anode materials

[da man]

I have been making potassium chlorate from electrolysing a solution of sodium chloride followed by double decomposition with potassium chloride. It has been quite succesful though the graphite anodes that i use erode very quickly and have to filter the solution during operation. I know that lead dioxide anodes can be used but they are poisonous and so are the chemicals needed for preparing it, so i would greatly appreciate it if someone could tell me another alternative for lead dioxide.

[zaibatsu]

I don't think this is the right section, because your question relates to the anode used, rather than the chlorate itself. However, here is a page you should see, its should be of great use <a href="http://huizen.dds.nl/~wfvisser/EN/chlorate_EN.html" target="_blank">http://huizen.dds.nl/~wfvisser/EN/chlorate_EN.html</a>

[nbk2000]

This is the appropriate section to ask since it does DIRECTLY relate to the production of chlorate.

I've never made it electrolytically so I can't comment on anode construction, but it would be helpful to do a websearch if you haven't already using "chlorate AND anode" to start with. Get more specific as details emerge.

[vulture]

i tried making chlorates with graphite anodes and a 12v battery and i also found that the electrodes erode very quickly. I think one of them can be changed for a stainless steel electrode ( you'll have to check that on wouter vissers page) but the other electrode has to be one with a high oxygen overpotential or one that doesn't gets attacked easily, for example platinum or titanium

[da man]

yes, i used graphite for the anode, and stainless steal for the cathode, the cathode doesn't erode, but the anode is eroded by evolving oxygen.

[Mr Cool]

Car batteries have lead dioxide electrodes on one polarity, don't they?
Might be worth checking out.

[vulture]

I wonder if you could create a lead dioxide layer on lead by heating it with a torch or something for several minutes?
Cause only the parts that come into contact with the solution have to have a oxygen overpotential.
Also, a pure lead dioxide electrode will have poor conductivity and crack easily.

[rikkitikkitavi]

sorry mate, but when lead is heated in air only
litharge ,PbO is formed.

the anode in a fully charge lead battery is
made out of lead covered with lead dioxide! :)

The cathode is made of lead.
when discharged they both turn into PbSO4.

thus , slaughtering a small motorcycle battery
could give you a nice anode. or , more likely several (each cell has 2 V)

/rickard

[Lagen]

If you have access to some nitric acid you can try these methods: Make lead nitrate and then oxidize it with potassium persulphate (hmm... PCB etchant!) or clorox (hypochlorite) bleach. You must thoroughly wash out the byproducts as they would make the anode useless. And if you can get some red lead (minium, in paint shops), you can try this reaction with warm HNO3:

Pb3O4 + 4 HNO3 ---> PbO2 + 2 H2O + 2 Pb(NO3)2

Either way, be careful, as the lead nitrate is a hell of a poison, and it absorbs through the skin easily.

[vulture]

How about using an iron electrode with MnO2 substrate?
Should be very similar to PbO2.
However, this might cause the formation of a little bit of manganate or permanganate no?

[Mr Cool]

Lead nitrate oxidation can also be done electrolytically - get two graphite electrodes, put them in a soln. of Pb(NO3)2, and run DC current across them. PbO2 will be deposited on one of the electrodes. Apparently it's a good idea to add some soap to the electrolyte, it stops bubbles sticking the the graphite and fucking things up.

[kingspaz]

hmmmm, i've used graphite anodes before and they haven't eroded much at all....
what graphite did you use. i know theres only one sort but was it pencil lead, what grade pencil, etc?
i used an 8B artists graphite stick....its about 8mm thick :D
also i beleive platinum can be used but that would be VERY expensive.

[megalomania]

Every electrode will erode a little, just hope it dosn't react. That is why carbon and platinum are the best. I use carbon electrodes in my electrolysis set ups because it is cheap and easy to get. Mine do degrade somewhat slowly leaving a powerdy residue in solution. I use carbon welding electrodes, $1 each. They are about 1 foot long (31 cm) and 1 cm diameter with copper coating at the tip (easy to scrape off). Thats a lot of carbon for the price. Mine degrade about 1 cm per week of 24-7 operation with a 6 v battery charger. I bought mine from a welding supply store (Home Depot or any major hardware store should have something similar).

[firebreether]

When i just tried it, with pencil lead:-P i really need to go up to get some bigger electrodes like mega said. My problem is that after about 10 hours there is salt buildup on the electrode surface that is not submerged, and on the connections, which one of them has turned green. I supposed this is from the copper oxidizing. On several chlorate cell pages they say that this happens because the salts will get conducted through the electrodes because graphite is prous. They say to impregnate the electrodes with linseed oil to stop this. My question is, wtf is linseed oil? I have never heard of this or seen it before. Can anyone point me in the right direction to finding what it is/maybe where to get it?

[RTC]

I've seen Linseed oil as a wood treatment, gives it a kind of varnish effect of some sort. So check out a paint store.

[10fingers]

I think there is a difference between graphite and carbon electrodes. The ones used for welding purposes look more like carbon. They're easy to find and cheap. I don't know where to find graphite rods or which one would be better.
I was thinking of making a lead dioxide anode by taking it out of a car battery and compressing it into a plastic pipe and then drilling many small holes in the pipe. Then insert a stainless steel wire in the top of it for a conductor.

[firebreether]

Thanks ill check out the paint shop. Graphite is just a different form of carbon (like diamond, sort of, not really) thats more dense so i guess it should be better in terms of erosion rate and the allowable current density. I think the term is an allotropic form of the element carbon. But both graphite and carbon can be porous so both could benefit from this treatment i think. Oh, but obviously they are both still inert which is why they are a good choice:)

<small>[ April 14, 2002, 10:30 PM: Message edited by: firebreether ]</small>

[Pots-O-Potash]

Battery carbons (from a dry cell 6v latern battery or D cell) work fine but degrade badly if the solution gets to warm (over 50* C) and also seems to wear more at 12v than at 6v.

I know platinum works as an anode but has anione heard of using silver or gold as one. or would they corrode or be incompatable with chlorates like copper is?

++++++

You picked a 5 year old thread as your first post? :rolleyes: NBK

[Bacon46]

I have been successful using graphite anodes treated with boiled linseed oil. I have found that filtering the electrolyte through fiberglass building insulation does an excellent job of removing the graphite.

I used a 5 gallon bucket and a plastic colander large enough so that the handles supported it by rested on top of the bucket. I lined the colander with a white cotton cloth (Tee shirt in this case) and packed it full of fiberglass building insulation. The electrolyte flows though the filter quickly and comes out surprisingly clean in one pass.

I buy my graphite at a salvage yard. Most of the pieces are 6” diameter rods between one and two feet long. I picked up a couple of 18” x 6” diameter pieces for $5.00. You can get a lot of anodes out of one piece that size. I cut an 1 ½” x 1 ½” x 18” bar out of one of them for use in a 4 gallon chlorate cell.

I let the cell run 28 days. It produced 4 pounds of KClO3. Not spectacular, but not bad.

[tintinteslacoil]

Lead Peroxide is very resistive. I have only had success gluing (wear gloves!), or, using acetone to cement it to PVC or Plexiglas rods. The tube is rolled in the PbO2. Epoxy can also be used to glue it. Then, to make it conduct at all, I needed to tightly wind about 1/2-1" of clean copper wire to the top. This, and both ends of the tube, must be sealed from the solution, and it still exhibits high resistance and gets hot, and may melt the plastic . It is better to epoxy the PbO2 over a SS tube, cap the ends, and try the copper wire, or, a bright brass hose clamp on it. I still needed about 50 volts D.C. to force 2 amps through a saturated solution of KCl.

[tintinteslacoil]

Bacon46;
I sent my reply a bit prematurely--PbO2 seems lame compared to graphite. I have tried Carbon rods and Pb anodes, with limited success (very dirty!) It seems Graphite is the Holy Grail, next to Pt or Iridium or Titanium (very expensive.) My problem is scrapyards are hostile around here, and I also never saw any Graphite there. Would you be willing to sell some? (At a 100% or more profit, of course, to you) ?

[Bert]

Try a welding supply house.

[stupid939]

What about Tantalum? It is very resistant to corrosion and acids (even aqua regia). I could not find anything about how rare it is, but I think it is more rare (and possibly more expensive) than titanium.

http://en.wikipedia.org/wiki/Tantalum

[rring]

For what its worth:

I have had great success using about a 3 square inch arrow head shaped piece of Magnetite (Fe3O4). It doesn't erode from the oxygen as it is already an oxide. I got my piece literally from an old mine shaft but I am sure it can be obtained from a comercial source

I have seen on the web, some descriptions of sintered iron oxide powder elctrodes which had poor results. I am not sure why? My piece of magnetite is an actual chip from a large rock of ore. I just clip an alligator clip to one edge and suspend it in a solution of KCl. The solution sits in a small stainless steel bowl - which of course is the cathode. With this setup, the soultion stays so clean that I can just filter the precipitate and be done with it.

Perhaps you could burn some very fine steel wool and twist it into an iron oxide "rope" and use that as an anode.

[prometheus unleashed]

I would say that platinum would be the best anode out there.

However it does cost a lot of money for a platnium anode.

Any metal with a high electronegativity (or a low reactivity) would be the best anode because low reactive metals bond less readily with oxide or cloride ions.

Metal oxide anodes work great because they are already bonded. If silverware is still made out of silver, you could make a anode out of a fork or spoon. Copper piping is another option but it will corrode over time.

[prometheus unleashed]

I experimented with this today and I found out it actually works.

If you electrolyze an aluminum rod in water, eventually an aluminum oxide layer will form on the outside of the bar and won't corrode anymore with oxygen or chlorine like in a chlorate cell.

The aluminum oxide layer is not porous and will stick to the aluminum rod providing a decent anode.

You can get aluminum rods at a hardware store, Home Depot, or Menards.

I am about to build a chlorate cell with this anode.

I will post again once I perform the first run.

[ChippedHammer]

If you want to make chlorate on the cheap use EDM graphite, its the most dense form of graphite you can buy (check ebay).

If you want to make perchlorate you really only have 2 options:

1. Platinum
2. Lead dioxide

Platinum is expensive but will last forever, do not buy anything plated as it will wear away very quickly. Try and buy some wire as that is suitable for a small home cell.

Lead dioxide is the holy grail but without the proper precursors its next to impossible to make and impossible to buy (I've tried). A proper made GSDL (Graphite substrate lead dioxide anode) will work well providing its made well and has a thick coat with no holes or the solution will destroy it very quickly. TSLD (titanium substrate lead dioxide) is the best anode to make. It involves coating a piece of titanium with tin oxide and then the lead dioxide.

[polar bond]

The thread starter mentioned making chlorate only. Graphite seems to work well if you run it about 6 volts. you do not need any more than 6 volts for most electrochemical reactions, and while allowing more current to be passed through the solution, more salt in the solution would accomplish the same goal without the excessive anode wear.

Other options, as people have stated, include MnO2 (beta form tends to be the best), lead dioxide, or just about any other CONDUCTIVE oxide (besides silver oxide)

I'm not sure if silver iodide is conductive or not, or silver iodate, but if it was, this would be a suitable anode for chlorate production, as silver actually has a greater affinity for iodine/iodate than chlorine does, as well as being insoluble.

The idea with aluminum anodes will NOT work, aluminum oxide is a rather good electrical insulator. It will not conduct any e- into solution.

[Frunk]

I experimented with this today and I found out it actually works.

If you electrolyze an aluminum rod in water, eventually an aluminum oxide layer will form on the outside of the bar and won't corrode anymore with oxygen or chlorine like in a chlorate cell.

The aluminum oxide layer is not porous and will stick to the aluminum rod providing a decent anode.

You can get aluminum rods at a hardware store, Home Depot, or Menards.

I am about to build a chlorate cell with this anode.

I will post again once I perform the first run.

You do realize that aluminium oxide doesn't conduct electricity?

[Yafmot]

I'm running low on KClO3, and a cell looks like a great way to get it on the cheap. As far as anodes go, Chipped Hammer mentioned that Platinum plated graphite should be avoided. With ELECTROPLATED graphite, he may be right since, as it has been run down to me by the owner of a plating shop, you can't just put a straight layer of Pt directly onto a graphite substrate. You've got to put down Lead, then Copper, THEN the Platinum which, for ornamental purposes, is quite thin, maybe .0002 in.

With Chemical Vapor Deposition, the Pt can go directly onto the graphite with no intermediary. I presume we're talking about high density, monolithic graphite here. We used it as a sacrificial mandrel for making one piece, hypergolic rocket motors out of pure Rhenium. We'd deposit about 50 mils of Re onto the shape, and then use a slightly Oxidizing flame to cook the carbon off, leaving a finished part. It also worked great for cannon barrel bore liners which could stand up to the new, Nitramine-based propellants that were shooting out the conventional barrels in about 75 rounds; not acceptable performance in an automatic weapon. One went 20,000 rounds with no measurable wear. The people at ARDEC thought we were GOD!

Going one better, I think CVD-ing Pt group metals onto, say, Silicon Carbide would result in an electrode that wouldn't contaminate the electrolyte as the metal wore through. When enough wore off that the anode would stop working, you could just send it back for reapplication of the good stuff.

Back about 20 years ago, there was only one company in the world that could CVD Platinum Group Metals. I know, because I worked for 'em. I still have a couple of friends there, so I think I'll just see if they can coat some of each for me, Monolithic Graphite, solid SiC and, for enhanced surface area, maybe some open-cell SiC foam.

I designed catalytic convertors using the latter, and with a porosity of about 45 pores per inch, you get about 40 sq. cm per CC. So, given the wattages for your average run, it would take quite a while to "burn off" enough of the metal to effect the efficiency of the anode. We're only talking about a couple of bucks worth of Pt per anode.

I'll keep you all apprised of any progress.

[ChippedHammer]

I don't remember saying anything about plating platinum onto graphite (why on earth would you want to do that anyway?). People electroplate platinum onto titanium.

Anyway, I recently purchased a commercial chlorate MMO anode which came from these folks in India (http://www.cpanode.com/). Its been running in a large 7L KCl cell for about 3 weeks now and there is about two inches of KClO3 on the bottom which is nice. The anode looks like it did when I got it - and so it should, its rated for 20 years in brine at up to 600 A/m2.

[wymanthescienceman]

ChippedHammer - How big and what substrate is your anode, and what did it run you? If this company will sell single anodes to individuals then I may have to give them a ring...

[Yafmot]

I don't know what I was thinking on that last thread. You don'r necessarily have to CVD the Pt onto the SiC foam. A repeated dip, flash & cook with a PtCl solution in water, or whatever other solvent will work with it, is orders of magnitude cheaper. In one afternoon, you could easily apply 200 Angstroms to a chunk of it (this being the standard thickness that will guarantee complete coverage.

And you don't want Ti for a substrate, since Chlorides will eat it right up when you toss in acids and electricity. One little scratch in the coating will allow the Ti to just disappear, and it happens fairly quickly. Niobium is the way to go here, and it's only marginally more expensive.

Anomet Products (just Google 'em) has some Platinized Nb mesh for $5.00 per sq. in. That will give you 2x10" strip that will run you $100 for an anode that should last damn near forever. And if the Pt does wear out, just send it back to be recoated for a fraction of the cost of a new one.

I'm working on a continuous process apparratus where you put in the feedstocks in one end, and get product out the other. I can't talk much about it except to say that almost everything is automated. Temperature, PH, and other parameters are all continuously monitored, so the electrolyte can be kept at optimum conditions. More than this I cannot say.

For my own amusement, I managed to scrounge a 6x10" platinized piece of Nb expanded mesh, which should keep me in more oxidizer than I can even use for the forseeable future. But I do have a couple of questions...

One has to do with the power supply. I've heard of everything from model train transformers to computer supplies to car batteries, but what I want is CONTROL. Not just to find the optimum voltage/current, but to maintain it or, perhaps, to alter it through PH/temperature alarms as the condition of the electrolyte changes.

The other thing that's bugging me is how to physically connect the grid to the lead. I've thought of things ranging from a Platinum Group Metal conductor bar to just hanging it with an alligator clip, keeping that end up & out of the soup, Theres one company that makes solders in all kinds of alloys and proportions, with the catalog heavy on Indium alloys. One of these might hold up as a built-up conductor bar, as well as for soldering and tinning the leads. As long as the only thing that will work isn't 80% Au or some other money eating stuff that's sold by the gram.

One more little item. I can find formulas and procedures for these things all day, but I'm hoping someone who has tried a number will be able to steer me toward the one that worked best for them. I don't want to spend a pile of time reinventing the square wheel.