[sazabi2001]

Hi:

I know nothing about chemistry untill I have this mass to deal with..

I have been building a water cooling system, the major body is made from Aluminium (unprotected) while some of the connectors are made from stainless steel and Nickel plated Brass.

I (now) know that Copper (Brass) plus Aluminium in electrolyte (water) results  electrochemical process, in others words Galvanic corrosion. I was hopping that the Nickel plated coating would help stopping the reaction but I was wrong. After a peroid of time the Nickel plate was gone and leave the copper exposed in the water.

The water of the system then became dirty with some gel like stuff inside, I suspect that is Aluminium hydroxide (Al OH₃). The worse thing is the some white power crystallized on the rubber sealings and damaged them. I eventually shut down and drain the system. When the system was fully dried out I found a lot of white powder inside the piping, also I think it's Aluminium hydroxide.

The question now is: Is there any quick easy way I can make sure it's Aluminium hydroxide, or at least identifly there is Aluminium someting in the powder.

I tried to burn the power in the fire to see the flame colour, maybe my gas cooker is not hot enough or it dosn't work with Aluminium hydroxide, I don't see the flame colour of Aluminium (white).


I read few webs and paper that when the Copper contact with water, they generate a little Cu²⁺, where:

Cu + H₂O = Cu²⁺ + OH^- +H₂

When the  Cu²⁺ full water contact with the Aluminium, it became:

Cu²⁺ + OH^- + Al = Al³⁺ + OH^- + Cu ,
Where the Al³⁺ + OH^- results Aluminium hydroxide (Al OH₃

Second question is: Dose this correct?

Also the Copper ions that exchanged the  Aluminium ions will grow Copper on the Aluminium surface which breaks the Aluminium oxide film and enhanced the reaction.

Anyway I'm going to change all possible Brass made part into Aluminium  or stainless steel.

The one last question is: Dose the 316 stainless steel (Cr of Fe) would do the same thing as what Copper dose to the Aluminium?

Many thanks

[Hunter2]

I would avoid aluminium parts in water systems. Aluminium is very innoble and can be dissolved like you described. Best is have everything made from same metal or have some plastic parts between as isolation.

[sazabi2001]

I would avoid aluminium parts in water systems. Aluminium is very innoble and can be dissolved like you described. Best is have everything made from same metal or have some plastic parts between as isolation.

Unable to avoid aluminium anyways.

1, The major part of the system is made in Aluminium, use of other material (Such as 316 stainless steel) would results seriously over-weight or over budgeted.

2, Will try to do anodizing on the Aluminium latter on.

[curiouscat]

Look up a corrossion series. Aluminium & Copper have ~0.55 V difference which almost guarantees Al will corrode badly over time.

With SS316 again, Al will be the one to corrode but things may be a bit better than with Copper. (0.3 V) Plain steel may fare a tad better.

Insulating washers are indeed an option. An impressed current or sacrificial anode may also work, but perhaps that's overkill.