Synthesis of thick zeolite 4A coatings on stainless steel

Zeolite coatings on metal supports having thickness ranging from few to several tens of microns could have important technical applications in adsorption heat pumps. Direct growth of zeolites on metal surfaces could improve the physical contact between the substrate and adsorbent leading to an improvement in the heat transfer performance on which pump operation is based. One of the major problems in zeolite coating technique is the final film thickness obtained by in situ synthesis, generally limited to few microns. In this work, thick zeolite A coatings have been prepared on stainless steel supports by direct synthesis. The metal supports were pre-treated before coating. Two surface pre-treatments have been compared: a surface oxidation at high temperature in air and an aluminizing process obtained by coating the metal surface with an aluminum-silicon eutectic alloy (Al-10%Si). After this, a layer of zeolite A seeds was deposited by dip-coating on the pre-treated supports. A first zeolite coating was obtained by secondary growth of the zeolite seeds. Coating thickness of up to 25 mum were obtained on aluminized stainless steel. Several procedures for further growth and accretion of the initial deposit were attempted. Addition of triethanolamine to the synthesis mixture allowed the zeolite coatings obtained on aluminized stainless steel to reach a thickness of 80 mum. (C) 2004 Elsevier Inc. All rights reserved.