Growth of Large Synthetic Diamonds

Large diamonds are best grown using the temperature gradient technique, where diamond is used as the source of carbon. In this technique, as described by Wentorf [52], the driving force for reconstitution, under diamond stable conditions, is provided by the higher solubility of diamond in a hot zone of the solvent/catalyst and the consequent crystallization of diamond in a cooler zone at constant pressure (Fig. 9). 

The nucleated diamond is restrained by the seed pad, resulting in truncated cubo-octahedral growth, whereas the orientation of the grown diamonds depends on the orientation of the seed. The habit of the reconstituted diamond depends largely on the solvent/catalyst, internal pressure and temperature of the reaction cell. 

Diamonds of a cubic habit tend to be formed at a lower growth temperature than those of an octahedral habit [47] (refer to Fig. 9). 

Crystal perfection is determined by a reasonably low growth rate which is achieved by optimizing, in combination, the space between seeds, the axial temperature gradient and the solvent/catalyst under diamond synthesis conditions. 

The choice of solvent/catalyst alloy for synthetic diamond growth not only has an influence on nitrogen content, but also on other diamond characteristics such as morphology, color, and inclusion content. The dependence of some of these diamond characteristics on solvent/catalyst typically used for research and commercial production by institutes and companies such as De Beers, Sumitomo, General Electric, and NIRIM, amongst others, are summarized in Table I. 

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