As we all know, silicon carbide or pressureless sintered silicon carbide is used in many parts of our magnetic pumps, fluorine-lined centrifugal pumps, and mechanical seals, so today I will show you what is silicon carbide and what is its nature ? First look at the following information:
As we all know, many parts of our magnetic pumps
, fluorine-lined centrifugal pumps
, mechanical seals and so on use "silicon carbide" or "pressureless sintered silicon carbide", so today I will show you what is silicon carbide How is it?
First look at the following information:
1. Material properties
Because of its stable chemical properties, high thermal conductivity, small thermal expansion coefficient, and good abrasion resistance, silicon carbide has many other uses besides abrasives, such as: coating silicon carbide powder on a turbine wheel or cylinder block by a special process. The inner wall can improve its abrasion resistance and extend its service life by 1 to 2 times. The high-grade refractory material used is made of heat-resistant shock, small size, light weight, high strength, and good energy saving effect. Low-grade silicon carbide (containing about 85% of SiC) is an excellent deoxidizer. It can accelerate the speed of steelmaking, facilitate the control of chemical composition, and improve the quality of steel. In addition, silicon carbide is also widely used to make silicon carbide rods for electric heating elements.
The hardness of silicon carbide is very high, Mohs hardness is 9.5, second only to the hardest diamond in the world (10), it has excellent thermal conductivity, is a semiconductor, and can resist oxidation at high temperatures.
Silicon carbide has at least 70 crystalline forms. α-Silicon Carbide is the most common kind of heterogeneous heteromorph, which is formed at a temperature higher than 2000 ° C, and has a hexagonal crystal structure (like fiber zincite). β-silicon carbide, cubic crystal structure, similar to diamond, is generated below 2000 ° C, the structure is shown in the page attached picture. Although in the application of heterogeneous catalyst support, it is noticeable because it has a higher unit surface area than the α-type, and the other kind of silicon carbide, μ-silicon carbide, is the most stable and has a pleasant sound when it collides. But to this day, these two types have not been applied commercially.
Because of its specific gravity of 3.2g / cm3 and high sublimation temperature (about 2700 ° C), silicon carbide is very suitable as a raw material for bearings or high temperature furnaces. It will not melt at any pressure that can be reached, and it has relatively low chemical activity. Because of its high thermal conductivity, high collapse electric field strength, and high maximum current density, many people have tried to use it to replace silicon in the application of semiconductor high power components. In addition, it has a strong coupling effect with microwave radiation, and all of its high sublimation points make it practical for heating metals.
Pure silicon carbide is colorless, while industrially produced brown to black are due to iron-containing impurities. The rainbow-like luster on the crystal is due to the protective silica layer produced on the surface.
Pure silicon carbide is colorless and transparent crystal. Industrial silicon carbide is light yellow, green, blue, or even black due to the different types and contents of impurities. Transparency varies with its purity. Silicon carbide crystal structure is divided into hexagonal or rhombohedral α-SiC and cubic β-SiC (called cubic silicon carbide). α-SiC constitutes many different variants due to different stacking sequences of carbon and silicon atoms in its crystal structure, and more than 70 species have been found. β-SiC turns into α-SiC at 2100 ° C or higher. The industrial method of silicon carbide is to use high-quality quartz sand and petroleum coke to make it in a resistance furnace. The refined silicon carbide block is crushed, washed with acid and alkali, magnetically separated and sieved or water-separated to make products of various sizes.
Through the introduction above, everyone knows that some basic characteristics of silicon carbide are: corrosion resistance and wear resistance (hardness is quite high).
Reaction sintered silicon carbide can withstand most acids, but it is not only resistant to hydrofluoric acid (HF), so how to solve it when the pumping medium is HF? What materials to use instead? The answer is: SSIC sintered silicon carbide without pressure.
In the next article, let's talk about SSIC.