Re-established congruent vapor-liquid diagram of alkali fluid metals as alternative to crossover VLE - interpretation

• Published in: Fluid phase equilibria Vol. 466; pp. 79 - 88
• Main Authors: Rogankov, O.V., Mazur, V.A., Shvets, M.V., Rogankov, V.B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25-06-2018
• Subjects: Congruent vapor-liquid diagram; Conventional VLE-diagram; Non-classical peculiarities of critical and low-temperature regions; Congruent vapor-liquid diagram; Non-classical peculiarities of critical and low-temperature regions; Conventional VLE-diagram
• ISSN: 0378-3812; 1879-0224
• DOI: 10.1016/j.fluid.2018.03.014

The universal predictive methodology termed the congruent vapor-liquid (CVL-) diagram was applied recently to the set of alkali metals for which the high-temperature data of vapor pressure, dew and bubble orthobaric densities cannot be reliably deduced from the direct VLE-experiment. We show in the present work that the unwonted but significant pressure drop in the region of overheated vapor revealed long ago by Ewing et al. for Na, K, Cs and reproduced soon after on for Cs by Novikov becomes explainable due to the concept of a heterogeneous non-Gibbsian interphase introduced by CVL-diagram. Its predictive capability based exclusively on the available data of a condensed phase at atmospheric pressure provides also the fairly well and purely predictive description of two Gibbsian single-phase regions (non-ordered gas-phase and ordered liquid-phase). The crucial rejection from the classical mean-field concept of a unified EOS (common for both coexistent fluid Gibbsian phases) leads, in accordance with GFA (global fluid asymmetry)-principle, to the non-classical exponent β=1/3. It is close to that from the Ising-like (Il) asymptotic criticality. Thus, CVL-diagram provides not only the impressive alternative support and extension of the near-critical Il-universality but it expands GFA-principle on the whole subcritical crossover region of alkali metals.
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•The only predicted critical parameters of Li, Na, K, Rb, Cs are used to re-establish VLE-diagram.•This information provides the reasonable description of any single-phase states.•The asymptotic criticality of alkali metals is independently predicted.