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Molecules (Basel, Switzerland) Nov 2020Recently discovered hybrid perovskites based on hypophosphite ligands are a promising class of compounds exhibiting unusual structural properties and providing...
Recently discovered hybrid perovskites based on hypophosphite ligands are a promising class of compounds exhibiting unusual structural properties and providing opportunities for construction of novel functional materials. Here, we report for the first time the detailed studies of phonon properties of manganese hypophosphite templated with methylhydrazinium cations ([CHNHNH][Mn(HPO)]). Its room temperature vibrational spectra were recorded for both polycrystalline sample and a single crystal. The proposed assignment based on Density Functional Theory (DFT) calculations of the observed vibrational modes is also presented. It is worth noting this is first report on polarized Raman measurements in this class of hybrid perovskites.
Topics: Calcium Compounds; Cations; Density Functional Theory; Ions; Manganese; Materials Testing; Microscopy, Confocal; Models, Molecular; Monomethylhydrazine; Oxides; Phosphites; Quantum Theory; Software; Spectrophotometry, Infrared; Spectroscopy, Fourier Transform Infrared; Spectrum Analysis, Raman; Temperature; Titanium; Vibration
PubMed: 33182446
DOI: 10.3390/molecules25215215 -
Military Medicine Feb 2021Hydrazines are highly toxic inorganic liquids that are used as propellants in military and aviation industries, such as the U.S. Air Force F-16 Emergency Power Unit and...
INTRODUCTION
Hydrazines are highly toxic inorganic liquids that are used as propellants in military and aviation industries, such as the U.S. Air Force F-16 Emergency Power Unit and SpaceX SuperDraco Rockets. The most commonly used derivatives include hydrazine, monomethylhydrazine, and 1,1-dimethylhydrazine (unsymmetrical dimethylhydrazine). Industrial workers in close contact with hydrazines during routine maintenance tasks can be exposed to levels well above the National Institute for Occupational Safety and Health relative exposure limits.
MATERIALS AND METHODS
A systematic review was performed using PubMed, Web of Science, Google Scholar, National Aeronautics and Space Administration Technical Server, and Defense Technical Information Center, and data related to hydrazine exposures were searched from inception to April 2020. Publications or reports addressing hydrazine toxicity, pathophysiology, and treatment of hydrazine fuel exposure were selected.
RESULTS
Acute toxic exposures to hydrazine and its derivatives are rare. There are few case reports of acute toxic exposure in humans, and data are largely based on animal studies. The initial search identified 741 articles, manuscripts, and government reports. After screening for eligibility, 51 were included in this review. Eight articles reported acute exposures to hydrazine propellant in humans, and an additional 14 articles reported relevant animal data.
CONCLUSIONS
Exposure to small amounts of hydrazine and its derivatives can cause significant soft tissue injury, pulmonary injury, seizures, coma, and death. Neurologic presentations can vary based on exposure compound and dose. Decontamination is critical as treatment is mainly supportive. High-dose intravenous pyridoxine has been suggested as treatment for hydrazine-related neurologic toxicity, but this recommendation is based on limited human data. Despite recent research efforts to generate less toxic alternatives to hydrazine fuel, it will likely continue to have a role in military and aviation industries. Aerospace and military physicians should be aware of the toxicity associated with hydrazine exposure and be prepared to treat hydrazine toxicity in at-risk populations.
Topics: Animals; Aviation; Humans; Hydrazines; Military Personnel; United States
PubMed: 33175959
DOI: 10.1093/milmed/usaa429 -
Chemistry, An Asian Journal Dec 2020Functionalized hydrazines and bishydrazines are interesting straightforward precursors for accessing higher nitrogenated compounds. They offer structural diversity and...
Functionalized hydrazines and bishydrazines are interesting straightforward precursors for accessing higher nitrogenated compounds. They offer structural diversity and promising energetic properties as well, namely for propulsion applications. A novel and scalable synthesis has been developed for a new family of bishydrazines, starting from monomethylhydrazine (MMH). This solvent-free route represents a suitable alternative to the one described in the literature. It was extended to design a new family of unsymmetrical hydrazines bearing various functional groups. A selected series of promising compounds, densified with nitrogenated groups (amino, hydrazino or azido functions), was identified as a class of plausible candidates for liquid propulsion. Indeed, the energetic interest of such hydrazines was demonstrated by computing their heats of formation and specific impulse values in bipropellant systems. This led to theoretical energetic performances comparable to that of the MMH/N O system already in use today.
PubMed: 33155765
DOI: 10.1002/asia.202001084 -
The Journal of Physical Chemistry. A Jul 2020Experimental, numerical, and theoretical studies are performed to understand the explosive thermal decomposition of monomethylhydrazine/argon mixtures. Ignition delays...
Experimental, numerical, and theoretical studies are performed to understand the explosive thermal decomposition of monomethylhydrazine/argon mixtures. Ignition delays of concentrated MMH/Ar mixtures (20-30%) have been measured behind a reflected shock wave around 1000 K and 1 atm. Although several detailed chemical kinetic models have predictive abilities for diluted and highly diluted mixtures, none of them showed predictive for concentrated mixtures. A new kinetic model is proposed, in which numerous rate constants and thermochemical data are reassessed based on theoretical calculations, with the purpose to determine whether, or to what extent, trends derived from diluted or highly diluted MMH/Ar mixtures can explain observations in concentrated MMH mixtures. The present kinetic model is found to predict speciation experimental profiles in diluted MMH/Ar mixtures and is a significant improvement in predicting the induction delays of concentrated MMH/Ar mixtures.
PubMed: 32603112
DOI: 10.1021/acs.jpca.0c03144 -
The Journal of Physical Chemistry. A May 2020Methylamine radicals (CHNH) and amino radicals (NH) are major products in the early pyrolysis/ignition of monomethylhydrazine (CHNHNH). kinetics of thermal...
Methylamine radicals (CHNH) and amino radicals (NH) are major products in the early pyrolysis/ignition of monomethylhydrazine (CHNHNH). kinetics of thermal decomposition of CHNH radicals was analyzed by RRKM master equation simulations. It was found that β-scission of the methyl H-atom from CHNH radicals is predominant and fast enough to induce subsequent H-abstraction reactions in CHNHNH to trigger ignition. Consequently, the kinetics of H-abstraction reactions from CHNHNH by H-atoms was further investigated. It was found that the energy barriers for abstraction of the central amine H-atom, two terminal amine H-atoms, and methyl H-atoms are 4.16, 2.95, 5.98, and 8.50 kcal mol, respectively. In units of cm molecule s, the corresponding rate coefficients were found to be = 9.63 × 10 exp(-154.2/), = 2.04 × 10 exp(104.1/), = 1.13 × 10 exp(-416.3/), and = 2.41 × 10 exp(-870.5/), respectively, in the 290-2500 K temperature range. The results reveal that abstraction of the terminal amine H-atom to form -CHNHNH radicals is the dominant channel among the different abstraction channels. At 298 K, the total theoretical H-abstraction rate coefficient, calculated with no adjustable parameters, is 8.16 × 10 cm molecule s, which is in excellent agreement with Vaghjiani's experimental observation of (7.60 ± 1.14) × 10 cm molecule s ( 1997, 101, 4167-4171, DOI: 10.1021/jp964044z).
PubMed: 32299215
DOI: 10.1021/acs.jpca.0c02389