Abstract
The water–ethanol (E) system was studied by differential thermal analysis (DTA) at atmospheric pressure and pressures up to 10 kbar. At atmospheric pressure, the system was shown to contain an incongruently melting hydrate of E · 2H2O composition (tdecomp = -65.0°C). In addition, the system involves two metastable hydrates: E · 3H2O (tdecomp = -69.0°C) and E · 4.75H2O tdecomp = -74.5°C)}. The hydrate compositions were determined by Tamman's method for the corresponding temperature invariants. Studies at pressures below 10 kbar showed that E · 4.75H2O metastable hydrate becomes stable at pressures above 0.25 kbar. At pressures from 1.0 to 7.3 kbar, this hydrate melts congruently, which allowed its composition to be determined more accurately. Presumably, this hydrate is of a semiclathrate nature (i.e., the ethanol molecule is involved in constructing the water framework) and has cubic structure I. In experiments at high pressures, E · 3H2O was not found. Concerning E · 2H2O hydrate, its peritectic melting was observed up to ∼ 5.0 kbar. Further extrapolation extends the incongruent melting curve to 7.5 kbar.
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