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During the electrochemical intercalation and deintercalation processes of sulfuric acid into graphite, the electrical resistivity along the graphene layers was followed with a contactless method. At 20°C, the intercalation process is associated with a large decrease of resistivity; the lowest values are observed for stages 8 to 5 formation, and remain nearly constant until stage 1. However, the...
The reactivity of fine-weave pierced 3D carbon-carbon composites in air at temperatures up to 3000°C was studied. The corrosion morphology and microstructure of oxidized samples were investigated by XPS, SEM, and XRD techniques, and the non-equilibrium nature of the oxidation process was pointed out. A thermochemical ablation model of C-C composites controlled by gas phase diffusion and reaction...
C-SiC binary matrix composites, made from a porous C-C preform infiltrated with SiC, are mechanically characterized under tensile, compressive, flexural, and shear loading. The results of these tests show that the materials exhibit non-brittle fracture and have excellent strength. The oxidation behavior of the materials has been studied. Measured mass loss data from the C-SiC binary matrix composites...
The formation and oxidation resistance of surface oxide layers formed on carbon-B 4 C-SiC composites with two different B 4 C-SiC ratios were investigated at elevated temperatures in dry and moist atmospheres. From SEM observation, X-ray diffraction analysis, EPMA, and ESCA measurements of the samples before and after oxidation, it was found that the oxidation resistance depended...
Oxidation protection systems or carbon-carbon composites have met limited success, particularly between 900 and 1500°C where internal glass inhibitors are relied upon to protect the composite. This study investigated potential halogenated glass protection systems for the protection of structural carbon-carbon composites. A series of fluoride and fluoroborate glass compositions were selected based...
Three commercial carbons (an activated cloth and two rayon-derived carbon cloths) were used as substrates for the preparation of low- and high-temperature carbon-carbon (C-C) composites by the liquid-phase impregnation/carbonization (LPIC) technique. A petroleum pitch was used as the matrix precursor. The carbon cloths were subjected to thermal treatment (in inert atmosphere) or activation (in CO...
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...
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...
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...
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...
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...
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...
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...
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...
An investigation has been made of the synthesis of formed (extruded) activated carbons from a bituminous coal by KOH activation. The coal was first pretreated by oxidation with nitric acid, at different levels of oxidation severity, in an attempt to introduce properties similar to those possessed by low-rank coals that can be directly processed in this way. It is found that hard, high-surface-area...
Ceramic coatings were prepared on the surface of carbon composites, using a process simpler than the ones presently known. The solid precursor is deposited on the substrate from a suspension, then submitted to heat treatment under controlled atmosphere.Owing to their good thermomechanical properties, β′-SiAlONs have been chosen as the coating agent. They were prepared by a low temperature process...
A continuous powder coating process was used to produce flexible, preimpregnated towpreg from a heat-treated Mitsubishi AR mesophase pitch powder (AR-120) and three different carbon fibers: T300 PAN-based fiber, P55 pitch-based fiber, and an experimental high thermal conductivity pitch-based ribbon fiber. The towpreg was hot-pressed into unidirectional composites, carbonized at 1100°C, oxidized and...
High temperature pyrolysis (1050-1200°C) of hexachlorobenzene under inert atmosphere leads to the formation of soot. The objective of this work is to characterize and study the soot and its reactivity with oxygen.SEM and TEM analysis show individual spherules with a mean diameter of 0.14 μm, and small aggregates and agglomerates are also observed. The bulk apparent density of 435 kg m - ...
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