Sciencemadness Discussion Board

Molten NaOH electrolysis troubleshooting

Jstuyfzand - 16-1-2016 at 13:33

Hello everyone,

I recently discovered this forum and I have been browsing through the topics ever since.
One thing that captured my attention was Len1`s design (http://www.sciencemadness.org/talk/viewthread.php?tid=9797) for an electrochemical cell to isolate sodium metal.
I was amazed by it and I would love to do it myself.
There, however, is one thing that slipped my mind.
The bath is heated by ohmic heating, but how does he (and everyone else on the internet) keep the temperature right so that the sodium doesn`t dissolve?
You want to keep the cell running for a couple of hours and not babysit it.
I read the post and he spoke of adjusting the current and heating element when there was a certain temperature, but he also mentioned "And go do something else for ~2.5hrs", which does not sound like babysitting! :)

I am still relatively new to chemistry, but I am learning, I appreciate all help!

Now we`re on the subject, is there a ~cheap~ material that is similar to plaster that could withstand the molten NaOH?
I am still young and thus I don`t have any acces to a welder, so it would make life alot easier.

Apologies for any english mistakes, dutch ;)
Thanks!

annaandherdad - 16-1-2016 at 13:48

Check out his book, "Small Scale Synthesis of Laboratory Reagents", by
Leonid Lerner. It's expensive to buy but you may be able to find it in a library. I don't know if the book has the information you need about a sodium cell but it is a great book.

Jstuyfzand - 16-1-2016 at 14:01

Quote: Originally posted by annaandherdad  
Check out his book, "Small Scale Synthesis of Laboratory Reagents", by
Leonid Lerner. It's expensive to buy but you may be able to find it in a library. I don't know if the book has the information you need about a sodium cell but it is a great book.


I doubt it, none of the libraries here have english books, maybe I could get it online though.

Oscilllator - 16-1-2016 at 15:32

Quote: Originally posted by Jstuyfzand  
I doubt it, none of the libraries here have english books, maybe I could get it online though.

while we're on the topic of libraries, Jstuyfzand I hope you've checked out the Sciencemadness library! It's pretty great. It doesn't contain Leonid Lerner's book, but you may find one that will help you.
I also seem to recall some discussion in a caster process thread about the use of fire cement or something. You could try and find that thread.
Or you could purchase a small nickel or stainless steel vessel, which should withstand the NaOH. Somebody (not on this forum) synthesised Caesium metal in a cheap stainless steel soap dispenser, so there's a good chance that will hold up to NaOH.

Jstuyfzand - 17-1-2016 at 01:40

Lovely, more information to chew on.
I was thinking about taking a food can and placing a smaller iron/steel container in it where the cathode is placed.
Then a pipe is insterted just above the hydroxide level of the cathode container and leads into a batch of mineral oil, so that any lroduced sodium will flow into the mineral oil.
I hope I made myself clear, and I will try some clay based materials.
But can anyone tell me about the temperature control in such cell?

Tsjerk - 17-1-2016 at 02:39

In order to control temperature you have to be able to measure this temperature. Then you have to somehow couple this measurement with the energy output of your heating.

As we are talking about highly corrosive circumstances here, you could think about an infrared thermometer (sort of gun). If you can somehow couple the output to controlling the (electric?) heating device, you are ready to go.

An other way of measuring temperature could be with the use of an RTC, which is probably easier to link to your heating device. Just make sure the coating is compatible with molten NaOH!

Jstuyfzand - 17-1-2016 at 02:57

So there is a perfect voltage/amps that will heat the batch to the desired temperature? I could just use a pwm and measure the temperature untill I have found the right voltage, am I right?

Tsjerk - 17-1-2016 at 03:57

That is not really what I meant. I meant electric heating as in something like a hot-plate. A current strong enough to keep the mixture heated would probably destroy the electrodes. Plus there is no current possible before the NaOH melts.

What I meant was a relay-like system that turns off the heater when you reach the upper limit of the temperature range and turns on when you reach the bottom limit. Maybe a "dimmer" like system in order to give the electric heater more or less power would be better in keeping the temperature stable, but that would make things a lot more complicated, better start off with constructing a temperature depended on/off switch.

Jstuyfzand - 17-1-2016 at 04:08

Yeah, that is problably the best way.
I am tempted to build a downs cell now, no spitting pools of NaOH and no temperature control needed. Just blast a heating element.
I think I will read len1s post again, he did not have a complicated temperature control system.
And is the downs cell heated by resistance heating?

Tsjerk - 17-1-2016 at 06:31

Did you have a look at how Len1 measured/controlled temperature? Doesn't really sounds simple to me... But it would be nice if you could make something working like that!

phlogiston - 17-1-2016 at 13:40

Len1's method is not very complex. He uses the ohmic heating that always occurs in the electrolysis of molten NaOH to keep the cell between 315-225 C and an external heating element to start up the cell initially. If the temperature drops too low, turn on the external heater. If it rises too high, turn of the cell to allow it to cool down a little. Pretty straightforward.

Jstuyfzand - 18-1-2016 at 06:25

Yeah, I have to read about the topic a bit more, I thought a heating element could heat up a salt and CaCl to around 600 degrees celsius, and then electrocolysing, but if I can find a way to automate that, that will be what I am going with.

Not to mention that NaCl is a bit safer than NaOH