Crystallization of Diamond and Graphite

Abstract

The key features of the complete, stable nickel—carbon phase diagram have been established at pressures up to 54 kbar, and these features have been directly related to the nucleation and growth characteristics of diamonds in this system. At pressures in excess of 52.5 kbar, a liquid+graphite+diamond eutectic is formed at approximately 0.3 at. % nickel which results in an effective displacement of the diamond—graphite equilibrium line. This displacement is shown to be of considerable importance in the nucleation and growth of diamonds in this system. Under low and moderate driving forces, the rate-controlling mechanism in the growth on a speed diamond is the diffusion of carbon across the molten metal film surrounding the diamond. The observed diffusion coefficients at 54 kbar and 1660°<T<1800°K lie in the range: 2×10−5<D<4×10−5 cm2/sec.

Metastable Solvent Epitaxy of SiC, the Other Diamond Synthetics

“…The liquid metal that is commonly used in diamond synthesis is Ni; the Ni-C phase diagram at 54 Kbar is shown in Fig. 6b (Strong & Hanneman, 1967). Although the graphite phase is the only stable phase at normal pressure, at 54 Kbar, the diamond phase is stable below 1740 K. Liquid Ni coexists with the diamond phase between 1667 K and 1728 K. Thus, the solution growth of diamond from liquid Ni is possible in this temperature range.…”

“…7. Ostwald ripening, also called coarsening, which occurs at the late stage of the precipitation, (Strong & Hanneman, 1967).…”

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

“…is formed from supersaturated solution, as suggested by Strong and Hanneman [4] from the nickel-carbon phase diagram under 5.4GPa pressure. On quenching, the same carbon content NixC is solidified.…”

Thermal resistance of PCD materials with borides bonding phase

“…The oxidation of carbon (at 800 °C and higher) proceeds yielding gaseous CO and/or CO 2 products. The graphitization and oxidation processes depend on size, purity of diamond particles and type of bonding phases for the polycrystalline diamond [5]. The growth temperature of diamond lies between the melting point of the solvent/catalyst/carbon system and the diamond-graphite equilibrium temperature [6].…”