Graphite Crystallite Size Research Articles

97/02791 Two-stage spouted-bed coal gasifier

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 N2 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.

Structural investigation of xenon-ion-beam-irradiated glassy carbon.

Raman spectroscopy, cross-sectional transmission electron microscopy, and electron-energy-loss spectroscopy have been used to monitor the ion-beam-induced transformation in glassy carbon irradiated with 320-keV Xe ions to doses between 5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ and 6\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ions/${\mathrm{cm}}^{2}$. It was found that (i) the ion beam amorphizes the glassy carbon structure; (ii) the amorphization is accompanied by a compaction of the glassy carbon from an initial density of 1.55 to 2.2\ifmmode\pm\else\textpm\fi{}0.2 g/${\mathrm{cm}}^{3}$; and (iii) approximately 15% of the graphitelike bonds in glassy carbon are converted to diamondlike bonds in the amorphization process. The transformation of glassy carbon to an amorphous state occurs in two distinct stages as a function of ion dose. For damage levels up to 0.2 displacements per atom (dpa) the effect of the ion beam is to decrease the average graphitic crystallite size. Above 0.2 dpa, disorder in bond length and bond angle away from ideal graphitic threefold coordination occurs leading to complete amorphization at high doses. The amorphization, compaction, and presence of \ensuremath{\approxeq}15% ${\mathit{sp}}^{3}$ bonds in the implanted layer of glassy carbon results in a surface layer which is significantly more resistant to abrasion than as-grown glassy carbon.

Graphite formation in diamond film deposition

In this paper we report on the existence, distribution, crystallographic orientation, size, and morphology of graphite crystallites within diamond films prepared by microwave plasma assisted chemical vapor deposition. Transmission electron microscopy and Raman spectroscopy techniques were used to characterize graphite formation in diamond films deposited under various conditions.

Analysis of Picosecond Pulsed Laser Melted Graphite

AbstractA Raman microprobe and TEM have been used to analyze the resolidified region of liquid carbon generated by picosecond pulse laser radiation. From the relative intensities of the zone center Raman-allowed mode for graphite at 1582cm−1 and the disorder-induced mode at 1360cm−1 , the average graphite crystallite size in the resolidified region is determined as a function of incident pulse energy density. By comparing with Rutherford backscattering spectra and Raman spectra from nanosecond pulsed laser melting experiments, additional information about the disorder depth in picosecond pulsed laser melted graphite is obtained. Comparisons of TEM micrographs for nanosecond and picosecond pulsed laser melting experiments show that the structure of the laser disordered regions in graphite are similar and exhibit similar behavior with increasing laser pulse fluence. The similarities in the resolidified regions under both irradiation schemes discourages a determination of the properties of liquid carbon after the liquid has resolidified.

Some techniques for the characterization of cokes and graphites

Methods used at the Coal Research Establishment of the UK NCB for characterizing the structure and physical properties of cokes and graphites are briefly reviewed. These include the use of X-ray diffraction and optical microscopy, and the measurement of a range of mechanical, thermal and electrical properties. Some relations between the structural parameters of graphites and their physical properties are discussed. Examples illustrating the application and practical importance of the results obtained are grouped loosely under three headings: 1. (1) Prediction of graphite properties from tests on cokes (e.g. prediction of coefficient of thermal expansion from coke mosaic texture). 2. (2) Exploration and monitoring of changes in process conditions (e.g. use of graphite crystallite size to monitor the effects of changes in graphitization temperature, use of coke mosaic texture to indicate effects of changes in temperature and time during coal-digestion stage of the solvent-extraction process). 3. (3)Prediction of the performance of graphite electrodes in an arc furnace (e.g. concept of thermal-shock resistance, estimation of thermal-shock resistance parameters from physical properties, and correlation between these and thermal-shock performance in laboratory tests).

X-ray Study of Electrographitized Garbon Products

Lattice constants and size of graphite crystallites in electrographitized carbon products were reportedin the previous papers (This Journal, 7 (3), 79, (1959); 8 (1), 2 (1960)). However, when a carbonproduct is composed of carbons of different origins, the X-ray diffraction profile of the product shouldalso be composed of diffraction profiles of component carbons. Therefore, values of crystal size calculated from the composite diffraction profile must be different from true values.Experimentally several carbon brushes were found to have composite asymmetric profiles of 004diffraction. It can be seen in the figures that profiles of brushes of carbon black base, such as Superior-E 47, C-1 and C-1*, can be separated into profiles of carbons of carbon black origin and coke origin.Angles of diffraction of brushes of carbon black base seem to give an estimation of carbon black variety, even when the profiles are symmetrical. Profiles of some brushes of coke base are asymmetric, havingsmaller inclination at the low angle side than at the high angle side, suggesting admixture of smallquantity of carbon black or other less graphitizable carbons. Diffraction angles of almost all brushes ofcoke base were smaller than those of electrodes and anodes. Half intensity breadths of 004 diffractionsof these brushes were larger than those of electrodes and anodes. More detailed and quantitative investigation on diffraction profiles of mixtures of different varieties of carbons will be published in theJournal of the Chemical Society, Japan, Industrial Chemistry Edition.

X-ray Study of Electrographitized Carbon Products IV.

Lattice constants and size of graphite crystallites in electrographitized carbon products were reportedin the previous papers (This Journal, 7 (3), 79, (1959); 8 (1), 2 (1960)). However, when a carbonproduct is composed of carbons of different origins, the X-ray diffraction profile of the product shouldalso be composed of diffraction profiles of component carbons. Therefore, values of crystal size calculated from the composite diffraction profile must be different from true values.Experimentally several carbon brushes were found to have composite asymmetric profiles of 004diffraction. It can be seen in the figures that profiles of brushes of carbon black base, such as Superior-E 47, C-1 and C-1*, can be separated into profiles of carbons of carbon black origin and coke origin.Angles of diffraction of brushes of carbon black base seem to give an estimation of carbon black variety, even when the profiles are symmetrical. Profiles of some brushes of coke base are asymmetric, havingsmaller inclination at the low angle side than at the high angle side, suggesting admixture of smallquantity of carbon black or other less graphitizable carbons. Diffraction angles of almost all brushes ofcoke base were smaller than those of electrodes and anodes. Half intensity breadths of 004 diffractionsof these brushes were larger than those of electrodes and anodes. More detailed and quantitative investigation on diffraction profiles of mixtures of different varieties of carbons will be published in theJournal of the Chemical Society, Japan, Industrial Chemistry Edition.

蒸着炭素の黒鉛化

Pure carbon deposits were prepared by the evaporation of graphite of atomic reactor grade in a vacuum furnace and were heat-treated at temperatures between 2000 and 3000 deg C either in vacuo or under the atmospheric pressure. The lattice constants, crystal size, and orientation of graphite crystallites in the heat-treated carbons were measured by the x-ray diffraction method. The specimens were also observed under an electron microscope. The original evaporated carbon was nearly amorphous and had the turbostratic structure of relatively large graphite-like layers. The degree of graphitization of the carbons increased rapidly from 2000 to 2500 deg C and gradually above 2500 deg C up to 3000 deg C as in the case of graphitizing petroleum coke, while with the heat-treatment in vacuo the degree of graphitization changed slightly up to 2500 deg C and the graphitization took place only at temperatures higher than 2500 deg C. The degree of graphitization of carbons treated at about 3000 deg C in vacuo was found to be almost equal to that of the carbons treated at the same temperature under the atmospheric pressure. The crystallite size of the carbons changed almost parallel with the change of the lattice constant c/sub 0/.more » The orientation of graphite crystallites parallel to the evaporated surface of the carbons increased with the heat treatment of the carbons. The effect of gas pressure on the graphitization and the change of the preferred orientation of crystallites in the carbons with the heat-treatment suggest that the process of atomic migration is one of the main factors of the graphitization process along with the translation and rotation of graphite-like layers of carbons and the coalescence of the layers. (auth)« less

X-ray study of coal from Logan County, West Virginia, and a discussion of the structure of coal

Seventy-four surface, drill core, and underground samples representative of the eight industrial seams within the limits of Logan County, West Virginia, were studied by X-ray methods. The coals are of Kanawha (Upper Pottsville) and Allegheny age. Samples, for the most part, were composite.The powder X-ray technique was utilized with a number of variations in specimen preparation. Copper and iron radiation were used with 114. 59 mm cameras employing the Straumanis technique of film calibration.Extraneous crystalline impurities identified through X-ray means alone were kaolinite, quartz, pyrite, calcite, and dolomite in order of decreasing occurrence. Of these mineral impurities, only kaolinite appears to occur with any preferred orientation.Information on the structure of coal derived from the study of these high-volatile bituminous coals was compared with the information obtained from specimens of Pennsylvania anthracite, Cretaceous low rank bituminous, and Pennsylvanian semi-bituminous. Results obtained suggest that the free carbon in coal is in the form of graphitic crystallites, as indicated by diffuse halos in the region of the prominent graphite diffraction lines. Volatile matter and moisture in the coal appear as secondary scattering on the film. Slight shifts of the {002} halo indicate a definite change of the graphite crystallite size with coal rank change.Previous literature on the X-ray study of coal is reviewed and discussed.Advantages and disadvantages of the X-ray method are compared with other methods of coal analysis, from the standpoint of structural determinations.

On the Relation between Quality and Graphite Crystallite Size of Coke.

On the Relation between Quality and Graphite Crystallite Size of Coke.