Deciphering atomistic mechanisms of the gas-solid interfacial reaction during alloy oxidation

Abstract

Gas-solid interfacial reaction is critical to many technological applications from heterogeneous catalysis to stress corrosion cracking. A prominent question that remains unclear is how gas and solid interact beyond chemisorption to form a stable interphase for bridging subsequent gas-solid reactions. Here, 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 strain in O2, and a “subsurface” one in H2O. Ab initio density functional 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 Ni-Al surface oxidation reaction and delineate the delicate coupling of chemomechanical effect on gas-solid interactions.

In situ anisotropic NiO nanostructure growth at high temperature and under water vapor

“…This study, however, reveals dissociative adsorption of hydroxyl groups during in situ heating, which causes continuous anisotropic NiO growth. Luo and coworkers propose that mechanical stress at the Ni/NiO interface affects oxidation rates in water, 24 which supports the observation of NiO growth only on select surfaces of the utilized Ni nanoparticles.…”

“…Proposed growth mechanisms rely on cation diffusion along the screw dislocation cores, that is, the longitudinal direction of the whiskers, while lattice diffusion is responsible for lateral growth. This mechanism was initially proposed by Tallman and Gulbransen 22 for the formation of 𝛼-Fe 2 O 3 whiskers during the oxidation of iron at 400-500 • C. Several studies on Ni alloys have demonstrated different oxidation behaviors in water vapor environments compared to molecular oxygen gas [23][24][25][26][27] .…”

“…Different mechanisms have been proposed for the effect of water vapor on metal oxidation. Norby 28 has suggested an increase in cation diffusion rate as a consequence of maintaining charge neutrality due to increased proton hopping between oxygen ions at temperatures as high as 1500 • C. In a more recent study, Luo and coworkers 24 found that Ni-Al alloy single crystal thin films oxidized in water vapor reveal a relaxed incoherent oxide/metal interface instead of a highly strained coherent interface that forms during oxidation in O 2 . A faster inward diffusion of oxidant molecules was observed in the presence of water vapor and is attributed to the lower interface energy.…”

“…A faster inward diffusion of oxidant molecules was observed in the presence of water vapor and is attributed to the lower interface energy. 24 This study reports the direct in situ observation of anisotropic growth of NiO nanostructures during the controlled oxidation of Ni nanoparticles at high temperatures in the presence of water vapor. In situ environmental scanning electron microscopy (ESEM) was used to observe morphological changes of nickel nanoparticles as a func-…”

The Adoption of Image-Driven Machine Learning for Microstructure Characterization and Materials Design: A Perspective

“…Significant advances in both experimental and computational methods have enabled advances in how we visualize and describe material microstructures. For example, three dimensional microstructures can be visualized with techniques such as serial sectioning and atom probe tomography [1,2], and in situ methods have been developed for direct visualization of atomic-scale phenomena, including oxide growth mechanisms and element redistribution [3,4]. Computational methods have been at the forefront of many materials research studies due to the need for accelerated materials discovery, design, and development emphasized in the Materials Genome Initiative [5].…”