Carbide carbon

Carbon, Carbides, and Nitrides. Carbon (graphite) is a good thermal and electrical conductor. It is not easily wetted by chemical action, which is an important consideration for corrosion resistance. As an important stmctural material at high temperature, pyrolytic graphite has shown a strength of 280 MPa (40,600 psi). It tends to oxidize at high temperatures, but can be used up to 2760°C for short periods in neutral or reducing conditions. The use of new composite materials made of carbon fibers is expected, especially in the field of aerospace stmcture. When heated under... 

Chromium carbide is important in powder preparations designed for thermal spray apphcations of corrosion and wear-resistant coatings on tool and machine parts. Lower carbon carbides of chromium are important in hardfacing tods and electrodes for weld-apphed ovedays on machine wear surfaces. However, these carbides are usually formed in situ from Cr and C in the rod and not added as preformed carbides. The properties of Ci2C2 are hsted in Table 2. 

Metal dusting usually occurs in high carbon activity environments combined with a low oxygen partial pressure where carburisation and graphi-tisation occur. Usually pits develop which contain a mixture of carbon, carbides, oxide and metal (Fig. 7.52). Hochmann" proposed that dusting occurs as the result of metastable carbide formation in the high carbon activity gas mixture which subsequently breaks down into metal plus free carbon. The dependence of the corrosion resistance of these nickel alloys on the protective oxide him has been described accelerated or internal oxidation occurs only under conditions that either prevent the formation, or lead to the disruption, of this him. In many petrochemical applications the pO is too low to permit chromia formation (ethylene furnaces for example) so that additions of silicon" or aluminium are commonly made to alloys to improve carburisation resistance (Fig. 7.53). 

Scientists from Politecnico di Milano and Ineos Vinyls UK developed a tubular fixed-bed reactor comprising a metallic monolith [30]. The walls were coated with catalytically active material and the monolith pieces were loaded lengthwise. Corning, the world leader in ceramic structured supports, developed metallic supports with straight channels, zig-zag channels, and wall-flow channels. They were produced by extrusion of metal powders, for example, copper, fin, zinc, aluminum, iron, silver, nickel, and mixtures and alloys [31]. An alternative method is extrusion of softened bulk metal feed, for example, aluminum, copper, and their alloys. The metal surface can be covered with carbon, carbides, and alumina, using a CVD technique [32]. For metal monoliths, it is to be expected that the main resistance lies at the interface between reactor wall and monolith. Corning... 

Recent investigations indeed are in support of some active form of carbon (carbide) involved at the catalyst surface. 

Two forms of carbon (carbidic and graphitic) have been observed by x-ray photoelectron spectroscopy (XPS) on polycrystalline cobalt foil during the disproportionation of CO by Nakamura et al.57 The dissociation of adsorbed CO occurred at temperatures higher than 60°C, and carbidic carbon and adsorbed oxygen were formed on the cobalt surface. After the surface is covered with adsorbed carbon and oxygen, no further dissociation of adsorbed CO occurs. Contrary to the dissociation of adsorbed CO, the deposition of carbon by the concerted Boudouard reaction continues on the carbidic carbon-deposited surface. The deposition of carbon increases... 

A large variety of catalysts, both homogeneous and heterogeneous, has been found active for dehydrohalogenation. The catalysts include a number of Br nsted and Lewis acids (liquid or soluble, as well as solid), metal oxides, active carbon, carbides, nitrides and some metals. However, in the latter case, the actual catalysts are most probably surface metal halides... 

Corrosion of iron is explained by the position of iron in the electrochemical series of the elements (Fe/Fe2+ —0.44 V). In steel, local anode and cathode areas are found due to the presence of phases containing, for example, carbon, carbides, and oxides. These latent local cells are activated by moisture, oxygen, and current-carrying electrolytes and the following reactions occur between the anode areas consisting of iron, and the cathode areas containing carbides or oxides. 

The reaction of metal oxide in powders in the presence of solid carbon. Carbides are obtained by closely mixing metal oxide powders with carbon, and heating, again as with the pure metals, at temperatures... 

Carbides and nitrides can be prepared in many ways (chemical vapour deposition, physical vapour deposition, precipitation of salts containing metal, carbon and oxygen followed by reduction and annealing, reaction of a metal or its oxides with a gas or with solid carbon). Carbides and nitrides are often nonstoichiometric with complex phase diagrams.4-9 The compounds sometimes contain multiple phases and impurities, notably oxygen. This can lead to even more complex compounds, like oxycarbides, carbonitrides or oxycarbonitrides. 

C02, at concentrations to effect the Boudoir equilibrium, cleaner surfaces were obtained. Ledoux et al., recently prepared carbides by depositing metal oxide vapors at 1373 K under vacuum over high surface area, 1200 m2 g-1, activated carbon. Carbides with Sg between 100-400 m2 g 1 were claimed.6 A comparison of several W03-based synthetic routes was made by Iglesia et al.1... 

Catalysts converted to -nitride were carburized very slowly at temperatures below 350°C. as shown in Table I. At 450°C., carbon (carbidic... 

Based on surface area measurements (hydrogen chemisorptions) the catalyst with 1 % alumina did not sinter as a result of reaction. This was in distinct contrast to the alumina-free catalyst initially used that sintered so completely upon re-reduction in hydrogen as to lose nearly 100% of its surface area. As for the potassium-promoted catalyst, SA measurements indcale a decrease in active metal sites of around 35% but it is not known whether this is due to sintering or unreduced carbon/carbide. 

Four iron catalysts promoted with varying amounts of potassium were reacted at 215°C in synthesis gas for 24 h and then tested using TPSR. The results of the experiments are shown in Figure 6, which tabulates the quantities of amorphous CHx carbon, carbidic, and graphitic carbon found on each catalyst. The most graphite formed on the unpromoted iron... 

Other reactions important to reforming are also considered in the reaction network in Figure 10, include the water-gas-shift reaction and its reverse, the reversible adsorption and decomposition of water, the desorption and adsorption of reforming products like CO, CO2, and H2, and the formation of hydrocarbons like CH. The formation of dissolved carbon, oxygen, and hydrogen in bulk nickel is also considered. Dissolved C, 0, or H may be important in the transport of those elements to or from interfaces with other solid phase (carbon, carbides, oxides, support). The possible formation of NiO from H2O is also shown. Finally, an important reaction to consider is the formation of a deactivating layer of carbons (6 or e carbon states). 

BeAI204 BERYLLIUM DIALUMINIUM TETRAOXIDE 180 CCN[g] CARBON CARBIDE-NITRIDE (GAS) 221... 

Alkali and alkaline earth metal salts of weak acids (carbonates, carbides, nitrides, silicates, etc.)... 

Gu, W., and G. Yushin. 2014. Review of nanostructured carbon materials for electrochemical capacitor applications Advantages and limitations of activated carbon, carbide-derived carbon, zeolite-templated carbon, carbon aerogels, carbon nanotubes, onion-Uke carbon, and graphene. Wiley Interdisciplinary Reviews Energy and Environment 3 424-473. 

A similar effect has been observed for many other hydrocarbons, i.e. adsorption and subsequent hydrogen flux reduction. Post-inspection of the surface often reveals carbonaceous surface contamination, like carbon, CH4 " or propylene. Secondary effects of CO adsorption is the catalytic decomposition and formation of carbon, carbide (Pdi xC )" " or carbonate phases. While reversible CO adsorption decreases with increasing temperature, catalytic decomposition appears to increase with temperature. The tendency of deposit forming due to catalytic decomposition is reported to be counteracted by the presence of steam " mitigating the flux reduction. 

Hydrocarbon formation is now believed to proceed via atomic carbon (carbide) to bridging methylene groups, and a chain polymerization process ... 

---