Deposition and consolidation of porous ceramic films for membrane separation

The deposition of porous ceramic films for membrane separation can be done by several processes such as thermophoresis [1], dip-coating [2] and spray pyrolysis [3]. Here we present a high-speed method, in which ceramic nano-particles form a porous film by filtration on top of a porous ceramic substrate [4]. Ceramic nano-particles are generated in a flame, using either a premixed (gas) flame, in which a metal-oxide precursor is evaporated in an N2 stream, which is combusted with methane and air, or using a flame spray pyrolysis, in which a liquid metal-oxide precursor is sprayed through a nozzle and ignited by a supporting flame (methane and oxygen). The thickness of the deposited layer can be closely controlled by changing the a) particle concentration and b) the filtration time. Using a new method termed surface annealing [5]; we can consolidate the films on the surface by switching off the precursor to the flame and directly anneal the deposited film surface using the particle-free flame. With a substrate pore-size of 4-5 micron, the deposited and annealed layer has an average pore-size of 400-500 nm; a reduction in the pore-size by a factor of 10. [1] Mädler, L., Roessler, A., Pratsinis, S.E., Sahm, T., Gurlo, A., Barsan, N., Weimar, U., Sensors and Actuators B, 114, 283-295, 2006 [2] Cini, P., Blaha, S.R., Harold, M.P., Venkataraman, K., J. Membrane Sci., 55, 199-225, 1991 [3] Stoermer, A.O., Rupp, J.L.M., Gauckler, L.J., Solid State Ionics, In press, 2006 [4] Andersen, S.K., Johannessen, T., Mosleh, M., Wedel, S., Tranto, J., Livbjerg, H., J. Nano Particle Research, 4:5, 405-416, 2002 [5] Tricoli, A., Graf, M., Mayer, F., Kühne, S., Hierlemann, A., Pratsinis, S.E., Advanced Functional Materials, Submitted, 2006