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Silicon Nitride Ceramic
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Silicon Nitride Ceramic

 

 

Silicon nitride ceramics is an inorganic material that does not shrink during sintering.Silicon nitride has high strength, 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.
 
Silicon nitride ceramic is a kind of covalent bond compound, the basic structure unit for [SiN4] tetrahedron, silicon atom is located in the center of the tetrahedron, there are four nitrogen atoms around it, which located in tetrahedral four vertices, then to every three tetrahedron Shared in the form of an atom, the three dimensional space form a continuous and strong network structure.

 
 

 

 
Many properties of silicon nitride are attributed to this structure.Pure Si3N4 was $3119, with two crystal structure, alpha and beta are hexagonal crystal shape, its decomposition temperature is 1800 ℃ in air, in the 110 mpa nitrogen is 1850 ℃.Si3N4 has good impact resistance due to its low thermal expansion coefficient and high thermal conductivity.Hot pressing sintering of silicon nitride heating to l000 ℃ after into the cold water will not break.In the not too high a temperature, Si3N4 has high strength and impact resistance, but in more than 1200 ℃ can grow along with the use of time and failure, reduce its strength, above 1450 ℃ prone to fatigue damage, so the use of Si3N4 temperature does not exceed 1300 ℃ in general.Since Si3N4 has a low theoretical density and is much lighter than steel and engineering super-heat-resistant alloy steel, it is most appropriate to replace alloy steel with Si3N4 ceramics where high strength, low density and high temperature resistance are required.
 
Silicon nitride ceramic material as an excellent high-temperature engineering materials, the most advantageous is its application in the field of high temperature.
 
The future development direction of silicon nitride ceramics:
1. Give full play to and utilize the excellent characteristics of SI3N4 itself;
2. In the sintering of Si3N4 powder, a number of new flux is developed to study and control the optimum components of the existing flux;
3. Improves pulverizing, molding and sintering processes;
4. Develops composites such as si3n4 and sic to make more high-performance composite materials.

Silicon nitride ceramics have high hardness, excellent acid and alkali resistance, as well as self-lubricating properties. Therefore, silicon nitride ceramic balls can be used as bearing balls to cooperate with metal or axle sleeve with the same material.In addition, the ceramic valve ball can be used in the field, and its electrical insulation can be made into insulation ring;Due to high sintering temperature, silicon nitride structural parts can be used as high-temperature supporting materials for high-tech fields.Silicon nitride ceramic knives for industrial machine tools and so on.


Physical properties Si3N4 Reaction sintered Si3N4 Hot pressed
Density (g/cm3) 3,27 3,29
Molecular weight (g/mole) 140 140
Maximum service temperature air (°C) 1200- 1500 1100- 1600
Mechanical properties    
Hardness (Mohs) - -
Modulus of elasticity (GPa) 170-220 280-310
Poisson's ratio 0,25-0,26 0,27
Fracture toughness (MPa.m1/2) 3,5-5 6,1
Electrical properties    
Dielectric constant 10 10
Electrical resistivity at 20°C (Ohm.cm) >10 7 10 12- 10 15
Dielectric strength (kV/mm) - -
Thermal properties    
Specific heat (J/K/kg) 690 680-800
Thermal conductivity (W/m/K) at 20°C 9月30日 15-43
Coefficient of thermal expansion ( 10-6) from 20 to 1000°C 3 3,3
Melting point (°C) 1900 1900

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