Dynamic formation of nanodiamond precursors from the decomposition of carbon suboxide (C₃O₂) under extreme conditions—A ReaxFF study

We use molecular dynamics simulations with the ReaxFF-lg potential to model the high pressure pyrolysis of carbon suboxide (C₃O₂) in mixture with argon as a pressure bath. We show that the reactive simulations catch the experimental behavior of the low-pressure detonation of C₃O₂ (around 10 bars in shock tube experiments) and allow extrapolations to the high-pressure range of solid-state explosive detonation (up to 60 GPa). While at low pressure carbonaceous nanostructures are formed through the aggregation of species such as carbon dimers C₂, it appears that the high pressure deeply modifies the process, with the aggregation of growing C_xO_y heterostructures, in which the oxygen amount is driven by the pressure and the temperature. Pressures in the order of 60 GPa lead to high oxygen ratios, which prevent carbon atoms to get four carbon neighbors (the first condition to get a diamond structure). But a pressure lowering leads to a substantial carbon enrichment through CO₂/CO release and facilitates the formation of pure sp³-carbon phases where diamond precursors can form. These results give new insights on the conditions leading to nanodiamonds during the detonation of carbon-rich high explosives.