Ceramics, which include all inorganic nonmetallic materials, constitute another high performance category. Some of them are commonplace. The cement and concrete used for highways and other construction purposes are manufactured in greater volume than any other product. At the opposite extreme are synthetic diamonds, first made by General Electric in 1955 by subjecting graphite to temperatures above 3,000°F and pressures of more than a million pounds per square inch. Diamond is a paragon among materials in many ways—the hardest of all substances, the most transparent, the best electric insulator, with the highest thermal conductivity and highest melting point. As grit or small crystals, synthetic diamonds give an ultrahard coating to such industrial equipment as grinding wheels or mining drills. In addition, diamond films for optical or electronic applications can be grown by heating a carbon-containing gas such as methane to very high temperatures at low pressures. Other ceramics include oxides, carbides, nitrides, and borides, all of them very hard, brittle and resistant to corrosion, high temperatures, and electric current. Some ceramics are so strong that they have replaced steel as the armor for military vehicles.
Perhaps nowhere has the promise of ceramics been more tantalizing than in the quest for materials called superconductors, which can carry electric current with zero resistance—that is, without giving up any of the energy as heat. The phenomenon of superconductivity was discovered back in 1911 by Dutch physicist Kamerlingh Onnes. He cooled mercury to 4.2 K (-452°F), just 4 degrees above absolute zero, and observed that all electrical resistance disappeared. (Scientists commonly use the Kelvin scale for studies in the realm of the supercold, with temperatures measured in Kelvin (K). On this scale, water boils at 373 K and freezes at 273 K; absolute zero is the temperature at which molecular motion theoretically ceases.) Because such low temperatures are difficult to reach, there was much excitement in the mid-1980s when IBM researchers in Switzerland found that the ceramic lanthanum-barium-copper oxide becomes a superconductor at 35 K (-406°F). The discovery of this new class of superconductors stirred hopes of identifying substances that superconduct with no chilling at all. A decade later the threshold was up to 135 K (-217°F), but prospects for reaching still higher levels remain unclear. If they can be attained and the materials can be reliably and inexpensively fashioned into wires (not easy with brittle ceramics), the technological consequences would be immense.