Correlation between anisotropic green microstructure of spherical-shaped alumina particles and their shrinkage behavior

Dimensional control is one of the basic problems in ceramic processing, especially for tape cast ceramic sheets which are used to build up multilayer structures for high-integrated components. Uncontrolled anisotropic shrinkage can cause geometrical distortion and circuit failure of multilayer ceramics during sintering. The understanding of the relationship between green tape microstructure and shrinkage anisotropy is of great importance for further miniaturization of multilayer devices. In this study, alumina powders with spherical particle shape were used to cast green tapes. The microstructure as well as the pore orientation and the shrinkage behavior were analyzed. According to the sintering theory, grain growth and pore elimination are the two most important mechanisms to describe sintering shrinkage. In this work, three-dimensional shrinkage behavior of tape cast alumina powders with spherical particle shape was investigated and correlated with pore orientation in the microstructure. Specifically, the reason for the different shrinkage in z-direction compared to the lateral shrinkage is in focus. The study is based on experiments as well as on mathematical visualization.