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 a high in-line transmission, which is suitable for use as an envelope of a high pressure vapour 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, La<Sub>2</Sub>0<Sub>3</Sub> or a compound forming La<Sub>2</Sub>0<Sub>3</Sub> in an amount of 0.001-0.05% by weight calculated as La<Sub>2</Sub>0<Sub>3</Sub>, and Y<Sub>2</Sub>0<Sub>3</Sub> or a compound forming Y20<Sub>3</Sub> in an amount of 0.001-0.05% by weight calculated as Y<Sub>2</Sub>0<Sub>3</Sub>, thoroughly mixing the resulting mixture, shaping the mixture into a desired form and firing the shaped article under vacuum or either an atmosphere of hydrogen gas or dissociated ammonia gas under an oxygen concentration of 10<Sup>-15</Sup>-10<Sup>-25</Sup> atm.