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Why is there a voltage when water freezes?

  1. Jan 1, 2013 #1
    Hi, I'm doing an experiment, where I'm freezing water, and I'm measuring the voltage of the water as it is freezing. For some time there is not much of voltage detected, but all of a sudden there is some voltage detected, and it fluctuates from positive to negative voltage, and back to positive. I tried to do some research but couldn't find much. Do you know why this might be happening?
     
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  3. Jan 1, 2013 #2

    phinds

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    What are you talking about? What is "the voltage of water" ???
     
  4. Jan 1, 2013 #3

    K^2

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    Fractures in ice can, indeed, induce voltage, and ice may be fracturing as it freezes. That would be my first guess.

    Another possibility is galvanic reactions, but you can exclude these by making sure your probes/electrodes are made from the same material.
     
  5. Jan 1, 2013 #4
    The only voltage associated with water I can think of is electricity in a thunderstorm.

    If changing the state of water created electricity...WOW, an endless supply of power!!

    sounds like a meter issue, not a water issue.

    edit: fractures in ice induce voltage???
    Any reference you can suggest??
     
  6. Jan 1, 2013 #5

    K^2

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  7. Jan 1, 2013 #6
    You should tell us how exactly you did that measurement.
    Did you just take a multimeter, put the two probes into a cup filled with water and placed it in the freezer? Was the water pure? How high was the voltage? For how long did you measure a voltage? Does it happen shortly after the water freezes or before?
     
  8. Jan 1, 2013 #7
    What I'm saying is I put a voltmeter in the freezing water, used a Vernier Labquest to graph the change in voltage, and what I found from the graph was that the voltage was changing and went as high as 0.400 V and down to -0.200 V.
     
  9. Jan 1, 2013 #8
    I'm going to look into the galvanic reactions because I'm using a wire which is in the water and attaching that to a probe, and both the wire and the probe are in the water.

    Could you please elaborate on what fractures in ice means?
     
  10. Jan 1, 2013 #9
    I used tap water for this experiment. I used a cable that has two ends to measure the voltage difference and put it inside the cup of water. The cable was attached to a LabQuest, and I graphed the change in voltage over time as the water froze. I voltage went up to 0.400 V and down to -0.200 V. I attached a screenshot of the graph.
     

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  11. Jan 2, 2013 #10

    NascentOxygen

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    So you had 2 pairs of stranded copper conductor immersed, to act as the probes? I think you had more than that immersed, too — how did you measure water temperature? Was it totally enclosed in plastic?
     
  12. Jan 2, 2013 #11
    After skimming the article posted by K2 I'd GUESS there is well less than a one percent chance fractures in this case are the explanation.
    [See "lab tests" section and decide for yourself.]

    It appears that in lab settings, one must cause a temperature differential to the ice sample, apply a test wave and view it's characteristics, perhaps dope the ice, use of single crystalline samples [not sure what that is] and perhaps special detection setups like an electrode consisting 'of a massive copper substrate' to detect ANY voltage.

    As an aside, galvanic reactions induced by typical probe metals in FRESH water would not
    induce the magnitude of voltages reported here. One needs some ions, charged particles, to carry the current in water....even in sea water, those reported voltages seem high.

    But in using, say, copper and zinc in sea water, an induced galvanic voltage of 900 mv..0.9... volts is typical: that's how zincs are used in cathodic protection. Those two metals are near opposite ends of the
    of the metal NOBEL chart. An easy way to eliminate this effect is to dip two pieces of identical copper wire in the water as test probes....
     
    Last edited: Jan 2, 2013
  13. Jan 2, 2013 #12
    I used a temperature probe as well. The water was in a Styrofoam cup.
     
  14. Jan 2, 2013 #13

    NascentOxygen

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    I was hinting there may be galvanic action between the different metals in the different probes. Try leaving out the temp probe.
     
  15. Jan 2, 2013 #14
    I tried that out yesterday. I just put the wires in, and left the temp probe out, but I still detected a similar voltage.
     
  16. Jan 2, 2013 #15
    The voltage in a galvanic reaction is mostly independent of
    the salt concentration. There is not much difference between salt and fresh water - which by the way also contains some ions. You will measure about the same voltage as long as your voltmeter has a sufficiently high impedance.
     
  17. Jan 2, 2013 #16

    K^2

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    This is really crazy. I'm going to try and see if I can reproduce the results using distilled water closer to the beginning of next semester. I should be able to get a bit more control over what's going on over at the physics lab at uni.
     
  18. Jan 2, 2013 #17
    A standard method for testing induced voltages in salt water, that is stray currents,
    is to place identical strips of copper maybe 50 to 100 feet apart and measure the induced voltage....I have done that over the years in connection with corrosion testing and found multiple tenths of a volt....maybe even slightly over 1 volt. When those identical probes are placed in salt water side by side, close together, no voltage is measured.

    And when rotating the probes 90 degrees, still 50-100 apart, it is easy to get variations in voltage readings between the two orientations.....and point in a general direction of the source if water flow is not significant.

    This is the basic start of isolating underwater corrosion problems in boats: there are only three possible explanations...dissimilar metals, external voltage/current leaks [as in the water or coming aboard shore power ground] and internal [aboard the boat] voltage/current leaks. Especially DC leaks.

    This is using a standard volt ohmmeter, probably 20,000 ohms/volt....nothing special.

    PS: current flow in fresh water is typically much less than salt water...fewer ions...and so a more active metal is used for cathodic protection.
     
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