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Silicon carbide, $\mathrm{SiC}$, is a compound of silicon and carbon with a strongly bonded extended structure. It is both a hard ceramic and a wide-band gap semiconductor, illustrating how one material can be useful for mechanical and electronic reasons.

Its local tetrahedral bonding can occur with different stacking sequences, giving multiple polytypes. These share composition while differing in long-range order and electronic properties. Consequently a statement about a silicon-carbide band gap, crystal symmetry or device behaviour must specify the structural form. An empirical formula alone does not determine a solid's full microscopic structure.

TRISO fuel uses coated nuclear fuel particles, each with a fuel kernel surrounded by four layers: a porous carbon buffer, an inner dense pyrolytic carbon layer, a silicon carbide layer and an outer pyrolytic carbon layer. The name abbreviates tristructural isotropic: the four layers use three coating material forms.^[ref]

The layers perform complementary functions. The porous carbon buffer accommodates released fission gas; the pyrolytic carbon supports the particle mechanically; and the silicon carbide supplies a strong barrier to fission products. Coated particles can be embedded in a graphite matrix. Their retention performance depends on coating integrity, material behaviour under irradiation, and the conditions experienced in service. The architecture makes a small particle itself part of the containment system, linking nuclear engineering closely to materials science.^[ref]