Diamond formation and behaviour of carbides in several 3d-transition metal-graphite systems

Abstract

The formation of diamond and the behaviour of coexisting carbides with diamond in several 3d-transition metals (manganese, iron, cobalt, nickel)-graphite systems was studied under 7 GPa pressure up to 1700 ~ C from the view-point of diamond formation. In the nickel-graphite and cobalt-graphite systems, no stoichiometric carbide was formed, but MxC, which is thought to be the interstitial solid solution of carbon, was formed. In the iron-graphite system, on the other hand, the formation of two stoichiometric carbides, i.e. Fe3C and FeTCs, was found. In the manganese-graphite system, only one stoichiometric carbide Mn7Cs, which is isostructural with Fe7Ca, was formed. The diamond formation process in the presence of these transition metals is discussed in relation to the carbide formation.

Synthesis of large-sized spherical Co–C alloys with soft magnetic properties though a high-pressure solid-state metathesis reaction

“…28 Under experimental conditions of 7 GPa and 1400-1500 °C, S. Naka et al reported absence of stoichiometric cobalt carbide when cobalt was used as a catalyst for diamond synthesis. 29 Absence of cobalt carbides was shown also by W. Utsumi et al in their in situ X-ray diffraction study of graphite-to-diamond transformation using various solvent-catalysts under high pressure and high-temperature conditions. 30 When measuring the solubility of diamond in metallic cobalt under conditions of 5 GPa and 1100-1300 °C, Y. Tian et al did not observe the presence of cobalt carbide products.…”

Determination of the Difference between the Solubility of Graphite and Diamond in Cobalt at 5 GPa

“…The formation and impact of cobalt carbides in a Co–C system during diamond synthesis have garnered considerable attention, as in the case of iron and nickel carbides, which have been thoroughly explored in previous studies. − Naka et al, who used graphite as the carbon source for diamond synthesis at 7 GPa using an 80 wt % graphite sample, did not observe cobalt carbides even at 1700 °C . Utsumi et al conducted in situ XRD observation of diamond growth in experiments using graphite as the carbon source and with a 50 wt % graphite sample, at a pressure of 6 GPa .…”

“…46−49 Naka et al, who used graphite as the carbon source for diamond synthesis at 7 GPa using an 80 wt % graphite sample, did not observe cobalt carbides even at 1700 °C. 39 Utsumi et al conducted in situ XRD observation of diamond growth in experiments using graphite as the carbon source and with a 50 wt % graphite sample, at a pressure of 6 GPa. 37 They also did not observe cobalt carbides even at the melting point of cobalt.…”

“…The main concern expressed with regard to metal-assisted conversion of graphite to diamond is the difference between the solubility values of graphite and diamond in metals; graphite has a higher solubility in metals than diamond. Once the saturation concentration of diamond is reached as graphite is dissolved in metal, diamond crystallization will commence, provided the specific pressure–temperature conditions required for diamond growth are met. ,− However, this theory, known as catalyst solvent theory, was established only through qualitative analysis; experimental quantitative data have failed to prove that the solubility values of graphite and diamond in metal differ. The solubility data of graphite in cobalt has only been reported under atmospheric pressure conditions, where at a temperature of 1285 °C, it is approximately 4.09 atom % (equivalent to 0.86 wt %) .…”

The Influence of Solvent Metal Microstructure on Synthetic Quality of Diamond Single Crystals

“…Synthetic mechanism has been intensively investigated for a long time [3][4][5][6][7], however there have been few reports on the corresponding relation between the microstructure of Fe-based catalyst and diamond growth, especially the morphology of Fe 3 C in the solvent metal. It has been confirmed that diamond synthesizing is closely related to the carbides formed by transition metal and graphite [8,9]. Literature [10] found that the decomposition of Fe 3 C can play an important role in diamond growth at HPHT.…”