Carbon
This paper deals with the attempts made at LCTS to replace part of the carbon matrix of C-C composites by silicon carbide in order to improve the oxidation resistance. Oxidation kinetics of C-C-SiC are presented, as well as the incidence of oxidation on the degradation of the microstructure and the tensile strength of the composites. Modelling of the oxidation kinetics allows prediction of mass...
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...
The approach of matrix modification has been used to increase the high-temperature oxidation resistance of carbon-carbon composites. A distinct effect has been obtained, and the oxidation law of matrix-modified composites at high temperature has been investigated. Initially, the change in weight loss with oxidation time for matrix-modified carbon-carbon composites at constant temperature was studied...
A new coating system to minimise high-temperature oxidation and degradation for C-C composites has been examined in both isothermal tests and in cyclic tests after water vapour has been introduced. The coatings used consisted of various multilayers containing CVD boron, CVD-SiC, and glasses containing both boron powder and SiC particles. For all coatings investigated, significant improvements in...
Because of the excellent mechanical properties at elevated temperature, carbon-fiber reinforced carbon (carbon-carbon) composites have received much attention for high-temperature structural applications. One serious drawback against actual use of carbon-carbon composites is their poor oxidation resistance in high-temperature oxidizing atmospheres. In many attempts to develop an effective oxidation-protection...
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 ...
Two multilayered coatings were designed for protecting a 2D carbon-carbon composite material from oxidation in a particular application. The principles of coating design are presented and the results obtained indicate that the protective effect met the predetermined requirements. It is concluded that a desirable coating should be a glass material, insensitive to moisture, which has a compositional...
Silicon carbide with its excellent oxidation resistance and chemical compatibility with carbon is an attractive coating material for the high-temperature oxidation protection of graphite and carbon-carbon composites. One of the major challenges in the development of protective SiC coatings is preventing oxidation of the graphite substrate due to crack formation in the SiC coating. A boron-containing...
Ceramic coatings have been developed for the protection of carbon-carbon composites against oxidation at temperatures up to 1700°C. Coatings based on phosphorous oxides derived from POCl 3 were quite effective up to 900°C, the weight loss up to 600°C with 60 minutes' isothermal heating time decreasing from 75% to 2.6%. The coatings based on silicon (SiC) were effective up to a temperature...
Activated carbon fiber is an effective reducing agent for many high oxidation state ions. The reduction-adsorption capacity for Pt(IV) of activated carbon fibers derived from viscose rayon, sisal, and pitch were studied by chemical analysis of the reaction solutions and XPS study of the deposited platinum. The reduction-adsorption capacity of the viscose-based fibers was found to be the highest...
The carbonization of an industrial coal-tar pitch was studied, by using a tube bomb, as a function of carbonization temperature (520°C-580°C) and inert gas pressure (1-20 bar) and resultant green cokes were evaluated according to yield and observation under polarized light microscopy. At 520°C, green cokes present large isotropic domains as well as Brooks and Taylor's spheres whatever the pressure...
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...
Recently, the development of carbon molecular sieves (CMS) for the separation of various gases, particularly air into oxygen and nitrogen, has gained widespread attention. In this paper, a simple method was presented for preparing carbon molecular sieves. Carbonized walnut shells were impregnated with a small amount of potassium hydroxide (KOH) and pyrolysed. In this way, the pore size can be easily...
It is shown that the oxidation of an Asturian bituminous coal by air, at 150° and 270°C, has a considerable influence on the microporous structure of the carbon obtained by subsequent carbonization and steam activation to 50% burn-off. The direct activation of the coal leads to an open micropore system of 0.2 cm 3 /g, with an average pore size near 0.8 nm. On the other hand, much larger...
Methylene-bridged oligomers were prepared from naphthalene, tetralin, biphenyl, and their alkyl-substituted homologues and carbonized under an atmospheric pressure. The carbonization properties of oligomers were improved by alkyl groups to give anisotropic mesophase. The structural changes of the oligomers suggested that radicals formed from alkyl groups would accelerate the condensation reactions...
The carbonization behaviors of a series of synthetic naphthalene-derived mesophase pitch powders subjected to different time and temperature profiles of oxidative stabilization were studied by thermogravimetric analysis (TGA) and thermal volatilization analysis/sub-ambient thermal volatilization analysis (TVA/SATVA). Qualitative and quantitative analysis of the carbonization products was made using...
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...
The transformation of mesophase pitch to an ordered carbon by high-temperature heat treatment in an inert atmosphere must be preceded by a suitable period of thermosetting or oxidative stabilization. The chemical process of oxidative stabilization is not well characterized, although research has clearly indicated that the oxidation history of the mesophase has a profound impact on the mechanical...
Resin B and C (separated from hexane insoluble-benzene soluble fraction of Akabira SRC) produced isotropic cokes after carbonization. The pretreatment of heteroatom removal followed by hydrogenation (two-staged pretreatment) was more effective in attaining the anisotropic textures of widely developed flow domain type from both resin B and C, than pretreatment with only hydrogenation. The analytical...