Hydrogen Arc Research Articles

Calculation of parameters of a cylindrical hydrogen electric arc from generalized relationships

Generalized expressions for various parameters of cylindrical arcs in hydrogen are presented. Results of calculations are compared with results of numerical and physical experiments.

Generalization of characteristics of cascade electric arcs in various gases

Generalization of differential volt-ampere and other characteristics of cascade electric arcs in air, nitrogen, argon, helium, and hydrogen is carried out for currents of 0.4-300 A and channel radii of 1-20 mm.

The effect of arc parameters on the growth of carbon nanotubes

The influence of starting carbon material on the generation of carbon nanotubes is investigated. Comparisons are made between oriented graphite, randomly oriented graphite, carbon black, and a polycyclic aromatic hydrocarbon as carbon sources in helium and hydrogen arcs. Transmission electron microscopy investigation of the redeposited rod formed on the cathode and the soot from the chamber walls provides evidence for the building blocks that lead to the nanostructures formed. It is postulated that polycyclic aromatic hydrocarbons are precursors for carbon nanotube growth in a hydrogen arc. While, in the case of helium, low molecular weight carbon ions and molecules have been previously hypothesized by others to be the building blocks for nanotube growth.

Catalytic properties of nanostructured hydrogen storage nickel particles with cerium shell structure

Abstract In this paper we examine a new kind of nanostructured nickel particle with cerium shell structure prepared by the hydrogen arc plasma method. The microstructural analysis of nano-Ni particles showed that the shell layer consisted of CeNi alloys and cerium oxide. The hydrogen storage property of the nanoparticles was investigated by mass spectroscopy. The results showed that the quantity of hydrogen released gradually increased with increasing temperature up to a maximum of 400 °C, then gradually decreased at temperatures above 400 °C. The catalytic activity of nanoparticles in the gas phase hydrogenation of benzene was related to their hydrogen storage properties and it reached the maximum value when the maximum amount of bulk H was released. By comparing the catalytic activity of nano-Ni particles with and without Ce shell structure, the higher activity of nano-Ni with Ce shell was attributed to the property of hydrogen storage and the synergistic effect of Ce and Ni in the shell structure, which was also illustrated by the result of gas phase benzene hydrogenation over supported nano-NiCe particles.

Production of petal-like graphite sheets by hydrogen arc discharge

By DC arc-discharge evaporation of graphite in the presence of rarefied hydrogen gas, not only carbon nanotubes but also petal-like graphite sheets were produced on the graphite cathode as a carbon deposit. A large number of interlaced petal-like graphite sheets were observed by scanning electron microscopy on the cathode surface which surrounded the region of carbon deposit including multiwalled carbon nanotubes. The crystal structure of these petal-like graphite sheets was confirmed to be stacking of graphene by using a selected area electron diffraction pattern. Here, we propose a mass production method of petal-like graphite sheets by hydrogen arc discharge evaporation.

Preparation of high-grade carbon nanotubes by hydrogen arc discharge

Fine and long multiwalled carbon nanotubes attached with less carbon nanoparticles were prepared by d.c. arc discharge plasma of graphite electrodes in hydrogen gas. These high-grade carbon nanotubes grew on the central part of the cathode as a carbon deposit like black soot. They were mainly observed by a scanning electron microscope and subsequently by a high resolution transmission electron microscope. By comparing with helium and methane gases, the predominance of the use of hydrogen gas as the environmental gas is discussed. A new type of carbon allotrope, namely petal-like graphite sheets consisting of a number of interlaced graphene sheets, was also found in the outside region surrounding the central cathode deposit.

Radiative emission analysis of an expanding hydrogen arc plasma—II. Plume region diagnostics through radial emission

An experimental investigation of the plasma plume of a 1 kW class radiatively-cooled hydrogen arcjet thruster is presented. The line-of-sight emission of the Balmer-alpha line is measured at several radial positions using a high resolution monochromator and photon counting detection. The line-of-sight spectra are deconvolved radially into Voigt profiles, from which radial distributions of translational temperature and electron number density are determined. Absolute intensity calibration is also performed providing radial distributions of atomic hydrogen m = 3 excited state number density. Electron temperature profiles are calculated using a non-equilibrium collisional-radiative model. The hydrogen translation temperature displays good agreement with previous measurements. The electron number density profiles are consistent with Langmuir probe measurements made downstream of the exit plane. The results of the model indicate that the plasma at the nozzle exit plane is strongly recombining.

Radiative emission analysis of an expanding hydrogen arc plasma—I. Arc region diagnostics through axial emission

A numerical and experimental investigation of the axial emission of 1 and 5 kW radiatively-cooled hydrogen arcjet thrusters is presented. The numerical study consists of an integration of the 1-D radiative transfer equation along the arcjet centerline to predict the axial emission spectral intensity. The complete visible spectrum is modeled, taking into account graybody thermal emission from the cathode and plasma radiation from hydrogen atoms and free electrons. A collisional-radiative model is used to determine the atomic hydrogen line emission. The modeling results suggest the feasibility of determining the cathode temperature and the arc region electron number density from the measured axial emission spectrum. Experimental measurements of the axial emission spectra were performed at several operating conditions. The cathode temperature is found to be in the neighborhood of the tungsten cathode melting point and increases with arcjet power at a constant mass flow rate, suggesting an increase in the current density at the arc attachment point. The measured arc region electron number density is also found to increase with power, confirming an increasing arc current density with arcjet power. Relatively flat radial profiles of electron number density measured in the arc indicate the importance of diffusional transport processes.

Synthesis and thermal properties of ultrafine powders of iron group metals

From the viewpoint of commercial production, the synthesis of ultrafine powders (UFPs) of iron group metals has been studied experimentally in detail by using activated plasma evaporation of the metals in a hydrogen and argon gas mixture. Different experimental parameters, including hydrogen content, arc current and gas pressure, were investigated for their effects on the evaporation rate of the metals. It should be noted that Co UFP, unlike Fe UFP and Ni UFP, consists of two phases: α-Co (h.c.p.) and β-Co (f.c.c.). The fraction of the former phase in Co UFP ranges from 10% to 25% as the average grain size decreases from 24 to 14 nm. The thermal stability of metal UFPs upon heating in a stream of helium can be understood by powder densification via integrain sliding and grain growth. Besides this, phase transitions from ferromagnetism to paramagnetism were clearly observed in the differential thermal analysis (DTA) curves of Fe UFP (at about 755 °C) and Ni UFP (at about 355 °C), indicating that there is a decrease of several degrees in the Curie point with respect to their bulk counterparts. In addition, a structural transition of α-Fe to γ-Fe occurred at 901–908 °C, a little lower than the bulk value (912 °C). The oxidation behavior of metal UFPs was attributed to oxidation reactions of metal grains, followed by grain growth and sintering of powder. Moreover, Co UFP exhibits one endothermic peak at 882–930 °C which was identified as due to the thermal decomposition of cobalt oxide formed in the oxidation reaction at low temperatures.

Synthesis of carbon-encapsulated nanowires using polycyclic aromatic hydrocarbon precursors

A method using polycyclic aromatic hydrocarbon (PAH) precursors for synthesizing carbon nanotubes filled with pure copper or germanium is reported. A model is proposed where the interaction of small copper or germanium clusters with PAH molecules is shown to form carbon-encapsulated nanowires. The validity of this model is demonstrated by showing that filled nanotubes are formed in a hydrogen arc which produces PAH molecules when graphite electrodes are used. Alternatively, we have also used pyrene (C 16H 10), a PAH molecule, to grow encapsulated nanowires directly. No filled nanotubes are found in a helium arc which does not generate PAHs.

A method for synthesizing large quantities of carbon nanotubes and encapsulated copper nanowires

A method using a hydrogen arc for synthesizing large quantities of carbon nanotubes filled with pure copper is reported. The interaction of small copper clusters with polycyclic aromatic hydrocarbons (PAHs) is shown to form carbon nanotubes and encapsulated copper nanowires. The effectiveness of this model is demonstrated by showing that no copper filled nanotubes are formed in a helium arc that does not generate PAHs. A direct proof of this model is demonstrated by using pyrene, a PAH molecule, to grow carbon nanotubes and encapsulated copper nanowires.

CeNi nanoparticles with shell structure for hydrogen storage

A new kind of Ce-Ni nanoparticle was prepared by hydrogen arc plasma method. The nanoparticles consist of a large Ni core and a thin outer shell of CeNi alloy and CeO 2 . A large quantity of hydrogen was stored in the particles, which was released at about 400 °C. The particles possess a lot of defects, dislocations and twin faults, which increase the number of surface active centers of the particles. The mechanism of shell structure formation of the nanoparticles is discussed in terms of the low solubility of Ce in Ni, and surface segregation under non-equilibrium cooling conditions.

Preparation of Petal-like Carbon Films by Hydrogen Arc Discharge

Preparation of Petal-like Carbon Films by Hydrogen Arc Discharge

Oxidation behavior of nano-Fe prepared by hydrogen ARC plasma method

Abstract Nano-Fe particles were prepared by an arc plasma method and sintered in air atmosphere at different temperatures to obtain nano-Fe2O3. The morphology and phase structure of nano-Fe2O3 particles were studied by TEM and XRD methods. TEM results show that the shapes of Fe2O3 particles are spherical and the average particle size is about 50 nm. Also, the Fe particles sintered at temperatures below 600 °C consist of lighter cores and darker outer shells; the latter disappear at temperatures above 600 °C. XRD results show that a phase transformation from γ-Fe2O3 to α-Fe2O3 occurs with increasing temperature. α-Fe2O3 was found at temperatures as low as 200 °C but only α-Fe2O3 exists above 600 °C.

The effect of hydrogen on the formation of carbon nanotubes and fullerenes

A novel method to synthesize “clean” carbon nanotubes with relatively high yield in a hydrogen arc discharge has been developed. The quality and yield of the tubes depend sensitively on the gas pressure in the arc discharge. Sharp, open-ended nanotubes with clear lattice fringes at the edges and empty interiors have been observed. The existence of these frozen-open-ended tubes as part of nanotube-bundles provides evidence for an open-ended growth model for nanotubes. Using time of flight mass spectrometry, it was found that fullerenes, such as C60 and C70, are almost absent from the soot collected in the hydrogen arc discharge. The effect of hydrogen on the formation of fullerenes, both in the laboratory and in space, will be discussed.

Carbon nanotubes synthesized in a hydrogen arc discharge

We have developed a novel method to synthesize ‘‘clean’’ carbon nanotubes with relatively higher yield using a hydrogen arc discharge. The quality and yield of the tubes depend sensitively on the gas pressure in the arc discharge. We have observed sharp, open-ended nanotubes with clear lattice fringes at the edges and empty interiors. The existence of these frozen-open-ended tubes in the buckybundles provides evidence for an open-ended growth model for nanotubes.

Powerful pulse generator of dense plasma with high concentration of metal vapour

The results of experiments on the heating of hydrogen and nitrogen of high initial pressure (20 – 40 MPA) by high-current discharge with discharge current amplitude up to 1,5 MA, initiated by wire explosion, are represented in the paper. Owing to high erosion of anode and cathode due to the discharge, equal to 200 – 300 C, passing through them, the average magnitude of metal vapours concentration in the discharge chamber is 10cm20 cm−3, that can be compared to working gas concentration. On the basis of the experimental results and metal plasma conductance calculations data the estimations of the temperature of the discharge channel are given.Using data of the experiments with arcs in hydrogen, nitrogen and helium with current discharge amplitude equal to 20 – 200 kA the conclusion about the defining influence of metal vapours on the properties of the arc itself and on the heat exchange between the arc and the environmental gas is drawn. For example, the increase of arc's turbulence level with the decrease of distance between electrodes is connected with metal streams introduction from electrodes to the near-electrodes areas. The increase of gas heating efficiency with the increase of initiating wire mass is stipulated by metal vapours radiation absorption in the cold zone.

Experimental characterization of a hydrogen/argon cascaded arc plasma source

A H2 /Ar cascaded arc plasma source has been experimentally characterized by determination of the efficiency, the electric field, and the pressure gradient of the arc. The results show that the efficiency of a H2/Ar cascaded arc drops when the hydrogen flow rate is increased. The electron temperature in the argon cascaded arc has been derived to be in the range 9000–12 500 K. For a hydrogen arc, the mass dissociation degree of hydrogen molecules has been derived to be above 60%.

Constrictor flow analysis of a medium power hydrogen arcjet

In a thermal arcjet the main heating of the propellant takes place in the constrictor. To gain more insight into arcjet operation and to obtain experimental data on the shape, size, and stability of the arc channel inside the constrictor, a modified arcjet thruster was built. Through a window in the nozzle throat the discharge channel in the constrictor was observed. With a fast CCD camera, images of the arc were taken, and using image processing methods a hydrogen arc was analyzed. The camera system was calibrated to measure absolute intensities. Thus, it was possible to determine the two-dimensional temperature profiles from electron continuum and from the line intensity ratio of the H« and the H^ line. In the second section, an analytical method to calculate the flow conditions inside the constrictor is described. The first version of the model is developed for hydrogen as propellant. The calculation results are compared with measurements. Nomenclature A = area, m2 B = magnetic induction, Vs/m2 c = thermodiffusivity of cold gas, m2/s ch = total heat capacity, J/kgK E = excitation energy, J / = absorption oscillator strength g = statistical weight 7 = arc current, A j = current density, A/m2 M = molecular mass, kg/mol Ma ~ Mach number m = mass flux, kg/s n — grade of current density parabolic n = particle density, 1/m3 p - static pressure, N/m2 q = heat flux, W/m2 $1 = universal gas constant, J/molK RL = radiation and reaction losses, W/m3 r = radius, m T = temperature, K v = velocity, m/s 2 = coordinate in flow direction, m 8r = radial step in cold gas contour calculation, m £, I = dimensionless quantities accounting for radiation losses K = adiabatic exponent A = heat conduction coefficient, W/mK A = wavelength, m v — frequency, 1/s p = mass density, kg/m3 a = electric conductivity, A/Vm

Recent results on the deposition of diamond thin films by arcjet plasmas and diagnostic measurements of the plasma-surface region

A gas jet is extracted from a dc arc in hydrogen with approximately 1% added hydrocarbons; polycrystalline diamond grows below the stagnation point of the jet on silicon and tantalum substrates. The diamond film is studied by ex-situ surface Raman spectroscopy, scanning electron microscopy and optical microscopy. The arcjet is examined by optical emission spectroscopy, laser induced fluorescence, mass spectroscopy and electrostatic probes. We discuss the results of the deposition experiments and correlations with the diagnostic measurements. Comparisons with model predictions are also made.