Residue on steel after caustic cleaning

[Mark Anderson]

After cleaning aluminum from steel I use with sodium hydroxide, there a brown chalky layer I want to clean off. Other than sanding, I cannot remove it. Is there a way to chemically remove it without affecting the steel?

 

[Bystander]

"Affecting?" Etching?

 

[Mark Anderson]

There's a scale residue left that I use sandpaper to remove.but sanding it also damages the steel. I've tried alcohol and degreasers with no luck.

 

[256bits]

There's a scale residue left that I use sandpaper to remove.but sanding it also damages the steel. I've tried alcohol and degreasers with no luck.

That won't work if it is what it could be.
Sodium aluminate should have dissolved in alcohol, so it can't be that.

You mean something like this perhaps.
http://www2.uni-siegen.de/~pci/versuche/english/v44-10.html

If so, aluminium oxide is fairly unreactive. In fact, it can be found on sandpaper since it is hard ( next to diamond I believe ).

You might try sanding with a very fine grit in the presence of sodium hydroxide solution, and see if some of the stuff will go back into solution.
Try a DILUTE solution, and a small section, since you don't want to be splashing the stuff around onto your clothes, skin and eyes.

I suppose previously, you just let the metal sit in an hydroxide solution to dissolve the Al.
Some of the Al went into the small microscopic indentations of the Fe during the original joining, and is now oxide.

Not 100% sure though if that is what you have there.

 

[Mark Anderson]

Yes I believe you are correct on the oxidization. As far as going over it again with the caustic solution, I think sanding it the normal way I do it is the best. I prefer not to deal with these chemicals more than necessary. Thank you for the input. This forum is very helpful and has much information.

 

[Nidum]

Concrete driveway cleaner removes general corrosion quite well but better to use an electrolytic method .

https://www.google.co.uk/search?q=e...&oe=utf-8&gws_rd=cr&ei=lEO5VauWA6blywPejKjwAQ

The electrolytic method can be tuned to remove different variants of rust , heat oxides and some platings and the process rate can be controlled .

 

[Mark Anderson]

This electrolytic method sounds like the ticket. When I get free time (tough with 3 kids), I will give it a test. I have all of the materials except for some rebar. I will let you guys know if it does.