Synthetic diamonds. They were first produced in 1955 in the USA by General Electric. The synthesis process necessary to produce diamonds artificially requires extremely high pressure and temperature levels and highly advanced technology, which has constantly been evolving in a period of almost fifty years. Diamonds are generated by precipitating a liquid metal flow with carbon (graphite) as a nutrient. The mesh of synthetic industrial crystals can be determined on the basis of a controlled growth: a slow growth speed favours the formation of larger crystals. Although synthetic diamonds are essentially meant for strictly industrial applications, nowadays artificial diamonds enable to produce gems with the same physical and optical properties of natural diamonds that look just like them. Therefore, diamond synthesis is gradually turning the jewellery scenario around. The main world producers of synthetic diamonds are De Beers DRL, General Electric (USA), Sumitomo (Japan) and the Specialized Laboratories of former Soviet Union.

ABRASIVE

Diamond can be:

• natural • synthetic Why synthetic diamonds are generallymore suitable for abrasive tools than natural diamonds .There are both production and technical/application reasons. As for production, it suffice to say that it is under control and therefore constant from a quality point of view. As for application, it takes much more time to give a comprehensive explanation and this should be done by following a technical/scientific approach. However, a clear explanation can be given also in simple terms. As was stated above, industrial abrasives made of natural diamond are produced through the mechanical crushing of single crystals or parts of them (natural diamonds are only found in monocrystalline form). The abrasive grains thereby obtained are actually fragments that do not have the geometry of diamond crystals, but rather irregular forms and dimensions with sharp edges. Besides, these fragments are much harder (or less friable) than the crystals they were part of (indeed, during the mechanical crushing phase, diamonds break in the weakest points, that is along breaking lines). Because of their extreme hardness, abrasive grains obtained from natural diamonds are fit only for abrasive tools with metal or electrolytic bonds, whereas diamonds produced through a synthesis procedure can have the desired dimensions and need not be crushed. Synthetic diamonds can be both monocrystalline (made up of a single crystal like natural diamonds and with a regular form and geometry) and polycrystalline (made up of an aggregation of several crystals, so that they have an irregular shape and a greater quantity of sharp surfaces). It is on the basis of the differences between monocrystalline diamonds and the various types of polycrystalline diamonds and their respective forms and friability that their specific applications are determined. For example, if you want a delicate surface polishing with no flakings, it is important for grinding wheels to contain tough diamonds of a compact form because this type of diamonds microfractures slowly during grinding operations. Raw natural diamond . It is extracted from rock or sand layers; the most important deposits are located in Zaire, South Africa and in former Soviet Union. Natural diamond, properly cut and worked, is used in jeweller’s shops as a precious stone. Raw diamonds that have flaws making them unsuitable for jewellery, are used for industrial/production purposes. They must be crushed mechanically to be turned into abrasive grit for industrial diamond tools; the crystal fragments that are thereby produced, with extremely sharp cutting edges, have different, irregular and random forms and dimensions. Through industrial sieves of different dimensions, abrasive grains of the various required sizes are obtained.
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