Silicon carbide (SiC), also known as carborundum or SiC,. is one of the lightest, hardest, and strongest technical ceramic materials. It has exceptional thermal conductivity, resistance to acids, and low thermal expansion.
Since the late 19th century, silicon carbide ceramics have been an important material for sandpapers, grinding wheels, and cutting tools. More recently, it has found application in refractory linings and heating elements for industrial furnaces, in wear-resistant parts for pumps and rocket engines, and in semiconducting substrates for light-emitting diodes.
Three preparation methods of silicon carbide ceramics
Do you know which three preparation methods of silicon carbide ceramics? Now let’s give you a detailed introduction.
One is reactive silicon carbide ceramics, reaction sintering silicon carbide is also known as self bonding SiC. Silicon carbide powder and graphite powder are mixed and pressed into green body in a certain proportion, heated to about 1650 degrees, and formed by gas phase reaction with C.
The other is hot pressing SiC ceramics. Although the temperature above 2000 ℃ and the pressure above 350Mpa can make the pure SiC hot pressed, the method of adding additives is usually used. There are two kinds of hot pressing additives: one is to form liquid phase with impurities in silicon carbide, and the other is to form solid solution with SiC and reduce grain boundary to promote sintering.
The third is atmospheric pressure silicon carbide ceramics. Pressureless sintered silicon carbide is also named pressureless sintered silicon carbide. High purity and high density silicon carbide ceramics are produced when the sintering temperature is above 2100 ℃.
Silicon carbide ceramics applications
Until the invention of boron carbide in 1929, silicon carbide was the hardest synthetic material known. It has a Mohs hardness rating of 9, approaching that of a diamond. In addition, SiC crystal has fracture characteristics that make them extremely useful in grinding wheels and in abrasive paper and cloth products.
Its high thermal conductivity, together with its high-temperature strength, low thermal expansion, and resistance to chemical reaction and thermal shock, makes silicon carbide valuable in the manufacture of high-temperature bricks and other refractories.
SiC ceramic is also classed as a semiconductor, having an electrical conductivity between that of metals and insulating materials. This property, in combination with its thermal properties, makes SiC a promising substitute for traditional semiconductors such as silicon in high-temperature applications.
Factory low wear high hardness ceramic burner silicon carbide tube
Silicon carbide material parameter comparison
| Item | RSiC | NSiC | SiSiC | Si3N4-SiC |
|---|---|---|---|---|
| Bulk Density(g/cm3) | 2.60-2.74 | 2.75-2.82 | >3.02 | 2.68 |
| Porosity (%) | 15 | 10-12 | <0.1 | <16 |
| Compression Strength(MPa) | ≥600 | 600-700 | -- | 180 |
| Bending Strength(MPa) | 90-100(20℃) | -- | 250(20℃) | ≥45(20℃) |
| 100-120(1100℃) | 160-180(1100℃) | 280(1200℃) | ≥50(1200℃) | |
| Young’s Modulus(GPa) | 280(20℃) | 220-260 | -- | ≥16(1200℃) |
| Thermal Conductivity(W/MK) | 26(1200℃) | 15(1200℃) | 45(1200℃) | -- |
| Thermal Expansion(20-1000 ℃) | 4.8×10-6 | 5.099×10-6 | 4.5×10-6 | ≤4.7×10-6 |
| Max. Working Temperature(℃) | 1650 | 1500 | 1380 | 1500 |
| PH Resistance | 1-14 | -- | Excellent | -- |
| Moh’s Scale of Thermal Expansion | -- | -- | 13 | -- |
| Si3N4 (%) | 0 | 20-40 | -- | ≥22 |
| a-SiC(%) | 98.5 | 60-80 | -- | ≥75 |
Good thermal conductivity of silicon carbide ceramics
Silicon carbide ceramics have been widely used in petroleum, chemical industry, microelectronics, automobile, aerospace, aviation, papermaking, laser, mining, atomic energy and other industrial fields. Here for you to introduce the good thermal conductivity of silicon carbide ceramics.
The excellent thermal conductivity of silicon carbide ceramics is closely related to its unique structure. SiC is a compound with strong covalent bond, and the ionic property of Si-C bond in SiC is only about 12%. Therefore, SiC has high strength, high elastic modulus and excellent wear resistance. Pure SiC will not be eroded by HCl, HNO3, H2SO4 and HF acid solutions and NaOH solutions. When heated in air, it is easy to oxidize, but the SiO2 formed on the surface will inhibit the further diffusion of oxygen, so the oxidation rate is not high. In terms of electrical properties, SiC is semiconductor, and the introduction of a small amount of impurities will show good conductivity. In addition, SiC has excellent thermal conductivity.