Atomistic simulations of surface reactions in ultra-high-temperature ceramics: O2, H2O and CO adsorption and dissociation on ZrB2 (0001) surfaces

Abstract

Understanding surface reactivity is crucial in many fields, going from heterogeneous catalysis to materials oxidation and corrosion. In order to better decipher the initial stage of surface reactions of ZrB2 exposed to the harsh environment of aerospace components, the chemical activity of both Zrand B-terminated (0001) surfaces is predicted and compared by using state-of-the-art density functional theory. In particular the adsorption, dissociation and diffusion of O2, CO and H2O are extensively examined through the calculation of the surface adsorption energies and reaction pathways. We find the dissociative adsorption of O2 dominating the reactivity of both Zrand B-surfaces, while the dissociation of H2O and CO is weakly active on Zr-terminated surfaces, and even less activated on B-terminated ones. Importantly, we discover that the reaction of O2 and H2O can trigger surface reconstruction at the B termination, an efficient mechanism for B removal. Our work thus provides thermodynamic and kinetic insights into the elementary reactions of the most dominant gases found in the environment typical of aerospace applications, and highlights the diverse surface reaction mechanisms when ZrB2 exposed to O2, CO and H2O.