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Thermochemical Investigations to the High-Temperature
Corrosion of Polycrystalline Alumina (PCA)
by Metal Halides
Torsten Markus
Abstract
The accomplished investigations in the context of the available work concerning the hightemperature
corrosion of polycrystalline alumina (PCA) by halides of the alkalis and the
lanthanides are from special interest in the lamp industry. Mixtures from alkali halides and
halides of the lanthanides are an indispensable component of modem metal halide lamps .
The halides of the lanthanides produce a very line-rich emission spectrum in the arc of the
gas-discharge lamp within the visible range which is very close to that of the natural
sunlight .
Caused by the high temperatures and temperature gradients in a burner vessel chemical
reactions between the lamp filling and the wall of the discharge vessel as well as the
electrodes take place . Chemical transport can be observed, which can finally lead to a
reduction of the wall thickness and to a failure of the lamp .
The goal of this work is the clearingup of the so far not understood mechanisms of the
corrosion processes observed in metal halide lamps with PCA bumers . For the
improvement of the lamp characteristics it is finally the goal of describing these lamps in a
computer-model in order to be able to make statements concerning the corrosion behavior .
Apart from the understanding of the corrosion mechanisms it is important for the
modelling to identify the foimed corrosion phases and to detemine their themochemical
data .
The available work makes a contribution to this .