Size and shape of crystallites and internal stresses in carbon blacks (original) (raw)
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Microstructure of carbon blacks determined by X-ray diffraction profile analysis
Carbon, 2002
The microstructure of carbon blacks is investigated by X-ray diffraction peak profile analysis. Strain anisotropy is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. Crystallite shape anisotropy is modeled by ellipsoids incorporated into the size profile function. Different grades of carbon blacks, N990, N774 and N134, untreated, heat-treated and compressed at 2.5 GPa have been investigated. The microstructure is characterized in terms of crystallite size-distribution, dislocation density and crystallite shape anisotropy. Heat treatment results in increased vertical and lateral sizes of graphitic crystallites. Postproduction pressure treatment has little effect on the average sizes of the crystallites, however, it affects the crystallite size distribution function. The average sizes of the crystallites obtained by X-ray diffraction agree with those estimated from Raman spectra. Applied pressure affects the magnitude of strain within the crystallites.
X-ray diffraction study of crystallite size-distribution and strain in carbon blacks
MRS Proceedings, 2000
The crystallite size and size-distribution in carbon blacks in the presence of strain is determined by recently developed procedure of X-ray diffraction peak profile analysis. The Fourier coefficients of the measured physical profiles are fitted by Fourier coefficients of well established ab initio functions of size and strain peak profiles. Strain anisotropy is accounted for expressing the mean square strain in terms of average dislocation contrast factors. Crystallite shape anisotropy is modelled by ellipsoids incorporated into the size profile function. To make the fitting procedure fast, the Fourier transform of the size profile is given as an analitical function. The method is applied to carbon blacks treated at different pressures and temperatures. The microstructure is characterised in terms of crystallite size-distribution, dislocation density, and crystallite shape anisotropy.
High pressure Raman and neutron scattering study on structure of carbon black particles
Carbon, 2000
High pressure Raman and neutron scattering study of carbon blacks and highly oriented pyrolytic graphite is reported. It is found that carbon black particles are composed of graphitic nanocrystallites and amorphous carbon. Pressure-induced order in inter-atomic distances within nanocrystallites is completely reversible. Relative concentration of amorphous carbon decreases slightly with increased pressure. This process differs from temperature induced transformation of amorphous carbon into ordered carbon. Post-production treatment at high temperatures results in lateral and vertical growth of graphitic crystallites, and at sufficiently high temperatures almost all amorphous carbon is transformed into graphitic structures. Within the pressure range under study, 5 GPa, only a small fraction of amorphous carbon is transformed into ordered structures. Pressure induced frequency shift of the E bands of various carbon blacks is explained in terms of a modified intermolecular 2g potential.
Carbon, 1993
Degree of graphitization, average interlayer spacing, and crystallite sizes were measured on various kinds gf carbon materials. The relation between graphitization degree P, and average interlayer spacing b2 was found to show a downward deflection; the increase in P, value was retarded in comparison with the approach of the b2 value to 0.3354 nm. The deflection depended strongly on the texture of carbon samples in the nanometric scale. The existence of structural strain in carbon materials had a stronger effect on the relation to-&,l than that to PI. This is the reason why the relation between P, and m&Z shows the downward deflection.
Microstructural evolution during charcoal carbonization by X-ray diffraction analysis
Carbon, 2003
X-ray diffraction (XRD) of monolithic pieces of carbonized medium-density fiberboard (c-MDF) provided new insights on the microstructural evolution occurring during charcoal carbonization. Classical XRD theory was used to correlate the h002j peak intensity to the amount of carbon in large turbostratic crystallites and to bulk dimensional changes. This new analytical technique could be used to study the microstructural evolution of other monolithic carbon materials (including soft carbons) or of specific processes (including chemical activation). The quasipercolation model, a new 'percolation-like' model, was created based on XRD analysis of monolithic c-MDF. As the carbonization temperature (T) increased above carb 600 8C, the large turbostratic crystallites grew very little, but the graphene sheets grew substantially. Volumetric shrinkage suggested that turbostratic crystallites were drawn closer together as the low-density disordered carbon was converted into high-density graphene sheets. At approximately 900 8C, the large graphene sheets and the large turbostratic crystallites significantly impinged on each other. The increased impingement of conductive phases with increasing carbonization temperature would cause the commonly observed nonmetal-metal transition of hard carbon materials. The quasipercolation model also suggested the source of the nanoporosity that is critical in activated carbons.
Crystal structure of graphite under room-temperature compression and decompression
Scientific Reports, 2012
Recently, sophisticated theoretical computational studies have proposed several new crystal structures of carbon (e.g., bct-C 4 , H-, M-, R-, S-, W-, and Z-carbon). However, until now, there lacked experimental evidence to verify the predicted high-pressure structures for cold-compressed elemental carbon at least up to 50 GPa. Here we present direct experimental evidence that this enigmatic high-pressure structure is currently only consistent with M-carbon, one of the proposed carbon structures. Furthermore, we show that this phase transition is extremely sluggish, which led to the observed broad x-ray diffraction peaks in previous studies and hindered the proper identification of the post-graphite phase in cold-compressed carbon.
Effect of Oxidation on the Microstructure of Carbon Blacks
Energy & Fuels, 1996
The evolution during oxidation of the internal structure of soot and carbon black particles was studied using high-resolution transmission electron microscopy (HRTEM) and an image analysis system. Increasing ordering to the carbon structure with increasing oxidation is observed. Measures of the increased order are increases in the fractional coverage of a cross section of the particles with a layered structure, a decrease in the mean interlayer spacing, and a decrease in the spread of the interlayer spacing. The changing structure of the carbon black impacts its properties, such as the rate of oxidation.
TANSO, 2019
The linear thermal expansion of two artificial graphite products, an isotropic graphite and an extruded nipple electrode, was measured during heating up to 2400 °C by a newly developed device with a non-contact laser micro-gage. The temperature dependence of the coefficient of thermal expansion (CTE) of two graphites was investigated. The test piece was 100 mm long a round rod of 20 mm diameter, which is large enough to reflect the different textures of these products. In the nipple electrode, two specimens taken from parallel or perpendicular to the extrusion direction were used. For the isotropic graphite and the parallel specimen of the nipple electrode, temperature dependences of the CTE below 500 °C were different. In the case of the parallel nipple specimen, a negative value of CTE was found in the temperature region from 150 to 400 °C, probably reflecting the negative CTE along the basal planes of a graphite crystal. In situ measurement of the dimensional changes of the specimens before graphitization process of these products during heat treatment up to 2400 °C was also attempted. For the isotropic product, two-step of thermal shrinkage was observed, but for the nipple electrode, growth above 1400 °C was clearly observed, resulting from the "puffing" of calcined needle cokes. For the puffing, it was found that there was clear anisotropy in the extruded direction of the nipple electrode.
Microstructural characterisation of nuclear grade graphite
Journal of Nuclear Materials, 2008
Field emission and transmission electron microscopy are used to characterise the microstructure and morphology of baked carbon block and graphitized grades (from the same carbon block stock) of nuclear graphite. Quantitative analysis using Raman and energy dispersive spectroscopy (EDS) were used to investigate the decrease of crystallinity with graphitization and sample purity. Both baked carbon and graphitized nuclear graphites show no sensitivity of the Raman band shift to strain, consistent with strain accommodation by the porous structure.
Determination of crystallite size in polished graphitized carbon by Raman spectroscopy
Physical Review B, 2012
A series of polished and unpolished sp 2-nanostructured carbons "nanographites" obtained from the pyrolysis of various precursor types have been systematically studied by both Raman spectroscopy and x-ray diffraction. The ratio between the intensities of the disorder-induced D band and the first-order graphite G band (I D /I G) commonly used up to now to estimate the "crystallite" diameter L a displays, in the case of polished graphitized sp 2 carbons, clear spatial heterogeneities and can lead to the overestimation of the intrinsic structural disorder. The full width at half maximum of the G band, which is shown to be insensitive to the polishing process, exhibits a linear dependence on the mean "crystallite" diameter [FWHM(G) = 14 + 430/L a ] and therefore can be used for an accurate structural characterization of these nanographites.