Vapor-solid process, silicon carbide

A vapor-liquid-solid (VLS) technique (Petrovic et al, 1985 Milewski et al, 1985) can be used to grow exceptionally strong and stiff silicon carbide whiskers. The name VLS comes from the fact that the process uses vapor feed gases, a liquid catalyst, and solid crystalline whiskers are the end product. Figure... 

The formation of silicon carbide whiskers can occur through one of three general methods vapor-solid (VS), chemical vapor deposition (CVD), vapor-liquid-solid (VLS). The processes vary widely in the raw... 

Transversely excited atmospheric (TEA) CO2 laser-induced decomposition of divinylsilane in the gas phase yields unsaturated C2-C4 hydrocarbons, benzene and vinylsilane, and it represents a convenient process for chemical vapor deposition of thin solid films composed of silicon carbide or polycarbosilane [16]. 

Silicon carbide whiskers, usually produced from silica and carbon, are widely used for ceramic matrix composites [38]. Tbe vapor-liquid-solid (VLS) process is accepted as the mechanism for SiC whisker production (Fig. 15.1.4). This process requires formation of a liquid phase of a transition metal at the reaction sites. Elemental sources of Si and C are usually supplied in vapor phase form as SiO and CH4, respectively [39]. The vapors are deposited on the surface of the liquid metal and dissolved into the liquid metal droplets. Since the whiskers are precipitated from the dissolved components, metal droplets are often observed at the tip of the whiskers [39]. 

The other method of developing fine, spherical particles is through the use of plasma techniques which may involve a phjrsical phenomenon or a chemical reaction [105]. In the former case, a simple spherodizing process takes place when irregular shaped powder is introduced into the plasma which melts it and then vaporizes it to form uniform spheres. When a chemical reaction is involved, the reactants in the solid or gaseous form in contact with the plasma are allowed to react in the vapor phase and the products are allowed to condense as deposits of tine powder on the cooler regions of tire chamber after leaving the plasma. Colloidal spheres of alumimun, copper, aluminum nitride and silicon carbide are made in this way. 

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