Optical method for evaluation of shrinkage in two dimensions during drying of ceramic green bodies

The evolution of shrinkage and mass during drying of kaolin and alumina green bodies was characterized. Standard practise uses a position sensor with simultaneous mass measurement. In this work an optical method was developed to follow shrinkage in two orthogonal directions. Green body samples were made by pressing of ceramic pastes. Results have been compared through the well known Bigot curves which show two distinct stages. First a linear shrinkage with the evaporated water loss is observed. Then in the second stage with further water loss, negligible dimension changes occur. For each material, the overall shrinkage values are identical in the two directions parallel to the pressing axis, but higher in the pressing direction. This difference is related to the shaping method yielding a preferential orientation of grains. Anisotropy in shrinkage is more significant for kaolin with tabular shaped grains compared to the more isometric grains of alumina.