The Sodium Transport in Polycrystalline Alumina

Abstract

In this work we present the investigations on the determination of the mechanism of sodium loss in High Pressure Sodium (HPS) lamps. The transport through the ceramic arc tube consists of several steps (solution in the ceramics, diffusion through the ceramics, leaving the bulk phase, evaporation from the surface). Among the listed processes the mechanism of the diffusion was investigated by model-experiments. A ceramic arc tube was applied as a reactor chamber, in which polycrystalline ceramic plates were heated at 600-1100°C in controlled Na and Xe atmosphere. The sodium diffusion profiles developed by the heat-treatment were measured by XPS and SIMS and from the measurements we tried to draw a conclusion about the mechanism of sodium diffusion through the ceramic discharge tube. The ceramic discharge tube were measured by X- ray diffraction, too. We found traces of some Na-O-Al compound.

Chemistry of materials science phenomena in high-intensity discharge light sources

“…In [18], the authors examined and modeled the possibility of the solid-state reaction between Na and the polycrystalline alumina arc tube under lamp conditions as well. The investigation indicated the following phases: NaAlO 2 after shorter heat treatment, the formation of some another Na-O-Al compounds after longer heat treatment, such as NaAl 11 O 17 (Na-β-alumina) with hexagonal structure, which is poorer in Na.…”

“…The transport through the polycrystalline ceramic arc tube consists of several steps. This complex process was separated into different parts, and the two most important partial processes (Na diffusion through the polycrystalline alumina wall, the solid-state reaction between alumina and Na) were examined separately from the disturbing effect by Lovas et al [18]. They investigated the outer surface of the ceramic arc tubes of experimental lamps burned for different times by X-ray photoelectron spectroscopy (XPS) in order to examine the different chemical and physicochemical processes in the wall of the ceramic arc tube during the lifetime of the lamp.…”