Views: 222 Author: Loretta Publish Time: 2025-02-13 Origin: Site
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● Properties of Silicon Carbide
● Applications of Silicon Carbide
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>> 1. How is silicon carbide made?
>> 2. What are the key properties of silicon carbide?
>> 3. What are the main applications of silicon carbide?
>> 4. How was silicon carbide discovered?
Silicon carbide (SiC), also known as carborundum, is a synthetically produced crystalline compound of silicon and carbon with the chemical formula SiC[6]. This material is exceptionally hard and has been an important component in various industrial applications since the late 19th century, ranging from abrasives to high-tech semiconductors[6].
Silicon carbide was discovered in 1891 by Edward G. Acheson[2][6]. Acheson was attempting to create artificial diamonds when he heated a mixture of clay and powdered coke in an iron bowl[6]. Instead of diamonds, he found bright green crystals attached to the carbon electrode[6]. Initially, Acheson believed he had created a new compound of carbon and alumina from the clay and named it "Carborundum," after the mineral corundum[6].
Realizing the hardness of the crystals was close to that of diamonds, Acheson patented his discovery, recognizing its potential as an abrasive[6]. The availability of silicon carbide from inexpensive raw materials soon made it an important industrial abrasive[6]. Around the same time as Acheson's discovery, Henri Moissan in France produced a similar compound from quartz and carbon[6]. Moissan credited Acheson with the original discovery in a 1903 publication[6]. Natural silicon carbide is found in the Canyon Diablo meteorite in Arizona and is known as moissanite[6].
Because naturally occurring moissanite is extremely rare, silicon carbide is primarily produced synthetically[1]. The most common method for manufacturing silicon carbide is the Acheson process[3][5].
The Acheson process involves combining silica sand and carbon in an Acheson graphite electric resistance furnace[1]. This mixture is then heated to a high temperature, between 1,600°C (2,910°F) and 2,500°C (4,530°F)[1]. The basic chemical reaction is:
SiO2+3C→SiC+2CO[2]
In the Acheson furnace, the material's purity varies depending on its distance from the graphite resistor, which acts as the heat source[1]. The purest crystals are colorless, pale yellow, or green and are found closest to the resistor[1]. Further from the resistor, the color changes to blue and black, indicating lower purity[1]. Common impurities include nitrogen and aluminum, which affect the electrical conductivity of the SiC[1].
1. Lely Process: Pure silicon carbide can be made by the Lely process[1]. This involves subliming SiC powder into high-temperature species of silicon, carbon, silicon dicarbide (SiC2), and disilicon carbide (Si2C) in an argon gas environment at 2,500°C[1]. These species are then redeposited into flake-like single crystals, sized up to 2 × 2 cm, on a slightly colder substrate[1]. The Lely process yields high-quality single crystals, mostly of the 6H-SiC phase due to the high growth temperature[1]. A modified Lely process uses induction heating in graphite crucibles to produce even larger single crystals, up to 4 inches (10 cm) in diameter[1].
2. Chemical Vapor Deposition (CVD): Cubic SiC is typically grown using chemical vapor deposition (CVD) of silane, hydrogen, and nitrogen[1]. Both homoepitaxial and heteroepitaxial SiC layers can be grown using gas and liquid phase approaches[1].
3. Preceramic Polymers: Complexly shaped SiC can be formed using preceramic polymers as precursors[1]. These polymers are pyrolyzed at temperatures between 1,000–1,100°C to form the ceramic product[1]. Common precursor materials include polycarbosilanes, poly(methylsilyne), and polysilazanes[1]. Silicon carbide materials obtained through this method are known as polymer-derived ceramics (PDCs)[1]. Pyrolysis is typically conducted under an inert atmosphere at relatively low temperatures[1]. This method is advantageous compared to CVD because the polymer can be shaped before thermal conversion into the ceramic[1].
Silicon carbide possesses a unique combination of physical and chemical properties that make it suitable for a wide range of applications[2][5].
- Hardness: With a Mohs hardness of around 9 to 9.5, SiC is one of the hardest synthetic substances, surpassed only by diamond and boron carbide[2][5][8].
- Strength: Silicon carbide has high mechanical strength, making it useful in high-stress applications[3].
- Wear Resistance: The material is highly resistant to wear, making it suitable for abrasive applications and components subject to friction[5].
- Thermal Conductivity: Silicon carbide has a thermal conductivity of 50 to 100 W/m·K[5].
- Temperature Resistance: It can withstand high temperatures, up to 1500°C in air and 2400°C in an inert atmosphere[5].
- Thermal Shock Resistance: SiC combines outstanding thermal shock resistance with low density and high mechanical strength[3].
- Coefficient of Thermal Expansion: 5·10-6/K[5]
- Chemical Inertness: Silicon carbide is chemically inert to all alkalies and acids[5].
- Chemical Stability: It offers outstanding chemical stability in aggressive environments[3].
- Semiconductor Properties: Silicon carbide is a wide bandgap semiconductor, making it suitable for high-speed, high-voltage, and high-temperature devices[2].
- Electrical Conductivity: The electrical conductivity of SiC can be affected by impurities such as nitrogen and aluminum[1].
- Density: 3.21 g/cm³[5]
- Crystal Structure: Pure silicon carbides have a colorless and transparent crystal structure. The addition of impurities like nitrogen or aluminum can turn the crystals green or blue, depending on the level of contamination[2].
The properties of silicon carbide make it useful in a wide array of applications[2][6].
Since its discovery, silicon carbide has been used as an abrasive in sandpapers, grinding wheels, and cutting tools[6]. Its hardness and wear resistance make it ideal for these applications[3].
SiC is used in refractory linings and heating elements for industrial furnaces due to its high-temperature resistance and chemical stability[6].
Silicon carbide is employed in wear-resistant parts for pumps and rocket engines, taking advantage of its hardness and chemical inertness[6].
As a wide bandgap semiconductor, SiC is used in semiconducting substrates for light-emitting diodes (LEDs) and high-power electronic devices[2][6]. Its ability to handle high voltages, high frequencies, and high temperatures makes it superior to traditional silicon in many applications[2].
Silicon carbide is commonly used to produce high-performance kiln furniture due to its high resistance to creep and long service life at temperatures above 1300°C[3].
Silicon carbide is also used in:
- Burner nozzles[3]
- Abrasive machining
- Ceramic armor
- Car brake disks
- Clutch facings
- Diesel particulate filters
Silicon carbide, discovered by Edward G. Acheson in 1891, is a synthetically produced compound with exceptional hardness, high-temperature resistance, and chemical inertness[2][6]. Primarily manufactured via the Acheson process, SiC is also created through methods like the Lely process and chemical vapor deposition[1]. Its versatile properties make it invaluable in applications ranging from abrasives and cutting tools to refractory materials and semiconductors[6]. As technology advances, silicon carbide continues to be a subject of research and development, driving innovations across various sectors[4].
Silicon carbide is primarily made through the Acheson process, which involves heating a mixture of silica sand and carbon to high temperatures in an electric resistance furnace[1]. The chemical reaction forms silicon carbide crystals[3]. Alternative methods include the Lely process and chemical vapor deposition, which are used to produce high-purity crystals and specialized forms of SiC[1].
Silicon carbide is known for its extreme hardness, high-temperature resistance, chemical inertness, and semiconductor properties[5]. It has a Mohs hardness of 9 to 9.5, making it one of the hardest materials known[8]. It also exhibits high thermal conductivity, thermal shock resistance, and stability in aggressive chemical environments[3][5].
Silicon carbide is used in a wide range of applications due to its unique properties[6]. These include abrasives, cutting tools, refractory linings, heating elements for industrial furnaces, wear-resistant parts, and semiconducting substrates for light-emitting diodes (LEDs)[6]. It is also used in high-power electronic devices and kiln furniture[2][3].
Silicon carbide was discovered accidentally by Edward G. Acheson in 1891 while he was trying to create artificial diamonds[6]. He heated a mixture of clay and powdered coke in an iron bowl and found bright green crystals of silicon carbide[6].
The Acheson process is used for the bulk production of silicon carbide by heating a mixture of silica and carbon in a resistance furnace[3][5]. The Lely process, on the other hand, is used to produce high-quality, single-crystal silicon carbide by subliming SiC powder and redepositing it on a substrate[1]. The Lely process yields crystals with higher purity and better structural perfection compared to the Acheson process[1].
[1] https://en.wikipedia.org/wiki/Silicon_carbide
[2] https://scienceinfo.com/silicon-carbide-structure-preparation/
[3] https://www.ipsceramics.com/how-is-silicon-carbide-made/
[4] https://rewiredz.com/tech-and-innovation/understanding-silicon-carbide-sic/
[5] https://www.fiven.com/world-of-silicon-carbide/sic-production-process/
[6] https://www.britannica.com/science/silicon-carbide
[7] https://www.preciseceramic.com/blog/methods-to-produce-silicon-carbide-and-their-advantages.html
[8] https://www.eletimes.com/silicon-carbide-overview-discovery-properties-process-uses
