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Author: Subject: Sodium!
len
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[*] posted on 24-8-2006 at 05:04


Double triode (forget your part number) I agree. From my experience using an AT supply for Na electrolysis is like using nickel cadmiums to jump start you car. Not enough voltage and not enough current. I have ever only ever had success with a well charged car battery.

You need to aim at about 1 globule/10 sec to compete with air-oxidation diffusion (1 globule/10sec = 0.1gms/10 sec ~ 0.0005 mole/sec ~ 50 Coulombs/sec === 100 Amps @50% cell efficiency, but this is a theoretical maximum 150Amps more likely).

So you need 100A. The voltage drop in leads etc generally means you need more than 5V to push this current through in home setups.

If you really are desparate about using an AT supply you can parallel them (some of them will cut out in this mode, depends on the type). You can also series connect. You can even up the voltage by varying the sampling resistor used as feedback from the 5V supply rail to the PWM chip (its generally easy to find).
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[*] posted on 24-8-2006 at 11:58


I am fortunate to have a spool of resistance wire (1 ohm/31") so did some testing of my computer PSU with various resistance coils.

Ignoring the label limit for the amps for the 12v and 5v outputs I tested the 12v at 12a (P=144w) and the 5v at 25a (P=125w). I assumed that since the PSU is rated for 145w these power levels should be OK. They were, i.e., there was no shutdown of the PSU.

The attached photos show the two test coils under power.

[Edited on 30-1-2007 by chemoleo]

5v25aPSUtest.JPG - 51kB




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[*] posted on 24-8-2006 at 12:00


And here's the photo for the 12v test:

[Edited on 30-1-2007 by chemoleo]

12v12aPSUtest.JPG - 49kB




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[*] posted on 24-8-2006 at 12:12


Has anyone tried an arc welder? Many units for stick welding supply a few volts at hundreds of amperes. Most will supply direct current. I have used arc welders on occasion, but never for electrolysis. Perhaps sodium could be made. Another robust source of high amperage DC are those heavy-duty devices designed to fast-charge car batteries as well as jump-start car engines.



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[*] posted on 24-8-2006 at 16:22


An arc welder is suitable current-wise, but its voltage is too high, typically 30-40V open circuit, plus you need the wire-fed DC variety. It can of course be rewound. A heavy duty jump starter would be just right.

Fleaker, thanks. I think that an alumina coating is more difficult than castners solution, which is having an underside electrode, plus it would be attacked as you say. I have though of the sodium outflow tube you mention, trouble is NA would have to flow down so the recepticle must be located below the surface of the NaOH melt!

[Edited on 25-8-2006 by len]
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[*] posted on 24-8-2006 at 20:05


Success this evening! :D with both 5v and 12v, but 12v was better. I also closed the cathode loop to 1/2cm ID. I don't think sodium at 308C has enough surface tension to stretch across the 1cm ID loop I tried previously.

There was the popping and throwing of hot NaOH previously mentioned by others. My hood glass served me well here. I used the series current limiting resistance coil of 0.2 ohm for the 5v and 1 ohm for the 12v. This was nice as I never had to worry about shorting out the electrodes.

Here's a photo of the few BB's I made with 12v. As you can see these are of varying purity:

Na BB's.jpg - 122kB




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[*] posted on 25-8-2006 at 04:52


Bravo Magpie!! I am seriously impressed with your sodium apparatus! From the picture it appears your yeild is substantial to say the least. Have you weighed it? I want to know how long it took to make your sodium. You were running about 12 amperes at 12V DC through your melt, right?

Great job! Thought about scaling the thing up?




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[*] posted on 25-8-2006 at 09:04


Thanks Elawr but I really just used the ideas of those ahead of me on this forum. As far as production rate with 12v it seemed like I was getting a BB about every minute. I haven't weighed them but will try to melt them together & purify later today. And yes, you are correct: the shorted electrode current would be 12a when using 12v. Of course this drops due to cell resistance and electrolysis when making sodium.

I tried to make sure I could always see some solid NaOH in the melt. As stated by others it is likely critical to keep the molten salt temperature at or near the melting point to avoid solublizing the Na in the NaOH melt.

The device is crude and there are several problems that you have to live with:

1. temperature control - trying to keep it even and near the melting point of NaOH (308C)
2. popping of H2 with attendant shooting bits of NaOH
3. low production rate for those interested in serious quantities of Na

On the plus side it is a great introduction to sodium making at a very low cost. The way we go though computers everyone likely has at least one old PSU laying around.

As far as will I scale up, well, I really don't need that much sodium so this will supply my needs for now. Building a really nice production cell that would solve the above problems would entail quite a bit more time & money, IMO.




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[*] posted on 25-8-2006 at 14:25
whoa there


I'm going to have to revise my earlier claims about producing sodium - at least of any purity. I placed my BB's in near boiling mineral oil (>250C) and they did not melt. When a BB is placed in water it vigorously emits H2 gas, but does not float and catch on fire like it should. They are grey and I assume are a mix of sodium and NaOH. I do remember seeing some very small droplets of silvery metal, however, but no significant quantity of them.

So, I'm beginning to see the light on what len has been saying about the requirement for high current. Tell me again how this NaOH forms by oxygen diffusion. Is this via the molten NaOH?




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[*] posted on 25-8-2006 at 14:34


I bet there is just a coating of NaOH covering the sodium and keeping the sodium from melting into a single blob. A NaOH coating could also be increasing the overall density of the BB above that of water, causing it to sink. I've tossed lumps of sodium the size of several peas into water, they have never caught fire for me, perhaps some yellow sparks, but no fire.

Crush them up a bit, then melt.
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[*] posted on 25-8-2006 at 17:52


Magpie, well done on making Na, but you will certainly be able to improve on that. The stuff I made is shinny like mercury (I sucked it up into a galss tube, and its still like that in my garage) and when I chucked some globules which remained in the melt after it solidified into water, the NaOH covering quickly dissolved off and a molten globule started skidding on water shooting of sparks from the burning H2, like Na should

The trick as you say is high current. A tiny drop of Na has a large surface area to volume ratio and its at that boundary where the destructive processes (O2 oxidation, emulsification in NaOH) occur. I believe that you want to form Na fast so the globules are small for a very short time, and you win the race against these processes. Slow rate of formation will lead to impure Na, and if too slow, to no Na at all.

[Edited on 26-8-2006 by len]
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[*] posted on 25-8-2006 at 18:39


len if you have read through this thread you know that there is a multiplicity of experiences and understandings of how electrochemical sodium is best produced. So forgive me while I dig up some background, but I'm trying to understand the root problems. My goal is to find the cheapest, easiest way for the home chemist to produce a few grams of high quality sodium.

Organikum enlightens us with drawings and operating conditions for the Castner Tiegel cell. I find it especially attractive that the cell voltage is 4v, as this would be perfect for the computer PSU 5v capability. Now to the amperage requirement. I understand what you are saying that time is not your friend and you must severely limit (<10 sec) the residence time of any formed sodium in the molten NaOH. Castner Tiegel does not do this. It uses a tight mesh screen to prevent gas bubble movement from one electrode to another. Is this just to prevent H2 movement or does it work for the O2 being produced at the anode also? Is the anode the source of the O2 that is fouling up sodium purity? Would the screen prevent this? I understand that the H2 produces a nice cover gas for the sodium to protect it from atmospheric oxygen and water. Castner Tiegel also provides for this. So if what I have stated is true it seems like we should be trying to optimize a Castner Tiegel cell on a small scale. In this way we would not have to depend on high currents and quick removal of sodium. I'm not implying that this would necessarily be optimum for every home chemist. It depends on whether you like to spend your resources on crafting a small scale Castner Tiegel cell, or buying a larger power supply, such as the battery charger on wheels recommended by excook. Or, as you have stated, a husky car battery that could always be brought to full charge when needed.




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[*] posted on 25-8-2006 at 19:19


Magpie, most of what I read said the screen in the Castner is to prevent Na globules from penetrating to the anode, and keep it in the upside-down bell. I did not use it in my set up since I had a large anode-cathode separation.

I dont believe I state anything at variance with Castner. Castner cells use a high current of the order of thousands of amps, they can not be easily scaled down. I dont mean the Na must stay in contact with NaOH for < 10s. I meant that small globules should become big ones on that time scale. After that the Na floats in the NaOH, but it has a much smaller surface area exposed to it. The O2 just comes from the oxygen in the air, to which the Na exposes itslef once it floats. I believe the biggest source of impurity in your Na is 1) the Na had partially dissolved in the surrounding NaOH 2) it has oxidised. To cure the problems I suggest up the current and keep closer control on temperature. Between +5C to +15C over melting point of NaOH (I think its 318C when pure)

I have read most of the thread, and it is still my opinion that most people have been using too little current. I back that up by saying, and I dont want to cause offence, most results in the thread have been disappointing. Nobody has demonstrated any substantial sodium production (by this I mean more than a few random globules) or a useful apparatus. If you can give me an appartus to produce relatively pure Na with small currents, thats great, but I dont believe it can be done without going to fancy cells and inert gases.

I find the real worth of postings on this forum over say professional chemical literature, is that they lie here less, people dont mind saying when something has not worked out, or descibing things in real terms. It would be true to say my profession, physics, is dying a slow death because of all the lies (if you dont publish faster than the next guy - you perish, and if theres nothing worthwhile to publish - you make mountains out of molehills)

[Edited on 26-8-2006 by len]
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[*] posted on 25-8-2006 at 21:05


len thanks for clarifying the purpose of the screen in the Castner cell (preventing liquid sodium migration). It's been a while since I read those old posts closely.

Assuming the atmosphere is the main route for oxygen contamination of the molten sodium some kind of cover over the sodium surface would help - such as inert gas or at least a bell or tube. Inert gas is getting fancy but a cheap, cleverly designed bell or tube should be achieveable. Incidentally, I measured the boiling point of my mineral oil at 330C. Pure NaOH melts at 318.4C. I wonder if paraffin or even petrolatum would work as a cover.

Temperature control is another key issue as you have noted. One could rig up a heating jacket with a nickel sheathed thermocouple and a PID controller. Again I hope we can find something simpler and cheaper.

Caution: Don't make the mistake I did and place your glass thermometer in the molten NaOH - even briefly. My thermometer's bulb now has a rough surface and I'm afraid to use it for critical applications. It's been retired. :(

[Edited on 28-8-2006 by Magpie]




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[*] posted on 25-8-2006 at 21:37


Magpie, your idea of a liquid sheath as opposed to a gaseous one is interesting. I know paraffin wont work, I recently tried it as an oil bath medium for my nitrobenzene. It boils too low - starts fuming heavily at 225C and boling at 250C. Some mineral oils will boil much higher, but I believe boiling oil with lye is a way to make soap. Maybe some oils dont react that way, dont know, maybe someone does? My handbook also lists them all as highly carcinogenic, if so their fumes at 300C cant be good. I am also currently working on the same problem as you.
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[*] posted on 25-8-2006 at 22:38


Mineral oils are out and out hydrocarbons, they won't saponify as vegetable oils will. There may be some slow reaction with NaOH, I suspect it will be more likely if oxygen is freely available.

This could be a way to help control the melt temperature. If the container was made deeper, vapours from the boiling mineral oil could be cooled with a condenser coil. Not only would oxygen be excluded, but by tweaking the oil you might be able to use its boiling to limit the rise in temperature.

Even with good reflux of oil vapours, you would not want to use flame as the heat source, unless you did extra work to keep flammable vapours away from the flame.

Note that mineral oils are a mix of compounds, and thus have a boiling range rather than a boiling point. There are different boiling ranges available, you might have to adjust that of whatever oil you can find by distilling off the lower boiling components.
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[*] posted on 26-8-2006 at 11:03


Are silicones inert around Na, NaOH?

Tim




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[*] posted on 26-8-2006 at 21:30


Under what conditions Tim? The temperature will dictate much of the reactivity. At 110 celcius, sodium won't touch PTFE, double that and it's serious degradation. I think silicone would handle it well, but sodium has amazing heat dissipation qualities: it easily warms up and it easily cools down.

I'm still not entirely sure why so many people are trying the NaOH method? Probably because it is cheaper and more forgiving I suppose (i.e. lower temperature). Still, NaCl/CaCl2 does work and it will work well--just expect some problems early on in the process. As many of you know, for manufacturing sodium to be worth your time, you must put a lot of amperage into the system, otherwise it is simply too slow.

Oh @ len, what I was referring to was what worked in the coffee-can-Castner. I'm sure I've posted about that before in either this thread or some other. The electrode still needs to be covered with an insulating mix, and it's hell to get it into the side of the cell without having the salt leak which is rather fluid and pretty volatile. It's long since destroyed/lost/thrown away, but if you'd like, I can describe the details/dimensions as best as possible?
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[*] posted on 26-8-2006 at 22:46


Duratherm S, a silcone oil, looks like it might have possibilities. See Duratherm S

[Edited on 27-8-2006 by Magpie]




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[*] posted on 29-8-2006 at 04:53


Fleaker, I serached this forum for you and Castner (or sodium) and couldnt find anything. You may be thinking of another forum?
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[*] posted on 30-8-2006 at 16:42


I could have sworn I posted something about it. Sorry for wasting your time then! I'm now set on sodium (through Ordenblitz I found a reasonable supplier and got 3kg of it) so have no need for a Castner, however, I can still draw out the design which worked, albeit not as efficiently as I would have liked. Just need to get hold of a scanner :\


Also, does anyone know of a cheap supplier for CsCl, like say 1000g for 150USD or so. I've been wanting to make cesium for quite a while now.
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[*] posted on 30-8-2006 at 17:25


Cesium salts, cheap:o. Let me know if you find any, I have never seen any for less than a dollar or two per gram. Companies in china may have some for cheap, assuming you can find a company that carries it.

I wish you luck in isolating metallic cesium, the stuff instantly catches fire in air. Firsthand experiance there unfortunatly.
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[*] posted on 30-8-2006 at 23:41


Quote:
Originally posted by Fleaker

Also, does anyone know of a cheap supplier for CsCl, like say 1000g for 150USD or so. I've been wanting to make cesium for quite a while now.


Cheapest I've see in several years, but I haven't been looking very hard; about twice what you want to pay.

http://www.cesium-chloride.com/
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[*] posted on 31-8-2006 at 07:13


The order page is on ordinary http, not https. In other words, the web site sends your credit card information over an <i>unencrypted</i> connection when you order.

I wouldn’t order online from them.




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[*] posted on 31-8-2006 at 12:45


They seem to be the cheapest place I can find too (exluding 25kg sacks from China) I plan on doing the reduction of CsCl with calcium metal under high vacuum. It obviously cannot be performed with sodium metal due to the Na distilling over with the Cs.

@ Rogue Chemist: Don't worry, I'm quite familiar with its spontaneous combustion in air. I will do it in vacuo then fill with argon as I fill ampoules with it, just a scaled up procedure of that in Brauer's. Anyone who would like to see the video of Cs burning automatically in air can see it here: http://www.smart-elements.com/index.php?arg=videos&PHPSE...

Hopefully the link works.
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