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Critical phenomena and three-liquid-phase equilibrium in the ternary system nitromethane – water – n-heptane
Svetlana I Sinegubova

The theoretical aspects of the appearance and development of the three-liquid-phase state in ternary systems at given or variable parameters of state are considered. The results of a polythermal study of the three-liquid-phase equilibrium in the ternary system nitromethane – water – n-heptane are presented. The three-liquid-phase region has been established to appear as a critical tie-line which connects the compositions of the noncritical heptane phase, l1, and the equilibrium critical water – nitromethane phase, l23, at 117.4 °C. Having one degree of freedom, Fk = 3 + 1 – 2 – 1 = 1 (p = const.), the critical tie-line, l1K23, develops into a three-liquid-phase region — a certain irregular triangle, the corners of which are directed to the compositions of the coexisting phases. The critical tie-line, l1K23, is turned to the binary system, nitromethane – water, for which the upper critical solution temperature (UCST) is a minimum.

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