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 NaAlO2 in 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 SiO2 concentration) keeping the molar ratios of Na2O: SiO2: Al2O3 fixed at 3.6: 3.0: 1.0. The foamed stainless steel substrate had about 90% of porosity and an average pore size of 600 mu m. It was dip-coated in the precursor solution four times, then hydrothermally treated at 80 degrees, 110 degrees and 150 degrees C for 6 - 48 h. The XRD patterns and SEM photographs revealed that faujasite-type zeolite was formed predominantly at a SiO2 concentration of 1.1 M, temperature of 110 degrees C and duration of 24 h, with a product particle size of 2 - 5 mu 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.