Corrosion Effects Of Metal Iodides On Ceramic Arc Tubes Of Metal Halide Lamps

Ceramic metal halide lamps (CMH lamps) are efficient, energy saving light sources with high efficacy and high color rendering index (CRI). They are in line with the current theme of energy efficiency and emission reduction. However, the performances of the lamps are still constrained by the corrosion reactions between ceramic wall of the arc tubes and the molten metal iodides. This thesis studies the effects of metal iodides (NaI+DyI3, NaI+HoI3, NaI+TmI3, NaI+CeI3, NaI+TlI) on their corrosion process with the ceramic wall and on the lamp performances.In Chapter One, The advantages and technical challenges of CMH lamps are pointed out to justify the importance of this study. Then topics related to this study in terms of material science, physical chemistry and various analysis and diagnosis methods are introduced. Also previous researches on this topic are reviewed and the creative point of this study is stated.In Chapter Two, the experiment methods are illustrated. First, the filling compositions of the seven groups of sample lamps are described. Then the lamp aging system and the way of aging is mentioned, followed by the four measurement and analysis systems:photometric, electric and colorimetric measurement system, infra-red thermal image system, X-ray transmission system and SEM/EDX analysis system.In Chapter Three, the main results are presented to reveal the effects of each metal iodide on luminous flux, efficacy, CRI, correlated color temperature (CCT) and spectral power distribution. The wall temperature distribution and corrosion content of arc tubes with specific filling compositions are compared. The results show that DyI3filled lamps have most serious corrosion; CeI3is conducive to high efficacy; HoI3and TmI3are beneficial to high CRI; TⅡ is applied mainly to adjusted CCT and it seldom causes corrosion; and arc in the horizontally burnt tubes filled with CeI3will bend upward, which causes lamp early failure.In Chapter Four, discussions focus on some lamp early failure mechanisms and their causes. The filling compositions of metal iodides are evaluated comprehensively based on their effects on lamp performances and on corrosion content. Accordingly, optimized compositions are suggested. Further research directions and the way of improving research are also stated.This thesis ends with Chapter Five, which is a summary of the study.