Corrosion-resistant alumina member and arc tube for high intensity discharge lamp

摘要

An arc tube is formed by polycrystalline alumina so that an average crystal grain diameter of a surface is two to ten times as large as an average crystal grain diameter of an inside including a center line of a thickness and the average crystal grain diameter on the center portion of the thickness is 10 mu m to 100 mu m. As a result, in the arc tube, the total transmittance is 98%, and a linear ray transmittance is 5%. <IMAGE>