Limiting withdrawal rate and maximum film thickness during dip-coating of titania sols onto a Si substrate |
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Authors: | Evgeny V Rebrov Jaap C Schouten |
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Affiliation: | a School of Chemistry and Chemical Engineering, Queen's University Belfast, Stranmillis Road, Belfast BT9 5AG, UK b Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands |
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Abstract: | The article highlights new insights into production of thin titania films widely used as catalyst support in many modern reactors including capillary microreactors, microstructured fixed-bed reactors and falling film microreactors. Dip-coating of a titania sol onto a Si substrate has been studied in the range of the sol viscosities of 1.5-2.5 mPa s and the sol withdrawal rates of 0.2-18 mm/s. Different viscosities of sols were created by addition of desired amounts of nitric acid to the synthesis mixture of titanium isopropoxide and Pluronic F127 in ethanol which allowed to control the rate of the condensation reactions. Uniform mesoporous titania coatings were obtained at the solvent withdrawal rates below 10 mm/s at sol viscosities in the range from 1.6 mPa s to 2.5 mPa s. There exists a limiting withdrawal rate corresponding to a capillary number of ca. 0.01 beyond which uniform titania films cannot be obtained. Below the limiting withdrawal rate, the coating thickness is a power function of the sol viscosity and withdrawal rate, both with an exponent of 2/3. The limiting withdrawal rate increases as the solvent evaporation rate increases and it decreases as the sol viscosity increases. |
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Keywords: | Dip-coating Titania thin films Mesoporous Viscosity |
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