Quartz metal halide lamps are commonly produced using ThCVdoped tungsten (thoriated) electrodes. ThO_2 reduces the work function of the electrodes. As a result, the glow-to-arc transition period is reduced and the extent of tungsten sputtering and collection of dark deposits on the quartz wall can be reduced. However, in lamps made with Nal-Scl.i doses and thoriated electrodes, a continuous increase in Thl4 content in the salt is observed as the lamps are burned [I]. It is thought that ThO_2 from the electrodes forms excess ThI_4 in these Operating voltage of lamps, lamps. In the present study, lamps were made using both thoriated and pure tungsten (non-thoriated) electrodes and the salt composition was analyzed at various stages of life to better understand the Thl,| increase in lamps and its effect on lamp operating conditions. Several alternate dopants such as La2O3, CeO2, ZrO2 and Y2O.i have also been studied to determine if they are substitutes for ThO2 [2]. It was thought that by adding Thl4 to the salt dose, one may be able to use dopant-free electrodes without adversely affecting the lamp performance.
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