387 replies to this topic

[sasman]

The rate of corrosion is'nt relevant to Tantalum... it wont produce either chlorate or perchlorate...Read wouters page..Read what alany has just said .

.The Tantalium oxide that is formed stops corrosion?...so there is no corrosion... ..But the Tantalum oxide is not catalytically active to produce oxidation of the chloride to chlorate... Thats the same reason why Ti is not used as an Anode it polarizes to the oxide which inhibits corrosion..and hence results in non oxidation of the chloride to chlorate?..

[alany]

I think I've fixed my anode connection corrosion and Pt I^2R heating problems in one hit:

http://nexus.cable.n...r-electrode.jpg

I sealed the Pt/Ir to Cu connection inside a soda-lime pasteur pipette so the electrolyte can't get to it. This lets me have the "hot end" of the Pt/Ir wire deep in the electrolyte for cooling. It also means I can run the current through thick copper wire most of the way and can maximise the surface area of the expensive Pt/It wire available to the solution.

Anyway, time will tell, I have a KCl cell running with it now at 5A. If that works I'll reset the experiment with NaCl and let it go until it makes NaClO4 in the one step.

[Old1953]

The rate of corrosion is'nt relevant to Tantalum... it wont produce either chlorate or perchlorate...Read wouters page..Read what alany has just said .

.The Tantalium oxide that is formed stops corrosion?...so there is no corrosion... ..But the Tantalum oxide is not catalytically active to produce oxidation of the chloride to chlorate... Thats the same reason why Ti is not used as an Anode it polarizes to the oxide which inhibits corrosion..and hence  results in non oxidation of the chloride to chlorate?..

That will depend on the exact form of the oxide, for example, Ta2O5 is a standard DSA coating for oxygen production. While catalysis reduces energy requirements, it isn't strictly needed for chlorate production, as witness the wide variety of materials reported to give success.

Given the nature of tantalum, I don't believe it's oxygen overpotential is low enough to cause the evolution of oxygen at the anode - which is the major chemical concern as far as I'm aware. It is possible the oxide coating will have a lower oxygen overpotential, but I don't think so.

This paper discusses the formation of oxide in KCL solution, but doesn't give any details of the solution chemistry during their experiments!

http://www.journals....e=1&pagecount=8

I would suppose less than a 20 nanometer coating of oxide would form, given the data in those graphs.

[sasman]

..Ok the Oxide That will form in an "Anodic enviroment is the oxide that forms a protective layer of oxide to prevent further corrosion of the metal substrate the oxide that is formed is NOT catalytically enough for the oxidation".thats to say it wont produce chlorate/perchlorate
Also this Tantalum oxide passivates the anode which severly decreases anode efficiency....Tantalums anodic breakdown potential is over 100V in a chloride containing solution..
.You can make exotic oxides and that's what DSA are made from..But thats far more complicated method..Also DSA anodes are not used for making perchlorates

Also that link you gave only mentions Tantalum oxide formation in a KCl electrolyte?and it then goes on to say more or less what alany mentioned earlier..that is the oxide film gets thicker and thicker...no mention of oxidation of chloride.. ..Any way basically what i am saying is Tantalum Anodes are no good for perchlorate production...i

I have done a patent search on Tantalum anodes and there are none listed for chlorate or perc production...

I have got 2 Platinized titanium electrodes they are diamond mesh about 8 mesh...But not sure how to make a good eletrical connection...wish i could come up with some nice method like alany did with his Pt wire...

Edited by sasman, 20 February 2005 - 01:28 AM.

[Old1953]

..Ok the Oxide That will form in an "Anodic enviroment is the oxide that forms a protective layer of oxide to prevent further corrosion of the metal substrate the oxide that is formed is NOT catalytically enough for the oxidation".thats to say it wont produce chlorate/perchlorate
Also this Tantalum oxide passivates the anode which severly decreases anode efficiency....Tantalums anodic breakdown potential is over 100V in a chloride containing solution..
.You can make exotic oxides and that's what DSA are made from..But thats far more complicated method..Also DSA anodes are not used for making perchlorates

Also that link you gave only mentions Tantalum oxide formation in a KCl electrolyte?and it then goes on to say more or less what alany mentioned earlier..that is the oxide film gets thicker and thicker...no mention of oxidation of chloride.. ..Any way basically what i am saying is Tantalum Anodes are no good for perchlorate production...i

I have done a patent search on Tantalum anodes and there are none listed for chlorate or perc production...

  I have got 2 Platinized titanium electrodes they are diamond mesh about 8 mesh...But not sure how to make a good eletrical connection...wish i could come up with some nice method like alany did with his Pt wire...

DSA anodes are listed in several places for making chlorate, by the manufacturers of the devices. And this page:
http://www.geocities...e/chlorate.html
mentions the use of various oxide coatings for DSA's that are or have been used to make chlorates. DSA's have not been used to make perchlorates.

The article I referred you to above shows a limiting factor in depth of oxide in KCL solution vs voltage across the cell. This is on a graph, and gives a depth of oxidation of 20nm or less for ten volts.

In any event, tantalum wire is certainly the ultimate connecting wire for these anodes, whether it can be used directly as an anode or not. It will not be attacked in any way by the solution. And there is a simple (and cheap) method for coating substances with platinum, which I'll try if the bare wire is inefficient.

[alany]

A titanium rivet or nut and bolt would probably work.

Titanium rivets are used commercially to join plate electrodes to titanium support structures.

If you can afford Chloroplatinic Acid you can plate your own electrodes.

[sasman]

Yes i have looked at doing my own Platinium plating but when i got a price for chloroplatanic acid i soon changed my mind...
Old1953

DSA anodes are listed in several places for making chlorate, by the manufacturers of the devices. And this page:
http://www.geocities...e/chlorate.html
mentions the use of various oxide coatings for DSA's that are or have been used to make chlorates. DSA's have not been used to make perchlorates

I didnt say DSA were not used for making chlorates i said they werenot used for Perchlorates.. ..

You can make exotic oxides and that's what DSA are made from..But thats far more complicated method..Also DSA anodes are not used for making perchlorates

..
Right lets get on with actually making some.....

[alany]

My Pt/Ir electrode test cell has been running for about 2 days now at 4.5 Amp and is looking pretty promising, it is already crystalising out a layer of chlorate at the bottom. Curiously there is virtually no chlorine loss at all, I could run the cell without the vent pipe if I wanted to, but I like the refluxing action it has to minimise evaporative water losses.

The graphite cathod has not eroded in the slightest, the electrolyte is still crystal clear. The anode appears to also be holding up perfectly, there was an iniitial glass/metal seal leak that cause some corrosion, but I fixed that and annealed the joint carefully to prevent any future cracking. Unfortunately I don't have much instrumentation (yet - working on it) to tell that is really going on in the cell, but it appears using Platinum is *far* more efficient.

I got a quote today for commercial MMO and Pt electrodes, both 160x160 mm on 1 mm Ti plate: $188 and $795 AUD. I laughed out loud. I could buy a Pt coin and plate a few square metres for a quarter of that! Even $150 AUD would buy me a lot of Pt and Ti.

This place sells anodes only slightly smaller *far* cheaper:

http://www.shorinter.../Rectifiers.htm

[Pretty green flames]

If anyone is interested, here's also an internet site that sells
Pt/Ir Wire, 50cm for 65$ (US)

As far as i cam they seem to ship internacionaly
http://www.store.nan...WPROD&ProdID=24

Edited by Pretty green flames, 22 February 2005 - 10:56 AM.

[The Alchemist]

Prepare sodium chlorate by electrolysis of sodium chloride and keep the electrolysis going untill you smell oxone being produced. At this point you have nearly 98 percent perchlorate. Remember that a little pot chromate is required in the sol. It increases yeild efficiency but it is very carcinogenic. them ppt the pot per chlor by addition of pot chloride sol. filter and recrystalise from boiling sol which elininates any remaining chlorate. Method is widely published in any good practical chemistry text. Pt electrododes work best and are quite reasonably priced if you make them from a piece lab pure sheet obtained from johnson matthey.
In a simple cell. A bucket. a kilo of salt in sol takes a couple of days to electrolise.
For an adventure in pyro visit
http://glassbeads.co.nz and open the chemistry page.
Ray

[paul]

For me the link worked AFTER adding the missing "www"

http://www.glassbeads.co.nz/

Interesting Site....

Edited by paul, 24 February 2005 - 11:28 AM.

[alany]

Why is the site going away in March?

I love your glass work! Sometimes I wish I was an artist, unfortunately I don't have an artistic bone in my body. Still I'd love to have the space to refine my technical skills in working with glass, there is always a project I have going that needs glasswork of one form or another.

Edit: just wrote up my Platinum anode cell run...

Edited by alany, 04 March 2005 - 09:00 PM.

[sasman]

Can anyone help me with this question?..I want to calculate how much lead dioxide would be deposited for a given amount of amps?..assuming 100% efficiency

I understand that 26.8 amps in electroplating cell will deposit the Gram molecular weight of that chemical?..

So if the GMW. of lead dioxide is 331g then in theory at 100 % efficiency 331g should be produced with 26.8 Amps?..Well thats what i assumed..But i have a funny feeling that i am wrong?..I find that if this IS corect then my lead dioxide cell is running at ony 25% ..which i find hard to belive..

So i am hoping that you realy need 3 moles of electrons thats 3 x26.8= 80.4 amps?..per 331g GMW PbO2..Any forum member who knows his chemistry?

Thanks

Rob

[alany]

Lead dioxide electrodeposition is not normal electroplating, it is anodic oxidation, not cathodic reduction. I have no idea of the anode reaction chemistry, but this bloke probably would:

http://legacywww.cov...mbs/iniesta.htm

My guess:

In a lead-acid battery durring "forming" of the plates the anodic reaction is:

PbO + H2O => PbO2 + 2(H+) + 2(e-)

It takes 2 moles of electons to oxidise on mole of litharge to one mole of lead dioxide. This suggests it takes at least *4* moles of electrons to oxidise solid lead to lead dioxide. I am unsure how the lead gets on the anode in the first place, that would be an "anodic reduction" reaction, can that even happen? If lead nitrate was present unionised something like this might happen requiring only two moles of electrons:

Pb(NO3)2 + 2(H2O) => PbO2 + 2(NO3-) + 4(H+) + 2(e-)

No idea how practical that is, seems to me we'd be dealing with Pb++ ions. Obviously the lead ends up being Pb++++ which is oxidation, so there is at least two moles of electrons envolved, if not more. Personally my guess is four or six Faradays for one mole of lead dioxide which says you got very close to 100% or something that deserves a nobel prize and would be the salvation of mankind.

I am probably wrong though, electrochemistry is not something I am good at.

[Old1953]

My little experiment should be dry and ready for its heat treatment today. By the end of the week, weather permitting, I should know if it works. Hopefully, I've got a method for producing anodes safely, cheaply and easily. I'm figuring the cost per each as very low, less than US$ 1.00 per sq cm. They won't stand up to low chloride concentrations though, I won't be able to use these for direct conversion of chloride to perchlorate.

Wish me luck!