Zeolite coating on foamed stainless steel by in-situ crystallization method

Faujasite-type zeolite films were prepared on foamed stainless steel by the in-situ crystallization method. Precursor solutions were prepared by dissolving water glass and NaAlO₂in a NaOH solution and aged at room temperature for two days. The concentrations of the starting materials were varied from 0.29 to 2.3 M (in SiO₂concentration) keeping the molar ratios of Na₂O:SiO₂:Al₂O₃fixed at 3.6:3.0:1.0. The foamed stainless steel substrate had about 90% of porosity and an average pore size of 600 μ m. It was dip-coated in the precursor solution four times, then hydrothermally treated at 80^∘, 110^∘ and 150^∘C for 6–48 h. The XRD patterns and SEM photographs revealed that faujasite-type zeolite was formed predominantly at a SiO₂concentration of 1.1 M, temperature of 110^∘C and duration of 24 h, with a product particle size of 2–5 μ m. At higher concentrations of the precursor solution, hydroxylsodalite becomes the major product rather than faujasite-type zeolite. The adherence strength of the zeolite grains deposited on the foamed stainless steel is higher in the in-situ crystallization method than when a conventional solution method is used. Thus, the in-situ crystallization method is concluded to be effective for preparing zeolite films even on metal substrates.