Graphitization of Diamond at Zero Pressure and at a High Pressure
Abstract
Natural diamonds have been heated in the temperature range of 1850 to 2000 degrees C at zero pressure and the rates at which diamond transforms to graphite measured. For {111} and {110} surfaces activation energies of 253 ± 18 and 174 ± 12 kcal mol-1 (1159 ± 75 and 728 ± 50 kJ/mol) respectively have been obtained. Diamonds have also been heated in the temperature range of 1950 to 2200 degrees C under a pressure of 48 ± 3 kbar (4.8 ± 0.3 GPa) and an activation volume of about 10 cm3 mol-1 obtained for both {111} and {110} surfaces. It is proposed that the rate controlling process in the graphitization of diamond is the detachment of a single atom from the diamond surface. This is contrary to previous proposals in which the detachment of groups of atoms have been considered to be the rate-controlling process. In the present work, it is suggested that the rate-controlling step for graphitization is the detachment of a triply bonded atom from a {111} surface and of a doubly bonded atom from a {110} surface.
- Publication:
-
Proceedings of the Royal Society of London Series A
- Pub Date:
- June 1972
- DOI:
- 10.1098/rspa.1972.0086
- Bibcode:
- 1972RSPSA.328..413D