Graphite Cylinder Research Articles

Electronic properties of bucky-tube model

Electronic properties of bucky tube modelled by a sheet of helical graphite cylinder named “grahelix” have been examined based on the one-dimensional tight-binding crystal orbital method in the framework of the Hückel approximation. It has been found that there are two types of grahelix depending on the helical pitch, that is, one is energetically stable and semiconductive whereas the other less stable with metallic nature. Moreover we elucidate that such metallic tubes are equivalent to those involving plural numbers of isolated cis-type polyacetylene skeletons arranged mostly in a helical manner on the tube surface. Such helical polyacetylene skeletons guarantee the metallic conduction path to the electons near the Fermi level (spiralons). Control of the flow of these spiralons may open up a stage for nanotechnology of the electronic devices such as molecular solenoid applicable to molecular electromagnet, molecular electric generator and so on.

Electronic properties of bucky-tube model

Electronic properties of bucky tube modelled by a sheet of helical graphite cylinder named “grahelix” have been examined based on the one-dimensional tight-binding crystal orbital method in the framework of the Hückel approximation. It has been found that there are two types of grahelix depending on the helical pitch, that is, one is energetically stable and semiconductive whereas the other is less stable with metallic nature.

The Fractures of Graphite Cylinders with a Transverse Hole under Torsion.

This study aimed at a theoretical approach which can be applied to the Fracture analysis of graphite cylinders with a transverse hole under torsion. It was found that the position of maximum tensile stress occurred at an intersection of hole and outer surface of the cylinder. Theoretical analysis has been carried out with the surface layer theory applied to the maximum tensile stress at the edge of the hole. The graphite is brittle material with a little ductility; therefore, we established the fracture criteria by taking the ductility into account. The fracture stresses of the solid and hollow cylinders were dependent only on the diameter of the hole, and were not influenced by the outer diameter of the cylinder. A hole with the comparatively small diameter had no effect on the fracture stress of the cylinder.

Effect of Slag Foaming on the Reduction of Iron Oxide in Molten Slag by Graphite.

A kinetic study has been made on the reduction of iron oxide in molten slag, held in an alumina crucible under argon gas atmosphere, with graphite, cylindrical in shape. The composition of the primary slag was 20.5%Li2O-38.4%CaO-41.1%SiO2 (molar ratio=1:1:1). The initial concentration of iron oxide was changed between 3% and 12.5%. The experimental temperature was 1300°C. The rotation speed of the graphite cylinder was varied from zero to 1900 rpm. The reaction rate was largely affected by slag foaming. At higher FeO concentrations, the apparent rate constant was almost independent of the mechanical stirring. At lower concentrations, the effect of the rotation on the apparent rate constant was found to be small at lower speeds but tended to become larger at higher speeds. This was an indication that the melt was strongly agitated by CO gas bubble evolution. The effect of foaming is taken into account by introducing gas holdup factor into ordinary (foam-free) kinetic equations. Values of the mass transfer coefficient of oxygen in the molten slag, calculated by applying the penetration theory, are close to those of the apparent rate constant, measured experimentally. This implies that the rate of the reduction is controlled predominantly by the mass transfer in the slag phase.

Extinction properties of infinitely long graphite cylinders

We have calculated the extinction efficiencies of randomly oriented infinite graphite cylinders, including hollow cylinders, using the rigorous Kerker-Matijevic formulae. The peak in the mid-ultraviolet extinction varies in wavelength with particle radius and cavity size in a way that makes such particles of limited interest as models of interstellar grains.

The role of Monte Carlo simulation of electron transport in radiation dosimetry

A brief overview is given of the role in radiation dosimetry of electron transport simulations using the Monte Carlo technique. Two areas are discussed in some detail. The first is the calculation of stopping-power ratios for use in ion chamber dosimetry. The uncertainty in stopping-power ratios is discussed with attention being drawn to the fact that the relative uncertainty in restricted collision stopping powers is greater than that in unrestricted stopping powers if the major source of uncertainty is the density effect correction. Using ICRU Report 37 stopping powers and electron spectra calculated in a small cylinder of graphite, the value of the Spencer—Attix graphite to air stopping-power ratio in a 60Co beam is found to be 1.0021 for an assumed graphite density of 1.70 g/cm 3 and 0.23% less for an assumed density of 2.26 g/cm 3. The second area discussed is the feasibility of using Monte Carlo techniques to calculate dose patterns in a patient undergoing electron beam radiotherapy.

A gage for measuring heat transfer to the bore of electromagnetic railguns

A calorimeter gage for directly measuring plasma armature heat transfer in electromagnetic railguns has been fabricated and tested. The concept utilizes a miniature thermocouple-instrumented pyrolytic graphite cylinder. The high vaporization temperature and anisotropic properties of the pyrolytic graphite combine to enable measurement of intense heat pulses (time integral of heat flux) beyond the capacity of any other calorimeter. Since the sensing surface does not melt or ablate, data interpretation is straightforward and gage destruction is avoided. Initial tests of the gage have been conducted in the plasma utility gun (PUG). Gage response was generally as anticipated, and heat transfer was determined at two bore locations for two PUG shots. Results from these preliminary tests indicate that heat transfer to bore insulators is less than that to the rails. Additional tests are planned including direct measurements of rail heating to confirm initial indications of the heat transfer distribution between rails and insulators. >

Impurity fluxes in ASDEX studied with a solid graphite collector probe

A high-purity graphite probe for collecting impurities in ASDEX has been used for the first time. The probe head consists of a rotatable graphite cylinder housed in a fixed molybdenum shield containing an exposure slit. Measurements were made on the scrape-off layer plasma streaming to the upper outer divertor plate and, after extraction of the probe, collected impurities were identified and quantified using surface physics techniques. Single null ohmic discharges produce a threefold increase in erosion of the Cu plate of the active upper divertor compared to similiar double null discharges. The radial distributions of scrape-off layer impurities change in both shape and intensity with vertical plasma position. Boronization of the main vessel reduces the amount of Fe collected by more than a factor of two but the oxygen deposit increases. Radial distributions of Cu and Fe deposits as a function of time for a neutral beam heated discharge are also discussed.

Structure and Dynamics of a Magnetron DC Arc Plasma

A direct-current arc plasma generator is described which uses a concentric electrode configuration and a magnetic field parallel to the electrode axis to obtain rotation of the arc current channel at a frequency in the 1–3 kHz range. The anode is a hollow graphite cylinder, and the cathode is a thoriated tungsten wire. A magnetic field of several hundred gauss is obtained from one or more ring-shaped permanent ceramic magnets. For a 5-mm anode diameter, the plasma is diffuse, and the current channel has the form of a thin radial sheet which undergoes relatively small periodic perturbations at the rotational frequency. Design features, performance data, and plasma structure are considered.

Al/Cl2 battery with slightly acidic NaCl electrolyte. II. Ti-Ti/Ru oxide chlorine cathodes

A new version of the Al/Cl2 battery previously described was investigated. Instead of a graphite cylinder, a porous titanium plate was used as a chlorine electrode (cathode). The electrolyte used was a moderately acidic aqueous NaCl solution of pH 2 containing small amounts of In3+ and Hg2+ as additives. The cell had an open-circuit voltage of 2.6 V and delivered a maximum power of 19.8 W at 1.1 V with a Faradiac efficiency of 69%. The power density was 280 mW cm−2. A module consiting of 4 submodules connected in series, where each submodule contained 4 double-unit cells connected in parallel, had an open-circuit voltage of 10.6 V, a maximum power of 200 W and an energy density of 110 Whl−1.

Oxidation of nuclear-reactor-grade graphite

An analytical solution is developed for transient, constant-temperature and constant-pressure oxidation of a hollow, porous graphite cylinder by oxygen diffusing from the cylinder surfaces. The following approximations are used: a binary diffusion approximation for all species, a constant value for the product of density and diffusion coefficient, negligibly small mass-average velocity and axial diffusion, a single heterogeneous reaction producing CO 2, and first-order reaction kinetics with respect to oxygen. The analytical results are in good agreement with data obtained by Klaschka et al for an experimental configuration designed to provide constant-temperature and constantpressure oxidation of a hollow graphite cylinder. Studies of the type presented in this paper are of interest in connection with evaluations of nuclear reactor safety, including possible graphite combustion of the type that may have occurred in connection with the Chernobyl reactor failure.

Melt/freeze heat transfer measurements in cryolite-based electrolytes

The need to maintain a solid electrolyte ledge on the sidewalls of aluminum smelting cells has recently provoked interest in the heat transfer rate from the molten to the frozen phase at this interface. In this work an electronic voltage to frequency conversion technique was developed to record thermocouple signals inside a vertical, air cooled graphite cylinder rotating in molten cryolite. Precise measurement of the solid electrolyte which freezes around the internally-cooled cylinder allowed determination of the interfacial heat transfer coefficient under both free and forced convection conditions. Correlation of the local Nusselt numbers for heat transfer to the stationary cylinder yields an expression similar to that obtained for natural convection in a rectangular enclosure. However, rotation of the cylinder at peripheral velocities of 0.09 to 0.12 m s−1 caused forced convection to dominate in the cavity and increased the heat transfer coefficients by 34 to 45 pct, respectively. The data provide a basis on which to calculate the convective heat flow to the sidewall ledge for a range of hydrodynamic conditions in the cell.

Mass transfer of mixed gas flow crossing a high temperature graphite cylinder with chemical reactions and in-pore diffusion

An experimental study on mass transfer with chemical reactions and in-pore diffusion was performed in cross flow containing oxygen past a porous graphite cylinder placed in a high temperature environment. Reynolds numbers ranged from 533 to 2490, and cylinder temperatures ranged from 848 to 1120°C. It is concluded that chemical reactions do not significantly influence the mass transfer, and that the effect of in-pore diffusion on mass transfer can be estimated by using empirical relations for the corrosion rate and mass transfer.

Mass transfer of mixed gas flow crossing a high temperature graphite cylinder with chemical reactions and in-pore diffusion.

In connection with the analyses of hypothetical massive air ingress accidents in High Temperature Gas-cooled Reactors (HTGRs), an experimental study on mass transfer with homogeneous and heterogeneous chemical reactions and in-pore diffusion was performed in gas mixture crossflow past a porous circular cylinder placed in a high temperature environment. The Reynolds numbers ranged from 533-2 490, and the temperatures of the cylinder from 848-1 120°C. The porous graphite cylinder was corroded in a nitrogen gas flow containing approximately 5 % oxygen. Mean and local mass transfer coefficients and corrosion rates were obtained to examine the influences of chemical reactions and in-pore diffusion on mass transfer. It is concluded that the chemical reactions do not influence significantly the mass transfer under conditions expected in HTGR air ingress accidents, and that the effect of the in-pore diffusion on the mass transfer can be estimated by the empirical relations of the corrosion rate and mass transfer.

Transport calculations of neutron energy spectra in a graphite cylinder with a D-T source

Neutron energy spectra resulting from the transport of 14.7 MeV neutrons from a collimated D-T source through a graphite cylinder, have been calculated with the discrete-ordinates 2-D transport dot 4.2 code, with multigroup cross-sections generated using the njoy code from the ENDF/B (IV & V) libraries. The results confirm the conclusion of Goldfeld et al. (1985), that energy spectra at mesh points close to the axis of the system, in front of the collimated beam, consist mainly of one-collision contributions of elastically or inelastically scattered neutrons. Investigation of the dependence of the calculated spectra on the order of truncation of the Legendre polynomials expansion of the flux and of the cross-sections (i.e. the order of scattering) leads to the following observations: 1. (a) the P 6 or P 7 approximations seem to be adequate enough for flux calculations, with less than 3% error, in spite of the high degree of the source and the cross-section's anisotropy; 2. (b) the calculation error is reduced significantly by increasing the order of scattering from P 4 to P 7, mainly in mesh points close to the axis and of those energies in which the anisotropy of the elastic and discrete level inelastic scattering processes is most pronounced. Finally, the dot 4.2 calculations are compared with Monte Carlo mcnp calculations; both calculated spectra are in a good agreement.

The fracture of hollow cylinders of brittle materials under dynamic internal gas pressure.

A cylinder loaded with equal internal and external pressure bears without failure. While unloading only the external pressure rapidly, the cylinder fractures dynamically under the internal pressure which is greater than that of the atmosphere. In our experiment, the mediums giving rise to internal and external pressure were nitrogen gas and turbine oil respectively. A hollow cylinder of graphite was used as the specimen, and the relation between internal gas pressure at the fracture of the cylinder and the number of fragments fractured at the longitudinal section were obtained. It was shown that the analytical explanation coincides with the experiment.

The Effect of Pressure Field on Bursting of Brittle Materials : The Second Report ; Bursting of Graphite and Cast Iron Cylinders under Lateral Fluid Pressure

In this paper lateral fluid pressure and combined loads of lateral fluid pressure and tension are applied on coated and naked graphite cylinders, and naked cast iron cylinder to study the size effect and the effect of pressure fluid on the bursting of brittle materials, and the following conclusions are obtained ; (1) On coated and naked graphite cylinders there is no size effect under lateral fluid pressure. (2) On naked cast iron cylinder there is size effect, and its bursting strength is different depending the kinds of pressure fluids under lateral fluid pressure. (3) Under combined loads of lateral fluid pressure and tension the bursting strengths of naked cast iron cylinders are different depending on the kinds of pressure fluids as in the case of lateral fluid pressure.

The use of an arc plasma rotating in a magnetic field for metal coating glass substrates

First results are reported about deposition of metals on glass substrate using a low current arc plasma source at atmospheric pressure. The arc source consists of a graphite cathode rod placed on the axis of a graphite anode cylinder aligned in a magnetic field. The carrier gas is argon. The deposition material, zinc or gold, is evaporated from a reservoir in the cathode. Depositions on flat substrates positioned on the periphery of the rotating plasma within the anode tube and in a jet outside the anode have been investigated. The investigations are planned to lead towards laser fusion target pusher layer fabrication. This fabrication would be facilitated by a high pressure deposition process where target levitation is readily performed.

Prospects for fission gas extraction from in-reactor UO 2 nuclear fuel elements

Due to the many problems encountered in the design of fuel rods for the safe operation of commercial nuclear reactors, caused by the fission gases generated by the fission of fissile material, it was considered opportune to make a theoretical analysis of the feasibility of extraction of fission gases from the fuel rod while in operation. This analysis in the steady state of a Zircaloy-2 sheathed fuel rod containing UO 2 as a fuel, with a 2 mm (2.7 vol.%) diameter porous graphite cylinder inserted in the centre, has demonstrated that a total volume of fission gases (xenon, krypton, and iodine) of about 1.1 × 10 −6 cm 3/s (at STP) can be extracted from the fuel rod at a controlled rate, determined by the inherent property of fission gas migration towards the centre of the fuel rod from its place of formation. In this analysis, the fuel rod was assumed to be subjected to irradiation in a reactor the size of a Bruce “A” reactor, operating at 3000 megawatts thermal power. The extracted volume of gas was calculated on a 900 h cycle after the first 90 h of reactor operation had elapsed.

黒鉛の溶鉄への溶解速度におよぼす硫黄および燐の影響

The influence of sulfur or phosphorus on the rate of carbon dissolution from rotating graphite cylinders into the liquid iron alloys was studied in the temperature range of 1573-1773 K. Electrode-grade graphites (graphitizing and non-graphitizing carbon) were used. The results are summarized as follows:(1) Non-dimensional correlation between mass transfer of carbon in the Fe-C melt and the rotational speed was obtained, which was expressed as(This article is not displayable. Please see full text pdf.) \ oindentWhen sulfur or phosphorus was added, the results deviated from this correlation, which was interpreted in terms of mixed control of mass transfer and interfacial kinetics.(2) Phosphorus decreased the overall mass transfer coefficient k, which was presumed to be due to the effect of phosphorus adsorption through its influence on the interfacial kinetics. The dependence of k on the structure of graphite was found to be negligible.(3) Sulfur decreased k more than phosphorus, which suggested the more intensive surface activeness of sulfur. Particularly in the case of non-graphitizing carbon, k extremely diminished. This result would be attributable to the greater degree of adsorption of sulfur on non-graphitizing carbon than the graphitizing carbon.