Graphitic Ribbons Research Articles

ABRASIVE WEAR BEHAVIOR OF LOWER BAINITE DUCTILE IRON IN CORROSION MEDIA

The corrosion-abrasive wear behavior of lower bainite ductile iron was investigated by corrosionabrasive wear tests. The main factors of mass loss rate were analyzed. SEM and TEM were used to observe the worn surfaces. The strain-hardening effects beneath the contact surfaces were analyzed by microhardness profiles.The influence of load to corrosion resistance was researched by polarization curves. The results show that the main corrosion wear mechanism was corrosion mass loss and furrow wear. The roughness of worn surface, friction between sample and abrasive, depth of furrow all increased with the test load, which increased the corrosion-abrasive wear rate sharply. Meanwhile, the corrosion micro-cell formed along with the appearance of graphite ribbon and delamination at a higher load, which enhanced the corrosion rate rapidly, and the fracture of delamination resulting from plastic deformation fatigue was another critical factor of the increased mass loss. With the increase of test load, dislocation multiplication and pile-up took place in the retained austenite, which improved the wear resistance of material to some extent. However, the improvement was limited. The average mass loss rate was still increased from 0.16 g/(cm2· h) to 0.42 g/(cm2· h) with the increase of test load; the corrosion current density(icorr) was enhanced from 0.56 m A/cm2 to 5.62 m A/cm2 along with the increase of roughness. In addition, the mass loss curves of lower bainite ductile iron were divided into three stages: point contact wear(initial stage), surface contact wear(transition stage) and fatigue wear(stability stage).

Fabrication and CO2 capture performance of silicon carbide derived carbons from polysiloxane

Microporous silicon carbide derived carbons (SiC-DCs) were obtained by chlorination with post treatment in ammonia (NH3) using a commercially available polymethyl(phenyl)siloxane resin. In this paper, attentions were focused on the compositional and structural evolutions as well as the CO2 capture performances of SiC-DCs as a function of chlorination temperature or affected by post-treatment. Microscopy analysis showed that the geometry and macrostructure, as well as the observed graphite ribbons were finely inherited from the as-received silicon carbide. Post-treatment under NH3 could introduce a few nitrogen-contained groups to SiC-DCs, and has an advantage on increasing the ultra-microporosity with little effect on the carbon crystallinity, both of which finally help increasing the CO2 adsorption capacity. Increasing etching temperature (900–1100°C) would lead to a tiny increase of carbon crystallinity and porosity (specific surface area and total pore volume). However, the ultra-micropore volume decreased instead, thus leading to a decrease of CO2 adsorption capacity. The final SiC-DCs samples exhibit excellent CO2 capture performances at 0°C under the ambient pressure, with a maximum value of 5.75mmol/g. Under the same condition, the N2 adsorption is as low as 0.46mmol/g, suggesting a potential selective adsorbent for CO2 and N2 separation.

Electrochemical performance of graphitized carbide-derived-carbon with hierarchical micro- and meso-pores in alkaline electrolyte

Graphitized carbide-derived-carbon (CDC) with hierarchical micro- and meso-pores is synthesized by chlorination of titanium carbide powder at 1000°C. The produced CDC has many bilayer graphenes and some narrow graphite ribbons, which contributes a large amount of micropores (∼1.35nm) and some mesopores. Although hierarchical pore is an attractive structure for supercapacitor, the low hydrophilicity of the graphitized CDC leads to poor electrochemical performance in alkaline electrolyte. The specific capacitance of the CDC in KOH aqueous electrolyte is only 5Fg−1. A strategy that adding ethanol to alkaline electrolyte is presented to improve its surface wettability. The specific capacitance of the graphitized CDC in KOH aqueous electrolyte with addition of ethanol increases to 60Fg−1 at a scan rate of 20mVs−1. The optimal content of ethanol in KOH electrolyte is 10wt.%. In addition, cyclic voltammogram curve can maintain a quasi-rectangular shape well even at a scan rate of 500mVs−1 and the retention rate of the specific capacitance is about 70%. The specific capacitance is stable at high current density (e.g. 1Ag−1), and almost no performance degradation is observed after 8000 consecutive cycles.

Developing a nanoelectromechanical shuttle graphene-nanoflake device

The superlubric sliding and self-retracting motions of graphene-nanoflakes (GNFs) have been of interest for developing graphene-based nanoelectromechanical systems, as well as for studying basic mechanical properties. Here we present the model schematics of a shuttle GNF device on a graphite ribbon. The operations of this device are based on the balance between the electrostatic force and the retraction vdW force. Its energetics and dynamic properties were investigated using classical molecular dynamic simulations, such that the movable GNF changed its position via the superlubric sliding behavior under electrostatic force and then settled on the force balance position. Since the position of the GNF on the graphite ribbon can be detected by using electric, magnetic, or optical methods, this proposed shuttle GNF can be utilized for nanoscale non-volatile memory, switches, sensors, and quantum computing.

Long-term stability test of Ni-based catalyst in carbon dioxide reforming of methane

A La-NiMgAlO catalyst, obtained after calcination of a hydrotalcite precursor, was evaluated in dry reforming of methane at 650 and 700°C and compared with a previous test performed at 750°C. At 700°C the catalyst showed no sign of deactivation during 200h, while it deactivated slowly afterwards. However, at 650°C conversion decay was detected from the beginning of the test. In both tests, CH4 and CO2 conversion were higher than thermodynamic equilibrium estimation which suggests the participation of other reactions such as methane decomposition or steam reforming of methane. The occurrence of reverse water-gas-shift reaction (RWGS) was responsible for the H2/CO ratios below unity and for the higher CO2 conversion compared with CH4.Used catalysts were characterized by several techniques (TEM, 27Al MAS NMR, XRD, TPO and Raman spectroscopy) in order to study catalyst structure and to establish whether carbon was deposited and its nature. Ni particle diameter increased when reaction temperature decreased but no differences in 27Al MAS NMR or XRD results were observed. A higher coke deposition rate was detected when the temperature was increased. At 700 and 650°C carbon species were mainly graphite ribbons, coating carbon and graphite nanoencapsulates, while at 750°C there were multi-walled carbon nanotubes (MWCNT), fibres and graphite ribbons. The deactivation of the catalysts tested at 650 and 700°C can be related to: (i) the presence of coating carbon, graphite nanoencapsulates and Ni particles embedded inside the carbon nanotubes (CNT); (ii) partial sintering and (iii) a lower hydrogen production what makes that carbon transportation away the surface was less favoured.

Effects of adding ethanol to KOH electrolyte on electrochemical performance of titanium carbide-derived carbon

Porous carbide-derived carbons (CDCs) are synthesized from TiC at different chlorination temperatures as electrode materials for electrochemical capacitors. It is found that the microstructure of the produced CDCs has significant influence on both the hydrophilicity in aqueous KOH electrolyte and the resultant electrochemical performance. Because the TiC-CDC synthesized at higher temperature (e.g. 1000 °C) contains well-ordered graphite ribbons, it shows lower hydrophilicity and specific capacitance. It is also found that addition of a small amount of ethanol to KOH electrolyte effectively improves the wettability of the CDCs synthesized at higher temperature and the corresponding specific capacitance. Compared with the CDC synthesized at 600 °C, the CDC synthesized at 1000 °C shows fast ion transport and excellent capacitive behavior in KOH electrolyte with addition of ethanol because of the existences of mesopores and high specific surface area.

Cobalt‐Mediated Crystallographic Etching of Graphite From Defects

Herein is reported a study of Co-assisted crystallographic etching of graphite in hydrogen environment at temperatures above 750 °C. Unlike nanoparticle etching of graphite surface that leaves trenches, the Co could fill the hexagonal or triangular etch-pits that progressively enlarge, before finally balling-up, leaving well-defined etched pits enclosed by edges oriented at 60° or 120° relative to each other. The morphology and chirality of the etched edges have been carefully studied by transmission electron microscopy and Raman analysis, the latter indicating zigzag edges. By introducing defects to the graphite using an oxygen plasma or by utilizing the edges of graphene/graphite flakes (which are considered as defects), an ability to define the position of the etched edges is demonstrated. Based on these results, graphite strips are successfully etched from the edges and graphitic ribbons are fabricated which are enclosed by purely zigzag edges. These fabricated graphitic ribbons could potentially be isolated layer-by-layer and transferred to a device substrate for further processing into graphene nanoribbon transistors.

Relationships between structure and activity of carbon as a multifunctional support for electrocatalysts

We report on new insights into the relationships between structure and activity of glassy carbon (GC), as a model material for electrocatalyst support, during its anodization in acid solution. Our investigation strongly confirms the role of CFGs in promotion of Pt activity by the "spill-over" effect related to CO(ads) for methanol electrooxidation (MEO) on a carbon-supported Pt catalyst. Combined analysis of voltammetric and impedance behaviour as well as changes in GC surface morphology induced by intensification of anodizing conditions reveal an intrinsic influence of the carbon functionalization and the structure of a graphene oxide (GO) layer on the electrical and electrocatalytic properties of activated GC. Although GO continuously grows during anodization, it structurally changes from being a graphite inter-layer within graphite ribbons toward a continuous GO surface layer that deteriorates the native structure of GC. As a consequence of the increased distance between GO-spaced graphite layers, the GC conductivity decreases until the case of profound GO exfoliation under drastic anodizing conditions. This exposes the native, yet abundantly functionalized, GC texture. While GC capacitance continuously increases with intensification of anodizing conditions, the surface nano-roughness and GO resistance reach the highest values at modest anodizing conditions, and then decrease upon drastic anodization due to the onset of GO exfoliation. We found for the first time that the activity of a GC-supported Pt catalyst in MEO, as one of the promising half-reactions in polymer electrolyte fuel cells, strictly follows the changes in GC nano-roughness and GO-induced GC resistance. The highest GC/Pt MEO activity is reached when optimal distance between graphite layers and optimal degree of GC functionalization bring the highest amount of CFGs into intimate contact with the Pt surface. This confirms the promoting role of CFGs in MEO catalysis.

Ultrafast Direct Ablative Patterning of HOPG by Single Laser Pulses to Produce Graphene Ribbons

AbstractUltrafast, single step and direct patterning of highly oriented pyrolytic graphite (HOPG) is achieved through pulsed laser interference ablation using a near field transmitting phase mask. Periodic arrays of lines are patterned on the HOPG surface over large areas by spatially modulating the laser intensity through the mask. Thus patterned surface serve as a source for multi and few layer graphene ribbons for transferring onto desired substrates using polydimethylsiloxane as transferring agent. The transferred regions are contained with few layer graphene (5–6 layers) ribbons as well as thick graphitic ribbons (30–40 nm), with widths ∼1 μm and lengths of several micrometers. Raman, TEM and electrical measurements have confirmed that the transferred ribbons are highly crystalline in nature. Using combinations of shadow and transmitting phase masks, other patterns such as checker boards and diamond‐shaped pits are produced.

Effect of oxygen adsorption on magnetic properties of graphite

Both experimental and theoretical studies of the magnetic properties of micrographite and nanographite indicate a crucial role of the partial oxidation of graphitic zigzag edges in ferromagnetism. In contrast to total and partial hydrogenation, the oxidation of half of the carbon atoms on the graphite edges transforms the antiferromagnetic exchange interaction between graphite planes and over graphite ribbons to the ferromagnetic interaction. The stability of the ferromagnetism is discussed.

Synthesis and characterization of Au supported on carbonaceous material-based catalysts for the selective oxidation of glycerol

Catalysts supported on carbon materials, with different structures: activated carbon (AC), graphite (G) and three types of carbon nanofibers (CNF) with different structures with respect to the arrangement of the graphitic planes (platelet (CNF-P), fishbone (CNF-F) and ribbon (CNF-R)) were prepared by the following methods: impregnation and gold–sol. CNF were synthesized by a chemical vapour deposition (CVD) method using C 2H 4 as the carbon precursor and Ni/SiO 2 as the catalyst. Different techniques were employed to characterize both the supports and the final Au catalysts: atomic absorption spectrometry, transmission electron microscopy (TEM), temperature-programmed oxidation (TPO), X-ray diffraction (XRD), Raman spectroscopy, elemental analyses (CNH), N 2 adsorption–desorption analysis, temperature-programmed reduction (TPR) and temperature-programmed decomposition (TPD), which have established distinct morphological, graphitic and porous characteristics. Both the crystalline nature of the carbon supports and the preparation method had a strong influence on the way in which Au particles were deposited on the carbonaceous supports. The higher the crystallinity and the smaller the particle size, the higher the activity and selectivity of the catalysts in the liquid-phase oxidation of glycerol. The following sequence in the catalytic activity was observed in terms of TOF (min −1): Au/G-SGT (0.07) > Au/CNF-R-SGT (0.067) > Au/G-IMP (0.053) > Au/CNF-F-SGT (0.052) > Au/CNF-P-SGT (0.051) > Au/AC-SGT (0.049) > Au/CNF-R-IMP (0.047) > Au/AC-IMP (0.045) > Au/CNF-F-IMP (0.040) > Au/CNF-P-IMP (0.036).

Flexible Nano‐felts of Carbide‐Derived Carbon with Ultra‐high Power Handling Capability

AbstractNano‐fibrous felts (nano‐felts) of carbide‐derived carbon (CDC) have been developed from the precursor of electrospun titanium carbide (TiC) nano‐felts. Conformal transformation of TiC into CDC conserves main features of the precursor including the high interconnectivity and structural integrity; the developed TiC‐CDC nano‐felts are mechanically flexible/resilient, and can be used as electrode material for supercapacitor application without the addition of any binder. After synthesis through chlorination of the precursor at 600 °C, the TiC‐CDC nano‐fibers show an average pore size of ∼1nm, a high specific surface area of 1390 m2/g; and the nano‐fibers have graphitic carbon ribbons embedded in a highly disordered carbon matrix. Graphitic carbon is preserved from the precursor nano‐fibers where a few graphene layers surround TiC nanocrystallites. Electrochemical measurements show a high gravimetric capacitance of 110 F/g in aqueous electrolyte (1 M H2SO4) and 65 F/g in organic electrolyte (1.5 M TEA‐BF4 in acetonitrile). Because of the unique microstructure of TiC‐CDC nano‐felts, a fade of the capacitance of merely 50% at a high scan rate of 5 V/s is observed. A fade of just 15% is observed for nano‐felt film electrodes tested in 1 M H2 SO4 at 1 V/s, resulting in a high gravimetric capacitance of 94 F/g. Such a high rate performance is only known for graphene or carbon‐onion based supercapacitors, whereas binders have to be used for the fabrication of those supercapacitors.

Study of C60 Peapods After a High-Pressure–High-Temperature Treatment

The present work is devoted to studying the products formed from C60 peapods after treatment at 8 GPa, from 200°C to 1200°C by SEM, TEM, XRD, and Raman techniques. It is confirmed that at temperatures up to 600°C the C60 molecules polymerize in forming the known 1D polymeric crystal with a C60 – C60 distance of 9 Å. In addition, we also find that at 1000°C the peapods begin to transform into different products including nanodiamond particles, amorphous carbon, and graphitic ribbons. At 1200°C only well-formed graphite is observed.

Current status of self-organized epitaxial graphene ribbons on the C face of 6H–SiC substrates

The current status of long, self-organized, epitaxial graphene ribbons grown on the (0 0 0 −1) face of 6H–SiC substrates is reviewed. First, starting from the early stage of growth it is shown that on the C face of 6H–SiC substrates the sublimation process is not homogeneous. Most of the time it starts from defective sites, dislocations or point defects, that define nearly circular flakes surrounded by bare SiC. These flakes have a volcano-like shape with a graphite chimney at the centre, where the original defect was located. At higher temperatures a complete conversion occurs, which is not yet homogeneous on the whole sample. This growth process can be modified by covering the sample with a graphite cap. It changes the physics of the surface reconstruction during the Si-sublimation process and, on the C face, makes more efficient the reconstruction of few selected terraces with respect to the others. The net result is the formation of strongly step-bunched areas with, in between, long and large reconstructed terraces covered by graphitic material. Despite the low intrinsic optical absorption of a few graphene layers on SiC, micro-transmission experiments, complemented by micro-Raman spectroscopy, demonstrate that most of this graphitic coverage is made of one or two homogeneous graphene layers. We show also that most of the thermal stress between the graphene layer and the 6H–SiC substrate is relaxed by pleats or wrinkles which are clearly visible on the AFM images. Finally, the results of transport experiments performed on the graphitic ribbons reveal the p-type character of the ribbons.

Linear and spiral forms of longitudinal cuts in graphitized N-doped multiwalled carbonnanotubes (g-N-MWCNTs)

Nitrogen-containing multiwalled nanotubes (N-MWCNTs), formed by CVD from anitrogen-containing feedstock have a ‘bamboo’ structure in which the axes of the grapheneplanes are not parallel to the axis of the nanotube and the core is periodically bridged. Wefind that thermal and chemical treatment of these materials can produce nanotubes thathave been cut longitudinally in either a linear or in a spiral manner. In addition, theselongitudinally cut nanotubes can be partially or fully unrolled by sonication in anaqueous surfactant, producing graphite platelets as well as narrow structuresthat could be thin graphite ribbons or very narrow, intact N-MWCNTs. Thesedifferent morphologies of graphite, available from one source, suggest that there aremultiple structures of N-MWCNTs present, few as simple as stacked cups or nestedscrolls.

Quasi-one dimensional graphite ribbon structures in the presence of a magnetic field and the on-site Coulomb correlation at half-filling

We have presented the role of the Coulomb interaction (U) and the magnetic field $\vec{B}$ on the ground state properties of the quasi-one dimensional graphite ribbon structures at half-filling. Mean field Hartree-Fock Approximation is used to study the systems. To understand the boundary effects in graphite structures, we have compared the results of these systems with those of the square lattice ribbon structures. Studying the density of states, the Drude weight and the charge gap, we have drawn the U – B phase diagrams for the zigzag and the armchair graphite ribbons.

Surface floating, air cathode, microbial fuel cell with horizontal flow for continuous power production from wastewater

A surface floating, air cathode, microbial fuel cell (MFC) with a horizontal flow is devised and characterized using glucose-based synthetic wastewater. The performance of the MFC is significantly affected by the current-collector of the electrodes. When graphite foil ribbon (150 cm) serves as the current-collector, the respective specific internal resistance and maximum power density are 0.362 Ω m −2 and 124.0 W m −3. The internal resistance can be reduced by increasing the length of the current-collector. For a graphite ribbon current-collector 256 cm long, the specific internal resistance is only 0.187 Ω m −2 and the maximum power density markedly increases to 253.6 W m −3; however, the maximum power density is affected by the current-collector material. When the current-collector is changed to a stainless-steel wire, the maximum power density is reduced to approximately 100 W m −3 because of its high liquid|solid interfacial impedance. During three continuous months of operation, issues such as leaking are not observed and as such, the MFC could be easily scaled-up for wastewater treatment by increasing the electrode size and stacking a number of cells without additional ohmic resistance.

Synthesis of ribbon type carbon nanostructure using LiFePO 4 catalyst and their electrochemical performance

Ribbon type of carbon nanostructure has been synthesized by chemical vapor deposition using a new catalyst (LiFePO 4) introduced for the first time and its electrochemical behavior has been determined from charge/discharge characteristics. The synthesized material characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and by Raman spectroscopy confirms the graphitic structure and ribbon type morphology of material. The performance of the single cell using purified carbon nanoribbon as the anode has been studied and the reversible lithium intercalation capacity has been found about 345 mAh/g, of which 335 mAh/g remain after 14th cycle. The columbic efficiency has been stabilized at approximately 98% from the 5th cycle.

First-Principles Study of Chemisorption of Oxygen and Aziridine on Graphitic Nanostructures

Using ab initio plane wave pseudopotential calculations, we study the energetics and structure of adsorbed linear arrays of oxygen and aziridine on carbon nanotubes, graphitic ribbons, and graphene sheets. Chemisorption of arrays of O or NH causes splitting of the CC bond and local deformation of the graphitic structures. The (3,3) nanotube cross section assumes a teardrop-like shape, while graphene sheets warp into a new local geometry around the chemisorbed molecules. The interior of a (3,3) nanotube is less prone to oxidation than the exterior because of steric effects. A zigzag (6,0) nanotube is less reactive and thus chemically more stable than an armchair (3,3) nanotube. The results suggest a partial explanation for the experimentally observed selective etching of metallic carbon nanotubes.

Pressure-induced Structural Phase Transition of Carbon Nanotubes into New Nanostructured Carbon Solids

AbstractWe study pressure-induced structural phase transition of carbon nanotubes using the constant-pressure tight-binding molecular-dynamics simulation. The systems studied are nanotube bundles composed of (6,6) armchair nanotube and/or (7,4) chiral nanotube, which are reported to be the nanotubes relatively abundant in experimentally purified sample. We find that the nanotube bundles transforms into a new phase that consist of graphitic ribbons and diamond blocks, “graphitic nanoribbon solid”. It is also found that sp3-rich phases obtained from the armchair nanotubes possess an anisotropic network and have high hardness which is comparable to that of cubic diamond. In the case of the bundles containing chiral nanotubes, on the other hand, amorphous diamond phase is obtained. Based on the local-density approximation in the density-functional theory, we also investigate the energetics and electronic structure of some of new carbon phases obtained in the molecular-dynamics study.