Chemically dissolve aluminum?

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I have a 6063 aluminun tube with a fiberglass/epoxy outer wrap. Is there an reasonably fast and effective way to chemically dissolve the aluminum tube, without seriously degrading the fiberglass outer shell? Appreciate any suggestions.
 

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  • #2
chem_tr
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Well, I wonder if you try a redox reaction, such as placing electrodes and using an electrolyte such as aqueous acid solution; with this way you might dissolve it as Al3+ ions and not give harm to the coating. However, it would be wise if you make a little hole inside the wall of the tube, so that the reaction proceeds efficiently.

By the way, is acid (or base; aluminum likes it too) harmful for the coating?
 
  • #3
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Well acids react very well with aluminium (i dont know about the outer shell). so i would try putting a few drops of concentrated HCl onto the tube to see if it does any dammage, if it does i would try a sodium hydroxide solution. then once i found the substance i need i would proceed to reacting the aluminium off. You can get concentrated HCl from a pool shop and sodium hydroxide is sold as drain cleaner and is also labeled caustic soda.
 
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Toilet cleaner reacts with aluminum but i do not know about the fiberglass, there is a high strength acid in it but i do not know what it is.
 
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The active chemical in toliet cleaners is usually hydrochloric acid. You could also try sodium hydroxide. That'll react with the aluminum, but it might do some damage to your epoxy.
 
  • #6
Borek
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Think about controlling pH - you don't need concentrated acids to dissolve aluminum, unless you want it to be done reall fast. Probably weak acid - like acetic - will do the trick. Slowly, but efficiently - and it will be most likely safe for fiberglass/epoxy. Test won't hurt.

Borek
 
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  • #7
Gokul43201
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You could also try sodium hydroxide. That'll react with the aluminum, but it might do some damage to your epoxy.
Most epoxy resins are fairly unaffected by NaOH.

In fact, when we build cryostats, there are joints that are bonded by a low temperature epoxy-based adhesive. The way we make these joints is using an aluminum jig to hold the pieces together, which we then dissolve in NaOH after the epoxy has cured.
 
  • #8
marcusl
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I didn't think NaOH dissolved aluminum. We've used it in the past to dissolve hard anodization off of parts and it seems to leave the base metal untouched...
 
  • #9
Gokul43201
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I didn't think NaOH dissolved aluminum. We've used it in the past to dissolve hard anodization off of parts and it seems to leave the base metal untouched...
It takes a while to dissolve the aluminum, but it does eat it all up. Does nothing to copper, brass or steel though.
 
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I didn't think NaOH dissolved aluminum. We've used it in the past to dissolve hard anodization off of parts and it seems to leave the base metal untouched...
At the beginning, and with a non-hot solution, the reaction is very slow. After the thick layer of aluminum oxide has been removed by the NaOH, the reaction proceeds fast.

If you want a slower and better controlled reaction, you can use NaHCO3 instead. You have to heat the solution and keep heating it. If you stop heating, the reaction becomes much slower.
 
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I used to use HgCl2 for the dissolution of aluminum, in the form of its amalgum. The process is fast enough, if some scretch over the surface. BUT, I do not reccomend to use the method, if you have other option. Even short exposure to the solution cause eye burnings and headache for few hours.
I cant use sodium hydroxide, because I have to protect the anodic oxide film. Though I have not tried acids, as mentioned in this thread. I will check it and will defenitely write in the forum. I hope you will share your experience as well.
 
  • #12
marcusl
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At the beginning, and with a non-hot solution, the reaction is very slow. After the thick layer of aluminum oxide has been removed by the NaOH, the reaction proceeds fast.

If you want a slower and better controlled reaction, you can use NaHCO3 instead. You have to heat the solution and keep heating it. If you stop heating, the reaction becomes much slower.
Isn't that baking soda? I had no idea it would attack anodization. How hot do you go? Any safety concerns (e.g., fume hood?)?
 
  • #13
Borek
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NaHCO3 solution is slightly basic. No idea if it is basic sufficiently to dissolve Al2O3, but it would not surprise me.

Borek
 
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  • #14
Gokul43201
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Isn't that baking soda? I had no idea it would attack anodization. How hot do you go? Any safety concerns (e.g., fume hood?)?
Yes, baking soda (saturated), and heated to about 150F is the standard technique for slow-etching aluminum. I think the etch rate is of the order of a couple microns a minute at that temperature.
 
  • #15
I have a 6063 aluminun tube with a fiberglass/epoxy outer wrap. Is there an reasonably fast and effective way to chemically dissolve the aluminum tube, without seriously degrading the fiberglass outer shell? Appreciate any suggestions.
We are trying to remove an aluminum shim .375 thick by 3” x 3” that is wedged between a 4340 metal Key block and a large roll mill. Question if we use sulfuric acid to eat the aluminum shim out, will it harm or erode the Steel encased on each side of the key.
 
  • #16
We are trying to remove an aluminum shim .375 thick by 3” x 3” that is wedged between a 4340 metal Key block and a large roll mill. Question if we use sulfuric acid to eat the aluminum shim out, will it harm or erode the Steel encased on each side of the key.
 
  • #17
Borek
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As told earlier - use basic solution instead of acid.
 
  • #18
What do you mean by basic solution
 
  • #19
Borek
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Basic as opposed to acidic. High pH. Caustic, alkalic.

--
 
  • #20
I am no chemist, what chemical do we use, be specific.

Thanks
 
  • #21
We ran a test shim; straight Hydrocloric acid removed .007 material in about 10 minutes very aggressive.
 
  • #22
chemisttree
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I've dissolved aluminum foil in methanol when I used a sonicator. That's as mild as it gets IMO. Anything that you do to dissolve the aluminum with either caustic or base will produce hydrogen gas. Is your steel part resistant to hydrogen embrittlement?

Have you tried either cooling or heating the part? Compare the CTE of both materials. Maybe you can cool the part and just remove the shim physically.

Edit. CTE of aluminum is about twice that of 4340. Try cooling it with dry ice or liquid N2 and physically removing it.
 
  • #23
Borek
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I am no chemist, what chemical do we use, be specific.
Sodium hydroxide.
 
  • #24
morrobay
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Sodium hydroxide does dissolve aluminum.
We used to make "gas" baloons by adding aluminum foil to a lye solution.
2H2O + 2NaOH +2Al ---> 2NaAlO2 + 3H2
 

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