woelen
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Electrolysis with high voltage and plasma "electrode"
I have done a funny experiment, where I did electrolysis of a salt solution with a copper wire as cathode, and a small plasma beam as anode. This is
really neat, I already posted it on SFN, but I also want to share it with you over here:
http://woelen.scheikunde.net/science/chem/exps/HV_electrolys...
I also have a question. At one of the experiments, the plasma beam is split in a blue/purple part, and an orange part, with nothing visible inbetween.
Can someone explain this phenomenon to me? I find this a really peculiar effect. On the webpage you can see a picture of this.
In the meantime I also did the experiment with a plasma cathode and an anode made of a wire. The result then is similar, except that the anode is
corroded slowly, and the plasma beam of the cathode is weaker under the same conditions, and the color of the beam is different. The cathode beam is
red/purple, while the anode beam is blue/purple.
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12AX7
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I would say the ion bombardment is causing the solution to boil, thus pushing sodium chloride into the discharge, which easily breaks into Cl- and
Na+, or other species (Cl(0) at the very least, and probably Cl+ as well; Cl(+2) seems less likely compared to other reactions such as H2O > H +
OH, O2 > 2O, etc.).
I don't have any explanation for the dark band in certain discharges. At a whopping 1 atm, there should be pretty of ion-fodder to knock the snot out
of, inbetween the ends of the discharge.
About the bubbles, are you certain they aren't from gas dissolved in the water? I would be interested to know if it also occurs with boiled salt
water.
Incidentially, most of the current is carried by electrons. There are certainly ions present, and ions which recombine at the cathode, but being over
a thousand times more massive than an electron, the ions move much slower through the electric field.
Tim
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Fluorite
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Wait! Can I electrolyse anything? chlorate, sulfate, perchlorate.. without corrosion? Cause the electrodes aren't submerged in the liquid?
Ugh but the arc is lethal
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Vomaturge
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My guess, with the dark band, is that it is actually slightly luminous and it's just overshadowed by the brighter parts. I'm not sure why it's so
bright blue right next to the wire, but, yes, I think the yellow color next to the liquid surface is probably due to a little sodium getting airborne.
Just like a flame test.
@Fluorite, I don't think you can really electrolyze a solution with this. We're only getting a few milliamps of current flow, electrolysis takes hours
at a few whole amps. If we used a very high power high voltage source of, say, 4000v and 1a, the electrolysis would be very slow, and only a few volts
would be across the solution. The rest would just create a hot arc that would melt the anode and boil the solution dry in minutes or even seconds.
I now have a YouTube channel. So far just electronics and basic High Voltage experimentation, but I'll hopefully have some chemistry videos soon. |
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Bezaleel
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Sorry, but for me the link does not lead me to the page. Instead, I am redirected to scheikunde.net, where I cannot find a link to your section.
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symboom
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I'm guessing woelen doesn't own that website anymore which he posted the link in 2006.
[Edited on 29-11-2020 by symboom]
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Metacelsus
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Try this link: https://woelen.homescience.net/science/chem/exps/HV_electrol...
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macckone
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Fluorite,
High voltage discharge tends to eat electrodes pretty quickly.
See Electrical Discharge Machining.
The electrode is literally a wire feed.
But it uses a lower voltage than what woelen used.
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woelen
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The setup, described in this experiment, absolutely has not any practical uses. As already mentioned, the current flow is very low, milliamperes at
most. Production of useful stuff in electrolysis cells is proportional to current and not to voltage. High voltage means high loss of energy. Redox
potentials are in the order of magnitude of 0.5 ... 2.5 volts for any practical reaction. Add a few tenths of volts for conversion to gas at the
electrodes (e.g. formation of H2) and for so-called overpotential and you end up with a total voltage of the chain in the order of magnitude of 3 ...
4 V. You also may add several tenths of volts (maybe 1 V) for ohmic resistance losses in the liquid between the electrodes and with that the total
voltage over the cell will be somewhere between 4 and 5 volt. A practical cell works perfectly fine at 5 volts and can consume quite a lot of current
and even at that low voltage quite a lot of heat can be produced.
Voltages of 10000 V or so are fun and completely different physical and chemical effects can be observed at that kinds of voltages, hence the
inclusion of this (dangerous) experiment. Actually, I quit doing that kind of experiments after an accident with an explosion, in which drops of water
were sprayed around so violently, that I had little holes in my skin. My wife does not want me to do any HV-experiments anymore and the last time I
did things with that is a few years ago. She has no objection at all to all my chemistry experiments, but the HV-experiments are too much of a risk.
@fluorite: Corrosion in this HV-experiment actually is intense. The anode is eaten away at a very high rate. The plasma has a very high temperature
and the extremely high voltages cause ionic degradation of the material of the anode. Most likely metal ions are blown away from the anode and I'm
quite sure that the ionic wind from the anode contains metal ions.
[Edited on 29-11-20 by woelen]
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