Zinc again

There are gaping holes in my knowledge of the world. History is probably the biggest and the most important. In the course of human existence, many, many important things happen about which I know nothing at all. A bunch of other things happened, about which I know a paltry little. There are only a few historical events about which I can claim even a cocktail-party level of expertise.

I read a bit about the French Revolution, and can join that large cadre of people who thank Simon Schama for making them sound reasonably well-educated on that subject. I know a bit about the reign of Queen Victoria, since I’ve spent an unconscionable amount of time reading every single novel written during it. I’m sorry to say that my understanding of ancient Greece comes primarily from Mary Renault, and ancient Rome, from Robert Graves. About the history of that part of the world known as ‘Asia,’ I know nothing whatsoever, until you get to Mao, with whom I have a macabre fascination.

I do better with literature. I’ve read most of the notable stuff written in English, but don’t do as well with the French or the Russians. And, of course, about the literature of that part of the world known as ‘Asia,’ I know nothing whatsoever. My excuse: I don’t like reading in translation. Since I’m a pathetic monoglot, that limits me to the notable stuff written in English.

Math and science, I’m at least conversant. Numbers speak to me – they always have – so I have a good shot at understanding statistics and calculations. And I often find that I know just enough science to ask the people who know a great deal of science the right questions – that’ll take you a long way in this world, I’ve found.

There is, however, one scientific phenomenon that might as well be black magic, for all I understand about it. I just don’t get electricity. It’s that really cool stuff that comes out of the walls, that keeps the lights on and the refrigerator running, and that can kill you if you touch the wrong two wires. It has to do with sub-atomic particles going from one place to another, but how that translates to actual power is a mystery to me.

Which is why I cannot, for the life of me, give you an adequate explanation of a sacrificial zinc anode. This is unfortunate, because sacrificial zinc anodes are pretty interesting, and we should all understand them.

Although they’ve certainly been mentioned in my earshot, both by Kevin and by Billy, our boat mechanic, before today, today was the first time I paid any attention to them. I did this because I found Kevin lying on a tarp under the boat motor, wrench in hand.

“Whatcha doing, honey?”

“Replacing the sacrificial zinc anodes.”

Because I had hazy memories of sacrificial zinc anodes being mentioned, I was a little embarrassed to admit I had not the foggiest idea of what they were and what they did. So I left Kevin lying on his tarp, and went inside to Google them.

There are several cogent explanations, but none is comprehensive enough to compensate for my complete lack of electrical expertise. Those of you with both expertise and interest can go over and read this explanation. Those of you with neither may be content with my rudimentary, incomplete, and possibly incorrect explanation.

When you submerge metals in salt water, you make a battery of sorts. The salt water either is an electrolyte or contains electrolytes, I’m not sure which, but, in either case, it is a conductor of electricity. Electricity is, apparently, made up of electrons, and those electrons come from one of the metals. Losing your electrons, if you’re a metal, is not a good thing. You corrode. Metals differ in their willingness to give up their electrons, and it is the most willing which will corrode.

Boat engines have metal. Generally, several kinds. Unless you take corrective action, one of those metals – the most willing – will corrode in sea water. The way you prevent that is to take a metal that is even more willing — in this case, zinc — and attach a chunk of it to your engine. Its job is to corrode so that the other metals don’t. When it reduces down to about half its original size, you spread a tarp under your motor, get out your wrench, and replace it. Or you do nothing at all, and simply assume your husband will take care of it.

All this has made me think it’s high time I made an effort to understand electricity. Can anyone recommend a book? I’ll get to it just as soon as I finish The Brothers Karamazov.

23 people are having a conversation about “Zinc again

  1. “The way you prevent that is to take a metal that is even less willing — in this case, zinc'”
    Should read “even more willing”.
    Because of it’s sacrificial nature the zinc is more than happy to corrode it’s life away for the Stainless, Bronze and Aluminum.

    • Sorry, didn’t mean to be nit-picky. I work on boats and when I lived out west I used to perform corrosion surveys on steel Alaskan seiners.
      Galvanic corrosion is something I know a lot about.
      And it is hard to explain! One part chemistry, two parts physics and three parts black arts.
      Love the blog!

      • Nit picky? Please! From here on in, I’ll ask you to proof-read everything — even things that have nothing to do with galvanic corrosion, which you could obviously explain much better than I did! I did mean “more willing,” of course, and have made the change. Thanks!

  2. Ben Franklin posited that electricity flowed from a source to a “sink”, something that attracts and holds electrons. Only, Ben thought that electrons were positive. Knowing what we do now, our electricity flows from an electron donor (Cathode, negative or “-“) to a receptor (Anode, positive or “+”). Silly Ben. The way I think of it, was Cathode Ray Tubes spewed electrons from the cathode to the anode. Like old-time televisions. Back before LCDs, or even I Love Lucy.

    Put two dissimilar metals in an electrolyte, and you have a battery. The chemistry involves lots of ions. An ion is an atom with more electrons or fewer than it has protons, ions are usually more chemically “active” and likely to clump up into molecules of stuff other than the initial metal, in the case of a battery.

    You almost never encounter water pure enough not to act as an electrolyte. So any metal in the water is likely to be acting as a battery with *something*. When the zinc acts as an anode, the metal quickly ionizes a bit, and the water responds by forming hydrogen and oxide ions — which combine with the now-ionized zinc and form zinc oxides, which we often call “corrosion”. Mostly the zinc is still there, but it is now a salt and inert, and no longer acting as a metal ready to preempt the “act as a battery” invitation of that promiscuous water electrolyte.

    Incidentally, agitating the electrolyte, by, say, moving an electrode (an electrode is either a cathode or anode, without labeling which is which) through the electrolyte, will increase the flow of electrons. Like when you move a boat through water.

    At least, that is how I think of it.

    • Brad — Thanks for that explanation. So the zinc isn’t donating its electrons? It’s receiving them? Then why aren’t the stainless steel and aluminum (presumably, the cathodes, or donors) corroding?

      Damn. This is complicated.

      • Tamar,

        I am sure that if you are engineering a solution to a system problem, or describing the chemistry, that the sordid details matter. What I am sure of, is that either giving up an electron or gaining an extra will cause energy changes, and we call the result an ion. And ions are prone to combine in fascinating ways. When we say the zinc corrodes, what happens can be described as some of the zinc metal becoming an ion of zinc (unbalanced proton/electron charge) and forming, typically when we call it corrosion, an oxide where an extra oxygen atom is added to form a molecule where a couple ions had been. Thus, the zinc oxide on the surface of what had been mostly pure zinc.

        Zinc, like magnesium, forms ions fairly readily, while steel and aluminum have much more stable electron arrangements. They will conduct electricity, but it is tough to form an ion from them. And zinc, unlike magnesium, doesn’t contribute to a special class fire. While magnesium fires are rare (outside magnesium flares), they don’t respond well to water. Zinc is just a commercially viable, reasonably safe compromise that seems to work.

        • I can feel enlightenment dawning, but only just. Thanks for the explanation — it’s tapping into some hazy memories of learning something about this.

          I certainly know more about it than I did three days ago, and that’s progress in my book.

  3. Accidental Mick says:

    It is quite simple really.

    Whenever you go to sea, Poseidon charges a toll. What he likes most of all is zinc and if you let him have some he doesn’t take anything else off of your boat.

  4. Tamar, your wonderful mind has once again shared the incredible complexity of our world, and how we all struggle with knowing enough to “get by!” I salute your admission of imperfection, and admit to the same perplexion with electricity. However, my spouse is also ignorant of the subject, so I imagine the candle-lit post-apocalyptic world can’t come quick enough for my ego’s sense of self-worth. As I know how to garden, fish, build primitive wooden structures, and hunt the few remaining Undomesticated species, I’ll be able to survive, and be On my way to being a tribal warlord. You think about running for office?

  5. Mick — Finally! *Now* I get it. (That made me laugh out loud, which I always appreciate.)

    Richard — If I were reluctant to admit imperfections, I’d have nothing to write about. But, even if you’re not so up on electricity, you’ve definitely got me beat in (at least) the hunting and gardening department. I’m getting better at fishing and my skills in the primitive wooden structures area are entirely dependent on what what you mean by primitive.

    Post-apocalypse, I won’t be running for office, and I’m afraid I won’t be able to support your warlord candidacy either, because I fully intend to go down with the ship.

  6. What I want to know is, how did Kevin know?

    Or is it just a side effect of his general genius? Probably Bob told him. But then how did Bob know?

    Somebody must have told him. This is starting to sound more and more like tribal knowledge.

    I suspect that Mick has been right all along.

    • Everything is tribal knowledge. In this case, the tribe of boaters. While I’m sure Bob knows all about these things, Kevin actually found out about them from Billy, or his sister Cindy, who are, together, Anchor Marine. They service our engines and, sometimes, amuse themselves at our expense. One day we were in there, and Billy was explaining something to us, and I said something along the lines of “There are so many things that can go wrong.” Billy nodded sagely and said, “It’s usually the little nut behind the wheel.”

  7. My husband says Poseidon likes magnesium even better than zinc. He has been an electrician for 30+ years so I am guessing he would know. He got a chuckle out of Mick’s explanation. As I understand it, the less noble metal gets eaten by the more noble metals. My guess is that it is a feudalism kind of thing, courtesy of the periodic table of elephants. Or elements. Depending on how much brandy was imbibed after dinner.

    • Jean, I saw your comment when I wasn’t fully caffeinated, and postponed answering it. And then promptly forget to tell you that you, as well as Mick, made me laugh out loud. That’s my kind of explanation — nobility will out.

      • Accidental Mick says:

        The idea of a periodic table of elephants will keep me warm on long winter nights.

        I’m picturing something the size of a pigmy shrew at the start going up to a woolly mammoth through 164 stages (or however many there are these days.

  8. ha! electricity is a mystery to me as well, and I confess I still don’t feel very enlightened, even after the very good explanations just provided. I guess I feel like James Thurber’s grandmother who “lived the latter years of her life in the horrible suspicion that electricity was dripping invisibly all over the house” (James Thurber, My Life and Hard Times, 1933).

  9. I like Mick’s explanation the best! It’s such an accurate reflection of the mixture of science and superstition that permeates sailing. My boyfriend is a diver and aside from scrubbing away barnacles and seaweed (I have tried, to no avail, to convince him to put “If you need your bottom scrubbed, I’m your man!” on his card) he replaces zincs. Underwater, in the murky San Francisco bay. Sometimes the zinc, or the screwdriver, falls out of his hands and he has to dive down and search for it on the bottom. Good times. Anyway, remind Kevin to tighten the zinc screws periodically throughout the season as the zinc corrodes away- it’ll prevent extra wear and tear and make it last a little longer.

    • An actual constructive suggestion! Jocelyn, you get extra points for that. Our best regards to your diving boyfriend!

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