Electrodeposition of metals after cation-exchange on modified carbon fibre electrodes

Several metals, Ag, Cu, Pb, Hg and Au, have been electrodeposited on carbon fibre electrodes after cation exchange of their salts with the acidic functional groups of oxidized fibres.Oxidation of carbon fibres was performed by thermal, photochemical and electrochemical treatment. The uptake of the metal cations is greater in the case of anodically oxidized and partially re-reduced carbon fibres, since this procedure leads to the formation of functional groups not only on the carbon surface, as in the case of thermal or photochemical oxidation, but also in the bulk of the fibres.The above-mentioned metals are deposited on the carbon support in a highly dispersed state, which decreases the hydrogen overvoltage and catalyses the reduction of nitroalkanes. These reactions take place on the metal-modified carbon electrodes at much more positive potentials than on carbon and at slightly more positive potentials than on the respective plain metallic electrodes.     

Lithium batteries and electric double-layer capacitors composed of activated carbon fibre electrodes

Commercially available activated carbon fibre (ACF) can be used as the electrode material of Li-batteries and electric double-layer capacitors. The cell, Li|LiClO₄ in propylene carbonate (PC)|ACF, showed an initial V_oc of 3.0 V. Upon discharging the cell, the voltage decreased to 1.5 V without a plateau due to doping of Li⁺ into ACF. When the cell was maintained on open circuit, V_oc increased gradually. About 200 Coulombs per 1 g of ACF could be obtained when the battery was discharged from 3.0 V to 1.5 V. The self-discharge of an electric double-layer capacitor, (ACF^?)Li⁺|LiClO₄ in PC|(ACF)⁺ClO₄^?, was investigated. Water, dissolved oxygen and chemical reactions of doped ACF with solvent and/or of ACF with dopants were found to be the main reasons for the self-discharge.     

Electrocatalytic reactions on carbon fibre electrodes modified by hemine II. Electro-oxidation of hydrazine

The electrocatalytic oxidation of hydrazine on pristine and on electro-oxidized carbon fibre electrodes modified by hemine is investigated in aqueous, methanolic and acetonitrile solutions.

The catalytic activity of the modified electrodes is attributed to the hemine monomers which, according to the mechanism proposed, form an intermediate adduct with hydrazine.

Hydrazine electro-oxidation produces nitrogen in aqueous and methanolic solutions, whereas in acetonitrile only one-third of the molecules are oxidized to the corresponding diimide.

The electro-oxidation of the fibers by potentiostatic double-pulse application provides a substrate that has an effective area four times that of the pristine fibres and enhances an analogous catalytic efficiency. The electro-oxidized fibres bear a large number of active functional groups, which cause chemical oxidation of hydrazine in methanolic and acetonitrile solutions.     

Electrocatalytic reactions on carbon fibre electrodes modified by hemine I. Electroreduction of oxygen

The electrocatalytic reduction of oxygen on pristine and on electro-oxidized carbon fibre electrodes modified by hemine is investigated in aqueous, methanolic and acetonitrile solutions.

The attached iron porphyrin on the modified electrodes exists in two forms, monomeric and dimeric, the latter consisting of two Fe(III)-protoporphyrin molecules held together with an oxygen atom. The catalytic activity of the electrodes is attributed to the hemine monomers, which have the ability to bond the O₂ molecule at the axial position of the metal ion of the porphyrin.

The catalytic reduction of O₂ in acidic aqueous and methanolic solutions produces H₂O, whereas in acetonitrile H₂O₂ is formed.

The electro-oxidized modified electrodes show a catalytic efficiency four-times greater than the pristine electrodes, which is consistent with the analogous increase of the effective electrode area after the electro-oxidation procedure.     

Characteristics of graphite felt electrode electrochemically oxidized for vanadium redox battery application

The graphite felt was oxidized at a positive electrode potential in sulfuric acid solution.The electrochemical performance of the treated graphite felt served as electrode for vanadium redox battery was investigated with FT-IR,SEM,XPS,BET,cyclic voltammetry and testing VRB system,respectively.The results show that the molar ratio of O to C increases from 0.085 to 0.15 due to the increase of—COOH functional groups during electrochemical oxidation treatment,and the GF surface is eroded by electrochemical oxidation,resulting in the surface area increase from 0.33 m2/g to 0.49 m 2/g.The VRB with modified GF electrode exhibits excellent performance under a current density of 30 mA/cm 2 .The average current efficiency reaches 94%and average voltage efficiency reaches 85%.The improvement of electrochemical activity for the electrode is ascribed to the increase of the number of—COOH group and the special surface of GF.     

X-ray absorption spectroscopy of electrochemically oxidized Cu exposed to Na2S

Copper surfaces have been investigated by X-ray absorption spectroscopy after electrochemical oxidation and subsequent exposure to sulfide solution. Oxide surface layers on bulk copper surfaces were electrochemically grown in an aqueous NaOH solution at two different potentials and the resulting chemical composition was investigated using X-ray absorption spectroscopy. At both potentials the resulting surfaces consisted largely of Cu₂O. At the more strongly oxidizing potential, an admixture of Cu²⁺-containing phases – mostly Cu(OH)₂ – was detected. Sulfide exposure of both surfaces was found to completely reduce the surface from Cu²⁺ to Cu¹⁺ and resulted in the formation of Cu₂S with an admixture of Cu₂O.     

Nanoscale friction of partially oxidized silicon nitride thin films

The nanoscale friction of partially oxidized silicon nitride thin films deposited by reactive magnetron sputtering was investigated. Post deposition thermal annealing in O₂, trying to simulate the oxidation by atmospheric oxygen in working conditions, formed a partially oxidized layer at the surface with maximum thickness around 10 nm. Unidirectional sliding tests showed a decrease of the low-load friction coefficients of the sliding pair for the samples annealed in oxygen as compared to the non-annealed ones. The results are discussed on the lights of our extension of the crystal chemistry model, which establishes a relationship between ionic potential and friction coefficient.     

High potential cathodic polarization of oxidized aluminium electrodes in neutral and acid media

The cathodic polarization of an oxidized 99.9995% aluminium electrode at potentials from −2 to −2.5 V(SCE) in several electrolytes of neutral and acid pH values has been studied. Potentiodynamic oxidation of cathodically polarized aluminium electrodes following the technique of Rozenfel'd et al. have been performed and analyzed. In solutions of pH 1–2.1, the oxide film present on the aluminium surface is partially removed by means of a continuous cathodic polarization at those potentials; there is evidence of a small amount of oxide formation following oxide removal and metal etching. The cathodic behaviour in acid and neutral media is interpreted on the basis of a local alkalization resulting from the H₂ evolution. A possible mechanism for the oxide removal is discussed.     

High resolution solid-state 13C CPMAS study of neutral and partially oxidized aluminium polyfluorophthalocyanines

This paper reports a high resolution solid-state ¹³C CPMAS study of the low dimensional phthalocyanine (Pc = C₃₂H₁₆N₈) conductors (PcAlF)-(MoF₆)_0.38, (PcAlF)(IF₅)_0.43 and (PcAlF)(XeF₂)_0.35 as well as the precursor (PcAlF)_n. This study confirms that the stacking configuration of Pc rings along polymeric chains of neutral polymer is eclipsed. The four inequivalent carbon sites resulting from this structure are clearly separate and identified. From this study it is concluded that intrachain disorder is more extended in MoF₆- and IF₅-doped compounds than in the XeF₂-doped one.     

Surface and structure modification of carbon nanofibers

The micro-structure of reinforcements, including surface characteristics, plays a critical role in the properties of composite materials that are ultimately produced. The purpose of this work is to investigate the micro-structure of carbon nanofibers (CNFs) with different core structures, which are hollow (PR) and solid (MJ) fibers, as a function of two treatments: CVD and thermal. From Raman spectroscopy and XRD analyses, an increase of crystallite thickness and width was observed after a heat treatment at 2200 °C for both types of fibers. Further, there was a more significant enhancement of crystalline structure in PR fibers. Also, an increase in thermal oxidation stability for heat-treated CNFs was observed. BET adsorption isotherms showed a significant reduction of specific surface area of MJ fibers after the heat treatment and also after the CVD surface treatment, resulting from the decrease of pore volume. However, even after heat treatment, MJ fibers possessed rougher surface than did PR fibers. Further, significant spatial discontinuity was observed with TEM micrographs due to reorganization of graphene layers during heat treatment for the both heat-treated CNFs. These results suggest that surface and structure of CNFs are important for maximizing their role in the performances of nanocomposites.     

Vibrational properties of the electrochemically synthesized polyindole/single-walled carbon nanotubes composite

Electrochemical polymerization of indole in a LiClO₄/CH₃CN solution on a single-walled carbon nanotubes (SWNTs) film was studied by cyclic voltammetry, Raman scattering and FTIR spectroscopy. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when carbon nanotubes films were previously deposited onto the Pt electrode, a down-shift of the indole reduction peak potential in the latter case was observed. Raman spectroscopy studies indicate that the electrochemical deposition of polyindole (PIN) onto the SWNT film results in a breaking of SWNT bundles into individual tubes. A covalent functionalization of SWNTs with PIN in the doped state is demonstrated by FTIR spectroscopy, when an increase in the intensity of the absorption band at 1045 cm^?1 is observed. Besides, Raman and FTIR studies performed on samples electrochemically prepared and thereafter post-chemically reacted with an NH₄OH solution, indicate both a roping process of individual tubes with PIN as a binding agent and a strong steric hindrance effect.     

碳纳米管的表面改性与镍的包覆

对碳纳米管进行酸处理后,碳纳米管表面产生大量的官能团;再将其在Sn和Pd溶液中进行敏化活化处理,使碳纳米管表面形成密集的活化点.结果表明:通过化学沉积方法,金属镍可在活化点沉积并形成包覆层;碳纳米管的改性、高密度的活化点及较低的沉积速率是得到连续包覆层的关键;热处理使得包覆层更加光滑致密.     

纳米金刚石磨粒表面修饰及其摩擦特性研究

通过纳米金刚石磨粒与三氯氧磷的酯化反应,合成了纳米金刚石磨粒磷酸酯衍生物。采用傅立叶转换红外线光谱仪（FTIR）、飞行时间二次离子质谱仪（TOF—SIMS）对该改性物进行了结构表征。利用四球摩擦磨损试验机研究了化学修饰后纳米金刚石磨粒在水基基础液的摩擦学行为,发现基础液中纳米金刚石磨粒磷酸酯衍生物浓度为0．05％～0．075％时,能够使水基基础液的承载能力提高10％,磨斑直径降低2．6％。经过三氯氧磷酯化反应后的纳米金刚石磨粒具有更好的摩擦性能。     

Development and characterization of liquid carbon fibre reinforced aluminium matrix composite

The progress and developments in materials technology have resulted in several new materials like metal–matrix composites (MMCs). On account of excellent physical, mechanical and development properties, MMCs are applied widely in aircraft and automobile technology. The present paper deals with the development of aluminium matrix composite reinforced with carbon preform having a volume fraction of 20–25% using squeeze casting infiltration process. Hardness, impact and tension test on the squeeze cast matrix and the composite was conducted to study the improvement in properties compare to that of matrix. Even though ultimate tensile strength of composite is found to be decreased, an increased Brinell hardness number and a four-fold improvement in toughness are noticed. Characterization of the materials done using optical and scanning electron microscope (SEM) revealed that the carbon fibers are evenly distributed in the matrix and the alloy is appeared to have smaller dendrite size. The lack of observed fibre pull-out on fracture and improved mechanical properties resulted due to the good wetting of the fibers by the liquid alloy.     

Processing and properties of copper-coated carbon fibre reinforced aluminium alloy composites

Aluminium alloy matrix composites with carbon fibre reinforcement were prepared by stir casting method. In order to avoid any interfacial reactions in the carbon fibre reinforced composites, the carbon fibres were coated with copper. The fibres were coated by electroless coating method and then characterized. Composites containing different amounts of carbon fibres were prepared by stir casting and then subjected to age-hardening treatment. Fibre distribution was fairly uniform in the composites containing up to 4 wt% carbon fibres. Tensile strength of the composites was found to be increasing up to 4 wt% carbon fibre.     

The effect of partially carbonized fibers on the mechanical properties of carbon/carbon composites

The carbon/carbon (C/C) composite with satisfactory mechanical properties were obtained through introduction of partially carbonized fibers as a precursor. Applying this procedure the production cost of C/C composites may be significantly reduced. Stabilized PAN fibers were partially carbonized at temperatures ranging from 400 to 1000 °C and reinforced with phenolic resin, resole type. Cured composite were carbonized up to 1000 °C in an inert atmosphere. Monofilament tensile test strength, Young's modulus and tensile strength of partially carbonized fibers were determined. Mechanical properties of carbon/carbon composites (flexural strength and flexural modulus) determined by using three-point bending test. The effect of partially carbonized fibers on the mechanical properties of C/C composites was examined by scanning electron microscope (SEM) through analysis of the fracture surface. The C/C composite reinforced with partially carbonized fibers at 600 °C showed quite satisfactory flexural strength. This confirms assumptions that through co-carbonization of partially carbonized fibers and resin C/C composite with suitable mechanical properties could be obtained.     

Abrasive points for drill grinding of carbon fibre reinforced thermoset

In this study, an approach for using diamond grinding tools to machine holes in epoxy carbon laminates is described. The development of a suitable tool design and the influence of the cutting parameters are presented. With these tools, large total drilling lengths can be achieved without significant grain wear. Analysis of the results shows that the coolant supply can be reduced without exceeding the resin's glass transition temperature. In addition to the experimental results, a process simulation is applied to improve the tool layout and hence to avoid material clogging at the grinding layer.     

Nitrogen plasma modification of viscose-based activated carbon fibers

Viscose-based activated carbon fibers (VACFs) were treated by a dielectric-barrier discharge plasma at different conditions. Nitrogen was used as the feed gas to create nitrogen radicals. The textural characteristics were analyzed by SEM, BET and XRD. The surface chemical functional groups were analyzed by XPS. The results show that after nitrogen plasma modification (NPM), the external surface of the VACFs was etched and became rougher, the surface area and pore volume decreased, the average micropore width barely changed, the PSD of the VACF became narrower and the graphitic crystallites of VACF had been destroyed slightly. XPS revealed that NPM could remarkably change the distribution of the oxygen functional groups on the VACFs surface and there were more nitrogen atoms incorporated into the aromatic ring. A tentative explanation for the modification process is proposed.     

Surface modification of polymer fibre by the new atmospheric pressure cold plasma jet

A new cold plasma jet has been developed for surface modification of materials at atmospheric pressure. This new cold plasma jet generator is composed of two concentric cylindrical all-metal tube electrodes. The argon is fed into the inner-grounded electrode, the outer electrode is connected to the high-voltage power supply and covered with a layer of dielectric, and then a stable cold plasma jet is formed and blown out into air. The plasma gas temperature is only 25–30 °C. Preliminary results are presented on the modification of polypropylene (PP) and polyethylene terephthalate (PET) fibres by this cold plasma jet. The water contact angle of these materials is found to decrease after plasma treatment and it will recover a little in two months. The chemical changes on the surface of polymers are studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) is used to study the changes in surface feature of polymers due to plasma treatment. The hydrophilicity and surface structure of these materials after plasma treatment are discussed. The results show that such a plasma jet is effective.