Noalox for copper to aluminum wire joints 2

[moltenmetal]

Apparently this material is zinc powder in a polymer grease binder which is commonly used in copper to aluminum wire joints. Apparently the idea is to put a film of the compound on the aluminum part, then wire brush the part or wire to remove the aluminum oxide, leaving the grease to prevent the reformation of the oxide. Then, after the joint is made up, the grease binder keeps moisture and oxygen out of the joint.

I'm a little suspicious about the usefulness of the zinc. Zinc is modestly up the galvanic series from aluminum, so I guess the hope is that it will protect the aluminum in the same way as cold galvanizing paint protects steel. But those paints must be over 70 wt% zinc so the zinc particles are in electrical contact with one another to work, from what I've read, and the MSDS says Noalox is about 20% zinc.

As someone who feels he's at least fairly knowledgeable about galvanic corrosion, this has me legitimately puzzled. The corrosion products of both Zn and Al are nonconductive. Is the Noalox doing anything? And if you use enough to act as a real physical water and air barrier, the stuff is combustible- so it must be kept to a thin film only to be safe. Will that likely do any good?

As I have some posts on LiFePO4 batteries to bolt with copper straps and lugs which will see currents short term as high as 500A, and be used in a damp (not wet) location, I'm wondering about the advisability of using this stuff versus a non combustible non conductive grease used only on the exterior surface of the joint post assembly. Bolts, just to add a little more galvanic action, are 18/8 garden variety stainless steel.

 

[Compositepro]

There was a thread in one of the electrical forums about a year ago on this. A grease for this application cannot be electrically conductive or it would cause shorts if it got between terminals. So 70% loading would not be good. I guess the zinc would be a mildly corrosion inhibiting pigment in the grease. It would act like galvanizing in the small area where a zinc particle was in actual electrical contact with a metal surface. It would also tend to consume any acids, moisture, or oxygen that will slowly diffuse through the grease, prior to them attacking the aluminum. Any inhibition of corrosion on the aluminum surface at the electrical contact could result in significant improvements in longevity of the electrical contact.

 

[moltenmetal]

Compositepro, I did a search first and read what was there, but the responses were mostly from electrical people rather than people knowledgeable in corrosion specifically.

The product claims from the vendor (Ideal Inc.) indicate that it is conductive enough to provide meaningful filament to filament conduction in multistrand conductors at connection points, reducing the temperature of the junctions, i.e. some people are using it on finestrand copper conductors before crimping a lug or ferrule onto them. I've noted that their official literature (at least what I can find) makes no claims about its suitability for use on Al to copper transitions, though it is widely used and indeed inspectors look for it as an indication of good/knowledgeable workmanship in such transitions.

Your guess is about the same as mine- that the zinc may do something but probably not much, and the grease is doing most of the heavy lifting in this product. But I'm interested to hear from others what they think.

 

[TomDOT]

Even after oxidation, the zinc may do something. Zinc oxide can act as a moderate corrosion inhibitor.

However, the real way to do this is to put together a bunch of connections with and without the grease, put them in a slightly harsh environment and see what happens.

 

[CoryPad]

Tom,

As I understand it, zinc oxide and similar pigments used as corrosion inhibitors work for steel parts because they are basic and raise pH to a level where steel is more passive. Aluminium is less passive in basic conditions, and I am not sure how well zinc, aluminium and copper would work when coupled. I agree with you regarding the proper testing method.

 

[moltenmetal]

Unfortunately there's been no systematic testing that I can find references to- perhaps that would be a good question for the electrical folks on their forum as somebody there probably knows- but again I neither want to bump a thread over two years old nor post what is probably a boring repeat question to them, even though in my mind the past threads didn't really answer the question to my satisfaction...

 

[Compositepro]

Google "zinc dust for corrosion protection" and will you find your answer. It is as I and CoryPad said. Galvanic protection is a very minor effect unless the pigment concentration is very high. However, zinc still provides a great deal of protection by reacting with moisture and acids prior to them getting to the substrate and thus keeping the pH slightly alkaline. So the zinc maintains a more benign local environment for anything covered by the grease. Apparently this mechanism is not at all subtle or minor but quite important. The zinc is reactive, and thus can be called sacrificial, but not galvanic.
As for improving the conductivity of contact by filling the gap with conductive particles, I think that is plain wrong. Zinc particles squeezed in the contact area between two current carrying conductors would raise the contact resistance, not lower it.

 

[EdStainless]

Are these the connectors that also have abrasive in them to 'cut' the aluminum oxide film?
I am sorry, which part of your system is Al?
Are you sure that the Al will carry the current?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[moltenmetal]

EdStainless: indeed the datasheet says something to the effect of, "Zinc particles cut the aluminum oxide coating...". However, a warning on the bottle itself says, "Do not use abrasives or wire brush on terminals"- which implies that the wire brush/abrasion method of application is to be used only on aluminum conductors, presumably in case the aluminum terminals already have an anticorrosion coating or plating on them. I presume what they mean is that the zinc scratches the soft aluminum, carrying away the aluminum oxide microlayer with it. I don't think there are actual hard abrasives in the mix, but there may be.

The part that is aluminum is the positive post on a LiFePO4 battery, and yes it's good for the current- if it isn't corroded! The geometry is a flat faced cylindrical stub at the top of the cell with a female threaded hole in the centre of the flat face, to which a lug or strap is bolted using an 18/8 bolt. The - post is identical dimension but solid copper. The vendor doesn't specify so I'm asking my supplier whether the Al post is solid Al or plated/coated with something already. It looks like solid uncoated Al to my untrained eye, and filing a shallow notch in one post near the threaded hole indicates that the material is the same colour through its thickness.

The posts will be accessible for inspection but a bear to clean up and re-torque if they get corroded in service.

 

[moltenmetal]

OK, I'm convinced. Definitely using the antioxidant paste, but only on the + terminals for now, not on the copper to copper connections, as the stuff says nothing about use on Cu/Cu joints. I'll coat those with fluorocarbon grease post assembly.

 

[racookpe1978]

Many good points above, but none conclusive: It seems like the long-term study needs to start with basic Al-Al conductivity (clamped bare metal-bare metal) compared to Al-Cu conductivity 9clamped bare metal - bare metal) compared to Al-through grease with Zn particles inside grease clamped through more grease with Zn to Al, etc.

As pointed out, positive to negative anode/cathode cable side differences may be important on DC circuits, but AC is going to oscillate each cycle.

Surrounding chemicals and temperature, tightness of the actual clamp, etc.

And, of course, basic care in assembly of the circuit: A company and foreman and crew who have decided they need to use a connection grease are going to be more interested in protecting that circuit and will be usually taking more care of each assembly (proper torques, cleanliness of the contacts, length of the contacts, using proper screws and bolts and crimping "because" (as a symptom of their interest and care), they have chosen to add grease! So, over time, their connections are going to be better anyway.

A sloppy crew in a "don't care" facility (or a cheap assembly area not supervised) are going to get bad connections (on average) regardless of what grease they (don't) choose to use.

A commercial products "test" about corrosion on a connections grease is going to be testing the connections, right? So, again, it will likely be a "self-selected" test - The advertising department will not want to "test" bad or poorly-fit up and tightened connections.

 

[EdStainless]

I went back and dug out some info from a past life. We used both Al and Cu conductors at high current levels.
We never made Cu to Al joints, when we needed a transition we used explosively bonded transition pieces.
When we made Cu-Cu we always silver plated them.
With Al-Al we always used a paste product similar to yours.

The long term problem that we had was keeping joints tight.
We tried many things but were never fully satisfied.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[moltenmetal]

Thanks EdStainless- appreciate your excavation from your past life- this is a real experience-related thing since I see no evidence of systematic testing to rely on (well, I can't say I've looked THAT hard!).

Nordlock washers have been recommended to me by one of the EV guys, and my supplier of various EV parts says that these connections coming loose is a periodic worry for him too. Some people use Bellevilles on the connections.

 

[EdStainless]

We ended up using Bellevilles, and putting the check on a regular maintenance list.
We found that the washers got hot enough to relax at times.
We used Si Bronze bolts for the AL joints also, it was as close as we could get in thermal expansion.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube