High Temperature Graphitization of Diamond during Heat Treatment in Air and in a Vacuum

This paper studies the morphological and structural changes that occur during the graphitization of synthetic diamond powder (with highly faceted edges) and micropowder during heat treatment in air at temperatures up to 1000 degrees C and in a vacuum at temperatures up to 1600 degrees C. The most developed facets of the original diamond crystals are the octahedral {111} and cubic {100} faces. It is established that graphitization begins from the vertices and edges of crystals. {111} faces are more susceptible to graphitization than {100} faces. The morphological analysis of graphitized diamond AC160 in air helps us to study the kinetics of graphitization: the growth of dendritic graphite crystals and the formation of "graphitization pits" on the surface of diamond facets. It is shown for the first time that graphite of different shapes is formed on different diamond faces at different rates; thus, on the {111} faces graphite forms and grows in the form of triangles, and on the {100} faces, in the form of squares. At a high temperature, the volumetric graphitization of diamond particles is observed, accompanied by their destruction, mainly in the growth stages.