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Evaporation rate of light bulb filaments exposed to air

by tuloste
Tags: bulb, evaporation, exposed, filaments, light, rate
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tuloste
#1
Apr14-13, 02:52 PM
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I know that incandescent bulbs are filled with some inert gas to reduce the rate at which the filament decays. If the filament was to be exposed to ambient air, how long before it evaporated? How long can a mesh of light bulb filaments (or other material with as high a melting point that can be woven to threads of similar width) be kept at a temperature of some 1000C-1500C under such conditions?
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Danger
#2
Apr14-13, 04:45 PM
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I don't know exact numbers, but the igniters for model rockets and homemade explosives are essentially lightbulb filaments exposed to air and electricity. The process is, for all practical purposes, instantaneous.
etudiant
#3
Apr14-13, 08:42 PM
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The filaments are tungsten metal, which oxidize essentially instantaneously, as Danger points out. Evaporation does not come into it, the hot tungsten just burns.
Do note the old Coleman lamps used a glowing wick open to the air, but the wick was heated by the burning of the lamp fuel and the light created by the hot rare earth oxides held in the wick.

Bobbywhy
#4
Apr15-13, 03:12 AM
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Evaporation rate of light bulb filaments exposed to air

Quote Quote by etudiant View Post
The filaments are tungsten metal, which oxidize essentially instantaneously, as Danger points out. Evaporation does not come into it, the hot tungsten just burns.
“During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster.”
http://en.wikipedia.org/wiki/Incandescent_light_bulb
etudiant
#5
Apr15-13, 05:19 AM
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Quote Quote by Bobbywhy View Post
“During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster.”
http://en.wikipedia.org/wiki/Incandescent_light_bulb
During ordinary operation = glowing white hot in the inert gas atmosphere held inside a light bulb.
The OP was asking about operation in the air, which is much more aggressive chemically.
Bobbywhy
#6
Apr15-13, 05:34 AM
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Yes, etudiant, you are right about what the OP was asking. Excuse me, I jumped the gun.
Bobbywhy
Danger
#7
Apr15-13, 12:08 PM
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A side-note that might be of interest to OP:
In a halogen lamp, the evaporated tungsten is "captured" by the iodine or bromine and redeposited onto the filament, thus extending its life.


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