Silicon nitride ceramic accessories
Aluminum oxide ceramics, silicon nitride ceramics, zirconia ceramics
Silicon nitride ceramics start to oxidize at 1300-1400°C in air, with a compressive strength of 490MPa and a hardness of HRA91-93, which is considered one of the hardest substances in the world. Silicon nitride is resistant to corrosion by almost all inorganic acids, caustic soda solutions with a concentration lower than 30% and many organic acids. In addition, Si3N4 ceramics also have the characteristics of good thermal shock resistance, low high temperature creep, and wear resistance.
Compared with other ceramic materials, silicon nitride ceramics have many excellent characteristics, such as high theoretical thermal conductivity, good chemical stability, non-toxicity, high flexural strength and fracture toughness, etc. At present, in the research reports on high thermal conductivity silicon nitride ceramics, the thermal conductivity can reach up to 177W·m-1·K-1, and the mechanical properties are relatively excellent (bending strength reaches 460MPa, fracture toughness reaches 11.2MPa m1/2). These characteristics make it considered as a potential heat dissipation and packaging material for high-speed circuits and high-power devices.
Adding Yb2O3 as a sintering aid in the sintering process of silicon nitride ceramics will be beneficial to the growth of silicon nitride grains, making it have a larger aspect ratio, and with the increase of Yb2O3 addition, silicon nitride The grain coarsening phenomenon is also more obvious.
The friction coefficient of silicon nitride ceramics is small. Under the condition of high temperature and high speed, the increase of friction coefficient is also small, so it can ensure the normal operation of the mechanism. This is a prominent advantage. When silicon nitride ceramics start to grind, the sliding friction The coefficient reaches 1.0 to 1.5. After precise running-in, the friction coefficient will be greatly reduced and kept below 0.5, so silicon nitride ceramics are considered to be self-lubricating materials. The main reason for this self-lubricity is different from graphite, boron nitride, talc, etc., in the scaly layered structure of the material organization. Under the action of pressure, a small amount of friction surface decomposes to form a thin gas film, thereby reducing the sliding resistance between the friction surfaces and increasing the smoothness of the friction surfaces. In this way, the more friction, the smaller the resistance, and the wear amount is also very small. However, after continuous friction, most materials tend to gradually increase due to surface wear or temperature rise and softening.