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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Maximize/Minimize Emissivity of Stainless Steel with Coatings & Processes
Q. I'm looking for a finishing process for 304 stainless steel which results in a high emissivity for thermal radiation cooling. The current plan is to electro polish so the surface is smooth for cleaning but this leaves a low emissivity surface. Something similar to anodizing for aluminum is what I have been thinking of. In addition, who can perform this work on a 180" x 85" D x 0.25" thick cylinder.
Note that the cleanability is important, no pits, cracks, etc..
Dick Hartung1998
A. Hi Dick. You might try B&M Finishers / Prismatic Stainless Steel [a finishing.com supporting advertiser] [Kenilworth, NJ] who offer Prismatic Finishing of stainless steel.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
1998
Q. I need to maximize the emissivity of a flat stainless steel plate approximately 9 inches in diameter. Operating conditions are as follows:
• temperature range: 20 °C - 550 °C (cycled on weekly basis)
• environment: high vacuum
I am open to surface treatments and/or coatings.
The component is used in semiconductor manufacturing, so contamination (sodium, potassium, etc.) is a big concern.
Steve C. [last name deleted for privacy by Editor]- Santa Clara, California, United States
2001
"Coating on SS to reduce emissivity"
I am needing to reduce emissivity on stainless steel. I want to get rid of some heat shields placed over the pipe of the exhaust system for a vehicle and wonder if there is any low-cost coating I could use in order to do that.
Dan EscarcegaAutomotive components - Chihuahua, Mexico
2004
? What is the purpose of the heat shields? From the sounds of it they are meant to control the migration of heat from the exhaust pipes. Are they there to stop heat from entering the inside of the vehicle space or are they there to protect certain components such as the starter motor?
Ceramic coatings can be used to control heat. Depending on how you answer the above will determine the type of ceramic coating you will require.
Race cars and motor homes have utilized ceramic coatings on the floors firewalls to control heat migration from the exhaust and engine compartment.
On the other hand yet another type of ceramic coating can be applied directly to a hot pipe to conserve energy or to protect one from getting burned. Price is really dependent on the objective and solution you choose. Nothing cheap is good, nothing good is cheap.
David Lawson- Surrey, BC, Canada
2004
Multiple threads merged: please forgive chronology errors :-)
Q. Hello,
I want to use to steel plates in an oven where the temperatures are around 700 °C. I was told that 310 stainless steel is a very good option. However, this kind of stainless steel has a low emissivity (usually) and therefore I am looking for finishing processes in order to increase the emissivity (preferably above 0.8)
If anyone knows an answer to my application then please tell me, btw the steel plates are 1 mm thick and about 1 x 1 m
Thank you
PhD student - France
2007
A. How about ceramics? Ceramic coatings are corrosion resistant, very hard and oxidation immune but I don't know about their emissivities. if you are looking for a metallic coating, highly emissive metals include aluminum (very low melting point), silver (m.p. 960 °C); gold (best for infrared wavelength).
Guillermo MarrufoMonterrey, NL, Mexico
2007
Q. Hello,
thank you for your answer,
The problem with ceramic coatings is that they might peel off due to the expansion/retraction of the stainless steel when subjected to continues heating/cooling cycles.
About the high emissive metal coating, I will look more into them but just practically can I buy a silver coating and apply it myself for example or is it just too complicated.
thank you
- Paris, France
2007
A. Generally, silver metallization is not too complicated if you have the right chemicals and equipment but doing it over stainless steel may be difficult. You may get very poor adhesion and peel-off during furnace operation.
Guillermo MarrufoMonterrey, NL, Mexico
2007
A. Hi. I confess to not quite understanding where you're trying to go. You seem to be wanting to build an oven from sheets of 310 stainless steel about 1 meter square, but you want to coat those sheets with a high emissivity material.
On the outside, so the oven will lose heat quickly and cool down rapidly? If so, high temperature paint might do on the outside. The inside? Why? A high reflectivity coating might be useful towards keeping the heat contained/focused, but what does high emissivity do for you? Engineeringtoolbox weathered says stainless can give you as much as 0.85 at 300 K (shouldn't be much lower at 973 K) -- So maybe plain stainless is all you really need :-)
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Low emissivity coating for vacuum insulation
Q. We have a tank with annular vacuum insulation. We were wondering if there was any way we could get a black body like coat on the hot surface exposed to the vacuum to reduce radiation. The material properties for this black body like substance (if possible) should be - low emissivity, low outgassing, low adsorption. The annular space is between two stainless steel tanks and the inner tank is wrapped with multilayer insulation.
Shruti Karwa- Buffalo, New York, USA
September 10, 2012
A. Hi, Shruti.
I was having some difficulty following your explanation, so tell me if I've got it please. The inner tank is cold, and the outside world is hot, so the surface that you want to put this coating on is the inside surface of the outside tank?
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 10, 2012
September 12, 2012
A. Hi Shruti
I too am confused. Black in general is a good absorber of radiation - that's why it appears black. A "black body" is a perfect absorber of all wavelengths. This is the exact opposite of what you appear to be seeking.
To reflect radiation silver coating is usual (as in vacuum flasks). If your requirement is particularly critical, gold is an even better reflector of infra red.
Geoff Smith
Hampshire, England
September 12, 2012
Hi Geoff.
Q. I think, but don't know, that Shruti has a cold, insulated, inner tank and that the insulation may be silver coated.
This inner tank, I think, is within an outer tank, the outside of which may also be silver coated, and there is a vacuum between the outer and inner tanks.
I believe his concern is about the inside surface of the outer tank and whether making it a black body will help it not radiate heat to the cold inner tank. Well, that will be my question anyway, if it's not his :-)
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
(to help readers better understand the Q&A's)
To those new to the subject, absorptivity & emissivity probably sound pretty like opposites rather than the same thing, but actually it is absorptivity & reflectivity that are more or less opposites.
Kirchhoff's radiation laws are a bit too deep for us, but in brief the principal here is that equilibrium demands that the heat emitted must equal the heat absorbed, so absorptivity & emissivity are equal.
Q. Hi,
I am sorry I made a huge error in my question and I realized it as soon as I posted my question. I couldn't figure out how to edit my question. Anyway, I was looking to say HIGH absorptivity. That would mean HIGH emissivity paint. The inner tank has cryogenic fluid in it. It is wrapped with multilayer insulation and placed inside a larger tank. The annular space between these tanks is under 10^-5 torr pressure. I am not sure if painting the inside surface of the outer tank will help reduce the radiative heat leak into the tank. I wanted to know if this has been attempted before? What kind of paint would be suitable to be exposed to high vacuum?
- Buffalo, New York, USA
September 17, 2012
A. Hi Shruti. It is heat that radiates, not cold, so the outer tank has no capability to 'capture' any cold from the cryogenic tank, so a high absorptivity paint on the inner surface of the outer tank would not help. To the contrary, the outer tank can radiate heat to the inner, and you don't want it to! So you want that surface to be LOW absorptivity/emissivity -- i.e., highly polished metal, not paint.
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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