SiC is a covalently bonded compound with strong bonding between Si-C, has a diamond structure, and has 75 crystalline forms. The basic structural unit of its lattice is the covalently bonded [SiC4] and [CSi4] tetrahedral coordination, and these tetrahedra are assembled into planar layers with common edges, and the layers These tetrahedra are assembled into planar layers with common edges, and one of the vertices in the layer is connected to the next stacked tetrahedron, so that the four tetrahedra are connected at each corner to satisfy the tetracoordination at any point of the formed skeleton. Various crystalline forms of SiC crystals are formed by stacking the same Si-C layers but in different orders. The main crystalline forms are 3C-SiC, 4H-SiC, 6H-SiC, and 15R-SiC. The symbols C, H, and R represent cubic, hexagonal, and rhombohedral hexahedral structures, respectively, and the numbers before C, H, and R represent the number of layers with repeating cycles along the c-axis. The most important of these crystal types are α-SiC and β-SiC: the former is a high The former is a high-temperature stable structure and the latter is a low-temperature stable structure. The transition from β-SiC to α-SiC starts at 2100°C and occurs rapidly at 2400°C. SiC has no melting point and has a decomposition temperature of 2830°C at 0.1 MPa pressure.
for silicon carbide ceramic,the unit cell in the SiC crystal structure is composed of identical Si-C tetrahedra with the Si atom at the center surrounded by C atoms. All structures consist of [SiC4] tetrahedra stacked up, differing only in whether they are bonded parallel or antiparallel. Pure SiC is colorless and transparent, generally black due to impurities, while green SiC can be obtained when residual C is removed before sintering.