Colloidal processing and optical transmittance of submicron polycrystalline alumina

摘要

Grain-boundary scattering due to intrinsic birefringence limits the optical transmittance of polycrystalline alumina (PCA). Smallest grain size and highest density are desired for maximum real in-line transmittance (RIT). Grain size versus density or sintering path plots were employed to compare different colloidal routes for fabricating green bodies followed by pressureless sintering and hot-isostatic pressing. Compacts fabricated by colloidal pressing showed superior density at similar grain size as compared to slip-cast compacts. The real in-line transmittance of the PCA was measured over a range of wavelengths (0.19-10 μm). The compacts fabricated by colloidal pressing showed higher transmittance as compared to slip-cast specimens. The measured transmittance was still, however, slightly lower than the theoretical values predicted by the grain-boundary scattering model of Apetz and van Bruggen. The grain-size dependence of RIT was analyzed using a model that combined grain-boundary scattering and scattering by isolated grain-boundary pores