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rikkitikkitavi
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teflon cant be melted.
but it can be grounded into a fine powder which then is sintered.
It is common to use different types of fillers for some applications, like glasfiber
see attached link.
http://www.worcestercontrols.co.uk/worcsonline/3piece.html
if you look at the end of the table you see the "seat material" which is usually a teflon packing with or without fillers used for sealing
the ball valve. It is manufactured with high tolerance
wether you can do this by mixing PbO2 with teflon powder I dont know.
edit: perhaps PVC can be used. It is not as inert as teflone, but is easier to come by and handle.
But the best is probably a completely inert substrate, or you have to remove the polymer after plating?
Could you not use a binder like CaSO4? This will be inert in the solution?
/rickard
[Edited on 8-10-2004 by rikkitikkitavi]
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axehandle
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I'm not too sure about this sintering process you mention. What temperature is typically needed?
I have a really whacky idea. What do you electrochemical gurus out there say to plating a pure Ag plate or mesh with PbO<SUB>2</SUB>? How
would silver behave in an anode if it were to come into contact with the brine?
Any other metals I should consider (apart from impossible to get ones like tantalum)?
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rikkitikkitavi
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about sintering teflon and filler I dont know exactly how to do it. There is probably a lot of information in books about polymers or on the net,
possibly patents aswell.
as for different metals, have you considered gold? A 10 um , 5*10 cm sheet is 0,05 cm3 or about 1 gr. 1 gr is around 15 €. If you are smart, you
cover one half with paint or something insulating. then perhaps the sheet can be removed from the electrode and recovered. gold is also a very good
conductor.
/rickard
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axehandle
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Gold sounds good if I could be sure it would work...
Today I'm going to try plating a platinized titanium mesh I have lying around with PbO<SUB>2</SUB>.
I also plan on trying to plate nickel. All platinum group metals supposedly make good substrates, so...
Otherwise, I have some ideas regarding palladium. Might be too costly though.
I have a novel idea regarding ceramic substrate anodes, and I see no reason why it wouldn't work with a plastic substrate: What about blending Ag
powder into the clay prior to shaping and firing? It should be very conductive. The clay will have to be one firing under the melting point of Ag
though.
[Edited on 2004-10-18 by axehandle]
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BromicAcid
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Soaking clay in strong acids can render it conductive. Rather then messing around with the silver idea.
Still though, I wish I knew a place where I could pick up some cheap tantalum for you 
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axehandle
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Soaking the substrate in acid? Worth some investigation.... but the absorbed acid might contaminate the plating bath in some way...
I had partial success with the platinized titanium mesh. Most of it got IMMEDIATELY clad with PbO<SUB>2</SUB> after just 15s in the
plating bath! Some of it did not, however, and I'm 99% certain it's because cooking oil had gotten onto it in that spot (long story
involving a filthy kitchen and stupidity). Apparently my boiling the mesh in detergent was insufficient, so I'm now soaking it in 30% ammonia.
The adhesion where the substrate was clean was VERY good, the PbO<SUB>2</SUB> deposited thereon stayed even when rubbed roughly with a
brush.
In worst case I'll have to buy a new platinized Ti mesh, but the only place I've found selling them charges an arm and a leg for them, and
I'm not exactly loaded with cash, gggrrrrrrr.
More info coming soon...
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TheBear
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Why not using a solvent to clean the mesh? I recall chlorinated hydrocarbons being ideal for neutral fats, but excess of cheap acetone should suffice.
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axehandle
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Result of plating the platinized Ti mesh
As can be seen in the closeup I've attached, the results are both encouraging and discouraging. However, I'm hypothesizing that those...
blank spots... were due to contamination of and/or damaging of the Pt layer. That mesh was treated very roughly by me before (getting tools thrown on
top of it, etcetera...).
Still, I'm not sure if the result is encouraging enough to motivate me spending SEK700-ish on a new mesh.
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MadHatter
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Mesh
Axehandle, The bald spots may be due to an imperfection during the production of the mesh.
I wouldn't worry about it as long as it works.
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chemoleo
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Nice - but waht I don't understand, why using PbO2-coated Pt(Ti), if Pt on its own is perfectly able to be used as an electrode for conversion of
KCl --> KClO3?
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Esplosivo
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I would also like to ask, why use a platinized-titanium mesh where there could be other cheaper alternatives? I mean, does it really
need to be a titanium mesh plated with Pt? Does anyone know of any other materials to which PbO2 adheres well and unreactive to Pb2+?
Theory guides, experiment decides.
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MadHatter
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ClO4 Production
I posted here and at RS the procedure for making perchlorates using carbon(gouging)
rods as the anode. The problem with this method is that the rods have to be replaced
frequently. YES, you can make your perc that way but you need a good and cheap supply of
gouging rods but don't bitch when the electrolysis tears them up !
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axehandle
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| Quote: |
Nice - but waht I don't understand, why using PbO2-coated Pt(Ti), if Pt on its own is perfectly able to be used as an electrode for conversion of
KCl --> KClO3?
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Good question. Thing is, I read in several places that Pt makes as excellent substrate for electrodeposited PbO<SUB>2</SUB>, and I wanted
to evaluate it first hand, to get a first hand account of it. Call it scientific curiosity or stupidity, your pick  .
Also, there's one reason: The Pt layer gets eroded if the chloride concentration drops below 10%. I doubt a puny micron-magnitude Pt layer could
stand up long.
| Quote: |
I would also like to ask, why use a platinized-titanium mesh where there could be other cheaper alternatives? I mean, does it really need to be a
titanium mesh plated with Pt? Does anyone know of any other materials to which PbO2 adheres well and unreactive to Pb2+?
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First question: Already replied. Second question: That's something I'd also very much like to know, but noone seems to know. Remember that
the substrate we're looking for must several very hard to meet criteria that I can think of:
Must be a decent electrical conductor.
PbO<SUB>2</SUB> must adhere extremely well to it.
Corrosion products resulting from the brine must be electrically conductive AND must not dissolve in the brine, otherwise the
PbO<SUB>2</SUB> must be completely hermetically sealing around it. The latter I don't find realistically achieveable with my plating
technique.
Again, the substrate must resist anodic oxidation OR the oxide layer must both not dissolve in the brine AND must adhere well to
PbO<SUB>2</SUB> as well!
Must hold up to weeks in a (per)chlorate cell, will all the chemical abuse that entails: Being half-boiled in an aqueous solution of
Cl<SUB>2</SUB>, being bombarded with bubbles of O<SUB>2</SUB>, etcetera.
Not easy criteria to meet.
Idly speculating, the only ones that I'm fairly sure of worth investigating are Ni/Pt/Ir (platinum group metals, only Ni worth really
investigating in solid form due to cost issues), Fe<SUB>3</SUB>O<SUB>4</SUB> and perhaps a couple other metal oxides, and
PbO<SUB>2</SUB> itself. Feel free to speculate, I'm always eager for someone to relieve me by suggesting a probably obvious answer
which I didn't think of...
Magnetite poses insane difficulties in melting and annealing it, otherwise I'd have tried it out a long time ago. Gold might work, but I
can't find any references as to whether PbO<SUB>2</SUB> adheres to it or whether it would be resistant to anodic oxidation.
| Quote: |
I posted here and at RS the procedure for making perchlorates using carbon(gouging)
rods as the anode. The problem with this method is that the rods have to be replaced
frequently. YES, you can make your perc that way but you need a good and cheap supply of gouging rods but don't bitch when the electrolysis tears
them up !
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Seen it. I might try it out (I know a somewhat cheap supplier of gouging rods) but not until persuing the holy grail... eh, mean
PbO<SUB>2</SUB> electrode, isn't fun anymore .
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neutrino
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Would it be feasible to plate a sheet of copper with PbO<sub>2</sub> and remove the copper afterward, leaving only a sheet of
PbO<sub>2</sub> behind?
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Esplosivo
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| Quote: | Originally posted by neutrino
Would it be feasible to plate a sheet of copper with PbO<sub>2</sub> and remove the copper afterward, leaving only a sheet of
PbO<sub>2</sub> behind? |
How do you propose of doing that? Do you mean plating a Cu electrode and then dissolving the electrode in some acid or something? That would require
very concentrated acids and I doubt that the fragile PbO2 would hold intact for long.
[Edited on 26-10-2004 by Esplosivo]
Theory guides, experiment decides.
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Hermes_Trismegistus
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| Quote: | Originally posted by neutrino
Would it be feasible to plate a sheet of copper with PbO<sub>2</sub> and remove the copper afterward, leaving only a sheet of
PbO<sub>2</sub> behind? |
if you could plate a sheet of copper with the lead oxide, why bother dissolving the copper out, why not just leave it in?
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Oxydro
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Wouldn't the copper reduce the plating as fast as it formed?
Edit: woops, never mind, bad morning!
[Edited on 26-10-2004 by Oxydro]
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Esplosivo
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| Quote: |
if you could plate a sheet of copper with the lead oxide, why bother dissolving the copper out, why not just leave it in?
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That is what I was wondering about. It could be done. There is a probelm though. If the Cu is exposed then the chlorine dissolved in the solution
would most probably react with the Cu contaminating the solution and eroding the electrodes.
Oxydro, I highly doubt any sort of rxn - remeber that Pb is more electropositive than Cu - this is why the rxn (CH3COO)2Cu with Pb occurs in the first
place.
[Edited on 26-10-2004 by Esplosivo]
Theory guides, experiment decides.
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neutrino
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Here’s an idea: make some PbO<sub>2</sub> powder, pack it down into the bottom of the plating vessel, attach an electrode, and let it
run for a while. You should eventually get a plate of PbO<sub>2</sub> with some powder on the bottom that should be easy to scrape off and
reuse.
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Twospoons
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| Quote: |
Oxydro, I highly doubt any sort of rxn - remeber that Pb is more electropositive than Cu - this is why the rxn (CH3COO)2Cu with Pb occurs in the first
place.
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But PbO2 is a good oxidiser, and this is precisely why finding a good substrate is so difficult. The reason Cu 2+ is added to the plating baths is so
that it will be deposited on the cathode preferentially to the lead, maintaining the lead ions in solution so they can form PbO2 on the anode. I
suspect a copper anode would dissolve rather rapidly 
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Esplosivo
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| Quote: |
The reason Cu 2+ is added to the plating baths is so that it will be deposited on the cathode preferentially to the lead, maintaining the lead ions in
solution so they can form PbO2 on the anode. I suspect a copper anode would dissolve rather rapidly
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I still cannot see why you think that the copper anode would react with the PbO2. The only route for the anode to dissolve is, as I mentioned
previously, due to the Cl2 formed.
Theory guides, experiment decides.
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Twospoons
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I was referring to the plating process, rather than chlorate production, though if you read through http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/chlorate.html, including all the lovely references in the 'Further Reading'
section, copper is metioned as being a particular no-no in the chlorate cell.
Can't remember where I saw the ref to PbO2 oxidising the substrate, but this is supposed to be one of the reasons it can be hard to maintain a
good electrical connection to the anode in service.
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Eclectic
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A good binder for chemically reactive systems would be PVDF (Kynar) dissolved in acetone or N-methylpyrrolidone (from environmentally safe paint
stripper). You wouldn't think a fluorocarbon would dissolve, but it does in those two solvents (and few others). It's also about as stiff
as plexiglass and can be melt formed.
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MadHatter
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Cu
Esplosivo, good call on that last post. Cu gets torn up rapidly during electrolysis in a
chloride solution. In fact this is how the Cu plating on gouging rods is removed before
using them for chlorate/perchlorate production. When removing this plating, the brine rapidly turns a dark green color as the Cu plating is eroded.
Eclectic, thanks for the info on Kynar ! This is something I have to try when I make my
next test anodes.
[Edited on 16-11-2004 by MadHatter]
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Battle
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lead dioxide electrode with lead or lead alloy substrate
I am making very weak attempts at the eelctrodeposition of lead dioxide onto a lead alloy or pure lead substrate. Anyone have any insite? I have
read every string, patent, discussion, argument, or forum on the web, and cannot find any information on this base material's use as a substrate.
I know a battery is the same thing but I want to electrodeposit the lead dioxide onto the lead, and use it in a cell. Any suggestions?
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