Shrinkage anisotropy of glass powder compacts sintered in dilatometers

Dilatometer push rods exert uniaxial compressive stresses on powder compacts undergoing sintering. In this study the effect of such stresses on the shrinkage anisotropy behavior of glass powder compacts is considered. A shrinkage anisotropy factor (k), defined by the ratio between axial and radial strain, is used to quantify the anisotropy in cylindrical compacts (k = 1 represents isotropic shrinkage). The available experimental data in the literature indicate that the effect of the applied dilatometer stress is to increase the value of k over that of free sintering conditions. For the small stresses exerted by the dilatometer push rods, it is shown that k is always >1. The common practice of calculating the sintered density from uniaxial dilatometer data, ignoring the existence of shrinkage anisotropy, is shown to lead to significant errors, even for values of k only slightly different from k = 1.