Factors influencing anisotropic sintering shrinkage in tape-cast alumina: Effect of processing variables

The effect of the processing variables shear rate, solids loading, and sintering temperature on the anisotropy of sintering shrinkage of aqueous tape-cast alumina was studied. Higher shear rates and higher solids loading resulted in higher in-plane shrinkage anisotropy, whereas the shrinkage anisotropy in the thickness direction was higher for low solids loadings. The in-plane shrinkage anisotropy was found to be fairly constant above a certain critical shear rate (similar to 100 s(-1)) independent of the solids loading. The shrinkage anisotropy through the thickness was higher than in-plane directions. A higher thickness direction sintering rate was observed and attributed to a greater number of interparticle necks in the thickness direction because of the platy nature of alumina particles and the greater thickness direction strains associated with binder removal. The binder did not significantly affect the in-plane sintering shrinkage but significantly affected the shrinkage in the thickness direction. It was suggested that emulsion binder particles occupy sites in between layers of particles in the thickness direction. The degree of anisotropic shrinkage was quantified using edge orientation polarograms and a direct correlation was obtained between the processing variables, shrinkage anisotropy, and the edge orientation index.