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careysub
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Platinum Wire for Electrolysis
I was wondering if someone could shed light on scaling rules for making platinum wire electrolysis electrodes.
Woelen, on his great page about bromine making:
http://woelen.homescience.net/science/chem/exps/KBrO3_synth/...
made an electrode using to lengths of platinum wire in parallel: 25 cm of 0.3 mm wire, pure platinum, and 12.5 cm of 0.4 mm of a 95% Pt/5% Ir alloy,
and ran his unit a 2 A.
The combined cross section of the two wires is 0.002 cm^2, or a current density in the wire of 1000 A/cm^2, and they had a combined surface area of
4.3 cm^2, so an electrode surface current density of about 0.5 A/cm^2.
What are the ranges of typical values for these two parameters?
Inquiring minds want to know because platinum is expensive, and one wants to go cheap, but not so cheap that is does not work properly.
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Fulmen
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Just of the top of my head:
You are looking for maximum useful surface area to keep the surface current density down, right?
You also want to keep the cross section as high as possible to keep ohmic losses down. That means many fine wires in parallel (the
surface-to-cross-section-ratio should increase with decreasing diameter) . But getting an even distribution of current densities with this
configuration could get tricky.
We're not banging rocks together here. We know how to put a man back together.
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careysub
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Indeed, asking "what it the most efficient design for a platinum electrode" would be another way of tackling the issue.
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WGTR
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If I were to buy another gram of platinum, I would get it on eBay, where they are going for about $50 right now. Not all jewellers can do it, but
some custom jewellers should be able to roll the bar into a thin sheet. The sheet can be used as is, or the jeweller can roll the sheet into a
cylinder, welded closed on one end. I would then electroplate copper onto the inside of the platinum cylinder for better current distribution and
stability.
Most of this is speculative; but it's an idea.
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j_sum1
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If you are going to do that, why not electroplate some Pt onto a copper rod?
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careysub
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Quote: Originally posted by WGTR  | If I were to buy another gram of platinum, I would get it on eBay, where they are going for about $50 right now. Not all jewellers can do it, but
some custom jewellers should be able to roll the bar into a thin sheet. The sheet can be used as is, or the jeweller can roll the sheet into a
cylinder, welded closed on one end. I would then electroplate copper onto the inside of the platinum cylinder for better current distribution and
stability.
Most of this is speculative; but it's an idea. |
That's a good suggestion. The market I am seeing on Pt wire is 20x the market cost of the metal, whereas the bullion "bars" (wafers actually) are only
1.5x market cost (that's pretty good really, for such a specialty item). I'm seeing $60 prices, not $50.
The cheapest one I spotted has a 1 g wafer that is 1 cm x 2 cm, which means that it is 0.25 mm thick and has a surface area of 4 cm^2, so it is about
right for an electrode as is. Woelen's wires together weighed 0.7 g.
I think a little creative glasswork could make this into an electrode rather well. Consider this: take a 3 mm glass rod. Wrap it in copper foil and
solder the foil to make a sheath. Draw a glass tube down to just a tad larger than the rod. Wrap the Pt foil around the bottom edge of the copper foil
covered rod, slip the tube over it, then collapse the tube onto the rod (like sealing an ampoule). If you remembered to solder a lead wire to the foil
before shrinking the tube, then you are golden (so to speak)!
You might be able to keep it flat if you fuse two slide covers together.
To people with a electric furnace hot enough to soften glass microscope slides (725 C for Corning 0215 used in premium slides) making a Pt bullion
wafer into an electrode might be rather easy.
They are 2.5 cm wide. Heat the slide up to close the softening point in the furnace, take out and place a thin strip of copper 1 cm wide extending
out the top end and running down almost to the bottom end on top of the slide, put the platinum wafer (1 cm wide) overlapping the copper slightly, and
put the second slide on top, then heat up enough to fuse them together. You could even lay the slides down so 2 cm of the bottom slide extends past
the top, so that the electrode has glass backing for handling protection.
[Edited on 14-3-2015 by careysub]
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WGTR
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Electroplated coatings aren't as durable as the bulk material. I would rather plate copper onto the back of platinum than the other way around, since
the platinum side would be exposed to the cell.
Here's a listing that I saw: http://www.ebay.com/itm/1-gram-Platinum-Bar-Valcambi-/141470...
The key is to get platinum from the secondary market. It's cheaper that way, much closer to spot price. The bars may have some blemishes, but they
are still pure platinum.
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deltaH
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Platinum leaf, while hard to find, is available from selected gilding suppliers, for example:
https://www.goldleafsupplies.co.uk/acatalog/Platinum_Leaf.ht...
If you could get a hold of a leaf, perhaps you could rub it onto an inert substrate. The downside is that they are frightfully thin, perhaps too thin,
so just a thought that might inspire some alternate possibilities.
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battoussai114
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I remember hearing that platinum wires have very smooth surfaces/very poor surface areas. I'm guessing you'd need a porous platinum electrode in order
to maximize the active surface area, and I don't think it'd be easy to modify the surface of the wire on the lab. Maybe you should consider using
platinum samples that are suited for catalysis or something like that... but don't write down my words, my electro-chemistry knowledge is beyond
limited and there's a big possibility that I'm making a fool of myself here.
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deltaH
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Something more about platinum leaf.
The previously linked site states that it's a minimum of 32g platinum per 1000 leaves. That would make the mass of one leaf about 32mg of Pt, which
doesn't sound too bad. A book of five 80*80mm leaves costs ₤13.30, which isn't exactly breaking the bank but using platinum's density, I've
back-calculated that a leaf's thickness is a mere 234nm or 834 Pt atoms 
You'd have to rub it onto a conductor at those thicknesses though.
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j_sum1
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I bookmarked that link deltaH. It might be a nice sample for the element collection. Ditto palladium. I have some gold leaf set in resin already
and it really shows off its colour. (Interestingly, you can also see through it when you hold it up to the light. Nice blue colour.) I haven't
been able to determine its mass but I am guessing it is even thinner than the Pt leaf you cited.
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careysub
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In round numbers the thickness of gold leaf is typically 100 nm, or about half that of the platinum leaf.
I don't see how leaf could be made to work for an electrolysis cell that is going to be a putting through amps of current in an extremely harsh
chemical environment (using it, say, as a reference potential electrode is another matter).
For example in an bromine electrolysis cell what is going to be an inert material you could bond it too? Inert materials don't generally stick to
platinum.
If you are thinking glass then you can easily (but not cheaply) get platinum coated glass from any of many metal film companies that produce optical
coatings. That is a routine order for them, but the time/labor cost of firing up a vacuum chamber means that no one-off can be cheap.
But how to get current though it? The substrate needs to be conductive to pass current through the leaf, no? If so then you have found a replacement
for platinum.
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deltaH
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I'm glad it served some purpose j_sum1!
Yes it's no simple matter indeed careysub, my thoughts were that using leaf is simpler than a DIY attempt at platinum electrolysis to
coat something.
As for a substrate, it would have to be a metal and you right, the selection is a challenge indeed. Nickel would be easiest, I would guess, in terms
of bonding to platinum leaf?
'Bulk' platinum in the form of wire, mesh or foil is still the most durable by far, but costly!
Another metal that is super inert is iridium, but is it cost effective/practical to obtain? I worked with iridium-nickel alloy wire once upon a time
for STM, but I suspect it's $$$
[Edited on 14-3-2015 by deltaH]
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j_sum1
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Look for a recent thread (by iwishihadakraken I believe) that discusses sputtering as a means for laying material on a substrate. He has built his iwn
machine and is looking for applications.
I once considered gold keaf as an electrode but the problem will always be effective covering of the substrate. That and the fact that it is thin and
likeky to be damaged be current density, chemical environment and physical handling. The same would be true of Pt.
Platinum is just so handy. Shame it is so scarce and expensive. I'm going to blame the supernovas.
[edit]
Excuse the phonebuttonbigthumbfumbles
[Edited on 15-3-2015 by j_sum1]
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careysub
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Don't blame the supernovas, they made plenty. The lack of platinum on Earth's surface is due to platinum being a chemically inert dense siderophile,
and Earth's gravity. It all alloyed with iron and sank to the earth's core. Lots of it there but out of reach.
The platinum group metals we find on the surface today were probably all brought to Earth by ancient asteroid bombardments. Asteroids have lots of
platinum, the average composition of the correct type of asteroid is 10-20 times richer than current platinum metal group ores.
There are several companies around now proposing to undertake asteroid mining for this purpose. The economics don't look good though, the market for
platinum metals is not large enough to underwrite such an effort.
A sudden massive increase in platinum availability will open new uses, sure, and increase demand, but that does not mean that the size of market in
dollars will grow very much. Such an increase would take quite a long time, probably too long for the investment pay-back to make it viable.
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Texium
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In a hundred years or so, who knows, maybe platinum crucibles and the like would be nearly as affordable as nickel ones? (instead of thousands of
dollars each!) Oh how nice it would be to actually be able to afford platinum and other PGMs in modest amounts. Imagine all of the cool inorganic
chemistry that would become feasible for amateurs!
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morganbw
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| Quote: Originally posted by careysub | I was wondering if someone could shed light on scaling rules for making platinum wire electrolysis electrodes.
Woelen, on his great page about bromine making:
http://woelen.homescience.net/science/chem/exps/KBrO3_synth/...
made an electrode using to lengths of platinum wire in parallel: 25 cm of 0.3 mm wire, pure platinum, and 12.5 cm of 0.4 mm of a 95% Pt/5% Ir alloy,
and ran his unit a 2 A.
The combined cross section of the two wires is 0.002 cm^2, or a current density in the wire of 1000 A/cm^2, and they had a combined surface area of
4.3 cm^2, so an electrode surface current density of about 0.5 A/cm^2.
What are the ranges of typical values for these two parameters?
Inquiring minds want to know because platinum is expensive, and one wants to go cheap, but not so cheap that is does not work properly.
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I have a few iriduim oxide coated DSA plates. They measure 10cm by 20cm. I also have a limited amount of grade 2 titanium metal and a few grade 2
titanium bolts and nuts which can be purposed to make an electric bus which should be inert to most electrochemical attacks.
I would be happy to loan part of what I have, if the experiments are shared on this forum.
Are you after the bromate?
I myself plan on making a K-chlorate cell sometime in the future and I am confident these DSA's would work well.
[Edited on 15-3-2015 by morganbw]
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careysub
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| Quote: Originally posted by morganbw |
Are you after the bromate?
I myself plan on making a K-chlorate cell sometime in the future and I am confident these DSA's would work well.
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I want to make bromate to make bromine, using Woelen's procedure.
I also want to make iodate for the iodine clock reaction.
Carbon electrodes would serve fairly well for bromine - carbon particle contamination not so much as an issue. But for the iodate and the clock
demonstration it is important for it to be clean.
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morganbw
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Let me know if you want to try one of my anodes. I think they should work well, and would cost you nothing but figuring out how to connect the
electricity, and I can help you with that. Add a cathode of your choice and you are golden. Just know that fluoride salts are the death of DSA's.
You can use as long as you want. I've had them for years and have not purposed them yet. One of these and you should have no current issues at an
amateur level.
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jock88
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Try to purchase a used Pt crucible (scrap) if you can get one.
It is easy to simply place a piece of Pt (1g bullion bar) between two pieces of Titanium and place the whole lot into the cell. So long as the joints
are submerged the junction seems to carry current OK.
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dermolotov
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This.
Alternatively, I just got some PdCl2 (gram) for $50 shipped. Search palladium chloride on ebay and it's the first thing that comes up (if you're in
the americas).
You can electroplate an entire metal crucible with palladium or platinum for this purpose. I have done multiple coatings of something similar.
Electroplate one layer on, then Flame it for a bit, electroplate, flame, rinse lather and repeat. More durable and efficient than any electrode you
can make.
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cyanureeves
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dermolotov how similiar?have you electroplated with palladium chloride?how many volts?i would love to electroplate a s.steel crucible or anything
really,it would be wonderful. i just bought a jewelers platinized titanium anode that i am going to use to plate gold with.the anode cost about 30
bucks but plating will go a long.long way though.
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dermolotov
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| Quote: Originally posted by cyanureeves | | dermolotov how similiar?have you electroplated with palladium chloride?how many volts?i would love to electroplate a s.steel crucible or anything
really,it would be wonderful. i just bought a jewelers platinized titanium anode that i am going to use to plate gold with.the anode cost about 30
bucks but plating will go a long.long way though. |
This was YEARS ago. It was just an avenue that I remember working. I now avoid all electrochemistry as much as I possibly can due to me specifying in
Organic Chemistry any my readily available access of chemicals.
Those were the days when I would boil down bleach or electrolyse salt solutions to get chlorate... Simpler times 
It looks like you got the stuff down, though. If you have an entire coated plate of Pt metal base, you won't need the crucible. I honestly can't
remember the setting on the voltage but I can guarantee it was not the ample setting, lol. If you told me to do this again, I would look at you and
call you insane.
Someone else here should be able to help you along. I may pester one of my physical chem colleagues and see what they say. They do their work in solar
panels so they have to know this kinda shit, right? 
Sorry I couldn't be of more help!
[Edited on 16-3-2015 by dermolotov]
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cyanureeves
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thanx dermolotov. i myself just tinker with homemade plating solutions and stuff and never bought literature on the matter.i can plate stuff but just
cant get it to stick permanently.
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dermolotov
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Two things that help immensely:
1. Dipping the base metal in HCl + O2- solution for 1 minute before placing in the coating area. This removes oxidation layers
and the flakey parts of the metal.
2. Applying 5+ coats for longer times. More coats means more durability.
3. Good chemistry hands (gotta go quickly and safely). The quicker you work, the less chance for side reactions.
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