Industrial diamonds grown in Ni70Mn25Co5--graphite--sulfur system under HPHT

This paper reports that diamond single crystals were synthesizedfrom sulfur-added Ni₇₀Mn₂₅Co₅+C system under highpressure and high temperature (HPHT). It was found that additivesulfur had inhibited the nucleation and growth of diamond to someextent. X-ray diffraction of the collected sample indicated thatunder the synthesis conditions, a new compound MnS had been formedthrough the reaction of additive sulfur with manganese in thecatalyst. The MnS has a fcc structure, and its average crystal sizewas about 30 nm. By scanning electron microscope, the{111} surface of diamond was found to be flat, while there wasusually a large depression on the central region of {100}.Further observation showed that there were many small upside-downpyramidal pits in the expression. The results of x-ray photoelectronspectroscopy shows that MnS can only be detected in the depressionin the range of detection precision. It was inferred that MnS hadbeen dissolved in the melted alloy during the growth experiment, andprecipitated in the sequent quenching process.