The graphite has a crystallite size which varies between 100 and 150 A in linear dimensions. Heavy graphitization produces a wide variation in the orientations of the c axis with a tendency for it to be parallel to all four directions of the diamond. As the amount of graphitization increases the c axis is mainly oriented in a cone around the direction which is perpendicular to the diamond surface. At the initial stages of graphitization the c axis of the graphite crystallites is oriented perpendicular to the underlying diamond surface with the a axes lying parallel to the directions in the diamond surface. Higher temperatures produce an increase in the rate of graphitization until at 1900 ☌ almost all the areas suitable for examination have been converted to graphite after heating for 5 to 10 min. Subsequent examination by transmission electron microscopy and selected area electron diffraction has shown that under some conditions very slight graphitization of the diamond can be detected after heating for 45 min at 1500 ☌. The fragments have been heated under non oxidizing conditions in the temperature range of 1500 to 1900 ☌. Diamond fragments with surfaces, thin enough for examination by transmission electron microscopy, have been prepared.

Diamond dimensions 226