Silicon Carbide

Silicon carbide, a non-oxide ceramic known for its hardness, strength and chemical resistance is widely used as an abrasive and diamond simulant material. Additionally, this non-oxide ceramic was the first material used to manufacture LEDs and detectors in early radios.

Synthetic silicon carbide is manufactured by reacting silica and carbon in a reaction furnace at high temperature, creating pellets or powder form as the final product.

Characteristics

Silicon carbide (SiC) is an engineering ceramic known for its outstanding high-temperature strength, oxidation resistance, superior hardness and low specific weight; making it suitable for large volume components. At room temperature it forms tetrahedral structures composed of Si atoms bonded to four C atoms in four corners; of its 215 polytypes only alpha form (a-SiC) and b-SiC with cubic zinc blende crystal structure are of technological interest.

Material with a wide band gap makes graphene an excellent material for gas sensors, while its high thermal conductivity allows it to withstand extremely high temperatures – making it perfect for furnace applications.

Iron oxides are both abrasive and resistant to wear, chemically inert to acids and alkalis, and second only to diamond in hardness. Due to these characteristics, it finds use in applications ranging from cutting materials, ballistic armor components and even aerospace applications; hence the nickname dragon skin.

Synthetic SiC is made using pure silica sand and coal coke carbon as raw materials. A mixture is assembled around a carbon conductor in a brick electrical resistance-type furnace and an electrical current is passed through it; the resultant chemical reaction produces SiC with carbon monoxide as an by-product.

Applications

Silicon carbide is one of the hardest substances known to man, making it ideal for use as wear resistant coatings in applications like disc brakes and electrical contacts. Furthermore, silicon carbide components form part of bulletproof armor such as Dragon Skin’s (wet/dry milled silicon carbide whisker-reinforced alumina).

Hardness and strength make carbon steel an ideal material to use when crafting cutting tools or other industrial products that may be exposed to high temperatures or vibrations, such as cutting tools. Carbon steel also makes an attractive non-slip choice for floor or stair treads or deck paint formulations – as well as being widely utilized as mechanical seal components on pumps, compressors and agitators that will likely operate in demanding environments, including highly corrosive ones.

SiC is typically an electrical insulator in its pure state; however, certain impurities can alter this property to transform it into a semiconductor material. When aluminum, boron and gallium dopants are added, they create P-type semiconductor properties; nitrogen and phosphorus dopants may turn it into N-type semiconductor properties. When combined with metal oxide dielectrics such as DiOXEs it can also be deposited for Schottky barrier diodes, bipolar transistors, MOSFETs capable of handling high voltages but low turn-on resistances – these devices then become indispensable tools in various electronic applications that demand fast operation.

Preparation

Numerous methods have been devised for producing silicon carbide. One such process, developed by Edward Goodrich Acheson in 1893 and widely utilized today by numerous silicon carbide plants worldwide is known as the Acheson process. This involves mixing silica with carbon in an electric furnace before heating. This method remains widespread today and numerous production facilities still employ it today in producing high quality silicon carbide product.

Recent work conducted at the University of New Mexico developed a more modern technique known as the top-down approach, wherein researchers exfoliated hexagonal bulk silicon carbide in either isopropyl alcohol or N-methyl-2-pyrrolidone before switching its bonding from sp3 to sp2, to isolate monolayer silicon carbide much faster and simpler than earlier methods which required expensive equipment. This top-down approach offers much faster isolation of monolayer silicon carbide.

Research team has also investigated gas phase approaches to synthesizing silicon carbide. These processes can be quick, produce high yields without needing solid state catalysts and are more eco-friendly than the traditional calcination method.

As part of these gas phase reactions, various oxygen-bearing organosilane precursors such as tetraethoxysilane and methyltriethoxysilane (MTES) precursors were tested, including tetraethoxysilane and MTES. Hydrolysis of MTES with phenolic resin, ethylcellulose, polyacrylonitrile and starch formed a gel which was carbonized at 750 degC to form mesoporous b-SiC catalyst support material.

Properties

Silicon carbide is an extremely strong ceramic material used in many fields. It features high strength, hardness, low thermal expansion coefficient and good wear resistance – as well as being thermal shock and chemical corrosion-proof. Silicon carbide finds applications across automotive, mechanical and chemical industries as well as environmental protection, space technology, information electronics energy sources as well as many others.

SiC is a wide bandgap semiconductor material (with electronic bandgaps ranging between 2.4eV for a-SiC and 3.3eV for b-SiC), featuring excellent conductivity and temperature stability, making it an attractive option for electrical components due to its superior reliability and efficiency, particularly at higher power applications.

Carborundum, another dense form of SiC and one of Earth’s two hardest natural minerals after diamond (9-10 Mohs), has a covalent crystal structure based on Si-C bonds with tetrahedra centered around silicon or carbon atoms forming hexagonal crystal structures similar to wurtzite; most common is the a-SiC polymorph with hexagonal crystal structure while beta modification with zinc blende crystal structure is less popular.

Modern production of synthetic SiC involves reacting powdered sand with carbon in an electric furnace at high temperatures and pressures, followed by sintering to bond its grains together into an exceptionally hard and durable material. Abrasives manufacturers typically utilize reaction-bonded sinter, while advanced electronics producers employ Lely method or chemical vapor deposition. Workers exposed to abrasives produced using either process could be at increased risk for diffuse interstitial pulmonary fibrosis or other lung conditions.