Silicon Nitride Ceramic Welding Positioning Block Used For Electronic Appliances

        Silicon Nitride Ceramic Welding Positioning Block Used For Electronic Appliances And Textile Machinery

1 . Descriptions:

Silicon nitride (Si3N4) ceramics is an inorganic non-metallic compound with strong covalent bonds. Its basic structural unit is a tetrahedron. The silicon atom is located at the center of the tetrahedron, and the four nitrogen atoms are located at the four vertices of the tetrahedron. The form of four tetrahedra sharing one silicon atom forms a continuous and strong network structure in three-dimensional space. Many properties of silicon nitride are due to its special structure. Therefore, the bonding force between nitrogen atoms and silicon atoms in the Si3N4 structure is very strong. As a high-temperature structural ceramic, it is known as the "all-around champion" in ceramic materials.

Silicon nitride (Si3N4) contains three crystal forms, and two crystal forms are common. One is α-Si3N4, needle-like crystal, which is white or off-white, and the other is β-Si3N4, which is darker in color and is dense granular polyhedron or short prism. Both are hexagonal.

A longer stacking order leads to a higher hardness of the α phase than the β phase. However, the α phase is chemically unstable compared to the β phase. So at the high temperature of the liquid phase, the α phase always transforms into the β phase. Therefore, β-Si3N4 is the main form used in silicon nitride ceramics.

2 . Performance characteristics of silicon nitride materials

A . Physical properties of silicon nitride:

a . Thermal properties: It is a high-temperature refractory substance with no melting point. It decomposes at about 1900°C under normal pressure. It has strong creep resistance under high pressure. The softening point of reaction sintered silicon nitride without binder can be as high as 1800°C;

b . Good thermal conductivity;

c . Small thermal expansion coefficient;

d . Good electrical insulation performance, small dielectric coefficient, high breakdown voltage.

B . Chemical properties of silicon nitride:

a . Oxidation resistance: It does not react with oxygen in a dry atmosphere below 800 °C;

b . Molten metal corrosion resistance: silicon nitride does not infiltrate and corrode elemental metal melt (except copper);

c . Resistance to acid, alkali and salt corrosion: easily soluble in hydrofluoric acid, and ineffective with dilute acid.

C. Mechanical properties of silicon nitride:

a . High temperature strength is good, and the high temperature strength at 1200°C has little attenuation compared with the room temperature strength. In addition, its high temperature creep rate is very low. These are determined by the nature of strong covalent bonds;

b .  High hardness, second only to a few superhard materials such as diamond, cubic BN, and B4C;

c . The friction coefficient is small and self-lubricating, which is similar to the metal surface with oil.

3 . Application of silicon nitride ceramics

Automotive industry: The main application of sintered silicon nitride is in the automotive industry as an engine part material. In spark ignition engines, silicon nitride is used for lower wear rocker pads, turbochargers for lower inertia and less engine lag, and waste gas control valves for increased acceleration.

Bearings: Compared with other ceramics, silicon nitride ceramics have good impact resistance. Therefore, ball bearings made of silicon nitride ceramics are used in performance bearings. A representative example is the use of silicon nitride bearings in the main engines of NASA's space shuttles. Since silicon nitride ball bearings are harder than metal, this reduces contact with the bearing track. Silicon nitride ball bearings can be found in high-end automotive bearings, industrial bearings, wind turbines, motorsports, bicycles, roller skates and skateboards.

High Temperature Materials: Silicon nitride has long been used in high temperature applications. In particular, it was identified as one of the few monolithic ceramic materials capable of surviving the severe thermal shocks and thermal gradients generated in hydrogen/oxygen rocket engines.

Medical: Silicon nitride has many orthopedic applications. The material is also an alternative to PEEK (polyether ether ketone) and titanium used in spinal fusion devices. Compared to PEEK and titanium, silicon nitride's hydrophilic, microstructured surface contributes to the material's strength, durability and reliability.