Natural and synthetic polycrystalline diamond, with emphasis on ballas - 'Ballas' - Radially grown, polycrystalline diamonds?

The successful synthesis of diamond by chemical vapor deposition (CVD) at low pressures has generated renewed interest in polycrystalline diamond. It is now possible to deposit on relatively large surfaces a metal-free 'polycrystalline diamond ceramic', which is nearly equivalent in optical, thermal and mechanical properties to single crystal diamond. Some microstructures found in CVD diamond are clearly related to those seen in natural ballas and the possibility of making an even better 'polycrystalline CVD diamond' and exploiting its capabilities is considered here. (C) 1997 Published by Elsevier Science Ltd.