The Unexpected Stability of Hydrazine Molecules in Hydrous Environment under Pressure*

Abstract

The incomplete decomposition product of metastable hydrazine (N2H4) instead of the energetically favorable ammonia (NH3) upon decompression is one drawback in applications of energetic material oligomeric hydronitrogens. We explore the stability of hydrazine molecules in hydrazine hydrate (N2H4·H2O) under pressure in diamond anvil cells (DACs) combined with in situ Raman spectroscopy and synchrotron x-ray diffraction (XRD) measurements. The results show that one NH2 branch forms NH3 group by hydrogen bonds between hydrazine and water molecules after the sample crystallizes at 3.2 GPa. The strengthening hydrogen bonds cause the torsion of hydrazine molecules and further dominate a phase transition at 7.2 GPa. Surprisingly, the NN single bonds are strengthened with increasing pressure, which keeps the hydrazine molecules stable up to the ultimate pressure of 36 GPa. Furthermore, the main diffraction patterns show continuous shift to higher degrees in the whole pressure range while some weak lines disappear above 8.2 GPa. The present peak-indexing results of the diffraction patterns with Materials Studio show that the phase transition occurs in the same monoclinic crystal system. Upon decompression, all of the hydrazine molecules extract from hydrazine hydrate crystal at 2.3 GPa, which may provide a new way to purify hydrazine from hydrate.

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

“…In the first compression run, the liquid hydrazine hydrate sample was compressed to the ultimate pressure of 16.6 GPa, which showed consistent behaviors with previous research results. 10 The in situ Raman spectra of hydrazine hydrate at evolutionary pressures are collected in Figure 1. After loading, the sample was in the liquid state with broad intramolecular bands of N 2 H 4 and H 2 O molecules up to 3.5 GPa.…”

“…8,9 Raman spectroscopy measurement revealed that the diverse hydrogen-bond networks played a vital role in structural stability and further isostructural phase transition. In hydrazine monohydrate, the sample also formed a pure component complex at high pressures, 10 and interaction of hydrazine and water molecules was continuously reinforced by the hydrogen bonds under compression up to 36 GPa. However, upon unloading to about 2.3 GPa, pure hydrazine had extracted from the complex solid, evidenced by the appearance of several characteristic stretching peaks, indicating a drastic change in the stoichiometric proportion of the sample with the abrupt breakup of H-bonds between heterogeneous molecules.…”

“…Only a handful of studies have been conducted on the high-pressure behaviors of the hydrazine hydrate system, which mainly focused on the pure hydrazine and hydrazine monohydrate. − Unlike H 2 O, hydrazine contracts upon solidification; thus, the pressure usually drops while the hydrogen bonds are strengthened during solidification into a translucent crystal. , Raman spectroscopy measurement revealed that the diverse hydrogen-bond networks played a vital role in structural stability and further isostructural phase transition. In hydrazine monohydrate, the sample also formed a pure component complex at high pressures, and interaction of hydrazine and water molecules was continuously reinforced by the hydrogen bonds under compression up to 36 GPa. However, upon unloading to about 2.3 GPa, pure hydrazine had extracted from the complex solid, evidenced by the appearance of several characteristic stretching peaks, indicating a drastic change in the stoichiometric proportion of the sample with the abrupt breakup of H-bonds between heterogeneous molecules.…”

Pressure-induced phase transition in transition metal trifluorides

“…The high pressure thus offers exciting opportunities for discovering new materials that do not exist under ambient conditions. [34][35][36][37][38][39][40] Highpressure does not necessitate the destruction of the MF 6 octahedron in MF 3 systems. In practice, the pressure-induced structural evolution is only the cooperative tilting of the MF 6 octahedra, [41][42][43] which can be summarized as follows: (i) an elongation of the MF 6 octahedra along the c axis leads to a small octahedral strain, (ii) the MF 6 octahedral strain disappears, and (iii) MF 6 octahedral elongation occurs along the a axis.…”

Pressure-Dependent Phonon Scattering of Layered GaSe Prepared by Mechanical Exfoliation*

“…On the other hand, the high-pressure technology is a powerful tool for tuning the bandgaps of materials, investigating the structures of 2D materials such as the superconductive MoS 2 , MoSe 2 and ReSe 2 . [11,12] In a previous work, a hexagonal type to an NaCl-type phase transition at around 29 GPa in the bulk sample has been demonstrated, but the pressure dependence of few-layered GaSe has not been reported yet. More-over, many problems arising from its special oxidation mechanism in ambient atmosphere limit their applications.…”