Synthesis of diamond and the influence of graphitisation on the formation of diamond

The success of diamond synthesis depends highly on the quality of the graphites used. In a systematic study with six different graphites the influence of graphitisation was studied. The experiments were carried out with and without evacuating the graphites. Graphitisation reflects the crystallinity, which can be improved significantly by heating. In addition the influence of pressure on the graphitisation was studied with a strong increase of graphitisation by treatments at 70 kbar and 1500°C. These graphites were then used for diamond synthesis. The experiments showed a clear dependence of the rate of conversion and the size of the diamond crystals obtained on the starting materials. Both quantities could be improved by evacuating and heating the graphites to 1100°C. This is a distinct indication that besides crystallinity also gas molecules absorbed on the surface of the graphites greatly influence the transformation. The samples were examined in polished sections with polarising microscopy and...