"A NOVEL PROCESS FOR MANUFACTURING IR TRANSPARENT POLYCRYSTALLINE ALUMINA ARTICLES AND THE ARTICLES SO MANUFACTURED"

IR transparent polycrystalline alumina articles having sintered grain sizes averaging in the sub-micrometer region and capable of transmitting >75% of infrared radiation of wavelengths between 3 and 5 micrometers can be produced by employing the thermal gelation property of methyl cellulose. In this process high purity alumina (99.96%) doped with 500ppm of MgO were made into a slurry with solid loading of 76-80wt% and further 0.1-0.5wt% of methyl cellulose was added followed by milling. The slurry was cast into a mould and subjected to thermal gelation temperature of 45-60°C to obtain the green alumina ceramics. The cast alumina ceramics thus produced through the environmentally benign process on sintering and hot isostatic pressing resulted in IR transparent polycrystalline alumina. Thus produced articles of thickness 1-1.4mm have exhibited close to theoretical IR transmission of 80-85% and a hardness of >20GPa.