Tech Talk
What is the history "Synthetic Diamond"?
In the 1950s, both the General Electric Company in the United States and ASEA in Sweden independently discovered a synthesis process which created a crystalline diamond from graphite. In 1957, the General Electric Company announced that the commercial manufacturer of diamond, for sale as a consumable abrasive, was possible. The synthetic diamonds were given the trade name "Man-Made". The first successful industrially manufactured diamond was achieved when iron sulfide, in a graphite tube closed with tantalum end disks, was subjected to a pressure of 95,000 bar (1,400,000 psi) and 1600 degrees C for several minutes. Tests on the crystal produced proved that it was indeed a diamond.
The industrial process for manufacturing diamond now uses pressures in the range of 55,000 to 130,000 bar (808,000 to 1,900,000 psi) at temperatures in the range of 1400 to 2500 degrees C (500 to 4500 degrees F). The catalyst-solvent metal interface is most important. Iron was first used, and since then chromium, cobalt, magnesium, nickel, platinum, rhodium, ruthenium, and tantalum have been used successfully. Different temperatures, solvents, and pressures produce different diamond types. Each crystal may be tailored to the best possible combination of size, shape, surface, and crystal structure for specific applications.
The metallic coating of the diamonds with nickel and/or copper provides better mechanical bonding in a variety of bond systems, as well as providing a path for the heat from the process to be conducted away from the diamonds, particularly in dry grinding applications.
Diamond is suited to grinding tungsten carbide, natural stones, granite, and concrete, as well as more sophisticated ceramics and cermets. Diamond, however, is most unsuitable for the grinding of steels due to the very aggressive chip formation which tends to tear the diamonds from their bond. Also, it is postulated that diamond, being a carbon-based material, has an affinity for the carbon in the steel and suffers accelerated wear by the dissolution of the diamond into the carbon in the steel, producing an iron carbide (Fe3C) with most unsatisfactory results. These are two of the prime reasons for the introduction of CBN, which is less reactive in the presence of carbon steel alloys and has better mechanical bonding properties, making wheel fabrication that much easier.
