Amorphous Graphite Research Articles

Amorphous Carbon-Derived Nanosheet-Bricked Porous Graphite as High-Performance Cathode for Aluminum-Ion Batteries

Graphite is an attractive cathode material for energy storage because it allows reversible intercalation/deintercalation of many compound anions at high potentials. However, because the sizes of the compound anions are greatly larger than the lamellar spacing of graphite, common graphite used as cathode may suffer from slow kinetics and large volume expansion. Here, it is demonstrated that graphite with high crystallinity and nanosheet-bricked porous structure can be an excellent cathode for aluminum-ion batteries. This porous graphite is derived from carbon black via asimple electrochemical graphitization in molten CaCl2, and the high crystallinity and thin layer characters facilitate the high capacity and high rate storage of aluminum tetrachloride ions. Moreover, the bricked porous structure endows the fabricated cathode with a providential porosity to perfectly match the huge volume expansion of graphite (650% against a charging capacity of 100 mA h g-1), thus this electrochemical graphite exhibits integrated high gravimetric and volumetric capacities as well as high structural stability during cycling.

Acoustic Emission Feasibility Study for Carbon Epoxy Coated Aluminum Corrosion Monitoring

In the presented research effort, cyclic polarization tests were conducted coupled with acoustic emission measurements, in order to monitor the corrosion phenomena. Previous studies have shown that epoxy composite coatings offer satisfactory corrosion protection to aluminum substrates minimizing and even eliminating some degradation phenomena. In the present effort, acoustic emission was applied during potentiodynamic cyclic polarization testing on as received, anodized and carbon epoxy coated aluminum substrates in order to correlate corrosion phenomena, like oxide layer development and localized corrosion, with characteristic acoustic emission signal descriptors. The epoxy coating was used both as received and as reinforced with various carbon fillers i.e. carbon nano-tubes, amorphous graphite or a combination of them. Acoustic emission detected signals due to hydrogen bubble related processes during cathodic polarization and signals due to deposition of thick soluble films during the final stage of anodic polarization. The acoustic profile between coated and uncoated aluminum substrates, exhibited substantial changes dependent both on the surface preparation and the employed reinforcing filler. The overall outcome of the experimental results, indicate that with further research, acoustic emission can be employed as an Aluminum Corrosion Monitoring tool.

Effects of spray distance on the microstructure and mechanical properties of reactive plasma sprayed TiCN coatings

The objective of this study is to evaluate the effects of spray distance on the microstructure and mechanical properties of reactive plasma sprayed titanium carbonitride (TiCN) coatings under nitrogen plasma gas. For this purpose, five different distances were adopted, and the morphology (single splats, surface and cross section) and composition (phase and chemical) of as-sprayed coatings were investigated. Mechanical properties of bonding strength, hardness, elastic modulus as well as indentation toughness of coatings were systematically evaluated. Results show that all of coatings consist of TiCxN1−x (0 ≤ x ≤ 1), TiOx, amorphous graphite and CNx phases, and the amount of ternary TiCN increases as the spray distance increases. Typical microstructure of plasma sprayed coatings containing fully melted particle, partially melted particles, un-melted particles and defects (pores and cracks) are observed. As the spray distance increase, the surface morphology and splats shape change from uneven and irregular ones to relatively flat and regular “disc splats” due to the improved dwell time and sufficient melting in plasma jet. In this case, the maximum hardness about 17.8 ± 1.9 GPa, elasticity modulus about 214.5 ± 18.3 GPa and bonding strength about 24.2 ± 2.1 MPa are obtained due to the relatively high TiCN content, favorable indentation toughness and compact microstructure. As the spray distance further increases to 150 mm, irregular “fingers splats” appear, and in this case the mechanical properties of coating are worsened. Therefore, a significant influence of spray distance on the microstructure and mechanical properties of as-sprayed TiCN coating is found.

Mechanochemical treatment of fly ash and de novo testing of milled fly ash.

Mechanochemical (MC) treatment has been widely proposed to degrade chlorinated organics in various matrix materials. In this study, fly ash from municipal solid waste incineration was grinded without any addition, using an all-dimensional planetary ball mill. The treated fly ash samples were characterised using X-ray diffraction, Raman spectra, scanning electron microscopy and X-ray energy-dispersive spectroscopy. The residual content of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) was monitored, as well as polycyclic aromatic hydrocarbons (PAH), a potential precursor of PCDD/F and amorphous carbon or graphite. Finally, de novo formation experiments were performed to test the chemical reactivity of the treated fly ash. The PCDD/F in milled samples was compared to those resulting from de novo tests on these same samples. The results suggest that both milling as well as de novo tests significantly alter the PCDD/F signature, suggesting substantial differences in the mechanisms of formation and destruction.

On the origin of the Neoproterozoic Peresopolis graphite deposit, Paraguay Belt, Brazil

The Peresopolis graphite deposit is located northeast of Brasilândia Town in Mato Grosso State (Brazil). It consists of an 1800 m long, 200 m wide low-crystallinity graphite-bearing tabular layer that trends ENE and dips 65°ESE. The deposit is hosted in carbonaceous phyllites, which along with basal metadiamictites and upper metarenites make up the upper unit (Coxipó Formation) of the Cuiabá Group in the late Cryogenian to Cambrian Paraguay Belt (ca. 650-500Ma). The carbonaceous phyllites show a mineral assemblage consisting mostly of graphite-quartz-muscovite-albite and pyrite and dolomite to a lesser extent; alteration minerals include tosudite and kaolinite. XRD analysis confirmed the gangue material and defined the graphite as low-order crystallinity. Carbon isotope data for graphite ore returned a light and very restricted range of δ13Corg between −29 and −28‰ suggesting organic matter as the source of carbon. One hundred and sixty measurements of Raman graphite spectrum returned a well-fit between full width at half maximum parameter (FWHM) which allowed its use as a geothermometer. Resulting temperatures are in the range between 285 and 300 °C ± 30 °C, indicating low-to very-low metamorphic conditions for transformation of organic matter into amorphous graphite. The deposition of the organic matter should have taken place in an outer slope of a glaciomarine system and its transformation into the ore occurred because of deformation and low-grade metamorphism related to the development of the Neoproterozoic Brasiliano/Pan-African Orogeny (850-500Ma).

Influence of Cu Content on the Structure, Mechanical, Friction and Wear Properties of VCN–Cu Films

VCN–Cu films with different Cu contents were deposited by reactive magnetron sputtering technique. The films were evaluated in terms of their microstructure, elemental composition, mechanical, and tribological properties by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), high resolution transmission electron microscopy (HR-TEM), Raman spectrometry, nano-indentation, field emission scanning electron microscope (FE-SEM), Bruker three-dimensional (3D) profiler, and high-temperature ball on disc tribo-meter. The results showed that face-centered cubic (fcc) VCN, hexagonal close-packed (hcp) V2CN, fcc-Cu, amorphous graphite and CNx phases co-existed in VCN–Cu films. After doping with 0.6 at.% Cu, the hardness reached a maximum value of ~32 GPa. At room temperature (RT), the friction coefficient and wear rate increased with increasing Cu content. In the temperature range of 100–500 °C, the friction coefficient decreased, but the wear rate increased with the increase of Cu content.

One-step synthesis of TiC/multilayer graphene composite by thermal plasma

Graphene hybrid materials have been attracting a great deal of attention due to their superior properties. Nevertheless, problems such as expensive and complicated production processes have limited their application to industrial fields. Here, we introduce a one-step synthesis of titanium carbide (TiC) nanoparticles on multilayer graphene nanosheet (TiC/multilayer graphene) composites using thermal plasma. Although there are three types of titanium alkoxides (titanium ethoxide, titanium isopropoxide and titanium n-butoxide), the TiC/multilayer graphene was synthesized from only titanium isopropoxide. The injection temperature of the precursor was varied to investigate the effects of the precursor concentration in the plasma region. A TiC/multilayer graphene hybrid material with crystalline TiC nanoparticles below 50 nm on graphene nanosheets was observed. The number of graphene nanosheet layers varied from one to over 10 according to the injection temperature. When titanium ethoxide and titanium butoxide were injected, TiC with amorphous carbon and graphite were synthesized. The formation of graphene is considered to be affected by the structure of the carbon chain in the precursors and the concentration in the plasma region.

Effect of deuterium on phase transformations in fullerenes at high temperatures and high pressures

The effect deuterium has on phase transformations is studied for amorphous and crystalline fullerenes C60 and C70 at high temperatures of up to 1300°C and high pressures (2–8 GPa). Amorphous fullerene phases are obtained via long grinding in a planetary mill. Structure is studied by means of neutron diffraction. In all cases, amorphous graphite (nanographite) forms in the temperature range of 800–1100°C. This material has different diffraction spectra distinguished by the heights of the halos observed on the graphite diffraction maxima and their relative intensities. These spectra (the structure of nanographite) are affected by preliminary amorphization, the number of carbon atoms in the fullerenes (C60 or C70), and the introduction of deuterium atoms. The different spectra of amorphous (disordered) graphite testify to its varying structure.

In situ nanostructured (TiCr)CN coating by reactive plasma spraying

In situ nanostructured (TiCr)CN composite coating was prepared by reactive plasma spraying Ti-Cr-graphite powder under air atmosphere. The phase composition, microstructure, mechanical properties and wear performance were investigated. The results show that the coating consists of a mixture of TiN, Ti(CN), (TiCr)N, Cr, Ti3O, and amorphous graphite and CrN phases. The grain size is about 70nm and the grains present equiaxed and columnar crystal morphologies. Moreover, 5nm-sized nanocrystals are embedded in an amorphous phase. The (TiCr)CN composite coating possesses high hardness (1325 ± 120 HV) and toughness (4.35 ± 0.53MPam1/2). The friction coefficient and wear rate of the coating are 0.46 and 3.01 ± 0.17 × 10−6mm3N−1m−1, respectively. The inclusion of metallic phase Cr could improve the toughness and wear resistance of the (TiCr)CN coating.

Laser-Plasma Driven Synthesis of Carbon-Based Nanomaterials

In this paper we introduce a laser-plasma driven method for the production of carbon based nanomaterials and in particular bi- and few-layers of Graphene. This is obtained by using laser-plasma exfoliation of amorphous Graphite in a liquid solution, employing a laser with energy in the order of 0.5 J/mm2. Raman and XPS analysis of a carbon colloidal performed at different irradiation stages indicate the formation of Graphene multilayers with an increasing number of layers: the amount of layers varies from a monolayer obtained in the first few seconds of the laser irradiation, up to two layers obtained after 10 s, and finally to Graphite and amorphous carbon obtained after 40 s of irradiation. The obtained colloidals are pure, without any presence of impurities or Graphene oxides, and can easily be deposited onto large surfaces (in the order of cm2) for being characterized or for being used in diverse applications.

Adsorption of Cd(II) at the Interface of water and graphene oxide prepared from flaky graphite and amorphous graphite

This study aimed to investigate the adsorption properties of Cd(II) on graphene oxide prepared from amorphous graphite and flaky graphite. The natural graphite was characterized by Scanning electron microscope, X-ray fluorescence spectrometer and X-ray diffraction. The equilibrium data were described well by both Langmuir model and Freundlich model, and the adsorption rate was fitted by Pseudo-second-order precisely. The GOs before and after adsorption were measured by Atomic force microscope, Fourier transform infrared spectrometer and Energy dispersive system. It was found that the larger adsorption capacity of Cd(II) on GO prepared from amorphous graphite was largely attributed to the more oxygenous functional groups appeared on GO-AG.

Cr(VI) Removal from Water with Amorphous Graphite Concentrate Contaminated by Iron

ABSTRACTThis work attempted to explore the feasibility of using iron-contaminated graphite concentrate as an effective adsorbent for Cr(VI) removal from polluted water. Adsorption isotherm and kinetics were conducted to investigate the Cr(VI) removal capacity by the iron-contaminated amorphous graphite concentrates. In addition, SEM-EDS, XPS were carried out to further examine the solid samples. The results showed that amorphous graphite concentrate had a 1.52 mg/g adsorption capacity of Cr(VI), with the adsorption being fitted well with the pseudo-second-order kinetics model. In addition, chemical adsorption of Cr(V) on iron-contaminated graphite concentrate due to the formation of ≡Fe-O4HCr and Fe2-(CrO4)3 complexes was proposed. This study revealed that iron-contaminated amorphous graphite concentrate would be a cheap and good adsorbent for the removal of Cr(VI) from contaminated water.

Formation of nanostructures during coagulation of semiconductors in superfluid helium

As in the case of metals, laser ablation of germanium and silicon in superfluid helium leads to the formation of thin nanowires; spherical nanoclusters are also present in ablation products. A decrease in the resistance of bundles of silicon nanowires with increasing temperature is typical of semiconductors. Laser ablation of amorphous graphite also leads to the formation of quasi-one-dimensional structures, but there are no spherical clusters among the coagulation products. The structure of carbon filaments is amorphous; they contain onion-like entities, and nanodiamonds appear as coagulation products when the concentration of carbon introduced into superfluid helium increases. The peculiar behavior of carbon is associated with the impossibility of its melting at low pressures.

A SOFIA FORCAST Grism Study of the Mineralogy of Dust in the Winds of Proto-planetary Nebulae: RV Tauri Stars and SRd Variables

Abstract We present a SOFIA FORCAST grism spectroscopic survey to examine the mineralogy of the circumstellar dust in a sample of post-asymptotic giant branch (post-AGB) yellow supergiants that are believed to be the precursors of planetary nebulae. Our mineralogical model of each star indicates the presence of both carbon-rich and oxygen-rich dust species—contrary to simple dredge-up models—with a majority of the dust in the form of amorphous carbon and graphite. The oxygen-rich dust is primarily in the form of amorphous silicates. The spectra do not exhibit any prominent crystalline silicate emission features. For most of the systems, our analysis suggests that the grains are relatively large and have undergone significant processing, supporting the hypothesis that the dust is confined to a Keplerian disk and that we are viewing the heavily processed, central regions of the disk from a nearly face-on orientation. These results help to determine the physical properties of the post-AGB circumstellar environment and to constrain models of post-AGB mass loss and planetary nebula formation.

Amorphous graphite/polymethyl methacrylate composite microspheres: design, preparation, and performance study

Amorphous graphite/polymethyl methacrylate (MAG/PMMA) composite microspheres were synthesized by suspension polymerization. It was found that the contact angle of amorphous graphite (AG) changed from 32.55° into 112.58° after modification by sodium(C16) alkylsulfonate, which showed that the surface of modified amorphous graphite (MAG) were hydrophobic. The modified AGs effectively improved the dispersion in monomer, which helped to improve the compatibility of amorphous graphite in the polymer. The experimental results showed that the thermal properties of the composites were improved effectively by increasing the loading amounts of MAGs, especially when the amount was 2.5 wt %. The compressive strength of MAG/PMMA composite microspheres with the same diameter (1 mm or 2 mm) was significantly 2 times higher than that of the pure PMMA crosslinked polymer microspheres. The specific surface area increased from 0.2347 m2·g−1 of pure PMMA to 3.4074 m2·g−1 when the amount of adding MAGs was 2.0 wt %. The N2 adsorption–desorption isotherms of pure PMMA and MAG/PMMA composite microspheres belonged to V type of IUPAC and H1 hysteresis loop, indicating that adsorption quantities were higher than that of PMMA with adding the MAGs.

(Invited) Advanced Carbon Structures for PEMFC

Interactions between advanced catalytic systems with ultra-low PGM (platinum group metal) loadings and various carbon supports have been investigated in order to harvest maximal catalytic performance without sacrifice in durability. Different classes of catalysts with controlled size, shape, surface morphology, composition and compositional gradients in the form of solid monometallic and multimetalic nanoparticles (NPSs), core-shell nanostructures and subsurface interlayers (CS), multimetallic nanowires (NWs), mesostructured thin film catalysts (MSTF) and multimetallic nanoframes (NFs) were evaluated at atomic level in conjunction with tailored carbon supports such as amorphous high surface area glassy carbon, carbon nanotubes (single and multiwall), carbon nanofoam, graphite, fullerenes and graphene. Activity and durability performance of the advanced classes of catalysts have been evaluated by rotating-disk electrode, membrane-electrode assemblies and various methods for structural characterization. Tailoring the properties of catalyst-support can lead to substantial increase of the electrode lifetime and superior fuel cell performance.

Fracture toughness enhancement of silicon carbide composites with hydrophilic-modified Tyranno® Si–Al–C fibre addition

ABSTRACTThe surface properties of Tyranno® Si–Al–C (SA) fibre (mean length: 0.7 mm) were modified from hydrophobic to hydrophilic nature by acid treatment of carbon-coated SA fibre, in order to enhance dispersibility or fracture toughness within silicon carbide (SiC) matrix. Two types of carbons, i.e. amorphous carbon and graphite carbon, were used to coat the surface of SA fibres (SA(AC) and SA(GC) fibres, respectively) by the pyrolysis of polyvinyl alcohol at 500°C for 30 min and 1800°C for 30 min, respectively. Then, carboxyl groups were formed on the SA(AC) and SA(GC) fibre surfaces through acid treatment (concentrated H2SO4 and HNO3) at room temperature. Owing to the acid treatment, SA fibre could be homogeneously mixed with SiC particles in polar solvent (acetone). The fracture toughness of SiC composites containing 40 mass% of acid-treated SA(GC) fibre (PVA/SA ratio = 2.5) hot-pressed at 1800°C for 60 min attained 8.3 MPa m1/2.

Electrochemical performance of natural graphite coated by amorphous carbon using two step synthesis processes at various temperatures for anode material in Li-ion battery

Electrochemical performance of natural graphite as anode material in the Li-ion battery has been modified by coating this particle with amorphous carbon through two step synthesis process. Citric acid as the amorphous carbon source was mixed with natural graphite (NG) in the ethanol solvent at 80 °C using magnetic stirrer. In the first step, the mixture of NG and CA were dried at 350 °C for 5 hours under argon atmosphere to evaporate the solvent. This dried mixture was then sintered at different temperature i.e. 500 °C (labeled CNG500), 600 °C (CNG600) and 700 °C (CNG700) under argon atmosphere to form amorphous carbon layer on the surface of NG. The crystal structure and morphology of the particles were characterized by using XRD, SEM and TEM. Electrochemical performance and charge-discharge of amorphous carbon-coated graphite has been evaluated by cyclic voltammetry and WBCS 3000, respectively. Cyclic voltammogram showed the working potential and redox reaction peak of the sample. Charge-discharge data was obtained to determine the specific capacity of the sample at 0.1C.

Composition of C–Si–Mn–Cr–W–V powder wire and quality of surfacing

The influence of the composition of powder wire on the properties of the applied layer on steel samples is studied in the laboratory. If amorphous graphite in 35V9Kh3SF powder wire is replaced by material containing carbon and fluorine, the porosity of the applied layer is reduced, and fewer nonmetallic inclusions (including row oxide inclusions and undeformable silicates) are present. Statistical analysis of the experimental data illustrates the influence of the carbon equivalent of the 35V9Kh3SF powder wire on the hardness of the applied layer (including the mean surface hardness and the microhardness of martensite). With increase in the carbon equivalent calculated by the Paton Institute’s formula, the hardness of the applied layer linearly increases.

Effects of in situ amorphous graphite coating on ablation resistance of SiC fiber reinforced SiBCN ceramics in an oxyacetylene flame

The effects of in situ amorphous graphite coating on ablation behavior of SiC fiber reinforced SiBCN ceramics in an oxyacetylene flame are explored. The ablation products for both the monoliths and composites are similar, comprising amorphous SiO2 and cristobalite. The ablation resistance stems from formation of dense, passivating oxide scale of B2O3 containing amorphous SiO2. In different ablation stages, the ablation rates are synergistically controlled by various mechanisms. Interfacial structure and degradation of SiC fibers both deteriorate ablation resistance. The crystallization of SiC fibers leading to strength reduction is the main reason for poorer performance vs monoliths.