|Researchers at Purdue University have developed new highly transparent polycrystalline alumina materials by
hot-pressing platelets alumina crystals and aligning its grain structure to induce low amounts of grain boundary refraction and reflection. This cost-effective transparent alumina processing technique can be used for applications including high-temperature and armored windows, nose cones for rockets, and ballistic blast as well as protective shields. Purdue researchers have fine-tuned fabrication parameters for the new alumina including specified powder and treatment steps sintering temperatures, green-body and hot-pressing geometries, pre-load pressures and hot pressing pressure to achieve a high density of upwards of 99.95%. This allows a real in-line transmission (RIT), defined as a transmission within a 0.5 degree cone of the center beam, of over 70% and a total transmission of over 80 % at 645nm, approaching the theoretical limit of single crystal sapphire (86%). Notably, the aligned grain microstructure limits grain-induced scattering typically seen with polycrystalline translucent alumina with variance of only 15% in RIT over the wavelength range 280 nm to 2500 nm, allowing this material to be continuously effective in a spectral range from UVB to NIR.
-Nose Cones for Rockets
-High-Temperature and Armored Windows
-Blast and Protective Shields
"Hot-pressing platelet alumina to transparency"
Journal of the American Ceramic Society
Dec 15, 2020
Mar 2, 2020
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