The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
The oxidation behavior of reactive carbon fibers, such as ex-Pan T300, is studied in oxidizing environments by means of TGA and tensile strength measurements. Different carbide coatings are investigated with a view to fiber protection during an air exposition at high temperature. Thin, continuous, and uniform films of TiC, SiC, B 4 C, or B 4 C/SiC multilayers are obtained by an RCVD...
Silicon carbide (SiC) was chemical vapor deposited (CVD) onto a carbon fiber to investigate oxidation protection of the coating. This thin film of SiC was analyzed before and after argon and oxygen ion beam etching with core and valence band X-ray Photoelectron Spectroscopy (XPS). The valence band of SiC could be reasonably interpreted by a spectrum generated by a multiple scatter-wave Xα calculation...
SiC coatings prepared by chemical vapor deposition and from polycarbosilane (PCS) solution; also, SiO 2 and Al 2 O 3 coatings by Sol-Gel method were investigated in detail, to improve the oxidation resistance of carbon fibers as important reinforcement in advanced composites. A β-SiC coating was obtained on carbon fibers by pyrolysis of CH 3 SiCl 3 and H ...
Epoxide functions were successfully bonded onto the surfaces of nitric acid-oxidized PAN-based high-strength carbon fibers by reacting surface acidic functions with epichlorohydrin. A two-stage process that included ring opening and ring closure under anhydrous conditions was employed to avoid polymer formation on the surface. Typically, more than 30 μeq of epoxy groups were bound to one gram of...
Angle-resolved X-ray photoelectron spectroscopy (ARXPS) and ion-scattering spectroscopy (ISS) are utilized to investigate the surface composition of BASF type II carbon fibers as a function of progressive exposures to aqueous nitric acid. To the authors' knowledge this is the first such study of carbon fibers to incorporate both of these surface analytical techniques. Overall, the ARXPS and ISS...
A method based on the decomposition of phenylacetylene and thiophene on a Ni-powder catalyst has been used to produce nanotubes, circular hollow structures, and other interesting graphitic morphologies. The structures obtained are analyzed using HREM. The stability of bent graphite sheets is studied.
Nitric acid oxidation effectively created acidic functional groups on PAN-based high-strength carbon fibers. The acidic capacities of carbon fibers increased with oxidation time. Typically, 60 minutes of oxidation created 60 μeq acidic functional groups on each gram of carbon fibers. Nitric acid oxidation also caused tensile strength decreases and fiber weight losses. By treating fibers in refluxing...
Poly(vinylacetylene) obtained by the selective polymerization of monovinylacetylene through the vinyl group has been investigated for its use as an alternative precursor for carbon fibers. The low yield of char obtained on pyrolysis of the polymer in an inert atmosphere was improved dramatically by subjecting its fibers to an oxidative treatment before the carbonization step. Optimization of this...
The shrinkage stress of the precursor polyacrylonitrile (PAN) fibers during oxidation was measured under various conditions, and was found to decrease with cooling the fibers from certain oxidation temperatures, depending strongly on the degree of oxidation, and to become constant below 180°C. Here, the stabilization index, SI, was proposed to be a measure of the oxidation of the PAN fibers, which...
Mesophase pitch-based carbon fibers with circular and non-circular (ribbon, C-shaped) cross sections were coated with a thin, approximately 100-150 nm SiC-layer, using a CVD technique. The surface free energy of the uncoated and SiC-coated carbon fibers was determined by measuring the contact angle of a variety of liquids with known polar and dispersive components of their total surface free energy...
The incorporation of 0.1-0.2 μm diameter carbon filaments (0.6 vol.%) between continuous carbon fiber (7 μm diameter, 56.5 vol.%) layers in an epoxy-matrix composite during composite fabrication was found under flexure to greatly increase transverse and longitudinal tan δ values, increase the storage modulus in the transverse direction, slightly decrease the storage modulus in the longitudinal direction,...
Intercalation of P-120 pitch-based fibers with bromine, from the vapor phase or liquid bromine, has been investigated. The maximum weight uptake was 20-25%, nearly independent of intercalation temperature. Intercalated samples were characterized by X-ray diffraction, Raman scattering and differential scanning calorimetry. Thermogravimetry experiments showed that a large amount (up to 50%) of bromine...
The surface of vapor-grown carbon filaments (types H79 and ADNH of Applied Sciences Inc.) was found to be covered with a layer of tarry substance (comprising primarily polyaromatic hydrocarbons and originating from the filament growth process), which degraded the electrochemical performance (as shown by cyclic voltammetry using the Fe(CN) 6-3 redox couple), increased the filament-to-filament...
The connection of two straight chiral or achiral cylindrical carbon nanotube sections of approximately the same diameters connecting at a ''knee'' angle of π is described. Such knees are based on the insertion in the plane of the knee of diametrically opposed pentagonal and heptagonal rings in the hexagonal network. Relationships are also established between the nanotubes and their concentric graphitic...
The fiber length distributions of carbon fibers grown on alumina substrates by the vapor phase decomposition of benzene have been measured at different lengthening times in the temperature range of 1283–1353 K and at two concentrations of benzene. The proportion of longer fibers increased with lengthening time. A two-parameter model has been used to compare the calculated and experimental fiber length...
Isocyanate functional groups can readily react with sterically accessible acidic functional groups on carbon fiber surfaces. Solvent effects on these reactions were investigated. Polar solvents such as DMF seem to favor this reaction. The grafting efficiency of isocyanate terminated-oligomers decreased with increasing molecular weight even though the total weight gain was higher when higher molecular...
A (6, 12) Lennard-Jones formulation is used to evaluate the enthalpy of formation of multilayered coaxial or scroll-like carbon nanotubes. The role of various parameters—such as interlayer spacing, value of the innermost radius, number of layers—is examined. Most of the nanotubes examined turn out to be metastable, with a small but positive heat of formation.
Results of Parts I and II on the surface chemistry of surface-oxidized carbon fibers were used (1) for an interpretation of the W SL /pH diagram, and (2) an assessment of the usefulness of surface analytical methods. Results of XPS (O1s:C1s ratio) can be correlated with the results of TPD. However, the work of adhesion results as determined by CAM (contact angle measurements) do not correlate...
The surface structure and chemistry of various surface oxidized HT carbon fibers, an IM and a HM carbon fiber were studied by SEM, STM, CAM (contact angle measurement), XPS and TPD with special reference to adsorbed oxidation products and adsorbed water. It is shown that a real image of surface structure and surface chemistry is only obtained after removal of adsorbed oxidation products by extraction...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.