Optically Translucent Mullite Ceramics

Abstract

The optical transmittance of pressureless sintered and of hot isostatically pressed (HIPed) mullite ceramics was studied in the near infrared (NIR), visible light (VIS), and the ultraviolet (UV) spectrum ranges. Both processing methods provided fine‐grained microstructures (mean grain size of 5–10 μm) with equiaxed grains and a narrow grain‐size distribution. In pressureless sintered mullite, the porosity was 5.5% and transmittance was 20% in the VIS and NIR ranges. In the HIPed mullite, with porosity <1%, a transmittance of 40% was measured in the VIS range and up to 80% in NIR. UV transmittance of both pressureless sintered and HIPed mullite samples was low. The optically translucent mullite was found suitable for optical windows in the VIS and NIR ranges, particularly at elevated temperatures.