Influence of starch content on microstructure of porous yttria-stabilized zirconia tapes

Abstract

Porous yttria stabilized zirconia (YSZ) substrates with volume fractions of porosity ranging from 28.9 to 53 volume % were developed using starch as a fugitive additive. Concentrated aqueous YSZ slips with different amounts of starch and an acrylic latex binder were prepared. The influence of the volume fraction of starch on the final microstructure was investigated by FE-SEM. The porosities were above those predicted for all the starch contents examined. Two kinds of pores were observed in the sintered tapes: large pores created by the starch particles with lengths between 15 and 80 µm and smaller pores in the matrix with lengths between 0.6 and 3.8 µm. The SEM image of a tape with 17.6 vol.% starch showed isolated pores; the individual pores started to interact with increasing starch concentration to 37.8 vol.% and an open structure interconnecting the coarse pores was being gradually established. The higher interconnection between pores resulted in larger cavities. The pores in the matrix reduced the sinterability of the YSZ leading to the retention of closed porosity in the sintered tapes.