POLYCRYSTALLINE TRANSLUCENT ALUMINA SINTERED BODY, A METHOD OF PRODUCING THE SAME, AND A HIGH PRESSURE VAPOUR DISCHARGE LAMP OBTAINED BY USING SUCH A SINTERED BODY

摘要

A polycrystalline translucent alumina sintered body having high in-line transmission, which is suitable for an envelope for a high pressure vapor discharge lamp, is produced by adding to alumina powder having a purity of more than 99.8% MgO or a compound forming MgO in an amount of 0.01-0.1% by weight calculated as MgO, La2O3 or a compound forming La2O3 in an amount of 0.001-0.05% by weight calculated as La2O3, and Y2O3 or a compound forming Y2O3 in an amount of 0.001-0.5% by weight calculated as Y2O3, thoroughly mixing the resulting mixture, shaping the mixture into a desired form and firing the shaped article under vacuum or either atmosphere of hydrogen gas or dissociated ammonia gas under oxygen concentration of 10-15-10-25 atm.