r~UTTERWORTH Influence of metal substrate properties on the kinetics of zeolite film formation Valentin Valtchev, Svetlana Mintova, and Ludmil Konstantinov Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Sofia, Bulgaria The primary stages of zeolite Y and silicalite-1 film formation on both untreated and plastically deformed copper substrates are considered from the viewpoint of the film growth kinetics and morphology. Experimental results indicate a satisfactory agreement between the kinetic and profilometric data. Keyworda: Zeolitefilms; kineticsof formation; substrateproperties INTRODUCTION cleaned following the procedure proposed by Jansen et al.X2; zeolite films were deposited through hydro- Zeolite molecular sieves play an important role in cat- thermal synthesis. The initial materials for the film alytic, ion exchange, and gas separation technologies, deposition were silica solution, sodium hydroxide, Several features make zeolites suitable for the design sulfuric acid, aluminum hydroxide, aluminum sul- of molecular thin films, coatings, and membranes.l fate, tetrapropylammonium bromide (TPA), and dis- Many recent papers concern the deposition of thin tilled water. All materials were from Merck. The zeolite films on ceramic, metal, metal oxide, Teflon, chemical composition of the prepared silicalite-1 gel and glass substrates. TM Metal substrates are most ap- was 33 Na20 : 17 (TPA)20 : 100 SiO 2 : 4,000 H20 propriate for preparing films of zeolite-containing : 20 H2SO 4. The zeolite Y gel was 8 Na20 : AI203 : 20 materials because of their high thermal stability, acid SiO2 : 400 HzO. The gel for the synthesis of zeolite Y resistance, and the possibility of forming modules of was aged for 24 h at room temperature before use. arbitrary shape. It has been shown that the synthesis The gels were put in lined autoclaves of Teflon of zeolite films on various metal substrates is very heated in air at 170°C for silicalite-1 and at 90°C for sensitive to the type of metal, the chemical and struc- zeolite Y. The copper substrates of an area of 10 x 20 tural properties of the metal surface, the conditions mm 2 in Teflon holders were immersed vertically in of preparation, and the substrate position in the re- the gel. To investigate the kinetics of film formation 1.914 actor. ' These factors influence the size, morphol- the samples were taken out of the autoclaves after ogy, and orientation of the zeolite crystals and thus various intervals of time. the film density and thickness. Detailed investigation The type of synthesized zeolites was determined by of the corresponding dependences can facilitate the X-ray powder diffraction using a Dron-3M diffracto- synthesis of zeolite films of desired parameters, meter with CuK~ radiation. The substrate surface In this paper we report some kinetic results on the and the zeolite film morphology were studied by deposition of zeolite Y and silicalite-1 films on copper scanning electron microscopy (SEM Philips 515). The substrates as well as the effect of substrate surface film thickness and surface relief were measured with treatment on zeolite film morphology, an accuracy of about 1 I~m by a standard stylus pro- filometer scanning the surface (Perthen). To form a EXPERIMENTAL sharp film boundary a part of the substrate surface was preserved from deposition by a Teflon coating. The zeolite films under study were grown on copper substrates of 99.99% purity. The influence of the me- RESULTS AND DISCUSSION chanical treatment was studied on copper substrates rolled at room temperature to reduce their initial The process of zeolite film formation on a metal sub- thickness from 5 to 2.5 mm. The substrates were strate is similar to that of bulk crystallization, al- though some differences exist. In the former case Address reprint requests to Dr. Valtchev at the Institute of Ap- heterophase reactions at the gel-substrate interface plied Mineralogy, Bulgarian Academy of Sciences, 92 Rakovsky are the main factors controlling the growth rate, and St., 1000 Sofia, Bulgaria the process moves through several stages depending Received 24 March 1995; accepted 1 June 1995 on the experimental conditions. In these terms the Zeolites 15:679-683, 1995 © Elsevier Science Inc. 1995 0144-2449/95/$10.00 655 Avenue of the Americas, New York, NY 10010 SSDI 0144-2449(95)00071-D