A review of liquid phase systems pertinent to diamond synthesis

The evidence from nature and from a wide range of experiments clearly indicates several routes via liquid phases for the synthesis of diamond, graphite, and poorly crystallized carbons over a range of temperatures and pressures. This review of the literature summarizes the following separate carbon-liquid regimes which are closely related to synthesis of various forms of carbon: (1) carbon as soot, carbon black, amorphous carbon, and graphite from C-H liquids derived from petroleum: (2) carbon from molten metal solvents including those containing hydrogen—especially the ideas proposed for solution/catalysis synthesis of diamond from different precursor carbons; (3) carbon from C-H-O liquids—primarily in natural systems—as evidenced by inclusions in quartz and diamond, coated diamond, diamond/graphite from metamorphic rocks and kimberlites, and poorly crystallized carbons from sedimentary rocks; (4) carbon from ionic liquids such as carbonates, silicates, and halides—both natural and synthetic. Also considered are the possibility of connections among these categories.