Silicon carbide properties and applications

Silicon carbide is not only an excellent refractory material. But also it is a commonly used grinding material, anti-corrosion material, and thermally conductive material. The main chemical of silicon carbide is SiC, with another name carborundum. It gets many excellent properties.

The silicon carbide used in industrial products is artificially synthesized at high temperatures of 2200-2500 ° C, which is almost non-existent in nature. The main raw materials of synthetic silicon carbide are quartz sand (silica), Petroleum coke, and the auxiliary materials are sawdust, salt, etc. The element of quartz sand is SiO2, which provides silicon for silicon carbide. The element of Petroleum coke is C, which provides carbon for silicon carbide. The auxiliary materials do not participate in the smelting reaction process, and the role of wood chips is to increase the permeability of the furnace charge. Table salt is only added to the smelting of green silicon carbide, making it appear green in color. 

Divided by color, silicon carbide includes black silicon carbide and green silicon carbide. They vary by purity and hardness. The purity of black silicon carbide is slightly lower than that of green silicon carbide. Black carborundum gets SiC content of no less than 98%. Green carborundum gets SiC purity of more than 99%.  They are both α-phase of silicon carbide crystals.

Both green and black silicon carbide have the following common properties:

Both green and black silicon carbide have the following common properties:

1. High-temperature chemical stability:

Silicon carbide has a very high melting point and good high-temperature resistance, which can maintain stable physical and chemical properties in high-temperature environments. Silicon carbide does not oxidize at a temperature of 1400 ° C but instead forms a layer of silicon dioxide thin film on the surface of the crystal. As a result, the thin film also gives the appearance of silicon carbide a colorful rainbow luster.

2. Good high-temperature resistance:

Silicon carbide has a very high melting point and can withstand high temperatures ranging from 1800 to 1900 ° C, with a downstream temperature of 2300 ° C. Silicon carbide also has good strength and impact resistance at high temperatures, making it a commonly used refractory material in steel production.

3. High hardness:

Silicon carbide has extremely high hardness, only lower than diamond. This enables silicon carbide to have excellent wear resistance and grinding performance in fields such as friction, cutting, and grinding. In the Mohs scale, the hardness of a diamond is Mohs 10.0, the hardness of green silicon carbide is Mohs 9.4-9.5 (Vickers hardness 33-34Gpa), and the hardness of black silicon carbide is Mohs 9.2-9.3 (Vickers hardness 28-32Gpa).

4. Excellent corrosion resistance:

Silicon carbide has excellent corrosion resistance to most acids and alkalis. It does not react with strong acids and bases and can be used stably for a long time under complex temperatures and chemical environments.

5. Excellent thermal conductivity:

Silicon carbide has high thermal conductivity, with a thermal conductivity of 60-200 W/M · K at room temperature, which can effectively transfer heat. Therefore, it is suitable for thermally conductive material or coating, such as heat sinks and heat sinks.

6. Lower thermal expansion coefficient:

The thermal expansion coefficient of silicon carbide is 3.9-4.5 x10-6/℃, used to make refractory products and SiC ceramics are less prone to creep and deformation.

7. Excellent insulation performance:

Silicon carbide has high insulation performance and can maintain stable insulation performance under high temperatures and high electric field conditions. Therefore, it is often used as electronic components and insulation materials and is also the main raw material for generating silicon carbide ceramics.

8. Lower bulk density:

The specific gravity of silicon carbide is 3.2g/cm3, which is lower than most metals and corundum.

9. Brittleness and toughness:

Although silicon carbide has high hardness, it has strong brittleness and slightly poor toughness. The toughness of black silicon carbide is higher than that of green silicon carbide.

Silicon carbide works well in many applications. It applies in mainly the following aspects:

1. Abrasives and abrasive tools:

Silicon carbide has excellent wear resistance and is widely used in the preparation of abrasive products. Black silicon carbide is suitable for producing grinding wheels, water sandpaper, silicon carbide abrasive brushes, steel paper sand discs, fiber grinding wheels, etc. Those abrasive tools are used for grinding metals, alloys, wood, and ordinary glass. Green silicon carbide is suitable for producing abrasive products such as resin grinding wheels, diamond grinding wheels, water grinding discs, honing stones, PVA grinding wheels, and diamond clay grinding blocks.

2. Grinding and polishing:

Silicon carbide, as an abrasive, can be widely used for sandblasting and passivation of marble, granite, titanium alloys, and copper alloys. The typical use is to perform edge passivation treatment on tungsten carbide hard alloys. Silicon carbide powder is used in double-sided grinding machines to grind alloy and ceramic products with water to achieve ideal surface roughness. In addition, silicon carbide, as the grinding medium for rolling grinders, can work together with grinding stones or walnut sand to deburr and polish stainless steel, alloy, and jade workpieces.

3. Ceramic products:

Silicon carbide can be used to prepare various ceramic products, such as ceramic seals, ceramic bearings, ceramic pipes, silicon carbide nozzles, etc. It can also be used to produce foam ceramics, metallurgical silicon carbide ceramic filter membranes, diesel particulate trap Ceramic membranes, and is often used to produce anti-bullet Ceramic plates, silicon carbide Boron carbide composite ceramics, and other industrial ceramics.

4. Refractory materials:

Silicon carbide can be used to make Fire brick, silicon carbide crucibles, silicon carbide furnace charges, and other products, and plays an important role in the production of iron and steel industry.

5. Coating industry:

Silicon carbide has high wear resistance and corrosion resistance. It can work as an additive to Teflon nonstick (Teflon) coatings, UV coatings, and Fluoropolymer. This additive greatly improves the oxidation resistance and corrosion resistance of coatings.

6. Electronic devices:

Silicon carbide has good thermal conductivity and high-temperature stability. It is suitable for making electronic heat sinks, electronic packaging materials, power semiconductor devices, etc.
In addition, SiC is also widely used in the chemical industry, aerospace, automotive manufacturing, and other fields, playing an important role.