Zinc spray and aluminum anodes?

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Gregory S

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Several of us have begun using aluminum anodes instead of zinc. As all anodes should be the same, if I use zinc spray ( Barnacle Buster) on all the running gear and water intake, do I now have dissimilar anodes?
 
Don't know GeeBee. I've been using Rustoleum cold galvanizing spray. Not Barnacle buster but Barnacle Barrier. I'm asking because the zinc spray didn't last very long as it has in years past. The only difference was I switched to Aluminum anodes.
 
The makers web site will have a materials data sheet listing the ingredieants.
 
quote:
Originally posted by Gregory S

Don't know GeeBee. I've been using Rustoleum cold galvanizing spray.

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I use that too, get it at Home Depot.
It works great!
 
The Rustoleum and Pettit zinc formulations are the same. I don't know about any other brand and any other brand would argue that their's is better.
 
I suspect that there are a lot of experts on this topic in your organization :D
 
An article referenced over at The SOC site does in fact state that zinc paint will act as an anode. So, maybe we are doing the wrong thing by using Aluminum for sacrificial anodes and painting running gear and water intakes with zinc?
 
Greg: They both have galvanic half cell potential.
It has been a long time since I thought about any of this but IMO they both will be sacrificed one faster than the other depending on many factors including distance from the other metal.
I think of it as two batteries of slightly different voltage connected to the same load. The one with the higher voltage will supply more current to the load and even try to supply current to the other lover voltage anode. We are talking tenths of a volt.
I don't think you have anything to worry about.

Zn is -1.25V while AL is -.95. Brass or bronze is
-.45 stainless steel -.6

You can see that ZN is preferred because of its higher potential.

Why would you switch from ZN?
 
Thanks Bruce, Everything I've read about aluminum anodes says they are more electrically active than zinc and are preferred for salt or brackish water over zinc. Apparently the Coast Guard and the Navy are required to use aluminum instead of zinc but I think that is for environmental reasons.
 
More active? I don't understand how they can conclude that.
note: I added the missing - sign to correct the AL potential
 
If you go to www.boatzincs .com and read about aluminum anodes, you will see that they say that. Supposed to be better than zinc in salt and or brackish water. Also significantly cheaper too, and supposed to last longer.
 
I'll check it later but lasting longer would hint to me that they weren't working as well as the half cell voltage would indicate.
But my electro chemistry studies are now ancient and dim.
 
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