L. A. Hussain

Assessment of size effect on the surface properties of some binary liquid alloys

Abstract The effect of size in the calculation of the surface properties of some liquid binary alloys has been studied using the theoretical model developed by Prasad et al. (Phys. Chem. Liq. 27 (1994) 179). The systems studied include Na–Cs, Sn–Ga and Cu–Ni, which manifest a tendency to phase separation, in addition to Li–Ba and Na–Te, which exhibit a tendency to compound formation. Our results indicate that for those systems studied with phase separating tendencies, effects due to size considerations are quite significant. In general, we infer from our calculations that for the same value of order energy W / K B T , the effect of size is to reduce the surface concentration and to increase the surface tension, while the reverse holds when size effects are neglected. Compound forming systems do not follow this trend as the impact of size appears to depend both on the relative sizes of the alloying components and the degree of compound formation in the alloy.

Structures and autocorrelation functions of liquid Al and Mg modelled via Lennard-Jones potential from molecular dynamics simulation

The structures and autocorrelation functions of Al and Mg in the liquid state are investigated through the pair distribution functiong(r), the diffusion coefficients as well as the shear viscosity via the Green-Kubo and Einstein relations. From the structure and the Enskog relation we determined the frequency of collisions of atoms in the first shell ofg(r) in the systems. We also discovered that the packing fraction of Lennard-Jones liquids should be approximately half the reduced density value. This approximation is accurate to within 99%. The temperature dependence of the pair distribution function and the atomic mean square displacement are investigated by performing simulations at various experimental temperatures and corresponding densities. The structures of the systems are affected by temperature via movements of atoms in the first minimum ofg(r).The Lennard-Jones model shows that density dependence of the shear viscosity is in agreement with what is expected of simple liquids in the range of investigated temperatures and densities. In the gas limit, the Stoke-Einstein relationDη =KBT/2πσ is grossly overestimated by Lennard-Jones model. This could not be attributed to deficiencies in the model, as other investigators using first principle method could not obtain the gas limit of the Stoke-Einstein relation.

A theory of atmospheric tides generated by the differential heating between land and sea

SummaryThe differential heating between land and sea is incorporated into the theory of atmospheric tides. This involves the representation of the land and sea distribution by a set of Fourier series.The theory postulates the existence of waves of angular speeds different from the angular velocity of the earth with some of the waves travelling from West to East instead of the usual East to West.By considering the diurnal variation of eddy diffusion of heat energy absorbed close to the surface, the semidiurnal standing waves at the poles was calculated by the application of this theory. The order of magnitude of the calculated tides agreed well with observation, though, contrary to observation, the calculated amplitude at the South pole is larger than that at the North pole.It is also shown that the polar standing oscillation is caused mainly by the land and sea distribution between 75°N and 45°S.

Thermodynamic properties of liquid Te-Ga and Te-Tl alloys

Abstract We have used a statistical mechanics model based on the assumption of compound formation in binary alloys to study the bulk and surface properties of Te–Ga and Te–Tl liquid alloys. The assumption of appropriate complexes, specifically, equiatomic TeGa for Te–Ga alloys and Tl 4 Te for Te–Tl in conjunction with the model enables us to gain a better insight into the nature of order in the two liquid alloys. Using the basic interaction parameters that characterize the model, we have been able to compute the bulk thermodynamic properties of the alloys. Essentially, from our calculations, we are able to show that the Te–Ga liquid alloy is one that undergoes an order–disorder transformation depending on the proportion of Te in the alloy. The Te–Tl system on the other hand exhibits compound formation over the whole composition range. With regards to surface properties, at lower concentration Te segregates more to the surface in Te–Ga alloys than in Te–Tl, however, at higher concentrations the two alloys exhibit quantitatively similar features in the composition dependence of surface concentration.

Thermodynamics of liquid Al - In, Ag - In and In - Sb alloys from a four-atom cluster model

Abstract A model based on a cluster of four atoms has been used to obtain higher-order conditional probabilities that describe the atomic correlations in Al–In, Ag–In and In–Sb liquid alloys. Using the value of the ordering energy obtained from the model, some thermodynamic quantities such as Gibbs energy of mixing and concentration-concentration fluctuations in the long wavelength limit were calculated for these alloys. Our study of the energetics of these liquid alloys reveals that while In– Sb and Ag–In are both chemically ordered or heterocoordinated systems, Al–In is a segregating system. Furthermore, the degree of order in liquid In–Sb alloys is higher than that in liquid Ag–In alloys.

A theoretical study of structure and ordering in Pb-Bi molten alloys

Abstract The solution of the Percus-Yevick (PY) equation for a binary mixture with a square well potential as a perturbation has been applied to the study of the Pb-Bi molten alloy system. The partial structure factors in the long wavelength limit is calculated and used to evaluate the long wavelength limit of the concentration-concentration fluctuations S cc(0). This has in turn been used to obtain the Warren-Cowley short range order parameter α1 and the chemical diffusion D. The calculations indicate compound forming tendencies in Pb-Bi molten alloys with greater magnitude at low atomic fraction of Bismuth.

Thermodynamic investigations of Bi - Cd, In - Pb, and Ni - Pd liquid alloys

Abstract A model based on the existence of self-associates has been used to compute bulk thermodynamic properties of Bi–Cd, In–Pb, and Ni–Pd binary liquid alloys. Also, a statistical mechanics model has been employed to calculate the surface properties of these three alloys. Our study reveals that the degree of phase separation increases in the order Bi–Cd, In–Pb and Ni–Pd. Essentially, we find that Bi–Cd, like Au–Bi and Bi–Sb alloys, does not belong exclusively to the class of either segregating systems or to the short-range ordered alloys. Furthermore, we were able to predict the temperature dependence of the surface properties for our binary liquid alloys based on the knowlege of the results at their melting points.

Electron radiation damage in diffused silicon solar cells

Detailed electrical measurements on silicon solar cells before and after electron irradiation show that the degradation in performance is due entirely to a reduction in minority carrier lifetime in the bulk material. The measurements also reveal a systematic difference between cells made from pulled and floating zoned crystals.

Structure of some liquid transition metals using integral equation theory

We present the results of calculations of the structure factorS(q) of some liquid 3d transition metals using the self consistent hybridized mean spherical approximation (HMSA) integral equation. The local pseudopotential used is composed of the empty core model and a part that takes care of s-d mixing through an inverse scattering approach to model the interionic pair potential. The results presented are in very good agreement with experiment for most of the systems investigated near freezing, as well as for the noble metals Cu, Ag and Au, thus, confirming the reliability of the pseudopotential in the present integral equation scheme.

A phenomenological approach for the phonon dispersion curves of barium

A phenomenological model which combines the axially symmetric ion-ion interaction with the electron-ion interaction scheme of Bhatia has been successfully used to calculate the phonon dispersion curves of bcc Ba. In particular, when the elastic constants determined by Mizukiet al are used as input data, the model successfully reproduces the anomalous feature of the dispersion curves measured by them. On the other hand, when the elastic constants determined by Buchenauet al are used, the model produces a cross over of the longitudinal and transverse branches in the [100] direction, a feature not established in their measurements. Thus the features of the dispersion curves in the [100] direction which is due to the hybridization of thes andd states are evident in the measured elastic constants and are consistent with the values of C12-C44.