Morphological features of natural diamond crystals treated in a rotary vortex apparatus and subjected to oxidative etching.

An understanding of the structural changes induced by the ovalization treatment of diamonds is necessary to produce crystals with controlled sizes and morphologies. In this investigation, the treatment of natural diamonds in a rotary vortex apparatus was used to modify the surface morphology of the particles and obtain the ovalized crystals. The size of the starting diamond crystals was in the 250–350 μm range. In the product of treatment in the rotary vortex apparatus, particles with sizes above 300 μm were ovalized, while those with sizes below 300 μm demonstrated irregular shape. The formation of particles of irregular shape during the treatment was caused by the fracture of the starting diamond crystals along the defect regions. The ovalized crystals were formed by "blunting" the edges and vertices of the starting crystals under the action of friction forces. The ovalized diamond consisted of a crystalline core and a defect shell. The crystals were subjected to oxidative etching to reveal the structural changes of the surface layers caused by the ovalization treatment. During oxidative etching, the ovalized crystals developed a system of etch pits over the entire surface. In contrast, the oxidative etching of the starting (untreated) diamonds showed the facet selectivity. [ABSTRACT FROM AUTHOR]