Emissivity of a very high temperature object

[onno]

I am looking for data on the total hemispherical emissivitie from a Platinum surface at high temperature 1400 - 2000 K. In this temperature range the Platnium surface will color from red, orange to white.
I learned that, practically, the bove mentioned emissivity will approach to one in this temperature range.
Platinum has a low emissivity at room temperature: something between 0.1 and 0.2 (as most website tables how). Does the emissivity of this metal go to 1 when white hot?
Materialquality of Platinum is shiny.

 

[hutchphd]

I once built a small wood stove from a shiny stainless steel beer keg.
First test I set a fire inside and set it alight, waiting for the lovely radiant heat. Good fire, no heat. Fire raging, no heat. Waiting. Finally the stove starts to be visibly emissive (orange glow) and there is suddenly good heat coming from stove.
Solution for the stove was black stove paint...worked fine. Second test behaved like a wood stove should.
I believe this represents a general response of metals...they are shiny reflective (and hence very bad emitters) only to frequencies below their plasma frequencies. So when hot enough they emit well,. Here is some data for Au and Ag:
https://en.wikipedia.org/wiki/Reflectance
Pt should be similar

 

[onno]

Hello Hutchphd

You say: "So when hot enough they emit well"
We are designing an oven using a current driven, very thin Pt filament. I have data on filament temperature as function of the heating current. If I compare the measured temperature with some heat transfer simulations I come to the conclusion that above a 1000 C the emissivity is way above the quoted Pt emissivity of 0.2 at room temperature .
I Its going the values 0.5-0.8 above 1000 C is my first estimation. Looking for data though to confirm this.

Best regards

 

[Tom.G]

From:
https://www.researchgate.net/publication/23557347_Temperature_dependence_of_the_emissivity_of_platinum_in_the_IR
the emissivity of platinum is measured in the near infrared as a function of temperature. In the wavelength range of study and the temperature range of 650-1100 K, we find the emissivity to be independent of temperature to within experimental error.

But this:
https://www.omega.co.uk/literature/transactions/volume1/emissivitya.html
Shows:
260°C e=0.05
538°C e=0.10

And this one that digs rather deeply into the subject shows it depends on the wavelength:
http://coimbra.ucsd.edu/publications/papers/2019c_Orosco_Coimbra.pdf(above found with:
https://www.google.com/search?q=emissivity+of+platinum+vs+temperature)

Cheers,
Tom

 

[onno]

Hello Tom

Thanks

http://coimbra.ucsd.edu/publications/papers/2019c_Orosco_Coimbra.pdf

That clears up the issue. Detailed but convincing. Pt keeps being a bad emitter (emissivity 0.1 to 0.2) up to high temperatures 1800 K.

Thanks that was very helpful

Onno