Translucent polycrystalline alumina ceramic, ceramic discharge vessel, and method of making

摘要

A translucent polycrystalline material suitable for use in ceramic discharge vessels for metal halide lamps is produced by sintering an alumina powder doped with a MgO sintering aid in a nitrogen atmosphere containing a partial pressure of a vapor phase carbon-containing species. The sintered polycrystalline alumina has a grain boundary phase containing aluminum, oxygen and nitrogen. The formation of the AI-O-N grain boundary phase is believed to facilitate the transport of nitrogen from entrapped pores during sintering. Preferably, the PCA is sintered in a carbon-element furnace under flowing ultra-high-purity nitrogen.