Structures silicon carbides

Sintered silicon carbides are formed by all the traditional methods as well as standard plastic forming techniques such as injection molding. These compacts are sintered with small amounts of additives at very high temperatures in inert atmospheres to form essentially a single phase silicon carbide structure. 

Nakagomi, S., Tobias, R, Baranzahi, A., Lundstrom, I., Martensson, P. and Lloyd Spetz, A. (1997), Influence of carbon monoxide, water and oxygen on high temperature catalytic metal-oxide silicon carbide structures. Sensors and Actuators 5,45,183-91. 

The basic element of the silicon carbide structure is the tetrahedron [17] due to sp hybridization of the atomic orbitals. This tetrahedron consists of a silicon or a carbon atom at the spatial center, surrounded by four atoms of the other kind. The SiC- bond is 88% covalent. The tetrahedra are arranged in such a way that units of three silicon and three carbon atoms form angled hexagons which are arranged in parallel layers as shown in Fig. 4. 

Copies of the report entitled "Characterization of Sintered Silicon Nitride and Silicon Carbide Structural Ceramics." prepared by Mr. M. E. Hatcher of KemaNord IndustrlkemI In Sweden and printed at ORNL, were distributed to all participants on December 8. 

A phosphoric acid fuel cell (PAFC) consists of an anode and a cathode made of finely dispersed platinum catalyst on a carbon and silicon carbide structure that holds the liquid phosphoric acid electrolyte. Typically, PAFC systems have an operating temperature of around 200°C. When used for the co-generation of electricity and heat, PAFC cells... 

Silicon carbide structures are formed by hot pressing, dry and isostatic pressing (preferred), CVD, or slip casting. Isostatic pressing using gas as the fluid provides optimum mechanical properties. 

Tobias, R, Baranzahi, A., Spetz, A.L. (1997). Fast chemical sensing with metal-insulator silicon carbide structures. IEEE Electron Deoice Lett., Vol.18, No. 6, pp. 287-289 Tomchenko, A. A., Harmer, G. R, Marquis, B. T. Allen, J. W. (2003). Semiconducting metal oxide sensor array for the selective detection of combustion gases. Sensors and Actuators B, Vol. 93, pp. 126-134... 

Phosphoric Acid Fuel Cell This type of fuel cell was developed in response to the industiy s desire to expand the natural-gas market. The electrolyte is 93 to 98 percent phosphoric acid contained in a matrix of silicon carbide. The electrodes consist of finely divided platinum or platinum alloys supported on carbon black and bonded with PTFE latex. The latter provides enough hydrophobicity to the electrodes to prevent flooding of the structure by the electrolyte. The carbon support of the air elec trode is specially formulated for oxidation resistance at 473 K (392°F) in air and positive potentials. 

The covalently-bonded silicon carbide, silicon nitride, and sialons (alloys of Si3N4 and AI2O3) seem to be the best bet for high-temperature structural use. Their creep resistance... 

There are, of course, many more ceramics available than those listed here alumina is available in many densities, silicon carbide in many qualities. As before, the structure-insensitive properties (density, modulus and melting point) depend little on quality -they do not vary by more than 10%. But the structure-sensitive properties (fracture toughness, modulus of rupture and some thermal properties including expansion) are much more variable. For these, it is essential to consult manufacturers data sheets or conduct your own tests. 

The very hard structural ceramics silicon carbide, SiC, and silicon nitride, Si3N4 (used for load-bearing components such as high-temperature bearings and engine... 

On silicon carbide, it is easier to see and measure step heights than in crystals like beryl, because SiC has polytypes, first discovered by the German crystallog-rapher Baumhauer (1912). The crystal structure is built up of a succession of close-packed layers of identical structure, but stacked on top of each other in alternative ways (Figure 3.24). The simplest kind of SiC simply repeats steps ABCABC, etc., and the step height corresponds to three layers only. Many other stacking sequences... 

Pure silicon carbide is colorless, but iron impurities normally impart an almost black color to the crystals. Carborundum is an excellent abrasive because it is very hard, with a diamondlike structure that fractures into pieces with sharp edges (Fig. 14.43). 

The atomic and crystalline structure of the two non-metallic carbides, boron and silicon carbides, is less complex than that of the... 

Silicon carbide (SiC) is a major industrial material with a considerable number of applications. CVD plays a significant role in its development and production, SiC is a covalent carbide with two phases a and [3. The phase of major interest here is pSiC, which has a cubic zinc blend structure. It is the one reported here. 

Silicon carbide occurs in two slightly different crystal structures a single cubic form, (3SiC, and a large number of hexagonal... 

CVD is used in the industrial production of inorganic structural fibers such as boron and silicon carbide. Boron fibers are, in... 

Roewer G, Herzog U, Trommer K, Muller E, Friihauf S (2002) Silicon Carbide - A Survey of Synthetic Approaches, Properties and Applications 101 59-136 Rosa A, Ricciardi G, Gritsenko O, Baerends EJ (2004) Excitation Energies of Metal Complexes with Time-dependent Density Functional Theory 112 49-116 Rosokha SV, Kochi JK (2007) X-ray Structures and Electronic Spectra of the n-Halogen Complexes between Halogen Donors and Acceptors with jc-Receptors. 126 137-160 Rudolf P, see Golden MS (2004) 109 201-229... 

Other stacking sequences than these are also possible, for example AaBpAaCy... or statistical sequences without periodic order. More than 70 stacking varieties are known for silicon carbide, and together they are called a-SiC. Structures that can be considered as stacking variants are called polytypes. We deal with them further in the context of closest-sphere packings (Chapter 14). 

Non-oxide ceramics such as silicon carbide (SiC), silicon nitride (SijN ), and boron nitride (BN) offer a wide variety of unique physical properties such as high hardness and high structural stability under environmental extremes, as well as varied electronic and optical properties. These advantageous properties provide the driving force for intense research efforts directed toward developing new practical applications for these materials. These efforts occur despite the considerable expense often associated with their initial preparation and subsequent transformation into finished products. 

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