Metal finishing Q&As since 1989

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Hard anodizing aluminium foil to build nanopores

April 28, 2011

Hello,

I work in a research lab in France.
We are trying to hard anodize pure aluminium foils (99.999% pure Al), to form long nanopores.
As electrolyte, we use Oxalic acid (0.3 M concentration), and run the anodisation at -5° C. The sample is put in a teflon cell (with a metallic bottom for the cathode), pressed with a O-ring to define the region to be treated and is then immersed in the electrolyte which is vigorously stirred.

I first anodize at 40V during 10 to 20 minutes. Then I increase the voltage slowly (about 0.5V /s) up to 120V. However at 110V, the current starts to increase and the Al foil burns.
There is a huge hydrogen gassing at the anode.
From the bibliography, the max voltage should be around 160V ... so I really wonder what is wrong in my process or setup.

As pretreatment, I usually polish the foils mechanically to very smooth roughness (less than 10nm rms). Then I perform an electropolishing, which might not be correctly optimized ? I use a ethanol and perchloric solution at 5° C, and apply 18V voltage for 5 minutes. The results seems fine.

What I generally observe is that the burning of the sample starts from its edges, where the O-ring presses the Al foil.

Any suggestion, on what I could investigate to improve my process would be greatly welcome.

Jean Bonot
Student - Paris, France

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May 21, 2011

you could try to do at +30° c 40-60 V 10 min (first step)
after etch the first layer and try again
you can get very nice pores of 20-40 nano very good assembled

Ricardo Burstein
Bnei Berak, Israel