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Topic: Remove anodised coating  (Read 11840 times)

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Offline jdurg

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Re:Remove anodised coating
« Reply #15 on: March 22, 2006, 10:14:08 PM »
Good luck with that.  Just be VERY watchful of the reaction going on and have a VERY dilute, but slightly acidic vinegar solution nearby to stop the reaction at once if it starts to get out of control.  The reaction between aluminum metal (anondized or not) and NaOH typically starts out quite slowly then picks up rapidly as the oxide layer is eaten away.  Once the oxide layer is eaten away, however, the aluminum metal will rapidly be corroded by the NaOH and the H2O.  So when you start to see some bubbling going on with some intensity, immediately remove the part and dunk it in your very slightly acidic solution.  Then dunk it in a large beaker of distilled water and finally just run a great deal of water over the part to ensure that there are no remnant basic or acidic solutions on it.
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Offline Borek

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Re:Remove anodised coating
« Reply #16 on: March 23, 2006, 04:13:25 AM »
Then dunk it in a large beaker of distilled water

Tap water will be enough.

I wonder if it is necessary to start with bath in acidic solution. While it may look logical, what you do is you not stop the reaction, you just replace dissolution in NaOH with dissolution in acid, as effect will be not a perfect neutralization. I think large amount of flowing water will do the trick better, removing hydroxide. Or - the best solution can be pH 7 buffer for the neutralization bath, but that will be probably overkill.
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jethro

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Re:Remove anodised coating
« Reply #17 on: April 01, 2006, 07:58:29 AM »
I missed the last two posts(frrom Borek and jdurg) but thanks for the advice. I'm pleased to report complete success with this process. I started with tap water which I measured to be 12°C and slowly sprinkled the sodium hydroxide granules into it while stirring constantly. The concentration was 100g NaOH/litre water which is approx 10%. There was an initial tendency for the mixture to solidify but as the temp increased this wasn't a problem. It was important to sprinkle the granules in slowly though to avoid this. I didn't measure the temp of the mixture but could feel it as 'warm' through my gloves. I did move the mixing container outside because of the fumes.
I immersed the anodised component and after about 30secs bubbles could be seen coming from it which increased in intensity rapidly. I removed the component after 60 secs and plunged it into a waiting bucket of cold tap water to stop the reaction. I then put it under a running tap just to make sure.
Although I was wearing eye protection and long gloves there was nothing too vigorous happening and I conclude that this is a safe process to use at home. The anodised coating was certainly removed and it was then easy to polish out the machining marks which was the objective.
Thanks for all the contributions and interest from all who posted and I hope this may be useful to anyone doing a 'search' on this forum about this subject.

Offline Borek

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Re:Remove anodised coating
« Reply #18 on: April 01, 2006, 08:17:13 AM »
The concentration was 100g NaOH/litre water which is approx 10%.

Probably closer to 9% due to volume change, but it doesn't matter much.

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Although I was wearing eye protection and long gloves there was nothing too vigorous happening and I conclude that this is a safe process to use at home.

As long as you are carefull and protected it is safe. Protection is necessary only when something goes wrong, but your never know it beforehand - so better safe then sorry :)

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Thanks for all the contributions and interest from all who posted and I hope this may be useful to anyone doing a 'search' on this forum about this subject.

Great thanks for posting the follow-up, way too often we don't know whether advice given was of use or not - and even negative information (it didn't worked) is good, as next time we know we have to think about something else.

All the best.
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Offline jdurg

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Re:Remove anodised coating
« Reply #19 on: April 07, 2006, 04:56:56 PM »
Awesome.  Glad it worked out as you had hoped.  And I concurr with Borek;  it's nice when people reply with the results of their experiment.  Too many times people never return to say whether or not their trials worked.   ;D
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