Mixed control chemical vapor deposition

VLS siiicon carbide whiskers with diameters ranging from <3 to 11 jm, and lengths ranging from 5 jm to <10 cm are readily obtained by metal catalyzed chemical vapor deposition. This process facilitates an exacting control over whisker shape and dimension in a batch or a continuous process. The diameter of the catalyst determines that of the whisker. Less well-defined whiskers have been obtained by vapor deposition, chemical mixing and carbothermal processes with diameters ranging from <3 pim to >30 nm. 

This expression should look vaguely familiar In fact, it is quite similar to the mixed-control equations we developed for active gas corrosion and for chemical vapor deposition (Equations 5.18 and 5.32). 

Aerosol-assisted CVD introduces rapid evaporation of the precursor and short delivery time of vapor precursor to the reaction zone. The small diffusion distance between the reactant and intermediates leads to higher deposition rates at relatively low temperatures. Single precursors are more inclined to be used in AACVD therefore, due to good molecular mixing of precursors, the stoichiometry in the synthesis of multicomponent materials can be well controlled. In addition, AACVD can be preformed in an open atmosphere to produce thin or thick oxide films, hence its cost is low compared to sophisticated vacuum systems. CVD methods have also been modified and developed to deposit solid phase from gaseous precursors on highly porous substrates or inside porous media. The two most used deposition methods are known as electrochemical vapor deposition (EVD) and chemical vapor infiltration (CVI). 

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