In the BaSiCs of SiC blog series, we’ll explore many different features of silicon carbide. Let’s kick things off with a quick primer on this unusual material’s properties and applications.
Although it might seem like a recent innovation, silicon carbide (SiC) has actually been in use since the late 1800s, beginning as an abrasive material and later finding applications in a wide variety of industries (including semiconductors). The wide-ranging use of SiC is a natural consequence of the material’s extraordinary physical traits.
SiC’s Fascinating Properties
SiC, also known as carborundum, is a combination of silicon and carbide in a crystalline structure, and there are about 250 different crystalline forms in which SiC can be found. Silicon carbide can take on many different forms: individual grains of SiC can be sintered together to form strong ceramics; fibers of SiC can be added to a polymer matrix to form a composite material, and large, individual crystals of silicone can be grown for use in semiconductor applications. SiC also appears in nature, although rarely, in the form of the mineral moissanite.
Lightweight and Stable
SiC has an average density on the order of 3 g/cm3, which makes it relatively light in weight. It is chemically inert and corrosion-resistant, and it is not attacked by any acids, molten salts, or alkalis even when exposed to temperatures up to 800°C. SiC is an extremely hard and strong material (which makes sense considering its application as an abrasive material).
SiC has a very low coefficient of thermal expansion, which means that even when exposed to extreme temperature changes, it remains dimensionally stable (e.g., it will not significantly expand when exposed to heat or significantly contract when exposed to cold). It also has excellent thermal shock resistance.
A Sublime Material
One of the most fascinating properties of silicon carbide is that it is capable of sublimation: when temperatures are sufficiently high enough, SiC skips the liquid form and goes directly to a gaseous form. This means that it turns into a vapor instead of melting. The sublimation temperature of silicon carbide (where this solid-to-vapor transition takes place) is around 2700°C (which is around half the surface temperature of the sun).
As a semiconductor material, metallic conductivity can be achieved by heavy doping with nitrogen, aluminum, or boron. It can be doped n-type by phosphorous or nitrogen and p-type of gallium, aluminum, boron, or beryllium.
The Many Applications of Silicon Carbide
Besides its applications in semiconducting, SiC is also used for products such as bulletproof vests, ceramic plates, thin filament pyrometry, foundry crucibles, and car clutches. In terms of electrical applications, one of its earliest uses was as a lightning arrester in a high-voltage power system as engineers and scientists recognized that silicon carbide performs well even in the presence of high voltages and high temperatures. More modern applications of silicon carbide in electronics include Schottky diodes, MOSFETs, and power electronics.
Whether it’s being used as an abrasive polishing material or as the semiconductor for a Schottky diode, SiC is certainly robust and multi-faceted. Sublimation, extreme chemical inertness and corrosion resistance, excellent thermal properties, and its ability to be grown as a single-crystal structure are just a few of its outstanding properties.