Pressure-Induced Extraction of Hydrazine Crystals by the Eutectoid Reaction in Hydrazine Monohydrate

The industrial concentration of hydrazine hydrate was usually accomplished by multistage distilling of hydrazine hydrate at hundreds of degrees, which has great technical challenges as well as economic cost considerations. Here, we report a pressure-induced extraction of pure hydrazine crystals in hydrazine monohydrate by multiple pressure treatments. Under normal compression, the liquid hydrazine hydrate solidified into a monohydrate complex above 3.6 GPa. During the following decompression, pure hydrazine crystals separated out by a eutectoid reaction below 2.6 GPa, as evidenced by the characteristic vibrations in Raman spectra and dramatic transitions of the sample morphology. The extracted hydrazine crystals can be reserved down to about 1 GPa at room temperature and even to atmospheric pressure at low temperatures; a recompression treatment could significantly promote the precipitation of hydrazine up to 3 GPa. The distinctive behaviors of hydrazine crystals under pressure treatments provided an alternative method for hydrazine purification in binary hydrate systems.