Formation Of Graphitic Layers Research Articles

Enhancing electrocatalytic activity in metallic thin films through surface segregation of carbon.

Thin layers of commonly used adhesion metals i.e., Cr and Ti were annealed to investigate and estimate their impact on the electrochemical properties of the carbon nanomaterials grown on top of them. The microstructure, surface chemistry, and electrochemical activities of these materials were evaluated and compared with those of as-deposited thin films. The results from X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD), time-of-flight elastic recoil detection analysis (TOF-ERDA), and conductive atomic force microscopy (C-AFM) indicated the formation of a catalytic graphite layer on Cr following annealing, while no such layer was formed on Ti. This is attributed to the formation of the Cr2O3 layer on annealed Cr, which acts as a barrier to carbon diffusion into the underlying Cr. Conversely, Ti exhibits a high solubility for both carbon and oxygen, preventing the formation of the graphite layer. Cyclic voltammetry results showed that annealed Cr electrodes are electrochemically active towards both dopamine (DA) and ascorbic acid (AA) while no electrochemical activity is exhibited by annealed Ti. Quantum chemical calculations suggested that the presence of carbon as graphene or an amorphous form is critical for the oxidation reaction of probes. These results are significant for comprehending how the distinct solubilities of typical interstitial solutes influence the microstructure of adhesion metal layers and consequently yield diverse electrochemical properties.

Active protection against fire: Enhancing the flame retardancy of sandwich panels using an expandable graphite layer formation

Active protection against fire: Enhancing the flame retardancy of sandwich panels using an expandable graphite layer formation

Effect of microwave assisted solvothermal process parameters on carbon dioxide adsorption properties of microporous carbon materials

In this work, production and characterization of carbon spheres from resorcinol and formaldehyde, using a microwave assisted solvothermal reactor, is presented. The influence of different experimental conditions, e.g., reaction time, pressure, and power, on the structure of the obtained materials, and carbon dioxide adsorption properties, was studied. Using the method described in this work, it is possible to significantly reduce the reaction time, to as low as 10 min, compared with widely described processes carried out in autoclaves, requiring several hours. Simultaneously, it was discovered that the application of higher reactor pressures, over 3 MPa, resulted in the destruction of spherical shape and the formation of graphitic layers. The importance of micropores below 0.4 nm, for adsorption of carbon dioxide, was also shown in this work. Microporous carbon spheres with efficient CO 2 adsorption properties (nearly 7 mmol/g at 1 bar and 0 °C) were synthesized using this process. Spherical shape collapse – effect on microporosity characteristics and CO 2 adsorption. • The effect of synthesis conditions of carbon spheres on their adsorption properties towards carbon dioxide were studied. • An increase of synthesis pressure from 10 to 40 atm caused a collapse of spherical shape and graphitization of the material. • An accompagnying dissappearence of micropores below 0.4 nm was observed, negatively influencing CO 2 physisorption. • Simultaneously, a positive effect for CO 2 chemisorption at 25 °C was obsserved, thanks to an increase in micropores of 0.5 nm.

Formation of nanostructured graphitic carbon from coconut waste via low-temperature catalytic graphitisation

We report a simple and relatively low-temperature method for producing graphitic carbon from renewable and abundant coconut coir. This study also aims to promote the utilisation and conversion of locally sourced coconut coir waste into value-added materials. We obtained amorphous charcoal by carbonising coconut coir and transforming it into graphitic carbon using a Ni-based catalyst at 1300 °C for 3 h. The HR-TEM, XPS, XRD and Raman spectroscopy results confirmed the structural transformation from amorphous to graphitic nanostructure. The formation of graphitic layers is observed in the form of well-defined lattice fringes that are separated by an interplanar distance of 0.3367 nm around Ni. Graphitic carbon has a high graphitisation degree of 84.88%, which is slightly lower than that of commercial graphite (90.23%). This structural change enhances the electrical conductivity of powder carbon from 14.97 to 25.75 S/cm under 741 kPa of pressure. Producing graphitic and conductive carbon from renewable coconut coir can alleviate the environmental burden of coconut waste.

PRODUCTION OF A NEW ACTIVATED CARBON PREPARED FROM PALM FRONDS BY THERMAL ACTIVATION

A new activated carbon has been thermally produced from palm fronds, obtained from palm trees, cultivated widely in desert areas. A (21.75%) yield of Palm Fronds Activated Carbon (PFAC) was obtained from via a physical method. Characterization of PFAC was studied. Welldeveloped porosities verified by SEM were about 14% higher than that of commercial activated carbon. The nature of the product was identified by XRD. The activation process caused both the formation of graphite layers and the increase in bulk density, the graphite layers occurred due to breaking of chemical bonds and carbon burn-off through weak carbon –CO2 oxidation. The development of micro porosity will lead to promising applications for the removal of metal ions, that can be achieved through the surface functional groups of PFAC, detected by FTIR. PFAC is very effective for the adsorption of methylene blue dye from aqueous solutions with great removal (99.5%).

Atomic layer deposition of Pd nanoparticles on self-supported carbon-Ni/NiO-Pd nanofiber electrodes for electrochemical hydrogen and oxygen evolution reactions

The most critical challenge in hydrogen fuel production is to develop efficient, eco-friendly, low-cost electrocatalysts for water splitting. In this study, self-supported carbon nanofiber (CNF) electrodes decorated with nickel/nickel oxide (Ni/NiO) and palladium (Pd) nanoparticles (NPs) were prepared by combining electrospinning, peroxidation, and thermal carbonation with atomic layer deposition (ALD), and then employed for hydrogen evolution and oxygen evolution reactions (HER/OER). The best CNF-Ni/NiO-Pd electrode displayed the lowest overpotential (63 mV and 1.6 V at j = 10 mA cm−2), a remarkably small Tafel slope (72 and 272 mV dec−1), and consequent exchange current density (1.15 and 22.4 mA cm−2) during HER and OER, respectively. The high chemical stability and improved electrocatalytic performance of the prepared electrodes can be explained by CNF functionalization via Ni/NiO NP encapsulation, the formation of graphitic layers that cover and protect the Ni/NiO NPs from corrosion, and ALD of Pd NPs at the surface of the self-supported CNF-Ni/NiO electrodes.

Implication of Three Dimensional Framework Architecture of Graphitic Carbon Nanosheets for Improving Electrical Conductivity Under Mechanical Deformation

In this study, based on three-dimensional (3D) framework architecture built-up with two-dimensional (2D) graphitic carbon such as graphene, we have prepared a mechanically robust polymer composite without exhibiting notable deterioration of electrical conductivity under mechanical deformation. In constructing 3D framework comprising of graphitic carbons, two sophisticated methodologies, direct formation of graphitic layers on metal foam by chemical vapor deposition (CVD), and lay-up of reduced graphene oxide (rGO) nanosheets on metal foam have been performed, respectively, and their sustainability of conductive performance under mechanical deformation has been comparatively examined in terms of electrical conductivity change by cyclic mechanical stress. The CVD-synthesized graphene (CGr) framework-embedded PDMS composite, which means a PDMS composite containing 3D graphene framework grown by CVD process, exhibited electrical conductivity of ∼5 S/m at graphene content of 1.0 wt%, which was ∼5 orders of magnitude higher than that of 3D rGO framework-embedded PDMS composite containing comparable loading of rGO. When subjected to repetitive mechanical stress, it was found that the superior conductivity performance of CGr framework over rGO framework was well retained, presumably due to the higher perfectness of graphitic layers, which would impart much longer electron transfer to the framework architecture of graphitic carbon nanosheets.

Carbon Formation Mechanism of C2H2 in Ni-Based Catalysts Revealed by in Situ Electron Microscopy and Molecular Dynamics Simulations.

Understanding the carbon formation mechanism is critical for designing catalysts in various applications. Here, we report the observation of the carbon formation mechanism on Ni-based catalysts by environmental transmission electron microscopy (ETEM) over a wide temperature range in combination with molecular dynamics simulations and density functional theory calculations. In situ TEM observation performed in a C2H2/H2 atmosphere provides real-time evidence that Ni3C is an intermediate phase that decomposes to graphitic carbon and metallic Ni, leading to carbon formation. Mechanisms of acetylene decomposition and evolution of carbon atom configuration are revealed by molecular dynamics simulations, which corroborate the experimental results. The modification of MgO on NiO can effectively decrease the formation of graphitic layers and thus enhance the catalytic performance of NiO. This finding may provide an insight into the origin of the carbon deposition and aid in developing effective approaches to mitigate it.

Textural properties dependent supercapacitive performances of mesoporous graphitic carbon nitride

In this article, the tunable capacitance properties of mesoporous graphitic carbon nitride (MGCN) by tailoring its textural properties are reported. MGCN with different textural properties is synthesized by a hard template method using two different templates namely, SBA-15 and KIT-6. The formation of graphitic layers in the as-synthesized samples is confirmed by X-ray diffraction studies and successful replication of morphology and mesoporosity of the templates into the as-synthesized samples is confirmed by microscopic and nitrogen adsorption-desorption studies. The bulk and surface chemical composition of the as-synthesized samples are analyzed using Fourier transform infrared spectroscopy, CHNS/O analysis and X-ray photoelectron spectroscopic studies. The specific capacitance values of 322 and 245 F g−1 are obtained at a current density of 0.5 A g−1 for MGCN synthesized using SBA-15 and KIT-6, respectively. Although, MGCN synthesized using SBA-15 (MGCN-SBA-15) exhibits higher specific capacitance than MGCN synthesized using KIT-6 (MGCN-KIT-6), its rate performance is slightly lower than that of MGCN-KIT-6. The higher specific capacitance of MGCN-SBA-15 is attributed to its high surface area, more number of mesopores and large pore volume, whereas the presence of highly ordered mesopores in MGCN-KIT-6 results in higher rate performance. Both MGCN-SBA-15 and MGCN-KIT-6 electrodes demonstrate excellent cycling stability over 15,000 cycles. These results demonstrate that the supercapacitive performances of MGCN can be improved by tailoring its textural properties.

Pulsed Electric Current Sintered Cr<sub>2</sub>O<sub>3</sub>-rGO Composites

Chromium oxide is a promising material for applications where excellent corrosion resistance, high hardness, and high wear resistance are needed. However, its use is limited because of low fracture toughness. Improvement of fracture toughness of chromium oxide while maintaining its afore mentioned key properties is therefore of high interest. In this communication we study the possibility of increasing the toughness of pulsed electric current sintered (PECS) chromium oxide by the addition of graphene oxide (GO). The indentation fracture toughness was improved markedly with the addition of graphene oxide. Materials prepared by direct chemical homogenization had better fracture toughness. In composites with 10 vol.% GO piling of thin graphene oxide layers resulted in the formation of graphite layers between Cr2O3 and in carbide formation, which were observed to be the main reasons for the degradation of the mechanical properties. The distribution of graphene oxide was more homogeneous, when the GO amount was 0.1 vol.% and the formation of graphitic layers were avoided due to lesser amount of GO as well as ultrasonic treatment following the ball milling.

A multilayer innovative solution to improve the adhesion of nanocrystalline diamond coatings

Nano-crystalline diamond (NCD) films grown under negative biased substrates by chemical vapor deposition (CVD) are widely used as surface overlay coating onto cermet WC-Co cutting tools to get better performances. To improve the diamond adhesion to the cermet substrate, suitable multi-layer systems have been added. They are composed of a cobalt diffusion barrier close to the substrate (single and sequenced nitrides layers) coated with a nucleation extra layer to improve the nucleus density of diamond during CVD processing. For all systems, before and after diamond deposition, transmission electron microscopy (TEM) has been performed for a better understanding of the diffusion phenomena occurring at the interfaces and to evaluate the presence of graphitic species at the interface with the diamond. Innovative multilayer system dedicated to the regulation of cobalt diffusion coated with a bilayer system optimized for the carbon diffusion control, is shown as an efficient solution to significantly reduce the graphite layer formation at the interface with the diamond down to 10nm thick and to increase the adhesion of NCD diamond layer as scratch-tests confirm.

Effects of molybdenum dithiocarbamate and zinc dialkyl dithiophosphate additives on tribological behaviors of hydrogenated diamond-like carbon coatings

The tribological behaviors of hydrogenated diamond-like carbon (DLC) coatings under varied load conditions lubricated with polyalpha olefin (PAO), molybdenum dithiocarbamate (MoDTC) and zinc dialkyl dithiophosphate (ZDDP) additives were investigated in this paper. Hydrogenated DLC coatings were synthesized through the decomposition of acetylene by the ion source. The tribological performances were measured on a SRV tribometer. The morphologies and chemical structures of the DLC coatings were investigated by the scanning electron microscope (SEM), Raman spectrometer (Raman) and X-ray photoelectron spectroscope (XPS). It was shown that the low friction and high wear were achieved on the hydrogenated DLC coating under MoDTC lubrication, while low wear was found on the hydrogenated DLC coating lubricated by ZDDP. The primary reason was attributed to different tribofilms formed on the contact area and the formation of graphitic layer. Both factors working together leaded to quite different tribological behaviors.

Enhancement of nucleation of diamond films deposited on copper substrate by nickel modification layer

A Ni layer with a thickness of about 100 nm was sputtered on Cu substrates, followed by an ultrasonic seeding with nanodiamond suspension. High-quality diamond film with its crystalline grains close to thermal equilibrium shape was deposited on Cu substrates by hot-filament chemical vapor deposition (HF-CVD), and the sp2 carbon content was less than 5.56%. The nucleation and growth of diamond film were investigated by micro-Raman spectroscopy, scanning electron microscopy, and X-ray diffraction. The results show that the nucleation density of diamond on the Ni-modified Cu substrates is 10 times higher than that on blank Cu substrates. The enhancement mechanism of the nucleation kinetics by Ni modification layer results from two effects: namely, the nanometer rough Ni-modified surface shows an improved absorption of nanodiamond particles that act as starting points for the diamond nucleation during HF-CVD process; the strong catalytic effect of the Ni-modified surface causes the formation of graphite layer that acts as an intermediate to facilitate diamond nucleation quickly.

CoCrMo metal-on-metal hip replacements

After the rapid growth in the use of CoCrMo metal-on-metal hip replacements since the second generation was introduced circa 1990, metal-on-metal hip replacements have experienced a sharp decline in the last two years due to biocompatibility issues related to wear and corrosion products. Despite some excellent clinical results, the release of wear and corrosion debris and the adverse response of local tissues have been of great concern. There are many unknowns regarding how CoCrMo metal bearings interact with the human body. This perspective article is intended to outline some recent progresses in understanding wear and corrosion of metal-on-metal hip replacement both in vivo and in vitro. The materials, mechanical deformation, corrosion, wear-assisted corrosion, and wear products will be discussed. Possible adverse health effects caused by wear products will be briefly addressed, as well as some of the many open questions such as the detailed chemistry of corrosion, tribochemical reactions and the formation of graphitic layers. Nowadays we design almost routinely for high performance materials and lubricants for automobiles; humans are at least as important. It is worth remembering that a hip implant is often the difference between walking and leading a relatively normal life, and a wheelchair.

갈색 Type I 다이아몬드의 고압 열처리에 따른 표면 흑연화 생성 연구

We investigated color and graphite layer formation on the surface of Type I tinted brown diamonds exposed for 5 minutes under a high-pressure high-temperature (HPHT) condition in a stable graphite regime. We executed the HPHT processes of Process I, varying the temperature from 1600℃ to 2300℃ under 5.2 GPa pressure for 5 minutes, and Process II, varying the pressure from 4.2 to 5.7 GPa at 2150℃ for 5 minutes. Optical microscopy and micro-Raman spectroscopy were used to check the microstructure and surface layer phase evolution. For Process I, we observed a color change to vivid yellow and greenish yellow and the growth of a graphite layer as the temperature increased. For Process II, the graphite layer thickness increased as the pressure decreased. We also confirmed by 531 nm micro-Raman spectroscopy that all diamonds showed a 1440 cm ?1 characteristic peak, which remained even after HPHT annealing. The results implied that HPHT-treated colored diamonds can be distinguished from natural stones by checking for the existence of the 1440 cm ?1 peak with 531 nm micro-Raman spectroscopy.

Simple fabrication of a Fe2O3/carbon composite for use in a high-performance lithium ion battery

A simple approach was developed for the fabrication of a Fe2O3/carbon composite by impregnating activated carbon with a ferric nitrate solution and calcinating it. The composite contains graphitic layers and 10wt.% Fe2O3 particles of 20–50nm in diameter. The composite has a high specific surface area of ∼828m2g−1 and when used as the anode in a lithium ion battery (LIB), it showed a reversible capacity of 623mAhg−1 for the first 100 cycles at 50mAg−1. A discharge capacity higher than 450mAhg−1 at 1000mAg−1 was recorded in rate performance testing. This highly improved reversible capacity and rate performance is attributed to the combination of (i) the formation of graphitic layers in the composite, which possibly improves the matrix electrical conductivity, (ii) the interconnected porous channels whose diameters ranges from the macro- to meso- pore, which increases lithium-ion mobility, and (iii) the Fe2O3 nanoparticles that facilitate the transport of electrons and shorten the distance for Li+ diffusion. This study provides a cost-effective, highly efficient means to fabricate materials which combine conducting carbon with nanoparticles of metal or metal oxide for the development of a high-performance LIB.

Structural Characterization of Selected Indian Coals by X-ray Diffraction and Spectroscopic Techniques

The structural parameters of three Indian coals were determined by X-ray diffraction, Raman, UV-Vis-NIR, FTIR spectroscopy and SEM-EDS. This study reveals that the coals contain crystalline carbon of turbo- stratic structure with some amount of amorphous carbon. The average lateral sizes (La), stacking heights (Lc) and interlayer spacing (d002) of the crystallite structures calculated from the X-ray intensities range from 28.15-38.43 A°, 22.64-20.16A° and 3.52-3.34 A°, respectively which is higher than that of pure graphite, suggesting a low degree of crystalline order in the studied sample. The decrease in La with rank shows that the carbon in coal is nano crystalline in structure. Raman spectroscopic study confirms the presence of multi layer formation of graphite layer. The defect band at 1355 cm-1 is due to benzene or condensed benzene rings present in amorphous carbon. The FTIR spectra of the coals show the presence of stretching vibrations of -OH bonds, aliphatic -CH, -CH2 and -CH3 absorptions, C = C and -CH of aromatic structure. The C-H bending frequencies have higher intensity than the C-H stretching band. This is due to the intense broad absorption produced in this region by graphite components. A strong linear relationship exists between the coal structural parameters (fa,d002,Lc) and the elemental carbon and volatile contents of the coal which reflects the dependency of the coals structure on their ranks. The SEM image shows the presence of layered structure on the surface. The EDS analysis confirms the presence of Carbon and Oxygen on the surface. The absorption maximum of benzene-oxygen system was found between 235-270 nm. The weak band at the 680 nm is attributed to the ∏-∏* electronic transitions of the polynuclear aromatic hydrocarbons.

Growth mechanism of multilayer-graphene-capped, vertically aligned multiwalled carbon nanotube arrays

The authors describe a rigorous investigation of the growth mechanism of composite structures consisting of graphene multilayers supported by vertically aligned multiwalled carbon nanotubes (VA-MWCNTs). The synthesis was performed via chemical vapor deposition with ethanol as a carbon source and iron films ranging in thickness from 1 to 9 nm as the catalyst. The morphology of grown films was investigated using scanning electron microscopy and transmission electron microscopy (TEM), and the crystallinity was studied using TEM and Raman spectroscopy. Thicker Fe films (8 or 9 nm) yielded composite structures, thin Fe films (1 to 4 nm) produced pure VA-MWCNTs, and Fe layers between 5 and 7 nm produced an intermediate structure composed of bundles of VA-MWCNTs fused together at their tips. The authors present growth mechanisms for all three structures. The authors attribute the change from VA-MWCNT to intermediate/composite with higher Fe film thicknesses to the formation of graphitic layers at the initial growth stage.

Silver Nanoparticles and Graphitic Carbon Through Thermal Decomposition of a Silver/Acetylenedicarboxylic Salt

Spherically shaped silver nanoparticles embedded in a carbon matrix were synthesized by thermal decomposition of a Ag(I)/acetylenedicarboxylic acid salt. The silver nanoparticles, which are formed either by pyrolysis at 300 °C in an autoclave or thermolysis in xylene suspension at reflux temperature, are acting catalytically for the formation of graphite layers. Both reactions proceed through in situ reduction of the silver cations and polymerization of the central acetylene triple bonds and the exact temperature of the reaction can be monitored through DTA analysis. Interestingly, the thermal decomposition of this silver salt in xylene partly leads to a minor fraction of quasicrystalline silver, as established by HR-TEM analysis. The graphitic layers covering the silver nanoparticles are clearly seen in HR-TEM images and, furthermore, established by the presence of sp2carbon at the Raman spectrum of both samples.

Morphological, Structural, and Chemical Effects in Response of Novel Carbide Derived Carbon Sensor to NH3, N2O, and Air

The response of two carbide derived carbons (CDCs) films to NH(3), N(2)O, and room air is investigated by four probe resistance at room temperature and pressures up to 760 Torr. The two CDC films were synthesized at 600 (CDC-600) and 1000 degrees C (CDC-1000) to vary the carbon morphology from completely amorphous to more ordered, and determine the role of structure, surface area, and porosity on sensor response. Sensor response time followed kinetic diameter and indicated a more ordered carbon structure slowed response due to increased tortuosity caused by the formation of graphitic layers at the particle fringe. Steady state sensor response was greater for the less-ordered material, despite its decreased surface area, decreased micropore volume, and less favorable surface chemistry, suggesting carbon structure is a stronger predictor of sensor response than surface chemistry. The lack of correlation between adsorption of the probe gases and sensor response suggests chemical interaction (charge transfer) drive sensor response within the material; N(2)O response, in particular, did not follow simple adsorption behavior. Based on Raman and FTIR characterization, carbon morphology (disorder) appeared to be the determining factor in overall sensor response, likely due to increased charge transfer between gases and carbon defects of amorphous or disordered regions. The response of the amorphous CDC-600 film to NH(3) was 45% without prior oxidation, showing amorphous CDCs have promise as chemical sensors without additional pretreatment common to other carbon sensors.