X-ray Photoelectron Spectroscopy Study of the Passivation of NiAl(100) by Water Vapor

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• 作者：Na Cai ; Qianqian Liu ; Xiao Tong ; Guangwen Zhou
• 刊名：Langmuir
• 出版年：2014
• 出版时间：January 28, 2014
• 年：2014
• 卷：30
• 期：3
• 页码：774-783
• 全文大小：455K
• ISSN：1520-5827

文摘

The oxidation of NiAl(100) surfaces by water vapor is studied using X-ray photoelectron spectroscopy (XPS) to elucidate the effect of temperature and vapor pressure on the surface passivation mechanism of the NiAl alloy. The water-vapor oxidation at ambient temperature (25 掳C) results in self-limiting Al(OH)₃/Al₂O₃ bilayer film growth to a less extent of the limiting thickness regimes, in which the growth of the inner Al₂O₃ layer occurs via dehydration of the outer Al(OH)₃ layer. The growth of the passivating overlayer at the ambient temperature depletes Al and forms a Ni-rich layer at the oxide/alloy interface that impedes supply of Al atoms to the outer surface for Al(OH)₃ formation via the hydration reaction, whereby resulting in a more Al-deficient structure of the outer Al(OH)₃ layer upon increasing the vapor pressure. In contrast, the water-vapor oxidation at 300 掳C results in Al₂O₃ single-layer film growth to a larger limiting thickness without involving the transient hydroxide phase of Al(OH)₃. It is shown that increasing the oxidation temperatures results in the formation of a more compact Al₂O₃ film owning to the enhanced bulk diffusion rate that maintains an adequate supply of Al atoms to the oxide/alloy interface to sustain the oxide film growth to the full extent of the limiting thickness.