Influence of binder layer of spray-dried granules on occurrence and evolution of coarse defects in alumina ceramics during sintering

Spray-dried granules are generally used to improve the fluidity of fine particles and to achieve structural uniformity in a powder compact. However, spray-dried granules also cause local inhomogeneous structures owing to the granule's characteristics, particularly the segregated binder layer on its surface. This paper demonstrates the influence of the binder layer of spray-dried granules on the occurrence and evolution of coarse defects in ceramics during sintering by sequential direct observation with optical microscopy, electron microscopy, and micro-focus X-ray computed tomography. Samples were sintered gradually at each temperature in the range of 1100-1350 degrees C. The results showed that the granule structures remained intact even after shaping, and sintering of the granule units induced inhomogeneous sintering and evolution of course defects at the granule interface. The sample strength was closely related to the presence of coarse defects in alumina ceramics.