The
mechanism is similar to that of vacuum lamps: The tungsten
evaporates from the hot filament, causing it to thin and
in the end to break.
Inert
gas atoms mechanically "get in the way" of the
tungsten atoms that want to break loose from the filament.
Therefore a filling gas slows the filament’s thinning
and increases life time.
The
bigger and heavier the gas atoms, the "better"
they slow the evaporation of tungsten.
