Special ceramics refers to a class of ceramics with special mechanical, physical or chemical properties, the raw materials used and the required production technology are greatly different from ordinary ceramics and development. According to the characteristics and uses, special ceramics can be divided into two categories: structural ceramics and functional ceramics. Among them, structural ceramics refer to ceramics that can be used as engineering structural materials, which generally have high strength, high hardness, high elastic modulus, high temperature resistance, wear resistance, corrosion resistance, oxidation resistance, thermal shock resistance and other characteristics.
There are many kinds of structural ceramics, advantages and disadvantages, and the application direction of the advantages and disadvantages are different, among which “silicon nitride ceramics” because of the balance of performance in all aspects, is known as the most excellent comprehensive performance in the structural ceramics family, and has an extremely wide range of applications.
Advantages of silicon nitride ceramics
Silicon nitride (Si3N4) can be divided into covalent bond compounds, with [SiN4] 4-tetrahedron as the structural unit. The specific positions of nitrogen and silicon atoms can be seen from the figure below, silicon is in the center of the tetrahedron, and the positions of four vertices of the tetrahedron are occupied by nitrogen atoms, and then every three tetrahedron shares one atom, constantly extending in three-dimensional space. Finally, the network structure is formed. Many of the properties of silicon nitride are related to this tetrahedral structure.
There are three crystalline structures of silicon nitride, which are α, β and γ phases, of which α and β phases are the most common forms of silicon nitride. Because the nitrogen atoms are very firmly combined, silicon nitride has good high strength, high hardness and high temperature resistance, and the hardness can reach HRA91~93; Good thermal rigidity, can withstand the high temperature of 1300~1400℃; Small chemical reaction with carbon and metal elements leads to low friction coefficient; It is self-lubricating and therefore resistant to wear; Corrosion resistance is strong, in addition to hydrofluoric acid, it does not react with other inorganic acids, high temperature also has oxidation resistance; It also has good thermal shock resistance, sharp cooling in the air and then sharp heating will not crumble; The creep of silicon nitride ceramics decreases at high temperature, and the slow plastic deformation is small under the action of high temperature and fixed load.
In addition, silicon nitride ceramics also have high specific strength, high specific mode, high thermal conductivity, excellent electrical properties and other advantages, so it has special application value in the extreme environment such as high temperature, high speed, strong corrosive media, and is considered to be one of the most promising structural ceramic materials for development and application, and often become the first choice in many applications that need to be tested.
Post time: Aug-15-2023