Effect of powder, binder and process parameters on anisotropic shrinkage in tape cast ceramic products

The effect of powder, binder and process parameters on the properties of cast alumina tapes and their anisotropic shrinkage were investigated. Three alumina powders with different particle shapes (platelets, spherical, standard) and three PVB binders with different chain lengths were used. In addition, casting velocity and blade gap height were varied. The orientation of the particles in the tape was detected quantitatively by image analysis of micrographs. The shrinkage anisotropy is more than 12% for the platelet shaped powder and 8% for the standard powder, whereas the spherical particles lead to almost isotropic shrinkage. The influence of the organic binder chain length proved to be minor compared to the influence of the particle morphology. The variation of casting speed and blade gap height has no effect on anisotropic shrinkage in the investigated parameter range. This is explained by theoretical considerations of particle rotation in a sheared fluid.