In a Mixed Metal copper and Aluminum Loop, which is Oxidized and which is Reduced?

[Nanook]

Title states it all. It's more of just a curiosity question.

[CT854]

Maybe I'm just ignorant to how these kinds of loops work but, from a chemist's perspective, I'm not sure why you'd expect redox chemistry to happen in this kind of environment. I'm curious, what begs the question?

[rafe_28]

My very limited 8th geade chemistry tells me metals can only get reduced... or oxidized? Idk. The onr were u write a upper number with a plus to it in the Formula.

 

So like Al+³Cl3-¹ (i have no idea if that exists but i think u get the point

[For Science!]

Aluminium is oxidized, copper is reduced. Aluminium is the anode, and Copper is the cathode.

[CT854]

24 minutes ago, For Science! said:

Aluminium is oxidized, copper is reduced. Aluminium is the anode, and Copper is the cathode.

What actually does the redox chemistry in this situation? I'm curious to know.

[For Science!]

Just now, CT854 said:

What actually does the redox chemistry in this situation? I'm curious to know.

This is galvanic corrosion, in essence electrolytic degradation through the loss of electrons from the aluminium to the copper.

[CT854]

Just now, For Science! said:

This is galvanic corrosion, in essence electrolytic degradation through the loss of electrons from the aluminium to the copper.

Yeah, that makes sense. I was just wondering where the exact applied potential would be to do the redox but framing like this makes much more sense.

[Nanook]

1 minute ago, For Science! said:

This is galvanic corrosion, in essence electrolytic degradation through the loss of electrons from the aluminium to the copper.

Okay, so aluminum is oxidized by copper. I wonder if using a piece of zinc connected through a wire to say aluminum rads would serve as cathodic protection?

[For Science!]

Just now, Nanook said:

Okay, so aluminum is oxidized by copper. I wonder if using a piece of zinc connected through a wire to say aluminum rads would serve as cathodic protection?

Thermaltake aluminium radiators used to have a sacrificial coat of zinc, and it caused a lot of troubles with coolant compatibility. If its external to the loop, it will not provide protection as the path of least resistance will still be Copper --> Aluminium, you then have another local circuit of Aluminium --> Zinc, so you just have two problems instead of one.

[Nanook]

8 minutes ago, For Science! said:

Thermaltake aluminium radiators used to have a sacrificial coat of zinc, and it caused a lot of troubles with coolant compatibility. If its external to the loop, it will not provide protection as the path of least resistance will still be Copper --> Aluminium, you then have another local circuit of Aluminium --> Zinc, so you just have two problems instead of one.

I want thinking about soldering a copper wire to my aluminum rad on one end. Then just a little pill capsule of elemental zinc connected to the wire on the other end, or maybe a solution of zinc and salt. Then just secure the pill capsule on the underside of a desk out of sight. Any copper oxidizing the aluminum will be replaced by the aluminum oxidizing the zinc. At least that how it should work in theory and how it does actually work on major underground oil and gas pipelines.

[Nanook]

24 minutes ago, CT854 said:

What actually does the redox chemistry in this situation? I'm curious to know.

Al + Cu(+1) -> Al(+1) + Cu

[For Science!]

10 minutes ago, Nanook said:

I want thinking about soldering a copper wire to my aluminum rad on one end. Then just a little pill capsule of elemental zinc connected to the wire on the other end, or maybe a solution of zinc and salt. Then just secure the pill capsule on the underside of a desk out of sight. Any copper oxidizing the aluminum will be replaced by the aluminum oxidizing the zinc. At least that how it should work in theory and how it does actually work on major underground oil and gas pipelines.

This will not work, but honestly why go through the hassle when you can just use anti-corrosives in the coolant that actually work.

[Nanook]

Just now, For Science! said:

This will not work, but honestly why go through the hassle when you can just use anti-corrosives in the coolant that actually work.

Because cool! This is exotic cooling after all right? I know cathodic protection like that I said in the post above does work in real life on other things. Not sure about a computer water loop though. The principles remain the same I think.

[For Science!]

7 minutes ago, Nanook said:

Because cool! This is exotic cooling after all right? I know cathodic protection like that I said in the post above does work in real life on other things. Not sure about a computer water loop though. The principles remain the same I think.

As you wish, putting together your previous post about trying to justify the alumium as a superior material over copper, I think you're trying to overcomplicate your justification for using it. This is not galvanic corrosion through physical contact, its through an electrolyte medium.

[IainC]

Short answer- the copper will eat the aluminium. Given the latter is (relatively) cheap, just replace when you start to see goo accumulating in your block. A sacrificial cathode will just add more goo more quickly  ... but will protect your components. Custom loops are, for me, about best performance, so gumming up your blocks is more of an issue than stripping ions from components. Just my $0.02 mind