Silicon carbide furnace decomposition

Apart from the reactions described above for the formation of thin films of metals and compounds by the use of a solid source of the material, a very important industrial application of vapour phase transport involves the preparation of gas mixtures at room temperature which are then submitted to thermal decomposition in a high temperature furnace to produce a thin film at this temperature. Many of the molecular species and reactions which were considered earlier are used in this procedure, and so the conclusions which were drawn regarding choice and optimal performance apply again. For example, instead of using a solid source to prepare refractory compounds, as in the case of silicon carbide discussed above, a similar reaction has been used to prepare titanium boride coatings on silicon carbide and hafnium diboride coatings on carbon by means of a gaseous input to the deposition furnace (Choy and Derby, 1993) (Shinavski and Diefendorf, 1993). 

Petroleum coke, obtained by subjecting the distillation bottoms to pyrolitic polymerization and thermal decomposition in a delayed or fluid coker, is used in the manufacture of calcium and silicon carbides, electrodes for aluminum manufacturing, and graphite. It also finds use as a utility fuel and as a construction material in foundry and blast furnaces. 

After the current is switched of, the furnace is allowed to cool for several days. Then the side walls are removed, and the excess reaction mixture is carried off. The roll of silicon carbide contains not only the original resistance core, but also graphite formed by decomposition of silicon carbide. The boundary between the graphite and the SiC is very sharply defined. The innermost SiC zone is of the highest quality, as the purest and largest crystals can form in this region. Moving... 

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