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Wednesday, 19 September 2007

electrical conductivity (of diamond).

The electrical resistance of diamond is very high; therefore, it is essen­tially a nonconductor. Pure, color­less, single crystals of diamond have a higher resistance than impure va­rieties such as bort. Type lib dia­mond, a rarely encountered form, is a semi-conductor. Diamonds with a natural blue color are all Type lib, whereas those to which a blue color has been imparted by electron bom­bardment are nonconductors. Thus, this kind of artificial coloration can be detected with a conductometer.

See CONDUCTION DETECTOR (AUDIO), CON­DUCTOMETER, ELECTRON-BOMBARDED DIA­MOND, TYPE II DIAMOND.

electron-bombarded diamond. A

diamond whose color has been changed to blue by bombardment with fast electrons in a Van de Craaff Generator. Such a stone can be de­tected readily by a conductometer, since treated blue stones are non­conductors of electricity and natu­ral blue stones are conductors. Gamma-ray radiation also has been used to produce blue colors. See

CONDUCTOMETER, CONDUCTION DETECTOR (AUDIO), ELECTRICAL CONDUCTIVITY (OF DIA­MOND), TYPE II DIAMOND, VAN DE GRAAFF GENER­ATOR.

electrostatic separation process. A

method of recovering tiny diamonds from mill concentrates that makes use of the fact that almost all dia­monds are very poor conductors of electricity, compared with the as­sociated minerals in the concentrate. The apparatus consists essentially of


a grounded electrode and a charged electrode placed opposite one another and fairly close together. A high-tension field is maintained between the two electrodes, the charged electrode being of positive polarity. When the concentrates are passed through the high-tension field, all particles obtain an induced charge. The associated minerals, being relatively good conductors, allow their charge to leak away to the ground as they pass over the grounded electrode of the separator. In this manner they acquire negative potential and are therefore attracted towards the positive high-tension electrode. The induced charge on the surface of the nonconductive diamonds cannot leak away quickly enough; they retain their positive charge, and are therefore repelled from the high-tension electrode. A separation is thus achieved. The method is much less expensive and time consuming than hand sorting and permits the recovery of small al­luvial stones and those from weath­ered kimberlite, neither of which will adhere to the conventional grease table. See x-ray separator.

 
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