Preparation Conditions of Yttria Stabilized Zirconia Thin Films by Sedimentation from Liquid Suspensions

Preparation conditions of sintered YSZ thin films by a sedimentation method from water suspensions have been examined. Employment of a poly (acrylic acid) ammonium salt as a dispersing agent was effective for increasing 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-supporting YSZ thick film with a relative density of 96.6% was obtained after a thick cake layer, precipitated from a concentrated YSZ suspension of 50g⋅dm-3, was sintered at 1300°C. Bending strength of the film was 239MPa. On the other hand, a thick film prepared from a suspension containing an acrylic emulsion binder showed smaller relative density of 92.1% and weaker bending strength of 190MPa. Based on these findings, preparation of YSZ thin films was carried out by sedimenting a dilute YSZ suspension of 2.0g⋅dm-3 containing the dispersing agent for 3d on a flat and porous substrate of La0.8Sr0.2MnO3, followed by firing at 1300°C for 3h. As a result, it was found that a well sintered YSZ thin film of about 1.5μm thick was obtained when the suspension was allowed to stand for 2d prior to sedimentation to eliminate large particles. The average grain size of YSZ in the film was 3-4μm, and the film showed almost negligible nitrogen gas permeation, compared with that of the porous substrate, at room temperature.