Strong protection capability of zeolite coating for AA6061 substrate from corrosion in NaCl, H 2 SO 4 and NaOH solution has been demonstrated with reduction of corrosion current by five orders of magnitude. Film resistance was identified as the governing parameter in the formation of a barrier shielding the penetration of aggressive species. For the MFI zeolite film growth on the surface of the AA6061 substrate, while the in situ crystallisation (InC) protocol generated loosely packed film made of large zeolite crystal, the dry-gel conversion (DGC) protocol prepared dense film comprising of nanoparticles. Superior protection ability of DGC-grown film is attributed to the increased film resistance associated with a dense and impermeable zeolite layer. As such, the DGCgrown film requiring thinner film thickness around 5 μm showed better anti-corrosion function than the InC-grown film.
MFI zeolite film coated on AA6061 alloy was prepared from fumed silica modified with/without n-octyldecyltrimethoxysilane (ODS) by means of dry gel conversion (DGC) method. The DGC-grown MFI zeolite film could form a strong barrier to protect AA6061 surface against the corrosion from NaCl solution. By using fumed silica as a starting material, the hydrophilicity and anti-corrosion capability of the MFI zeolite film declined with increasing humidity in the DGC synthesis. By silanization with ODS, the surface hydrophobicity of the MFI zeolite film increased, leading to substantial enhancement in anti-corrosion capability. On the other hand, MFI film grown from ODS-modified fumed silica exhibited low hydrophilicity and a much improved anti-corrosion protection property by four orders of magnitude, even stronger than the ODS post-treated MFI film. The strong anti-corrosion capability is attributed to the “thick layer” surface hydrophobicity of zeolite crystal.
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