ions was accompanied by consumption of these electrons by reduction of Fe2+ ions in the slag into metallic Fe which dissolved in the metal/ matte phase. This was supported by the experimental equilibrium data. Hence the slagmetal/ matte reaction defining the chromous capacity involved both O2- and Fe2+ ions of the slag phase. Moreover for matte smelting the thermodynamic activities of species in the matte phase were assumed to conform to ideal associated solution model due to lack of data. For future work it is advisable to determine such activities. Practical implications: The calculated chromous capacities were in the 10-8 range for ferrochrome smelting slags and 10-4 range for matte smelting slags. The results clearly indicate that in matte smelting lower basicity slags would be preferable to render chromium more soluble in the slag in contrast to ferrochromium smelting where higher basicity slags would be suitable to minimize chromium losses to the slag. Originality/value: This research and hence the paper is probably the first on dissolution of chromium as chromous ion in slags, thus it is novel and original.

Theoretical Modeling to Predict the Thermodynamic, Structural, Surface and Transport Properties of the Liquid Tl−Na Alloys at different Temperatures

<p>Theoretical modeling equations are developed by extending regular associated solution model to predict the thermodynamic and structural properties of the liquid Tl−Na alloys at higher temperatures. The thermodynamic properties have been predicted by computing activities of unassociated monomers (a_Tl and a_Na) and free energy of mixing (G_M) at temperatures 673 K, 773 K, 873 K and 973 K. The structural properties have been predicted by computing concentration fluctuation in long wavelength limit (S_CC(0)), short range order parameter (α₁) and ratio of mutual to intrinsic diffusion coefficients (D_M/D_id) at aforementioned temperatures. These properties have been then correlated with the modified Butler's model to predict the surface properties, such as surface concentrations of free monomers (X^S_Tl and X^S_Na) and surface tension (σ) of the alloy at above mentioned temperatures.</p><p><strong>Journal of Nepal Physical Society</strong><em><br /></em>Volume 4, Issue 1, February 2017, Page: 101-110</p>

Thermodynamic and structural properties of Mg-Tl liquid alloy

The concentration dependent asymmetry in mixing properties of Mg-Tl liquid alloys at 923 K has been investigated on the basis of regular associated solution model. The concentration of ApB type complex in a regular associated solution of Mg and Tl have been determined. We have then used the concentration of complex to calculate the free energy of mixing, enthalpy of mixing, entropy of mixing, activity, concentration fluctuations in long wavelength limit SCC(0) and the Warren Cowley short-range parameter 1 α .The analysis suggests that heterocoordination leading to the formation of chemical complex Mg2Tl is likely to exist in the melt. The analysis reveals that there is a tendency of unlike atom pairing (Mg-Tl) in Mg-Tl alloy whole range of concentration.Keywords: Mg-Tl alloy; microscopic structure; pairwise interaction energy; chemical short range orderDOI: http://dx.doi.org/10.3126/bibechana.v8i0.5692BIBECHANA 8 (2012) 81-89

Concentration Fluctuation in Long Wavelength Limit in Liquid Magnesium Alloy

The microscopic structure of MgSn liquid alloy at 1073K has been studied by using regular associated solution model. For this we have calculated the concentration fluctuation in long wave length limit [SCC(0)] and chemical short range order parameter (α1) of liquid MgSn alloy at 1073 K.Keywords: Binary Alloy; Complex; Chemical order; Microscopic FunctionThe Himalayan Physics Vol.2, No.2, May, 2011Page: 47-49Uploaded Date: 1 August, 2011

Energy Disorder in Liquid Fe-Si Alloy

The observed asymmetry in the properties of mixing of Fe-Si alloy in molten state is successfully explained on the basis of regular associated solution model. We have determined the free energy of mixing, heat of mixing and entropy of mixing of Fe-Si alloys in molten state at 1873 K. The analysis suggests that heterocoordination leading to the formation of complex Fe 2Si is likely to exist in the liquid and is of a strongly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature.Keywords: Liquid alloy; Clusters; Thermodynamic propertiesThe Himalayan Physics Vol.1, No.1, May, 2010Page: 37-40Uploaded Date: 28 July, 2011