PREPARATION CONDITIONS OF YTTRIA-STABILIZED ZIRCONIA THIN-FILMS BY SEDIMENTATION FROM LIQUID SUSPENSIONS

Preparation conditions of sintered YSZ thin films by a sedimentation m ethod from water suspensions have been examined. Employment of a poly (acrylic acid) ammonium salt as a dispersing agent was effective for i ncreasing the negative zeta potential of YSZ particles and stabilizing the suspensions, while addition of a polyacrylic emulsion as a binder enhanced coagulation of the YSZ particles. A sintered, self-supportin g YSZ thick him with a relative density of 96.6% was obtained after a thick cake laver, precipitated from a concentrated YSZ suspension of 5 0 g . dm(-3), was sintered at 1300 degrees C, Bending strength of the film was 239 MPa. On the other hand, a thick film prepared from a susp ension containing an acrylic emulsion binder showed smaller relative d ensity of 92.1% and weaker bending strength of 190 MPa, Based on these findings, preparation of YSZ thin films was carried out by sedimentin g a dilute YSZ suspension of 2.0 g . dm(-3) containing the dispersing agent for 3 d on a flat and porous substrate of La0.8Sr0.2MnO3, follow ed by firing at 1300 degrees C for 3h. As a result, it was found that a well sintered YSZ thin him of about 1.5 mu m thick was obtained when the suspension was allowed to stand for 2 d prior to sedimentation to eliminate large particles. The average grain size of YSZ in the film was 3-4 mu m, and the film showed almost negligible nitrogen gas perme ation, compared with that of the porous substrate, at room temperature .