Silicon nitride ceramic is an inorganic material ceramic that does not shrink when sintered. Silicon nitride is very strong, especially hot pressed silicon nitride, which is one of the hardest substances in the world. It has high strength, low density and high temperature resistance.
Si3N4  ceramic is a covalent bond compound. The basic structural unit is a  [SiN4] tetrahedron. The silicon atom is located at the center of the  tetrahedron. There are four nitrogen atoms around it, which are located  at the four vertices of the tetrahedron, and then every three A tetrahedron shares the form of an atom, forming a continuous and robust network structure in three dimensions.
Basic nature
Many of the properties of silicon nitride are attributed to this structure. Pure  Si3N4 is 3119, with both α and β crystal structures, all of which are  hexagonal crystals. The decomposition temperature is 1800 ° C in air and  1850 ° C in 011 MPa nitrogen. Si3N4 has a low thermal expansion coefficient and a high thermal conductivity, so its thermal shock resistance is excellent. The hot-pressed sintered silicon nitride is heated to l000 ° C and then put into cold water without cracking. At  less high temperatures, Si3N4 has higher strength and impact  resistance, but it will break with the increase of use time above 1200  °C, which will reduce its strength and fatigue damage will occur more  than 1450 °C, so Si3N4 The use temperature generally does not exceed 1300 ° C. Due  to the low theoretical density of Si3N4, it is much lighter than steel  and engineering superalloy steel. Therefore, it is better to use Si3N4  ceramic instead of alloy steel in places where high strength, low  density and high temperature resistance are required. It is.
Material properties
 As  an excellent high-temperature engineering material, Si3N4 ceramic  material has the most advantage in its application in high temperature  fields. The  future development direction of Si3N4 is: (1) to fully utilize and  utilize the excellent characteristics of Si3N4 itself; (2) to develop  some new flux during the sintering of Si3N4 powder, to study and control  the optimal composition of existing flux; (3) to improve milling ,  molding and sintering process; (4) development of Si3N4 and SiC and  other materials, in order to obtain more high-performance composite  materials. The  application of Si3N4 ceramics on automotive engines has opened up a new  dimension for the development of new high-temperature structural  materials. The  automobile industry itself is a multidisciplinary industry that  integrates all kinds of science and technology. China is an ancient  civilization with a long history. It has made brilliant achievements in  the history of ceramic development. With the progress of reform and  opening up, one day, China also It is bound to be among the world's major auto industry countries, creating new glory for the development of ceramics.
It  is extremely resistant to high temperatures, its strength can be  maintained to a high temperature of 1200 °C without falling, it will not  melt into a melt after heating, it will decompose until 1900 °C, and it  has amazing chemical resistance and can withstand almost all inorganic  acids. And  less than 30% caustic soda solution can also resist the corrosion of  many organic acids; at the same time it is a high-performance electrical  insulation material.
Related applications
 Utilizing  the light weight and high stiffness of the Si3N4, it can be used to  make ball bearings, which have higher precision than metal bearings,  generate less heat, and operate in higher temperature and corrosive  media. The  steam nozzle made of Si3N4 ceramic has the characteristics of wear  resistance and heat resistance. It is used for 650 °C boiler without  obvious damage after several months, while other heat-resistant and  corrosion-resistant alloy steel nozzle can only be used for 1-2 months  under the same conditions. The  Si3N4 glow plug jointly developed by the Shanghai Institute of Ceramics  of the Chinese Academy of Sciences and the Shanghai Internal Combustion  Engine Research Institute of the Ministry of Electrical and Mechanical  Engineering solves the problem of the difficulty of cold start of the  diesel engine and is suitable for direct injection or non-direct  injection diesel engines. This glow plug is the most advanced and ideal diesel engine ignition device available today. The  Japan Atomic Energy Research Institute and Mitsubishi Heavy Industries  Co., Ltd. have developed a new crude pump with a rotor consisting of 11  Si3N4 ceramic turntables. Because  the pump uses a Si3N4 ceramic rotor with a small coefficient of thermal  expansion and a precision air bearing, it can operate normally without  lubrication and cooling media. If  this pump is combined with an ultra-vacuum pump such as a  turbo-molecular pump, it can form a vacuum system suitable for use in  nuclear fusion reactors or semiconductor processing equipment.
 The  above are just a few examples of Si3N4 ceramics as structural  materials. It is believed that with the improvement of Si3N4 powder  production, molding, sintering and processing technology, its  performance and reliability will continue to improve, and silicon  nitride ceramics will be more widely used. Due  to the improvement of the purity of Si3N4 raw materials, the rapid  development of Si3N4 powder forming technology and sintering technology,  and the expanding application fields, Si3N4 is playing an increasingly  important role in the industry as an engineering structural ceramic. Si3N4  ceramics is an ideal high-temperature structural material with  excellent comprehensive performance and abundant resources. It has a  wide range of application fields and markets, and all countries in the  world are competing for research and development. Ceramic  materials have the characteristics of wear resistance, corrosion  resistance, high temperature resistance, oxidation resistance, thermal  shock resistance and low specific gravity which are difficult to compare  with general metal materials. It  can withstand the harsh working environment where metal or polymer  materials are difficult to handle, and has broad application prospects. It  has become a key basic material supporting the 21st century pillar  industry after metal materials and polymer materials, and has become one  of the most active research fields. Today, all countries in the world  attach great importance to its research and development, and as an  important member of the high temperature structural ceramic family. A  Si3N4 ceramic has better mechanical properties, thermal properties and  chemical stability than other high-temperature structural ceramics such  as oxide ceramics and carbide ceramics. Therefore, it is considered to  be the most promising material in high-temperature structural ceramics.
Product parameters
The  company mainly produces hot-sintered silicon nitride. The bulk density  (g/cm3) of the product is between 3.2 and 3.3, the hardness (HRA) is  between 90 and 92, and the flexural strength (MPa) is between 800 and  1200. The maximum working temperature (°C) is 800 °C.