Numerical Simulation of a Low-power Hydrazine Arcjet Thruster

A modeling study is conducted to investigate the plasma flow and heat transfer characteristics of low-power (kW class) arc-heated thrusters (arcjets) with 2:1 hydrogen/nitrogen to simulate decomposed hydrazine as the propellant. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, the Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. Typical computed results about the temperature, velocity and Mach number distributions within arcjet thruster are presented for the case with arc current of 9 A and inlet stagnant pressure of 3.3×105 Pa to show the flow and heat transfer characteristics. It is found that the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip, and the flow transition from the subsonic to supersonic regime occurs within the constrictor region. The effect of gas viscosity on the plasma flow within arcjet thruster is examined by an additional numerical test using artificially reduced values of gas viscosity. The test results show that the gas viscosity appreciably affects the plasma flow and the performance of the arcjet thruster for the cases with the hydrazine or hydrogen as the propellant. The integrated axial Lorentz force in the thruster nozzle is also calculated and compared with the thrust force of the arcjet thruster. It is found that the integrated axial Lorentz force is much smaller than the thrust force for the low-power arcjet thruster. Modeling results for the NASA 1-kW class arcjet thruster with simulated hydrazine as the propellant are found to be reasonably consistent with available experimental data.

Antioxidant N-acetylcysteine attenuates the acute liver injury caused by X-ray in mice

The aim of this study was to evaluate the protective effects of different doses and administration modes of N-acetylcysteine (NAC) against X-ray-induced liver damage in mice. Kun-Ming mice were divided into four groups, each composed of six animals: two control groups and two NAC-treated groups. An acute study was carried out to determine alterations in lipid peroxidation (determined by measuring malondiadehyde (MDA) level), glutathione (GSH) content and superoxide dismutase (SOD) activity (assayed by colorimetric method), and DNA damage (characterized by DNA-single strand break using with comet assay) as well as cell apoptosis (measured by flow cytometry) at 12 h after irradiation. The results showed that there were dose-related decreases in MDA level, DNA damage and cell apoptosis, and dose-dependent increases in GSH content and SOD activity in all NAC-treated groups compared to control groups, indicating that pre-treatment or post-treatment with NAC significantly attenuates the acute liver damage caused by X-ray. In addition, significant positive correlations were observed between MDA level and DNA damage or cell apoptosis, implying that lipid peroxidation plays a major role in X-ray-induced liver injury. The data suggest that NAC exerts its radioprotective effect by counteracting accumulated reactive oxygen species in the liver through its properties as a direct antioxidant and a GSH precursor, when administered before or after X-ray irradiation.

The reaction route and active site of catalytic decomposition of hydrazine over molybdenum nitride catalyst

The catalytic properties of the passivated, reduced passivated, and fresh bulk molybdenum nitride for hydrazine decomposition were evaluated in a microreactor. The reaction route of hydrazine decomposition over molybdenum nitride catalysts seems to be the same as that of Ir/gamma-Al2O3 catalysts. Below 673 K, the hydrazine decomposes into N-2 and NH3. Above 673 K, the hydrazine decomposes into N-2 and NH3 first, and then the produced NH3 further dissociates into N-2 and H-2. From the in situ FT-IR spectroscopy, hydrazine is adsorbed and decomposes mainly on the Mo site of the Mo2N/gamma-Al2O3 catalyst. (C) 2004 Elsevier Inc. All rights reserved.

Catalytic decomposition of hydrazine over supported molybdenum nitride catalysts in a monopropellant thruster

The catalytic decomposition of hydrazine over a series of MoNx/gamma-Al2O3 catalysts with different Mo loadings was investigated in a monopropellant thruster (10 N). When the Mo loading is equal to or higher than the monolayer coverage of MoO3 on gamma-Al2O3, the catalytic performance of the supported molybdenum nitride catalyst is close to that of the conventionally used Ir/gamma-Al2O3 catalyst. The MoNx/gamma-Al2O3 catalyst with a loading of about 23wt% Mo (1.5 monolayers) shows the highest activity for hydrazine decomposition. There is an activation process for the MoNx/gamma-Al2O3 catalysts at the early stage of hydrazine decomposition, which is probably due to the reduction of the oxide layer formed in the passivation procedure.

Electrochemical Detection of Hydrazine Based on Electrospun Palladium Nanoparticle/Carbon Nanofibers

In this work, we developed an electrochemical method for the detection of hydrazine based oil palladium nanoparticle/carbon nanofibers (Pd/CNFs). Pd/CNFs were prepared by electrospinning technique and subsequent thermal treatments. The electrocatalytic behaviors of Pd/CNFs modified glassy carbon electrode (Pd/CNF-GCE) for hydrazine oxidation were evaluated by cyclic voltammetry (CV), an obvious and well-defined oxidation peak appeared at -0.32 V (vs. Ag/AgCl). The mechanism of the oxidation of hydrazine at Pd/CNF-GCE was also studied, which demonstrated an irreversible diffusion-controlled electrode process and a four-electron transfer involved in the overall reaction. Furthermore, the wide linear range, low detection limit, good reproducibility and excellent storage stability were obtained utilizing differential pulse voltammetry (DPV).

Hydrazine-based polyimides from isomeric bis(chlorophthalimide)s

3,3-Dichloro-N,N'-biphthalimide (3,3'-DCBPI), 3,4'-dichloro-N,N'-biphthalimide (3,4'-DCBPI), and 4,4'-dichloro-N,N'X-biphthalimide (4,4'-DCBPI) were synthesized from 3- or 4-chlorophthalic anhydrides and hydrazine in glacial acetic acid. The yield of 3,3'-DCBPI (90%) was much higher than that of 4,4'-DCBPI (33%) because of the better stability of the intermediate, 3-chloro-N-aminophthalimide, and 3,3'-DCBPI. A series of hydrazine-based polyimides were prepared from isomeric DCBPIs and 4,4-thiobisbenzenethiol (TBBT) in N,N-dimethylacetamide in the presence of tributylamine. Inherent viscosity of these polymers was in the range of 0.51-0.69 dL/g in 1-methyl-2-pyrrolidinone (NMP) at 30 degrees C. These polyimides were soluble in 1,1,2,2-terachloroethane, NMP, and phenols. The 5% weight-loss temperatures (T(g)s) of the polymers were near 450 degrees C in N-2. Their glass-transition temperatures (T(g)s) determined by dynamic mechanical thermal analysis and differential scanning calorimetry increased according to the order of polyimides based on 4,4'-DCBPI, 3,4'-DCBPI, and 3,3'-DCBPI. The hydrolytic stability of these polymers was measured under acid, basic, and neutral conditions and the results indicated that the order was 3,3'-DCBPI/TBBT > 3,4'-DCBPI/TBBT > 4,4'-DCBPI/TBBT.

Detection of hydrazine, methylhydrazine and isoniazid by capillary electrophoresis with a 4-pyridyl hydroquinone self-assembled microdisk platinum electrode

Capillary electrophoresis (CE)/electrochemical detection (EC) for the simultaneous detection of hydrazine, methylhydrazine, and isoniazid has been developed with a 4-pyridyl hydroquinone self-assembled microdisk platinum electrode. Such an electrode has very high catalytic ability for hydrazines and they could be detected even at 0.0 V. The responses for hydrazine, methylhydrazine, and isoniazid are linear over 3 orders of detected concentration and of magnitude of 0.2-400 mu M, 0.2-400 mu M, 0.5 mu M-2 mM, with correlation coefficients of 0.9998, 0.9991, and 0.9982, respectively. And they could be detected to levels of 0.1, 0.1 and 0.2 mu M, respectively. This modified electrode was found to be very stable and reproducible when continuously used as detector for capillary electrophoresis for period of at least 4 weeks with no apparent loss of response. (C) 1999 Elsevier Science B.V. All rights reserved.

Electrocatalytic oxidation and flow amperometric detection of hydrazine at an electropolymerized 4-vinylpyridine/palladium film electrode

A poly(4-vinyl)pyridine (PVP)/Pd film electrode was constructed for the electrocatalytic detection of hydrazine. The preparation of the PVP/GC electrode was performed by electropolymerization of the monomer 4-vinylpyridine onto the surface of a glassy carbon electrode. Subsequently, palladium is electrodeposited onto the polymer modified electrode surface. The ion-exchange function of PVP polymer is helpful to this process in view of the tetrachlorapalladate anion. Compared with the Pd/GC electrode, the modified electrode displays a better mechanical stability in a flowing stream. The PVP/Pd film electrode exhibits higher sensitivity when detecting hydrazine with a detection limit of 0.026 ng (S/N=3).

Detection of hydrazine, methylhydrazine, and isoniazid by capillary electrophoresis with a palladium modified microdisk array electrode

A palladium particle-modified carbon fiber microdisk array electrode was designed and employed in capillary electrophoresis for the simultaneous detection of hydrazine, methylhydrazine, and isoniazid. The Pd-modified microdisk electrode had high catalytic ability for hydrazines and exhibited good reproducibility and stability. The response for hydrazine was linear over 3 orders of magnitude with a correlation coefficient of 0.993. The detection limits far hydrazine, methylhydrazine, and isoniazid were 1.2, 2.1, and 6.2 pg, respectively.

Determination of isoniazid and hydrazine by capillary electrophoresis with amperometric detection at a Pt-particle modified carbon fiber microelectrode

Capillary electrophoresis (CE)/electrochemical detection (EC) for the simultaneous determination of hydrazine and isoniazid has been developed. The electrochemical method uses a novel modified electrode dispersed with ultrafine platinum particles on the surface of a 30 mu m carbon fiber microelectrode. The unique characteristic of the Pt-particles modified carbon fiber microelectrode is its excellent stability. The current measurement for hydrazine is more sensitive than that of isoniazid. Selective determination of trace amount of free hydrazine in isoniazid and its formulation can be achieved at applied potential of 0.5 V.

ANODIC-OXIDATION OF HYDRAZINE ON GLASSY-CARBON ELECTRODES IN ACETONITRILE

The anodic oxidation kinetics of hydrazine on glassy carbon electrodes in acetonitrile were examined by cyclic voltammetry, a rotating ring-disc electrode technique and chronoamperometry. The experimental results of the rotating ring-disc electrode prove that hydrazine is oxidized to HN=NH, which cannot be oxidized further in acetonitrile. Hydrazine molecules are adsorbed on the electrode surface. One-third of the adsorbed hydrazine molecules are oxidized to HN=NH and the other two thirds act as proton acceptors. A possible mechanism of hydrazine oxidation is proposed.

ELECTROCATALYSIS AND DETERMINATION OF HYDRAZINE COMPOUNDS IN LIQUID-CHROMATOGRAPHY AT A MIXED-VALENT COBALT OXIDE CYANOCOBALTATE FILM ELECTRODE

A glassy carbon electrode coated with an electrodeposited film of mixed-valent cobalt oxide/cyanocobaltate (Co-O/CN-Co) enabled hydrazine compounds to be catalytically oxidized at the greatly reduced overpotential and in a wide operational pH range (pH 2.0-7.0). Electrocatalytic activity at the Co-O/CN-Co modified electrode was evaluated with respect to solution pH, film thickness, supporting electrolyte ions, potential scan rate, operating potential, concentration dependence and other variables. The Co-O/CN-Co film electrode was completely compatible with a conventional reversed-phase liquid chromatographic (RP-LC) system. Practical RP-LC amperometric detection (RP-LCEC) of hydrazines was performed. A dynamic linear response range over three orders of magnitude and a detection limit at the pmol level were readily obtained. The Co-O/CN-CO film electrode exhibited excellent electrocatalytic stability in the flowing streams.