High Carbon Materials Research Articles

Comparative study of Pt catalysts supported on different high conductive carbon materials for methanol and ethanol oxidation

Different carbon materials with high electrical conductivity have been studied as electrocatalyst support for direct alcohol fuel cells (DAFCs). The aim of the work was to establish the influence of the support on the catalyst properties and to improve their efficiency in the fuel cell. Carbon nanofibers (CNFs), carbon nanocoils (CNCs) and ordered mesoporous carbons (gCMK-3) have been used for synthesizing platinum catalysts by the polyol method. Results have been compared with those obtained for a platinum catalyst supported on Vulcan XC-72R, prepared by the same method, and for the commercial Pt/C catalyst from E-TEK. It has been demonstrated that novel carbon supports could help to oxidize CO adsorbed on platinum particles more easily than the commercial carbon support and improve the alcohol oxidation reaction, both in terms of onset potential and current density. The catalyst supported on gCMK-3 carbon resulted to be the most effective in both the methanol and ethanol oxidation, which can be attributed to its ordered structure and high electrical conductivity.

Economic Development: Environmental Friendly Materials or High-Carbon Materials Produced by who?

The comparative advantage of low-carbon and high-carbon materials is determined by one country’ history and natural conditions, which is also the starting point of studying on policy trends for a country to develop low carbon economy. In this paper the method system of international economics is applied, two dimensional coordinate system is set up with environmental friendly materials and high-carbon materials. In this extreme model with only two countries , only to produce and make use of two materials above; we analyzed the cross-border exchange mechanism determined by the relative price level arising from comparative advantage , and then indicated political factors will be an important influence factor in the division of labor between developed and developing countries about carbon reduction.

Protic ionic liquids extract asphaltenes from direct coal liquefaction residue at room temperature

Asphaltenes in direct coal liquefaction residue (DCLR) are highly aromatic and polydisperse mixtures, which are important precursors for producing high value-added carbon materials. In this research, a series of protic ionic liquids (PILs) with organic carboxylate anions were synthesized and applied to extract asphaltenes from DCLR at room temperature. The extracts were characterized by elemental analysis, FTIR, 13C-NMR, quinoline insolubles tests and so on. The results show that asphaltenes with the potential of precursors of carbon materials can be separated from DCLR at room temperature using PILs and the solid–liquid separation is carried out facilely due to the lower viscosities of PILs. The influences of PILs structures on extraction yields and atomic ratios of H/C were also investigated. As alkyl chain length of PILs anions increases, extraction yields of asphaltenes increase while H/C ratios decrease. Moreover, extraction yields vary with various cations of PILs and increase according to the order of N-methylimidazolium ([MIM]+)<triethylammonium ([TEtA]+)<3-methylpyridinium ([MPy]+), but H/C ratios decrease following the order of N-methylimidazolium ([MIM]+)>triethylammonium ([TEtA]+)>3-methylpyridinium ( [MPy]+). The asphaltenes extracted from DCLR with PILs have the excellent properties for preparing carbon materials, such as lower H/C ratios, higher aromaticities, lower sulfur contents and nearly no quinoline insolubles.

Application of leading structure on thermal protection of nosetip

The structure of embedded high thermal conductivity carbon material leading thermal protection is considered as thermal protection system to prevent hypersonic vehicle nosetip which requires sharp figure during hypersonic flying, from being seriously aerodynamically heated. By fluid structure interaction method, we analyze leading thermal protection of nosetip and validate that embedded high thermal conductivity carbon material structure has a good effect on thermal protection. The maximal temperature of the nosetip which uses leading thermal protection structure is reduced by 21.9% and the lowest temperature of aft is increased by 15.2% when Mach number is 9. The transfer of heat from head to after-body is achieved, the thermal load of the front head is weakened and the ability of leading-edge thermal protection is strengthened. The influences of structure parameter and material attributes of coating and thermal conductivity of high conductivity carbon material on thermal protection are discussed. The highest temperature of the nosetip decreases with thermal conductivity of coating increasing to a steady value and descends with blackness level of coating ascending and increases with the thickness of coating increasing, and it descends in parabola form as thermal conductivity of carbon materials increases.

Study on Extraction Asphaltenes from Direct Coal Liquefaction Residue with Ionic Liquids

Direct coal liquefaction residue (DCLR) contains about 25% asphaltenes which are proved to be important precursors for preparing high value-added carbon materials. In this work, ionic liquids (ILs) were used as potential solvents to extract asphaltenes from DCLR, and a series of dialkylphosphate ILs, i.e., imidazolium-based, pyridinium-based, and ammonium-based, were synthesized and used to extract asphaltenes from DCLR. The influences of extractive time, extractive temperature, and mass ratio of ILs to DCLR on extraction efficiency of asphaltenes were investigated and the optimized conditions were determined. In order to understand the mechanism of extraction asphaltenes with ILs, the extracts were characterized by elemental analysis, FT-IR, 13CNMR, and so on. The results show that it is feasible to extract asphaltenes from DCLR with dialkylphosphate ILs. The structure and size of anion and cation of ILs probably are the main factors that influence the extraction yield and the physicochemical characteristics of extracted asphaltenes, such as atomic ratio of H/C, the structure and aromatic cluster size, and so on.

Near Infrared Spectroscopic Evaluation of Biochars Made from Wheat Straw: A Second Look at the near Infrared for the Study of Chars with Implications for Coal and other High Carbon Materials

Biochars result from the pyrolytic processing of organic materials. There is an increasing interest in the production and use of biochars from agricultural wastes, to sequester C in the soil and improve soil quality. Near-infrared spectroscopy, which has been used for decades to determine the composition of the varying agricultural materials used in making biochars would thus appear to be an obvious method for analysing these materials. However, previous work on charred cellulose, lignin, pine bark and wood showed that, while near-infrared spectroscopy using a Fourier transform spectrometer could be used for quantitative analysis, spectral interpretation beyond the bands found in the 4000 cm−1 to 5000 cm−1 (2500–2000 nm) region was difficult, to near impossible, due to the nature of the char spectra produced, the high degree of baseline curvature and the tendency to be very noisy. The objective of this work was to re-examine the question of near infrared (NIR) spectroscopy and chars using biochars made from wheat straw charred at various temperatures for 3 h. Results indicated that using spectrometer settings which work well for other materials such as soils or forages, especially with a Fourier Transform spectrometer, are not satisfactory for working with biochars or similar materials such as coals. Results obtained with a scanning monochromator, which also scanned a larger sample area (25× to 100× as large), were far superior to those obtained with a Fourier spectrometer with a praying mantis-style diffuse reflectance device and similar scanning conditions. Although previous work has shown that quantitative analysis can be carried out using NIR spectra collected on the same Fourier transform instrument, under the same conditions, these results and those show that qualitative analysis or spectral interpretation in the NIR require a different setup/procedure to be used. Collecting more scans, and at a lower resolution, greatly improved the spectra, although heating the sample could be a problem. Using a different DRIFTS device, which allowed a significantly larger sample area to be scanned, could also be useful, but was not tested.

The simplex optimization for high porous carbons preparation

The simplex optimization for high porous carbons preparation The microporous carbon materials were prepared by chemical activation of Polish coal with potassium hydroxide using the simplex design method for planning the experiments. The experimental parameters were varied to identify the optimum conditions. Coal can be an excellent starting material for the preparation of high porous carbons for natural gas storage. The porosity of the resultant carbons was characterized by nitrogen adsorption (-196°C). Methane adsorption was investigated in a volumetric laboratory installation at range pressures from 1 to 3.5 MPa (25°C). The best results of methane storage capacity (557 cm3 · g-1) were obtained when using an impregnation ratio 3.41/1 KOH/precursor and temperature at 592°C, (SLANG = 2091 m2 · g-1). The parameters of the preparation of high porosity and high methane adsorption carbon were determined by a fast and simple method.

Photocatalytic degradation of phenol with mesoporous TiO2−xBx

We report a facile approach for preparing mesoporous boron-doped TiO2 materials by combining the sol–gel process with the dehydration of glucose. Specifically a high surface carbon material was formed by dehydration of glucose, then used as template. This material and the TiO2 dry gel were calcinated to produce porous TiO2. The as-synthesized boron-doped TiO2 was in pure anatase crystallite phase with high surface area. X-ray photoelectron spectroscopy (XPS) results showed that boron was incorporated into the anatase TiO2 lattice to form TiO2−xBx. The absorption spectra of TiO2−xBx extended into the visible region to 460 nm. The TiO2−xBx exhibited much higher photocatalytic activity on phenol degradation than pure TiO2. It showed that the phenol degradation by-products of TiO2−xBx were different from that of pure TiO2. Mechanism of the photocatalytic degradation of phenol at TiO2−xBx was also proposed.

High density carbon materials obtained at relatively low temperature by spark plasma sintering of carbon nanofibers

Abstract Graphitic materials obtained at low temperatures are interesting for a wide range of industrial applications including bipolar plates. In this work, graphite based nanocomposites have been obtained starting from carbon nanofibers and a mixture of carbon nanofibers with 20 vol.% of alumina nanopowders. High density carbon components were obtained by using Spark Plasma Sintering at temperatures as low as 1500–1800°C for this kind of materials. The effect of spark plasma sintering parameters on the final density, and the mechanical and electrical properties of resulting nanocomposites have been investigated. Pure carbon nanofibers with around 90 % of theoretical density and fracture strength of 60 MPa have been obtained at temperatures as low as 1500°C applying a pressure of 80 MPa during sintering. It has been proved that attrition milling is a suitable method for preparing homogeneous mixtures of carbon nanofibers and alumina powders.

Solutions for technological performances increasing at ultrasonic aided electrodischarge machining

The paper deals with researches concerning phenomenology and solutions for technological parameters improvement at finishing through electrodischarge machining (EDM) aided by ultrasonic (US) longitudinal vibrations of electrode-tool (EDM + US). The stability of EDM + US finishing process was obtained increasing the working gap through ignition voltage growing and amplitude decrease of US oscillations. Pulse energy minimization aimed to reduce the craters volumes produced by discharge. We used consumed power values to supply the acoustic chain (PcUS) so the created acoustic pressure was over the cavitation threshold, but simultaneously, the PcUS value was minimized in order to not damage the surface quality and even to reduce the surface roughness. The number of discharges within an oscillation period was maximized and thus, material amount removed by ultrasonically induced cavitation was increased. Machining high content carbon and alloy elements materials by frontal flat surface electrodes improves volumetric relative wear. The flexibility concerning acoustic chain construction can be increased by Computer Integrated Machining, CNC processing acoustic horns and electrodes, previously elaborated through CAD and CAE.

Densification of in situ prepared mesocarbon microbead/carbon nanotube composites by hot-press sintering

In situ prepared mesocarbon microbead/carbon nanotube(MCMB/CNT) composites are potential precursors of high density carbon materials for various applications. Integrated MCMB/CNT composites were successfully fabricated by hot-press sintering at 550 °C under 30 MPa. After further calcination at 900 °C, the hot-press sintering fabricated MCMB block has an apparent density of 1.77 g/cm 3 and the open porosity 5.1%. With the addition of 5%(mass fraction) CNTs, the density of the composite block is elevated to 1.84 g/cm 3, and its open porosity is reduced to 3.5%. The flexural strength of composite block with 5% CNTs is elevated to 116 MPa. Through the hot-press sintering, pores of 10–50 nm in the calcinated bulks are remarkably eliminated. The interstice between microbeads in the composite blocks is filled up by CNTs together with β-resin and quinoline-insoluble spheres, which can further contribute to the densification.

High value carbon materials from PET recycling

Poly(ethylene) terephthalate (PET), has become one of the major post-consumer plastic waste. In this work special attention was paid to minimising PET residues and to obtain a high value carbon material. Pyrolysis and subsequent activation of PET from post-consumer soft-drink bottles was performed. Activation was carried out at 925°C under CO2 atmosphere to different burn-off degrees. Textural characterisation of the samples was carried out by performing N2 adsorption isotherms at −196°C. The obtained carbons materials were mainly microporous, presenting low meso and macroporosity, and apparent BET surface areas of upto 2500m2g−1. The capacity of these materials for phenol adsorption and PAHs removal from aqueous solutions was measured and compared with that attained with commercial active carbons. Preliminary tests also showed high hydrogen uptake values, as good as the results obtained with high-tech carbon materials.

Pin-on-plate studies on the effect of rotation on the wear of metal-on-metal samples.

An important cause of osteolysis and subsequent loosening of replacement hip joints is the body's biological response to polyethylene wear debris. Interest has thus been renewed in hard bearing surfaces such as metal-on-metal implants. Tests were performed on a pin-on-plate machine to determine the effects of pin rotation on the wear of two different compositions of cobalt chrome molybdenum (CoCrMo) against itself (high carbon and low carbon). With reciprocating motion only, the low carbon material gave an order of magnitude higher wear than the high carbon material. The overall wear (that for both the pin and the plate) was significantly reduced with added rotation for the low carbon material but remained approximately the same for the high carbon material. However, the wear of the low carbon material was not reduced below that of the high carbon material which remained the best material in terms of wear.

Adsorption and electrosorption at high-area carbon-felt electrodes for waste-water purification: Systems evaluation with inorganic, S-containing anions

Removal or modification of pollutants in industrial or mineral-processing wastewaters by electrosorption at high specific-area carbon materials (felts or powders) has been envisaged in previous work. Electrodes based on high-area substrates behave as quasi-three-dimensional interfaces, thus minimizing diffusion limitation in removal of trace impurities in waters. In the present paper, processes of open-circuit adsorption and electrosorption at electrochemically polarized, high-area C-felt electrode modules are quantitatively examined by means of in situ electrical resistance and optical absorbance measurements made in appropriately designed cells. The effectiveness of the procedures is examined by application to the adsorption and electrosorption of a series of related S-containing anions and the kinetics of their adsorption at the C-felt electrodes have also been evaluated in two cases. The adsorbability of such impurity ions is related to their hydration properties in water.

Uptake of lithium by layered molybdenum oxide and its tin exchanged derivatives: high volumetric capacity materials

The materials A 0.25MoO 3 (A=Na, Li, Sn), prepared by a ‘chimie douce’ route, are a promising alternative as anode materials in Li ion batteries. These materials present large reversible charge capacities, greater than 900 mAh/g, with a good capacity retention on cycling. At least 65% of the charge capacity (600 mAh/g) is maintained under 1.5 V vs. Li. The gravimetric capacities, on the order of 4000 mAh/cm 3, are three to four times greater than for high capacity carbon materials and twice that of Sn oxide-based glasses. A mild heat treatment and an appropriate discharge cut-off potential stabilizes the cycling behavior. A discharge cut-off of 5 mV is associated with a large polarization, and fading charge retention, probably related to the oxygen diffusion process into the highly sub-stoichiometric oxide during the charge sweep. Conversely, raising the charge potential to 200 mV may conserve the oxygen environment surrounding the Mo centre to some degree, thus facilitating oxygen migration during charge. The irreversible capacity and the high average potential in charge are the major drawbacks in these systems. By utilizing the exchange capability of the interlayers ions, Sn can be incorporated into the material, thus lowering the average charge potential but at the expense of capacity fading. Finally, a catalytic effect of the carbon black in these composite electrodes via an interface effect is present, which must be accounted for by methods other than simple subtraction of the carbon contribution to the total capacity by mass fraction.

Reduction of hexavalent chromium by polypyrrole deposited on different carbon substrates

Pollution due to toxic hexavalent chromium has reached dangerous levels in some parts of the world, especially in Third World countries. This work focuses on the reduction of Cr(vi) ions in aqueous media by polypyrrole deposits on porous, high area three-dimensional carbon electrodes. Since many properties of deposited polymers are known to depend on the method of synthesis we performed the electropolymerization of pyrrole either at varying potential scan rates or at constant potential on different high area carbon materials. The deposits thus obtained were then put in contact with acidic hexavalent chromium solutions; high reduction yields were obtained (up to 80%). In addition, the possibility of repeating this cycle was studied as well as the wear resistance of these deposits. Finally, the morphology of the deposits was monitored at different stages of the process by scanning electron microscopy.

97/02818 Pitch mesophase and a new type of high strength carbon material

97/02818 Pitch mesophase and a new type of high strength carbon material

Narrow gap automatic gas shielded arc welding of high carbon steel

Summary Rail steel is a typical high carbon material and has previously been extensively researched to improve its weldability. This paper describes an investigation of narrow gap automatic gas shielded arc welding of rails to determine the effects of the process parameters, weld metal carbon content, and post weld heat treatment through observations of defects and microstructures, hardness measurements, and tensile tests of welded joints. Through adjustment of the temperature of the water-cooled copper block surrounding the rail welds, the heat input to the base material can be controlled and the weld quality thus improved. Suitable post weld heat treatment and welding conditions improve the weld properties. Control of the weld metal carbon content is an important factor in prevention of hot cracking. Hot cracking in the HAZ is influenced by MnS inclusions and can be prevented through application of suitable process parameters.

A study of gettering efficiency and stability in Czochralski silicon

Internal gettering efficiencies and stabilities of high and low carbon doped silicon have been compared with standard and ramped annealing conditions. The gettering efficiency of low carbon silicon has been found to be greatly enhanced with ramped annealing by creating a high concentration of oxygen precipitates and related defects. This ramped low carbon material and both the standard and ramped high carbon materials have a greatly enhanced oxygen precipitation rate, relative to the standard low carbon standard anneal. However, the high carbon material’s gettering efficiency and stability are low, compared to the ramped low carbon material, due to a reduction of the oxygen precipitate’s strain field and concentration of related defects.

A Study of Gettering Efficiency and Stability in Czochralski Silicon

AbstractGettering efficiencies and stabilities of internal gettering sites for metallic impurities in high and low carbon doped silicon have been compared with ramped and standard two-step pre-annealing conditions. This study was intended to compare two proposed techniques to shorten the long low temperature nucleation step in the standard Hi-Lo-Hi internal gettering site formation treatment. Specifically, we compare the affect of carbon and a ramped annealing sequence on oxygen precipitate formation and gettering effectiveness. Our results show both techniques accelerate oxygen precipitation, however, only the low carbon ramped materials produced efficient and stable gettering sites. The high carbon materials did not with either annealing treatment. This disparity in performance is due to a difference in the oxygen precipitate’s strain field. The precipitates in the low carbon material possessed a high strain field with strain-induced defects while in the high carbon material they were strain-free with no defects. These results indicate the strain stabilizes the gettered impurity such that the gettering rate is increased and stability is enhanced.