Abstract
The doped-tungsten filament for tungsten halogen lamps evolves potassium at such an elevated temperature that they are normally operated.
This potassium plays a role to accelerate initial bulb-blacking in these lamps.
The authers confirmed the above effect through gas analysis and life tests of experimental lamps.
The thermodynamic equilibrium calculations also supported the results of life tests.
These results will contribute to obtain higher luminous efficacy lamps with normal life performance.
The gases evolved from doped tungsten wire during a vacuum heat treatment were analyzed bymeans of a quadrupole mass spectrometer.
Detected gases were K, CO, CO2, H2 and hydrocarbons.
When tungsten wire was heated to 2, 900-3, 200°C, CO, CO2, H2 decreased and K increased.
Three kinds of tungsten wires different in potassium evolving degree have been compared through life tests of lamps.
Lamps using wire with highest potassium were blackened with only four hours operation at 3100°C.
Equilibrium calculations have been performed at the temperature range 500-4000 K on the heterogeneous systems of tungsten-hydrogen-bromine and of tungsten-hydrogen-potassium-bromine.
