Anisotropic shrinkage in tape-cast alumina: Role of processing parameters and particle shape

Aqueous suspensions of alumina and other powders containing no visible morp hological anisotropy were tape cast under different conditions to study the role of processing parameters and powder characteristics in the origin of inplane sintering shrinkage anisotropy, High anisotropic shrinkage, with th e typical shrinkage in the transverse direction exceeding that in the casti ng direction by more than 10%, was observed for tape-cast alumina cast at h igh solids loading and high shear rates. Tape casting without any binder al so resulted in similar anisotropy, Lower solids loading with increased aggl omeration resulted in a drastic reduction of shrinkage anisotropy. Under si milar casting conditions, BaTiO3 did not show any shrinkage anisotropy unli ke alumina. Cubic zinc ferrite and titania powders also showed some consist ent shrinkage anisotropy. A correlation was found between in-plane particle orientation and anisotropic shrinkage proving that powder characteristics, particularly particle shape, control anisotropic shrinkage even in apparen tly equiaxed powders.