Effect of oxide layers of Ni-free stainless-steel on silane coupling agent immobilization

This study is concerned with the characterization of oxide layers formed on Ni-free stainless-steel and the immobilization of a silane coupling agent, i.e. γ-aminopropyltriethoxysilane (APS). The Ni-free stainless-steel was oxidized at three different temperatures, 800 K, 1000 K and 1200K in air, and then the APS molecules were immobilized on the surface at room temperature. The surface of the samples was characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The composition of surface oxides formed through the oxidizing treatment was identified to be two types of oxide, namely Fe₂O₃ and Cr₂O₃. The atomic ratio of Cr to Fe+Cr increased with an increase in the oxidizing temperature. The amounts of APS immobilized on each surface followed the sequence of 1200K < 1000K < 800 K of the oxidizing temperature. It was found that the surface oxide formed at 800 K is the best carrier of APS under these conditions. It is apparent that Fe₂O₃ is more easily fixed by APS than Cr₂O₃.