Basal Plane Of Graphite Research Articles

Growth mechanisms of vermicular graphite in cast iron

To steadily produce high-quality vermicular graphite cast iron (VGI), it is essential to have a deep understanding of the growth mechanism of vermicular graphite. The morphology and microstructure of graphite in VGI were studied using various techniques, including both experimental and theoretical methods. An abnormal graphite structure with an anomalous layer distance of 6.60 Å was observed by transmission electron microscopy (TEM) imaging, which is approximately two times larger than the normal structure (3.40 Å). The theoretical simulations of possible trace elements added (approximately 34 different elements) to the graphite basal planes were studied and analyzed individually to understand the observed phenomenon and their effects on graphite growth. The theoretical calculations (6.56 Å) show good agreement with the experimental results (6.60 Å), which proves that the lattice anomaly is caused by Mg. The abnormal graphite was believed to be the remains of the transition state during the growth of graphite. Based on the investigation, a mechanism is proposed to describe the influence of Mg during the growth process of vermicular graphite.

Anisotropic friction behavior of aligned and oriented graphite flakes/copper composite

Graphite flakes as lubricant are widely used for friction materials, but little is known about the friction behavior at sliding surface oriented at some angle to the basal plane of graphite. In this paper, oriented graphite flakes/copper (volume ratio of 7/3) composite was prepared by vacuum hot-pressing sintering. The friction coefficient evolution of the composite with the dihedral angle (φ) between sliding surface and graphite basal plane was estimated based on the numerical solutions of the anisotropic stiffness at the contact plane, and measured experimentally. Theoretical estimates suggested an increase of the friction coefficient induced by adhesion with raising the dihedral angle, and a decreased one caused by ploughing. A pronounced trend of the former happened with the dihedral angles of more than 75°, while for the latter it was conspicuous with the dihedral angles of less than 15°. Through ball-on-disk friction experiments, the friction coefficients were fairly low with the dihedral angles from 30° to 60°, which was consistent with the theoretical prediction, and a monotonous decrease of the wear rate was exhibited with increasing the dihedral angle due to increased shear modulus and hardness. This anisotropic friction behavior may provide new ideas for the designs of friction materials.

Effects of crystallite stacking on adsorption of ethylene on graphitized thermal carbon black

Adsorption of gases on graphitized thermal carbon black (GTCB) is frequently modelled as a homogeneous planar graphite with infinite extent in the directions parallel to the surface. TEM micrographs of GTCB, however, show polyhedral crystallites with a finite basal plane on their faces. The stacking of these crystallites results in wedge shaped spaces in which the interaction energy with an adsorbate is enhanced by overlapping potentials from the graphitic basal planes of adjacent crystallites in the vicinity of their junction. This enhancement facilitates clustering of molecules and the subsequent formation of a condensate, in addition to molecular layering on the basal planes. As a result, contributions to the adsorbed density observed experimentally originate from both molecules on the basal graphitic planes, and those at the junction of the planes. The former is favoured entropically because of the large area of the basal planes, while the latter is favoured energetically. We have tested this new wedge model by comparison with the experimental data of Menaucourt, Thomy and Duval [Le Journal de Physique, 1977, 38, C4-195] for ethylene adsorbed on exfoliated graphite at three temperatures and show that the simulation results describe the data better than those based on a homogeneous planar graphite model.

Modified-edge-support heat treatment method of polyimide for crystalline, large-area, and self-standing ultrathin graphite films

Using a newly developed edge-support heat treatment method of polyimide, self-standing graphite thin films (GTFs) with a frame were prepared. The graphite basal plane in the GTF was oriented in the direction of the film surface, resulting in GTFs with high quality, large area, and a uniform thickness of 50–120 nm. The thickness distribution (3σ) with an area of 25 mm × 25 mm and a thickness of 54 nm sample was 5.17 nm (measurement area 7.8 mm × 10.4 mm). The electric conductivity of a similarly prepared sample was 1.81 × 104 S/cm. The Young's modulus and ultimate tensile strength of a 60-nm-thick GTF were 1.02 × 102 and 5.34 GPa, respectively. Approximately 50 nm thick GTF samples were thinned by reactive ion etching using oxygen to fabricate a thickness between 10 and 20 nm. A film with an area of 10 mm × 10 mm and thickness of 16.7 nm exhibited a 3σ value of 1.80 nm which means that the thickness difference corresponds to 5 layers of graphite. The conductivity of a 16.2-nm-thick GTF was 1.79 × 104 S/cm. These results indicate that the etching proceeded uniformly. The proposed top-down method is an industrially superior method that overcomes the drawbacks of conventional bottom-up methods.

Room-temperature ferromagnetism in oxidized-graphenic nanoplatelets induced by topographic defects

This work reports on room-temperature ferromagnetism of pyrolytic oxidized-graphene nanoplatelets obtained from bamboo pyroligneous acid by varying the density of extended defects. Topographic defects, created during the fabrication process, arise from a natural formation of clusters; such clusters drastically distort the graphitic basal plane, giving rise to abrupt surface curvatures. Topographic defects were found to be sources of the magnetic signal, as evidenced by bulk magnetization and magnetic force microscopy measurements. Increased defect density, tuned by carbonization temperature, results in enhanced magnetization.

Improvement of mechanical and tribological performances of carbon nanostructure films by cryogenic treatment

The work presents data on mechanical properties, tribological performances and microstructure changes of hydrogenated amorphous, fullerene-like and graphite-like carbon films (a-C:H, FL-C:H and GL-C:H) after post cryogenic treatment. It is shown that post cryogenic treatment more effectively improves the mechanical and tribological performances of carbon nanostructure films as compared to the a-C:H films. By the combination of Raman and TEM studies, the performance improvement can be attributed to the introduction and enhancement of defects such as pentatomic and heptatomic carbon rings in their carbon structure matrices, which facilitate cross-linking between the graphitic basal planes via sp3-hybridized carbons. The results provide an important reference for achieving solid lubrication under the cryogenic environment that is both reliable and presents longevity.

A reactive molecular dynamics study of hyperthermal atomic oxygen erosion mechanisms for graphene sheets

Carbon-based composite materials are widely used in the aerospace field due to their light weight and excellent physical/chemical properties. The mechanisms of the erosion process, e.g., surface catalysis and ablation, during the impact of oxygen atoms, however, remain unclear. In this study, the surface catalysis and ablation behavior during the erosion process of hyperthermal atomic oxygens were achieved through the molecular dynamics method with the reactive force field potential. The concomitant impacts of energy flux density of energetic oxygen atoms, the presence of multiple layers beneath the graphene sheet, and the morphology of graphite surfaces, i.e., graphite basal plane, armchair (AC) edge surface, and zigzag edge surface, respectively, were discussed. The results show that the adsorption of oxygen atoms dominates at the beginning by generating O2 molecules, suggesting the importance of surface catalytic for any ablation study. A unique “layer-by-layer” ablation phenomenon by hyperthermal atomic oxygen is observed for multi-layered graphite slab, and the ablation rate reduces as the number of graphene layers increases. The morphology/structure of the surface shows significant effects on the ablation rate, with AC surfaces showing the largest etching rate and the basal one showing the lowest. The low binding energies of the AC edge are responsible for the difficulty in the formation of stable functional group structures to resist the etching of high-enthalpy oxygen atoms. Such revelation of the detailed surface catalysis and ablation mechanism at the atomistic scale provides insight into design of future materials for the augmentation of the thermal protection effect.

Adsorption of Pentane and Hexane Thin Films on the Surface of Graphite(0001)

The thermodynamics of adsorption were obtained for n-pentane and n-hexane adsorbed on the basal plane of graphite in the temperature ranges 190–235 and 230–280 K, respectively, using high-resolutio...

Anchoring silicon on the basal plane of graphite via a three-phase heterostructure for highly reversible lithium storage

Interfacial stability is crucial to electrochemical performance, especially the cycle life and Coulombic efficiency (CE), of anodes for lithium-ion batteries (LIBs). However, stabilization of silicon (Si) nanoparticles on the basal plane of graphite nanosheets (GNs) and their effect on both cycling performance and CE have been lacking. Herein, deposition of Si nanoparticles on the basal plane of GNs is achieved by magnesiothermic reduction of mixture of silica (SiO2) nanoparticles and GNs. When the molar ratio of SiO2 to GNs in the reactant is above 0.33, Si nanoparticle and GN form an interfacial 3C-SiC layer. Both Si and interfacial 3C-SiC are oriented in their [111] crystallographic direction in parallel with [002] direction of GNs. The energetics of this three-phase heterostructure, (111) [11¯0]Si//(111) [11¯0]3C-SiC//(002) [110]GNs, is calculated using density functional theory (DFT), which indicates strong bonding at two interfaces of Si(111)/3C-SiC(111) and 3C-SiC(111)/GNs(001). The composite anode with a three-phase heterostructure demonstrates a high initial CE of 97.8% and a rapid increase of the CE to 99.4% after only five cycles with a capacity retention of 82.9% after 100 cycles, owing to the strong bonding between Si and GNs via the interfacial 3C-SiC layer, which maintains electrical connection despite the volume changes of Si during cycling.

Superlubricity between Graphite Layers in Ultrahigh Vacuum

Graphite has been conventionally believed to exhibit an inferior lubricating performance with significantly larger friction coefficient and wear rate in a vacuum environment than in ambient air. Dangling bonds at the edge planes of graphite, accounting for the high friction in inert atmosphere are saturated by chemisorbed vapor molecules in air, which contributes to low surface adhesion and low friction. However, there is still a lack of direct experimental evidence whether basal planes of graphite excluding the negative effects of edges or dangling bonds shows intrinsic lubricity when sliding under ultrahigh vacuum (UHV) conditions. By the interlayer friction measurement enabled by graphite flake-wrapped atomic force microscope tips in UHV, we show a record-low friction coefficient of 4 × 10-5 (slope of friction vs normal force curve) when sliding between graphite layers, which is much lower than that in ambient air. This discrepancy manifests the intrinsic sliding frictional behavior between the graphite basal planes when the tribo-materials and experimental conditions are well-designed and strictly controlled. In addition, the temperature dependence of the kinetic friction between the graphite layers has been investigated under UHV conditions over the temperature range of 125-448 K, which is consistent with the thermally activated process.

Interfacial effect between graphite and iron substrate on basal plane orientation and lubricity of graphite

The role of graphite/substrate interface in low-friction behavior of graphite was investigated. Iron and graphite powder mixtures were plastically deformed in either Ar–H2 or air atmospheres to obtain bare iron or iron oxide surface. Then, graphite particles adhered to and formed interfaces with surfaces. Friction force microscopy revealed that friction on particle surface milled in Ar–H2 atmosphere was obviously higher. X-ray absorption near-edge structure and transmission electron microscopy revealed that although the basal plane of graphite oriented along the oxidized surface, it did not occur along the bare iron surface, which explains the difference in lubricity on each surface.

Molecular dynamics simulation study on the wetting behavior of liquid iron and graphite

Understanding the wetting behavior of the molten iron and graphite is of great significance to guide the gas permeability of the blast furnace. This paper used the molecular dynamics simulation method to analyze the wetting behavior of molten iron on the graphite substrate at the atomic scale. In this paper, it was found that high temperatures can help reduce the time it takes for the wetting process to reach equilibrium. And the graphite basal plane can promote the melting of the iron block at a temperature lower than the melting point. In addition, the graphite basal plane showed good hydrophilicity to the molten iron, and the contact angle can reach 55.65° at 2000 K. The graphite prism plane is hydrophobic to the molten iron. And the results of molecular dynamics simulation showed that high temperature can improve the hydrophilicity of graphite basal plane and reduce the hydrophobicity of graphite prism plane. Therefore, adjusting the temperature and the contact surface between graphite and molten iron can provide theoretical guidance for improving the gas and liquid permeability of blast furnace.

The preparation of graphite/silicon@carbon composites for lithium-ion batteries through molten salts electrolysis

High-specific-capacity materials are crucial for the high-energy-density lithium-ion secondary batteries as the automakers and customers are both eager to extend the cruising range of electric vehicles. The current commercial silicon/carbon composites are based on the mechanical mixture of silicon and graphite, but this weak combination is not suitable for the higher-capacity materials. Here, low-cost raw materials are used for the preparation of a graphite/silicon@carbon composite negative electrode material, which synergizes ball milling, molten salts electrolysis and carbon coating. Silica is in situ electrochemically reduced to silicon on the flaky graphite serving as the conducting substrate during the electrolysis process. It is found that ball milling increases the active sites on the basal plane of graphite, which is beneficial for the nucleation and growth of the silicon, and enhances the bonding of silicon particles and graphite. As for the electrochemical results of coin-type cells, this graphite/silicon@carbon composite material exhibits a better cycle performance than the commercial Si/C 650 silicon-based composite material.

Direct-space-self-consistent-phonon treatment of monolayer structures and dynamics.

Computations, which would have been intractable just a few years ago, are now possible on desktop workstations. Such is the case for the application of the Self-Consistent-Phonon (SCP) approximation to large monolayer clusters on structured surfaces, combining a SCP approach to the system dynamics with a random walk approach to finding the optimum positions of the adsorbed atoms. This combination of techniques enables the investigation of the stability, structure, and dynamics of incommensurate adsorbed monolayers at low temperatures. We refer to this approach as the Direct-Space-Self-Consistent-Phonon framework. We present the application of this framework to the study of rare-gas and molecular hydrogen adsorbates on the graphite basal-plane surface and (for xenon) the Pt(111) surface. The largest cluster size consists of 4096 particles, a system that is large enough to examine incommensurate phases without significant adverse boundary effects. The existence of "pseudo-gaps" in the phonon spectrum of nearly commensurate monolayers is demonstrated, and the implication of such "pseudo-gaps" for the determination of the location of any commensurate ↔ incommensurate phase transition is explored. The stability of striped incommensurate structures vs hexagonal incommensurate structures is examined. The inherent difficulties of using this approach for the highly quantum monolayer solids is shown to generate some particular problems. Nevertheless, we demonstrate that this approach to the stability, structure, and dynamics of quantum monolayer solids is a very useful tool in the theorist's arsenal. By implication, this approach should also be useful in the study of adsorption on graphene and carbon nanotubes at low temperatures.

In situ measurement of elastic and total strains during ambient and high temperature deformation of a polygranular graphite

In situ neutron diffraction and synchrotron X-ray diffraction, combined with image correlation analysis of 2D optical and 3D X-ray tomography datasets, have been used to investigate the relationship between elastic lattice strain and total strain during deformation of Gilsocarbon (IM1-24) polygranular nuclear grade graphite. The specimens were flat-end Brazilian discs under diametral loading, such that a compressive-tensile biaxial stress state was developed in the central region. The X-ray study was at ambient temperature, and the neutron diffraction was conducted at temperatures from ambient to 850 °C. When under compression, there is a temperature-insensitive linear relationship between the total strain and the lattice strain that is measured perpendicular to the graphite basal planes. However, when under tensile stress, the total strain and elastic strain relationship is temperature sensitive: below 600 °C, the lattice tensile strain saturates with increasing total tensile strain; above 600 °C, significantly higher tensile lattice strains are sustained. The saturation in tensile lattice strain is attributed to microcracking in the graphite microstructure. Improved resistance to microcracking and damage tolerance at elevated temperature explains the increase in tensile strength of polygranular graphite.

In situ atomic force microscopy: the case study of graphite immersed in aqueous NaOH electrolyte

In situ atomic force microscopy (AFM) measures, with the scanner head immersed inside a liquid (namely an electrolyte), are—generally speaking—not easy to be acquired in real time, i.e., during electrochemical processes, the immersion of a massive and wide system (with respect to the electrochemical cell mean radius) can significantly perturb the electrolyte and the I/V profile of the electrochemical characterization (CV). Despite this fact, the information that can be obtained from an electrode morphological inspection is very precious, and the coupling between an AFM and an electrochemical cell is in any case successful. In this work, we discuss the surface morphological evolution of a graphite electrode when immersed inside an aqueous NaOH electrolyte. 1.0 M sodium hydroxide added inside electrochemical baths was shown to promote the intercalation of ions between the stratified graphite structure or graphene layers. Possible consequences of diluted NaOH electrolyte on the quality of the graphite basal plane have been never considered in detail yet. By means of an in situ AFM, we show the effects of CVs on the surface morphology of the graphite basal plane. Our result shows that a 1.0 M NaOH solution, generally used for promoting intercalation, changes the electrode surface quality as a consequence of a partial carbon corrosion.

Why is Graphite Spherical in Ductile Iron? A Study of Elemental Distributions at Interfaces in Ductile Iron Using Atom Probe Tomography and Transmission Electron Microscopy

Atom probe tomography (APT) with high sensitivity and spatial resolution was applied to study the elemental distributions in spheroidal graphite in ductile iron. A specimen of quenched ductile iron with some graphite nodules in direct contact with liquid phase was used in this study to understand the role of alloying elements in spheroidal graphite formation. Compositional analysis was performed at the graphite/matrix interface and graphite/nuclei interface using APT and EDX (energy-dispersive X-ray). Distributions of various alloying elements at interfaces were obtained. Compositional gradients were observed at both the graphite/liquid interface and the graphite/nuclei interface. The spheroidal graphite nuclei were differentiated as the complex compound made of oxide, nitride and sulfide. The graphite–nuclei interface was shown to be semi-coherent/incoherent using the transmission electron microscopy, with a high density of crystallographic defects and high curvatures in the graphite basal planes growing off the nuclei. Intercalation of large nodulizing elements within and in between the graphite basal planes may account for the spherical morphology of the graphite in ductile irons.

Studies on the sonochemical polymorphism of Sb2O3 on activated graphite for the electrochemical determination of imipramine.

This work reports the simultaneous sonochemical activation of graphite and sonohydrolysis of antimony chloride (SbCl3) in the alkaline medium. The experiments conducted by bath sonicator operated at 37kHz of frequency and a maximum power of 150W. The simple sonohydrolysis of SbCl3 alone produced an orthorhombic phase of Sb2O3, whereas, it produced mixed phases of cubic and orthorhombic Sb2O3 when introduced with graphite. Herein, the activated graphite (aGR) provides the best support to the growth of cubic phase. This cubic Sb2O3 is grown only on the graphite basal planes, which confirmed by scanning electron microscope. Moreover, the phase changes have identified by the X-ray diffraction, Raman and X-ray photoelectron analysis. The prepared aGR-Sb2O3 composite has applied to the electroanalytical studies of anti-depressant drug imipramine (IMP). The results showed that aGR-Sb2O3 revealed better activity than Sb2O3; the reasons are discussed comprehensively. Furthermore, aGR-Sb2O3 exhibited comparable analytical results for the determination of IMP.

Bifunctional Oxygen Electrodes with Highly Step-Enriched Surface of Fe–Nx Containing Carbonaceous Thin Film

Carbonaceous air cathodes in zinc-air batteries have attracted attention due to their high electron conductivity and low cost; however, the increment in the catalytic activity for the oxygen reduction and evolution in addition to the durability are demanded. Based on a fundamental study about the substantial effect of a three-dimensional active site at a step on a highly-oriented pyrolytic graphite basal plane on the electrode reactions, we attempted to extend the idea to a graphitic carbon fiber surface as a more applied form for the air electrode. Coating of a carbonaceous thin film derived from iron phthalocyanine on finely-etched graphitic carbon fibers produced a highly step-enriched surface demonstrated by the field-emission scanning electron microscope image and Raman spectra with a developed defect peak. The iron K-edge X-ray absorption fine structure showed a step-oriented iron atom coordinated by two nitrogen atoms and a basal plane oriented iron atom coordinated by 4 nitrogen atoms. The step-enrichment enhanced the oxygen reduction and evolution; in particular, the low overpotential phenomenon observed for the fundamental graphite system was reproduced in the carbon fiber paper, both in a half cell and a full cell of the zinc-air battery, which also showed a favorable cycling performance.

Nanoscopic Combination of Edge and Flat Planes in the Active Site for Oxygen Reduction and Evolution

An iron‐containing carbonaceous flat plane was enriched with edges by substrate fine etching and metal oxide loading, resulting in substantial enhancement of the catalytic activity for the oxygen reduction and evolution, which was fundamentally shown using the highly oriented pyrolytic graphite basal plane as the substrate. The evolution close to the standard electrode potential was elucidated by a mechanism involving the nanoscopic edge‐flat plane combination.