Graphite Bar Research Articles

Degradation of 2,4,5-trichlorophenoxyacetic acid by a novel Electro-Fe(II)/Oxone process using iron sheet as the sacrificial anode

A novel electrochemically enhanced advanced oxidation process for the destruction of organic contaminants in aqueous solution is reported in this study. The process involves the use of an iron (Fe) sheet as sacrificial anode and a graphite bar as cathode. In the oxidation process, once an electric current is applied between the anode and the cathode, a predetermined amount of Oxone is added to the reactor. Ferrous ions generated from the sacrificed Fe anode mediate the generation of highly powerful radicals (SO 4 •−) through the decomposition of Oxone. The coupled process of Fe(II)/Oxone and electrochemical treatment (Electro-Fe(II)/Oxone) was evaluated in terms of 2,4,5-Trichlorophenoxyacetic acid degradation in aqueous solution. Various parameters were investigated to optimize the process, including applied current, electrolyte and Oxone concentration. In addition, low solution pH facilitates the system performance due to the dual effects of weak Fenton reagent generation and persulfate ions generation, whereas the system performance was inhibited at basic pH levels through non-radical self-dissociation of Oxone and the formation of ferric hydroxide precipitates. Furthermore, the active radicals involved in the Electro-Fe(II)/Oxone process were also identified. The Electro-Fe(II)/Oxone process demonstrates a very high 2,4,5-T degradation efficiency (over 90% decay within 10 min), which justifies the novel Electro-Fe(II)/Oxone a promising treatment process for herbicide removal in water.

Anodic oxidation of chlorpyrifos in aqueous solution at lead dioxide electrodes

The aim of this work is the use of electrochemical process for the total mineralization of water contaminated with organophosphorus pesticides like chlorpyrifos. This pesticide is widely used both for agricultural pest control and in households as a termiticide. The process was studied under galvanostatic polarization mode using Nb/PbO 2 anodes and graphite carbon bar as cathode. The kinetic of organic matter decay and the mineralization efficiency were evaluated by means of the chemical oxygen demand (COD) measurement. The influence of the experimental parameters such as the initial concentration of chlorpyrifos, the apparent current density and the temperature, on the electrochemical process performance was investigated. The experimental results showed that COD removal always follows a pseudo-second-order kinetics. The degradation rate increased significantly with increasing the apparent current density and temperature. However, it decreased with the increase of the initial pollutant concentrations. The best COD removal (76%) was obtained when using an apparent density of 50 mA cm −2, initial COD = 450 mg O 2 L −1 and at 70 °C in 10 h electrolysis time.

Electrochemical degradation of chlorpyrifos pesticide in aqueous solutions by anodic oxidation at boron-doped diamond electrodes

Laboratory experiments were carried out on the kinetic of the electrochemical degradation of aqueous solutions containing chlorpyrifos as model compounds of organophosphorus pesticides. The process was studied under galvanostatic polarization mode in acidic medium using boron-doped diamond (BDD) anodes and graphite carbon bar as cathode. The chemical oxygen demand (COD) measurement during the processing permitted the evaluation of the kinetic of organic matter decay and the instantaneous current efficiency. The results showed that the degradation of this pesticide is dependent on its initial concentration, current density and temperature. COD decay follows a pseudo first-order kinetic and the process was under mass transport control within the range studied, regardless of the experimental conditions. The removal rate of COD increases with applied current density until 20 mA cm −2 and decreases for higher values. The degradation rate increased significantly with increasing temperature and initial concentration of chlorpyrifos. The best obtained conditions for COD removal on the BDD anode to degrade chlorpyrifos solutions (COD(0) = 456 mg L −1) include operating at 20 mA cm −2 and 70 °C. This arrangement allows to completely degrade chlorpyrifos in just 6 h. Compared with PbO 2, BDD anode has shown more performance and rapidity in the COD removal in the same electrolysis device.

Headspace trapping of the hydrides on a Pd(II)-coated graphite adsorptive bar as a microextraction method for ETV–ICP-MS determination of Se, Te and Bi in seawater and human hair samples

A new, simple and sensitive method by combining headspace Pd(II)-coated graphite bar microextraction (GBME) with electrothermal vaporization-inductively coupled plasma mass spectrometry (ETV-ICP-MS) was developed for the determination of trace Se, Te and Bi in seawater and human hair. In this method, the graphite bar was coated with Pd(II) and then used for headspace trapping of the hydrides of Se(IV), Te(IV) and Bi(III). The graphite bar with enriched hydrides of analytes was inserted directly into the graphite tube and subsequently determined by ETV-ICP-MS according to the established temperature program. The experimental parameters, which may affect the extraction and vaporization of target analytes, were systematically investigated and the optimal experimental conditions were established. Under the optimal conditions, the detection limits of the method were 8.6, 2.6 and 0.2 ng l(-1) and the relative standard deviations (RSDs) were 7.0%, 6.2% and 8.0% (C=0.20 microg l(-1), n=7) for Se, Te and Bi, respectively. Linearity was obtained over the range of 0.05-20.00, 0.01-5.00 and 0.01-20.00 microg l(-1) with the correlation coefficients of 0.9942, 0.9997 and 0.9976 for Se, Te and Bi, respectively. The proposed method was successfully applied for the determination of trace Se, Te and Bi in seawater and human hair samples. In order to validate the method, the proposed method has also been applied for the determination of trace Se, Te and Bi in the certified material of GBW07601 human hair, and the determined values were in good agreement with the certified values.

Cobalt electrodeposition onto highly oriented pyrolytic graphite (HOPG) electrode from ammonium sulfate solutions

-2 M of CoSO 4 + 1M (NH 4 ) 2 SO 4 at pH 4.5 (natural pH). All solutions were prepared by using analytic grade reagents with ultra pure water (Millipore-Q system) and were deoxygenated by bubbling N 2 for 15 min before each experiment. Once the solution was deoxygenated a nitrogen atmosphere was maintained over the solutions. During the experiment the bubbling was stopped to avoid the presence of additional diffusional variables caused by the nitrogen bubbles on the electrode surface. The working electrodes were freshly cleaved HOPG surfaces. A graphite bar with an exposed area greater than the working electrode was used as counter electrode. A saturated silver electrode (Ag/AgCl) was used as the reference electrode, and all measured potentials are referred to this scale. The electrochemical experiments were carried out in a BAS potentiostat connected to a personal computer running the BAS100W software to allow the control of experiments and data acquisition. In order to verify the electrochemical behavior of the electrode in the electrodeposition bath, cyclic voltammetry was performed in the 0.600 to -1.300 V potential range. The kinetic mechanism of Co deposit onto HOPG was studied under potentiostatic conditions by the analysis of the experimental potentiostatic current density transients obtained with the potential step technique. In all cases, the perturbation of the potential electrode always started at 0.600 V because this is the null current zone in where the Co deposition had not still begun. Thus, the application of this potential guarantees that the electrochemical signals recorded during the cathodic polarization are caused by the cobalt electroreduction on the electrode. 20

Raman and X‐ray diffraction analysis on unburned carbon powder refined from fly ash

AbstractThe bonding and crystalline structures of oil‐fried fly ash collected from a power plant were analyzed by using Raman spectroscopy and X‐ray diffraction (XRD), respectively. These carbon powders underwent a series of annealing treatment for graphitization and crystallization. In Raman spectra, the refined, unburned carbon contains clearly the D, G and D′ peaks under 2000 or 2700 °C treatment. The Raman spectral line shape of refined, unburned carbon heated at 2700 °C is similar to that of commercial graphite made from graphitization process. In the XRD spectra, the refined, unburned carbon contains (002), (100) and (004) diffraction peaks under heating at 2000 or 2700 °C. The XRD spectral line shape of refined, unburned carbon heated at 2700 °C is similar to that of a commercial graphite bar. The quantitative graphitization level from Raman spectra and crystallization degree from XRD spectra on refined, unburned carbon powders serve as preliminary guide for the qualitative evaluation of these unburned carbon powders. Copyright © 2009 John Wiley & Sons, Ltd.

Development of an absolute neutron dosimeter

An Absolute Neutron Dosimeter was developed to be used as a calibration standard for the Radiation Metrology Laboratory at CCHEN. The main component of the Dosimeter consists of a Proportional Counter of cylindrical shape, with Polyethylene walls and Ethylene gas in its interior. It includes a cage shaped arrangement of graphite bars that operates like the Proportional Counter cathode and a tungsten wire of 25 μm in diameter μm as the anode. Results of a Montecarlo modeling for the Dosimeter operation and results of tests and measurements performed with a radioactive source are presented.

Tensile Properties of Boronized N80 Steel Tube Cooled by Different Methods

The microstructures and tensile properties of boronized N80 steel pipes by pack boriding under four different cooling conditions were investigated. The boride layer was composed of FeB and Fe2B phases with a hardness range of 1200-1600 HV. Fan cooling and fan cooling with a graphite bar in the center of the boriding agent were employed to improve the tensile properties. As cooling velocity was increased, the thickness of boride layer and grain size of the steel substrate were consequently reduced, whereas the pearlite volume in steel substrate was increased, resulting in improvement of tensile properties. Boronized N80 steel pipe which was fan cooled with a graphite bar inside possessed the highest ultimate tensile strength and yield strength, in accordance with the mechanical properties required by API SPEC 5L. Fracture surface analysis revealed that the boronized N80 steel showed ductile fracture at room temperature.

Copper electrowinning in a moving-bed cell based on reactive electrodialysis

A two-compartment lab-scale reactive electrodialysis (RED) cell with a moving particulate cathode has been used for copper electrowinning. The cathodic reaction was copper electrodeposition on a bed of copper particles forced to circulate inside a fixed cylindrical enclosure by the action of rotating paddles; the anodic reaction was ferrous to ferric ion oxidation on an anode made of static graphite bars. The anolyte (aqueous FeSO 4 + H 2 SO 4 ) and catholyte (aqueous CuSO 4 + H 2 SO 4 ) are kept separate by an anion membrane which prevents cation transport between the electrolytes. Experiments were carried out in order to characterize cell performance under various conditions. When operating with 40 g/L Cu (II), I = 6 A, T = 50°C, 40 rpm paddle rotation and 990 mL/min electrolyte recirculation flowrate, the specific energy consumption (SEC) for copper electrowinning was 2.25 kWh/kg. An optimization of cell dimensions gave an improved SEC of 1.55 kWh/kg whereas a temperature increase from 50 to 56°C (without changing cell dimensions) produced a SEC of 1.50 kWh/kg, which is 25% lower than normal values for conventional copper electrowinning cells. A comparison was drawn between the performance of this cell and a squirrel-cage cell previously developed by the authors.

Effect of boronising on mechanical properties, wear and corrosion of N80 steel

The effect of boronising on N80 steel tube was investigated by pack boriding. During the present investigation, microstructures of boride layer and substrate, hardness, mechanical properties, wear and corrosion were examined. In order to improve the tensile properties of the steel substrate after boronising, four different cooling methods were employed including annealing, air cooling, fan cooling and fan cooling with a graphite bar in the centre of boriding agent. Among these methods, the fan cooling with a graphite bar in the centre of the boriding agent makes the microstructure of ferrite and pearlite finest and the mechanical properties highest, in accordance with the mechanical properties required by API SPEC 5L. The borided N80 steel showed a better wear resistance at an applied load of 50 N with a sliding velocity of 0˙785 m s–1, it also displayed a better corrosion resistance in both H2SO4 and HCl acid environments.

The Formation of Onions at Shock-Wave Loading of Graphite

The results of experiments with shock – loading of graphite bar by sliding detonation wave of HE are presented in this paper. It were revealed the nano – sized onions at the SEM investigation in the preserved sample of Graphite. The estimation of the values of pressures of shock – loading permits to assume that the observed structures were formed directly by solid – solid transformation.

Zirconia‐coated graphite adsorption bar micro‐extraction combined with ETV‐ICP‐MS for the determination of trace amounts of Cd, Hg and Pb in environmental and biological samples

In this work, a new and simple micro-extraction method termed graphite adsorption bar micro-extraction was developed, for the first time, for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) determination of trace Cd, Hg and Pb. In this method, the graphite bar was first coated with zirconia and then inserted into the sample solution for extraction. The graphite bar enriched with the analytes was inserted directly into a graphite tube, and subsequently analyzed by ETV-ICP-MS according to an established temperature program. The experimental parameters, which had influence on the extraction and vaporization, were systematically investigated and the optimal experimental conditions were established. Under the optimized conditions, the detection limits of the method were 0.05, 0.42 and 0.06 pg/ml for Cd, Hg and Pb and the relative standard deviations (RSDs) for 11 replicates at the 0.1 ng/ml level were 7.4, 8.2 and 7.7%, respectively. The proposed method was successfully applied to the determination of trace Cd, Hg and Pb in environmental and biological samples. The results of the experiments indicate that the method has a high enrichment factor and sample utilization efficiency. Furthermore, the method is fast and environment-friendly.

Electrowinning of copper in two- and three-compartment reactive electrodialysis cells

Two- and three-compartment copper electrowinning (EW) cells based on reactive electrodialysis (RED) have been studied. The catholyte was cupric sulphate and the anolyte was ferrous sulphate, both dissolved in sulphuric acid. Copper mesh cathodes and graphite bar anodes have been used. The effects of cell current density, temperature, electrolyte recirculation flowrate and nitrogen sparging flowrate on cell performance (cathodic current efficiency, cell voltage and specific energy consumption (SEC)) have been determined. The cell voltage increased with cell current and it decreased with temperature and nitrogen sparging flowrate. The effect of nitrogen sparging flowrate on the cell voltage is stronger than the effect of electrolyte recirculation flowrate, whereas its enhancing effect on mass transfer is stronger than its deleterious effect on electrolyte conductivity. The SEC ranged from 0.94 to 1.39 kW h/kg at cell current densities between 200 and 600 A/m 2. These values are considerably better than those for conventional copper EW (about 2 kW h/kg at 350 A/m 2). The morphology of the electrodeposits has been observed and a comparison between a three-compartment cell and a previously studied squirrel-cage cell (both based on RED) has been drawn.

遠心焼結によるＣｕ厚膜のち密化とクラック除去

Films with thickness ranging from several ten μm to several mm are of great interest due to their application or necessity in highly integrated, small electric devices. In this work, we report the processing merit of a novel centrifugal sintering, which densifies metallic film by applying high pressure, in the absence of a pressure medium such as graphite bar in hot-pressing equipment. Cu thick film on SiO2 substrate has been prepared for studying the sintering behaviour. It is observed that the pores and cracks in the specimens were drastically removed, and then promoted its densification by centrifugal firing, compared with conventional firing.

Prediction of Brittle Failure of Notched Graphite and Silicon Nitride Bars

High stress gradients occur at metal-to-ceramic joints due to the different thermal and mechanical properties of the materials. In some cases, the magnitude of the highly localized stresses lead to failure thus compromising the structural integrity of such joints. The study of notched ceramic bars with high stress gradients can assist with the prediction of failure of metal ceramic joints. Experiments and fracture mechanics analysis were performed on notched and un-notched POCO E.D.M 3 graphite and AS800 Silicon Nitride bars with different notch parameters. The twoparameter, multi-axial Weibull statistics method and a brittle fracture criterion based on the average stress over an area approach were used to predict the failure of the bars and the results obtained were compared with experimental results. The brittle failure criterion appears to give much better correlation with experimental results than the multi-axial Weibull statistics approach. The findings also appear to highlight the limitations of the Weibull’s statistics method in cases involving very high stress gradients.

Characteristic dynamic behavior of dc arc near graphite bar electrodes with short gap

Periodic sawtooth patterns were observed for arc voltages of dc free burning air arcs between 16 mm diameter graphite bar electrodes with a gap length of 15 mm. Observation with a high-speed video camera showed that the sawtooth wave forms of the arc voltages were brought about by the dynamic motions of the arc spots on the electrodes. The anode spot showed a periodic movement on the electrode edge a few hundreds milliseconds after arc ignition, while no movement of the cathode spot was observed. The deflection of the arc column near the anode spot also showed a characteristic pattern during the periodic movement of the anode spot. In order to investigate the factors influencing the dynamic behavior of the arc column near the anode spot, the Lorentz force applied to the arc column near the anode spot was calculated by taking into account the flux induced by the current distributed inside the anode. It was pointed out that the dynamic behavior of the arc column near the anode spot was interpreted as caused by the Lorentz force.

A DC electrochemical method for studying the inhibition of metal corrosion by chromate-containing paint

A DC potentiodynamic curve method is used to observe the effect of a pigmented organic coating on the passivity of a metal substrate. In this method, a painted metal coupon, which is scribed to expose metal, functions as the working electrode (WE) of an electrochemical cell; the cell includes a graphite bar counter electrode (CE), a saturated calomel reference electrode (RE), and aqueous electrolyte. Increasingly oxidizing potentials are imposed on the WE by a potentiostat, and current between the WE and CE is measured at each applied potential. The resulting current–voltage (I–V) curve indicates effects of the coating on the metal's open circuit potential and passivity. The passivating effect of a chromate-containing primer paint on mild steel is demonstrated and compared to the passivity of 316 stainless steel.

Application of rapidly solidified amorphous and microcrystalline filler metals in brazing of divertor components

Abstract Rapidly solidified (RS) amorphous and microcrystalline ribbon-type brazing filier metals (FMs) represent a promising facility for fastening heterogeneous materials together. The advantage results are followed from the homogeneity of element and phase compositions and the strictly specified geometrical dimensions of such FMs. Produced by rapid solidification technology amorphous FMs–Zr-Ti-Fe-Be (STEMET∗ 1403), Zr-Ti-Ni-Cu (STEMET 1406) and Ti-Zr-Ni-Cu (STEMET 1201) and microcrystalline FMs–Al-Si (STEMET 1501) and Cu-Sn-Mn-In-Ni (STEMET 1120) were used. Brazing of beryllium and graphites with metals (Be + Cu; MPG-6 + Cu; RGT + Cu; MIG-1 + Mo; M1G-1 + V; RGT + V) was performed using ribbon-type FMs. Two types of brazed samples were produced in the form of plates and rakes. The rakes were made by brazing three smali graphite bars to the metal, the 2 mm space between bars being 0.25 of the bar height. The results of the brazed zone metallographic analysis and of the investigations of brazed joints treated by pulsed energy fluxes are discussed.

Application of amorphous filler metals in production of fusion reactor high heat flux components

Abstract Amorphous ribbon-type filler metals represent a promising facility for fastening heterogeneous materials together. The advantage results from the homogeneity of element and phase compositions and the strictly specified geometrical dimensions of such fillers. Amorphous filters ZrTiFeBe, ZrTiNiCu and TiZrNiCu and microcrystalline fillers AlSi and CuSnMnInNi were produced by quenching at a rate of about 10 6 K s −1 . Brazing of graphite with metals (Cu + MPG-6, Cu + RGT, Mo + MIG-1, V + MIG-1, V + RGT) was accomplished using ribbon-type fillers. Two types of metal-based samples were produced in the form of plates and rakes. The rakes were made by brazing three small graphite bars to the metal, the 2 mm space between the bars being 0.25 of the bar height. The results of metallographic studies of the brazing zone and of tests on brazed structures treated by pulsed energy fluxes are discussed.

マンドレル押出法を用いたステンレスネット‐アルミニウム複合パイプの製造

Aluminum composite pipes reinforced with stainless steel nets were fabricated in the following procedure. A mould core was first prepared by a graphite bar wrapped with both stainless steel nets and aluminum foils. Hollow shaped billets were made using a unidirectional solidification technique after pouring aluminum melt into the mould having the core. Then, the hollow shaped billets were extruded into composite pipes using a mandrel. Aluminum foils used with nets were useful for positioning nets, adjusting spacing between net layers and improving melt filling into billets. The original shape was maintained even after extrusion without failure. The torsional properties of the pipe were improved by adjusting the radial position of nets and by increasing the wrapping number of nets.