Extended law of corresponding states: square-well oblates

The vapour-liquid coexistence collapse in the reduced temperature, Tr=T/Tc, reduced density, ρr= ρ/ρc, plane is known as a principle of corresponding states, and Noro and Frenkel have extended it for pair potentials of variable range. Here, we provide a theoretical basis supporting this extension and show that it can also be applied to short-range pair potentials where both repulsive and attractive parts can be anisotropic. We observe that the binodals of oblate hard ellipsoids for a given aspect ratio (κ=1/3) with varying short-range square-well interactions collapse into a single master curve in the Δ B*2--ρr plane, where Δ B*2= (B2(T)-B*2(Tc))/v0, B2 is the second virial coefficient, and v0 is the volume of the hard body. This finding is confirmed by both REMC simulation and second virial perturbation theory for varying square-well shells, mimicking uniform, equator, and pole attractions. Our simulation results reveal that the extended law of corresponding states is not related to the local structure of the fluid.

Spinodal and thermodynamic limit of superheat of gold

A four-parameter generalized Berthelot equation of state has been employed to determine the spinodal and the thermodynamic limit of superheat of liquid gold. It is established that gold obeys the two-parameter law of corresponding states. It is also established that the new parameters introduced in the attractive term of the equation of state are thermodynamic similarity parameters. It is shown that liquid gold can be superheated to a temperature 6719K. That is, liquid gold, under rapid heating, can be superheated to temperature 3476K above the boiling temperature without undergoing liquid-vapour phase transition. Above this temperature, liquid gold will undergo explosive boiling owing to homogeneous nucleation.

Superheating Limit of Hydrocarbons Based on a Generalized Dieterici Equation of State

A new three-parameter Dieterici type equation of state is employed for studying the high-temperature thermodynamic characteristics of hydrocarbons. This generalized equation of state differs from the known Dieterici equation of state by a modified attractive term. That is, a new thermodynamic similarity parameter is introduced in the attractive term of the Dieterici equation of state. The parameters of the equation of state are determined through the experimental values on the critical-point parameters of hydrocarbons. The equation of state is presented in the reduced form, from which follows the single-parameter law of corresponding states. The proposed equation of state gives the value of maximum attainable superheat for hydrocarbons of about 0.887 to 0.894 times the critical temperature. The new three- parameter generalized Dieterici equation of state offers an acceptable compliance with experimental results of maximum attainable superheat of hydrocarbons.

Determination of Second Virial Coefficient of Gold by a Modified Berthelot Equation of State

The present study aims to determine the second virial coefficient of gold over a wide range of temperatures from the boiling point to the critical point. A three - parameter modified Berthelot equation of state has been employed to determine the second virial coefficient of gold. The parameters of the equation of state are determined through the critical - point parameters of gold. The temperature -dependence of the second virial coefficient of gold has been investigated. The obtained results are compared with that of the van der Waals equation of state, Berthelot equation of state, Tsonopoulus correlation, and McGlashan correlation. The results of this work agree well with that of other correlations in the vicinity of the critical point. It is also established that gold obeys the single - parameter law of corresponding states. And, the new parameter introduced in the attractive term of the equation of state is found to be a thermodynamic similarity parameter. Doi: 10.28991/HEF-2020-01-04-02 Full Text: PDF

On the Self - and Impurity Diffusion in High Entropy Alloys

General trends in self- and impurity diffusion data are analyzed in high entropy alloys. Our analysis is based on the similarity of inter-atomic potentials in metals, which is in fact equivalent to a three-parameter description of the system (the mass, m, the lattice spacing, a, and the melting point, Tm, are only used). This leads to the so-called law of corresponding states in metals, manifested in many empirical rules (e.g. compensation laws or the proportionality between the self-diffusion activation energy and the melting point) if one uses dimensionless/reduced variables (like the homologous temperature: T*=T/Tm). It was shown in our previous papers, using the concept of a hypothetical crystal composed of simple atomic species whose properties are an average of the components, that the tracer diffusion of any species (let it be either one of the constituent atoms or a foreign atom) can be considered as impurity diffusion in the pure many-component matrix. Using this concept, we illustrate that the diffusion coefficients, Di, follow the same rule which obtained for impurity diffusion in pure metals: lnDi=A(T*)(Tmi/Tm-1)+r, with the same fitting parameters A(T*) and r. According to this, the diffusion of the constituent elements in high entropy alloys indeed shows some sluggish character, which can be attributed to a more or less temperature independent factor.