Sciencemadness Discussion Board

How thick can an anodized layer be?

Tacho - 30-11-2007 at 05:51

In the aluminum anodizing process, does the oxide layer grows indefinitely as long as current flows? Or how thick can it get?

My intention is to anodize a tube to electrically insulate it. This way I can wind Ni-Cr wires directly around it to make a mini hot air gun.


jpsmith123 - 30-11-2007 at 09:16

Hello Tacho,

I admire your resourcefulness, but is it worth it to even fool around like that when you can get a heat gun for $10.00? (I would think in Brazil there must be something similar?)

Anyway, here's an article from the Electrochemistry Encyclopedia that might be helpful.

One concern I would have would be the difference in thermal expansion between the metal and the oxide, especially if the oxide were thick and subject to repeated thermal cycling.

12AX7 - 30-11-2007 at 10:26

Hardcoat may suffice. I know electronics professionals (good ones :P ) who have been known to mount transistors on hardcoat heatsinks. It's also very thermally conductive, being aluminum oxide.

Aluminum goes up to 500V or so- think aluminum electrolytic capacitors. As the anodization grows, the voltage must be increased.


Tacho - 3-12-2007 at 02:48

Thank you.

The link ( Electrochemistry Encyclopedia ) is the best information on anodizing I have seen so far.

My Idea is really a small scale thing and, as Tim pointed out, oxide insulation layers can be useful in many other projects. Besides, I really never saw one of those for sale for U$10 (or equivalent). Bless China.

Nixie - 17-12-2007 at 04:59

Originally posted by 12AX7
It's also very thermally conductive, being aluminum oxide.

Bah, you can get beryllia insulators from eBay.

unionised - 17-12-2007 at 13:03

You can get a fair few carcinogenic things on eBay if you look hard enough.
I don't know how thick a layer you can get but there's another neat trick you can do. You can anodise a layer of oxide onto the Al then dissolve away the Al from the other side with I2 soln. That way you might get an Al2O3 tube without the metal.

Nixie - 17-12-2007 at 14:43

Originally posted by unionised
You can get a fair few carcinogenic things on eBay if you look hard enough.

How is it carcinogenic? Only the dust is. Cut/drill under water and it's perfectly safe (the diamond bits you need to work this hard ceramic are intended for wet use anyways, as they overheat otherwise).