Diamond

Diamond

Diamond consists of extremely pure carbon and has a hardness of 7,000 N/mm²; the hardest substance known. Natural diamond loses its extreme hardness above about 800ºC, and its synthetic form, the artificial diamond produced in a retort, loses it at about 850ºC. Diamond then disintegrates back into its original carbon lattice and becomes soft "like a pencil lead". There are no striking differences in principle between natural diamond and that produced synthetically. Some publications indeed point out that not only does artificial or synthetic diamond have a somewhat higher thermic resistance, it also reacts slightly differently in respect of its mechanical properties, i.e. is somewhat more resistant to impact.

Diamond grinding wheels are produced from both types of diamond, artificial diamonds mainly being used nowadays for wheels with small grain sizes. The grain sizes range from 0.002 mm to over 0.500 mm. Diamond wheels – like CBN grinding wheels – also have different concentrations, i.e. the carat weight per cm³ is determined by the wheel producer on the basis of the conditions of use.

Diamond grinding wheels are suitable for working amorphous and/or extremely hard materials (e.g. carbides) and for fibre-reinforced plastics. They should not be used for low-carbon steels because the carbon of the diamonds diffuses into the peripheral zone of the workpiece due to its chemical affinity for steel. The hard diamond is then degraded relatively rapidly (severe wear) and if sufficient heat is present hardening due to carbide formation may even occur in the peripheral zone of the workpiece.

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