| Pages:
1
..
7
8
9
10
11
..
18 |
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
I didn't know cheap storebought lye and crappy electrodes could give that kind of purity. Nice. 
Does anyone think they can answer my electrode question?
|
|
|
Magius
Harmless
Posts: 20
Registered: 9-6-2004
Location: Green Bay
Member Is Offline
Mood: Constrianed
|
|
Current density?
At neutrino: As for current density, all the literature and patents I've read on Molten electrolysis points to high current density.
For example This site makes a passing reference to high current densities of molten salts. In aqueous solutions, low current densities are desired to prevent
errosion and side reactions, but in molten electrolysis...? It appears things are a tad different. I'm not sure, AP chem didn't teach much
electrochem.
Now, call me ambitious, but within the end of January, I'll be recieving materials for the castable refractory mix mentioned in the Furnace thread,
and aside from building an actual furnace for, building a downs cell is next on my list. The current design is some thing likeThis with the heating element coiled around the container, which is most likely going to be a coffee can. Both the annode and cathode will have
the outsides coated with something nonconductive, probably... more castable refractory mix if it adheres to piping. The real problem lies in the
production of chlorine. What material stands up to chlorine at 700C?
Wait for it...
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
Your first link is broken.
I'm still playing with sodium electrolysis. My current setup of two thick copper wire electrodes isn't holding up too well. The copper seems to be in
tact, but there is a heavy nonconductive oxide layer on both (?) electrodes. Not sure how it would have gotten on the cathode, especially with the
sodium there. The oxide kills my yields; at 20A I should have .3g/min, instead I have a total of 1g for several hour-long runs.
Well anyway, I'm planning on etching the oxide off with some sulfuric acid and plating a more resistant metal onto them. Would Ag or Pt hold up under
these conditions? I was thinking about attaching some odd Pt foil scraps I had lying around, but I have no way of keeping them on the electrodes. Any
suggestions?
|
|
|
The_Davster
A pnictogen
Posts: 2861
Registered: 18-11-2003
Member Is Offline
Mood: .
|
|
Neutrino, despite the powersupply you are using is rated for 20A, it is not delivering that. 20A is the max current it could apply, the actual
current is dependant on the voltage applied and the resistance of the sodium hydroxide. You could move your electrodes closer together(not always
possible), or put another supply in series, so that instead of 5V you have 10V, that should double the amperage pulled.
|
|
|
neutrino
International Hazard
Posts: 1583
Registered: 20-8-2004
Location: USA
Member Is Offline
Mood: oscillating
|
|
I would think the resistance of a molten salt wouldn't be high enough to cause such a large drop in yeild. I still think that the extreme resistance
of the electrodes is the main cause.
In any case, I only have one PSU because these things are a little expensive. I will try to plate the electrodes with Ag and hope that changes things.
edit:
A qiuck question for those plating gurus here: do I have to start with a platinum salt to plate the metal, or is it possible to use some other
electrolyte?
[Edited on 23-12-2005 by neutrino]
|
|
|
The_Davster
A pnictogen
Posts: 2861
Registered: 18-11-2003
Member Is Offline
Mood: .
|
|
Arent your electrodes copper? Resistance of them is pretty much a non-issue here, especially considering the length of your electrodes. Get an
ammeter, stick it in series with your cell, and experiment by manually bringing the electrodes closer together and further apart, you will see a
difference in the current pulled.
EDIT: Realized you are talking about resistance of the oxide layer, not the actual metal, but the resistance of the salt is still important. Copper
is really not ideal electrode material, you get the oxide even under moderate heating of the bare metal. If nickel does not form a sponge, it would
be worthwile to try plating on copper.
[Edited on 24-12-2005 by rogue chemist]
|
|
|
len
Harmless
Posts: 35
Registered: 17-7-2006
Location: Australia
Member Is Offline
Mood: No Mood
|
|
As a kid I was one of 3-4 children at school fascinated by chemistry and doing his own chemistry experiments. We showed off to each other about what
we could make - as you can imagine the experiments had to be sensational. But very few of them produced something I can now be proud of. About the
most interesting thing I managed to make was sodium.
I placed about 0.5gm of sodium azide (NaN3) in a test tube, tied a party balloon to the top, clamped it and heated with a bunsen burner. After 20
seconds, pop, the balloon filled up (about 1/3 full). And in place of the white powder, a shiny globule, the size of a small pea appeared. The globule
gave a good speedboat-on-fire display when dropped into a bucket of water.
As the years passed, the most important thing that helped improve results is not theory, but patience and perseverence. If you are not prepared to
invest time (and money) dont even bother, you will get nothing.
Heres my procedure to produce sodium. Similar results have been posted, but this is simple, complete, and with a bit of a difference. The aim is to
get, in about half an hour, a shiny specimen of Na sitting in a tube, to show to your friends.
You MUST wear a face mask. You need: a fully charged car battery, a long iron skewer, a jar of NaOH (drain cleaner), a hot plate, a stainless steel
mug (you can get them at discount shops for $1), a long glass tube (about 5mm diameter), a suction device on it, some parafin, car starter leads, a
clamp with stand. Do not substitute any other power source for the car battery, you need about 100Amps to get the sodium forming quickly so a) it
doesnt dissolve/oxidise, b) it forms before the melt solidifies.
It strikes me that many people earlier in the thread were using far too low a current. It takes a lot of Coulombs to deposit even a little bit of
substance. Theoretically 100000 are needed to deposit one electron mole, or 23gms of sodium, but that is a minimum. With cell efficiency capped at
50% (and 40% more likely) you will need about 1000C for 0.1gm Na (about the weight of a globule). At 10A that is 1min40s which is far too long
conisdering the competing processes. At 100A its 10s, much better!
Place the NaOH in the mug and heat on a hot plate till it melts (wearing the face mask!) Attach the +ve of the 12V battery to the mug with one of the
starter leads. The negative must be clipped to the skewer with the other starter lead.
The NaOH will melt in stages, first a pool will appear down one side due to uneven heating, then the pool will extend, until the whole mix has just
melted. Some brown-grean discolouration will appear in the NaOH melt, due to attack of the SS and formation of Fe2+ and Fe3+, dont worry about it. If
a crust remains on the surface of the melt due to surface cooling, push it into the mealt with an iron rod. Now the melt is at its most viscous and
this is the perfect time to produce Na.
Dip the skewer into the middle of the melt, about 2cm, and clamp, at the same time turn off the hot plate. After about 30s globules of shinny Na will
start to appear, adhering to the skewer. Move the skewer to coalesce them as much as you can. Do not conduct the experiment in a droughty area. The H2
produced at the cathode must be allowed to bathe the Na as much as possible. I added some Ar gas at times, but that does not seem essential. The melt
will soon start solidifying, and before that happens, suck up as many globules as you can into the glass tube - they will look like mercury in a
thermometer. You do not want any of the NaOH sucked up, so apply suction until the globule is not quite gone. Start with the smaller globules first.
They can be sucked up, and then sucked back into other globules, to make one big globule. Dip the end of the tube into parafin, and you will have Na
forever to show off to your friends.
Why turn the hot plate off as soon as the NaOH fuses? Why not collect more Na.? The setup I described is cheap and quick, the price for that is that
it does not have the required temperature stability for a continuous process. I have found that most of the Na you get is produced, just after the
melting. After that the mixture loses viscosity, and the sodium formed in microdroplets produces a constant whirl cathode-to-anode in the melt. At the
anode it is destroyed. I then made a note that tight temp control is required, and am working on this. I hence read in this thread, and in a book
bromicacid posted that tight temperature control is indeed required in the reaction - to within 5C! Go 25C over and no Na is produced, as I observed.
NONE of the other 10+ sources on the Castner process mention this (and this includes a large chemcial technology encyclopoeadia series devoting
several pages to the Castner process).
PS Has anyone read the original acount of Na production by Davy. Its full of interest, passion, and tips on how real discoveries are made. The stuff
presented in school chemistry classes, is just a dried up stale version of what chemistry really is about. Most people who teach chem. shouldnt teach.
Not only do they bore you to death, you will never succeed with what they teach you.
[Edited on 24-7-2006 by len]
|
|
|
excook
Harmless
Posts: 1
Registered: 25-7-2006
Member Is Offline
Mood: No Mood
|
|
This will be my 1st and only post (most likely) but I decided that to save you gentlemen alot of wasted effort I'd give you my method of making sodium
metal. The equipment needed: battery charger; large one with wheels ($100.00), stainless saucepan (1 quart or less in size), several 1/2" 6inch (or
longer) carriage bolts ( stainless is best but galvenized works just as well), 1/2 nut, 2 feet of 1/2" steel conduit, 4 or 5 feet of copper wire (12
gauge or heavier), hot plate (temp. adjustible), several stainless steel teaspoons; wood to cover the ends of the handles and a means of attaching it
to the spoons (screws, wire, etc.) a stainless bowl to fill with mineral spirits to drop the metal in, and ideally a box with a light a glass front, a
place to insert your arms, with a exhaust hose that will take the fumes out of the room you set up in. and some more stuff that i'll remember as I go
along.
First thing put your pan on the hot plate, weld (or some-how attach) the nut to the end of the conduit. Screw the bolt to this giving your self at
least 2 inches of adjustment. To turn the bolt you'll need pliers; don't rely on your fingers to do it as it will be hard to turn when it's hot. Bend
the conduit so the rounded head of the bolt will be suspended so as to just touch the surface of the melted sodium hydroxide (red devil lye and make
sure it is dry; not a solid mass in the container)and attach it to your bench so it does not touch the pan. The copper wire is used to connect the
battery charger leads to the pan and the conduit. You can use the chargers clamps, but after a couple of times they will be ruined. The negative lead
goes to the bolt; the positive to the pan (you can reverse them when the metal production slows to keep produsing). prepare the pan (even if its new)
by first washing it, then take muratic acid; wet a paper towel with it, wipe the spoons, bolt and the inside of the pan with it. Then soak some more
paper towels in toulene and wipe everything with it. Everything must be clean. When dry turn on hot plate on high, put pan on it and pour 1/2 can of
lye in it to melt; when melted pour the rest of the can in to melt. Put on a longsleeve cotton shirt put on some latex gloves and put on some cotton
gloves over them; tape your sleeve ends so no flesh is exposed, the gloves won't fully protect your hands, but welding gloves (and the like), are
almost to clumsy to wear.If not using a fume box, protect your self from flying lye and the fumes which will leave a coating of lye on everthing
including your hair.
When 1st can of lye has melted put a spoon in it (to raise its temp.) put the bolt so its head is just touching the surface; a little off-center if
needed to manuver the spoon around just don't let it contact the pan. Set the battery charger at the middle value (Around 30 amps) and turn it on. If
everything was clean and the lye was dry, and attemps at hurrying the melting with a propane did not occur(it puts to much moisture in the lye with
the burning propane) The sodium metal will form along the bottum of the bolt head, grow in size and then will breakoff and will go to the out side of
the pan. They will keep combining and will grow to a size that will almost fill the spoon you will use to get it out of the pan and into the other pan
with the solvant.
The lye is also forming hydrogen gas; the bubbles caused by excess electricity from the charger, These bubbles then shortout; you'll see a a
electrical spark which ignits the hydrogen gas, causing flying molton lye. When the charger is on; it will produce enough heat to keep the lye
melted,but, be prepaired for the Charger to shut down to cool-off. When this occurs turn the hotplate up to keep the lye melted. As the lye starts to
produce less, add a couple of tablespoons of lye to keep it going. To produce one big piece from all of the little pellots that you will have
collected; get a 1 cup stainless measuring cup, turn the hot plate on high, remove the pellots from solvant and place on paper towel and qiuckly
absorbed most of the solvant. put the pellots in the measuring cup and with a pair of pliers; start swirlng the pellots; never letting the pellots to
stay in one spot to long so they don't ignite. when the metal in molten and in one piece; quickly dump it into a tall glass filled with solvant; it
needs to be tall enough that the metal cools and hardens before it hits the bottom. Cut away the green lye that will stick to the sodium. this method
will work well if:
everything is dry and clean Use the metal carefully and legally
|
|
|
Organikum
resurrected
Posts: 2339
Registered: 12-10-2002
Location: Europe
Member Is Offline
Mood: frustrated
|
|
Cyrus wrote: | Quote: | | If the sodium hydroxide gets too hot, it will just melt more NaOH |
He got the idea. Thats exactly why the original "Castner Tiegel" is such a genius invention. The solid NaOH at the walls and at the bottom of the
reaction chamber provides protection against corrosion, insulation AND temperature control.
|
|
|
len
Harmless
Posts: 35
Registered: 17-7-2006
Location: Australia
Member Is Offline
Mood: No Mood
|
|
| Quote: |
He got the idea. Thats exactly why the original "Castner Tiegel" is such a genius invention. The solid NaOH at the walls and at the bottom of the
reaction chamber provides protection against corrosion, insulation AND temperature control.
|
What it does is add some heat capacity to achieve better temperature control. Have you tried it out in practice, on a home scale rather than
industrial Castner cell scale? Try to melt the NaOH just in the centre so it doesnt spread out to the walls, and then keep it just like that with
current regulation. You'll be constantly adjusting current and turning your hot plate on and off. The heat conductivity of the NaOH is just too great.
Either youll overshoot and melt the whole thing, or it will all solidify on you together with your sodium.
Whats important here is the ratio of heat capacity to heat conductivity (or time constant of the system). The heat capacity goes with the volume,
conductivity with the area, so the problem does'nt scale.
We have electronics now, thats what its for. We can just sit back and watch the Na form 
I dont see the point in the elaborate HCL/toluene cleanup suggested two posts above. Your NaOH will likely contain far more impurities, and even that
will be insignificant compared to the impurities formed when the SS starts dissolving.
[Edited on 25-7-2006 by len]
|
|
|
Organikum
resurrected
Posts: 2339
Registered: 12-10-2002
Location: Europe
Member Is Offline
Mood: frustrated
|
|
Using the pot as electrode is flawed. You obviously didn´t get what I wanted to say. Have a look at the original Castner Tiegel and you might
understand.
|
|
|
len
Harmless
Posts: 35
Registered: 17-7-2006
Location: Australia
Member Is Offline
Mood: No Mood
|
|
| Quote: | Originally posted by Organikum
Using the pot as electrode is flawed. You obviously didn´t get what I wanted to say. Have a look at the original Castner Tiegel and you might
understand. |
Ive seen it many a time, and I know what you are saying. But Ill repeat what I said because you did'nt understand that. You cant achieve it manually
on a small scale (i.e. in a SS mug). Ive tried it, you've no control. The molten region either quickly spreads out to the walls, or it all
solidifies on you. In fact a central anode is a red herring here. One could still have all the benefits of the partially thawed NaOH conducting the
electrolysis at one spot on the wall. It will still be equally difficult to achieve.
Anyway all this theorising is pointless cause you obviously have'nt done it. If you want, go do it, and post pictures of the melt and the pile of
sodium you have made. I meanwhile will concentrate on something more achievable.
[Edited on 25-7-2006 by len]
|
|
|
len
Harmless
Posts: 35
Registered: 17-7-2006
Location: Australia
Member Is Offline
Mood: No Mood
|
|
Right well, Im developing ideas for a steady-state electrolysis to produce sodium in the Castner process.
The first thing to decide is whether to adopt a topside or bottomside cathode. The advantage of topside is simplicity, disadvantage is feasibility.
First consideration is Organicum's idea of a bell over the cathode to collect Na. The idea of having it NaOH coated on the inside to prevent shorting
by the sodium seemed feasible at first.
Alas I think it has a fatal flow. Density of Na is 0.95'ish, NaOH melt about 2.0. So about 50% of the Na is under the liquid. As the Na collects
this will necessitate further lowering the bell into solution. Its tip will get hotter and eventually a short will form. Any ideas appreciated?
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
That's another problem with small setups, removing the sodium if you are making more than a small bit. When the apparatus is large enough it's easier
to get access to the molten sodium for removal.
When I was much younger, the Ls and I tried this route. We used a couple of ceramic cups that we'd drilled holes in the bottoms of for bells. The
cathode bell got a second, smaller hole that received a length of small steel tubing, bent into a squared U. The other end ran through the cork of a
bottle containing mineral oil and having a second tube to pull a vacuum on. Oh, and the steel tube ended high in the bottle, not touching the oil.
Ever so often apply a bit of vac to the out tube and pull a dollop of liquid sodium over into the oil. The steel tube was hot enough from conducted
and intercepted radiated heat that the the sodium stayed liquid in it.
We had it working to some extend, running into the problems with eregulating the temperature of the NaOH but able to make 100 to 200 grams before
thing went foobar. Then we ran into a source of sodium ingots, and drpped the electrolysis.
I remember that adding other salts to the NaOH would help, but it's so long ago I'm not sure what they were. Sodium carbonate comes to mind, at about
5% total, but that could be wrong and I'm sure there was a second salt added. They both lowered the melting point slightly, and reduced the tendency
for the sodium to disperse in the hydroxide. We got it out of some turn-of-the-century inorganic chemistry book that had an odd lab technique with an
industrial bent.
|
|
|
len
Harmless
Posts: 35
Registered: 17-7-2006
Location: Australia
Member Is Offline
Mood: No Mood
|
|
Does anyone know thermal conductivity of molten/solid NaOH?
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
This does have some information
http://www.iop.org/EJ/abstract/0022-3727/4/3/313
http://unit.xjtu.edu.cn/xb/zrb/02/0211/xbe21109.html
My book on moltensalts in chemistry, which might have such information, seems not to want to be found.
|
|
|
The_Davster
A pnictogen
Posts: 2861
Registered: 18-11-2003
Member Is Offline
Mood: .
|
|
I melted 50g or so of NaCl and electrolysed it today. When the salt is molten it is a nice glowing orange. Used nickel electrodes. Really annoying,
the melt solidifies around where the electrodes are placed instantly. After fiddling with it a bit I actually was able to get a small lump of Na,
which on contact with the air caught fire. I dont think my temp control was good at all(electric furnace on full) as after a while the melt just gave
off white smoke when it was electrolysed. I am pretty sure that this is because the sodium was actually boiling off and reacting with the air.
Nickel electrodes were corroded badly. Melt still stuck in crucible, so I am not sure of the damage to it. Got lots of the grey crap like in NaOH
electrolysis.
Molten NaOH is much much easier to manage.....
[Edited on 23-8-2006 by rogue chemist]
|
|
|
len
Harmless
Posts: 35
Registered: 17-7-2006
Location: Australia
Member Is Offline
Mood: No Mood
|
|
rogue chemist, from what I read pure NaCl is unsuitable for electrolysis because at its melting point 801C Na actually forms an emulsion in it and
wont separate into globules. CaCl2, something like 10% I believe, is added to lower the mp to somewhere around 650C. I believe it will be worthwhile
trying that, keeping the current above 50A, and using thermally insulated Ni electrodes,counteracting the increased resistance by upping the voltage a
bit. Also at this temperature its probably worthwhile keeping the Na under a bell through which you poke your electrode. The solidifying effect at
the walls of the bell will isolate it from the solution.
|
|
|
The_Davster
A pnictogen
Posts: 2861
Registered: 18-11-2003
Member Is Offline
Mood: .
|
|
Yes, there was definate emulsion forming, I will have to give the eutectic with CaCl2 a quick try. Seems like a very small ammount of Na excaped the
emulsion in this attempt however.
|
|
|
Fleaker
International Hazard
Posts: 1252
Registered: 19-6-2005
Member Is Offline
Mood: nucleophilic
|
|
| Quote: | | Originally posted by len Alas I think it has a fatal flow. Density of Na is 0.95'ish, NaOH melt about 2.0. So about 50% of the Na is under
the liquid. As the Na collects this will necessitate further lowering the bell into solution. Its tip will get hotter and eventually a short will
form. Any ideas appreciated? |
You can coat the collection/receiving pipe with a refractory (alumina-based) clay. At that temperature, it's electrical conduction is minimal but IIRC
the sodium attacked the clay. Alternatively, one could position the electrode such that any sodium formed will flow into a bell with a narrow neck so
that the majority of the sodium is stuck in the narrow tube.
|
|
|
Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline
Mood: Chemistry: the subtle science.
|
|
This evening was my first attempt at making sodium. I used a 5cm diameter food can (smaller than a soup can) and the PSU (12VDC) salvaged from an old
computer. Cathode was a 1/16" iron wire (coat hanger) with a 1 cm loop in the end. See photo attached.
I poured about 3cm of granulated NaOH into the can and melted it with a bunsen burner. I felt I must measure the cell reistance before I dare apply
electrical power so did so with an ohmmeter. I checked it several times and read 30-35 ohms each time. This seemed high but I really had no idea
what it should be. This would be safe for my 12VDC (4a max) PSU so I applied electrical power. After a few minutes I checked the electrode loop for
sodium but nada. Then I noticed that the PSU cooling fan was off so assumed I'd blown the PSU. I terminated the experiment at this point. I checked
the PSU a few minutes later and it appeared to be fine.
So, I'm not sure what happened but wonder if a circuit breaker internal to the PSU shut it down. I really need to get an ammeter so I can more
closely tell what's going on. It would also be nice to have a continuous temperature reading of the melt.
Any comments and/or suggestions are welcome.
[Edited on 24-8-2006 by Magpie]
[Edited on 24-8-2006 by Magpie]
[Edited on 30-1-2007 by chemoleo]
The single most important condition for a successful synthesis is good mixing - Nicodem
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
If it's an ATX power supply, you need to add a jumper so it thinks the motherboard says "ok".
I've overcurrent-ed a switching supply or two before, I think. I'm not sure how they shut down, if it's a latch or what, and what resets it.
Next time, try the 5V output instead, or use a 1 ohm resistor in series.
Tim
|
|
|
chromium
Hazard to Others
Posts: 284
Registered: 27-6-2005
Member Is Offline
Mood: reactive
|
|
Most computer PSU-s (no matter ATX or older) switch outputs immediately off when overcurrent occurs. If switched off mechanically or disconnected from
mains for less than minute they are OK again. Maybe your electrodes touched each other for moment or maybe resistance of melt at higher voltages is
much lower. Resistance of electrolytes is not the same at all voltages and your ohmmeter might be using very low voltage.
[Edited on 24-8-2006 by chromium]
|
|
|
The_Davster
A pnictogen
Posts: 2861
Registered: 18-11-2003
Member Is Offline
Mood: .
|
|
I have pulled 18A out of a PSU line rated for 9A, they lie about max rated amperages. Ran it at this current for 3 days, it still works.
Stick a 10 W 10 ohm resistor on the 5V line, and be sure you connect the green and black wires. I think one of these is what Tim mentioned.
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Eh, I once tried running a chlorate cell from an AT supply.
First try: it seemed to work. After some time, I discovered the 5V rectifier had failed shorted (probably after overheating). Replaced with beefier
part.
Second try: choke on 5V output burnt to black. (30A rating with mere 16AWG wire?) Power supply still operational, but 5V went open circuit. Modded
filtering scheme.
Third try: finally, the power transistors exploded...
My best guess is the cell wanted about 50A, which should be within the VA capacity of the supply...but go figure...
Also keep in mind the V/I characteristic of an electrolytic cell...it isn't ohmic, hence my suggestion of a series resistor.
Tim
|
|
|
| Pages:
1
..
7
8
9
10
11
..
18 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
