Synthetic diamond , an artificial diamond that is usually obtained by exposing graphite to very high temperatures and pressures. Synthetic diamond resembles natural diamond in most of its basic properties, preserving extreme hardness, wide transparency (in its pure form), high thermal conductivity and high electrical resistivity, for which diamond is highly regarded. Since synthesis is an expensive process, large gemstones are rarely of high quality. Instead, most synthetic diamond is produced in the form of grains or small crystals, which are used to provide hard coatings for industrial equipment such as grinding wheels, machine tools, drawing dies, quarry saws and rock drills. In addition, diamond films can be grown on a variety of materials.
In 1880, Scottish chemist James Ballantyne Hanney claimed that he made diamonds by heating a mixture of paraffin, bone oil and lithium to red heat in sealed cast iron tubes. In 1893, French chemist Henri Moissant announced that he was able to make diamonds by placing a crucible containing pure carbon and iron in an electric furnace and subjecting a very hot mixture (about 4000 ° C [7000 ° F]) to strong pressure by sudden cooling in a water bath . None of these experiments were successfully repeated.
During the first half of the 20th century, American physicist Percy Williams Bridgman conducted extensive research on high-pressure materials. His work led to the synthesis of General Electric, Schenectady, New York, from diamonds in his laboratory in 1955. The stones were made by exposing graphite to pressures approaching 7 gigapascals (1 million pounds per square inch) and temperatures above 1700 ° C (3100 ° F) using a metal catalyst. Tons of industrial grade diamonds have been produced in variations of this process every year since 1960.