Conversion of diamond polishing powder to high-density isotropic nano-crystalline graphite through spark plasma sintering

Abstract

Conversion of diamond polishing powders into graphite nano-crystals and simultaneous densification to high-density graphite were achieved through spark plasma sintering at 2000 °C with 45 MPa pressure. The sintered graphite had a density of 1.84 g/cm 3 and hardness of 12.1 ± 0.4 HV. The phase evolution was characterized by X-ray diffraction and Raman spectroscopy. Scanning electron microscopy and transmission electron microscopy revealed that the converted highdensity graphite consisted of randomly oriented nano-crystalline grains. The formed graphite was also isotropic in nature.

Cubic and hexagonal boron nitride phases and phase boundaries

“…[45][46][47] driven by the industrial relevance, emergence of 2D nanomaterials, and adaptation of new processes like SPS. 48,49 A consensus is reached that the graphitization of cubic diamond powder on a micron scale is a surface energy-driven transformation, transitioning into polycrystalline graphite as the particle size increases. 43,50,51 Such surface energy-driven graphitization is believed to be a rather general phenomena applicable not only to diamond but also to c-BN structure, as h-BN phase is predominantly observed near the surface and grain-interface of c-BN particles.…”

“…52 Considering the time-consuming multi-step graphite densification processes involved in current industrial practice, 53 SPS might feature a single-step conversion process of dense graphitic material. 48,49…”