| Pages:
1
..
12
13
14
15
16
..
18 |
len1
National Hazard
Posts: 595
Registered: 1-3-2007
Member Is Offline
Mood: NZ 1 (goal) - Italy 1 (dive)
|
|
I am posting this exerpt from a U2U in case it might be of help to others.
Im indeed in Australia, and will be pleased to help you if you are going to make an Na cell.
You ask a very pertinent question about nickel. We are one of the biggest producers but on of the smallest consumers of nickel, and finding it was a
heck of a job. However, the Nickel Institute of Australia, I think its called, or a very similar name, does have some off-cuts. Its not cheap though,
$100+.
A microwave transformer is no good. Thats because its step-up, not step down. It gives 1000+ secondary volts at low current. You need to get a
current-adjust welder. There is a great deal on precisely this in thrifty-link stores at the moment, $95 for an adjustable 140A welder. Rip out the
transformer and the fan, and use the leads as the high current leads.
The current adjusting screw, is essential, voltage control at high currents is very difficult (unless done on the primary). There is a screw on the
transformer which adjusts the position of some shunt metal in the core, to reduce or increase the amount of magnetic flux from the primary passing
thru the secondary. I have found that without such adjustment the procedure for getting sodium just doesnt work well. The cell easily overheats with
all the attendant consequences.
The holes in the collector are not critical, make them as large as you can cosnistent with structural integrity (and of course containment of the Na
at the top of the pipe). I made mine by milling 4 uniformly spaced straight channels 10mm wide by 60mm long. The collector is not floating, and is
electrically connected to the cell body at the top, at the bottom theres about a 10mm gap from the bottom of the cell, which is covered with gauze, to
allow good circulation.
|
|
|
Xenoid
National Hazard
Posts: 775
Registered: 14-6-2007
Location: Springs Junction, New Zealand
Member Is Offline
Mood: Comfortably Numb
|
|
Anode material.
Hi len1,
I was going to ask you about the nickel myself, as to where in Australasia you obtained it. You note it is by far the best material for an anode, do
you have any feeling for the difference in corrosion rates between nickel and SS in this situation. If thicker (say 2mm) SS was used for the anode,
how long would it last, 1 hour, 10 hours etc. How is your 1mm nickel holding up, how many hours has it done!
Regards, Xenoid
|
|
|
JohnWW
International Hazard
Posts: 2849
Registered: 27-7-2004
Location: New Zealand
Member Is Offline
Mood: No Mood
|
|
Nickel? I have a hoard of the old cupronickel coins that were removed from circulation in New Zealand last year, which were identical in size to the
ones still used in Australia (and also Fiji and Samoa). They were replaced by much smaller coins, made of a cheaper alloy with nickel plating or
cladding. I am holding on to them mostly for their Cu and Ni content, or as alternatives to using stainless steel washers where required.
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
Could one use a nickel plated SS or maybe Cu anode? Nickel salts can be made from readily available nickel carbonate (online pottery supplier) and
used to plate nickel onto another metal.
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Canadian nickels used to be pure nickel. And I think their cents, too. Might be worth importing some. Do beware, they switched their coin metal
like every five or ten years... the Canadian Mint's listing boggles the mind...
Edit: Don't forget your old friend, the welding store. Besides graphite, they should also have nickel rods, 55 and 95% or so IIRC, used for welding
cast iron. Use as-is or pound flat (with heat if necessary).
Tim
[Edited on 10-2-2007 by 12AX7]
|
|
|
len1
National Hazard
Posts: 595
Registered: 1-3-2007
Member Is Offline
Mood: NZ 1 (goal) - Italy 1 (dive)
|
|
I have indeed made some investigation of corrosion rates of different anodes in NaOH. The anode in this cell is the point most subject to attack
because of 1) the positive anode voltage creates oxidizing conditions which tend to dissolve the anode material in the bath 2) the O2 and H2O
evolved at the anode tend to oxidize the anode material. I am more concerned in the contamination and shortening of bath life by the presence of
anode cations in the bath, rather than the dissolution of the anode per-se, although, using nickel in the anode has allowed me to spot weld the anode
material, something I would not have been able to do if it was subject to rapid dissolution.
I have taken the cell apart now after about 30hrs operation and 200gms of Na, and the nickel anode shows no signs of corrosion whatsover. Zilch. I
think it can be regarded as a permanent item of the cell. The copper cathode shows more corrosion, but not really significat. Copper can not be used
in the anode, it dissolves and contaminates the bath rapidly. S/S I have used in mock-ups before. High Ni SS (which can be detected by the fact that
they are non-magnetic) I believe these types are called austenitic, seem to stand up us anodes the best. Their dissolution rate just as a very rough
estimate is less than about 100microns/hr at the current densities of this cell. The best material, without any doubt however, is the original Ni
chosen by Castner. Another source I havent mentioned is ebay. Now and then Ni appears - though sometimes wat is claimed as nickel is actual Ni SS.
As garage chemist says you can plate Ni using a sacrificial anode and NiCl2 or NiSO4 bath. I thought of that, but youd want a thick layer, and rather
than hassle with that getting the sheet seemed a better deal. Len
|
|
|
Tacho
National Hazard
Posts: 582
Registered: 5-12-2003
Member Is Offline
Mood: No Mood
|
|
Congratulations len1, your cell is a fantastic job.
About nickel anodes: A good electroless plating on a ceramic substrate should be a cheap option. I have obtained good electroless nickel plating in
the past fairly easily, but hypophosphites are hard to find and even controlled in some countries.
I remeber obtaining a good, smooth, shiny nickel plating on carbon using nickel chloride and ascorbic acid as electrolyte. Ascorbic acid (vitamin C)
is the key here. Low voltages are required.
|
|
|
len1
National Hazard
Posts: 595
Registered: 1-3-2007
Member Is Offline
Mood: NZ 1 (goal) - Italy 1 (dive)
|
|
Thanks for your kind words Tacho. I have not heard of electroless plating onto ceramics using hypophosphites. Can you explain how it works or give
me a reference? Thanks Len
|
|
|
Tacho
National Hazard
Posts: 582
Registered: 5-12-2003
Member Is Offline
Mood: No Mood
|
|
Here is a specific thread with links:
http://www.sciencemadness.org/talk/viewthread.php?tid=8614&a...
Here are some related threads:
http://www.sciencemadness.org/talk/viewthread.php?tid=553&am...
http://www.sciencemadness.org/talk/viewthread.php?tid=534&am...
Nickel ions get reduced by hypophosphite to produce a solid layer on non-conductive substrates, similar to that produced by silver in the mirror
making process.
I have obtained solid shiny (not silver shiny, more like dull aluminum shiny) platings on my very first crude attempts, so it's not not a very
difficult procedure.
I gather that hypophosphites are controlled in many countries because it has uses in drug making.
|
|
|
len1
National Hazard
Posts: 595
Registered: 1-3-2007
Member Is Offline
Mood: NZ 1 (goal) - Italy 1 (dive)
|
|
Thanks Tacho for the info.
Further on how to coalesce/purify the Na ingots obtained from the cell (from oxide and bath crusts). I have tried the isopropyl alcohol method
sugegsted by garage chemist and unfortunately it doesnt work with the large-size ingots obtained from the cell. Its addition to the Na in parafin
causes vigorous bubbling but no coalescence or freeing from the bath crust, it also introduces a light-brown precipitate/impurity which floats on the
Na globule (can be seen in the picture). Perhaps it operates better with small amounts in glass capiliaries.
I have found the best method for coalesceing the globules is as follows. Once the Na has melted below the parafin surface the temperature needs to be
brought up to 140C+ to decrease the surface tension of the Na. The small globules can be sucked up by a 5ml pipete on the picture, and injected into
the larger globules. It is best if some parafin is sucked up first to reduce oxidation of the exposed Na surface at the top of the pipete. The
action needs to be performed quickly to avoid the Na solodifying in the pipete. Once one big globule is obtained, large bits of crust, which due to
the surface tension are ejected from the Na to the surface can be picked off with tweezers. When all the large bits are gone a fork can be used to
trawl thru the molten ingot several times, this will collect all the oxide and small crusts to the side where it can be easily picked off. The end
result is an effectively pure Na ingot as the accompanying pictures show. Purification by distillation is considered inappropriate for an amatuer
set-up since the apparatus needs be completely evacuated.
|
|
|
len1
National Hazard
Posts: 595
Registered: 1-3-2007
Member Is Offline
Mood: NZ 1 (goal) - Italy 1 (dive)
|
|
The solidified purified ingot
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
Very nice work len1! As elusive as alkali metal production has been for all the rest of us amateurs it is hard to believe that potassium was first
isolated around 200 years ago with very limited material selections. It's quite inspiring to see someone else has succeeded in this endeavor.
I have always thought the Castner Cell to be too touchy for my taste, requiring a very narrow operating temperature range. Not to mention you can get
a 40lb bag of NaCl for about the same price as a 1lb jar of NaOH, and making pure NaOH electrolytically is relatively involved requiring either
fractional crystallization from a membrane cell, or an amalgam cell which has relatively low production rate and requires a good amount of mercury.
I have been working for some years now on a 500A cell similar to a downs cell which liquefies the chlorine off the anode by means of a cascade cooler
which chills the condenser coils to -50C and runs it into a tank. Meanwhile the sodium would run into an argon filled hopper. It will run eutetic
CaCl2 and NaCl and has a riser pipe just like an industrial downs cell. After the process, the chlorine would be brought up to vapor pressure at room
temperature and fed into a reactor to produce anhydrous ferric chloride. The project is still in a highly incomplete stage and I am still waiting on
a special refractory piece made from cut pieces of ceramic tiles with low-alkali borosilicate glaze. I have at least built the steel part of the cell
and the central graphite anode. I have also partially built the chlorine liquefier system and a set of casting trays for the sodium metal.
Production should be about 1lb/hour at 500A. I still hope to finish the thing sometime, but it's a major project and it doesn't look like it's coming
as soon as I had hoped. There are several safety measures that need put in place before this cell can be operated, too. It will contain something
like 60MJ of thermal energy plus a large amount of liquid sodium and hot chlorine when operating. In the mean time I have made a few other (all
failed) attempts at alkali metals.
Lithium should be much easier to make than sodium as lithium chloride melts at 605C while a eutetic mixture of that and KCl melts at something like
400C if I remember right. I once tried to make lithium metal in a small nickel plated crucible as a cathode, with a central graphite anode and a
glass tube with a stainless steel screen around it dipping into the bath as a divider. I had a continuous flow of argon over the cathode area of the
cell to shield the produced metal. It was all held in a single piece of caved firebrick. The soda-lime glass of the divider tube ended up being
relatively conductive in the bath at that temperature, which I didn't know at the time, and it destroyed it. The stainless steel screen was
completely dissolved, too. No metal could be collected, even though early in the electrolysis I could see some shiny metallic blobs form briefly.
Once the divider dissolved away there was no trace of metal produced and it all vanished.
Later I tried to make a very small tubular sort of cell out of a solid piece of graphite for electrolyzing eutetic NaCl/CaCl2. It had 3 holes drilled
into the block from the top, and one hole bridging them all inside which was plugged at the end with a bolt. It was operated manually with a graphite
anode, while the cathode was a little ceramic feedthrough with a nickel plated brass rod coming though. The cathode chamber was liquid tight, and a
tube ran out the side and into an oil filled jar. I made a rather large error in designing the thing and any sodium produced would have shorted the
cathode to the cell body. It ended up that the cell body acted more like a cathode than the cathode did as a result, and any sodium developed at the
anode compartment immediately combusted in the air and chlorine there. When I opened the cathode chamber, there was some sodium/calcium carbide
formation (evidenced by the release of acetylene when I was cleaning it out), and brass cathode and the nuts on it had thoroughly alloyed with
sodium/calcium and it was spongy and all stuck together, despite the nickel plate.
Here is my latest endeavor, with which I hope to electrolyze either eutetic NaCl/CaCl2 or LiCl. It looks almost halfways promising so far. I was
almost able to finish the thing this weekend but I didn't quite have time and I didn't have a good way to vent out or otherwise dispose of the
chlorine gas. Now it will probably be at least a few weeks before I can get home and work on it more.
http://www.chrisf.4hv.org/projects/chem/HPIM1388.JPG
http://www.chrisf.4hv.org/projects/chem/HPIM1391.JPG
http://www.chrisf.4hv.org/projects/chem/HPIM1392.JPG
The cell body is made from one of those 16oz propane canisters cut roughly in half. It is relatively thick steel. That will be suspended by bolts
running through the firebrick on either side of the setup. I still need to braze a wire across the thing in the other direction to hang the stainless
steel screen that will divide the cell in half. Both electrodes are held in a graphite block by a set screw, and surrounded by a tube made of fused
quartz.
On the left is the graphite anode. A small hole in the top of the graphite block is to be connected to the chlorine vent tube. The fused quartz tube
around the anode is held in by a set screw, which will no doubt need tightened as the cell warms up, and then loosened again before it can be allowed
to cool down. There isn't anything more to the anode assembly really.
On the right is the cathode assembly, a little more complex. The cathode itself is a hollow stainless steel tube with a couple holes drilled in it
above the cell liquid level so sodium can go inside it. The fused quartz tube around the cathode is sealed into the graphite block with boric oxide.
It seemed to have no real problems with contraction when this assembly was cooled from something like 500C where I cast the boric oxide in down to
room temperature. Nothing cracked, anyhow. The top of the tube and the graphite block will operate at a much lower temperature than the cell, and
much lower than the melting point of boric oxide, because stainless steel is a poor thermal conductor and most of the outer tube will be filled with
argon gas. Since the top of the assembly should be air tight, the sodium should not be able to rise higher than the hole where it enters the cathode
itself. Obviously if the sodium did rise up into the top of the assembly it would reduce the boric oxide and screw everything up. The cathode has an
outlet there above the graphite block, where it empties into a heated oil filled jar, which is in turn connected to a liquid filled tube with a valve
at the bottom. That tube will be used to provide suction on the cathode tube until the piping is all primed with sodium, so it can run out into the
collection jar under gravity. Obviously this will take some care since if any salt is sucked up into the tubing it will freeze and clog the thing.
The cell will be rather well surrounded by refractory ceramic and firebrick to get it up to 600C. It is fired with propylene gas and the electrolysis
runs on a large battery charger. Due to the rather small, distant, and otherwise inefficient electrode placing, I expect the full 12V of the battery
charger will be dropped across the cell, and even then it will probably need additional heat from the torch. So far my major concerns are how well
the thing will hold together under more temperature cycling, and how quickly liquid sodium might dissolve the brazed joints used here and there in the
cathode assembly.
Edit: I think I will run sodium nitrate in this cell. Melting at only 307C, it should yield sodium at the cathode and NO2 + O2 at the anode according
to our favorite online sodium texts thanks to BromicAcid. Those anodic gasses will then be fed through a low pressure bubbler with water to form
nitric acid.
[Edited on 18-10-2007 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
|
|
|
len1
National Hazard
Posts: 595
Registered: 1-3-2007
Member Is Offline
Mood: NZ 1 (goal) - Italy 1 (dive)
|
|
Working with NaCl is much more tricky I have found. For a start Na at that temperature attacks glass (see my posts above), also I have found that
iron rusts really quickly at these temperatures and with Cl present. Cost wise, the price of NaOH is about 3 times that of NaCl here, but when you
include CaCl2, the costs are the same per kg of bath.
I dont think NaNO3 is a good candidate, this is nitre saltpetre. It starts decomposing as soon as it melts, to NaNO2 and Na20, which absorbs H2O and
CO2 from the atmosphere. The NO2 is highly acidic and will attack the anode, and percolate to the cathode to unite with the sodium. I think some Na
can be obtained this way, but very little and its not worth the hassle. My advise is you attack the problem in the easiest possible way, and then
build in complications. regards Len
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
| Quote: |
Working with NaCl is much more tricky I have found. For a start Na at that temperature attacks glass (see my posts above) |
Yes, molten chlorides attack ordinary glass as well as borosilicate to some degree at those temperatures, and they are conductive enough to draw the
ions through, making it a useless barrier. However, the molten salts will not attack fused quartz which is pure silica and contains no free ions
(like Na+ and Ca2+ found in ordinary glass). I have used fused quartz tubes for this latest cell.
I have decided to use eutectic LiCl and KCl for the first run of this mini cell, as lithium production was its original purpose anyway. I will
probably need to heat the pickup tube from the outside for lithium to remain molten, where I would not have had to with sodium. The collection jar
will simply be filled with argon since lithium floats on any would-be barrier liquid anyway, and an oil layer will be used in the suction tube. This
cell should also work with eutectic NaCl/CaCl2, but there could be difficulties with calcium clogging the riser pipe. The alkali metal nitrates would
probably prove too problematic for this design, plus NaNO3 requires something like a 15V cell drop. The Darling Cell, which actually does electrolyze
NaNO3 to get sodium metal and NO2/O2, is a nice design, but what I have here is probably not too suitable for one.
The mind cannot decide the truth; it can only find the truth.
|
|
|
nitroglycol
Hazard to Self
Posts: 56
Registered: 28-10-2005
Location: close to the centre of North America
Member Is Offline
Mood: curious
|
|
| Quote: | Originally posted by 12AX7
Canadian nickels used to be pure nickel. And I think their cents, too. Might be worth importing some. Do beware, they switched their coin metal
like every five or ten years... the Canadian Mint's listing boggles the mind... |
There's a link here that goes into detail about Canadian nickels and pennies. The nickel was 99.9% nickel from 1946 to 1951 and again from 1955 to 1981. The
quarter and dime aren't covered in this article, but IIRC they were pure nickel from the early 1960s until 2000; those made after 2000 are
nickel-plated steel. The outer ring of the toonie is also virtually pure nickel, and the loonie is bronze-plated nickel.
Canadian readers should take note that destruction of Canadian coins is technically illegal here.
WARNING: Do not urinate on distributor while engine is in operation.
|
|
|
LSD25
Hazard to Others
Posts: 239
Registered: 29-11-2007
Member Is Offline
Mood: Psychotic (Who said that? I know you're there...)
|
|
Could I plate lithium metal out of the LiI:KI eutectic (MP around 260C)? If so, what would be the best material for the electrode? Could one use an
all glass setup if one was doing this? Also, is it possible to use a glass coated electrode - ie. could I expect sufficient electrical current to go
through the glass (such electrodes are used for some purposes - just unaware if they could be used in this endeavour - the idea of course being that
glass is one of the very few materials which cope well with iodine/iodide/iodate/hydrogen iodide/etc.
Alternatively, if one used a sacrificial Al anode, would one not get AlI3 out? If that was so, it may be worthwhile considering the use of Hydrogen
gas as the blanket for the Li metal - which upon reaction with the AlI3 should give LiAlH4 should it not? This would be a nice target to work toward,
the LAH would be useful (to say the least) while the side product of LiI would be fed back into the modified Downs cell.
This is merely the start of an idea, it will need a lot of research, development and consideration.
[Edit]
Of course, on consideration, glass would be a poor choice of material for lithium (it apparently attacks it).
Len, where does the Na collect in the NaOH cell (top or bottom)?
[Edited on 6-1-2008 by LSD25]
Whhhoooppps, that sure didn't work
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
The bath will definitely attack normal glass; I have tried using glass in such a cell before. Lithium is somewhat soluble in the bath and will alloy
too easily with most electrode metals except iron and the like. The bath is also well above the melting point of lithium. Obtaining a decent lithium
plating this way would be difficult or impossible; I'm not even sure if it will wet to an iron electrode.
I would suggest just dipping a brass piece into molten lithium metal if you want a lithium plating, or electroplate it out of an exotic cold
electrolyte solution like discussed in the unconventional sodium thread if you want to obtain it as an electrowon solid.
The mind cannot decide the truth; it can only find the truth.
|
|
|
franklyn
International Hazard
Posts: 3026
Registered: 30-5-2006
Location: Da Big Apple
Member Is Offline
Mood: No Mood
|
|
JUST A THOUGHT
The direct combination of 2 mols CO2 with 2 mols of sodium metal at 360 ºC
forms Na2C2O4 . Sodium oxalate itself will melt with decomposition above 250 ºC.
It seems a promising prospect to subject a melt of sodium oxalate to electrolysis
driving off carbon dioxide to recover the pure metal.
.
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Won't that disproportionate to carbonate and CO?
|
|
|
franklyn
International Hazard
Posts: 3026
Registered: 30-5-2006
Location: Da Big Apple
Member Is Offline
Mood: No Mood
|
|
That's my understanding, but it's not instantaneous. Maintaining the temperature well
below 360 ºC where Oxalate forms from Sodium and CO2, under pressure by metering
the excape of CO2 with a spring loaded pintle, will inhibit the normal decomposition at
atmospheric pressure into carbonate and monoxide at it's more moderate melting point
of around 260 ºC. These reactions are temperature driven , the applied electric field
should bias decomposition into CO2. Think of it as CO2 solvation. Sodium melts at just
98 ºC and floats on the oxalate of density 2.34, a hollow cathode insulated on the outside
will collect the sodium on the interior shielding it from the gas products that form in
the reaction container. That's why it's called Technochemistry.
UPDATE
The prospect of an oxalate anion decomposing into 2 mols CO2 seems a reach.
It looks more likely that some part of the melt will convert into Na2CO3 as a final
product. NaCO3 melts at 858 ºC so in this low temperature scheme it could only
be solvated if that, otherwise with a 2.54 density, being greater than the oxalate
it would precipitate out. The decomposition into Na2O and CO2 could not occur.
2 mols of NaHCO3 decomposes at above 50 ºC into Na2CO3 + CO2 + H2O vapor
but here the anhydrous bicarbonate anion cannot produce water but only CO2.
Electrolytic cell bias
2 NaC2O4 -> 2 Na(+) + 2 NaC2O4(-)
_________________
Cathode reaction
2 Na(+) + 2e- -> 2 Na
Anode reaction(s)
2 NaC2O4(-) -> 2 NaCO3(-) + 2 CO
2 NaCO3(-) -> 2 NaO(-) + 2 CO2
2 NaO(-) + CO -> Na2CO3 + 2e-
___________________
Final anode products
Na2CO3 + CO + 2 CO2
From this we see the occurence of two reactions,
1. Decomposition of half of the melt into Na2CO3 and CO.
2. Decomposition of the other half of the melt by circuitous reactions
into 2 Na + 2 CO2
[Edited on 14-2-2008 by franklyn]
|
|
|
LSD25
Hazard to Others
Posts: 239
Registered: 29-11-2007
Member Is Offline
Mood: Psychotic (Who said that? I know you're there...)
|
|
Len1,
Why does the use of the vessel as the anode preclude using nickel as the anode? Wouldn't it be better just to plate the vessel with nickel? IIRC
Nickel plating solutions, kits, etc. are still available online in Oz....
Assuming that I may or may not have just purchased a cheap, portable Arc Welder rated at a max of 150A, how exactly should I modify this (or can I
simply attach it via jumper leads to an external voltage reducer/regulator) to give no more than 5V? Quite simply, I'd like to set the welder up as a
high amperage PSU for arc-furnaces, electrolysis, etc. Is this workable, or is it a pipedream which should be discarded?
PS I am at home with turning, cutting, milling and welding (inc. threads, etc.) - but electricity is well and truly outside my comfort zone. Please
dumb it down if you do answer this.
Whhhoooppps, that sure didn't work
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
You really want more than 5V for a Downs cell; about 8 is good. Not sure about a Castner cell. I would see how much voltage the welder puts out
under the load of such a cell, by building the cell first and then measuring the voltage drop across it, but you really can't lower this without
physical access to lower voltage taps on the transformer. The welder is more or less a constant current source, so the lower the resistance you put
on it the lower the output voltage will be. It can't hurt the cell to drop more voltage than you might like either; it will just generate more heat
and may need external cooling. If it's really too high then your best bet would be to put more cells in series. Industrial downs cell banks run on
240V DC and have about 16 cells in series. A 150A cell is gonna be pretty small; the industrial ones run about 25kA.
I think I'm going to try my little cell with NaCl/KCl eutectic next time I get home. This way I can still run at a fairly low temp (not as low) but
won't have to deal with crystallizing calcium, and I know potassium will reduce sodium out of the bath.
[Edited on 13-2-2008 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
|
|
|
DJF90
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
How about electrolysis of molten sodium thiosulphate? It melts at about 50C and decomposes at its boiling point, which I cannot find. The sodium metal
wouldnt be molten at this temperature and so I'm not really sure what would happen. I just thought I would mention it incase it had been overlooked.
If sodium metal can be produced this way then it wouldnt be the most economical method of production but it isn't too bad, thiosulphate is reasonably
priced and electricity bills would be cut compared to the other electrolysis methods?
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
Like any complex ion electrolysis (for example the Darling electrolysis cell which uses sodium nitrate) it will likely go through a process where it
is first reduced to thiosulfite, then to sulfide, and a gradient of concentrations of these will be established in the cell. Sodium sulfide melts at
950°C and may freeze up around the cathode. It depends on what the gradient is like.
The mind cannot decide the truth; it can only find the truth.
|
|
|
len1
National Hazard
Posts: 595
Registered: 1-3-2007
Member Is Offline
Mood: NZ 1 (goal) - Italy 1 (dive)
|
|
| Quote: | Originally posted by LSD25
Len1,
Why does the use of the vessel as the anode preclude using nickel as the anode? Wouldn't it be better just to plate the vessel with nickel? IIRC
Nickel plating solutions, kits, etc. are still available online in Oz....
Assuming that I may or may not have just purchased a cheap, portable Arc Welder rated at a max of 150A, how exactly should I modify this (or can I
simply attach it via jumper leads to an external voltage reducer/regulator) to give no more than 5V? Quite simply, I'd like to set the welder up as a
high amperage PSU for arc-furnaces, electrolysis, etc. Is this workable, or is it a pipedream which should be discarded?
PS I am at home with turning, cutting, milling and welding (inc. threads, etc.) - but electricity is well and truly outside my comfort zone. Please
dumb it down if you do answer this. |
Well having the cell walls acting as anode does not literally preclude the anode being nickel at the same time - only if money is an object. If you
check the price for nickel you will see that proposition very expensive. I could only get nickel in sheet form (several hunderd dollars worth) which
I utilised as in the cell. To get it welded to act as the container as well is possible but would be more expensive. In addition the anode is a
consumable part, so having the cell walls consumed is not a long-term solution.
Plating is a long-winded option, you want a thick good-quality (non-porous) nickel plate and thats difficult and long-winded to achieve.
You can use a welder transformer for the cell provided its of the adjustable current variety as I described. You measure the AC voltage on the
secondary open circuit, and establish how many turns the secondary carries. That gives you how many turns per volt. Next you want at least two taps
- 6V AC and 8V AC open circuit. So you know how many turns you need to wind down.
Alternatively you can modify the 5V output of a PC power supply as described in Silicon Chip. Its simple - but you have to know more electronics than
with a welder. Most PC PS's can supply 60A @5V which is suited to the castner I decsribe.
The NaCl cell I would not recommend - its harder to get going than the Castner - and its not going to be nearly as long-term judging by my experiences
with the oxidation of materials at 700C Len
|
|
|
| Pages:
1
..
12
13
14
15
16
..
18 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
