Welding & Blue Light: Is Nitrogen the Cause?

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Discussion Overview

The discussion centers around the phenomenon of blue light emission during welding, specifically exploring whether nitrogen in the air contributes to this effect. Participants examine the underlying physics of light emission, the energy involved in welding processes, and the types of welding techniques that may influence the color of the flame or arc.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether nitrogen in the air is responsible for the blue light emitted during welding.
  • Another participant explains that welding involves high energy, which correlates with high-frequency light emission, leading to blue light being emitted.
  • A claim is made that blue flames, such as those from alcohol, burn cooler than gasoline flames, prompting a discussion on the relationship between flame color and temperature.
  • One participant suggests that the comparison of flame temperatures should consider molar density and the ideal gas law, indicating that blue flames can be hotter than yellow flames under certain conditions.
  • A participant notes that multiple processes occur during welding, including black body radiation and electric arc discharge, which may contribute to the observed light emissions.
  • Another participant asks for clarification on the type of welding being discussed, highlighting that shielding gases typically used in welding (like CO2 or Argon) may mean nitrogen is not a factor.
  • A later reply proposes that the blue color of arc discharge in air may be due to the ionization of O2 molecules, which have a lower ionization energy compared to nitrogen.

Areas of Agreement / Disagreement

Participants express differing views on the factors contributing to blue light emission during welding, with no consensus reached on the role of nitrogen or the specific mechanisms involved.

Contextual Notes

Some claims depend on specific conditions, such as the type of welding and the gases involved. The discussion includes references to physical principles like black body radiation and electric arc discharge, but these concepts are not universally agreed upon in their application to the welding context.

cragar
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when someone welds , why does it emit blue light , is it because of the ntirogen in the air.
 
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Welding uses/has a very high amount of energy. From E=hf, high energy implies a high frequency of light scattered/emitted. And blue light has a higher frequency than red, green yellow etc...

That's why yellow/orange flames are less hotter than blue flames.
 
alcohol has a blue flame and it burns cooler than gasoline.
 
Good question.
It depends on the molar density when comparing alcohol vs gasoline. You would need to use the ideal gas law to work out their temperatures.

My explanation above applies to one particular fuel.
ie. a blue alcohol flame is hotter than a yellow alcohol flame OR a blue gas flame is hotter than a yellow gas flame.
 
ok i see
 
I'm not a materials engineering, but I believe that in welding (as opposed to complete vs. incomplete combustion, as alluded to by n0_3sc) you have a few different things happening simultaneously. The hot sparks flying off (which radiate black body depending on the temperature of the sparks), and the electric arcing--breaking down (and ionizing) either the air or whatever process gas is being used, and the material in the electrode.

Black body radiation (what happens when you heat something up to a certain temperature):
http://en.wikipedia.org/wiki/Black_body

Electric arc discharge:
http://en.wikipedia.org/wiki/Electric_arc

Flame testing (happens with various metal ions, including trace ones):
http://en.wikipedia.org/wiki/Flame_test

Hope this helps!
 
Your question needs to be more specific. What kind of welding are you talking about, MIG, TIG, Arc? Welding usually requires a shielding gas (typically CO2 or Argon) so nitrogen isn't a factor.
 
mig , argon
 
n0_3sc said:
Welding uses/has a very high amount of energy. From E=hf, high energy implies a high frequency of light scattered/emitted. And blue light has a higher frequency than red, green yellow etc...

I think the reason that arc discharge in air looks blue (just like lightning), is because O2 molecules are easier to ionize (lower ionization energy) and therefore, ionized O2 emits blue color.
Am I right?
 

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