Evolution of High-Temperature Oxygen Clusters and Radical Release: A Molecular Dynamics Study in Pure Oxygen and Titanium Tetrachloride Oxidation Environments.

Despite decades of research into high-temperature oxidation kinetics, the atomic-scale origin of oxygen radical formation-a critical driver of the synthesis of functional oxide materials, oxidation corrosion of alloys, and combustion of fuels-remains elusive. Here, we unveil a previously unrecognized "oxygen clustering-radical release" pathway at the molecular level, wherein transient van der Waals aggregates of oxygen molecules, rather than isolated O2, serve as the primary radical source. Through an integrated computational strategy combining first-principles calculations and deep neural network potential function molecular dynamics, we demonstrate that oxygen clusters exhibit a pronounced odd-even oscillation in stability: even-numbered clusters (especially O6/O8 subunits) are chemically inert, whereas odd-numbered clusters (dominated by O3) possess high reactivity. Kinetically, clusters evolve via reversible aggregation-dissociation, and upon reaching a critical size, undergo structural collapse accompanied by radical release-a process initiated predominantly by large odd-numbered clusters. This mechanism persists in both pure O2 and TiCl4-containing environments, with TiCl4 modulating only the aggregation kinetics, not the fundamental pathway. Our work establishes oxygen clustering as a universal, spontaneous source of radicals in high-temperature oxidation, providing a new molecular-level mechanistic framework for understanding and controlling radical-driven processes in materials synthesis, corrosion and combustion.