Graphite Crystallite Size Research Articles

Phase and stress evolution in diamond microparticles during diamond-coated wire sawing of Si ingots

Diamond microparticles undergo changes to their structure and stress state during diamond-coated wire sawing of Si ingots. This phenomenon is revealed using confocal, micro-Raman spectroscopy of diamond microparticles attached to wires which perform the sawing action. Post-wafer-sawed diamonds show the appearance of D (1350 cm−1) and G (1597 cm−1) bands of graphite besides the characteristic diamond T2g band at 1332 cm−1. The graphitic phase extends inside the diamond to a depth of ~ 14 μm. The ratio of the intensities of D and G bands allows an estimate of the graphitic crystallite size. The grain size varies from 10 nm close to the surface to 53 nm near the graphite/diamond interface. On other diamonds, blue shifts in the T2g peak position are observed indicating the presence of compressive stress. The peak shifts (up to 3.6 cm−1) are anisotropic, i.e., along the direction of wire cutting, and are estimated to be 2.9 GPa. It is proposed that the cumulative effect of compressive stresses over multiple cutting events during the sawing process can lead to local graphitization of diamond particles, thus contributing to loss in cutting efficiency.

Effect of heat treatment temperature on the microstructure and properties of polyimide-based carbon fibers

Polyimide(PI)-based carbon fibers with different properties were prepared by carbonization of PI fibers at 800 °C, followed by heat treatment from 800 to 2800 °C. The effect of heat treatment temperature (HTT) on elemental composition, surface morphology, mechanical properties, and the thermal and electrical conductivities of PI-based carbon fibers were investigated by elemental analysis, SEM, HRTEM, Raman spectroscopy, mechanical testing, and electrical and thermal conductivity measurements. Results showed that as a result of HTT the carbon content increased from 78.97% to 99.72%, the tensile strength exhibited a maximum of 924.4 MPa, and the degree of graphitization and the size of graphite crystallites were both increased. Distinct reductions in strain-to-failure and electrical resistivity were observed with increasing HTT. The thermal conductivity can reach 228.4 W m−1 K−1 after heat treatment at 2800 °C. PI fiber may be a good precursor for carbon fibers with a high thermal conductivity.

Iodine Treatment of Lignin–Cellulose Acetate Electrospun Fibers: Enhancement of Green Fiber Carbonization

Pure biopolymer-based electrospun precursor carbon fibers are fabricated using an abundant and inexpensive biopolymer lignin blended with renewable resource-based cellulose acetate (CA). Iodine treatment on the fabricated green fiber was successfully performed in order to enhance the carbonization process as well as the retention of fiber morphology. The absorption mechanism of iodine by lignin and cellulose acetate and their derived electrospun green fibers has been investigated by means of thermal behavior and morphological retention. It was found that iodine treatment plays a vital role in altering the graphitization behavior as well as morphology retention during the carbonization process. With the help of iodine treatment, the green precursor fibers were successfully converted into thin carbon fibers, and scanning electron microscopy analysis confirmed the retention of fibrous structures with diameters around 250 nm. Raman spectroscopy revealed that although the overall level of graphitization was lower compared to polyacrylonitrile-based fibers, the graphitic crystallite size was larger in the produced carbon fibers. The produced pure biopolymer fibers and iodine treatments show promise for the production of green and cost-reduced carbon fibers.

Nanoimprinted Carbon Structures As High Performance Lithium Ion Battery Anodes

We demonstrated the synthesis of carbon thin film with ordered nanostructure via nanoimprint lithography starting from thermal plastic polymer polyvinylpyrrolidone (PVP). After the pattern is completely transferred onto PVP thin film during the nanoimprinting process, a three-step thermal treatment is performed to convert the polymer into patterned carbon thin film. Feature size of the pattern ranges between 250 nm up to 2 um with various shapes including 1D line, 2D hole and pillar. Characterized with Raman spectroscopy, the carbon thin film shows a high degree of disorder with a small in-plane graphitic crystallite size of about 1.346 nm calculated using the peak intensity of D band and G band of sp2carbon. Those patterned carbon thin film exhibits good electrical conductivity. When used as anode of lithium ion battery, it shows an enhanced cyclic performance compared to those unpatterned carbon thin films and also graphite. Further study with Electrochemical Strain Microscope (ESM) helps to understand the enhanced Li ion storage capacity locally on the nanoscale.Figure 1. (A) Atomic force microscopy topography scan of imprinted carbon thin film, (B) cyclic charge/discharge performance of imprinted and unpatterned carbon.

Edge‐functionalized graphene nanoplatelets with polystyrene by atom transfer radical polymerization: grafting through carboxyl groups

AbstractThe surface modifier 3‐((4‐hydroxybutoxy)dimethylsilyl)propyl methacrylate (CD), which contains a double bond and a hydroxyl group, was synthesized through a coupling reaction of 1,4‐butanediol and (3‐methacryloxypropyl)dimethylchlorosilane. Subsequently, graphene oxide (GO) was functionalized with different amounts of CD from its edge carboxyl groups. Then, grafting through atom transfer radical polymerization of styrene in the presence of various amounts of the edge‐functionalized GO was carried out to evaluate the effect of graphene loading along with graft density. A peak at 3.8 ppm in the 1H NMR spectrum of CD associated with the methylene adjacent to the Si–O group indicated a successful coupling reaction. Attachment of CD on the edges of GO was evaluated using X‐ray photoelectron and Fourier transform infrared spectroscopies. Expansion of GO interlayer spacing by functionalization was evaluated using X‐ray diffraction. The ordered and disordered crystal structure of carbon was studied using Raman spectroscopy. The close ID/IG values for GO and various kinds of functionalized graphenes show the preserved graphitic crystallite size. Relaxation behaviour of polystyrene chains in the presence of graphene nanoplatelets and also the effect of graft content on chain confinement were studied using differential scanning calorimetry. High‐graft‐density nanocomposites show higher glass transition temperatures. Morphology of graphene nanoplatelets was studied using scanning electron and transmission electron microscopies. The flat and smooth morphology of graphene nanoplatelets is disturbed and also the transparency of the nanoplatelets decreases during the oxidation and functionalization processes. © 2014 Society of Chemical Industry

Growth and oxidation of graphitic crystallites in soot particles within a laminar diffusion flame

The growth and oxidation behaviors of graphitic crystallites in soot particles within a laminar co-flow propane diffusion flame were investigated experimentally. Soot was sampled along the flame axis and collected on a quartz–fiber filter. The soot nanostructure, i.e., the graphitic crystallite size and the amorphous carbon content in the soot particles, was characterized by Raman spectroscopy. The spatial distributions of the fuel, PAHs, soot and OH measured by laser diagnostic techniques are presented to examine the effect of the flame structure on the soot nanostructure. The Raman spectra of the soot show that both the graphitic crystallite size and the amorphous carbon content in the soot particles increase during the soot growth process. In addition, the crystallite size and the amorphous carbon content simultaneously decrease during the soot oxidation process by OH. HRTEM images of soot particles support that these findings obtained from the Raman spectroscopy are reasonable. The influences of the soot formation and oxidation history within the flame on the soot nanostructure are validated.

The use of a nanocellulose-reinforced polyacrylonitrile precursor for the production of carbon fibers

Polyacrylonitrile (PAN) reinforced by nanocellulose (NC) in different concentrations was used as a precursor for carbon fiber production. The NC was prepared by mechanical and chemical treatments. For control of the spinning process, the rheological properties of PAN–NC solutions were investigated. The strong polar interaction between the nitrile groups of PAN and the hydroxyl groups of NC resulted in the formation of an interconnected structure, as shown by the rheological properties. In addition, the NC was an effective reinforcement for PAN precursor because of its high aspect ratio and good interfacial adhesion to the PAN matrix. The spun PAN–NC fibers, containing NC in different concentrations, were oxidatively stabilized at 280 °C in air and carbonized at 1000 °C in nitrogen. Using Raman spectroscopy the Tuinstra–Koenig formula was used to estimate the graphite crystallite size of the resulting carbon fiber and it was found to have been increased by incorporation of the NC. The possibility of a decrease in energy consumption by lowering the carbonization temperature as a result of incorporation of NC was confirmed.

Influence of Combustion Conditions on Hydrophilic Properties and Microstructure of Flame Soot

Previous studies suggest that structure and reactivity of soot depend on combustion conditions like the fuel/oxygen ratio and nature of fuels. However, the essence of how combustion conditions affect physical and chemical properties of soot is still an open question. In this study, soot samples were prepared by combusting toluene, n-hexane, and decane under controlled conditions, and their hydrophilic properties, morphology, microstructure, content of volatile organic compounds, and functional groups were characterized. The hydrophilicity of n-hexane and decane flame soot increased with decreasing fuel/oxygen ratio, while it almost did not change for toluene flame soot. Fuel/oxygen ratio had little effect on the morphology of aggregates and the graphite crystallite size. The primary particle size and the content of volatile organic compounds on soot decreased with decreasing fuel/oxygen ratio. Less hydrophobic groups (C-H) and more hydrophilic groups (C═O) were observed on lean n-hexane and decane flame soot than that on the corresponding rich flame soot. Volatile organic compounds had little effect on the hydrophilicity of soot while the hydrophilicity correlated linearly with the ratio of C═O content to C-H content. The hydrophilic functional groups were found to be mainly located at graphene layer edges and on surface graphene layers in soot.

Surface modification of hollow carbon fibres using plasma treatment

A plasma treatment is developed to modify the surfaces of micrometre sized hollow carbon fibres. After oxidisation and activation, hollow carbon fibres exhibit pores on the outer surfaces. With a further treatment in a mixed plasma of CH4–H2 at 3000 W for 2 h, many cavities of about 3–5 μm in size are formed by plasma etching on the outer and inner surfaces. Nanoscale whiskers are uniformly distributed inside the cavities by plasma deposition. The ID/IG Raman ratio increases from 2·09 to 5·93 after the plasma treatment, suggesting that graphite crystallite size has been reduced from 2·11 to 0·74 nm. The nanoscale whiskers are disorder graphite and are aligned inside the micrometre scale cavities. A whisker/cavity structure is generated on the outer and inner surfaces of the hollow carbon fibres.

Densification mechanism of polyacrylonitrile-based carbon fiber during heat treatment

Polyacrylonitrile (PAN)-based carbon fibers were heat treated at various temperatures for varying durations to simulate the graphitization process in the manufacture of C/C composites. Densification of the resulting fibers was confirmed by density measurement. The composition and structure of the fibers were investigated by means of elemental analysis, X-ray diffraction and Raman spectroscopy. For specified isothermal heat treatment time, the structural parameters depended strongly on heat treatment temperature. The nitrogen content decreased with increased heat treatment temperature and extended time at constant temperature. Nitrogen loss was complete at temperatures above 1900 °C. The graphite crystallite size increased rapidly with increasing heat treatment temperature, and slowly with extended isothermal heat treatment time. At 2100 °C a more ordered graphitic structure appeared. Denitrogenation induced “puffing”, which made the fibers expand. Decrease in density in the heat treatment temperature range 1500–1900 °C originated from the abrupt evolution of nitrogen, and above 1900 °C the graphitization transition induced steadily increasing density. Densification of the carbon fibers was determined both by the rate of denitrogenation and the rearrangement of carbon atoms.

Microstructure difference between core and skin of T700 carbon fibers in heat-treated carbon/carbon composites

The core and skin microstructure of T700 carbon fibers in carbon/carbon composites, prepared with chemical vapor infiltration (CVI) at 1000 °C and heat treated at 2300 and 2800 °C, have been studied by means of high-resolution transmission electron microscopy (HRTEM). The orientation angles of the graphitic basal planes obtained from selected-area electron-diffraction patterns show that the structure difference between the core and skin is a change of the degree of preferred orientation of the graphitic basal planes which decreases gradually from the skin region to the core region after CVI at 1000 °C. With increasing heat-treatment temperature, the basal planes orient parallel to the fiber axis, first in the skin region and then in the core region. In addition, the diameter of the core region decreases considerably from about 3.3 to 2.2 μm after heat treatment at 2800 °C. HRTEM lattice-fringe images show that the graphitic crystallite size increases significantly both in the core and skin, but more in the skin. Moreover, with increasing crystallite size, pores of nanometer scale start to form in the fiber.

Structure of the carbon layer deposited on the steel surface after low pressure carburizing

During low pressure carburizing a carbon layer precipitates on the surface of steel parts. The structure of the carbon layer was tested by means of optical and electron microscopy and Raman spectroscopy as well. It was found out that the carbon layer is composed of fine-crystalline graphite. A sample was carburized (boost step), and was subsequently observed with an optical microscope. The dominant shade of the previously existing austenite grains was gray with few brighter areas (observation with a scanning microscope showed that these areas were darker). Within the gray areas the size of graphite crystallites was 7–20 nm, and within the brighter areas 1–7 nm. The diffusion step led to a change in the grain shade and to a decrease in the size of graphite crystallites. Gray-shaded grains were made of a mixture of gray and dark areas. The areas of homogenous brightness contained graphite made of crystallites of size 1–2 nm, and the areas where the gray shade was not homogenous contained grains of size up to 4 nm.

Uniaxially aligned carbon nanofibers derived from electrospun precursor yarns

AbstractUnlike conventional electrospun polymer fibers deposited on a target electrode as a randomly oriented mesh, poly(p‐xylenetetrahydrothiophenium chloride) was electrospun into centimeters‐long yarns vertically on the surface of the electrode but parallel to the electric field. The diameter of the yarn was strongly affected by the concentration, spinning rate, and viscosity of the polymer solution, but less dependent on the applied voltage. The subsequent carbonization of thus‐electrospun yarns at 600–1000 °C resulted in uniaxially aligned carbon nanofibers with average diameters of 127–184 nm. On the basis of Raman spectra, the graphitic crystallite size and the molar fraction of graphite were estimated to be 1.2–1.4 and 0.21–0.24 nm, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 305–310, 2008

Characterization of chemically modified carbon black for sorption application

A commercial grade carbon black was chemically modified using mineral acids (either with HNO 3 or H 2SO 4 or mixture) and the sorption performance of the virgin and modified forms were investigated. Chemical modification resulted in the creation of surface acidic functional groups ( COOH, SO 2OH) and was verified by FTIR spectra. This was further verified by TGA analysis revealing higher weight loss characteristics of the modified carbons in comparison to virgin carbon black. Morphological changes were observed from BET surface area measurements and SEM analysis. XRD study revealed the change of graphitic crystallite size as a result of modification. The suspension pH of the materials in deionized water and the point of zero charge (pH pzc) in inert electrolyte were determined. The measured values of suspension pH and pH pzc for all the carbons were found to be acidic with more acidic character in the modified carbons. These materials were used as sorbents for the removal of arsenic from aqueous medium and showed excellent adsorption performance.

Raman characterization of carbon nanofibers prepared using electrospinning

Ultrafine fibers were spun from polyacrylonitrile (PAN)/ N, N-dimethyl formamide (DMF) precursor solution using a homemade electrospinning setup, and then pyrolyzed in vacuum at 873, 1073, 1273 and 1473 K, respectively. The pyrolyzed fibers, with diameter of the order of 100 nm as revealed by a scanning electron microscope (SEM), were characterized using Raman microspectrometry. Their Raman scattering spectra manifested D and G peaks, characteristic of disordered carbon and graphite, respectively. The D and G peak parameters were fitted using a Gaussian–Lorentzian mixed shape, and graphitic crystallite size and mole fraction in the nanofibers were estimated from the ratio of the integrated intensity of D and G peaks. The graphite domain size was found to be between 1.5 and 2.6 nm, increasing with the pyrolyzing temperature. The graphite mole fraction was found to obey an Arrhenius relation with the pyrolyzing temperature, with the graphitization activation energy of 7.36±0.11 kJ/mol.

Raman spectra of nano-structured carbon films synthesized using ammonia-containing feed gas

We examined the Raman spectra of nanostructured carbon films grown using the ammonia-containing feed gas at two excitation wavelengths, 514.5 and 1064 nm. The increase of the ammonia concentration in the feed gas resulted in two prominent changes: the complete morphology change (from nanoparticle dominance to nanotube dominance) and the degradation of the graphitic sheet quality. However, the Raman spectra preserved strong resemblance to those of graphite and glassy carbon and showed only systematic variation in the peak position, width, and the intensities. We noted that the ammonia-concentration-dependent broadening of D and G bands, the up-shift of D band, and the increase of the intensity ratio I(D)/I(G) of these films could be interpreted as the signature for the increase of disorder in the graphitic structure and/or the reduction of the graphitic crystallite size in accordance with the similar observation from other carbon-based films. We attributed the observed excitation-energy-dependent shift of the D-band position and the variation of I(D)/I(G) value to the resonance phenomena in Raman scattering. Moreover, we showed that the dispersion of the D band was in good quantitative agreement with the model proposed by Matthews et al. [Phys. Rev. B 59, R6585 (1999)].

Effects of doped sulfur on electrochemical performance of carbon anode

An amorphous carbon doped with sulfur to be used as anode material for lithium ion batteries is prepared by heat-treatment of a mixture of polyacrylonitrile (PAN) and sulfuric acid. With X-ray photoelectron spectroscopy (XPS), elemental analysis, X-ray powder diffraction (XRD), scanning electron microscopy, and electrochemical capacity measurements effects of sulfur on properties of the carbon anode are investigated. The added sulfur favorably increases the charge capacity in close correlation with an increase of the size of graphite crystallites, L c, the interlayer distance, d 0 0 2 , and the number of micropores, and the doping of sulfur in the state of CSC. On the other hand, it also causes detrimental changes, for example the formation of amine-group nitrogen, sulfate/sulfonate deposits, and macropores. Nevertheless, as a result, both reversible and irreversible capacities are enhanced. This clearly shows, that added heteroatoms may have opposite influences, good and bad, on electrochemical performance of carbonaceous anode materials. Approaches towards suppressing the unfavorable ones in the application in lithium ion batteries are discussed.

Graphitization behavior of wood ceramics and bamboo ceramics as determined by X-ray diffraction

Wood and bamboo ceramics are newly developed porous carbon materials from wood and bamboo impregnated with resin, and they possess some special properties and can be expected to be used as electromagnetic materials, absorbents, catalyst carrier materials, etc. In this work, the graphitization behavior of wood and bamboo ceramics was investigated by X-ray diffraction. Experimental results show that the d002 spacing of the bamboo carbon, wood and bamboo ceramics decreased and the apparent graphite crystallite size Lc(002) increased with the increase of graphitization temperature. However, even after heat treatment at 3273 K, the d002 and Lc(002) value was only about 0.341 and 9 nm, respectively. These results indicate that all of the bamboo carbon, wood and bamboo ceramics investigated are typical non-graphitizable carbon or hard carbon.

Carbon anode materials based on melamine resin

We have obtained carbon anode materials based on a melamine resin. Through elemental analysis, X-ray powder diffraction, BET measurement and X-ray photoelectron spectroscopy, the effects of heat-treatment temperature and doping of phosphorus were investigated. Temperature affects mainly the nitrogen content, the size of graphite crystallites and the number of micropores in the carbons, and thus their reversible capacity changes with temperature. The highest reversible capacity occurs at 600 °C. The addition of phosphoric acid can affect the carbon structure and relative content of graphene nitrogen. Its behaviour changes with temperature. Only at high temperature, can the doped phosphorus favour the enhancement of reversible capacity.

Pore structures of activated carbon fibers from organometallics/pitch composites by nitrogen adsorption

A series of activated carbon fibers (ACFs) produced from organometallics compounds such as Y(acac) 3 or Al(acac) 3/pitch composites were characterized. The pore-size, surface state and graphitic crystallite size were examined by means of N 2 adsorption isotherm, X-ray photoelectron spectroscopy and X-ray diffraction (XRD) analysis. The presence of Y or Al increased the pore-size. Y(acac) 3/pitch and Al(acac) 3/pitch-based ACFs activated at 1148 and 1173 K, respectively, had an appreciable amount of mesopores. The size of the micrographites structure of the organometallics/pitch-based ACF composites by XRD was slightly greater than that of the pitch-based ACF. Ar ion etching using X-ray photoelectron spectroscopy showed that Y or Al atoms are coated with carbon layers.