Thermodynamics Of Fluctuations Research Articles

Thermal hysteresis of mesoscopic phase transitions in fluid metals: From tantalum to aluminum and gold with their critical points and non-mean-field global diagrams

The light soft metal – Al-IIIB in Periodic Table and the heavy soft metal – Au-IB were analyzed within the predictive model of fluctuation–thermodynamics (FT). The similar extrapolative approach was applied for re-establishing of the global phase diagram and non-mean-field criticality of the refractory heavy and rigid tantalum Ta-VA earlier. The revealed then correspondence between the onset point of nano-droplets at atmospheric pressure and the point of instability, observable at much higher pressures by the fast dynamic measurements, found its confirmation for the considered metals as well. It may indicate the universality of the mentioned “dew”-point for any elements and compounds. The mesoscopic nanoscaled time- and length- simultaneous consideration matters especially for all metallic vapors at sub-atmospheric pressures and temperatures beneath the normal boiling one. The FT-predicted critical points of Al and Au are consistent with the available low-temperature thermostatic and rapid dynamic experimental data.

Elongate coexistence curve and its curvilinear diameter as factors of global fluid asymmetry

Some inconsistencies of the conventional predictive methodologies applied in the region of vapor-liquid VLE-coexistence and its criticality are considered. As a rule, they are related to the semi-empirical concept of “rectilinear diameter” accepted in the temperature-density plane. The often curved, in practice, "rectilinear diameter” of coexistence curve (CXC) is discussable in both alternative descriptions of criticality: 1) by the Ising-based (Ib-) complete scaling phenomenology and 2) by the classical van der Waals-Maxwell-Gibbs-based (Wb-) phenomenology of VLE-transition. The latter has been essentially modified by the model of fluctuational thermodynamics (FT). The new transformation of CXC-representation based on the measurable equilibrium data obtained far away from criticality is proposed in the present work. It leads to the well-established location of critical point (CP) which corresponds to the intersection between the elongate CXC depicted in the compressibility factor-density plane and its strongly curvilinear here diameter. The universality of global fluid asymmetry (GFA)-principle introduced earlier by FT-model becomes apparent in the whole temperature range of VLE-transition. The developed predictive CP-methodology can be especially useful for the set of substances in which the direct experiment on criticality is hardly realizable.

The critical parameters and congruent vapor-liquid diagram of ten metallic alkali and alkaline earth fluids and one H-bond organic (methanol)

We report the first reliable prediction of the critical point (CP) (Tc,Pc,ρc) and two separate branches of the coexistence curve (CXC) for 10 alkali and alkaline earth fluids metals as well as for methanol. It is based on the recently proposed methodology of the congruent vapor-liquid (CVL) – diagram following from the developed earlier model of the fluctuational thermodynamics (FT). Both CXC-branches are predicted by the quite different (i.e. asymmetric and non-“symmetrized” artificially) FT-correlations. They are completely conformed in the asymptotic CP-region not only to the non-classical (with the exponent β≈1/3) projection of CXC on the (T,ρ)-plane but also to the well-known classical Clausius-Clapeyron approximation of the vapor-pressure curve in the (P,T)-plane. The respective interrelations between two phase-dependent factors of thermodynamic similarity introduced, originally, by Riedel (Ri) and Trouton (Tr) in the classical principle of corresponding states (PCS) are estimated without any fitting. We show that neither any analytic expansion (it fails near CP) nor the known non-analytic Wegner's expansion (it diverges far from CP) are necessary to predict with the reasonable accuracy the entire range of CXC including its CP. The only input data for this aim are the standard low-temperature measurements of one-phase liquid performed at atmospheric pressure. The reasons of violation of the classical PCS for the metallic and ionic fluids have been analyzed. Despite the widespread belief on the contrary, FT-methodology predicts the striking similarity of all studied fluid metals revealed by their CVL-diagrams.

Can the Boyle's and critical parameters be unambiguously correlated for polar and associating fluids, liquid metals, ionic liquids?

An independent test of thermodynamic consistency applied to a presently widespread methodology of Zeno-line (ZL) has demonstrated its restricted predictive abilities. Unfortunately, a subjective choice of the reference Boyle (B) parameters for the reduced critical temperature Tc/TB and the critical density ρc/ρB as well as the imposed empirical linear constraints on their presumably universal correlation can lead to unadjusted predictions of critical properties for liquid metals, polar and associating fluids, water and many other complicated substances. To study such “difficult” compounds the alternative universal set of correlations between the critical compressibility factor Zc, the Riedel's factor of similarity Ac and both B-parameters ρB,TB is introduced. It follows from the model of fluctuational thermodynamics (FT) and the principle of global fluid asymmetry (GFA) formulated recently as its consequence. This new FT-methodology describes a set of known B-temperatures with an excellent accuracy while the respective B-densities are fixed by the empirical Timmermans correlation. We believe that critical properties for the afore-mentioned “difficult” fluids can be reasonably represented and/or predicted by the proposed universal FT-methodology. The revealed interrelation between the effective potential parameters established in terms of the actual critical properties forces us to disavow the tentative supposition about the violation of PCS (principle of corresponding states) in complex liquids.

Scaling Model of Low-Temperature Transport Properties for Molecular and Ionic Liquids

The universal scaling concept is applied to the low-temperature range of any liquid states and substances located between the melting (Tm) and normal boiling (Tb) points far away from the critical region. The physical reason to develop such approach is the revealed collapse of all low-temperature isotherms onto the single universal one argued by the model of fluctuational thermodynamics (FT) proposed recently by author. The pressure reduced by the molecular parameters of the effective short-range Lennard-Jones (LJ) potential depends here only on the reduced density. To demonstrate the extraordinary predictive abilities of the developed low-temperature scaling model it has been applied to the prediction of equilibrium and transport (kinetic and dynamic viscosity, self-diffusion, and thermal conductivity) properties not only for molecular liquids but also for molten organic salts termed ionic liquids (ILs). The best argument in favor of the proposed methodology is the appropriate consistency with the scarce experiments prediction of transport coefficients for ILs on the base of universal scaling function constructed for the simplest LJ-like liquid argon. The only input data of any substance for prediction are the linear approximations of T-dependent density and isobaric heat capacity taken from the standard measurements at atmospheric pressure.