Silicon carbide resistivity

Other solid-state applications of silicon carbide include its use as an electroluminescent diode for use in sound recording equipment and photomultipliers and controllers. It has been studied as a reflective surface for lasers. By combining its excellent thermal conductivity and high electrical resistance, silicon carbide has also found application as an insulating material for integrated circuit substrates. 

Due to its great hardness, heat resistance, and oxidation resistance, silicon carbide has become firmly established as an abrasive as well as a raw material for producing refractories such as firebricks, setter tiles, and heating elements. Another major use of silicon carbide is as a siliconizing and carburizing agent in iron and steel metallurgy. 

The MFEs are coated particles similar to TRISO fuel with the outer diameters of about 2 mm. They consist of 1.5-1.64 mm diameter uranium dioxide spherical kernels coated with 3 ceramic layers. The inner layer, called a buffer layer, is made of 0.09 mm thick porous pyrolythic graphite (PyC) with the density of 1 g/cm, providing space for gaseous fission products. The second layer is made of 0.02 mm thick dense (1.8 g/cm ) PyC, and the outer layer is 0.07-0.1 mm thick corrosion resistant silicon carbide (SiC). The fourth, outer PyC layer is assumed to be absent. SiC protection layers, manufactured by chemical vapour deposition (CVD) method, create resistance of graphite components against water and steam at high temperatures. Small fuel elements are able to confine fission products indefinitely at temperatures below 1600°C. 

Sliding rings Wear resistance Silicon carbide... 

The formation of silicon carbide, SiC (carborundum), is prevented by the addition of a little iron as much of the silicon is added to steel to increase its resistance to attack by acids, the presence of a trace of iron does not matter. (Addition of silicon to bronze is found to increase both the strength and the hardness of the bronze.) Silicon is also manufactured by the reaction between silicon tetrachloride and zinc at 1300 K and by the reduction of trichlorosilane with hydrogen. 

Silicon Carbide. Sihcon carbide is made by the electrofusion of siUca sand and carbon. SiUcon carbide is hard, abrasion resistant, and has a high thermal conductivity. It is relatively stable but has a tendency to oxidize above 1400°C. The siUca thus formed affords some protection against further oxidation (see Carbides). 

Silicon carbide has very high thermal conductivity and can withstand thermal shock cycling without damage. It also is an electrical conductor and is used for electrical heating elements. Other carbides have relatively poor oxidation resistance. Under neutral or reducing conditions, several carbides have potential usehilness as technical ceramics in aerospace appHcation, eg, the carbides (qv) of B, Nb, Hf, Ta, Zr, Ti, V, Mo, and Cr. Ba, Be, Ca, and Sr carbides are hydrolyzed by water vapor. 

The engineering properties of electroless nickel have been summarhed (28). The Ni—P aHoy has good corrosion resistance, lubricity, and especiaHy high hardness. This aHoy can be heat-treated to a hardness equivalent to electrolytic hard chromium [7440-47-3] (Table 2), and the lubricity is also comparable. The wear characteristics ate extremely good, especiaHy with composites of electroless nickel and silicon carbide or fluorochloropolymers. Thus the main appHcations for electroless nickel are in replacement of hard chromium (29,30). 

In the Premier Mill the rotor is shaped hke the frustrum of a cone, similar to that in Fig. 20-53. Surfaces are smooth, and adjustment of the clearance can be made from 25 [Lm (0.001 in) upward. A small impeller helps to feed material into the rotor gap. The mill is jacketed for temperature control. Direct-connected hquid-type mills are available with 15- to 38-cm (6- to 15-in) rotors. These mills operate at 3600 r/min at capacities up to 2 mVh (500 gal/h). They are powered with up to 28 kW (40 hp). Working parts are made of Invar alloy, which does not expand enough to change the grinding gap if heating occurs. The rotor is faced with Stellite or silicon carbide tor wear resistance. For pilot-plant operations, the Premier Mill is available with 7.5- and 10-cm (3- and 4-in) rotors. These mills are belt-driven and operate at 7200 to 17,000 r/min with capacities of 0,02 to 2 mVh (5 to 50 gal/h). 

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. 

Bricks of silicon carbide, either recrystaUized or clay-bonded, have a high thermal conductivity and find use in muffle walls and as a slag-resisting material. 

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... 

A wide range of applications for hard, wear-resistant coatings of electroless nickel containing silicon carbide particles have been discussed by Weissenberger . The solution is basically for nickel-phosphorus coatings, but contains an addition of 5-15 g/1 silicon carbide. Hiibner and Ostermann have published a comparison between electroless nickel-silicon carbide, electrodeposited nickel-silicon carbide, and hard chromium engineering coatings. 

Silicon Carbide. SiC has low thermal expansion, high hardness, and good resistance to oxidation. It is used extensively in the coating of graphite and carbon to impart wear and oxidation resistance. 

Two fibers are presently produced by CVD on a commercial scale boron and silicon carbide. The production of these two fibers requires a monofilament starter core capable of being heated resistively such as a tungsten or graphite fiber. I l The deposition apparatus is shown schematically in Fig. 19.1. 

Keywords Inorganic fiber Oxide fiber Silicon carbide fiber Heat resistance Photocatalyst... 

Abrasion-resistant white cast irons, molybdenum in, 17 17 Abrasive Grain Association (AGA), silicon carbide standards by, 22 537, 538 Abrasive materials, phenolic resins in,... 

Shrink-resist science/technology development of, 26 391 Shrink-resist treatments, 26 391-393 additive, 26 393 chlorine-based, 26 392 chlorine-free, 26 392-393 Shuiskite, 6 471t Shutdown period, 29 494 Shutdown systems, 20 671-672 Shuttle vectors, 26 482-483 Sialon-bonded silicon carbide, 22 541 Siberian red lead, 6 468 S-iB-S block copolymers, 24 707 SiC-ceramic, 22 525. See also Silicon carbide... 

Use of the ceramic honeycomb packing structure in the recuperator keeps fuel and air substantially isolated as they travel through the recuperator. Various ceramic materials such as cordierite, mullite, alumina and silicon carbide can be used to fabricate honeycomb beds. While metallic materials have the potential to be used in honeycomb bed, corrosion resistance is a major issue... 

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