Analytical Representation of the Curves of Liquid–Vapor Phase Equilibrium for Saturated Hydrocarbons

A unified two-parameter approximation formula is used to derive analytical dependences for P(T) curves of liquid–vapor phase equilibrium of saturated hydrocarbons C _n H_{2n + 2} (alkanes) with numbers 1 n 20 from methane (n = 1) to eicosane (n = 20). Two approximation options are given, namely, that involving the use of individual values of parameters for each alkane, and that in the form of a unified formula in which the only parameter characterizing an individual component is the number n.     

Light Scattering Study of Aqueous Poly(Vinyl)pyrrolidone–Fullerene C70 Solutions

Abstract

It was shown by static and dynamic light scattering that poly(vinyl)pyrrolidone (PVP) molecules form large intermolecular complexes (clusters) with C₇₀ in aqueous solutions. The molecular weights and dimensions of PVP–C₇₀ clusters increase both with the increase of fullerene content and the molecular weight of the matrix PVP. However, two different diffusion coefficients were detected by dynamic light scattering. The slow mode was explained as diffusion of large PVP–C₇₀ clusters. The fast mode represents free PVP molecules in solution. Dimensions of clusters revealed in aqueous PVP–C₇₀ solutions are less than that for PVP–C₆₀ by factor of 2.5–3.     

On the Interpretation of Near-Critical Gas–Liquid Heat Capacities

This comment is in response to a comment by Sengers and Anisimov on the article “Gibbs density surface of fluid argon” that contradicts prevailing theory. It has not “been established experimentally that the thermodynamic properties of fluids satisfy scaling laws with universal critical exponents asymptotically close to a single critical point of the vapor–liquid phase transition.” Here we explain why an apparent divergence of \(\hbox {C}_{\mathrm{v}}\), in historical experimental “evidence,” is based upon a misinterpretation of near-critical gas–liquid heat capacity measurements in the two-phase coexistence region. The conclusion that there is no “singular critical point” on Gibbs density surface still stands.     

Molecular Simulation of Joule–Thomson Inversion Curves

A method to determine Joule–Thomson inversion curves, using isobaric-isothermal Monte Carlo molecular simulations, is presented. The usual experimental practice to obtain the locus of points in which the isenthalpic derivative of temperature with respect to pressure vanishes is to process volumetric data by means of thermodynamic relations. This experimental procedure requires the very precise measurement of volumetric properties at conditions up to five times the fluid's critical temperature and twelve times its critical pressure. These harsh experimental conditions have hindered the publication of data for even simple fluids and mixtures. By using molecular simulation, these problems may be circumvented, since the computational effort is roughly independent of the actual value of the pressure or the temperature. In general, Joule–Thomson inversion curves obtained by molecular simulation may be used either as an unambiguous test for equations of state in the supercritical and high-pressure regions or for the prediction of real fluid behavior, should the potential be well known. Both applications are exemplified for a Lennard-Jones fluid for which the complete inversion curve is obtained.     

Interfacial Stresses and the Anomalous Character of Thermoelastic-Deformation Curves of a Cu–Al–Ni Shape-Memory Alloy

Thermoelastic-deformation curves of a single-crystalline Cu–13.5 wt % Al–4.0 wt % Ni shapememory (SM) alloy have been studied. Cyclic temperature variation in a 300–450 K interval revealed an anomalous character of thermoelastic hysteresis loops with regions of accelerated straining at both heating and cooling stages. The observed phenomenon can be used for increasing the response speed of SM-alloy based drive and sensor devices. Analysis of this phenomenon in the framework of the theory of diffuse martensitic transformations showed that the anomalous character of thermoelastic hysteresis loops may be related to the influence of interfacial stresses on the dynamics of martensitic transformations in these SM alloys.     

Investigation of Metrological Characteristics of Silver–Silver Chloride Electrodes of GET 54-2011, the State Primary Standard for the pH Activity of Hydrogen Ions in Aqueous Solutions

Measurement Techniques - The technique of manufacturing silver–silver chloride electrodes and the method of their subsequent selection for the State Primary Standard of pH activity of...     

Evolution of the Inner Liquid–Solid Interface During Metal Freezing

The influence of the inner interface initiation method on the interface shape (formation of the planar interface or the interface with the dendrites growing into the liquid metal) was studied both theoretically and experimentally. The results of numerical simulation of the process of heat removal from the metal, corresponding to different initiation methods, revealed the existence of different species of the inner interface. The interface modification during freezing arises from the inequality of temperature gradients on opposite sides of the interface, i.e., from imbalance of heat fluxes on the interphase boundary (Stefan problem). For indium point, the results of numerical simulation were confirmed experimentally.     

Vapor–Liquid Equilibria of Silicon by the Gibbs Ensemble Simulation

Vapor–liquid equilibrium simulations of silicon were performed using the Stillinger–Weber potential with the Gibbs ensemble Monte Carlo method (GEMC). In the low temperature region, from about 3000 to 3500 K, our calculations show the stability of phases and good agreement with several experimental results. On the whole, there is little dependence on the size of the system except near the estimated critical point of silicon: T _c = 7500 ± 500 K and _c = 750 ± 100 kg · m^–3 as determined by the law of rectilinear diameter. Above 3500 K, vapor–liquid coexistence properties which have not been obtained by experiment are derived.     

Phase Relations in the Reduction of Solid Solutions in the Co–Mn–Ti–O System

The hydrogen reduction of spinel solid solutions in the Co–Mn–Ti–O system was investigated by a static method. Six phase regions were identified in which the gas phase is in equilibrium with various combinations of -Co, TiO₂ (rutile), and solid solutions of variable composition: Co _A Mn _B Ti_{3 – A – B} O₄ (spinel), Co _m Mn_{2 – m} TiO₄ (spinel), Co _N Mn_{1 – N} TiO₃ (ilmenite), and Co _n Mn_{1 – n} O (NaCl). The equilibrium compositions of the solid solutions and the corresponding oxygen partial pressures were determined, and the general trends of the reduction of spinel solid solutions in the Co–Mn–Ti–O system were established.     

Predictions of Phase Distribution in Liquid–Liquid Two-Component Flow

Ground-based liquid–liquid two-component flow can be used to study reduced-gravity gas-liquid two-phase flows provided that the two liquids are immiscible with similar densities. In this paper, we present a numerical study of phase distribution in liquid–liquid two-component flows using the Eulerian two-fluid model in FLUENT, together with a one-group interfacial area transport equation (IATE) that takes into account fluid particle interactions, such as coalescence and disintegration. This modeling approach is expected to dynamically capture changes in the interfacial structure. We apply the FLUENT-IATE model to a water-Therminol 59^® two-component vertical flow in a 25-mm inner diameter pipe, where the two liquids are immiscible with similar densities (3% difference at 20°C). This study covers bubbly (drop) flow and bubbly-to-slug flow transition regimes with area-averaged void (drop) fractions from 3 to 30%. Comparisons of the numerical results with the experimental data indicate that for bubbly flows, the predictions of the lateral phase distributions using the FLUENT-IATE model are generally more accurate than those using the model without the IATE. In addition, we demonstrate that the coalescence of fluid particles is dominated by wake entrainment and enhanced by increasing either the continuous or dispersed phase velocity. However, the predictions show disagreement with experimental data in some flow conditions for larger void fraction conditions, which fall into the bubbly-to-slug flow transition regime. We conjecture that additional fluid particle interaction mechanisms due to the change of flow regimes are possibly involved.     

Modeling the Process of Liquid Flow in the System “Formation–Pipeline”

Journal of Engineering Physics and Thermophysics - A model of the process of nonstationary motion of a liquid in the conjugate system “formation–pipeline” has been constructed,...     

Deposition of Pb1 – x Cu x S1 – δ Substitutional Solid Solutions from Aqueous Solutions

Thin films of Pb_{1 – x} Cu _x S_{1 –} metastable substitutional solid solutions containing up to 3.5 mol % Cu₂S were deposited from aqueous solutions and characterized by physicochemical methods.     

3D Ordering at the Liquid–Solid Polar Interface of Nanowires

The nature of the liquid–solid interface determines the characteristics of a variety of physical phenomena, including catalysis, electrochemistry, lubrication, and crystal growth. Most of the established models for crystal growth are based on macroscopic thermodynamics, neglecting the atomistic nature of the liquid–solid interface. Here, experimental observations and molecular dynamics simulations are employed to identify the 3D nature of an atomic-scale ordering of liquid Ga in contact with solid GaAs in a nanowire growth configuration. An interplay between the liquid ordering and the formation of a new bilayer is revealed, which, contrary to the established theories, suggests that the preference for a certain polarity and polytypism is influenced by the atomic structure of the interface. The conclusions of this work open new avenues for the understanding of crystal growth, as well as other processes and systems involving a liquid–solid interface.     

Isobaric–Isothermal Polyhedra of Solid Solutions in the Li–Ni–Mn–Co–O System

Inorganic Materials - Isobaric–isothermal composition polyhedra of solid solutions existing in the Li–Ni–Mn–Co–O system at a temperature of 800°C and oxygen...     

Size Effect in the Phase Separation of Cr–W Solid Solutions

Size effects in phase transformations of nanoscale systems show up as significant changes in their phase diagram. Here, using a thermodynamic approach we demonstrate how the immiscibility region of Cr–W solid solutions is influenced by their particle size. For 40- and 70-nm-diameter particles, we consider two thermodynamically stable states with a core–shell configuration, differing in the composition of the core phase. It is shown that, in the nanometer range, one of these states becomes metastable and that the phase diagrams of the stable and metastable states differ significantly. Reducing the particle size leads to a decrease in the upper critical dissolution temperature (UCDP) by 300–400 K and marked changes in the mutual solubility of the components at temperatures comparable to the UCDP.     

Application of Liquid Solution Models for the Prediction of Corrosion Phenomena in the Na–K Melt

With the mathematical tool of pseudo-regular solutions, we calculated the solubility of Fe, Cr, Ni, V, Mn, and Mo in eutectic Na–K melt and compared the calculation results with the available experimental data in the literature on the mass transfer of austenitic chrome-nickel steel components in a sodium-potassium loop in nonisothermal conditions. We show that the Wagner parameters of the interaction between oxygen and transition metal might be applied to predict the corrosion behavior of the construction materials in sodium-potassium melt under the presence of oxygen impurity. We present the calculation results of the threshold oxygen concentration required to form ternary sodium oxides with transition metals (Fe, Cr, Ni, V, Mn, Mo) in conditions in which the pure metal is in contact with eutectic Na–K melt.     

On the Naor–Reingold Pseudo-Random Function from Elliptic Curves

We show that the elliptic curve analogue of the pseudo-random function, introduced recently by M. Naor and O. Reingold, produces a uniformly distributed sequence for almost all values of parameters. This result generalizes some previous results of the author about the distribution of the original function of M. Naor and O. Reingold. The proof is based on some recent bounds of character sums over subgroups of the point group of elliptic curves. Received: June 21, 1999; revised version: January 28, 2000