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tomb
10-06-2005, 03:29 PM
I work in the lighting industry and an oddball item came up that I thought someone here might be able to help with.

We're looking on quoting a small heat shield. It is made from 3002 aluminum. It is cone shaped, 3" at the large end tapering to 2.75" at the small end and is 1.625 high. My question is this: since this is to act as a heat shield - will the finish of the aluminum affect reflectivity of heat? For instance - if I was to anodize it, would it reflect more heat? Does the hardness of the aluminum affect how much heat is reflected off of it?

Thanks for any help you can offer.

Tom

Evan
10-06-2005, 04:10 PM
Anything you do to the finish will affect the reflectivity. The highest reflectivity is from what is called "specular lighting sheet" or "reflector sheet". You can also get it in many finishes but any finish will reduce the reflectivity.

The theoretical reflectance of pure aluminum drops in the infrared to no more than 85%. This would be for the best sputtered coatings on a front surface mirror. For lighting sheet it will be considerably less. Any surface coatings or treatment make it even less. Hardness doesn't matter although the alloy type does. All alloys have a lower reflectance than pure aluminum.

If you are looking for the best possible heat reflectance then a protected gold (real gold) finish is best. It only needs to be a few microns thick and has a reflectivity of better than 96% across the infrared spectrum