Si3N4 Customized Silicon Nitride Ceramic Tube High Hardness

      Si3N4 Customized Silicon Nitride Ceramic Tube, High Hardness And High Temperature Resistant Ceramic Parts

1 . Descriptions:

Silicon nitride ceramics is an inorganic material that does not shrink during sintering and is an important structural material. Silicon nitride has high strength and is one of the hardest substances in the world. It has lubricity, and has properties such as wear resistance, high strength, low density, and high temperature resistance. Silicon nitride has a low thermal expansion coefficient and high thermal conductivity, so it has excellent thermal shock resistance. Silicon nitride will not crack when heated to 1000°C and put into cold water. It is extremely resistant to high temperatures, and its strength can be maintained to a high temperature of 1200°C without falling. It will not melt into a melt after being heated, and will not decompose until 1900°C. It also has amazing chemical corrosion resistance. Except for hydrofluoric acid, it does not react with other inorganic acids or caustic soda solutions below 30%, and it is also resistant to corrosion by many organic acids. At the same time, it is a high-performance electrical insulating material. It is precisely because of the excellent characteristics of silicon nitride ceramics that it is more appropriate to replace alloy steel with silicon nitride ceramics in those places where high strength, low density, and high temperature resistance are required. People often use it. To manufacture bearings, turbine blades, mechanical seal rings, permanent molds and other mechanical components.

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.

Metal cutting tools: Bulk monolithic silicon nitride is used as a material for cutting tools due to its hardness, thermal stability and wear resistance. Especially recommended for high speed machining of cast iron. Hot hardness, fracture toughness and thermal shock resistance mean that sintered silicon nitride can cut cast iron, hard steel and nickel-based alloys.

Electronics: Often used as insulators and chemical barriers in the manufacture of integrated circuits to electrically isolate different structures or as etch masks in bulk micromachining. As a passivation layer for microchips, it is superior to silicon dioxide because it is a significantly better diffusion barrier to water molecules and sodium ions, two major sources of corrosion and instability in microelectronics.

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