Sodium halide discharge lamp with an alumina silicate barrier zone in fused silica envelope

摘要

A graded alumina silicate glass layer or zone is formed at the surface of fused silica by first applying a polycrystalline coating of aluminum oxide to the silica and then fusing the coating into the silica at a high temperature. Such a zone on the outside of the fused silica arc tube of a metal halide lamp containing sodium is particularly effective to inhibit sodium loss by diffusion through the tube walls.