Please use this identifier to cite or link to this item:
Full metadata record
|Thesis submitted to T.M. Bhagalpur University, for the degree of Doctor of Philosophy in Faculty of Science (Physics), 2011.
|There are large numbers of binary alloys which possess characteristic features that most of their thermodynamic properties, such as free energy of mixing, heat of mixing, entropy of mixing and many other electrical properties are asymmetrical as a function of concentration. The liquidus lines for these systems are complicated and usually S-shaped. Such behavior of liquid alloys is still an active area of research and it demands an extensive theoretical investigation. The importance of these properties can be understood as they can provide enormous amount of information for understanding metallurgical process and material preparation of metal alloys. Moreover, investigating the physicochemical properties of binary liquid alloys is of major significance in connection with their extensive application in various branches of science and novel engineering. Since long metal Physicists have been trying to interpret the physical properties of liquid alloys so that their alloying behaviors could adequately comprehended. Several models have been proposed to solve the complexities of obtaining thermodynamic and microscopic parameters of binary liquid alloys. In present work, we have studied the thermodynamic properties and microscopic structure of Fe-Si, Cd-Na, Cu-Sn, Ag-Al, Ag-Sb, Hg-Na and Mg-Tl alloys in their liquid state near melting point using regular associated solution model. In regular associated solution model, it is assumed that strong associations among the constituent species exist in the liquid phase close to the melting temperature. These associations are given different names such as 'complexes', 'pseudomolecules', 'clusters', 'associations' etc. This assumption has been used by several researchers to explain the asymmetry of the properties of mixing for binary alloys. If type A and type B metals are mixed in the melt to form an alloy, the melt consists of three species namely unassociated A-atoms, unassociated B-atoms and complex ApBq (where p is small integer and q =1). Thus binary alloys in a liquid phase can be considered as a ternary mixture of unassociated atoms of components and complexes, all in chemical equilibrium. In regular associated solution model, it is assumed that the thermodynamic behaviour of the components A and B is governed by the true mole fractions xA , xB and xApB rather than the gross mole fraction x1 and x2. It is further assumed that the intermolecular forces between the species and the complex are no longer equal, and hence unassociated species do not interact equally strongly with the complex. To study the properties of the alloy systems considered in our investigation, we have assumed respective complexes Fe2Si, Hg4Na, MgTl, Ag3Al, Cu3Sn, Ag3Sb and Cd2Na in the liquid state of Fe-Si, Hg-Na, Mg-Tl, Ag-Al, Cu-Sn, Ag-Sb and Cd-Na alloys. In making selection of chemical complexes which might exist in the liquid phase, we have been guided by the fact that these are the most stable intermetallic compounds in their corresponding solid phase. We have determined pairwise interaction energies (ωij), equilibrium constant (K) and the mole fraction of corresponding complexes (xApB) for all alloys under investigation separately using their own experimental data of activity treating the solution as a ternary mixture on the basis of regular associated solution model. Our study reveals that maximum association occurs at or near compound forming composition of the alloys. It has been found that the maximum association occurs at 69 at. % of Fe for Fe-Si, 66 at. % of Cd for Cd-Na, 75 at. % of Cu for Cu-Sn, 71 at. % of Ag for Ag-Al, 70 at. % of Ag-Sb, 75 at. % of Hg for Hg-Na and 56 at. % of Mg for Mg-Tl alloys. All interaction energies have been found to be negative for Fe-Si, Hg-Na, Ag-Al, Ag- Sb and Cu-Sn liquid alloys whereas they are negative as well as positive values for Mg- Tl and Cd-Na liquid alloys. The computed value of free energy of mixing (GM ) for all liquid alloys has been found to be in a very good agreement with their corresponding observed values. We have found that the free energy of mixing is negative for all the alloys taken in our investigation at all concentrations. The effect of equilibrium constant and interaction energy parameters on GM has been found to be accompanied by the other parameters together with activity coefficient of pure species in a particular system and the activity data. The free energy of mixing for different systems differs considerably from each other both in magnitude and nature. The value of G / RT M clearly indicates that Hg-Na is strongly interacting system followed by Fe-Si, Mg-Tl, Ag-Al, Cu-Sn, Ag-Sb and Cd-Na.
|Binary liquid alloy
|Regular associated solution model for the properties of binary liquid alloys
|Appears in Collections:
|500 Natural sciences and mathematics
Files in This Item:
|110. Dr.Devendra Adhikari.pdf
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.