Evaporation rate of light bulb filaments exposed to air

In summary, incandescent bulbs are filled with a inert gas to slow down the rate of filament decay. If the filament is exposed to ambient air, it will essentially burn instantaneously. The filaments are made of tungsten metal and oxidize quickly. In halogen lamps, the evaporated tungsten is captured and redeposited onto the filament to extend its life.
  • #1
tuloste
1
0
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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  • #2
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.
 
  • #3
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.
 
  • #4
etudiant said:
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
 
  • #5
Bobbywhy said:
“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.
 
  • #6
Yes, etudiant, you are right about what the OP was asking. Excuse me, I jumped the gun.
Bobbywhy
 
  • #7
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.
 

What factors affect the evaporation rate of light bulb filaments exposed to air?

The evaporation rate of light bulb filaments exposed to air is affected by several factors, including temperature, humidity, air flow, and the material of the filament. Higher temperatures and lower humidity levels can increase the evaporation rate, while increased air flow can help dissipate the vapor. Additionally, different filament materials may have varying rates of evaporation.

How does the evaporation rate of light bulb filaments affect their lifespan?

The evaporation rate of light bulb filaments can have a significant impact on their lifespan. High rates of evaporation can cause the filament to thin and eventually break, leading to a shorter lifespan. Additionally, as the filament evaporates, it can deposit on the inside of the bulb, reducing its efficiency and further shortening its lifespan.

Can the evaporation rate of light bulb filaments be slowed down?

Yes, it is possible to slow down the evaporation rate of light bulb filaments by controlling environmental factors such as temperature, humidity, and air flow. Using a higher quality filament material can also help reduce evaporation and extend the lifespan of the bulb.

How does the evaporation rate of light bulb filaments impact the performance of the bulb?

The evaporation rate of light bulb filaments can directly affect the performance of the bulb. As the filament evaporates, it becomes thinner and less efficient, resulting in reduced light output and a shorter lifespan. High rates of evaporation can also cause the bulb to overheat, leading to a higher risk of malfunction or fire.

Can the evaporation rate of light bulb filaments be measured?

Yes, the evaporation rate of light bulb filaments can be measured through various methods such as weighing the filament before and after exposure to air or using specialized equipment to monitor the vapor pressure in the bulb. These measurements can help determine the effectiveness of different factors in slowing down the evaporation rate.

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