| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-transmittance polycrystalline alumina light emitting tube (10) for a metal halide discharge lamp by treating an alumina light emitting tube material having several % of closed cells by two-stage processes. SOLUTION: The starting porous light emitting tube is formed by extruding or die pressing light emitting tube parts consisting of an alumina powder-containing mixture, integrating the parts to form a light emitting tube body and partially sintering the light emitting tube body to hermetically seal the parts to each other. Two-stage processes including stages of hot isotropic pressurization of the partially sintered light emitting tube and chemically polishing the light emitting tube surface is carried out. The first pressurizing stage includes a stage of heating the alumina light emitting tube for about one to three hours at and under temperature of 1,600 to 1,900 deg.C and pressure of about 700 to 2,100 kg/cm<2> under an inert atmosphere, thereby lowering the porosity of the crystalline structure of the alumina light emitting tube. In the second stage, the light emitting tube surface is immersed into a molten alkaline metal borate-containing flux at an adequately high temperature or is coated with the flux material and is heated to form the flux, by which the surface defects are removed. The transmittance of the light emitting tube is approximately comparable to the transmittance of a single crystal sapphire light emitting tube. |
