silicon carbide
Silicon carbide is SiC — a very hard, very refractory, heat-conducting ceramic that shrugs off temperatures and chemicals that would destroy most materials. You meet it as the black grit on the toughest sandpaper and grinding wheels, as the glowing heating elements in industrial furnaces, as brake discs on supercars, as the armour on some vehicles, and increasingly as the semiconductor chip inside efficient electric-car power electronics. First made in an electric furnace in 1891 and sold as carborundum, it was one of the earliest synthetic engineering ceramics, and it remains a favourite wherever hardness plus heat is the demand.
SiC is almost entirely covalently bonded: each silicon atom sits at the centre of a tetrahedron of four carbon atoms, and each carbon likewise bonds to four silicons, giving a rigid three-dimensional network much like diamond's (it comes in many stacking variants called polytypes). That strong directional bonding is the source of its property set: extreme hardness (about 9.5 on the Mohs scale, just below diamond and boron carbide), high stiffness, chemical inertness, stability to very high temperatures, and — unusually for a ceramic — high thermal conductivity, comparable to some metals. High conductivity plus a modest thermal expansion give it good thermal-shock resistance, so it tolerates rapid heating and cooling that would crack a lower-conductivity ceramic. It is also a wide-bandgap semiconductor, which is what makes it valuable in electronics.
Those properties map straight onto its jobs. As an abrasive it grinds glass, stone, and hard alloys. As a refractory and heating element it runs hot furnaces (silicon-carbide igniters and Globar-type heating rods). As a wear and structural ceramic it forms seals, bearings, pump parts, and kiln furniture. As armour and in ceramic brake discs it trades on hardness and low weight. The honest limits: like all covalent ceramics SiC is brittle and hard to densify — it barely sinters on its own, so it is made either by reaction bonding, by hot pressing, or by sintering with boron and carbon additives, each route giving a different microstructure and strength. And in air at very high temperature it slowly oxidises, growing a protective silica skin that is a virtue up to a point but can fail under fast-flowing gas.
A silicon-carbide heating element glows at 1400 degrees C in a kiln for years because SiC keeps its strength hot, resists oxidation behind a silica skin, and — thanks to its high thermal conductivity and modest expansion — survives being switched on and off without cracking from thermal shock.
Silicon carbide (SiC): diamond-like covalent bonding gives extreme hardness, high-temperature stability, and — rare for a ceramic — metal-like thermal conductivity.
SiC barely sinters by itself because its bonds are too strong and stiff for atoms to move. Real parts are made by reaction bonding, hot pressing, or sintering with boron-and-carbon additives — the route chosen sets the density, purity, and strength you get.