Types Of Graphite Research Articles

The graphitization process and the synthesis of diamonds from a C–Ni–Mn system

The influence of the “degree of graphitization” on the synthesis of diamond obtained from a HP–HT process using an anvil type high pressure device was studied for different types of graphites. The “degree of graphitization” was measured by a new parameter the percentage of hexagonal perfection (PHP). Results have shown that for samples with a PHP below 50% no diamond was formed. This suggested that a minimum “degree of graphitization” must be present for a successful HP–HT for diamond synthesis.

Electromagnetic imaging of Variscan crustal structures in SW Iberia: the role of interconnected graphite

The western part of the Iberian Peninsula (Iberian Massif) is the best exposed fragment of the Variscan orogen in Europe. Its southern half was generated by an oblique collision between three continental terranes belonging to the margins of Laurassia (Avalonia) – the South Portuguese Zone (SPZ) – and Gondwana – the Ossa Morena Zone (OMZ) and the Central Iberian Zone (CIZ). The boundaries between them are considered to be suture zones. A 200 km long magnetotelluric profile across the three Variscan terranes was done in a NNE direction, approximately perpendicular to the main tectonic features. The results of two-dimensional inversion of the MT dataset reveal high-conductivity zones coinciding with the transitions SPZ/OMZ and OMZ/CIZ. These conductive bodies related to the sutures at depth were interpreted as graphite enrichments along shear planes formed due to the overall transpressive regime. A high-conductivity layer extending along the whole OMZ was found at a depth of 15–25 km, the top of which spatially correlates with a broad reflector detected by a recently acquired deep seismic reflection profile. The high conductivity was interpreted as caused by the Precambrian Serie Negra graphite-rich rocks. Carbon and oxygen X-ray mapping with electron microprobe on polished sections of Serie Negra samples from OMZ revealed the presence of interconnected graphite, which supports the hypothesis that graphite is determinant for the high conductivity. Two graphite types, which help to record the geological evolution, were identified: graphite accumulations in the schistosity surfaces produced by folding and metamorphism, and metallic films of graphite developed along late faults. The conductive layer shows blobs of higher conductivity suggesting macro-anisotropy. Additional mylonitisation and shearing produced by thrusting at depth can be the origin of these zones of enhanced conductivity, given that the detachment level is located within the Serie Negra. Several high-resistivity features were found in the upper crust, related to Devonian and Carboniferous successions and probably to some unexposed plutons in the SPZ and the Palaeozoic series of OMZ plus some granitic intrusions. In the CIZ, a high-resistivity zone extending to the whole crust is correlated with extensive late Variscan granite intrusions.

The role of the ‘graphitation degree’ on the high pressure-high temperature diamond synthesis

The influence of the ‘graphitation degree’ on the formation of diamond in an anvil type high pressure was studied using different types of graphites. The ‘graphitation degree’ was measured by a new parameter PHP, related to the percentage of hexagonal perfection. Results have shown that in samples, which presented PHP ‘graphitation degree’ below 50% no diamond was formed. This suggested that a minimum ‘graphitation degree’ should be attained in order to have a successful synthesis for diamond production.

Determination of grey iron strength on the microscale

The tensile strength of a series of test bars has been determined in the whole section including the casting skin and after gradually reducing the diameter. The tensile test results revealed two different phenomena: a strong effect in the peripheral layer and a slight variation in the central part of the section. Both phenomena have been noted when using various types of non-standardized test bars and different graphite and matrix structures.When the peripheral layer of cylindrical test specimen is removed, the tensile strength increases strongly except for low strength irons. The effect takes place in the outer layer of about 1 mm. When the size of the test bar corresponding to the maximal tensile strength, is further reduced, the tensile strength fluctuates around a constant value.

Effect of Surface Characteristics on Compressive Stress and Leakage Rate in Gasketed Flanged Joints

The effect of surface characteristics on compressive stress and leakage rate in gasketed flanged joints is discussed qualitatively and quantitatively based on experimental verifications. The sensitivity of the sealing phenomenon to the sealing surface characteristics, gas pressure and stress level is presented. Sealing surfaces produced with grinding, turning and milling procedures of different roughness values were the subject of the tests with three types of gasket, namely, PTFE (polytetrafluoroethylene), graphite, and spiral wound. The experimental results indicated that the roughness value Ra (average arithmetic height) has no effect on the sealing performance of the gasket, except for the ground type sealing surfaces. The platen (flange) surface forms were found to be the determining factor on the leakage rate and flow regime for gasketed flanged joints. It is shown that the surface characteristics have no effect on the leakage rate and on the gasket performance for the PTFE gasket at high stress levels. However, at low stress levels the rougher ground and milled sealing surfaces having radial channels on the surface produce larger leakage rates. The effect of surface characteristics, stress level, and gas pressure was more evident on the graphite and spiral wound gasket types, at both low and high stress levels. It is also shown that the leakage rate follows an exponential law as a factor of surface stress and gas pressure, for all sealing surface characteristics and gasket types. While there is little difference in the leakage rate for the PTFE gasket when the gasket stress level is increased by a factor of two, from S3 to S5, a substantial leakage rate reduction by a ratio of 17.5 times was observed for the graphite and spiral wound gaskets for most sealing surfaces. On the other hand, when increasing the helium gas pressure from 200 to 800 p.s.i., the leakage rate increased by 5 times for the PTFE, and up to10 times for the graphite and the spiral wound gaskets. It was determined that while molecular flow regimes can be achieved for the PTFE gasket for all sealing surfaces, the two other gasket types provided laminar flow under the same operating conditions.

Electronic band structure and x-ray spectra of boron nitride polytypes

The electronic band structures of boron nitride crystal modifications of the graphite (h-BN), wurtzite (w-BN), and sphalerite (c-BN) types are calculated using the local coherent potential method in the cluster muffin-tin approximation within the framework of the multiple scattering theory. The specific features of the electronic band structure of 2H, 4H, and 3C boron nitride polytypes are compared with those of experimental x-ray photoelectron, x-ray emission, and K x-ray absorption spectra of boron and nitrogen. The features of the experimental x-ray spectra of boron nitride in different crystal modifications are interpreted. It is demonstrated that the short-wavelength peak revealed in the total densities of states (TDOS) in the boron nitride polytypes under consideration can be assigned to the so-called outer collective band formed by 2p electrons of boron and nitrogen atoms. The inference is made that the decrease observed in the band gap when changing over from wurtzite and sphalerite to hexagonal boron nitride is associated with the change in the coordination number of the components, which, in turn, leads to a change in the energy location of the conduction band bottom in the crystal.

Determination of ambroxol hydrochloride in pure solutions and some of its pharmaceutical preparations under batch and FIA conditions

New ambroxol (Amb) ion selective plastic membrane electrodes of both conventional and coated graphite types based on the ion-pair of ambroxolium tetraphenylborate (Amb–TPB) ion-pair are prepared. The conventional type electrode was fully characterized in terms of membrane composition, life span, pH, ionic strength and temperature. It was applied to potentiometric determination of ambroxol in pure solutions and pharmaceutical preparations under batch and flow injection conditions. The potentiometric determination was used in the determination of ambroxol in muco syrup in four batches of different expiry dates, also the amounts of ambroxol released after 1, 8 and 16 h from the muco sustained release type (S.R.) capsules were also assayed. The selectivity of the electrode toward a large number of excipient like inorganic cations, sugars and amino acids was tested. The solubility product of the ion-pair and the formation constant of the precipitation reaction leading to the ion-pair formation were determined conductimetrically.

Electrochemical treatment of distillery effluent using catalytic anodes

Electrochemical treatment processes can provide valuable contributions to the protection of the environment through the minimization of waste and toxic materials in effluents. Complete decolourisation of the distillery effluent is a difficult task. The industry treated effluent still has a brown colour. This paper reports complete colour removal of industry treated distillery effluent through an electrochemical technique. Electrolysis of distillery effluent was carried out in a static electrochemical reactor. Two different types of anodes, planar graphite (Gr) and titanium substrate insoluble anodes (TSIA) were chosen for the treatment of distillery effluent. Lead dioxide coated on titanium (PbO2–Ti) and ruthenium oxide coated on titanium (RuO2–Ti) electrodes were used as TSIA. Current density (C.D.) was varied from 1.5 to 5.5 A dm−2. Complete decolourisation was obtained in both cases. A maximum of 92% of chemical oxygen demand (COD) reduction, 98.1% of biological oxygen demand (BOD) reduction and 99.5% of absorbance reduction were obtained in the set up in which RuO2–Ti as anode and stainless steel as cathode were used. A probable mechanism has been proposed for the oxidation of organics present in the effluent.

Multistage graphite precipitation through protracted fluid flow in sheared metagranitoid, Digana, Sri Lanka: evidence from stable isotopes

The Digana metagranitoid, situated within the Digana shear zone, a critical junction between the Highland and Wanni complexes of Sri Lanka, hosts a variety of graphite types with structural evidence showing formation during different stages prior to and after deformational events affecting this terrain. Here we discuss their occurrence, association and stable isotopes. The carbon isotopes of graphite reported in this study from the Sri Lankan high-grade metamorphic terrain differ significantly from the composition of graphite reported elsewhere in other Precambrian terrains. The stable isotope composition from random crystals depicts an enriched carbon isotopic composition in the range −1.6‰ to −8‰, suggesting precipitation by reduction from CO 2-rich fluids. Intracrystalline microscale traverses made on graphite crystals indicate the δ 13C composition of the rims becoming progressively lighter in 13C, in metagranitoid hosted samples, with the variation reaching up to 1.5‰, consistent with the changing fluid regimes induced by decreasing temperature during the graphite growth, and shows the preservation of core at higher temperatures. A highly enriched carbon isotopic composition (−0.6‰) with a rimward enrichment of 13C observed in migmatites, contrary to the values in metagranitoid, indicates preferential enrichment of heavy isotopes as a result of the partial melting and dissolution/reprecipitation of graphite. The oxygen isotopic composition of a quartz–calcite vein show values in the range 18.5‰ to 20‰, typical for recycled crustal source. The tight constraint in the isotopic data from different graphite types studied indicates a homogeneous fluid source for the deposits. Prolonged fluid flow in this region is envisaged in this study, which is related to the multistage deformation of the crustal scale shear zone.

Flammability characterization and synergistic effects of expandable graphite with magnesium hydroxide in halogen-free flame-retardant EVA blends

The flammability characterization and synergistic effects of different types of expandable graphite (EG) with magnesium hydroxide (MH) in halogen-free flame-retardant (HFFR) ethylene vinyl acetate (EVA) blends have been studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and UL-94 test. The results show that the particle size and expansion ratio of EG have a great effect on the flammability of the HFFR EVA/MH/EG blends. The EG with bigger particle size and higher expansion ratio can apparently increase the LOI value and improve the UL-94 flammability properties of EVA blends. The data obtained from the CCT indicate that the heat release rate (HRR), the effective heat of combustion (EHC), and the mass loss rate (MLR) of EVA/MH/EG blends decrease remarkably with increasing the particle size and expansion ratio of EG. However, the specific extinction area (SEA) data show that the addition of EG can apparently increase the smoke emission of EVA/MH/EG blends. The TGA results show that the thermal stability of EVA/MH/EG blends increase with increasing the EG particle size and expansion ratio.

Auto‐analysis system for graphite morphology of grey cast iron

The current method to classify graphite morphology types of grey cast iron is based on traditional subjective observation, and it cannot be used for quantitative analysis. Since microstructures have a great effect on the mechanical properties of grey cast iron and different types have totally different characters, six types of grey cast iron are discussed and an image-processing software subsystem that performs the classification and quantitative analysis automatically based on a kind of composed feature vector and artificial neural network (ANN) is described. There are three kinds of texture features: fractal dimension, roughness and two-dimension autoregression, which are used as an extracted feature input vector of ANN classifier. Compared with using only one, the checkout correct precision increased greatly. On the other hand, to achieve the quantitative analysis and show the different types clearly, the region segmentation idea was applied to the system. The percentages of the regions with different type are reported correctly. Furthermore, this paper tentatively introduces a new empirical method to decide the number of ANN hidden nodes, which are usually considered as a difficulty in ANN structure decision. It was found that the optimum hidden node number of the experimental data was the same as that obtained using the new method.

Flow injection potentiometric determination of amantadine HCl

New amantadine (Am) ion selective plastic membrane electrodes of both conventional and coated graphite types based on the ion-pair of amantadinium tetraphenylborate (Am-TPB) ion-pair are prepared. The conventional type electrode was fully characterized in terms of membrane composition, life span, pH, ionic strength and temperature. It was applied to potentiometric determination of amantadine in pure state and pharmaceutical preparation under batch and flow injection conditions. The selectivity of the electrode toward a large number of inorganic cations, sugars and amino acids was tested. The solubility product of the ion-pair and the formation constant of the precipitation reaction leading to the ion-pair formation were determined conductimetrically.

Enzyme Based Amperometric Biosensors for Food Analysis

This review introduces the principles of amperometric detection e.g. oxygen electrodes, hydrogen peroxide electrodes, NADH detection, mediators-aid detection, conductive organic salts and wiring electrodes. A short categorization and description of the materials commonly used for the construction of electrodes, e.g., platinum, glassy carbon, different types of graphite, screen-printed electrodes, rigid carbon-polymer biocomposites, zeolites, clays, and polymeric membranes is given. Approaches to construction of biosensors with respect to various strategies of enzyme immobilization, e.g., physical binding, covalent binding, gel entrapment, electropolymerization, sol-gel techniques and self-assembled architectures are also presented. The requirements and problems for sensing in food industry, examples of enzyme electrodes, published in the literature during the last half-decade, commercial biosensors released into the market along with the current and modern instrumentation, are also presented.

Sintering of co-reduced tungsten-copper powders with added transition elements

EDM has been used extensively in the tool and die industry. The materials normally used in EDM electrodes are various types of copper, graphite, tungsten, brass and silver. Copper–tungsten (Cu–W) electrodes have been used widely to machine die steel and tungsten carbide work-pieces owing to the high thermal conductivity of Cu, and the better spark erosion resistance, low thermal expansion coefficient and high melting temperature of W. TiC is an extremely hard refractory material with a high melting temperature, and high thermal shock and abrasion resistance. The effect of the titanium carbide (TiC) in sintered copper–tungsten (Cu–W) electrodes on their EDM performance was investigated. Six batches of specimens with TiC content varying from 5 to 40% were fabricated by mixing, ball milling, pressing, and liquid phase sintering. The densification was improved by the addition of Nickel (Ni) due to the good solubility of Ni with Cu and W. The distribution of particle size became narrower with increasing TiC. A uniform dispersion of fine TiC particles in the Cu–W system and a narrower particle size distribution provide the possibility for obtaining dense electrodes. The relative density first increased and then decreased with increasing TiC while the electrical resistivity correspondingly first decreased and then increased. The tool material with added TiC showed good performance. The surface roughness decreased with the increase of relative density and vice versa. The highest relative density, lowest electrical resistivity, and best EDM could be obtained by 15% TiC addition, i.e. the lowest TWR, highest MRR and best surface finish.

Physical properties of thermoplastic/graphite composites

Thermal and electrical conductivity, thermal diffusivity of high density polyethylene, polystyrene/graphite composites were investigated in this paper. Two different types of graphite (different distribution of the particle size, different specific surface) were used. For HDPE/graphite composites, also mechanical properties were investigated. Experimental data were compared with some theoretical models. In a semicrystalline matrix (HDPE) different values for the percolation concentration for two types of graphite particles of different surface area were observed.

Effect of TiC in copper–tungsten electrodes on EDM performance

EDM has been used extensively in the tool and die industry. The materials normally used in EDM electrodes are various types of copper, graphite, tungsten, brass and silver. Copper–tungsten (Cu–W) electrodes have been used widely to machine die steel and tungsten carbide work-pieces owing to the high thermal conductivity of Cu, and the better spark erosion resistance, low thermal expansion coefficient and high melting temperature of W. TiC is an extremely hard refractory material with a high melting temperature, and high thermal shock and abrasion resistance. The effect of the titanium carbide (TiC) in sintered copper–tungsten (Cu–W) electrodes on their EDM performance was investigated. Six batches of specimens with TiC content varying from 5 to 40% were fabricated by mixing, ball milling, pressing, and liquid phase sintering. The densification was improved by the addition of Nickel (Ni) due to the good solubility of Ni with Cu and W. The distribution of particle size became narrower with increasing TiC. A uniform dispersion of fine TiC particles in the Cu–W system and a narrower particle size distribution provide the possibility for obtaining dense electrodes. The relative density first increased and then decreased with increasing TiC while the electrical resistivity correspondingly first decreased and then increased. The tool material with added TiC showed good performance. The surface roughness decreased with the increase of relative density and vice versa. The highest relative density, lowest electrical resistivity, and best EDM could be obtained by 15% TiC addition, i.e. the lowest TWR, highest MRR and best surface finish.

Expandable graphite systems for halogen‐free flame‐retarding of polyolefins. I. Flammability characterization and synergistic effect

AbstractThe use of some types of expandable graphite (EG) as an intumescent flame‐retardant additive in polyolefins was studied using the cone calorimeter test (CCT), thermogravimetric analysis (TGA), the limiting oxygen index (LOI), and the‐UL 94 test and through measurement of EG's mechanical and electrical properties. The present study has shown that some suitable EG systems combined with other organic and inorganic halogen‐free flame‐retardant (HFFR) additives apparently can improve the flame‐retardant capacity with good mechanical properties of polyolefin blends. For linear low‐density polyethylene and/or ethylene vinyl acetate/EG/HFFR blends the limiting oxygen index can reach a rating above 29, and the UL‐94 test can produce a value of V–0. The CCT and TGA data show that the EG and EG/HFFR additives not only promoted the formation of carbonaceous char but also greatly decreased the heat release rate and the effective heat of combustion and increased the residues after burning. The synergistic effect of EG with other HFFR additives, such as zinc borate, the phosphorus–nitrogen compound NP28, and microcapsulated red phosphorus is examined and discussed in detail in this article. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1181–1189, 2001

Tritium retention in neutron-irradiated low- Z materials for use as plasma facing materials

Among the presently available low- Z materials, graphite, carbon-based composites (CFC) and beryllium represent the primary candidate materials to be used as protection for both the first wall and the high heat flux components (e.g., the divertor) in the next-step fusion reactor. Research and evaluations are underway to study the characteristics of several graphite and CFC as well as beryllium grades associated with safety, tritium release, heat transfer, thermal-mechanical and irradiation stability. Several types of graphite and CFC samples were irradiated in the high flux reactor (HFR) at different temperatures but with the same irradiation damage, while beryllium samples were irradiated in the BR2 reactor at low temperature but with a very high neutron fluence. In this paper, the result of a series of out-of-pile annealing tests aiming at investigating the tritium release kinetics after both neutron irradiation and tritium-loading from three graphite grades (i.e., A05, RGTi(91), CL5890), two DunlopCFC grades (i.e., Concept 1, Concept 2) and four SepCarbCFC grades (i.e., N312C, NS11, N112, N312B) are presented. Furthermore, the tritium and helium release behavior in a beryllium grade (i.e., S-200E) produced by the Kawecki Berylco Industries is also presented.

Interaction of graphite with atomic hydrogen

The kinetics of sorption of atomic hydrogen by pyrolytic, quasi-single-crystal, and RGT commercial-grade graphite was studied. The processes of sorption and subsequent thermal outgassing are shown to proceed in a similar manner for all the three types of graphite. Thermal desorption spectra obtained during linear heating of hydrogen-saturated samples have two peaks. A mathematical model including features of the thermal desorption kinetics that are observed when heating is terminated is suggested. According to this model, two types of traps with binding energies of 2.4 and 4.1 eV are present in graphite. The physical justification of the model is given.

O 2 erosion of graphite tile substrates

The removal of codeposited tritiated carbon films from the next generation of fusion reactors may rely on the use of baking in an O 2 environment to remove the films. In the present study, we have investigated the effect of baking in O 2 on graphite tile substrate materials. After baking five types of graphite in 2.1 kPa O 2 for 100 h at 623 K, no change in mass was observed. An upper limit on the erosion rate was calculated to be ∼ 4×10 −10 C/ O 2 , whereas the codeposited films obtained from tokamaks have erosion rates as high as 10 −5 C/ O 2 .