Commerically available yttrium oxide nanopowders were evaluated as starting materials for preparation of transparent materials. The objective is an yttria optical ceramic exhibiting approximately one micrometer grain size to provide increased strength and thermal shock resistance. Three vendors were selected to provide nanoscale powders for testing and evaluation. They were compared to a conventional (5 μm) powder previously used to prepare optical quality ceramic yttria. While all of the selected nanopowders had impurity levels that were too high to allow processing to full transparency, two of the samples were processed to full density and moderate transparency was produced in one. In preparation for processing via Hot Isostatic Press (HIP) samples were sintered to a closed pore state at temperatures as low as 1400 °C, and with soak times as short as 12 minutes at 1550 °C. The use of ultrasonic attenuation as a technique for measuring particle size distributions in slurries was explored and found to be an invaluable tool when colloidally processing nanopowders. Finally, the areas most important for continued improvements were identified.
Emissivity measurements of ZnS, Sapphire, ALON, MgO, and Yttria were performed in 3.9-4.0 micrometers and 4.4-4.9 micrometers bands, for temperatures between 300 degrees C and 600 degrees C. The average radiance was measured over each waveband. Emissivity was calculated as the ratio of the radiance of the sample to that of a black body source at the same temperature. The results of the emissivity measurements for the above-mentioned materials will be reported. Measurement techniques that allowed increasing the dynamic range of the measurement and significantly reducing the noise will be discussed.