Processing and properties of sintered submicron IR transparent alumina derived through sol–gel method

For the first time, sintered alumina with high transparency in mid infrared region, composed of submicron grains, has been fabricated using sol–gel processing. Commercially available boehmite powder was used to prepare the stable sol. The sol was mixed with appropriate amount of sintering aids and alumina seeds. The sol was further gelled, dried, and heat treated at 1000 °C for producing alumina powder. The powder was further shaped into pellets by compaction and sintered at temperatures between 1200 and 1400 °C in air. Sintered samples were further pressed hot isostatically to produce sintered submicron transparent alumina. The synthesized powder was characterized for its morphology and phase. The sintered and hot isostatically pressed samples were characterized for their physical, mechanical, and optical properties. The present method produced transparent alumina with transparency upto 87% in mid-wave infrared region. These transparency values were at par with the transparency of single crystal sapphire in the mid-wave infrared region and the hardness values were even superior than sapphire.