In situ X-ray diffraction study of diamond nanopowders spark plasma sintering under very high pressure

The sintering behavior and the thermal stability of different nanodiamond powders, produced either by detonation or by high-pressure high-temperature (HPHT) synthesis, is studied in situ during spark plasma sintering at 5 GPa. A portable high pressure spark plasma sintering device allowed the transformation of nanodiamonds during the sintering process to be followed by synchrotron radiation X-ray diffraction, in order to determine the optimal sintering conditions and investigate the impact of the sample environment. The powders were also characterized ex situ using advanced bulk and surface techniques to evaluate how the sp 2 carbon shell, agglomeration state, and surface chemistry affect sintering while preserving the diamond structure and particle size. A purified and deagglomerated detonated powder (5 nm) and a nanodiamond powder (