Cou
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Castner Process
Though the castner process has been successfully carried out in a stainless steel crucible: https://www.youtube.com/watch?v=RJ21jQiOv2E
The problem is that, as I've tried it, the molten NaOH appears to react with the stainless steel to form an iron compound gunk, which stains the NaOH
red and creates bubbling in the process when it gets above melting temperature. And I don't like how this might affect the purity of the resulting
sodium created at the cathode. Another difficulty of using a metal container is that if the electrodes touch the walls, it will cause a short circuit
and destroy your power supply.
Alternate container ideas:
WOOD: Get a wood bowl and heat until it becomes inert black charcoal, which can even act as a crucible for molten copper. As a bonus, you don't need
to worry about short circuiting caused by electrodes touching the container walls.
COPPER: Copper is relatively inert and cheap, so I don't expect it to react with the molten NaOH. But you'll still have to suspend the electrodes in
solution, and don't let them lean against the container.
[Edited on 31-3-2016 by Cou]
[Edit] Fixed obnoxiously formatted thread title
[Edited on 3-31-2016 by zts16]
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elementcollector1
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Funnily enough, this same thing happened years ago when I tried to electrolyze molten NaCl with copper wires. The red formed around the copper, so I'm
not sure if iron has anything to do with it.
Also, to avoid or at least partially solve the issue of electrodes touching the crucible walls, you can just make the crucible one of the electrodes.
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Cou
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How did you get the temperatures required to melt NaCl? I imagine you would need a coal furnace powered with an air compressor to reach those temps.
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elementcollector1
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Quote: Originally posted by Cou  | | How did you get the temperatures required to melt NaCl? I imagine you would need a coal furnace powered with an air compressor to reach those temps.
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...A blowtorch.
Needless to say, it only partially worked. Especially because I had to hold the blowtorch, and the wires, and the 9V battery. The NaCl did melt,
though.
Don't judge, I was 13 years old.
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BromicAcid
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Remember Cou, there is but a narrow range that a Castner cell can run at, too hot and the sodium formed reacts back with the melt, I think the range
is only ~50C or so but you could probably find the value somewhere around here. Also note that the original material of construction for these cells
is just iron. I don't know if I would consider bubbling under these conditions (since you're making a gas at both the anode and cathode) indicative
of reaction with the material of construction, and although you are getting color that does not necessaritly mean you are making significant
quantities of anything harmful (it doesn't take much of some compounds to impart a strong color). What's your electrode materials? Note that
electrolysis of molten KOH with iron electodes produces ferrates.
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Cou
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Here is what happened when I tried melting NaOH in a stainless steel dish:
After the initial water boiled off (which deposited the light brown slag at the sides), the molten NaOH appears to have corroded the stainless steel,
turning red with some iron compound while leaving the stainless steel bottom stained black. It also emitted an unknown noxious gas that irritated my
throat to the point of coughing. This even happened in a non-rusted container, so it's not just iron oxide leaching into the molten NaOH.
Needless to say, I don't think this is an ideal container for making sodium.
EDIT: I tried this again in a cleaner stainless steel container, still turned red to a lesser degree, still made noxious gas, but I also saw some
green forming too: chromium compounds, something to not play around with.
[Edited on 31-3-2016 by Cou]
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