2020, №2

сс. 67-78

Immiscibility of Liquid Phases and Critical Phenomena in the Na2SO4—Na2B4O7—H2O System at 350—460 °C and Pressure up to 100 MPa

2020, №2

сс. 67-78

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M.A. Urusova, V.M. Valyashko

Key words: aqueous salt solutions, phase equilibria, immiscibility, critical phenomena

The study concerns phase equilibria and critical phenomena in the
Na2SO4—Na2B4O7—H2O
system with two boundary subsystems: Na2B4O7—H2O (type 1 with liquid phase
immiscibility of solutions) and Na2SO4—H2O (type 2) at 350—460 °C and pressure
up to 100 MPa. It is shown that there are two three-phase regions — (l1-l2-s) adjacent
to two aqueous salt subsystems and separated by a fluid region at the temperatures
from 440 °C (critical point Q (l1=l2-s) of the type 2 binary system) to ~455 °C when
these regions integrate with each other. The three-component system is characterized
by two critical curves in saturated solutions. The curves extend from different critical
points of the type 2 binary subsystem — g=l-s (point p) and l1=l2-s (point Q). These
curves end at the ternary critical points — pR (g=l1-l2-s) and QN (g-l1=l2-s), respectively,
with a four-phase equilibrium (g-l1-l2-s) between them in the temperature
range of 350—380 °C, according to the visual observations in sealed quartz ampoules.

doi:10.1134/S1990793120080072