Silicon carbide powders, formation

A trivalent hard chromium bath has recently been described . The bath contains potassium formate as a complexing agent, and thicknesses in excess of 20 m can be deposited. Hardnesses of up to l650Hy can be obtained by heat treatment at 700°C. The deposits contain 1.6-4.8% carbon, and the bath is suitable for the deposition of composite deposits containing diamond or silicon carbide powder. 

Acceptor dopants are introduced in the crucible either in elemental form or in the form of carbides. If a dopant is introduced in elemental form, it is placed in a special internal crucible with carbon or silicon carbide powder. This is required to prevent the dissolution of the crucible, in the case of aluminium doping, and to reduce the boron vapour pressure to the equilibrium value for the SiC-C system, in the case of boron doping. If elemental boron is placed in the vicinity of the substrate, this results in the formation of boron carbide on the crystal faces of SiC [46]. For moderate doping of crystals, grown at high temperatures, doped SiC sources also can be employed. 

The main objective of the project, ie. to study the reaction bonding technique as an effective way to produce porous silicon carbide ceramics, has been successfully achieved. This includes the colloidal processing of the precursor powders, compaction through slip-casting, and finally sintering to achieve the muilitization reaction. Characterization of the sintered and polished samples using SEM and XRD have confirmed the formation of the muliite phase. 

RE, REL, REO, REOL, RER, RES, REX, REXH, REXR. Symbols for various shapes of ceramic wall tiles and fittings (see Fig. 7, p350). Reaction-bonding. The formation of a polycrystalline ceramic by a chemical reaction between the powder and a gas or a liquid. Cf. reaction sintering and see silicon nitride, silicon carbide. 

Kharlamov Al, KiriUova NV (2002) Gas-phase reactions of formation of sihcon carbide nanofilaments from silicon and carbon powders. Theor Exp Chem 38(l) 59-63... 

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