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janger
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More on PbO2 electrodes
Has anyone had luck preparing their own PbO2 electrodes?
The refs I have say after completion, the electrode should be shiny black. Yet, other refs say PbO2 by itself is brownish.
I have achieved a coating on a carbon rod from a fairly simple procedure, although it wasn't a well conducted experiment. All chemicals are
easily available. It is chocolate brown in color. After sitting for several days, it seems to have adhered fairly well.
AFAIK, it must be the dioxide. Can anyone tell my if this might be correct?
I will see how it holds up in a chlorate cell.
If anyone is interested, I'll post more details on the procedure.
Dave.
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Esplosivo
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I have discussed with axehandle a method of making a PbO2 electrode. I don't know if he has tested it yet. On my part I made a small electrode
using the procedure I am going to mention.
The procedure basically involves dissolving PVC in MEK and then adding finely powdered graphite. This 'liquid' PVC mixed with a high
proportion of graphite is then made into a slurry. The PbO2 is made to adhere to its surface by 'sprinkling' it on the surfaces of the
liquid slurry. A wire with an exposed part is then inserted in the slurry and the whole thing is left to dry in the sun.
I did not have the time to experiment with different ratios of 'dissolved PVC':'Graphite powder'. I simply mixed used the
aprroximate ratio of 2:1. The formed electrodes held quite well, though one of them was fragile (probably due to a lot of graphite powder). The
surviving electrode I made is quite small. When I'll have the time I will try to build larger ones.
[Edited on 23-8-2004 by Esplosivo]
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janger
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That sounds an interesting idea. Did you get a chance to measure the resistance of the electrode? Can you explain how all surfaces of the slurry are
coated in PbO2?
Dave
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axehandle
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After having that nice idea about conductive plastic, I found that someone had already done lots in that area. Check out this guy's homepage:
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...
His plastic substrate PbO<SUB>2</SUB> anodes are made by smearing THF on the surface of the substrate, rolling it in
PbO<SUB>2</SUB>, then letting the THF evaporate, then electroplating a nice thick layer ontop of the "painted-on" layer using
lead nitrate.
No reason it shouldn't work with any Pb(II) salt, like Pb(Ac)<SUB>2</SUB>...
Making the whole block conductive with graphite would have the somewhat huge advantage of making it VERY much easier to provide a reliable connection
to the cell once the anode is in use, I'd think.
[Edited on 2004-8-23 by axehandle]
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Esplosivo
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| Quote: | Originally posted by janger
That sounds an interesting idea. Did you get a chance to measure the resistance of the electrode? Can you explain how all surfaces of the slurry are
coated in PbO2?
Dave |
Sorry Dave, but I didn't experiment with it a lot. Right now I do not have as much free time as I wish.
I have a simple question. When electroplating with PbO2, the substrate being plated should be + or - charged. Last time I did this, the lead on the
anode 'dissolved' while lead was formed at the cathode. Was there something wrong with the concentration of the lead (II) ethanoate solution
I used? It might have been somewhat dilute. Thanks for the help.
[Edited on 24-8-2004 by Esplosivo]
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janger
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| Quote: | Originally posted by Esplosivo
I have a simple question. When electroplating with PbO2, the substrate being plated should be + or - charged. |
It should be the anode (+). Otherwise as you found, lead metal would be deposited, which ain't what you want.
In some procedures, especially in nitrate baths, copper salts are added to the electrolyte. The theory goes that copper first plates out on the
cathode. As the concentration of copper falls, lead will begin plating out. But this forms a sort of miniature electrochemical with the copper,
causing the lead to dissolve again! This isn't really necessary. Just means you need less lead.
I tried some of my impure lead acetate today using carbon electrodes (both of them). Sure enough lead began covering the cathode. I switched off the
power to see what would happen. In a few minutes the lead had been replaced by copper. I did get (presumably) PbO2 on the anode. However I hadn't
cleaned the carbon rod properly and it didn't adhere very well.
So you've tried creating electrodes using the acetate? I'd like to hear more.
Dave
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Esplosivo
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| Quote: |
So you've tried creating electrodes using the acetate? I'd like to hear more.
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I actually did try, but as you might have noticed the attempt was unsuccesful. Thanks a lot for the help. I will try this procedure out soon, I hope.
Theory guides, experiment decides.
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MadHatter
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Axehandle
I saw that page and downloaded to my PC some time ago. It looks
promising as there are several methods to create an anode using
PbO2. I haven't tried this recently as I have all of the KClO4 I need
for the moment. Great post in any event ! I've done it with gouging
rods but the erosion rate is extremely high if the cell exceeds 40 C.
Also, adding sodium fluoride or potassium persulphate increases
the efficiency of the cell.
My idea for my next anode is to dissolve a plastic(probably with acetone)
for use as a binder for MnO2 or PbO2. I need a plastic that won't be
attacked by the chlorine or oxygen created during the electrolysis.
Janger, sounds like your ready to rock with your anode ! GO FOR IT !
[Edited on 24-8-2004 by MadHatter]
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axehandle
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There's a list of plastics resistant to the conditions in a the (per-)chlorate cell in the page I linked to. Seems the guy has tested many
different kinds (QUOTE: "Plastics that are suitable for the task are polyester, polypropylene, polyethylene, teflon, ployvinylchloride (PVC) and
polystyrene (...and counting)." .
Someone should invite that guy to SM, he seems really really clever. I'm reluctant to spread my email address myself...
[Edited on 2004-8-24 by axehandle]
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MadHatter
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Axehandle
I get the impression that the guy is a free-lancer, putting out his
info to all who care to read ! I've found other sites related to rocketry
where the writer even included a relatively cheap source for KNO3 !
Now if someone could give us MAD SCIENTISTs a comparable
source on cheap NH4ClO4, I'd be delighted !
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axehandle
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Well, you can order 8kg for 2100 SEK (+ VAT, totalling in at approx €252) from a Swedish mail order company I know, but that hardly qualifies as
"cheap"...
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MadHatter
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NH4ClO4
Definitely not cheap so I think I'll just keep making my own.
Thanks for the info anyway !
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Esplosivo
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I don't suppose that the wearing out of the PbO2 electrodes would be a big problem. I read the stated amount of lead 'lost' form the
electrode but currently I forgot hw much it was. Anyway, one can always electroplate the electrode with more PbO2 after a certain number of runs. The
Pb 'dissolved' in the solution would form either the chloride or the sulphate, bot of which are sparingly soluble and can therefore be
filtered out before precipitating the perchlorate.
Theory guides, experiment decides.
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Jome
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Why not make NH4ClO4 if it's needed? If you manage to go all through the chloride-->chlorate-->Perchlorate process without adding K-ions
you should be able to precipate NH4ClO4 by adding f.ex NH4Cl and lower the temperature of the solution down to like 0 degrees centigrade.
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MadHatter
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NH4ClO4
Jome, there is a danger in making NH4ClO4 when using perchlorate
from your own electrolysis. You have to make DAMN sure that there is little
or no residual chlorate. If NH4ClO3 is produced in any appreciable amount
you risk the chance of detonation of the entire mix given the instability of
that substance. The indigo carmine test that I use is adequate for the
detections of chlorates.
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axehandle
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Can anyone think of a suitable, easily available piece of plastic to use as the substrate for the anode? I've been unable to find PVC rod (or
any plastic rod actually) and the best I've come up with is a piece of PE (I think) from one of those things you cut vegetables on in the kitchen
(word eludes me but you probably get the idea) -- problem with that solution is that the plastic is too soft (wouldn't want the
PbO<SUB>2</SUB> layer on the anode to break).
Another idea would be a piece of very thin plastic pipe plated on the outside..... one of those pipes for electrical installations would work I guess
but I've no idea what type of plastic they're made of and whether it's soluble in THF...
Round shape would be good, square shape workable if plated on one side I suppose...
The surface area I'm after is probably something like... well... say 50 square centimeters or so-so, no problem if too much since the
anode's depth in the perchlorate cell is easy enough to adjust.
I hate not having any good ideas...
BTW, about making NH<SUB>4</SUB>ClO<SUB>4</SUB>: It can be done with NH<SUB>4</SUB>NO<SUB>3</SUB> as
well as NH<SUB>4</SUB>Cl --- good good, finally some use for all the ammonium nitrate I've stashed away!
Also, anyone having any objections to my plan of using a DC arc welding transformer (or AC one with humongous full bridge rectifier) to power my
soon-to-be perchlorate cell?
Shit, I seem to have pulled an all-nighter. I'm too old for this... time for bed.
[Edited on 2004-9-17 by axehandle]
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Esplosivo
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An idea which sprang out of anything was to use formica, the one used for covering table-tops. Different varieties exist, some even
colourless (avoiding unneccessary impurities). I don't know about its solubilty in solvents and its capablity to resist chemical attack though.
According to my own experience it is fairly stable though, resisting most dilute acids (for example 45% H2SO4). Hope this helps.
Edit: Typo
[Edited on 17-9-2004 by Esplosivo]
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axehandle
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Good idea! It also gave me another: Acrylic, Plexiglass! Perhaps even polycarbonate (although that beast might not be THF soluble)...
What IS formica and what might it otherwise be called in construction stores?
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Esplosivo
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Formica is a condensation polymer formed by reacting methanal (formaldehyde) with urea (carbamide). Where I live it is usually known as formica. It
comes in sheets usually. Hope this site can help you understand what formica is:
http://www.formica-europe.com/index.cfm?Fuseaction=product.d...
As you can see the site is European, so using the mentioned brand names you could propably find it in stores.
What is plexiglass exactly? Is it also knwn as perspex, the methylmethacrylate polymer?
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axehandle
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Yes, plexiglass is polymethyl methacrylate (PMMA) or polymethyl-2-methylpropanoate.
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neutrino
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If you don't have any luck finding suitably sized plexiglass, many chem and bio suppliers sell plexiglass petri dishes pretty cheap, in many
different sizes.
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axehandle
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Oh, plexiglass I can find easily, but not until tomorrow  ... thanks for the idea
though.
Gonna get 8mm thick sheet, should be sturdy enough...
I see that it's soluble in acetone, even! No need to waste the little THF I have!
I intend to test plating several different sorts of plastic once I've gotten the immersion heater for my plating tank (also to be bought
tomorrow...). Titanium plate for the cathode(s) I already have...
[Edited on 2004-9-17 by axehandle]
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rikkitikkitavi
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axehandle, formica is also known as the polymer used in "perstorpsplattan".
have you considered using epoxy? Epoxy mixes well with fillers (like PbO2 or carbon) and is quite chemical inert.
/rickard
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MadHatter
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Axehandle
Axehandle, using an arc welder for your cell shouldn't be a problem as
long as the cell is big enough. The only problem I could think of is if
your arc welder has a limitation on the time it can be run. I use a battery
charger rated at 6 volts and 15 amps for my cell. It does a great job !
I stress the time factor because the chloride has to be converted into
chlorate at 1st. I don't know if this is a problem for an arc welder,
but I can tell you it's not a problem for a battery charger or a power
supply for a computer. I'd say go ahead. The worst that can happen
is that the arc welder will probably trip an internal breaker if the current
gets too high.
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axehandle
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Hmm, that's a point I've given some thought actually --- I don't know if a welding transformer can cope with "continous"
running for long; I would suspect that those that can cope with it are not the cheapest kind.
Anyone know or have a pointer?
MadHatter, do you have data as regards to your cell volume and your anode area?
Also, a question for those more versed in electronics than me: Are there any caveats to connecting 2 or more power supplies in parallell to the cell?
(if this works ATX PSUs can be used...)
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