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Author Topic: What colour is produced by heating iron bars of different sizes?  (Read 3458 times)

Offline taregg

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if we have two iron bars one is 5 mm thickness and the other is 10 mm and we heated both with same teperature...so which one will glow red and the other is blue. and why...
« Last Edit: 23/09/2012 22:40:43 by chris »


 

Offline Bored chemist

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Re: test question ?
« Reply #1 on: 23/09/2012 21:06:22 »
If they are at the same temperature they will glow the same colour.
 

Offline taregg

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Re: test question ?
« Reply #2 on: 23/09/2012 21:26:05 »
what a bout if one is 1cm and the other 5cm . the same temperature..
« Last Edit: 23/09/2012 21:35:37 by taregg »
 

Offline syhprum

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Re: test question ?
« Reply #3 on: 23/09/2012 22:03:02 »
I would like to know the actual temperature if it so low that there is little visible radiation factors such as oxide films would come into play

PS I am using windows 8 now and get a spell checker included so my posts may be easier to understand !.
 

Offline taregg

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Can some body answer my question
 

Offline RD

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Iron would melt long before it got to blue hot, (above 6000K) ...
https://en.wikipedia.org/wiki/Color_temperature#Categorizing_different_lighting


[ this is the only blue iron I've heard of ... https://en.wikipedia.org/wiki/Bluing_%28steel%29 ]
« Last Edit: 24/09/2012 13:49:57 by RD »
 

Offline Bored chemist

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what a bout if one is 1cm and the other 5cm . the same temperature..

If they are at the same temperature they will glow the same colour.
 

Offline lightarrow

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if we have two iron bars one is 5 mm thickness and the other is 10 mm and we heated both with same teperature...so which one will glow red and the other is blue. and why...
If one becomes "blue" then it's not properly "glowing". The colour, as syhprum says, depends in that case on the oxide layer. At higher temperatures, when it really "glows", the colour of the light emitted depends only from the temperature, if the surfaces are equally polished.
 

Offline taregg

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what type of hard metal when heated it will glow blue.....?
 

Offline lightarrow

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what type of hard metal when heated it will glow blue.....?
I'm not native english speaking, but "to glow" should only mean "to emit light by itself", so no solid object could "glow blue" because it would melt much before that temperature (that is many thousands of degrees, remember the blue color of an electric discharge in air).
That said, if you slowly heat a smooth polished stainless steel surface (for example) you will see it taking some different colurs (including blue) depending on the temperature reached.
Mechanics or engineers used to evaluate the temperature reached by some mechanical pieces of an engine (example piston rods) by their surface colour (and if piston rods become blue it's a bad sign).
« Last Edit: 01/10/2012 15:03:39 by lightarrow »
 

Offline imatfaal

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Lightarrow - I would say your english language interpretation is spot on!

I wonder if Taregg means burn with a blue flame?  Perhaps he could clarify?
 

Offline evan_au

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If you light magnesium in oxygen, that reaches a pretty high temperature. I was so dazzled by it in high school that I couldn't really tell if it was blue or not. The metal strip just needs to be thin enough to quickly reach ignition temperature in a bunsen flame.

Copper makes a nice blue colour, when it burns: http://en.wikipedia.org/wiki/Fireworks#Pyrotechnic_compounds

But if you aren't burning the metal (perhaps heating it in a vacuum): then the size and thickness of the bar doesn't affect the colour, only the temperature and composition of the bar matters.
 

Offline Phractality

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Iron melts at 1536C. Chart of melting points of metals.

The metal with the highest melting point is tungsten, at 3400C. That's why tungsten is used in incandescent light bulb filaments. Most incandescent light bulbs are designed to glow at about 2800 to 3000C; the actual temperature depends on the exact voltage, which varies from 110 to 120 volt. Halogen lamps can last longer while operating closer to the melting point of the tungsten filament, so they operate at about 3100C. More about light bulbs.

Glowing metals are black bodies, even if they are white at lower temperatures. The color of black body radiation is the same for all black bodies, varying only by surface temperature. Thickness is irrelevant.

Metal halide bulbs use an electric arc in vaporized metal and halogen gas. Their output is not black-body radiation.

White LEDs use the LED radiation to ionize the phosphor coating, which then emits colors characteristic of the various phosphors.

The hottest stars emit black-body radiation in the blue range, which looks bluish white to the eye. If you view a blue star thru a blue filter, it will look blue. If you view a yellow star (other than the Sun) thru a blue filter it will appear black. The Sun is yellowish, but there is enough blue in it to be seen thru an aluminum film.

 

Offline syhprum

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I feel that what Taregg might be doing is heating the metal in a gas flame and noting the effect on the colour of the flame, here the thickness might well affect the result.
 

Offline lightarrow

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I feel that what Taregg might be doing is heating the metal in a gas flame and noting the effect on the colour of the flame, here the thickness might well affect the result.
In this case it depends on the exact metal's composition and on other reactions as oxidation. If then with "heated" he could mean "with an electric arc" is even more complicated  :)
 

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