High-Pressure, High-Temperature Synthesis of Nanodiamond from Adamantane

— We have studied the high-pressure, high-temperature behavior of adamantane (C10H16) and the associated formation of diamond nano- and microcrystals. Diamond microcrystals have been synthesized at a pressure of 8 GPa and temperatures above 1300–1400°C, whereas large-scale synthesis of nanodiamond has been carried out at higher pressures, near 9.4 GPa, in the narrow temperature range 1250–1330°C. Our experimental data suggest that diamond microcrystals are formed in a fluid growth medium as a result of recrystallization of graphite, an intermediate carbonization product, and that nanodiamond formation is a direct result of adamantane carbonization.