Study of thermodynamic properties of liquid binary alloys by a pseudopotential method

On the basis of the Percus–Yevick hard-sphere model as a reference system and the Gibbs–Bogoliubov inequality, a thermodynamic perturbation method is applied with the use of the well-known model potential. By applying a variational method, the hard-core diameters are found which correspond to a minimum free energy. With this procedure, the thermodynamic properties such as the internal energy, entropy, Helmholtz free energy, entropy of mixing, and heat of mixing are computed for liquid NaK binary systems. The influence of the local-field correction functions of Hartree, Taylor, Ichimaru–Utsumi, Farid–Heine–Engel–Robertson, and Sarkar–Sen–Haldar–Roy is also investigated. The computed excess entropy is in agreement with available experimental data in the case of liquid alloys, whereas the agreement for the heat of mixing is poor. This may be due to the sensitivity of the latter to the potential parameters and dielectric function.     

The kinematic viscosity of liquid copper-aluminum alloys

The method of damped torsional vibrations of crucible with liquid under investigation is used for measuring the temperature dependences of kinematic viscosity ν of Cu_{100 ? x} Al _x melts (x = 0–100 at.%) in the range of temperatures t between the liquidus and 1100–1450°C. Unlike the majority of such experiments, the measurements are performed both in the process of heating the sample after its melting and in the course of subsequent cooling. The branching of ν(t) curves corresponding to the foregoing modes is revealed below certain temperatures dependent on the composition of sample (viscosity hysteresis). The curves obtained under cooling have a simple exponential shape predicted by activation theories of viscous flow. The obtained temperature dependences are used for constructing isotherms of kinematic viscosity, on which maxima are observed in the vicinity of stoichiometric concentration of CuAl₃ and composition of Cu-30 at.% Al. For the same compositions, extrema are observed on the concentration dependence of activation energy of viscous flow.     

Electrical conductivity, thermoelectric power and viscosity of liquid Sn-based alloys

Shear viscosity of liquid Sn–Ag, Sn–Cu and Sn–Ag–Cu eutectics from melting temperature up to 1100 K and their electrical conductivity and thermoelectric power up to 850 K have been investigated. The electrical properties of liquid Sn with additions of Fe and Ni have also been studied. It is shown that small amounts of metal admixtures affect noticeably the behavior of the physical properties of liquid Sn.     

Effective viscosity of puller-like microswimmers: a renormalization approach

Effective viscosity (EV) of suspensions of puller-like microswimmers (pullers), for example Chlamydamonas algae, is difficult to measure or simulate for all swimmer concentrations. Although there are good reasons to expect that the EV of pullers is similar to that of passive suspensions, analytical determination of the passive EV for all concentrations remains unsatisfactory. At the same time, the EV of bacterial suspensions is closely linked to collective motion in these systems and is biologically significant. We develop an approach for determining analytical EV estimates at all concentrations for suspensions of pullers as well as for passive suspensions. The proposed methods are based on the ideas of renormalization group (RG) theory and construct the EV formula based on the known asymptotics for small concentrations and near the critical point (i.e. approaching dense packing). For passive suspensions, the method is verified by comparison against known theoretical results. We find that the method performs much better than an earlier RG-based technique. For pullers, the validation is done by comparing them to experiments conducted on Chlamydamonas suspensions.     

The viscosity of liquid R134a

The paper reports new measurements of the viscosity of liquid R134a over the temperature range 235 to 343 K and pressures up to 50 MPa. The measurements have been carried out in a vibrating-wire viscometer calibrated with respect to the viscosity of several liquid hydrocarbons. It is estimated that the uncertainty in the viscosity data reported is ±0.6%. The data therefore have a lower uncertainty than that of earlier measurements of the viscosity of this environmentally acceptable regrigerant. The viscosity data have been represented as a function of density by means of a formulation based upon the rigid, hard-sphere theory of dense fluids with a maximum deviation of ±0.3%. This representation allows the present body of experimental data to be extended to regions of thermodynamic state not covered by the measurements.     

Fermi liquid viscosity in a finite geometry

Forced flow of a Fermi liquid is studied for a cell geometry consisting of two planes with a separation on the order of the mean free path. An approximate transport equation is used to derive an integral equation for the velocity profile, which is solved numerically. Results for the total flux through the cell, which determines the dissipation, are given as a function of the Knudsen number (ratio of cell thickness to mean free path.) Effects of specular reflection at the boundaries are considered. It is found that the dissipation has a minimum at 1/2, and behaves linearly for 3. Implications for present experimentation are discussed.This work was supported in part by the National Aeronautics and Space Administration through grant no. NGR-33-010-188 and the National Science Foundation through grant No. DMR-77-18329.     

Calculation of the viscosity of real gases

A method of determining the constanta in Golubev's equation is given. The values determined in this way are found to be in good agreement with experimental values.     

Relation of the viscosity of a liquid to its thermal properties

It is shown that all points on an- diagram for a liquid must lie on a single curve, and the curves of constant viscosity in P-T coordinates are straight lines.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 5, pp. 837–841, November, 1973.     

The viscosity of liquid carbon dioxide

The viscosity coellicient of carbon dioxide in the liquid phase has been measured by means of a vibrating-wire viscometer at temperatures of 220, 230, 240, 2411, 260, and 380 K. The measurements extended beyond both phase transition lines into the coexistence region (superheated liquid) and into the solid range (undercooled liquid). At 3811 K. the measurements extended only to 3511 MPa since no density data are available for high pressures. The accuracy of the measurements is estimated to be I % The agreement with the data of Ulybin and Makarushkin is rather good, but our values are in general a few percent lower than those of Diller and Ball. The results show, for the most part, a linear pressure dependence for the various isotherms, with a common intersection with the negative pressure axis of 113.7 MPa. The fluidity, the reciprocal of the viscosity, shows a linear dependence of the molar volume in adjacent density ranges. After reduction of the molar volume with the volumes of close packing, two sets of linear functions result, with common intersections of the axis forV/V ₀=1.31 andV/V ₀=1.40.Paper presented at file Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

The viscosity of liquid carbon dioxide

The paper reports new masurements of the viscosity of liquid carbon dioxide along three isotherms at 260, 280, and 300 K for pressures up to 100 MPa. The measurements have been carried out in a vibrating-wire viscometer and have an estimated accuracy of ±0.5%. The results are employed to distinguish between conflicting data sets that already exist in the literature and that have inhibited accurate representations of the viscosity of this important fluid. It is shown that the experimental results can be represented with a high precision by means of procedures founded on the hard-sphere theory of liquids, although the observed density dependence of the viscosity is different from that characteristic of hydrocarbons.     

Predicting the viscosity of liquid refrigerant blends: comparison with experimental data

A method is presented for predicting the viscosity of liquid refrigerant mixtures. The method has no adjustable parameters and, in essence, relies upon the knowledge of the viscosity of the pure components to predict the viscosity of a mixture by means of kinetic theory and rigid-sphere formalism. The predictions have been compared with the available experimental data for a number of refrigerant mixtures. Based on this comparison and previous studies, the accuracy of the proposed method is assessed to be of the order of ±7%.     

Temperature dependence of the dynamic viscosity of the working liquid of a continuous-medium hydro-integrator

Results are presented of an experimental determination of the dynamic viscosity of solutions of Vinipol in vaseline oil.Notation dynamic viscosity (N· sec/cm² - T thermodynamic temperature of liquids (° K) - A and B coefficients of empirical formula     

Analysis of errors of liquid viscosity measurement with a vibration viscosimeter

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 41–42, June, 1991.     

Structure of liquid aluminium-silicon alloys

The Kumar-Samarin technique of centrifuging was adopted to study the structure of aluminium-silicon alloys in terms of the concept of the existence of clusters in liquid state. The investigation shows that in hypo-eutectic alloys the clusters are denser than the monatomic matrix whilst in hyper-eutectic alloys they are lighter. It is suggested that this difference in the distribution of silicon in liquid state could account for the difference in the solidification behaviour of hypo- and hyper-eutectic alloys.     

Structure of liquid cadmium-antimony alloys

The structure of liquid Cd-Sb alloys was determined with the help of the Kumar-Samarin technique of centrifuging liquid metals. Alloys containing 7, 29, 50, 57 and 79 at. % Sb were examined in the range 350 to 650° C. It shows that (i) all alloys except in the vicinity of equi-atomic composition, consist of a colloidal dispersion of compound clusters in a random monatomic matrix, and (ii) the cluster size depends on composition with minima occurring at the two eutectic compositions. The volume fraction of clusters and their heat of formation were determined. The composition of the compound cluster was deduced as Cd₄₀Sb₃₀. Concentration gradient was not established in the equi-atomic alloy during centrifuging. The investigation shows that residual structure can exist far into the liquid state and is not confined to liquids of stoichiometric compound compositions.     

Study of superconducting state parameters of ternary metallic glasses through pseudopotential approach

A theoretical investigation on the screening dependence of the superconducting state parameters (SSPs) viz. the electron-phonon coupling strength λ, the Coulomb pseudopotential μ∗, the transition temperature T_C, the isotope effect exponent α and the effective interaction strength N₀V of some ternary metallic glasses such as Ti₅₀Be₃₄Zr₁₀, (Mo_0.6Ru_0.4)₇₈B₂₂, (Mo_0.6Ru_0.4)₈₀B₂₀, (Mo_0.4Ru_0.6)₈₀P₂₀, (Mo_0.6Ru_0.4)₇₀Si₃₀, (Mo_0.6Ru_0.4)₈₄B₁₆, (Mo_0.6Ru_0.4)₇₂Si₂₈, (Mo_0.6Ru_0.4)₈₆B₁₄, (Mo_0.6Ru_0.4)₇₆Si₂₄, (Mo_0.6Ru_0.4)₇₈Si₂₂, (Mo_0.6Ru_0.4)₈₀Si₂₀, (Mo_0.6Ru_0.4)₈₂Si₁₈ and (Mo_0.6Ru_0.4)₈₀P₂₀ is reported for the first time using Ashcroft''s empty core (EMC) model potential. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al (F) and Sarkar et al (S) are used in the present investigation to study the effect of screening on the aforesaid properties. It is observed that λ and T_C are reasonably sensitive to the selection of the local field correction functions, whereas μ∗, α and N₀V show weak dependences on the local field correction functions. The transition temperature T_C obtained from the H-local field correction function is found to be in excellent agreement with available experimental data. Also, the present results are found to be in qualitative agreement with other earlier reported data, which confirms the existence of the superconducting phase in the above ternary metallic glasses.