The basic structural units of the Silicon Carbide Crystals are covalently bonded SiC and CSi coordination tetrahedra. These tetrahedra are assembled into planar layers with common edges, and one vertex in a layer is in turn connected to the next stacked tetrahedron.Thus four tetrahedra come up through each corner to satisfy tetra-coordination at any point of the resulting skeleton. These tetrahedra have different stacking orders, which determines that SiC has a large number of polymorphs. Cubic and simple hexagonal stacking can be found in SiC at the same time, i.e., a and B structures, respectively, and the relative rotation of the layers around the eccentric vertices of the bond can, in turn, produce a large number of polymorphs.
The relative rotation of the layers around the eccentric vertices of the bond produces a large number of more complex structures. The coordination number of all types of SiC is 4. The tetrahedra have three axes of symmetry with respect to each other.The three axes of symmetry of these tetrahedra are parallel to each other, and the adjacent bottoms of the tetrahedra can be parallel or antiparallel to each other combinations. Theoretical calculations show that 78% of the total Si-C bonding energy in silicon carbide is covalent, and the Ionic bonding is about 12%, and the remaining 10% is in a mixed state.
The excellent properties of silicon carbide are largely dependent on the refinement of the microstructure of the sintered body. The microstructure of the sintered body is related to the particle size of the raw material.microstructure is closely related to the particle size, shape, morphology and distribution of the raw material. Therefore
high-quality powder is the key to the preparation of high-performance SiC ceramic materials.
Silicon Carbide Crystals has a low-temperature form of B-SiC, cubic structure; high-temperature form of a-Sicl3, hexagonal structure; and due to the Silicon Carbide Crystals, the microstructure of SiC ceramics structure; and due to the different atomic arrangements in the crystal structure of silicon carbide and a series of other variants, there are about a hundred kinds.There are about a hundred kinds. SiC variants exist in the temperature range: below 2100 ℃, B-SiC is more stable, therefore, below 2000 ℃, B-SiC is more stable.Therefore, the SiC synthesized below 2000℃ is mainly B-SiC. At temperatures above 2100℃, B-SiC is converted to a-SiC, and B-SiC is converted to a-SiC.At temperatures above 2100℃, B-SiC is transformed to a-SiC, and the transformation is rapid at 2300℃-2400℃, so SiC synthesized above 2200℃ is mainly a-SiC.Therefore, SiC synthesized above 2200°C is mainly a-SiC, and 6H is the main one.