Hydrate formation in the tetraethylammonium hydroxide-water system

A phase diagram of the tetraethylammonium hydroxide-water binary system was studied by differential thermal analysis. Seven crystal phases of tetraethylammonium hydroxide were found. Two of them are stable: tetrahydrate (T _m = 47.0°C), two phases of a compound with the hydration number 7.5 (T _m = −18.1 and −23.2°C); five are metastable phases: two polymorphs of pentahydrate (T _m = 39.4 and 0.9°C), hexahydrate (T _m = −70.1°C), and a compound with hydrate number 10–11 (T _m = −112°C).