Silicon carbide commercial potential

Polysilanes can be regarded as one-dimensional analogues to elemental silicon, on which nearly all of modern electronics is based. They have enormous potential for technological uses [1-3]. Nonlinear optical and semiconductive properties, such as high hole mobility, photoconductivity, and electrical conductivity, have been investigated in some detail. However, their most important commercial use, at present, is as precursors to silicon carbide ceramics, an application which takes no advantage of their electronic properties. 

Silicon carbide is also a prime candidate material for high temperature fibers (qv). These fibers are produced by three main approaches polymer pyrolysis, chemical vapor deposition (CVD), and sintering. Whereas fiber from the former two approaches are already available as commercial products, the sintered SiC fiber is still under development. Because of its relatively simple process, the sintered Ot-SiC fiber approach offers the potential of high performance and extreme temperature stability at a relatively low cost. A comparison of the manufacturing methods and properties of various SiC fibers is presented in Table 4 (121,122). 

Partially pvrolvzed poivsilastyrene membranes. Molecular sieve membranes can also be made from porous solids other than carbon and zeolitic materials. One such potential candidate is the family of precursors of silicon carbide. Among the possible precursors, polysilastyrene (phenylmeihylsilane-dimethylsilane copolymer) is commercially available and soluble in many common solvents such as toluene and tetrahydrofuran and can be crosslinked by UV radiation. Polysilastyrene is comprised of long chains of silicon atoms ... 

Non-oxide ceramic materials such as silicon carbide has been used commercially as a membrane support material and studied as a potential membrane material. Silicon nitride has also the potential of being a ceramic membrane material. In fact, both materials have been used in other high-temperature structural ceramic applications. Oxidation resistance of these non-oxide ceramics as membrane materials for membrane reactor applications is obviously very important. The oxidation rate is related to the reactive surface area thus oxidation of porous non-oxide ceramics depends on their open porosity. The generally accepted oxidation mechanism of porous silicon nitride materials consists of two... 

Superhard compounds are obviously formed by a combination of the low atomic number elements boron, carbon, silicon, and nitrogen. Carbon-carbon as diamond, boron-nitrogen as cubic boron nitride, boron-carbon as boron carbide, and silicon-carbon as silicon carbide, belong to the hardest materials hitherto known. Because of their extreme properties and the variety of present and potential commercial applications, silicon carbide (SiC) and boron carbide (B4C) are, besides tungsten carbide-based hard metals, considered by many as the most important carbide materials. 

The hot fiber (wire) CVD process has been commercially used for 30 years to produce continuous sheath/core bicomponent boron/tungsten and silicon carbide/carbon fibers. Since they are continuous fibers, they are discussed in Chapter 3.3. More recently, this process was used to produce discontinuous, i.e., short, experimental sheath/core diamond/carbon fibers by depositing a thick diamond sheath on short pieces of a potentially carbon fiber. 

Recent advances further enhance their commercial potential in metal matrix composites such as aluminum, nickel, and copper ceramic matrix composites, such as alumina, zirconia and silicon nitride and glass ceramic matrix composites such as lithium aluminosilicate. Silicon carbide whiskers increase strength, reduce crack propagation, and add structural reliability in ceramic matrix composites. Structural applications include cutting tool inserts, wear parts, and heat engine parts. They increase strength and stiffness of a metal, and support the design of metal matrix composites with thinner cross sections than those of the metal parts they replace, but with equal properties in applications such as turbine blades, boilers and reactors. 

In principle, any material that can be obtained as a film by conventional CVD can be obtained as a fiber by LCVD and therefore by high pressure LCVD with relatively high growth rates. To date, chemically pure and structurally uniform boron, carbon, silicon, silicon nitride, silicon carbide and germanium fibers [2] [12-23] were formed (Table I), thereby potentially facilitating the development of a commercial process. 

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