Drying of Ceramic Layers with a Graded Pore Structure

Thin self-supporting ceramic TiO2-layers with a graded pore structure were prepared by using centrifugal deposition of powders and sols with different particle size distributions from mixed, diluted suspensions. During the evaporation drying step the layers have a strong tendency to warping and crack-formation because of the resulting difference in the capillary pressure in the upper and the bottom side pores. Four drying methods were investigated concerning their suitability for diminishing or eliminating capillary forces and for the production of planar, crack-free dried specimens. The drying techniques used in the experiments are briefly introduced. It should be emphasized that the most successful drying method for the layers mentioned above is a combination of microwave drying and subsequent critical point drying.