Translucent polycrystalline alumina and method of making same
 An optically transparent polycrystalline alumina sintered body consists essentially of alumina, magnesia, yttria and zirconia. The magnesia is present in an amount of about 0.020 wgt. percent, the yttria is present in an amount of about 0.035 wgt. percent, and the zirconia is present in an amount of about 0.018 wgt. percent. An arc tube for a high pressure sodium lamp made from this composition has greatly increased resistance to sodium loss and concomitant outer jacket darkening, whereby the effective amount of lumen output is increased. 
Osram Sylvania Inc.
C H
C04B H01J
inventional inventional
George Arlene David
Wei Hecker Goodman