Characterization of Particle Alignment in Pre-Sintered Alumina Body Using Birefringence Imaging Microscopy
The packing structure in green alumina bodies has been studied using thin sections of prefired bodies impregnated with refractive-index liquid examined with an automatic, polarizedlight microscope equipped with liquid-crystal adjustable quarter-wave plate and analyzer, and circularly polarized light. The combined intrinsic birefringence (caused by the anisotropy of the hexagonal symmetry of the alumina particles) and form birefringence (due to packing of the slightly elongated particles oriented in the green structure), can be quantified on a small scale. Birefringence values and slow-vibration directions are mapped for the anisotropic fine particles and agglomerates circumferentially or radially aligned in the structure. For some pre-sintered bodies, the interference pattern shows three radial dark brushes with relatively low birefringence, coming from the spider in the extruder. Slow-axis distribution shows random particle orientation in the spider region. The birefringence pattern often indicates a relatively high degree of circumferential alignment in the surface area where frictional force is present during forming. A uniform distribution of the birefringence represents a consistent green structure. The improved procedure for characterization of prefired body provides considerable insight to the optical crystallography of powder/particle arrangement in pre-sintered ceramic body and the relationship of the particle alignment with respect to flow and forming.
G. C. Wei "Characterization of Particle Alignment in Pre-Sintered Alumina Body Using Birefringence Imaging Microscopy", Advances in Science and Technology, Vol. 45, pp. 486-490, 2006