This title appears in the Scientific Report :
2006
Please use the identifier:
http://hdl.handle.net/2128/535 in citations.
Grundlegende Untersuchungen zur Korrosion von Al$_{2}$O$_{3}$ durch Metallhalogenidschmelzen und zur Thermochemie korrespondierender Korrosionsphasen
Grundlegende Untersuchungen zur Korrosion von Al$_{2}$O$_{3}$ durch Metallhalogenidschmelzen und zur Thermochemie korrespondierender Korrosionsphasen
Ceramic discharge vessels in metal halide lamps made of polycrystalline alumina (PCA) instead of quartz glass find application at higher temperatures and this results in increased efficiency of the lamps. Discharge vessels contain a mixture of various metal halides like NaI, DyI$_{3}$, CeI$_{3}$, wh...
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Personal Name(s): | Möllenhoff, Marc (Corresponding author) |
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Contributing Institute: |
Werkstoffstruktur und Eigenschaften; IWV-2 |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2006
|
Physical Description: |
145 p. |
Dissertation Note: |
Aachen, Techn. Hochsch., Diss., 2005 |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
Rationelle Energieumwandlung |
Series Title: |
Berichte des Forschungszentrums Jülich
4214 |
Subject (ZB): | |
Link: |
OpenAccess |
Publikationsportal JuSER |
Ceramic discharge vessels in metal halide lamps made of polycrystalline alumina (PCA) instead of quartz glass find application at higher temperatures and this results in increased efficiency of the lamps. Discharge vessels contain a mixture of various metal halides like NaI, DyI$_{3}$, CeI$_{3}$, which influence the spectral properties of the lamps. Under operating conditions, these metal halides form, apart from the gas phase, a liquid phase also. In particular the liquid phase reacts with the wall material PCA resulting in the formation of rare-earth-aluminates. Furthermore, a transport of aluminum oxide, along a temperature gradient parallel to the vessel wall, takes place. This transport results in reduction of wall thickness and finally causes a leakage in the vessel wall. The corrosion of the wall material is the most frequent reason for the failure of the lamps. The aim of the investigations presented in this work is to elucidate the particular influence of the liquid phase in the corrosion and the chemical transport of Al$_{2}O_{3}$. For this purpose, solubility data of Al$_{2}O_{3}$ in lamp-relevant salt systems were determined by isothermal annealing experiments. The observed corrosion phenomena were described and interpreted with respect to the temperature distribution inside the burner vessels and the compositions of the halides. Additionally annealing experiments in a temperature gradient were conducted. Furthermore thermodynamic data for the corrosion phases $Dy_{3}Al_{5}O_{12}$, DyAlO$_{3}$ and $Dy_{4}Al_{2}O_{9}$ were determined by the method of Knudsen Effusion Mass Spectrometry. The present work shall contribute to model the observed corrosion processes in order to increase the lifetime of the lamps by selective means. |