Anisotropic sintering shrinkage of tape-cast alumina

In tape casting the particles and polymers aligned during casting can later cause anisotropic sintering shrinkage. In this study the anisotropic sintering shrinkage between the casting direction and the direction transverse to casting, defined as (1-K) with K as the shrinkage ratio of the casting direction compared to the transverse direction, was investigated. Two different latex binders and three alumina powders with different morphology were used and compared. An organic solvent-based system with PVB binder was used as a reference to these aqueous systems. The rheological behaviour was measured and related to the sintering anisotropy. The sintering anisotropy varied in the range -0.005 up to 0.11. It was found that the anisotropy increased with increasing shear rate and an increased volume fraction of solids. The viscosity level had a minor influence on the anisotropy. The anisotropy of the aqueous system at a comparable volume fraction and at the same shear rate was comparable to that of an organic solvent-based system. It is possible, however, to reach higher solids volume fraction in aqueous systems and this results in more particle orientation.