Metal finishing Q&As since 1989

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Aluminum anodized pore diameter

I am working with photosensitive aluminum sheet metal and I try to put some pigment in the pore of the Al. So I'd like to know the diameter of those pores if anybody can tell me.

Thank you in advance.

Samuel Guerin
plating shop - Chicoutimi, Quebec, Canada
2004

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2004

If its sulfuric acid anodized, pore sizes typically range from 125-225 angstroms. This, of course depends on what type of anodizing it is, and what the process parameters are/were.

Marc Green
anodizer - Boise, Idaho

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2004

There is no accurate single answer. The pore size depends on the type of anodising carried out and the forming voltage. As guideline, the pores are about 100-250A in diameter and the wall thickness is between 100 and 200A, giving a cell width of between 300 and 900A. The pore length is orders of magnitude longer than the pore diameter and can be as much as between 5,00 and 25,000 times the diameter. If you use an orthophosphoric acid anodising system at 120V, the pore diameter has been shown to be about 330A, the wall thickness about 1200A and the cell size about 2,750A. As an example of the variability in pore size, there are about 19 X 10^^9 pores/cm^^2 in a phosphoric acid (at 25C) processed surface when done at 20V, but if done with sulfuric acid (at 10C) this increases to 52 X 10^^9 pores/cm^^2. Consequently, the sulfuric acid pores are much smaller than the phosphoric acid ones. Again, for comparison, using sulfuric acid at 10C, the number of pores is 76 X! 10^^9/cm^^2 at 15V, but only 52 X 10^^9 at 20V and 28 X 10^^9/cm^^2 at 30V.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

What is effect of pore size in anodized aluminium on reflective properties?

Cyavash
- Tehran, Iran
2006