Synthesis and corrosion resistance of high-silica zeolite MTW, BEA, and MFI coatings on steel and aluminum

High-silica zeolite ZSM-12Na(n) (AlnSi28-nO56) similar to4H(2)O with n = 2 (MTW), Beta Na-n (AlnSi64-nO128) with n = 7 (BEA), and ZSM-5 Na-n (Si96-nO192) similar to16H(2)O with n < 27 (MFI) coatings were synthesized by hydrothermal crystallization without seeding using a new two-silica method on Al-alloy (Al-2024-T3 and Al-6061-T4) and stainless steel (SS-304). The pure-silica MTW and BEA coatings synthesized in this study have not been previously reported. All coatings are continuous and have excellent adhesion. The as-synthesized zeolite coatings were tested by a dc polarization technique and found to be highly corrosion resistant in severely corrosive acidic (0.5 M H2SO4 aqueous solution) and alkaline (0.1 M NaOH aqueous solution) media. In particular, a pure-silica MFI coating of only a few hundreds of nanometers thickness was formed within a relatively short crystallization time (e.g., 15 min), and was shown to provide sufficient protection against corrosion. (C) 2002 The Electrochemical Society.