Spontaneous formation of mono-n-butyl phosphate and mono-n-hexyl phosphate thin films on the iron surface in aqueous solution and their corrosion protection property

Abstract

Mono-n-butyl phosphate (BP) and mono-n-hexyl phosphate (HP) thin films were directly formed on an iron surface by immersing pure iron samples in aqueous solutions containing BP or HP. FTIR analyses, XPS characterizations and water contact angle data show that the iron surfaces were covered with the BP or HP thin films. The spontaneous formation of alkyl phosphate thin films on the iron surface is largely attributed to the electrostatic interaction between Fe²⁺ ions on the surface of iron and RO–PO₃H⁻ (R represents n-butyl or n-hexyl) ions and the specific adsorption of phosphate groups on the iron substrate. Moreover, electrochemical results clearly demonstrate that the as-formed thin films can effectively protect the iron substrate from corrosion in NaCl corrosive solutions.