Interface structure and corrosion protection of hybrid particles prepared via surfactant- and silica-assisted wet ball milling

Abstract

The paper proposes a simple way to simultaneously modify iron particles with both silica and surfactant molecules, which involves wet ball milling of iron with silica glass and surfactants (stearic and n-perfluorononanoic acid). The structure of interfaces in the as-modified particles was analyzed by XPS and NEXAFS spectroscopies. Silica glass is finely powdered and its mechanical rubbing into ductile iron particles induces chemical transformations at interfaces between iron and silica with the formation of various products. Surfactants are then adsorbed on silica-enriched particle surfaces. In the case of stearic acid, the surfactant is attached through the hydrogen bonds between the carboxyl and silanol groups of the outermost hydrated layer, whereas n-perfluorononanoic acid is adsorbed through carboxylates formed with iron atoms in the outer silicate layer. The angle-dependent NEXAFS analysis has shown predominantly up-right arrangement of the surfactant molecules with respect to the particle planes. Hybrid layers of silica and n-perfluorononanoic acid exhibit better corrosion resistance than those comprised of only SiO2 or only n-perfluorononanoic acid, which contrasts to stearic acid molecules providing proper anticorrosive efficiency alone.