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Thermal conductivity of aluminum finishes

Q. Is there a reduction of thermal conductivity after applying a conversion coat to aluminum? We have some 5052 aluminum plates (.093 thick) with conversion coat per MIL-DTL-5541 Type II Class 3. The color is gold. We're doing some testing and noticing less thermal transfer using these plates as opposed to our prototype unfinished plates.

A. Hi Susan. Aluminum is a metal with high thermal conductivity as you already know. Conversion coatings are gels and definitely have significantly lower conductivity, and we would be very interested in any numbers you can offer us from your testing.

But what usually matters practically is the thermal conductance (the heat that is transferred across the surfaces that are in contact), and this is inversely proportional to the thickness of the conversion coating, and they are usually very thin -- thus the claims on this page that conversion coating doesn't usually have a major effect.

Still, exceptions are always possible: if, for example. it is crucial to you that your plates not just transfer heat across them efficiently but remain virtually the same temperature for some reason (very low ΔT), the conversion coating could be a problem :-)

Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 2021

⇩ Closely related postings, oldest first ⇩

Q. Hello!

I would like to know of where I can find information on how both Iridite/Alodine and anodize finishes affect the thermal conductivity of aluminum. Specifically, in fabricating a heatsink for an electronic component, it is typical to mask the actual contact area when anodizing, but is this absolutely necessary for Iridite/Alodine? Since the latter preserves the electrical conductivity of the aluminum, does it also have a negligible affect on the thermal conductivity?

Thank you!

Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

"Iridite thermal conductivity?"

Q. Anybody know the thermal conductivity of Iridite layer on aluminum? Is it as thermally conductive as aluminum?

Thanks!

A. It is nowhere near as thermally conductive as aluminum, but it is so darn thin a layer that it of no concern to almost all applications. James Watts - Navarre, Florida 2004 A. I am not certain, but I believe that the conversion coating is slightly less thermally conductive but is so thin that it doesn't provide much in the way of insulating properties. I do know that the corrosion resistance properties start to break down above 140 °F though - so if you are going to be using your part in a high temp environment a chemical conversion coating would probably not be your best choice regardless of its thermal conductivity. Jim Gorsich Compton, California, USA 2004

Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

Thermal conductivity of chromate conversion coating

Q. I am designing a mounting bracket for a rectifier, and looking to maximize heat transfer. I am looking for information on thermal conductivity of chromate conversion coatings as applied over zinc plating. I have found the thermal coefficient of zinc to be about 5x that of steel, but can not find any information on chromate coatings. Any information would be appreciated,
Thanks,
Darren

A. The thickness of the chromate will vary from part to part and even some on the part. For a mounting bracket, the decrease in thermal conductance should be negligible as the normal yellow is very thin. James Watts - Navarre, Florida November 21, 2008 A. Darren, Due to the nature of the chromate film, I do not see most films as having any effect. Sealed films are a different matter. Chromate thickness varies with the type of chromate use, hence, for your purposes you would need to specify some additional information regarding corrosion protection and/or other specifics. Gene Packman process supplier - Great Neck, New York November 22, 2008