Influence of starch content and sintering temperature on the microstructure of porous yttria-stabilized zirconia tapes

Porous yttria-stabilized zirconia (YSZ) substrates with volume fractions of porosity ranging from 28.9 to 53 vol.% 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 and sintering temperature on the sintering behavior and final microstructure were investigated. Two kinds of pores were observed in the sintered tapes: large pores created by the starch particles with lengths between 15 and 80 mu m and smaller pores in the matrix with lengths between 0.6 and 3.8 mu m. The porosities were above those predicted for each of the starch contents. However, larger deviations from the predicted porosity were found as more starch was added. The top surface of the sintered tapes had a greater porosity than the bottom one for all the starch contents examined. The total porosity and the percentage of open porosity in the sintered tapes could be controlled by the volume fraction of added starch as well as by the sintering temperature. The open pores between the YSZ particles were removed by sintering at 1600 A degrees C. As the volume fraction of starch increased from 17.6 to 37.8 vol.%, there was a gradual increase in the interconnectivity of the pore structure.