Diamond-graphite phase boundary

Fig. 9. Pressure and temperature estimates for 114 nodules (see McKenzie 1989) from the Kaapvaal Craton calculated using (a) Brey Kohler s (1990) geothermometer and geobarometer, and (b) Bertrand Mercier s (1985) geothermometer and Finnerty Boyd s (1984) geobarometer. The solidus is from McKenzie Bickle (1988), and the diamond-graphite phase boundary from Kennedy Kennedy (1976).

Figure 36, P-T phase and reaction diagram of carbon as results from Refs. 509 and 510. Solid lines represent equilibrium phase boundaries. The dashed line is the threshold for conversion of hexagonal diamond and both hexagonal and rhombohedral graphite into cubic diamond.

Since F = 2 results in an area (phase field), and F = 1 results in a line (phase boundary), we can predict that F = 0 should occur at a point, and indeed it does. Point B is such a point = 3 graphite, diamond, and liquid C = 1, carbon), as is... 

The non-diamond carbon phase in polycrystalline diamond films (often referred to as graphite, although this conclusion is far from accurate [23]) is first and foremost the disordered carbon in the intercrystallite boundaries. Their exposure to the film surface can be visualized by using a high-resolution SEM techniques [24] the intercrystallite boundaries thickness comes to a few nanometers. In addition to the intercrystallite boundaries, various defects in the diamond crystal lattice contribute to the non-diamond carbon phase, not to mention a thin (a few nanometers in thickness) amorphous carbon layer on top of diamond. This layer would form during the latest, poorly controlled stage of the diamond deposition process, when the gas phase activation has ceased. The non-diamond layer affects the diamond surface conduc-... 

In the initial state of graphite (point A), one phase exists. Temperature is held constant (3000 K), and the pressure is allowed to vary freely. The C(graphite)-C(diamond) phase boundary is reached at approximately 230 kbar. At this point, C(diamond) forms and exists in equilibrium with C(graphite). All the C(graphite) is eventually converted to C(diamond). (This process may be quite slow.) In the diamond region, one phase exists. Additional increases in the pressure on C(diamond) result in the equilibrium of C(diamond) and liquid carbon at about 400 kbar. When all the diamond has melted, the pressure on C(l) is free to increase to attain the final state (point B). 

Figure 1 A graphitic phase at a grain boundary in diamond predicted by a simulation using a many-body analytic potential function. The simulation conditions are described in Ref. 16.

Figure 2.3. The phase diagram for carbon. Solid lines represent equilibrium phase boundaries Position A commercial synthesis of diamond from graphite by catalysts B P/T threshold of very fast (< 1 ms) transformation of diamond to graphite C P/T threshold of very fast transformation of graphite to diamond and D single-crystal hexagonal graphite transforms to retrievable hexagonal-type diamond (Bundy, 1996).

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