Very high & very low emissivity, high temp resistant materials

[Soderdahl]

Wow, I didnt know of this forum love it

 

Looking for a material with very high emissivity to work as a 1m2 black body, absorbing concentrated solar light transferring the heat to the material under, standing a temperature preferably around 1000-1200c for longer periods of time. It will be in vacuum too.

 

 

Also I'm looking for material with very low emissivity material that can stand temperatures of at least 1200c preferably more, over long periods of time It will reflect concentrated solar light

 

Both of them will be in 1pa vacuum and preferably somewhat abundant.

 

 

[John Cuthber]

Chromium is shiny and has a high melting point.

Carbon is black and has a very high melting point.

Neither is very strong.

What are you hoping to do?

[Soderdahl]

A "simple" Thermal energy storage. Might deserve its own thread..

 

What Im thinking is:

Concentrate sunlight with e.g mirrors or a Fresnel lens guided through a window to heat up a mass bellow.
The reflective surface acts like a cone above the black body to reflect any stray light down again.

The whole black body could be carbon, I have been considering t it, since it have very good conductivity and ok specific heat. However it is an expensive material and far from the most environmental friendly. (Im trying to go somewhat abundant and eco-friendly)

 

So my thinking is to use one material as a surface black body material to absorb the light and conduct the heat down as effectively as possible. Maybe som kind of carbon/graphite would be good for this since its only a small amount. It sure can take the temperature.

Then Im thinking to have a storage material of something like magnetite, high temp concrete, aluminum oxide (all got different pros and cons)

[Enthalpy]

Hi Soderdahl, nice to see you again!

 

Emissivity isn't the same at 1200°C. It won't be small.

Big emissivity is attained by roughening the surface. It provides multipath absorption.

 

1Pa is still a lot. Resistance to oxidation is essential then. Low emissivity after hours or years at 1200°C implies noble metals. A ceramic would be a more natural choice, but don't expect a low emissivity from it neither.

ZrO2 0.25

 

I have data for short-term 1200°C emissivity of metals...

Cr >>0.38

Inconel 0.3-0.6

W ~0.22

Co, Ni >>0.22

Pt 0.18

Mo clean 0.18, polished 0.16

Gold polished 0.03

 

For some metals, sublimation is already a worry at 1200°C.