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Re: halogen bulbs



As I recall, hexaflourides of the metals form on the cold surface.

Is the cold surface to which you refer the quartz envelope? I note
these things used to be called "quartz halogen" bulbs, and when I
replace one I'm told not to touch the envelope. Vitreous quartz
devitrifies when it gets hot if contaminants common in hand soil
are present. Perhaps the hexafluoride forms more readily on a
heated quartz surface than it would on a cool glass surface, or
perhaps it needs a higher temperature to sublime?

The
hexaflouride is volatile, and unstable at the temperature of the
filament, so when the molecule hits the filament, it decomposes so that
the metal is deposited and the fluorine is free to do its thing.

Are chlorine and bromine also used in lamps?

Leigh