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Nanometric graphitic structures (fullerenes, nanotubes, bucky-onions, etc.) form in different harsh environments (electric arc, electron irradiation, plasma torch). In particular, the onion-like graphitic particles may display a wide range of structures, going from polyhedral to nearly spherical. High-resolution electron microscopy is the primary tool for studying these systems. On the basis of...
Encapsulation of foreign materials within a hollow graphitic cage was carried out for rare-earth and iron-group metals by using an electric arc discharge. The rare-earth metals with low vapor pressures, Sc, Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, and Lu, were encapsulated in the form of carbides, whereas volatile Sm, Eu, and Yb metals were not. For iron-group metals, particles in metallic phases...
Structural and spectroscopic studies of a new graphite uranyl sulfate phase are performed. By using X-ray diffraction, an electron distribution pattern along the graphite c-axis for stages 1-4 is calculated, based on [001] analysis; [hk0] and [hkl] reflection analysis allows the determination of the parameters of the planar primitive cell and demonstrates the existence of a three-dimensional order...
The electrochemical properties of carbon fibres (CFs) differentiated by heat treatment at temperatures up to 2400°C and oxidation in concentrated nitric acid were studied.Changes in the shapes of cyclic voltammetric curves for working electrodes prepared from carbon fibres (CFs) were analysed in aqueous and nonaqueous electrolytes. Possible ranges of the sweep potential were estimated for the electrochemical...
A high resolution transmission electron microscopy study of fluorine-intercalated carbon fibers has been carried out on two types of host materials: high-temperature treated pitch-based and PAN-based fibers. TEM images and corresponding Fourier transforms have shown that only stage-1 compounds and graphitic-type domains are detected in the experiment conditions. In particular, no interlayer spacing...
Plasma-assisted Chemical Vapor Deposition (PACVD) B 4 C coating and a hybrid PACVDB 4 C Si 3 N 4 coating were deposited on a two-dimensional C-C substrate. Oxidation behavior of coated and uncoated C-C composites was studied using a thermogravimetric analyzer (TGA) in both the isothermal and kinetic mode. The PACVD coating provided an excellent oxidation protection...
Different preparation methods of Pt(IV) chloride-graphite intercalation compounds from micrometer sized graphite powder and their subsequent chemical reduction are described. The reaction products were investigated by XRD, SEM, EDX and neutron activation analysis. Pt(IV) chloride-GIC was obtained by the isothermal vapour transport method of PtCl 4 between 350 and 500°C under a pressure of...
Active carbons of different origins (ex-coconut shell, ex-coal, ex-peat and ex-wood) have been used as adsorbents of potassium aurocyanide. Various treatments were applied to the active carbons: heat treatment at 800°C, heat treatment at 800°C followed by HCl (1) washing, heat treatment at 650°C, washing with HCl 10%, esterification with methanol, oxidation with nitric acid and extraction with toluene...
Carbon/carbon composites with porosities as low as 7% were fabricated within 8-12 hours using the forced flow-thermal gradient chemical vapor infiltration (FCVI) process. Preforms consisting of 40 layers of T-300 plain weave carbon cloth were infiltrated with a feed containing a carbon source and a diluent. The carbon sources studied in the present work included propylene, propane, and methane and...
Chemical vapor deposition (CVD) coatings used for the oxidation protection of carbon-carbon (C-C) composites provide inadequate oxidation protection due to extensive thermal cracking. One method to reduce the thermal cracking is to use plasma-assisted chemical vapor deposition (PACVD). In this study a PACVD SiC coating and a hybrid PACVD SiC Si 3 N 4 multilayer coating were deposited...
The synthesis of electrochemical carbyne from perfluorinated hydrocarbons was optimized. The relative yield of carbyne was monitored by Raman spectroscopy using the C C stretching mode. The position and relative intensity of this band depend on the type of fluorocarbon and reducing agent used. Optimum conditions were attained for electrochemical reduction of poly(tetrafluoroethylene) with K- or...
1 3 C NMR and FTIR analyses have been employed to follow the evolution of chemical structure in relation to porosity development, as a function of heat treatment temperature (HTT), for activated carbons produced from white oak by phosphoric acid activation. The chemical changes affected by acid treatment at low HTT are: by 50°C there is significant alteration of the lignin structure; by 100°C...
To improve the performance of adsorption machines using the activated carbon-methanol pair, a new procedure for shaping adsorbent materials as bricks was developed. In this paper, research activity on the preparation of composite carbon samples is described together with the results on methanol adsorption capacity and on thermal conductivity measurements. Carbon bricks of a pre-defined form were...
This study is concerned with the use of air-blowing to improve pitch properties as matrix precursor of carbon-carbon composites. Two commercial coal-tar pitches, an impregnating pitch and a binder pitch, and their air-blown products obtained at temperatures between 250 and 300°C, were pyrolyzed in a horizontal tube furnace at 1000°C. Cokes were characterized by light microscopy to monitor the influence...
Analysis of data for the adsorption of various molecular probe molecules on a number of different microporous carbons has revealed an empirical relationship between log(n 0 ) and log(V m ), wheren 0 /mmol g -1 is the micropore capacity for a given adsorptive andV m /cm 3 mol -1 the corresponding adsorptive molar volume. It is shown...
The elastic properties of individual vapor-grown carbon fibers have been studied via the low-strain, vibrating-reed technique. The average Young's modulus is found to be 680 GPa, with some indication that the intrinsic modulus of CVD carbon may be much higher. This value exceeds those found by earlier high-strain, static-pulling methods. Although the amplitude of vibrational response for these...
Pulse chemical vapor infiltration (P-CVI) was developed to study both the texture and density of infiltrated pyrocarbon. In this work model pores were machined in graphite with various diameters. Compared to classical chemical vapor infiltration (I-CVI) where the deposition of pyrocarbon is mainly controlled by temperature, pressure and precursor type, P-CVI provides an additional controlling parameter:...
A new adsorbent was prepared by chemical activation of elutrilithe with potassium hydroxide. A systematic study of the effect of the synthesis parameters, the mixing ratio of KOH, activation temperature and time, on the final products was investigated. The prepared samples were subjected to benzene adsorption at room temperature for characterization by the Dubinin-Radushkevich (DR) method for the...
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