Comparison of different binders for water-based tape casting of alumina

Three different types of binders, latexes, polyvinyl alcohol and cellulose ether were studied for tape casting of alumina. The rheological properties of the different systems were compared by continuous shear and oscillatory measurements. The cast tapes were evaluated with regard to particle packing, binder burnout and sintering behaviour. The microstructure of the final materials was investigated as well. Owing to the different characteristics, mainly the viscosity of the binders, the solids loading of the suspensions had to be varied between 0.2 and 0.55. All compositions gave stable suspensions but the rheological behaviour varied from viscous to viscoelastic. It was found that the latexes were the easiest ones to work with as they gave low-viscosity suspensions and fewer foaming problems. They had the highest solids loading, which enables quick drying and resulting high green density. Significant differences in sintering behaviour and final microstructure were observed between the formulations with different binders. Upon sintering, anisotropic shrinkage was observed between thickness direction and the other directions, and all formulations had larger shrinkage in the thickness direction. Sintering anisotropy between the casting direction and the direction transverse to casting was also found, but there was a large variation between the binders. The anisotropic sintering shrinkage is believed to be caused by the orientation of the particles/polymer during casting and drying. (C) 1998 Elsevier Science Limited All rights reserved.