Abstract
The effect of minor constituents in alumina arc tubes on lamp performance has been investigated. It is found that arc tubes containing calcia are less resistant to sodium vapor and accelerate early failures. Microstructural studies reveal extensive formation of β—alumina phases and sodium penetration across the wall of the reacted alumina. A number of other interactions, including calcia-doped MgAl2O4 spinel have been studied. Mechanisms of sodium migration in terms of structural defects and chemical constitution of the grain boundary are presented and discussed.

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