PNNL

Abstract

Gas-solid interfacial reaction is critical to many technological applications from heterogeneous catalysis to stress corrosion cracking. A prominent question remains unclear is that how gas and solid interacts beyond chemisorption to form a stable interphase for bridging subsequent gas-solid reactions. Herein, we report real-time atomic-scale observations of Ni-Al alloy oxidation reaction from initial surface adsorption to interfacial reaction into the bulk. We found distinct atomistic mechanisms for oxide growth in O2 and H2O vapor, featuring a “step-edge” mechanism with severe interfacial lattice mismatch strain in O2, while a “subsurface” mechanism in H2O. Ab initio density function theory simulations rationalize the H2O dissociation to favor the formation of a disordered oxide, which promotes ion diffusion to the oxide-metal interface and leads to an eased interfacial strain, therefore enhancing inward oxidation. Our findings depict a complete pathway for the gas-solid reaction and delineate the delicate coupling of chemo-mechanical effect on gas-solid interactions.