Luo Langli, Li Liang, Schreiber Daniel K, He Yang, Baer Donald R, Bruemmer Stephen M, Wang Chongmin
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA 99352, USA.
Institute of Molecular Plus, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, 92 Weijin Road, Tianjin 300072, China.
Sci Adv. 2020 Apr 24;6(17):eaay8491. doi: 10.1126/sciadv.aay8491. eCollection 2020 Apr.
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 O and HO vapor, featuring a "step-edge" mechanism with severe interfacial strain in O, and a "subsurface" one in HO. Ab initio density functional theory simulations rationalize the HO 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.
气-固界面反应对于从多相催化到应力腐蚀开裂等许多技术应用至关重要。一个尚未明确的突出问题是气体和固体如何在化学吸附之外相互作用，以形成一个稳定的中间相来连接后续的气-固反应。在此，我们报告了对镍铝合金氧化反应从初始表面吸附到界面反应直至体相的实时原子尺度观测。我们发现了在氧气和水蒸气中氧化物生长的不同原子机制，氧气中以具有严重界面应变的“台阶边缘”机制为特征，水蒸气中则是“次表面”机制。从头算密度泛函理论模拟解释了水蒸气的解离有利于形成无序氧化物，这促进了离子向氧化物-金属界面的扩散并导致界面应变缓解，从而增强向内氧化。我们的研究结果描绘了镍铝表面氧化反应的完整路径，并阐明了化学机械效应在气-固相互作用中的微妙耦合。
