Deposition of a thin film of carbon nanotubes onto a glassy carbon electrode by electropolymerization

A novel and easy route for the deposition of a thin film of carbon nanotubes onto an electrode surface by electropolymerization is described. Multi-wall carbon nanotubes (MWNTs) were “dissolved” in aqueous alizarin red S (ARS, 3,4-dihydroxy-9,10-dioxo-2-anthracenesulfonic acid, sodium salt) solution, and a very stable and well-distributed aqueous MWNTs–ARS solution was obtained. A thin film of MWNTs–ARS was successfully deposited onto the electrode surface by an in situ electropolymerization in aqueous MWNTs–ARS solution. The MWNTs–ARS thin film was characterized by scanning electron microscopy, Raman spectroscopy, UV–Vis spectroscopy and electrochemical techniques.     

X-ray structure analysis and elastic properties of a fabric reinforced carbon/carbon composite

The effect of heat treatment on microstructure of a plain-weave carbon fabric reinforced carbon-carbon composite with phenolformaldehyde-derived carbon matrix was investigated by X-ray diffraction. The diffraction patterns were analysed by the least-square fitting program Carbonxs. After heat treatment from 1000 to 2800 °C the interplanar distance of (002) planes decreased from 3.488 to 3.420 Å and the lattice parameter in basal plane increased from 2.440 to 2.464 Å, respectively. Simultaneously, the coherent block size in the basal plane directions increased from 18 to 54 Å, which was accompanied by an increase of the fraction of organised carbon atoms from 0.50 to 0.85. The 002 diffraction profile of the composite was much narrower than the sum of peaks of the matrix and fabric alone. This can probably be caused by a better crystallographic ordering (or by a partial graphitisation) of the matrix in the composite. On the other hand, the composite Young’s modulus slightly decreased with the treatment temperature increasing from 2200 to 2800 °C in spite of the established strong improvement of fibre crystallinity and, therefore, fibre modulus. The mechanisms diminishing the modulus of composite (e.g. partial matrix graphitisation at the fibre/matrix interface and decreasing fibre/matrix contact area) probably prevailed over the increasing contribution of the fibre modulus.     

Surface activation of a polymer based carbon

A highly mesoporous carbon was synthesized by the conventional sol-gel method involving the polymerization of resorcinol and formaldehyde followed by carbonization. Oxygen activation was employed to modify the surface properties of the polymer based carbon material. The textural properties (surface area, micropore volume) were evaluated from the nitrogen adsorption isotherm at 77 K. The samples were also characterized by XPS, TGA and by elemental analysis. The pH_PZC of the oxidized carbon was also determined. The amounts of oxygen surface complexes generated were quantitatively determined using temperature programmed desorption analysis (TPD). The oxidation treatment was found to be quite effective in the generation of oxygen rich surfaces at moderate burn off.     

Analysis of degradation processes of carbon/carbon composites in a high temperature chemical flame by a spectrovideo camera

The purpose of this study is to develop a measurement technique for in situ monitoring of the degradation processes of thermal-resistance materials, such as C/C (carbon/carbon) composites, in high temperature fields. Spatially, spectrally and temporally resolved images of emission from diatomic molecules were observed in an acetylene–air flame by a spectrovideo camera, assembled by combining a monochromator and a high speed ultraviolet (UV) video camera. In order to calculate flame temperatures around the given test samples, C/C composite disks, emission intensity images of two Cr lines were observed by spraying a Cr 1000 ppm solution. The emission intensity images of OH, CH and C₂ bands were measured to investigate the degradation processes from their changes. The test samples employed in this study were graphite, two-dimensionally textile C/C composites and oxidation-resistive C/C composites with double layer coatings of SiC and glass materials. Graphite was tested as a reference raw material of the C/C composites. The result indicated that the time dependencies in the spatial distribution of OH and C₂ emissions observed by the spectrovideo camera proved to be an effective measure to monitor the degradation/oxidation processes of the C/C composites in high temperature fields.     

Helical carbon nanofibers with a symmetric growth mode

Helical carbon nanofibers with a symmetric growth mode were synthesized by the decomposition of acetylene with a copper catalyst. There were always only two helical fibers symmetrically grown over a single copper nanocrystal. The two helical fibers had opposite helical senses, but had identical cycle number, coil diameter, coil length, coil pitch, cross section, and fiber diameter. The irregular tips and helical reversals of the two helical fibers further revealed the symmetric growth mode. This mirror-symmetric growth mode was induced by the shape changes in copper nanocrystals during catalyzing the decomposition of acetylene. Upon contacting the initial copper nanocrystals with irregular shapes, acetylene began to decompose to form two straight fibers (the irregular tips). At the same time, shape changes in copper nanocrystals began. Once they changed from an irregular to a regular faceted shape, the two straight fibers ceased to grow and two regular helical nanofibers with opposite helical senses began to grow. If the regular faceted nanocrystals continue to change shapes during fiber growth, the two helical fibers possibly changed helical senses at the same time, resulting in helical reversals. The shape changes were caused by the changes in surface energy resulting from the acetylene-adsorption on the copper nanocrystals.     

Effect of carbonization rate on the properties of a PAN/phenolic-based carbon/carbon composite

The effect of carbonization rate in a wide range (1, 100 and 1000 °C/min) on the properties of a PAN/phenolic-based carbon/carbon (C/C) composite was studied. The results indicated that the composite processed at a higher carbonization rate had a higher porosity level, more large pores and a more graphitic structure than that processed at a lower carbonization rate. After second graphitization the bending properties of composites carbonized at 1 °C/min and 1000 °C/min were comparable. The composite carbonized at 1000 °C/min had the highest fracture energy. The composite carbonized at 100 °C/min showed the worst mechanical performance among three. The large increase in carbonization rate can be beneficial to the industry from an economic point of view.     

The pull-out and failure of a fiber bundle in a carbon fiber reinforced carbon matrix composite

The interfacial failure is examined for a unidirectionally reinforced carbon fiber/carbon matrix composite. A novel tensile test is conducted which realizes the processes of interfacial debonding and subsequent pull-out of a fiber bundle from the surrounding composite medium. The critical stress at the onset of delamination cracking is related to the fracture energy (the critical energy release rate for mode II cracking). A force-balance equation of a fiber bundle, which is quasi-statically pulled-out of the composite socket, is formulated in terms of the inter- and intra-laminar shear strengths of the composite. This equation is successfully used to estimate the delamination crack length along the debonded fiber bundle, as a function of the stress applied to the bundle.     

Carbon nano-rod as a structural unit of carbon nanofibers

The structure of carbon nanofiber (CNF) with platelet texture was found to be constructed by a primary structural unit named carbon nano-rod by the authors through comprehensive examination of X-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), and scanning tunneling microscopy (STM). Single carbon nano-rod resembles multi-walled carbon nanotube with 4–5 graphene sheets nested (ca. 2.5 nm diameters), but appears to have a hypothetical transverse of hexagonal shape with the inner diameter corresponding to the interlayer spacing. Three-dimensional model of CNF was suggested based on the carbon nano-rods, which are densely stacked perpendicular to the fiber axis to form a typical platelet CNF. Such a structural concept of CNF gives novel views on the correlation between structure and properties of CNFs for potential applications.     

Combustion joinining of carbon/carbon composites by a reactive mixture of titanium and mechanically activated nickel/aluminum powders

Combustion joining of carbon/carbon (C/C) composites using a mixture of titanium and mechanically activated Ni/Al powders as a reactive medium is reported. A minimum preheating of the sample stack to 630 K is required to initiate the joining process. A robust crack- and pore-free joint layer (∼75−100 μm in thickness), which is composed of NiAl_x and TiC_y(O_z) phases, is produced. Tensile-strength testing of the joined C/C composites shows that the fracture does not occur along the joint layer.     

Surface treatments of vapor-grown carbon fibers produced on a substrate

Vapor-grown carbon fibers (VGCF) were grown from a methane-hydrogen mixture on a reconstituted graphite support using different catalyst precursors, the [Fe₃(CO)₁₂] complex being found to be the most efficient for the production of VGCF. The fibers thus produced were characterized and submitted to different oxidative treatments, namely nitric acid, plasma, air and carbon dioxide. From analysis performed by scanning electron microscopy (SEM), nitrogen adsorption (BET) and X-ray photon spectroscopy (XPS) it appears that the air and carbon dioxide treatments do not lead to significant increase either of the surface area, or of the quantity of surface oxygen containing groups, despite the considerable weight loss attained (50%). This peculiar observation has been interpreted by considering the presence of traces of iron at the fibers surface, which can catalyze the gasification of carbon. The presence of iron on the VGCF has been evidenced for the first time by the time-of-flight secondary ion mass spectrometry technique. The cleansing of the fibers surface with concentrated hydrochloric acid results in the removal of the iron and leads, after CO₂ activation, to an improvement of the BET surface area. The use of nitric acid or plasma as oxidation agents does not affect significantly the surface morphology of the fibers, but greatly increases the number of surface oxygen functions.     

Natural gas storage in activated carbon pellets without a binder

Activated carbon pellets without a binder from cellulose microcrystals as a raw material were investigated. After compression of the raw materials, the thus obtained raw material pellets were slowly carbonized to 1073 K under nitrogen. To activate them, the carbon pellets were heated to 1173 K under carbon dioxide. The activated carbon pellet shape, after heat treatment, was columnar by using the previous employed compression of the raw material. The total surface area, pore volume, and average pore diameter for all the samples were evaluated from the analysis of N₂ adsorption isotherm data. The total surface area and the pore volume were decreased with an increase in compression pressure under the same heat treatment conditions. On the contrary, the bulk densities of the activated carbon pellets were increased. However, these properties can be easily controlled by changing the sintering temperature and time. The bulk density of sample pellet was 0.56 g/cm³. It is 2.3 times higher than activated carbon powder, which was made without the compression process. The total methane storage capacity at 298 K reached 164 cm³ in 1 cm³ volume of activated carbon pellets at 3.5 MPa.     

Densification of a 2D carbon fiber preform by isothermal, isobaric CVI: Kinetics and carbon microstructure

Chemical vapor infiltration of a 2D carbon fiber preform with a 0/0/90/90° fiber architecture and a fiber volume fraction of 22.5% was investigated as a function of methane pressure at various temperatures as well as a function of infiltration time at constant pressure. Inside-outside densification was obtained at the most attractive temperature of 1095 °C up to 29 kPa resulting in a maximum bulk density of 1.84 g cm⁻³ and a matrix density of 2.17 g cm⁻³, which corresponds to high-textured carbon. Texture formation can be perfectly explained with the earlier proposed particle-filler model. Studies at increasing infiltration times suggest a recrystallization of carbon deposited in the early stages of the infiltration.     

Synthesis and characteristics of iron nanoparticles in a carbon matrix along with the catalytic graphitization of amorphous carbon

Iron nanoparticles in a carbon matrix were synthesized by in situ pyrolysis of maleic anhydride and ferrocene, using different molecular weight percentages. The characterization and magnetic properties of the carbon-iron system were investigated systematically. Transmission electron microscope (TEM) images showed that the as-prepared samples consist of nanometric dark grains (iron-rich phase) embedded in a light matrix (carbon-rich phase). X-ray diffraction and TEM selected area diffraction revealed catalytic graphitization and iron phases present in the sample. The carbon-metal system shows a finite hysteresis loop even at room temperature indicating its ferromagnetic nature. The saturation magnetization equals the bulk iron carbide value at low temperature. The coercive force exhibits 1/d dependence at low temperature having a maximum H_C of 2 kOe for the lowest iron concentration sample.