Silicium carbide

Fired ceramic spheroids have been described for use as a well proppant [1051], Each spheroid has a core made from raw materials comprising mineral particulates, silicium carbide, and a binder. The mixture includes a mineral with chemically bound water or sulfur, which blows the mixture during firing. Therefore the core has a number of closed air cells. Each spheroid has an outer shell surrounding the core, comprising a metal oxide selected from aluminum oxide and magnesium oxide. The fired ceramic spheroids have a fired density less than 2.2 g/cm. ... 

The VPO catalyst was prepared by a method described previously [5]. The bulk molar PA ratio of the catalyst was 1.26 and the surface area was 44 m2/g. The catalyst was equilibrated for over 80 hours at the n-pentane/air reaction mixture at the temperature of about 390°C before measurements. Silicium carbide (Prolabo, purity > 99 % grain fraction 0.35 mm), n-pentane (Aldrich, purity > 99 % impurity identified as 2-pentenes) and methyl-tert-butyl ether (MTBE) (Aldrich, purity > 98 %) were used without further purification. 

Catalytic partial oxidation of o-xylene and naphthalene is performed mostly in intensively cooled multi-tubular fixed bed reactors, but systems with a fluidized bed were also developed. Typically, V20s/Ti02 catalysts with K2SO4 or A1 phosphates as promoter are used. In fixed bed reactors, the conversion of both feedstocks per pass is around 90%, and the selectivity is in the range 0.86-0.91 mol PA per mol naphthalene and 0.78 mol per mol o-xylene. (Note that the selectivity would be 100%, if only the reactions according to Eqs. (6.13.1) and (6.13.2), respectively, would take place.) The active compounds are distributed on spheres of porcelain, quartz, or silicium carbide (shell catalyst). The thickness of the shell is only around 0.2 mm, and the diffusion paths for the reactants are short. By this means, the influence of pore diffusion is small, and the unwanted oxidation of phthalic acid anhydride to CO2 is suppressed compared to a catalyst with an even distribution of active compounds where the influence of pore diffusion would be much stronger (see Section 4.5.6.3 Influence of Pore Diffusion on the Selectivity of Reactions in Series ). Thus the intrinsic reaction rates are utilized for the modeling of a technical reactor (next Section 6.13.2). 

Due to the upper temperature constrain for polymeric-based membranes (Mulder, 1997), there is a growing market for membranes based on solvent-resistant materials able to withstand high temperatures. Ceramic materials (silicium carbide, zirconium oxide, titanium oxide) endure harsh temperature conditions and show stable performance in solvent medium and so are excellent materials for membrane preparation. On that basis a new generation of OSN membranes have been developed, the inorganic composite membranes. 

Kohlenstoff-hydrat, n. carbohydrate, -kalium, n. potassium carbide, -kem, m. carbon nucleus. -kette,/. carbon chain, -legiening,/, carbon alloy, -metall, n. carbide, kohlenstoffrelch, a. rich in carbon. Kohlenstoff-silicium, n. carbon silicide. -ske-lett, n. carbon skeleton, -stahl, m. carbon steel, -stein, m. carbon brick, -sticlKtoff-titan, n. titanium carbonitride. -sulfid, n. 

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