Does the color of a hot body depend on its composition ?

In summary, the color of a hot body can depend on its material composition and temperature. The electronic structure of atoms and the conditions in which a blackbody spectrum occurs play a role in determining color. Metals at high temperatures may have similar spectra due to their shared outer electrons. However, different materials may also exhibit thermochromism, causing a change in color with temperature. Changes in reflective color can also indicate temperature, as seen in the hardening and tempering of metals.
  • #1
bksree
77
2
Hi
Does the color of a hot body depend on its material composition ? For eg. will bodies made of steel, Stainless steel, Ti, Cu etc. all look red in color if the temperature is ~ 550 deg C ?

TIA
 
Physics news on Phys.org
  • #2
"material" is quite broad.

In general, "sort of".
Atoms have a characteristic spectrum with dominant lines.
It depends on their electronic structure.
http://en.wikipedia.org/wiki/Emission_spectrum

The blackbody spectrum occurs under specific conditions.
But those conditions are pretty common.
http://outreach.atnf.csiro.au/education/senior/astrophysics/spectroscopyhow.html [Broken]

Your examples are not going to be all that different at that temp though - heat them up and see. Metals share their outer electrons across the whole solid as a kind of big tub of charge so they all have very similar spectra under heating. Also heavy elements have more options to emmit from, allowing thermal emmissions ot spread over a wider range of wavelengths.
http://911research.wtc7.net/cache/wtc/analysis/fires/metcolor.htm
Compare the emmission spectrum of H with Fe in the wikipedia article.

You normally bring out the characteristic colors by EM "pumping" as in florescent lights ... hydrogen is pink, sodium is orange, and mercury is blue-grey.

The bottom line is that you can use the color to work out the temperature.
 
Last edited by a moderator:
  • #3
If you can get a body hot enough to radiate significantly at optical frequencies then I think its reflectivity of different frequencies (it's apparent colour) could have an effect on the spectrum of radiation it emits (i.e. radiated colour). After all, emissivity and absorptivity go together, so if the body 'looks green' it will be absorbing reds and blues and reflecting greens. So, if the body were at a 'white hot' temperature reds and blues would then be radiated better than green (making it 'glow' magenta more than white). HOWEVER, at that temperature, the energy levels in the surface molecules would be much modified and their interaction with different frequencies of em would probably be changed. So what I say may not apply at all.
 
  • #4
bksree said:
Hi
Does the color of a hot body depend on its material composition ? For eg. will bodies made of steel, Stainless steel, Ti, Cu etc. all look red in color if the temperature is ~ 550 deg C ?

TIA

It's probably not what you are thinking of, but there are thermochromic materials that show a wide variation in color with temperature.

http://en.wikipedia.org/wiki/Thermochromism

Aside from that, if the refractive index (and thus the emissivity) varies with temperature, the color of an object will also change with temperature.
 
  • #5
Andy Resnick said:
It's probably not what you are thinking of, but there are thermochromic materials that show a wide variation in color with temperature.

Got the T shirt! Way back.

Actually, there is mention of heating metals, earlier. The change in surface (reflective) colour of metals (tool steel in particular) when you heat them is a great indication of their temperature and is often used when hardening and tempering etc. but that's at lower than 'red heat'.
 

1. What is a hot body?

A hot body is an object that has a high temperature, typically due to an external heat source or internal energy production.

2. Does the color of a hot body change as its temperature changes?

Yes, the color of a hot body changes as its temperature changes. As the temperature increases, the color changes from red to orange to yellow to white to blue.

3. How does the composition of a hot body affect its color?

The composition of a hot body can affect its color by influencing the types of particles, such as atoms and molecules, that are present. Different particles absorb and emit different wavelengths of light, which can contribute to the color of the hot body.

4. Can a hot body change color without changing its temperature?

Yes, a hot body can change color without changing its temperature. This can happen if the composition of the hot body changes, such as through a chemical reaction or a change in the surrounding environment.

5. Is the color of a hot body solely determined by its composition?

No, the color of a hot body is not solely determined by its composition. Other factors such as temperature, surface texture, and surrounding environment can also influence the color of a hot body.

Similar threads

  • Materials and Chemical Engineering
Replies
21
Views
1K
Replies
2
Views
809
  • Special and General Relativity
Replies
1
Views
1K
  • Mechanics
Replies
5
Views
6K
Replies
29
Views
2K
Replies
1
Views
1K
  • Astronomy and Astrophysics
Replies
1
Views
1K
  • Materials and Chemical Engineering
Replies
12
Views
2K
  • Sci-Fi Writing and World Building
Replies
21
Views
850
  • Materials and Chemical Engineering
Replies
3
Views
2K
Back
Top