High temperature - high emissivity coating

[Feldmann359]

Hi everybody,

I am currently searching for a method to increase the total emissivity of a metallic surface to 0.85 or higher at temperatures up to 3000F (1650°C).

There are many manufacturers of plasma sprayed coatings on the market stating that their products (like iron tianate, aluminium titanate, boron nitride, etc)
will be compatible with the high temperature but emissivities are in most cases not known.

Other methods, like paints, CVD/PVD coatings may also be possible, but at the moment I am not sure how to start, so I would be happy to hear
some helpful statements,

thanks in advance and best regards
Feldmann

 

[coatingengineer]

Hello, Feldmann. Consider doping your coating (metal finish) with yttrium or an ytterbium-based rare-earth material. Higher band widths, less heat reflection should result. The industry of photonics may be a good place to learn.

William Gunnar Naschak

http://www.IndustrialCoatingsWorld.com

http://www.nationalsurfacesolutions.com

 

[IRstuff]

What is the reason for wanting the high emissivity? How do you know its emissivity? Why is >0.85 emissivity sufficient?

There are a number of possibilities, but they depend on what you intend to do with the surface.
A couple of possibilities:
> Carbon nanotubes will act as a light trap
> Texturing the surface with anechoic chamber-like features will do about the same

TTFN
faq731-376

 

[Feldmann359]

Hello and thanks for the replies,
the reason for the high emissivity is the need for better radiative cooling. The eps=0.85 value comes from our thermal analysis guys. The 0.85 is the minimum acceptable value.
There are many possibilities from the gas turbine industry involving a base layer with improved adherence, a ductile intermediate layer and the functional layer on top. But I am not sure if I really a need a multilayer option.
I need only 20 hours of operation at 3000F, involving approx 20 full thermal cycles, meaning much less accumulated operation time compared with gas turbine applications.
@irstuff: Do you know a manufacturer for these carbon nanotube coatings?

Best regards
Feldmann

 

[IRstuff]

Is this thing glowing at temperature? If so, then its emissivity is probably already there.

TTFN
faq731-376

 

[Feldmann359]

Yes, it is. Very bright and with yellow color.

 

[TomDOT]

Instead of coating, can you texture the surface? For example, a polished steel plate (~.07) has a much lower emissivity than an abrasive blasted steel plate (~.5-.85) - sharp grit and a ~2 mil profile should be pretty darn good for emissivity.

 

[Maui]

If you are reaching a temperature in excess of 3000F with a metallic material and it is below its solidus temperature (and very few metallic materials would be at that temperature) and glowing with a bright yellow color then your emissivity should exceed 0.85. You shouldn't need to coat it with anything.

Maui

http://www.EngineeringMetallurgy.com