Silicon carbide has a myriad polytypes depending on the varied stacking of closed atomic planes.23 Only CVD SiC material is inherently highly crystalline, pure, and stoichiometric, which is critical to irradia­tion stability. Much emphasis is placed on CVD SiC in this chapter, as it corresponds very closely to the matrix of CVI SiC/SiC. The reader will find further details on the SiC structure-property relationships in the excellent comprehensive review by Snead and colleagues.23 Here the main data from Snead’s paper are summarized.

Only the 3C-SiC crystal, known as p-SiC, has the sequence showing cubic symmetry out of the infinite number of variations. All the other polytypes which show noncubic symmetry are classified as a-SiC. a-SiC is formed above 2373 K and p-SiC at 1273-1873 K.

Various fabrication techniques, such as sintering, direct conversion, gas-phase reaction, and polymer pyrolysis, are currently used for the synthesis ofSiC. The CVD technique is one ofthe most familiar gas — phase reaction methods for the synthesis of highly crystalline, stoichiometric, high-purity p-SiC.