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Author: Subject: More on PbO2 electrodes
dann2
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[*] posted on 3-4-2008 at 09:45


Hello,

The Cell running the LD anode has been now been declared an official Perchlorate cell. The Perchlorate in on the increase.
It is slow, hopeing that it's not the LD anode that is slow to convert the Chlorate to Perchlorate but rather that there is still quite alot of Chloride still being converted to Chlorate in the cell. I am taking samples every two days. The cell has a run time of 50 days (all Chloride to Chlorate) at 20% efficiency.

Attached is a file I came accross on DSA in Chlorate cells. It would appear that the optimum pH is somewhat lower that I had seen elsewhere. The seem to run their cell at not the optimum Chlorate formation pH but also to minimize Chlorine escaping from cells. (Environmental or Economics??)



Dann2

Attachment: urn_nbn_se_kth_diva-4681-2__fulltext.pdf (2MB)
This file has been downloaded 498 times

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hashashan
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[*] posted on 3-4-2008 at 16:39


Hi,
Im really sick of salts creeping up to the connections.
How do you guys install the anodes in your cell?
dann I didnt understand what is that liquid resin from your website.

Anyone has a good method for a connection?
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dann2
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[*] posted on 4-4-2008 at 13:45


Hello,

For connection to Ti I just use a brass bolt through a hole. The bolt goes through a loop on the end of Copper wire.

The resin is polyester resin. It will be available in car accessory shops or garages. It is used to make Fiber glass reinforced plastic. (FiberGlass). Also used to make/repair fiberglass boats.
It's like epoxy resin. It is a liquid which sets rock hard in about 5 to 10 minutes (after hardner, Benzoly Peroxide has been mixed it).
'Wets' things well and seals well. I find with silicon sealer or hotmelt that the salts get around them.

http://www.halfords.com/webapp/wcs/stores/servlet/SearchCmd?...

Can you get roofing pitch. Black stuff for felt roofs. This would probably do the trick. I never used it. Definitely cheap. You local builders providers might give you a sample.





Dann2

[Edited on 4-4-2008 by dann2]
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hashashan
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[*] posted on 4-4-2008 at 16:18


I think that pitch might react with all the chlorine and stuff.
The hotmelt glue and epoxy reacts with it, and gets brittle and falls off with time
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[*] posted on 4-4-2008 at 21:51


I have a nice chlorate cell using a MMO anode and Ti cathode but in my design the electrodes are bolted (with brass bolts) to a copper rod that extends into the electrolyte. So far I have tried to cover the rod with two different types of epoxy both failures. The first was a special gray colored marine epoxy designed for permanent immersion in salt water. It turned white and began to come off as a soft white powder after only about 24 hours in a hot chlorate cell. Next I carefully sanded the white powder off until I got to the undamaged epoxy (the epoxy was about 4mm thick at the beginning) and put a coating of a different brand of epoxy on. This layer lasted about 36 hours but turned soft, yellow and could be peeled off the first layer.
My cell is now on hold until I can find a suitable replacement.
I was thinking about Devcon Titanium filled epoxy putty, or Devcon Alumina filled epoxy coating as their properties are outstanding. (max working temp about 177C as well as being resistant to solvents, acids, most bases, and salts.) The alumina filled putty is 90% alumina so it really has outstanding chemical resistance.
However, last time I checked they were about $130/lb on eBay and that was the smallest you could purchase.
Does someone know of a putty or claylike substance that would not require firing, adhere to metal/epoxy and solidify to a non-porous form that would not conduct any moisture/salts?
Or does fiberglass resin hold up semi-permanently in a hot chlorate cell environment?

I am aware that some websites (Dann2 I think) claim that MMO coatings should not be used above 40C but the literature I have read states that MMO anodes can have life times on the order of 7years, even in a hot cell. (I am saying this because I don’t want to have someone discuss temperature and MMO anodes in this lead dioxide thread).
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dann2
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[*] posted on 6-4-2008 at 10:04


Hello,

My Chlorate cells have never been up at 70 or 80C for long periods of time. The resin works ok when temperature is lower for long periods of time. Never had it fail.

Car body filler (Made by Isopon may do too).

@Markgollom You are right about the temperature.

Dann2
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dann2
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[*] posted on 12-4-2008 at 17:36


Hello,

Titrated my LD anode cell two days ago. 310 grams per liter Chlorate. This cell is sloooooooooowww.
I am beginning to wonder if the whole concept of Chloride to Perchlorate is a bit daft. If the cell is working at 20% CE (ie. my cell) for making Chlorate. When the cell starts to make Perchlorate there will be a bottle neck when it destroys all Chlorate present (converts it to Perk) and then sits around waiting for more Chlorate to form. The bottle neck will occur because it only takes 1/3 the amount of electrons to make a mole of Perchlorate from Chlorate when compared to making Chlorate from Chloride + the fact that the Perchlorate formation may operate at say 70%CE.

Anyhow, anode looks fine. There is Lead depositing on the (Ti) Cathodes, at least I think it is Lead. Will scrape off some and see if it will melt. It this anode fails by wearing out it will last for a year or so judging on the amount of deposit on Cathode. You would not know looking at the Anode that there was any wear at all.

Dann2
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hashashan
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[*] posted on 13-4-2008 at 02:25


Dann
did you try to check CE in cells with Graphite, or MnO2 anode?
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dann2
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[*] posted on 13-4-2008 at 05:50


Hello Hashashan,

Never titrated with Graphite. Never used MnO2.
Will try soon.

Dann2
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[*] posted on 2-5-2008 at 15:17


Hello Folks,

My Ti substrate anode has been working now for 9 weeks in a cell going from Chloride to Perchlorate, approx. 2.250 liters.
It is ridiculously slow. Can now get yougart ppt when I add some KCl. The Chloride continues to fall as well as the Chlorate. Have not had time to titrate Chlorate lately. I check Chloride by taking a 0.5cc sample. Dilute with 30cc water. To this I add drops of known dilution Silver Nitrate solution untill I get no more ppt. This takes a few days as I must leave the cloudy solution to settle for 12 hours or so.
Some pics of anode below.
There is a large amount of Lead ppt on Cathodes. I scraped it off, dried and weighed. It was 6.7 grams.
I think I can smell Ozone coming from cell. The current has fallen by about 10% in the last 3 days.
<a href="http://s168.photobucket.com/albums/u200/anodes_2007/?action=view&current=top.jpg" target="_blank"><img src="http://i168.photobucket.com/albums/u200/anodes_2007/top.jpg" border="0" alt="Photobucket"></a>

<a href="http://s168.photobucket.com/albums/u200/anodes_2007/?action=view&current=lead_2.jpg" target="_blank"><img src="http://i168.photobucket.com/albums/u200/anodes_2007/lead_2.jpg" border="0" alt="Photobucket"></a>

<a href="http://s168.photobucket.com/albums/u200/anodes_2007/?action=view&current=lead.jpg" target="_blank"><img src="http://i168.photobucket.com/albums/u200/anodes_2007/lead.jpg" border="0" alt="Photobucket"></a>

<a href="http://s168.photobucket.com/albums/u200/anodes_2007/?action=view&current=cleaned.jpg" target="_blank"><img src="http://i168.photobucket.com/albums/u200/anodes_2007/cleaned.jpg" border="0" alt="cleaned"></a>

D2
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dann2
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[*] posted on 15-5-2008 at 19:50


Hello,

I stopped the cell today. The end had arrived as I cannot detect any Chlorate using the titration method I am using from a cell sample size of 30ml (alot).

Checked Chloride level 5 May and it was at 6 grams per liter.
Chlorate level was at 108 grams per liter.

Today I could not detect any Chlorate.
When I attempted to check Chloride level (using known dilute solution of Ag Nitrate in a
measured and diluted cell sample as I did before) I got a light brown/fawn colour that is taking a very long time to settle. It would appear that Chloride levels have increased (if the brown ppt is Chloride).
Can anyone suggest what the light brown/fawn ppt is?

What is the actual colour of Silver Chloride anyways. When you are doing a Chloride test using Silver Nitrate the Siver Chloride appears as white clouds. When it settles to the bottom it looks black. What colour is the stuff if you purchase it (Silver Chloride) in a jar?

This cell has been running for approx. 10 weeks at 10 amps. Thats 16,800 amper hours.
With approx. 720 grams Na Chloride at the start, 12.3 moles, it will take 2640 amper hours to convert to Perk. at 100% CE.
I calculate this cell current efficiency at approx. 15.7% CE.
It is too slow, but gets there in the end. At least the Lead Dioxide is capable of taking the Chlorate to very low concentration.

The cell has been emitting Ozone for the past three weeks, at least that what I presume the smell is. There is only a small amount of Lead being deposited onto the Cathodes. It would appear that most of the Lead deposited onto the Cathodes approx. 3 weeks ago and has since slowed down. I cleaned the electrodes as shown in picture above.
There is a small amount of brown material at the bottom of the cell, perhaps one gram weight. The liquid is crystal clear. Cell is 2.25 liters BTW.
A drop of K Chloride solution causes an immedieate ppt of K Perk that sits on the surface of the solution.

Will extract Na Perchlorate.

Next up is a pure Perchlorate cell using pure Chlorate (containing approx. 2% Chloride).

Dann2
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dann2
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[*] posted on 15-6-2008 at 09:32
Anode update


Hello,

The beginning of the end of the Ti substrate LD Anode is beginning (if ya know what I mean).

It had been running for a total of three months. Current efficiency in a Chlorate cell was poor.

When it was used in a pure Perchlorate cell is give low CE and was inclined to wear. The coating was already thin when it was placed into the Perchlorate cell.
The anode has been lying idle for some weeks now as I did not have time to post.

I don't have much data for same reason.
CE in Perchlorate cell was low but it did the job.
It still works OK. The voltage of the cell has increased a volt or so though.

Next anode will have a much much thicker coat of LD on it.

If I get time to titrate Perchlorate cell samples I will report here.

Dann2

anode.jpg - 71kB
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hashashan
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[*] posted on 15-6-2008 at 20:57


Dann are you using stirring?
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dann2
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[*] posted on 16-6-2008 at 15:15


Hello Hashashan,

Did not use any stirring. The cell was shallow (the anode and cathodes went all the way to the bottom) so I presumed that the Cathode and Anode bubbles were sufficient to keep the cell stirred.
Perhaps stirring would have helped. Garage Chemist (in a Pt Anode cell) says stirring is essential.
Brown (LD) started to appear on the cell bottom from day one. Some Lead on Cathodes too.

The anode is still going to last quite a long time even though the Ti is exposed in places. The thichness of LD at the top of the anode is still quite thick. I (alas) don't have any Chlorate for to start up a new Perchlorate cell. I have gallons of Perchlorate contaminated Chlorate solution.
The final Chlorate concentration of the Perchlorate cell was 11 grams per liter. Cell volume was 0.88L. Current efficiency for the first day running was 47%. After 32 hours running a 'yougart precipitate' was obtained when KCl solution was added to a cell sample.

Will begin a pH controlled Chlorate cell with the (weary looking) anode.

Dann2
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hashashan
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[*] posted on 26-6-2008 at 00:15


Hi, got a question here.
anyone tried to electrolyze Barium chloride with PbO2 anodes straight to barium perchlorate?
I guess it will demand high current densities and the erosion rate might be too high.
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[*] posted on 26-6-2008 at 00:33


I've tried electrolyzing with graphite to make chlorate, which worked fine. I don't see why perchlorate would be very different from electrolysis of the sodium salt.

Tim




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hashashan
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[*] posted on 26-6-2008 at 01:06


did you manage to separate the chlorate from the chloride?
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[*] posted on 26-6-2008 at 02:30


Not yet. I have some isolated, but there is still plenty of chloride left to convert. I should run some more amps through that some day. Given the solubilities, barium is definitely a batch process, not like sodium chlorate.

Tim




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hashashan
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[*] posted on 26-6-2008 at 02:43


How are you plannning to separate the products?
both of them are highly soluble
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hashashan
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[*] posted on 26-6-2008 at 03:08


Sorry for about the double post
but I just got this crazy idea of making a composite anode that will be made from Carbon rods impregnated with PbO2 all the way through them.

How about soaking Carbon rods in Pb(NO3)2 solution (preferably under vaccum) and then oxidising them with bleach.
After that a short electrodeposition will ensure that all the PbO2 will be converted to the beta form. Also the electodeposited PbO2 will protect ehe Carbon at all times, even after heavy usage there will still just be loose Carbon particles in a single piece PbO2 anode, thus we will get a reliable strong PbO2 anode with an electrical connection.
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[*] posted on 26-6-2008 at 08:16


I don't see that working, the graphite is already a more-or-less continuous matrix. You would get PbO2 particles in a graphite matrix. Extremely porous graphite (I'm thinking foam here) might have enough space that you could eventually be left with a PbO2 foam as the graphite erodes out.

Tim




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hashashan
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[*] posted on 26-6-2008 at 11:22


Ill try that
I dont think that the graphite will erode out.
I do believe that the PbO2 will coat it. And the more porous it is the better.
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dann2
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[*] posted on 26-6-2008 at 15:09


Hello,

I cannot see the Graphite not eroding out. If it is chemical erosion only they you may be left with a LD 'sponge'.
Graphite erosion is both a chemical and physical process. The physical process (helped by sealing porous Graphite with Linseed oil etc) involves pieces of Graphite being removed not unlike the way water/ice weathers rocks. Graphite particles get heaved out. This will crack and destroy the LD IMHO.

Dann2
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[*] posted on 18-8-2008 at 08:36


Just a quick question on using lead dioxide.
I now make my PbO2 by electrolosis of H2SO4 using Pb electrodes.
This deposits a black/brown ( i guess PbO2) layer on the cathode(i think... maybe anode)
will this layer be enough to use in a perchlorate cell? I have never made chlorates/perc's myself but this is something i would really like to learn how to do,
thanks,
Picric-A
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[*] posted on 18-8-2008 at 08:48


Not likely, it's not adherent in my experience. Like, it's flaking off right?

Tim




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