No abstract

Extensive computations have been performed using the Lebowitz solution of hard sphere mixtures as a reference system, and perturbed the hard sphere direct correlation function, C O ij (r), with square well attractive tail. We used mean spherical model to compute the total and partial direct correlation functions in the attractive and repulsive regions of the interacting potential of Ag-In alloy at different compositions. The potential parameters were those obtained for pure metals. With these potential parameters (the partial and total) structure factors were evaluated, and then Fourier transformed to get the partial and total radial distribution functions. Further the well-known Bhatia-Thornton correlation functions namely the numbernumber, concentration-concentration, and number-concentration correlation functions have been computed. We also obtained total and partial coordination numbers from partial and total pair correlation functions respectively. With the help of these pair correlation functions we give the distances between atoms namely Ag-Ag, In-In and Ag-In at different compositions of In in Ag-In alloy. It is found that these distances practically remain constant and are independent of composition, which has been attributed to the formation of segregated clusters of atomic dimensions. Using Kirkwood-Buff's equation, compressibillities have been calculated as a function of composition. The temperature derivative of diffusion coefficient for pure constituents has been formulated and the computed results were compared with the available experimental values. With this model the diffusion coefficients and the friction coefficients of the constituents have been obtained through the use of Helfand's trajectory principle with a reasonable success in the alloy as well. It is found that these metals of the alloy tend to segregate. The ratio of diffusion coefficients of the metals in the alloy is almost a constant and is equal to 0.9. This shows that the alloy forms a regular solution in spite of their tendency to segregate.

A closed form expression for S(k), the structure factor, has been derived, taking the square well potential as a perturbation in the mean spherical model approximation. This expression has been used to calculate the structure factor and radial distribution function, q(r), for liquid mercury and aluminium a t various temperatures and densities. The very good agreement between theory and experiments suggests that the representation of the attractive tail by a square well potential is a satisfactory one and the concept of pairwise interactions is a useful tool in understanding some of the structural problems of liquid metals.Es wird ein geschlossener Ausdruck fur den Strukturfaktor S ( k ) abgeleitet, wobei das Kastenpotential als Storung der mittleren Kugel-Modell-Naherung angenommen wird. Dieser Ausdruck wurde zur Berechnung des Strukturfaktors und der radialen Verteilungsfunktion g ( r ) fur fliissiges Quecksilber und Aluminium bei verschiedenen Temperaturen und Dichten benutzt. Die sehr gute Ubereinstimmung zwischen Theorie und Experiment zeigt, da13 die Darstellung des attraktiven Auslaufers durch ein Rechteckpotentiad befriedigend ist und da13 das Konzept der paarweisen Wechselwirkung ein nutzliches Hilfsmittel fur das Verstandnis einiger Strukturprobleme flussiger Metalle ist.

The partial structure factors defined by Ashcroft and Langreth and also the number-number, nil mbcr-concentration, and concentration-concentratiori structure factors of Bhatia and Thornton arc calculated for liquid sodium-cesium alloys a t various concentrations with a square-well potential. The total structure factor obtained from these partials compares very well with experimental rcsolts. Isothcrmal compressihilities obtained from the partial structures in the long wave limit are also found to compare satisfactorily with those calculated from sound velocity data. Dic yon Ashcroft und Langceth definiertcn Teil-Strrikturf~~ktoren sowie die Zahl-Zahl-, Zahl-Konmntrnt ions-nnd Konzentrations-Konzentrations-Strukturfaktoren von Bhatia und Thornton nertlen fur flussige Natriiim-Caesium-LF.gierungen bei verschiedenen Konzentrationen mit einemRcclitcck-Potential bcrechnet. Die a m diescn Purtiulfaktoren erhaltenen Gesurntstniktiirf~iktoren stimmcn schr gut mit experimentellen Werten iiberein. Es wird gefunden, daB die isothermen Kompressi'bilitatcn tius den Partialstrukturen im Grenzfall langer Wellen befriedigend mit dencn nus Sch

Hg-In alloy consisting of Hg, which shows several anomalous features in its properties and In, has been studied with a square-well attractive tail as an interaction potential between the atoms in the amalgam. The partial and the total interference functions have been computed with the Lebowitz hard-sphere mixture solution for the Percus-Yevick equation with an attractive square-well potential over a hard-sphere mixture. In addition, the Bhatia-Thoronton correlation functions have also been calculated. From the partial structure factors the number of nearest neighbors has been calculated. All the computed results have been found to be in very good agreement with the x-ray diffraction results obtained by Halder and Wagner [Z. Naturforsch. 22a, 1489[Z. Naturforsch. 22a, (1967] except at 62% atomic fraction of indium. All these results were computed purely from the potential parameters of the pure metals. The alloy is found to show a shoulder in the S&c(IC) cross correlation function. This may be due to either compound formation or internal segregation, even though the metals mix freely at all concentrations. The compressibilities at various concentrations of In have been computed from the Kirkwood-Buff formula. The diffusion coefficients have been calculated from Helfand s linear-trajectory principle. The self-diffusion coefficients as evaluated correctly predict them for both metals because of the attractive wells associated with these Inetals. Thus Hg, in spite of its heavy mass, has a comparatively higher diffusion coefficient than In, which has a lower mass.The melt appears to form a regular solution, as predicted by Bearman and Jones.