Silicon carbide-carbon systems

Particulate Matter Other Than Systemic Poisons. Silica and asbestos dust produce fibrosis. Silicon carbide, carbon (other than exhaust emissions), and emery are inert dusts. Many organic dusts, eg, pollen, wood, and resins, cause allergic reactions. Acids, alkalies, fluorides, and chromates are irritants. 

The fuel for the Peach Bottom reactor consisted of a uranium-thorium dicarbide kernel, overcoated with pyrolytic carbon and silicon carbide which were dispersed in carbon compacts (see Section 5), and encased in graphite sleeves [37]. There were 804 fuel elements oriented vertically in the reactor core. Helium coolant flowed upward through the tricusp-shaped coolant channels between the fuel elements. A small helium purge stream was diverted through the top of each element and flowed downward through the element to purge any fission products leaking from the fuel compacts to the helium purification system. The Peach... 

If the composite is left only partially densified, it can be used as a filter for high temperature filtering systems with high collection efficiency as required in direct coal-fired gas and steam turbines. Similar systems are considered for particulate filtering in diesel engines by a carbon foam or felt coated with silicon carbide by CVI. 

Carbon isotopic compositions of silicon carbide grains from the Murchison meteorite compared with the carbon isotopic compositions of carbon stars (low- to intermediate-mass AGB stars). The composition of carbon in the solar system is indicated by the vertical line. Note the similarity in the distributions of compositions in the two plots. These data indicate that the silicon carbide in the Orgueil meteorite came from a population of carbon stars very similar to that in the galaxy today. 

Photochemical reduction of C02 was also achieved in the presence of the p-type semiconductor (copper oxide) or silicon carbide electrodes [97]. Irradiation of this system generates methanol and methane as the main products in the case of CuO electrode whereas hydrogen (with efficiency about 80%), methanol (16%), methane, and carbon monoxide in the case of SiC electrode. Also Ti02/CuO systems appeared relatively efficient (up to 19.2% quantum yield) in photocatalytic C02 to CH3OH reduction [98]. 

The catalysts and electrode materials used in PAFCs are also similar to those in acidic H2/air fuel cells. Carbon-supported Pt is used as the catalyst at both anode and cathode, porous carbon paper serves as the electrode substrate, and graphite carbon forms the bipolar plates. Since a liquid electrolyte is used, an efficient water removal system is extremely important. Otherwise, the liquid electrolyte is easily lost with the removed water. An electrolyte matrix is needed to support the liquid phosphoric acid. In general, a Teflon -bonded silicon carbide is used as the matrix. 

Many body potentials e.g. Sutton-Chen, Tersoff, " Brenner can be used to describe metals and other continuous solids such as silicon and carbon. The Brenner potential has been particularly successful with fullerenes, carbon nanotubes and diamond. Erhart and Albe have derived an analytical potential based on Brenner s work for carbon, silicon and silicon carbide. The Brenner and Tersolf potentials are examples of bond order potentials. These express the local binding energy between any pair of atoms/ions as the sum of a repulsive term and an attractive term that depends on the bond order between the two atoms. Because the bond order depends on the other neighbours of the two atoms, this apparently two-body potential is in fact many-body. An introduction and history of such potentials has recently been given by Finnis in an issue of Progress in Materials Science dedicated to David Pettifor. For a study of solid and liquid MgO Tangney and Scandolo derived a many body potential for ionic systems. 

The known presolar/circumstellar phases diamond, silicon carbide, and graphite each contain a distinct noble-gas component which, like the major (except perhaps for carbon in diamonds), minor, and other trace elements in these phases, is radically anomalous compared to normal solar-system composition. These components are listed in Table 2 and illustrated in Figure 5. In the exploratory studies in which an understanding of these components was being developed, a variety of more-or-less complicated names, typically an acronym for some descriptive phrase or arbitrarily selected alphabetic characters (not all from the Latin alphabet), have been used. Some... 

Included in the term nonoxide ceramics are all non-electrically conducting materials in the boron-carbon-silicon-aluminum system. The industrially most important representatives, apart from carbon (see Section 5.7.4), are silicon carbide (SiC), silicon nitride (Si3N4), boron carbide (B4C), boron nitride (BN) and aluminum nitride (AIN). 

Proton studies using MQ techniques have been made to determine the proton distribution in systems such as hydrogenated amorphous silica films (Levy and Gleason 1993a) and silicon carbide (Petrich et al. 1987). Hydrogen doping of carbon-based... 

Silicon carbide has attracted considerable interest because of its good mechanical and physical properties and chemical inertness. One of the most important applications of SiC is to produce a matrix reinforced by fibres, forming ceramic-matrix composites. These composite materials exhibit much better fracture toughness than monolithic ceramics. Compared with carbon/carbon composites, fibre-reinforced SiC matrix composites possess superior oxidation resistance and mechanical properties. The Si-C-H-Cl system (e.g. methyltrichlorosilane, CH3SiCl3) has been used for SiC deposition because it is easy to produce stoichiometric SiC deposits. 

Acceptor dopants are introduced in the crucible either in elemental form or in the form of carbides. If a dopant is introduced in elemental form, it is placed in a special internal crucible with carbon or silicon carbide powder. This is required to prevent the dissolution of the crucible, in the case of aluminium doping, and to reduce the boron vapour pressure to the equilibrium value for the SiC-C system, in the case of boron doping. If elemental boron is placed in the vicinity of the substrate, this results in the formation of boron carbide on the crystal faces of SiC [46]. For moderate doping of crystals, grown at high temperatures, doped SiC sources also can be employed. 

JOINING AND INTEGRATION OF ADVANCED CARBON-CARBON AND CARBON-SILICON CARBIDE COMPOSITES TO METALLIC SYSTEMS... 

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