Revelations about zinc electrodes.

Discussion in 'Boat Design' started by CDK, Jan 7, 2011.

  1. BertKu
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    BertKu Senior Member

    O.K. thus those engineers of this website believe that the extra electrons, which get added to the zinc material forms the corrosion.( if the zinc is the anode, because any electronic person will confirm that electrons will flow from lower potential to higher potential) Now we have a new theory contradicting Einstein.
    Bert
     
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  2. gonzo
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    gonzo Senior Member

    Michael: Which of the lists you claim is correct? You posted two with metals in different order.
     
  3. viking north
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    viking north VINLAND

    The way it see it and it conforms with basic electrical theory which we all studied prior to advancing onto electronics, technicions, technologists, and finally engineer is electrons are looked upon as particles(part of) and flow from the more neg(least pos.) or cathode acting to the least neg.(more pos.) anode acting(plate, collector,). Thus the cathode or zinc becomes depleted much in the same way old vacuum tubes cathodes became weak emitting over time. Thats my story and i'm sticking to it, and now i have to put the snow tires on the car, as we are having our first snow here in Halifax, Nova Scotia, Certified Electronic Engineering Technicion, Geo.
     
  4. gonzo
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    gonzo Senior Member

    It is important to remember that the positive pole on an electrical circuit has a negative charge. That is where the charge(electrons) are accumulated.
     
  5. viking north
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    viking north VINLAND

    Gonzo, welcome to my world, this time i have to say you are wrong, The key word here is as you have used,"circuit" no electrons gather at the positive pole as it is part of a closed circuit othewise no electron flow takes place. The pos. pole, (anode, plate, collector is just a physical location for the sake of convenience to explain a circuits operation. From this pos. pole(anode,plate,collector) the electrons do not really accumilate but are merely attraced and from there move on thru the circuit back to their source. Geo.
     
  6. BertKu
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    BertKu Senior Member

    Folks, we all have a car, or most of us. We all have wondered why the plus of the battery got sometimes that white substance. You see, you see, Bert you are wrong. It is the plus which is oxidizing, therefore the anode must be the zinc. Sorry guys, wrong. You forgot that the voltage regulator is 14,4 Volt and therefore the plus pole of the battery becomes negative towards the higher regulator voltage. Hereby given the proof, that the zinc has to be the cathode and cannot be the anode. (sorry to illustrate it in a simple form, whereby we all can visualize the reasoning)

    Bert
     
  7. CDK
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    CDK retired engineer

    There is even a poster here who still believed the world was flat, but with help from Google and cut&paste he is an expert in every field now.
     
  8. viking north
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    viking north VINLAND

    Ok enought of this babble, First we have to determine if the zinc is acting as a battery with salt water as the electrolite and apparently the concensis is that is the case. So now we have to get into the internal operational theory of a battery which involves another factor the chemical reaction. The other discussion that is happening here is the external operation of circuits, external to the battery where there is no chemical action involved thus a slightly different take on what occurs. Two more factors play a role, are we working with AC or DC. In the case of zincs depleting we could be working with one or both within the hull or with the external stray electrical energy. It is not as simple as it seems as believe it or not the zinc hull external circuit could actually be rectify the AC into pulsating DC(solid state theory). So maybe we're all right, the important thing is Zincs seem to work as long as they deplete. Be interesting to play around with studying if they are as equally effictive against AC, DC or Pulsating DC. Just kidding, Geo.
     
  9. gonzo
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    gonzo Senior Member

    Flow, according to electric theory, can be calculated in two ways. The electrons flow from the positive to the negative, or holes flow from the negative to the positive. The only difference is on a plus or minus sign in the formula.
    Viking, yes you are correct, the electrons are not accumulated at the pole. It was not the most technically correct statement ;)
     
  10. MikeJohns
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    MikeJohns Senior Member

    Cornelius et al

    Confusion about Anode and Cathode abound. Sometimes it's not obviously apparent which is which depending on your frame of reference and your adopted definition.

    In an electrochemical cell, such as a galvanic cell in seawater, the electrodes are defined by the reactions that occur at the electrode.

    I said before the key is to consider where the Cations are reduced. This is by definition the Cathode, the oxidation reaction is always at the anode.

    People from all walks of life get very confused and hung up on misleading definitions of Anode and Cathode, particularly the Electrical fraternity ;).

    Consider a rechargeable battery and try and define the electrodes in terms of current flow !
    Consider an electronic component and try and define its leads in terms of polarity across the device ! What I'm trying to say is that one simple definition doesn't hold. There are convenient frames of adopted reference but they are not definitive.

    However it is definitive that in an electrochemical cell you consider the oxidation and reduction reactions to define your Anode and Cathode.

    This even works with the rechargeable battery, Anions are oxidised at the Anode when anions are being produced and Cations are reduced at the cathode when cations are being produced.

    As we saw above all of this is made even more confusing by the adopted convention of the electrical fraternity that talk of current as the movement of holes (which they understand implicitly) but contrary to the actual movement of electrons.

    So Cornelius is arguing from an adopted Electrical perspective but he's falling into a common trap. IMHO
     
  11. gonzo
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    gonzo Senior Member

    The hole thing takes some effort to get your head around.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    Sure does...ive read loads of books on this, none 100% clear..but all saying roughly the same thing.

    But, to confuse matters further, corrosion is correctly interpreted by the pH of the solution. Since what is going on was first discovered by Nerst, when he found that copper in copper sulphate solution becomes positive whilst zinc in zinc sulphate solution becomes negative. The Nerst equation basically represents the corrosion behaviour of metals in aqueous solutions in terms of pH and the potential E and thus leading to the formation of the Pourbaix diagrams. And if that wasn’t enough, these diagrams only provide information on reactions that can occur, not necessarily on reactions that will occur. Which then leads back to polarization and overvoltage and gives us the relationship between the current and the electrode potential. The degree of polarisation is a measure of how the rates of the anodic and the cathodic reactions are retarded by various environmental and/or surface process factors.
     
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  13. BertKu
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    BertKu Senior Member

    This is vry much true.

    Can I add some more confusion to this issue, by stating, that I have charged some hunderds of SLABs and was very puzzled why the negative terminal of the battery often got oxidized with white powder and not the plus terminal. I could only conclude that it has to do with the crocodile clips (different material) , together with the salt in the air (close to the coast) My conclusion is that one has to be damn carefull what kind of bolts to use when mounting the zinc. I am not buying AC, Viking North, otherwise both, also the noble material maybe oxidised. The hole theory is another story. When the electrons are removed of the outer ring, yes a hole exsist, but the hole is not moving. The electrons does.
    Bert
     
  14. Wynand N
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    Wynand N Retired Steelboatbuilder

    I just have to chime in and will then slide back into the obscurity of retirement;)

    To keep busy Im running a small electroplating business from home and do electro zink, nickle, tin, copper, chrome and gold plating and of course aluminum oxidizing - plain, colors et all.

    The principle of electrolysis is used for plating where an anode (positively charged) and a cathode (negatively charged) is placed in an electrolyte (in boating world, sea water).
    Positive ions flow from the anode toward the object being plated (cathode), through the plating solution (the electrolyte), and
    are deposited onto the surface of the object. The longer the system is left on, the thicker the resulting plating will be.
    Regardless of the size of object plated the voltage used is only 3 - 5VDC max (sometimes less with copper plating) although current is adjusted as needed.

    IOW, not a lot of electric flow is needed to start the electrolysis process and the nearer the cathode is to the anode, the higher the current drawn is gonna be. (same principle as old liquid controller rheostats).
    So it makes sense to place anodes as close as possible to the more noble material such as the SS prop shaft, brass propeller etc to be efficient. That said, the positively charged zink ions of the sacrificial anode did not disappeared in the seawater, but is deposited on the nearest cathode say for instance the brass prop...


    As AdHoc pointed out, aluminum should be mentioned as well.

    Anodising is an electrochemical process that thickens and toughens the naturally occurring protective oxide layer in aluminium (on surface). The
    resulting finish, depending on the process, is the second hardest substance known to man, second only to the diamond. The anodic coating is part of the metal, but has a porous structure that allows secondary infusions (organic and inorganic coloring, etc.)

    Basically the process is reversed from the "normal" electrolysis process whereas the aluminum to be anodized become the anode (positive) and a negative charged electrode is put in the electrolyte and the current releases hydrogen at negatively charged electrode and oxygen forms on the surface of the positively charged aluminum (anode) creating a buildup of aluminum oxide - basically speeding up the natural oxidizing process that makes ally durable and controlling the thickness thereof.
    Although different electrolytes are used, the most common is a water and sulfuric acid mix and the voltage used much higher than normal electrolysis at about 19VDC.
     
    Last edited: Jan 10, 2011

  15. BertKu
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    BertKu Senior Member

    You know guys, this story reminds me to the new vacuum cleaner I bought some time ago. Until my wife asked me. Please may I have the HOOVER" What hoover I never bought a hoover , I bought a cheap China one.

    But it is so ingraved in peoples mind, that we still call a vacuum cleaner a hoover.

    So again, we still call the zinc anodic, while actual it is the cathode.
    Bert
     
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