Contactless Electrodeposition of Palladium Catalysts

Site-selective electrodeposition of catalytically active metals on electrically conducting support particles was achieved by polarization with an electric field in a nonconductive matrix in the presence of metal salt solutions. The transmission electron micrograph shows a graphite particle to which Pd and Au were applied sequentially to opposite ends by reversing the direction of the electric field.     

A new process of fabricating electrically conducting nylon 6/graphite nanocomposites via intercalation polymerization

A new process was developed to fabricate electrically conducting nylon 6/graphite nanocomposites via intercalation polymerization of ϵ‐caprolactam in the presence of expanded graphite. The transition from an electrical insulator to an electrical semiconductor for nylon 6 occurred when the graphite volume content was 0.75, which was much lower than that of conventional conducting polymer composites. The electrical conductivity reached 10⁻⁴ S/cm when the graphite content was 2.0 vol %. The TEM microphotographs suggested that the low percolation threshold and the great improvement of electrical conductivity could be attributed to the high aspect ratio (width‐to‐thickness), the high expansion ratio in c axis of the graphite sheets and the homogeneous dispersion of the nanoscale graphite particles in the nylon 6 matrix. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1626–1633, 2000     

Functional properties of microwave‐absorbent nanocomposite coatings based on thermoplastic polyurethane‐based and hybrid carbon‐based nanofillers

This paper describes the effect of nanofillers, such as nanographite, nickel–zinc ferrite (NiZnFerrite), and in‐house developed hybrid nanographite particles (i.e. iron‐coated nanographite [FeNG] and iron–nickel co‐deposited nanographite [FeNiNG] particles), on microwave‐absorption properties of thermoplastic polyurethane (TPU) based nanocomposite coatings on textile substrate. The flexible coatings were tested for various functional properties such as microwave absorbency, gas barrier property, impedance, and weather resistance. The comparison has also been made with other fillers such as bulk graphite (G) and iron powder (Fe) and carbon nanofiber (CNF) in coating form. The nanoparticles' dispersion was observed through optical microscope and phase image analysis on atomic force microscopy. The impedance behavior of such coated samples with 10 wt% nanofillers is frequency dependent except for CNF, which shows frequency‐independent behavior even at 2 wt% loading. The gas barrier property of the FeNG‐based and FeNiNG‐based coatings is better than that of pure TPU; however, G‐based, NG‐based, and NiZnFerrite‐based coatings show excellent barrier property. The coatings were evaluated for their microwave absorbency at low‐frequency (from 0.3 to 1.5 GHz) as well as high‐frequency (8–18 GHz) ranges. The FeNG‐based and FeNiNG‐based nanocomposite coatings showed good absorbency over a frequency range of 8 to 14 GHz as compared with those of others. The flexibility of the nanocomposite films is almost retained even at 10 wt% nanofiller loading. The weather resistance of the films was also evaluated, and the FeNiNG‐based coating outperformed the FeNG‐based coating as the latter is prone to oxidation on exposure to environment. Copyright © 2011 John Wiley & Sons, Ltd.     

Deposition of electrically conducting polymeric coatings using copper-plated silica

Silica was metallized by chemical copper plating, and the possibility of using this kind of silica as an electrically conducting filler by itself and with addition of carbon or metal-carbon fibers for preparing polymeric and paint-and-varnish electrically conducting coatings was studied.     

Electrically conducting,transparent, graphene based nanocomposite coatings on flexible film substrate

Transparent, electrically conducting nanocomposite coated polyethylene terephthalate (PET) films are prepared using two types of bulk synthesized few layered graphene; namely reduced graphene oxide (rGO) and liquid exfoliated graphite (EG) dispersed in ultra high molecular weight polyethylene (UHMWPE). This study focuses on application of high concentration of such nanofillers (1: 1 to 2.5: 1 ratios with polymer) in order to develop a highly conducting but ultrathin coating for better transparency. The coated PET films are characterized for their surface morphology, electrical and optical properties. High resolution transmission electron microscopic (HRTEM) images and corresponding selected area electron diffraction (SAED) patterns confirm that the graphite has been exfoliated to few layer graphene using both the synthesis routes. Transmittance values of these coated films are measured in UV visible spectrum. The rGO based samples have high transmittance (~90–95%) compared to EG based samples (~40–50%). From current-voltage (I?V) graph and surface resistivity studies, it has been observed that rGO based samples are dielectric in nature similar to UHMWPE while EG based samples are electrically conducting and its conductivity increases with its concentration. EG based nanocomposite coated samples show much better electrical conductivities (resistance 338 to 66 kΩ at different concentrations of EG) than rGO based samples.     

Design and properties of a microwave boosted glow discharge lamp

The operation of a glow discharge lamp with integrated microwave resonator for the analysis of electrically conducting solid samples by atomic emission spectrometry is described. While the glow discharge in argon at a pressure of 300 Pa mainly serves for the production of free sample atoms by cathodic sputtering, a 40 W microwave discharge is applied for additional excitation of the ablated material. The construction of the lamp and the optimization of the working conditions are described. The intensities as well as the signal-to-background ratios of many analytical lines were found to be improved as compared to a conventional glow discharge lamp. The analytical performance is demonstrated by analysis results for steel samples. Detection limits for 13 elements in steel are between 0.05 and 1 μg/g. Because of the optically thin plasma the new lamp shows a large linear dynamic range.     

Fabrication and characterization of nylon 6/foliated graphite electrically conducting nanocomposite

In this study, the nylon 6/foliated graphite (FG) electrically conducting nanocomposites with a low percolation threshold of less than 0.75 vol % have been prepared via an in situ polymerization approach in the presence of FG nanosheet filler. Based on laser counting, scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction characterization techniques, the structures and morphologies of the nanoscale filling particles and the resulting nanocomposites were examined. Using percolation theory, the conductivity behavior of the nanocomposite samples were modeled and analyzed. Through the use of mean‐field and excluded volume approaches, it was demonstrated that the experimentally observed percolation threshold values could be approximately estimated, and a correlation between the percolation threshold and the aspect ratio of FG particles could be quasi‐quantitatively established. Also, preliminary studies on the effects of FG nanosheets on the thermal properties of the host nylon 6 were performed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2844–2856, 2004     

Colloid aspects of chemical-mechanical planarization

The essential parts of interconnects for silicon based logic and memory devices consist of metal wiring (e.g. copper), a barrier metal (Ta, TaN), and of insulation (SiO2, low-k polymer). The deposition of the conducting metal cannot be confined to trenches, resulting in additional coverage of Cu and Ta/TaN on the surface of the dielectrics, yielding an electrically conducting continuous but an uneven surface. The surplus metal must be removed until a perfectly flat surface consisting of electrically isolated metal lines is achieved with no imperfections. This task is accomplished by the chemical-mechanical planarization (CMP) process, in which the wafer is polished with a slurry containing abrasives of finely dispersed particles in submicrometer to nanometer size. The slurries also contain dissolved chemicals to modify the surfaces to be planarized. Eventually the final product must be cleared of any adhered particles and debris left after polishing is completed. Obviously the entire process deals with materials and interactions which are the focal subjects of colloid and surface science, such as the natures of abrasive particles and their stability in the slurry, the properties of various surfaces and their modifications, adhesion and detachment of the particles and different methods for the characterization of constituents, as well as elucidation of the relevant interfacial phenomena. This review endeavors to describe the colloid approach to optimize the materials and processes in order to achieve desirable polish rates and final surfaces with no imperfections. Specifically, the effects of the composition, size, shape, and charge of abrasive particles on the polish process and the quality of planarized wafers is described in detail. Furthermore, the interactions of metal surfaces with oxidizing, chelating, and other species which affect the dissolution and surface modification of metal (copper) surfaces are illustrated and related to the planarization process. Finally, using the packed column technique the adhesion phenomena of abrasives on metals and oxides is evaluated on suitable model systems, that contain the same additives in the slurries as in the actual planarization process. A close correlation is established in all cases between the attachment and detachment results with experimentally determined polish rates.     

Functionalized single graphene sheets derived from splitting graphite oxide

A process is described to produce single sheets of functionalized graphene through thermal exfoliation of graphite oxide. The process yields a wrinkled sheet structure resulting from reaction sites involved in oxidation and reduction processes. The topological features of single sheets, as measured by atomic force microscopy, closely match predictions of first-principles atomistic modeling. Although graphite oxide is an insulator, functionalized graphene produced by this method is electrically conducting.     

Fabrication of polytetrafluoroethylene- and graphite-containing oxide layers on aluminum and titanium and their structure

Stable aqueous electrolyte emulsions with negatively charged micelles containing dispersed particles of polytetrafluoroethylene (PTFE) or graphite are obtained using siloxane-acrylate emulsion as an emulsifier. The oxide coatings formed in such electrolytes contain carbon, polytetrafluoroethylene, or graphite. The coatings with PTFE particles are similar to monolithic polytetrafluoroethylene with respect to its hydrophobic characteristics. According to X-ray photoelectron spectroscopy data, the surface of the formed coatings predominantly contains aliphatic carbon (C-C and C-H bonds) and some fraction of oxidized (or, in the case of PTFE-containing electrolytes, fluorinated) carbon.     

均匀Fe~3O~4胶体粒子形成机理II. 低温Mossbauer谱研究

在液氮温度下, 测定了均匀Fe~3O~4胶体粒子制备过程中陈化时间为1小时内的不同时间所得样品的Mossbauer谱。结果表明, γ-FeOOH为Fe~3O~4均匀胶粒形成过程的中间产物, 并提出均匀Fe~3O~4胶粒的形成机理。     

Electrical Conductivity of Hydrophobized Electrodes Fabricated from Thermally Expanded Graphite and Their Activity in Electroreduction of Oxygen

Intercalation compounds of GT-1 and GAK-3 graphites were electrically synthesized in concentrated sulfuric and nitric acids. Porous composite samples based on thermally expanded graphite produced from electrochemically synthesized GT-1 graphite hydrosulfate, chemically synthesized GSM-1 graphite nitrate, and fluoroplastic-4D (1–15 wt %), with a volume density of 650–1090 g l^?2, were fabricated and studied.     

Demulsification of Solids‐Stabilized Emulsions Under Microwave Radiation

Experimental data are presented to show the influence of solid particles on demulsification. It was found that the solid particles could effectively resist demulsification. Compared with conventional heating, microwave radiation can enhance the demulsification rate by an order of magnitude and increase the demulsification effectiveness. The demulsification effectiveness of the emulsions stabilized by graphite powder can reach 82%–89% in a very short time under microwave radiation, whilst that of the emulsions stabilized by barium sulfate can attain 100% under similar conditions.     

Underpotential deposition of copper on electrodes modified with colloidal gold

This communication is concerned with the electrochemical addressability of gold colloidal particles deposited on a conducting substrate. Cyclic voltammetry of electrodes modified with gold colloid layers indicates that an underpotential deposition of copper onto the gold surface takes place. Analysis of the charge associated with the underpotential deposition permits the electroactive gold area to be calculated. The total gold area may be determined from transmission electron microscopy (TEM) images. Comparison of the geometric and electroactive areas obtained indicates that electrochemically all the gold particles are addressable and the entire colloid surface is accessible.     

Platinum Nanosheets Intercalated into Natural and Artificial Graphite Powders

Insertion of sheet-type platinum particles (platinum nanosheets) between graphite layers was achieved by a thermal treatment of a mixture of platinum chloride (IV) and graphite powder (natural graphite or artificial graphite) under 0.3 MPa of chlorine at 723 K, followed by the treatment under 40 kPa of hydrogen pressure. Similar platinum nanosheets, which were 1–3 nm in thickness and 100–500 nm in width and had a number of hexagonal holes and edges with 120° angle, were formed between the layers of both natural graphite or artificial graphite; however, their location in the graphite layers depended on the type of graphite used. A number of platinum nanosheets were observed in the edge region of natural graphite particles which have flat surface. On the other hand, a number of platinum nanosheets were found inside and away from the edge of the artificial graphite particles especially in the vicinity of the cracks. Both the platinum nanosheet-containing artificial and natural graphite samples showed high selectivity to cinnamyl alcohol in cinnamaldehyde hydrogenation under supercritical carbon dioxide conditions, while spherical platinum particles, which were located on the surface of natural and artificial graphite, showed lower selectivity.     

PMMA/graphite nanosheets composite and its conducting properties

Graphite nanosheets (NanoG) were prepared by treating the expanded graphite with sonication in aqueous alcohol solution. Nanocomposites of poly(methyl methacrylate) (PMMA) with NanoG were prepared via an in situ polymerization of MMA in the presence of NanoG with the aid of sonication. The nanocomposites were then dispersed with chloroform (CHCl₃) and casted on glass slides to form conducting films. The percolation threshold of PMMA/NanoG conducting films at room temperature was as low as 0.31 vol%, much lower than that of the composites filled with conventional graphite particles. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area diffraction (SAD) and etc. were used to characterize the structure of the graphite nanosheets and the nanocomposites. Results showed that the high-aspect-ratio structure of graphite nanosheets played an important role in forming conducting network in PMMA matrix. The conducting behavior of the composite was interpreted by percolation theory.     

Site-resolved X-ray scattering studies,I investigations on plates from PP-graphite composites

Cross-sections cut from rectangular plates injection or compression-molded from composites of isotactic polypropylene and varying amounts (up to 40 mass%) of different grades of graphite were investigated by site-resolved wide-angle X-ray scattering (WAXS), using a two-circle goniometer and a specially adapted Kratky camera, respectively. The measurements yielded detailed information about the orientation of both the filler particles and the PP crystallites, in dependence on the position in the cross-sections. In the plates molded from composites, the graphite particles are preferentially oriented with their (002) planes parallel to the surface of the plates and the α-PP crystallites prefer the same orientation for their (040) planes. In plates devoid of graphite, the PP crystallites show a different orientation behavior, however, the presence of 0.2% graphite is already sufficient to change the orientation to the afore-mentioned mode. The observed parallelism in the preferential orientation of the graphite particles and the PP matrix suggests the assumption of hetero-epitaxial growth of α-PP crystallites on the (002) surface of oriented graphite particles. According to our results, the effects of the PP-graphite interaction are dependent on the nature and properties of the graphite particles and may be modulated by treating the graphite surface with different coatings.     

Electrodeposition of composite Ni–B coatings in a stirred heterogeneous system

The formation of composite electrochemical coatings of a nickel matrix with boron microparticles was investigated. Electrolytical nickel–boron layers were deposited on a paraffin-impregnated graphite electrode in a stirred heterogeneous system formed by a Watts-type nickel plating bath and dispersed boron powder particles. The polarisation behaviour of the composite plating bath as a function of the boron particle loading was examined. The effect of deposition conditions, as well as of the amount of boron powder in the plating bath on the boron content in the composite Ni–B coatings, was examined. The composite coating structure was established using scanning electron microscopy and light optical microscopy. The distribution of boron particles in the composite deposits was investigated by dynamic secondary ion mass spectrometry. The boron particles content was determined gravimetrically. The obtained results suggest that the content of incorporated boron particles increases with an increasing amount of boron in the plating bath. The potentiodynamic deposition method is demonstrated to be more suitable for production of composite coatings with a high content of boron particles than the potentiostatic one. Homogeneous distribution of boron particles in the nickel matrix without coagulation or sedimentation was associated with the electrochemical fabrication method in stirred heterogeneous systems.     

尼龙6/石墨纳米导电复合材料的制备与性能

通过原位插层聚合制备了尼龙 6 /石墨纳米导电复合材料 ,其室温导电渗滤阈值为 =0 75vol% ,远远低于常规导电粒子填充的聚合物复合材料 .当石墨体积分数为 2 0vol%时 ,室温电导率可达 10 -4 S/cm .透射电镜研究表明 :由于石墨经高温膨胀后其片层被剥离导致了片状石墨粒子具有巨大的径厚比 ,经原位插层聚合其片层厚度进一步被剥离为几十个纳米 ,同时原位插层聚合使得石墨粒子能够均匀分散在尼龙 6基体中 ,因而导致了该导电复合材料的低渗滤阈值和高导电性能 .     

Intercalating oleylamines in graphite oxide

Graphite oxide has been synthesized from raw graphite particles and been treated with various mass amounts of oleylamine as intercalants to form intercalation compounds. X-ray diffraction patterns reveal that the inter-sheet distances strongly depend on the graphite oxide to oleylamine mass ratios. The equilibrium-like behavior implies diffusion-dominated oleylamine adsorption on graphite oxide in solution and excluded volume intercalations among oleylamine-adsorbed graphite oxide during restacking. The intercalation compounds are soluble in organic solvents, and their applications in the fabrication of transparent and conductive coatings have been demonstrated.