Too much zinc? - SailNet Community
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post #1 of 25 Old 08-07-2012 Thread Starter
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Too much zinc?

A diver was telling me about a boat he worked on. The boat's prop was eaten away because the owner had installed a ridiculous amount of zink in the prop area. The diver explained that the only way that amount of zink could have been justified was in a very "hot" Marina. As I understand it, under normal conditions, the excessive volume of zinc makes the zink more noble than the prop. I found this interesting, as I was not aware you could install too much zinc. Few people I talk to know it either. Thoughts?

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post #2 of 25 Old 08-07-2012
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Re: Too much zinc?

A marina owner told me years ago that you could really put too much zinc on your boat. I could not understand and some years later I was thinking about it again and the only reasoning that I could come up with is the larger volume of zinc will offer protection over a wider area....so....maybe controlling this wider area may in fact lead to problems that you would not otherwise have with the smaller amount of zinc. FWIW
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post #3 of 25 Old 08-07-2012
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Yes, too much zinc is as bad as none.
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post #4 of 25 Old 08-07-2012
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Re: Too much zinc?

Zinc corrodes before bronze or stainless because of it's position on the galvanic scale. That position has nothing to do with the amount of zinc.

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post #5 of 25 Old 08-07-2012
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Re: Too much zinc?

On another boating forum I frequent, some guy came on once with the same premise that you can have too much zinc.
He had some mathmatical formulas/calculations to back up his claim...which all went way over my head....but he seemed to be pretty knowledgable on the subject and it seems that no one came forward to dispute his claim.

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post #6 of 25 Old 08-07-2012
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Re: Too much zinc?

I found this at http://freespace.virgin.net/roger.al...r/concept.htm: "There are several other problems, however, as too much current passing onto a steel surface can cause embrittlement, which under certain circumstances can be as detrimental as corrosion itself. This is manifest in such applications as the protection of the external surfaces of drill pipe casings, where a considerable amount of cathodic protection current is used."

The article is discussing galvanic coatings in steel pipes buried underground, but it appears that there might be issues associated with "over protection", i.e. using too much zinc. Who'd have thunk it?

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post #7 of 25 Old 08-07-2012
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Re: Too much zinc?

Until someone gives me reasoning that makes sense I am with SBS on this. The only way you can have "too much zinc" is if it weighed so much it sank your boat or cost so much you exhausted your cruising or beer or rum stash.

The reactions that occur are strictly a function of oxidation potential and the activity series for metals and have nothing to do with the amount of zinc or steel as long as there is enough zinc to react.
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post #8 of 25 Old 08-07-2012 Thread Starter
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Re: Too much zinc?

The link doesn't work for me. Can you fix it?
Quote:
Originally Posted by johnnyquest37 View Post
I found this at http://freespace.virgin.net/roger.al...r/concept.htm: "There are several other problems, however, as too much current passing onto a steel surface can cause embrittlement, which under certain circumstances can be as detrimental as corrosion itself. This is manifest in such applications as the protection of the external surfaces of drill pipe casings, where a considerable amount of cathodic protection current is used."
The article is discussing galvanic coatings in steel pipes buried underground, but it appears that there might be issues associated with "over protection", i.e. using too much zinc. Who'd have thunk it?
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post #9 of 25 Old 08-07-2012
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Re: Too much zinc?

Hi,
Unfortunately as an engineer that knows how to do mass balances, you can have too much zinc as proven by Le Chatelier's Principle,

proven in the 1600's and still valid today

Electrons are flowing away from the zinc equilibrium. According to Le Chatelier's Principle, the position of equilibrium will move to replace the lost electrons.

Electrons are being dumped onto the piece of brass in the brass/copper equilibrium. According to Le Chatelier's Principle, the position of equilibrium will move to remove these extra electrons.

Hope this explains it, in simple terms, the extra electrons have to go someplace.

R
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post #10 of 25 Old 08-08-2012 Thread Starter
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Re: Too much zinc?

Thanks! Searched the web for the theory and it seems it is from the 1800's. The best (most understandable for me) explanation I found is here Le Chatelier's Principle The introduction was especially helpful. It seems that the variable in the theroy that would apply to our example would be the "change of concentration"? (still digesting it!) Thanks again!
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Originally Posted by rackham the red View Post
Hi,
Unfortunately as an engineer that knows how to do mass balances, you can have too much zinc as proven by Le Chatelier's Principle,

proven in the 1600's and still valid today

Electrons are flowing away from the zinc equilibrium. According to Le Chatelier's Principle, the position of equilibrium will move to replace the lost electrons.

Electrons are being dumped onto the piece of brass in the brass/copper equilibrium. According to Le Chatelier's Principle, the position of equilibrium will move to remove these extra electrons.

Hope this explains it, in simple terms, the extra electrons have to go someplace.

R
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