Preparation of multilayers porous ceramics
Zofia Puff, Jerzy Raabe, Ewa Bobryk Politechnika Warszawska, Wydział Chemiczny, ul. Noakowskiego 3, 00-664 Warszawa
Annals 3 No. 8, 2003 pages 444-449
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abstract Ceramic filtering elements in the shape of single- or multi-channel pipes are multilayer materials composed of the substrate (with pore size of 5÷10 μm) and filtering layers applied on the inner surface of channels. As for the microfiltering layer, its grains are more than ten times smaller than the size of substrate pores, and when the layer is applied, these grains may penetrate into the substrate, and increase the flow resistance (Fig. 2). The increased flow resistance obstructs the filtration, especially in multi-channel filtering elements, in which the filtrate flows along a significantly elongated route (Fig. 3). The research was undertaken to eliminate the phenomenon of mutual penetration of layers with varied grain sizes, when the microfiltration layer is applied directly using the dip-coating method (Fig. 4) on the macro-porous substrate, with no intermediate layers used. Two methods were used to „block” penetration of layers with significantly different grain sizes: saturation of the macro-porous substrate with acrylamide sol and adding that sol to the slurry used in the dip-coating method to apply the microfiltration layer. In the first case the expected effect was not detected, as the tiny grains were sucked into the substrate interior (Fig. 7a). Good results were obtained when the macro-porous substrate was covered with the slurry made of fine-grain powder (d ~ 0.5 μm) of YSZ, composed of an adequate proportion of water solution of polyvinyl alcohol and acrylamide sol, which causes „blockage” of the potential penetration of the fine-grain powder into the substrate interior (Fig. 7b). Key words: ceramic membranes, mikrofiltration layer, porous layer unpenetrating each other, dip-coating