Carbon nanotube–metal–oxide composites (metal=Fe, Co or Fe/Co alloy; oxide=Al
2O
3, MgO or MgAl
2O
4) have been prepared by hot-pressing the corresponding composite powders, in which the carbon ...nanotubes, mostly single or double-walled, are very homogeneously dispersed between the metal–oxide grains. For the sake of comparison, ceramic and metal–oxide nanocomposites have also been prepared. The microstructure of the specimens has been studied and discussed in relation to the nature of the matrix, the electrical conductivity, the fracture strength and the fracture toughness. The carbon nanotube–metal–oxide composites are electrical conductors owing to the percolation of the carbon nanotubes.
Des composites nanotube de carbone–métal–oxyde (
m
e
́
tal
=
Fe
, Co ou alliage Fe/Co; oxyde=Al
2O
3, MgO ou MgAl
2O
4) ont été préparés par frittage sous charge des poudres composites correspondantes, dans lesquelles les nanotubes de carbone, essentiellement mono- ou bi-feuillets, sont dispersés de façon très homogène entre les grains métal–oxyde. Des céramiques et des nanocomposites métal–oxyde ont aussi été préparés pour permettre des comparaisons. La microstructure des échantillons a été étudiée et discutée en relation avec la nature de la matrice, la conductivité électrique, la résistance à la rupture et la ténacité. Les composites nanotube de carbone–métal–oxyde sont conducteurs électriques grâce à la percolation des nanotubes de carbone.
The weight and density of carbon nanotubes are calculated as a function of their characteristics (inner diameter, outer diameter, and number of walls). The results are reported in the form of ...diagrams which may be useful to other researchers, in particular in the fields of synthesis/production, materials and composites, health/toxicity studies.
In situ Raman spectroscopy allows for a detailed and time-resolved investigation of the kinetics of complex physical or chemical processes. Oxidation has become a frequently used method for the ...removal of disordered carbon species from carbon nanotubes. Oxidation, however, can also induce damage to the tubes and destroy most of the sample. We conducted an in situ Raman spectroscopy study of the oxidation of double- and single-walled carbon nanotubes (DWCNT and SWCNT) under isothermal and nonisothermal conditions to identify the temperature range in which the oxidation of amorphous carbon occurs without any changes with respect to the tubes and their structure. In situ Raman spectroscopy analysis of the oxidation of DWCNTs showed a decrease in the intensity of the D band starting around 370 °C, followed by complete D band elimination at 440 °C. Oxidation studies of SWCNTs showed a similar decrease in the D band intensity, but the D band was not completely eliminated. Furthermore, in situ measurements allow us to determine the different contributions to the D band feature and show the relationship between the D band, G band, and RBM Raman modes in the Raman spectra of DWCNT upon heating. Isothermal oxidation provides an efficient purification method for DWCNTs and SWCNTs, which is also selective to tube diameter. After oxidation, tubes show clean surfaces without disordered or amorphous carbon impurities.
In this Letter, we present an in situ Raman spectroscopy study of oxidation-induced changes in the structure and composition of double-wall carbon nanotubes (DWCNTs). Above 480
°C, the intensity of ...the D band decreases to less than 0.01% of the G band intensity, when measured using the 780
nm laser excitation. The D band was absent from the Raman spectra recorded with the 514.5
nm excitation. Thermogravimetric analysis and high-resolution transmission electron microscopy are used to explain the observed results. We conclude that oxidation provides a purification method for the DWCNT which leads to a sample containing tubes having nearly clean surfaces without disordered carbon.
•Ultrasonication results in replacement of edge CBr bonds by the COH ones.•Adsorption energy of Br2 molecules is higher for pre-sonicated DWCNTs.•Bromine molecules prefer to sit near the edge ...hydroxyl groups.•Hydroxyl-terminated DWCNTs accept electron density from Br2.
Bromination of double-walled carbon nanotubes (DWCNTs) was carried out using a saturated vapor of Br2 at room temperature with or without a pretreatment in bromine water. X-ray photoelectron spectroscopy revealed that ultrasound pretreatment modified the chemical state of bromine in the product. The binding energies of the Br 3d electrons in the pre-sonicated DWCNT sample were between those characteristic of the covalent C–Br bonds and the negatively charged Br2 molecules, observed when the pretreatment was not performed. Raman spectroscopy, however, clearly evidenced Br–Br vibrations in both brominated samples. Calculations of CNT–Br2 models within density functional theory were used to propose that the electronic state of a Br2 molecule depends on the adsorption site. The bromine molecules prefer to be located near edge hydroxyl groups, which acept the electron density from Br2. This increases the binding energy of Br 3d levels as compared to that for Br2 molecules in other adsorption sites.
We report the influence of catalyst preparation conditions for the synthesis of carbon nanotubes (CNTs) by catalytic chemical vapour deposition (CCVD). Catalysts were prepared by the combustion route ...using either urea or citric acid as the fuel. We found that the milder combustion conditions obtained in the case of citric acid can either limit the formation of carbon nanofibres (defined as carbon structures not composed of perfectly co-axial walls or only partially tubular) or increase the selectivity of the CCVD synthesis towards CNTs with fewer walls, depending on the catalyst composition. It is thus for example possible in the same CCVD conditions to prepare (with a catalyst of identical chemical composition) either a sample containing more than 90% double- and triple-walled CNTs, or a sample containing almost 80% double-walled CNTs.
We report on the enhancement of magnetic properties of multiwalled carbon nanotubes (MWNTs) functionalized with a gadolinium based supramolecular complex. By employing a newly developed synthesis ...technique we find that the functionalization method of the nanocomposite enhances the strength of magnetic interaction leading to a large effective moment of 15.79 µ
and non-superparamagnetic behaviour unlike what has been previously reported. Saturating resistance at low temperatures is fitted with the numerical renormalization group formula verifying the Kondo effect for magnetic impurities on a metallic electron system. Magnetoresistance shows devices fabricated from aligned gadolinium functionalized MWNTs (Gd-Fctn-MWNTs) exhibit spin-valve switching behaviour of up to 8%. This study highlights the possibility of enhancing magnetic interactions in carbon systems through chemical modification, moreover we demonstrate the rich physics that might be useful for developing spin based quantum computing elements based on one-dimensional (1D) channels.
This paper presents the performances of 4
cm
2 supercapacitors cells assembled with 200
μm thick active material films composed with activated carbon and carbon nanotubes mixture in organic ...electrolyte. Galvanostatic and electrochemical spectroscopy impedance measurements have been carried out. Galvanostatic measurements show that both internal resistance and specific capacitance decrease when the carbon nanotubes content increases in the active material. With 15% of carbon nanotubes, the internal resistance is 0.65
Ω
cm
2 and the specific capacitance is 90
F
g
−1 measured at 20
mA
cm
−2. This performances remain stable during 10,000 cycles.
The characterization of the frequency behavior was made by Electrochemical Impedance Spectroscopy. For 15% of CNTs content in the active material, the relaxation time (
φ = −45°) is divided by 3 as compared to a supercapacitor using pure activated carbon electrodes.
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