Diamond formation and wettability in a Mg-Cu-C system under high pressure and high temperature

In order to decrease the pressure and temperature region for diamond formation from a Mg-C system, MS-Cu alloys with a wide range of composition have been used as the catalyst for diamond synthesis. Diamond growth layer has successfully been formed on seed crystals at 6 GPa and 1550 degrees C in the Mg-Cu system, which is 2 GPa and 200 degrees C lower than in pure Mg. Morphology of the grown crystal depends on composition of the alloys, namely, smooth growth surfaces were formed only in a range between 40 and 50 at.% Mg in the Cu-Mg alloys. Rough growth surfaces were formed in the Cu-rich side, and the seed crystals were dissolved in the Mg-rich side. Measurement of wettability between graphite and the Mg-Cu alloys at the high P-T condition gave a curve of wetting angle vs. Mg-Cu composition in which a plateau and bending points are present. The curve is explained to be due to attractive interaction between Mg and Cu. The experimental results conclude that the morphological change depending on the Mg-Cu composition is closely related to the wetting angle, i.e., interaction between metal and carbon.