Introduction to SiC

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In some news of the past ones, we have mentioned SiC in several electric vehicles & chip industries. What is it and how it works?

Silicon carbide (SiC) is an inorganic substance with the chemical formula of SiC. It is made by smelting quartz sand, petroleum coke (or coal coke), sawdust (salt is needed to produce green silicon carbide) and other raw materials through resistance furnace at high temperature. Silicon carbide also exists in nature as a rare mineral, morimorimorite. Among C, N, B and other non-oxide high-tech refractory raw materials, silicon carbide is the most widely used and most economical one, which can be referred to as emery or refractory sand. The silicon carbide produced by Chinese industry is divided into black silicon carbide and green silicon carbide, both of which are hexagonal crystals with specific gravity of 3.20~3.25 and microhardness of 2840~3320 kg/mm2.

History of SiC

Silicon carbide is a kind of carbide accidentally discovered by American Acheson in the laboratory during the electrofusion diamond experiment in 1891. At that time, it was mistaken for a mixture of diamond, so it was named emery. In 1893, Acheson developed a method of industrial smelting silicon carbide, which is also known as Acheson furnace, which has been used to this day, using carbon materials as the furnace core, Electrify and heat the mixture of quartz SiO2 and carbon to generate silicon carbide.

Several events about silicon carbide:

Silicon carbide was first discovered in meteorites in 1905.

In 1907, the first silicon carbide crystal light emitting diode was born.

In 1955, with a major breakthrough in theory and technology, LELY put forward the concept of growing high-quality carbonization, and since then SiC has been regarded as an important electronic material.

In 1958, the first World Silicon Carbide Conference was held in Boston for academic exchange.

Silicon carbide was mainly studied by the former Soviet Union in the 1960s and 1970s. By 1978, the "LELY improved technology" grain purification growth method was first adopted.

From 1987 to now, CREE's research achievements have been used to establish silicon carbide production lines, and suppliers have begun to provide commercialized silicon carbide bases.

Properties & Applications of SiC

Due to its stable chemical properties, high thermal conductivity, low thermal expansion coefficient and good wear resistance, silicon carbide has many other uses besides abrasive. For example, coating silicon carbide powder on the inner wall of water turbine impeller or cylinder body by special process can improve its wear resistance and extend its service life by 1 to 2 times; The advanced refractory material made from it is shock-resistant, small in size, light in weight and high in strength, and has good energy-saving effect. Low-grade silicon carbide (containing about 85% SiC) is an excellent deoxidizer. It can speed up 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, with Mohs hardness of 9.5, second only to the hardest diamond in the world (grade 10). It has excellent thermal conductivity and is a semiconductor, which can resist oxidation at high temperature.

Silicon carbide has at least 70 crystalline forms. α- Silicon carbide is the most common isomorphic substance, which is formed at a temperature higher than 2000 ° C and has a hexagonal crystalline structure (like fibrous zinc ore). β- Silicon carbide, with cubic crystal structure, is similar to diamond, and is generated at less than 2000 ° C. The structure is shown in the figure on the page. Although in the application of heterogeneous catalyst support α. The higher the unit surface area, the more attractive the silicon carbide, μ- Silicon carbide is the most stable and has a pleasant sound when it collides, but until now, these two types have not been used commercially.

Due to its specific gravity of 3.2g/cm3 and high sublimation temperature (about 2700 ° C), silicon carbide is very suitable for use as raw materials for bearings or high-temperature furnaces. Under any pressure that can be reached, it will not melt and has relatively low chemical activity. Due to its high thermal conductivity, high collapse electric field strength and high maximum current density, many people try to replace silicon in the application of semiconductor high-power components. In addition, it has a strong coupling effect with microwave radiation, and all its high sublimation points make it practical for heating metals.

Pure silicon carbide is colorless, while industrial brown to black is due to impurities containing iron. The iridescent luster on the crystal is caused by the silica protective layer produced on its surface

It is due to the low natural content, silicon carbide is mainly man-made. The common method is to mix quartz sand with coke, use silicon dioxide and petroleum coke in it, add salt and wood chips, put them in an electric furnace, heat them to about 2000 ° C, and then get silicon carbide powder after various chemical processes.

Silicon carbide (SiC) has become an important abrasive due to its great hardness, but its application range is beyond the general abrasive. For example, its high temperature resistance and thermal conductivity make it one of the preferred kiln furniture materials for tunnel kilns or shuttle kilns, and its conductivity makes it an important electric heating element. To prepare SiC products, first of all, SiC smelting block [or SiC granular material] should be prepared. Because it contains C and is super hard, SiC granular material was once called: carborundum. However, it should be noted that its composition is different from that of natural carborundum (garnet). In industrial production, SiC smelting block usually uses quartz, petroleum coke and other raw materials as raw materials to assist in recovery of raw materials and waste materials, and is prepared into furnace charge with reasonable proportion and proper size through grinding and other processes (In order to adjust the permeability of the furnace charge, an appropriate amount of sawdust needs to be added, and an appropriate amount of salt needs to be added when preparing green silicon carbide) It is prepared at high temperature.

Summary

SiC is a stable and functional matter which has already been applied in different industries. It is another good example to prove the ability of silicon products.