Sciencemadness Discussion Board

Thoughts On Anodes

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Xenoid - 20-12-2009 at 13:07

Hi Swede - your discussion with DeNora is interesting, I wasn't aware there was any difference between bipolar and normal MMO mesh or why there would need to be. If I recall, there was a bit of a discussion of bipolar electrodes a while back, in one of the threads.

It is my understanding that a bipolar electrode has one side an anode (facing a cathode) and electrons pass through and the other side operates as a cathode (facing an anode). The advantage (especially to industry) is the saving on connections, contact resistance and the higher voltage (lower current) operation (thinner cables). I guess this is an advantage to amateurs as well!

Many (more modern?) chlorinator cells are operated in a switching mode (I don't know what the timing is (seconds, minutes, days or weeks) to avoid build up - but I wouldn't have thought it would be referred to as AC.

I have come across several 5 and 7 plate normal monopolar electrode assemblies that are operated in this switching mode. They have, of course, all MMO electrode construction. Non-switching (polarised) chlorinators usually have just plain Ti mesh cathodes, although I did find one marked with a + and - that was all MMO. There is a lot of variety out there!

The interesting feature of the assembly pictured above is that it is both switching and contains bipolar electrodes. I guess that once you get up to a large number of electrodes (10) it makes sense to make some bipolar and run the cell at a higher voltage. The assembly is running in a 3 x 3 cell series-parallel arrangement rather than 9 cells in parallel, thus requiring 3 x voltage and 1/3 current. There would be a lot of tricky spot welding to put that above assembly together as a fully monopolar set-up!

I can't understand why a bipolar MMO electrode would need to be a different construction to a normal electrode. Possibly coated on only one side only, but that would be more trouble than it was worth, and you could only run the cell in a non-switching mode. There would always be the possibility of some dork assembling it back to front :(

dann2 - 20-12-2009 at 16:13

Hello,

Deary me, I think I need to brush up on some series/parallel stuff!!!!!!!!!! (Year one, Chapter one, Page one).

US Pat. 6391176 is about a pool Chlorinator. The cycle times are shown in the picture of some text below and are of the order of 10's of seconds.

Going to another subject, his link
http://www.corrosion-doctors.org/CP/non-consum.htm
states that Pt Anodes do not like AC ripple. I guess people need to know that if using crude DC (transformer and rectifier with small or no capacitor) on their precious Pt Anode.

Dann2

clean.JPG - 12kB

Swede - 21-12-2009 at 10:31

Hi Xenoid - I may be using the term bipolar incorrectly, and definitely using the term AC incorrectly. My limited understanding of the advanced pool chlorinators is that on a periodic schedule, the polarity is swapped for a short time, which is supposed to clean the anode of deposits. But still, the vast majority of its function is DC.

Denora offered what they called "biploar mesh" and it was indeed more expensive than DC-only mesh material. Either the oxides are different, the substrate prep different, or both.

My own actual pool chlorinator appears to be interleaved solid sheets of MMO and Ti. The spacing is very tight, about 2mm. You might fit a knife blade between them, but nothing larger.

It has been chlorinating my pool for several years now and shows no signs of wear or tear. I clean it annually in a 1/2 dilution of conc. HCl to strip what appear to be calcium or carbonate deposits... otherwise, no maintenance required.

Best guess is that bipolar or DC-only MMO would work for chlorates so long as it is primarily Ruthenium.

Swede - 6-1-2010 at 13:14

Some experiments with a drip (gravity fed) HCl system...

We have discussed this in some detail in the past. I previously used a peristaltic pump with a good timer to deliver the HCl based upon an electrical current rule of thumb. The problem was the coarseness of the delivery, and the fact that the tubes from the pump to the cell often filled with gas between HCl deliveries, making precision difficult.

I decided to attempt a drip system, and the initial results show great promise. A drip system consists of three important components:

1) An electrically-activated solenoid valve
2) A metering or flow valve
3) A decent timer capable of good precision

Obviously too, you need a vat of HCl positioned above the system.

All of the components must be impervious to HCl, either concentrated (near 32%) or dilute. I picked up a surplus 12VDC solenoid valve that has 100% PTFE wetted surfaces. This one was from Cole Palmer, but others would do fine. Next, an Aalborg VT-PTFE needle valve was obtained; again, all PTFE where it counts. I turned up an adapter from Teflon to connect the two, although PVDF hose barbs would do fine as well.



The vat of "HCl" (water for now) was positioned 1/2 meter above the assembly.



Applying 12V to the solenoid triggered it to the ON state, and the water began to flow through even the narrow tubing (1/8" or 3mm ID) rapidly. Working the excellent Aalborg needle valve allowed a very precise control, down to 1 drop every 10 seconds or so:



The only thing that is going to alter the flow of this unit is head pressure. As the HCl vat depletes, the flow rate will drop off. But experimentation with positioning of the vat showed that the effect was very minimal. If the level of the HCl drops 10 cm, but the overall height of the vat is at 200 cm, the head pressure will vary at worst 5%, and in reality, since the flow rate is so slow, the actual delivery variation is even less.

The Aalborg needle valve produced a control so fine that possibly the timer itself could be skipped, and the HCl delivered on a continuous basis... but I still prefer the concept of timed delivery.

Overall, though, gravity feed eliminates a lot of the expense and hassle of HCl delivery. One important aspect is that it must be engineered well; otherwise, the possibility exists of a leak draining the entire vat and causing a mess or hazard, but we are only dealing with a couple of PSI or maybe 150 millibar, depending upon the height of the vat.

The most expensive component was the Aalborg needle valve. I bought mine new for $45 US, because I could not find one used on eBay. The solenoid was maybe $10 NIB on eBay.

A less fancy rig could be made up with cheaper components, and still get excellent results. How about a $2 pinch clamp on the tubing, setting the system up for a continuous IV drip?

Gravity-fed HCl is the way to go! :P

Cheers, & Happy new year!

dann2 - 8-1-2010 at 20:30

Hello,

Nice tidy job Swede.

Another pump that will do this job and ideal for the cheap skate is a pump made from some tubing and an aquarium air pump. It would have to be on a timer of course.
A diagram of the pump is shown in picture.
The pump is totally unsuitable (BTW) for pumping fluids with dissolved salts as crystals are inclined to form just above where the air enters the 'upwards' pipe. I think this type of pump is only good for pumping fluids with no dissolved solids.

Another alternative might be a simple solenoid pinching a pipe to turn acid on/off. The pipe would need to be silicon tubing so that it would be nice and soft for pinching.

Regarding the HCl vat. If you place only enough HCl into it to do (say) one or two days, as opposed to a gallon! then if a fault developes and acid is added to cell in one go, only one or two days worth can enter cell.

On another note.
I made some Sodium Nitrite (from Sodium Nitrate + Lead metal) to try out my Aquarium Nitrite testing kit (same as Swedes). The testing fluid is green/blue and the test card is as pictured above a few posts.
When far too much Nitrite (way out of kit range) is added to the solution to be tested the test solution, (when dropped into) the solution to be tested, turns dark red or purple before it reaches the bottom the test tube. When you shake the test tube the contents are purple(ish). When you wait five minutes as stated in the instructions to let the colour develop the colour changes to a blue colour as if the PPM of the Nitrite is very very low (zero PPM). This can be confusing. When concentrations of Nitrite are within the normal range for the kit then it works OK.
I have only tried the Nitrite kit on water + Sodium Nitrite (low ppm) + Sodum Nitrate (high concentration) + tiny amount (tint of blue) of Copper Nitrate. The Nitrates do not interfer with the test. Will have to try it on Lead Nitrate + Copper Nitrate solution (plating solution). The blue of the Copper Nitrate may not help as it may be difficult to see the proper colour thouht we will be diluting 1:32 (see below).
A patent states that 0.1% Nitrite reduces plating efficiency to 30% so (wild ass guess) we should try to keep below 0.01% Nitrites (100 ppm, or 100mg per Litre). To bring this into the range of the aquarium Nitrite testing kit (5mg per litre or lower) would require the plating solution sample to be diluted at approx. 1:32 (with water) to bring the 100ppm down to 3 ppm for the kit to test.

Dann2




[file]9391[/file]

Bikemaster - 11-1-2010 at 08:10

Nice set-up Swede!

I am pready sure that your gravity systheme can be easily put on a cell an it will hold the ph as steady as your dosing pump for a fraction of the price. The only add that you should put on your systheme is a small lenght of tubing, let say 15 cm, from the end of the droping tip to the cell. Because if you put the tip directly in the cell, salt will stick to the tip and will change the flow. I know that in your big cubic cell you have a pipe that going in the solution, i am pready sure that this thing to can prevent salt on the tip. I think you were using it to disperce the acid, but it will also prevent the hydrogen and chloride bubble to throw salt on the tip.

The only think i am not really sure, is that you need to put your acid tank very high in the air... I don't really feel safe with a tank on HCl over my head that is NOT totaly close... For my systheme I think i will use the steady liquid leveler to let me put the tank less high.

Swede - 11-1-2010 at 09:42

Thanks Bikemaster. The plan for this thing uses an injector fitting with a length of PTFE tube (maybe 10 cm) that delivers the HCl to the interior of a PVC diffusion pipe. The diffusion pipe is drilled with a number of very fine holes. As the acid enters, it mixes with the interior of the diffusion pipe and is slowly leached into the cell, so there is (hopefully) no "spiking" of the cell with an acid addition.

The pipe can be seen here:



This should keep any gases or pressure inside the system from climbing up the acid tube, and the orifice is below the electrolyte level. As for vat height, I don't think it'll take more than a meter, probably 1/2 meter would work. The only true requirement is to calibrate the system at a given height, and determine volume of acid per minute at a given valve setting. The needle valve is so fine that one full turn of the valve barely increases the flow, so to set up differing flows is going to require multiple turns of the valve knob.

@Dann2: Thanks for the description of the nitrite test. The little I've done with it seemed to indicate that the coloration of the copper (and/or nickel) nitrate shouldn't interfere too much with the interpretation of the results. Perhaps the sample can be "cleansed" of Cu/Ni nitrates via some sort of reagent that will ppt out the metals into an insoluble salt that will leave behind only a clear solution of aqueous nitrites plus perhaps sulfates, chlorides, or whatever reagent is used to pull the colored metals from the test sample.

The other question is what level of nitrites is considered acceptable? And how do we remove them? Peroxide?

12AX7 - 11-1-2010 at 14:47

Won't that diffusion tube tend to hold a higher concentration of HCl, resulting in Cl2 bubbling up the line?

I'd rather, say, run a tube to the bottom, then hook the end of it, so bubbles (Cl2 or H2) rise away from it.

Tim

dann2 - 11-1-2010 at 17:27

Hello,

My (very nice :P) diagram of a pump based on an air aquarium pump did not appear above so it is attached.

@Swede. US Pat. 2994649 gives some info. on Nitrites. They use H202 to Oxidize the Nitrites back to Nitrates. When Nitrites get to 0.1%, CE drops to 30% (Lead Dioxide plating).

I did some more testing with the kit. Added 0.012 grams Nitrite to 100ml water (approx. 120 ppm Nitrite). The amount was out of range for the kit and when you add a few drops they sink to the bottom of the test tube and turn a purple colour in a few seconds. I do not shake the tube. The drops are inclined to sink to the bottom (like little Lead balloons as it were).
I started to addd 35% H2O2 in 0.25 cc increments and kept testing for the Nitrites using the kit. I heated the solution and water perhaps 5 minutes each time. I had to add 1.25cc of the H2O2 to stop getting a positive test for Nitrites. Seems a lot. The last test I done, (zero Nitrites as they were all now destroyed by H2O2) I shook the test tube and waited for colour to develop but I did not get a blue colour as I should have but rather a green colour. I don't really know what this means. There is no green colour on test card.
I guess we will have to wait for when an LD plating session begins to really see if kit will work in an LD plating solution.

I had thought/hoped that Methylene blue might detect Nitrites in water. Excess of Hydrogen Peroxide giving a blue colour and excess of Nitrite (reducing conditions?) would give a clear colour but this does not work at all. I used an acidic (some Nitric acid) solution to try it out. Mehylene blue is a REDOX indicator BTW.


I cranked up a Perchlorate cell approx. 3 weeks ago using (whats left of it) the Ti substrate LD Anode. It has been sitting around for approx. six months. The Anode works OK, no passivation between the LD and the Ti. Will let it go for a month and pull the plug. I will be doing no testing etc, I am just seeing will the Anode continue to work.

I am getting around to setting up a Chlorate cell with a large and a little Cathode. Will use pH controll. When cell has stabalized (constant amount of acid addition to keep pH at around 6.7) I will swap in and out the bigger/smaller Cathodes each 24 hours and see how much the CE changes by doing some titrations.


Dann2


PUMP.GIF - 4kB

[Edited on 12-1-2010 by dann2]

Swede - 12-1-2010 at 09:21

Quote: Originally posted by 12AX7  
Won't that diffusion tube tend to hold a higher concentration of HCl, resulting in Cl2 bubbling up the line?

I'd rather, say, run a tube to the bottom, then hook the end of it, so bubbles (Cl2 or H2) rise away from it.

Tim


That's a good point Tim, and I hadn't really thought about it. I was hoping that evolved chlorine would dissolve and become aqueous, but it is worthy of consideration.

Wherever the conc. HCl contacts the liquor, you are going to have evolved chlorine. If using timed doses, it'd be nice to either very slowly add the dose, or add it in such a manner that it gets diluted very rapidly.

My new cell has mechanical stirring via a motor and a Ti paddle. Perhaps the best place for acid addition would be right next to the rotating paddle for instant dilution.

Leander - 13-1-2010 at 06:21

I was planning to make Ba(ClO3)2 by electrolysis of BaCl2 solution. I have some sources indicating that barium salts (along with cadmium) shouldn't be used with MMO anodes. Can anyone confirm this, and is there any logical explanation?

Contrabasso - 13-1-2010 at 10:40

A research document I have suggests that Barium has adverse cathode zone reactions and needs careful treatment.

dann2 - 13-1-2010 at 11:03

Hello,

Would it be possible to give us links to the sources that say Cd and Ba are harmful to MMO and by all means upload the research document on Barium Chloride.
I have also read that Ba is harmful to MMO. How harmful I don't know. It's on my page.
TIA,
Dann2

dann2 - 13-1-2010 at 11:50

Hello,

I bubbled air through a solution (0.35 grams in 640ml water) of Sodium Nitrite for 24 hours using a plastic 'air stone' and a tall vase. The solution still gives a similar positive indication of Nitrites (using the Aquarium Nitrite detection kit) to when bubbling was started. Bubbling air through a plating solution to get rid of Nitrites in a non starter IMO.
There is some info. on Nitrites at this link
http://library.sciencemadness.org/library/books/Mellor_ACTIT...
on page 459, if anyone is interested.
Also see this link:
http://www.nature.com/nature/journal/v133/n3354/abs/133213b0...

I think it may be possible to lower the Nitrite concentration of fairly concentrated solutions of Nitrite by bubbling air but the very dilute solutions (of Nitrite) we will be dealing with are not going to be lower in concentration by air bubbling. See Mellor.

Dann2

purple.jpg - 15kB

12AX7 - 13-1-2010 at 14:21

Maybe we can use some nitrobacter to oxidize it for us?

Or maybe not... :P

Tim

Swede - 14-1-2010 at 07:22

Have you tried peroxide yet? Or how about bubbling ozonated air? There are a number of fairly inexpensive low-dose ozonators available (yet again) for the aquarium trade.

dann2 - 14-1-2010 at 15:26

Hello,

I have tried H Peroxide in my post of 11 Jan. It seemed to take alot of Peroxide to destroy the amount of Nitrite present.
Just wondering, when LD plating is taking place and their are Nitrites present (what we want converted back to Nitrates) does the H Peroxide we add act directly on the Nitrites or does it perhaps involve some reaction at the Anode involving the Nitrites + the H Peroxide???????
Wild assed thought, my chem's not red hot............

I will check out the Ozonators. Sound like something that could work. I do not love the idea of bubbling air/gas into an LD plating set up because of the extra splashing/mist it may create but I guess a good cover on the tank would deal with that end of things.


On a different note, just wondering if something like cabosil, or powdered aeroboard or floating beads were placed into a Chlorate or Perchlorate cell, would it stop the terrible mist (Satans breath, that rusts all in sight)?

I have attached a good read on making K Chlorate from K Chloride using Lead Dioxide Anode. Thanks to Solo over in references. I have never seen the article before.
They state that coating Graphite Anodes with Lead Dioxide makes the Graphite Anodes last at least three to four times longer!!! Marvelous!!
They used 2N HCl (7.3%) for pH controll.

Dann2



Attachment: Lead_dioxide_anodes_in_the_large_scale_production_of_potassium_chlorate_from_potassium_chloride.pdf (234kB)
This file has been downloaded 1174 times

Swede - 15-1-2010 at 07:26

Until I get my LD plating rig set back up, I can't help with the nitrite issue. The used liquor from the last run probably will be altered from what it was... it's been almost a year.

I agree with the thought that any bubbling in the bath is a really bad idea. There's enough gassing from the electrodes. We don't need to add to it with hard, rolling bubbles from an aquarium pump.

I am excited to give my mechanical stirring rig a shot on my next run. I have extensively modified my "T-Cell" using what I've learned, and the next major run will consist of mechanical stirring, no lousy bubbler to jam, and a gravity-fed HCl system. Since the cell is opaque, I set up a "dip stick" method to check the liquor level. I trimmed a glass pipette, added a PTFE collar, and to check the level, all I have to do is close off the end of the pipette and remove it from it's fitting. The liquid will be trapped, and I can compare it to a pre-made scale.

I have about 300 cm^2 of Pt mesh coming. I haven't given up on LD, but I do want to work with Pt as well. A couple of miniature test runs with a small Pt anode produced beautiful results. I need to scale it up a bit.

Nice paper, dann2, it's got some good info on it. Thanks. Right into my electrochemical PDF collection it goes.

[Edited on 15-1-2010 by Swede]

dann2 - 15-1-2010 at 19:50

Hello,

Pt is the King of electrodes. The poor mans Pt takes some time, effort and less cash............ I think.

Attached is a paper on a pilot scale plant for the production of Ammonium Perchlorate in Europe.
Have not seen this myself before.
It came from this link:
http://www.nt.ntnu.no/users/skoge/prost/proceedings/ecce6_se...

Have a good read.

Dann2

Attachment: Ammonium Perchlorate pilot plant_2007.pdf (520kB)
This file has been downloaded 1129 times

dann2 - 16-1-2010 at 06:46

Hello,

Keep reading.
Attached is a must read on Potassium Perchlorate (and Sodium Chlorate and Perchlorate) manufacture.
I have not come accross this paper before.
Thanks to Solo.

Some salient points (IMO, everyone will have their own):
A good laugh at the top of page 64.
They check pH and add acid to the Chlorate cell every 24 hours only :o for to contoll pH.
The Chloride content is reduced to 84g per litre with Graphite Anodes.
The Chlorate content is reduced to 20g per litre with Pt.
pH not controlled in Perchlorate cell stage and goes to 10.5.

What is 1:1 and 1:2 HCl acid? Is it 36%HCl diluted with one parts water and two parts water?

Cheers,
Dann2



Attachment: Production_of_Potassium_Perchlorate.pdf (673kB)
This file has been downloaded 879 times

[Edited on 16-1-2010 by dann2]

Swede - 16-1-2010 at 08:29

Another interesting read. They have the batch process down pretty nicely, considering it was 1942.
Quote:

What is 1:1 and 1:2 HCl acid? Is it 36%HCl diluted with one parts water and two parts water?


I think we can be confident that that is exactly what it is, 32 to 36% commercial HCl diluted 1:1 or 1:2.

They use tubular cathodes and axial Pt rod anodes for the perchlorate cell. I found this to be interesting:
Quote:
Operation of the cell is greatly affected by the chloride content of the cell liquor. At concentrations of more than 2% (dry basis) no perchlorate is formed. The effect is abrupt, and it appears that a critical chloride concentration is involved. No explanation of this effect can be offered.


In other words, Pt does not, and never did, like chloride. I know Pt is supposed to work all the way from chloride to perchlorate, but something doesn't ring true, and this document supports the notion: "Use LD/Pt for perchlorate. Use MMO or graphite for chlorate." A one pot process from chloride to perchlorate is going to be very difficult, materials-wise. Perhaps LD can do it, but given the availability and low cost of both graphite and MMO, it makes little sense to risk the precious perchlorate anodes on chlorate.

Getting a harvest of chlorate that is well below 2% chloride is not difficult at all, and that is your feedstock for the perchlorate cell.

Additives: They use dichromate in the chlorate cell to prevent cathodic reduction. Is there an additive recognized to be helpful in a Pt-based perchlorate cell to do the same thing? We don't want our oxidized products reduced to chloride, which will increase anode erosion and slow or inhibit the process.


dann2 - 16-1-2010 at 14:08

Hello Swede,

They actually use Dichromate at (approx.) 1 gram per litre in the Perchlorate cell. See page 57.
With LD you cannot use Dichromate so Flouride seems to do a similar job. Persulphate as also been used in LD cells.
One problem I have with coaxial arragements (pipe and rod) it that you are forced to have a large Cathode area in relation to Anode area. This may have serious implications if running cells with no additive (green cells) to stop Cathodic reduction reactions. Large Cathode area ==> large amount of reduction AFAIK and no additive to stop it. Four or five wires in parallel with the rod would be good if using a green cell. Less area and still a good current distribution on Anode.

The cells are actually not bipolar even though they look like they are since a 'comb' arrangement is used. All Anodes are actually physically connected to the + of supply with 3.1-3.5V accross cell.

I think the 'Holy Grail' method of making Perchlorate should perhaps be renamed the 'Unholy' method. Far too much time and wear on the precious Anode (Pt or LD) during the Chlorate stage and if you are not using pH controll during the Chloate stage then it's simply crazy.
As stated by yourself and others, seperate the two processes.

Bit of a paper splurge (with more to come). This one discusses some history. Some interesting 'garage like' pictures of early Perk making stuff.

Dann2

Attachment: History of establishing K and Amm Perk sources.pdf (916kB)
This file has been downloaded 928 times


[Edited on 17-1-2010 by dann2]

Reading Material

Lambda - 16-1-2010 at 16:31

Chlorates and Perchlorates.rar (15.5 MB) contains the following Files:

1. - Lead Dioxide Anodes - HTML

2. - US Patent 5.104.499 - Electrolytic Production of Alkali Metal Chlorates and Perchlorates.pdf

3. - Chlorates and Perchlorates.pdf

4. - An Idiots Guide to Making Chlorate's and Perchlorate's - By WarezWally.pdf

5. - A Study of the Production of Sodium Perchlorate Electrolytically - By Frederic A. Maurer (Thesis - California Institute of Technology - 1923) 33s.pdf



6. - Materials Handbook - A Concise Desktop Reference - 2nd Edition - By François Cardarelli (Springer-Verlag - 2008) 1365s - Including Bookmarks

* Lead Dioxide (PbO2) Electrodes; Starting at Scan Page 606 with Preparation and References on Scan Page 607

iFile.it Download Link:

http://ifile.it/35xrnhz

No Password Required !

Enjoy !

Lambda

Contrabasso - 17-1-2010 at 01:46

While Pt seems not to like going through from chloride to perchlorate in one step, there was a cell in the UK running a lead dioxide anode from saturated chloride to perc. The guy did loads of write ups on his own www with all the testing and the first run. IIRC he ran it at 80a continuously!

Then a UK supplier offered him a drum of perc so he stopped playing. He's been very ill since and not maintained the www sadly.

Pt Porn

Swede - 19-1-2010 at 08:34

My long-delayed raw 3 micron Pt over Ti mesh finally arrived. I absolutely have not given up on LD and other anode attempts, but I did want some Pt mesh to experiment with.





Pt is expensive - in any form. A reagent-grade salt to pure Pt metal; it doesn't matter. I think in the end, it would cost as much to plate an anode with an equivalent Pt coating beginning with a Pt salt, as simply buying this material from the start. The Pt load of this mesh is 50 grams per square meter.

I am probably going to craft tubular Ti shanks for these, filled with Pb, to fit a 1/2" PVDF compression fitting.

dann2 - 19-1-2010 at 12:25

Hello Swede,

You have got yourself some lovely Platinum coated Ti substrates for Lead Dioxide Anode's there...................;)

Doing a calculation from the 3 Micron thick coating of Pt I was amazed to find out that the total Pt per square Meter is indeed 64 grams per square meter. (You quote 50 but it's around the same). That's 64 X 50 (Dollars per gram, roughly) = $3200 of Pt on a square meter :o

Do you know if the Pt on the Anode's is actually electroplated onto them or put on with a chemical decomposition method. (bakeing I guess)? Just wondering for the record.

EDIT:
There is a very dodgy dude selling dodgy materials on ebay here though I must admit 4 + grams of ChloroPlantinic acid would be great....... O stop Dann2
I think I will stick to the less dodgy black molars :D:D:D

Dann2 (going off to the morgue)


molars.jpg - 44kB


[Edited on 19-1-2010 by dann2]

Swede - 20-1-2010 at 07:58

Hahaha! That is awesome! I don't know jack about Pt dental implements, but I thought gold was more commonly used. At 4.2 grams for that molar, we are looking at 0.135 troy ounces, and at $1600 per troy ounce, you're looking at $216 worth of Pt.

It sucks that Pt is so expensive. Why can't it be more like silver? We'd never have to worry about a good perchlorate anode again.

I'll gamble that it will sell for about $180 given it's state... perhaps stolen from a dead person.

For small quantities of platinum, I'll bet there are 1/10 and 1/4 ounce bullion coins out there of 0.999 Pt, nice and pure.

The use of a Pt mesh to act as a substrate for LD is an interesting one. The worst case is that all the LD falls off, and you are left with... a valuable Pt anode. You really don't lose anything except the work. If it DOES work, then you have zero Pt loss so long as the LD adheres and functions properly.

[Edited on 20-1-2010 by Swede]

Thoughts on Cathodes

dann2 - 28-1-2010 at 17:10

Hello,

Perhaps we need a new thread!
I set up a pH controlled Na Chlorate cell today using a Graphite Anode. I intend to use different Cathodes in the cell to see if using big or small Cathodes makes much of a difference when a cell is run without Cathodic reduction additives (like Chromate, Flouride etc).

I have three Cathodes I will be trying. Large Ti, small Ti and a large mild Steel one.
The large Ti and Steel Cathodes are shown in the picture. The shiney one is mild Steel. The other is Ti but it is more grey than the picture depicts.
I will be letting the cell stabalize for approx. two days untill acid additions are steady using small Ti Cathode. Then add large Ti Cathode for one day, small one for next day, large one next day, small one next day, large steel one next day, small Ti next day, large Steel next day and then add Dichromate next day (or something like that).
Samples of cell will be taken at the end of each day and titrated. Should show up any large advantages/disadvantages associated with using small/large Cathodes.
The surface area of the two small flat Ti Cathodes (one each side of Anode) is 40 square cm, These two Cathodes have their backs covered with plastic. The total surface area of the large Ti and mild Steel Cathodes are 714 square cm (2 * 357, counting back and front)
I am using a CC supply (homemade from computer power suppy) giving 4 Amps into cell.
Acid addition is with a syringe pump.
The cell I am using is the same as the one I used before for making Chlorate with Graphite with pH controll (way up the thread somewhere) and contains approx. 2.2 litres.

@Swede
I would be inclined to agree that Sulphuric acid would definately be worth trying in a Perk. cell if it helps Anode erosion. Sulphates are not good news with Chlorates so it would not be a good idea at all in a Chlorate cell (assuming is does any good in a Chlorate cell anyways and HCl is not a problem in a Chlorate cell).

I am slowly but surely getting around to making a new LD Anode.

Cheers,
Dann2



cats.jpg - 24kB

Swede - 29-1-2010 at 18:26

Hi guys - I have worked a bit with the tubular Ti shank concept, and one of the real problems is the poor conductivity of the Ti tube. We tossed about some ideas like filling the tube with lead or an alloy of lead, and using that to carry the bulk of the current. I bought some alloys and also some 1/4" tin wire from Rotometals and attempted to fill a 1/2" OD Ti tube (flattened on one end for welding to an electrode) with tin so that the tin will carry the bulk of the current rather than the Ti, a poor conductor.

It was painfully easy, AFTER heating the Ti to dull red:



The interior was scored for mechanical purchase:



And it was filled with pure tin using a simple propane torch:





The end of the tube was cleaned up, drilled and tapped 1/4" X 20, and is ready to accept a crimp terminal:



The whole idea was to create an electrode shank for production - solid and leak-proof mounting using a PVDF compression fitting, and an ability to carry a current that puts the Ti tube skin to shame. An earlier attempt using a brass cap to make the connection:



So far, so good. Tin drills and taps well. I think this will work. :)


Swede - 29-1-2010 at 18:33

@ dann2: I posted the former before seeing yours - I am really interested in seeing what sort of results you see. I know you are a fan of appropriate cathode current density, and I hope you can gather data that will shed some light on this issue. I think the goals of most hobbyists are:

1) Preserve the integrity of the anode, be it Pt or LD
2) CE

I would happily give up some % of CE if it preserves the anode, especially when dealing with Pt. If there is a specific cathode CD or orientation, or if there is an additive that helps, then it would be a real boon to the hobbyist.

I look forward to your resuts!
:D

dann2 - 30-1-2010 at 18:31

Hello,

Swede, if any salts appear at the top connection of that shank I will eat my boots!

I cranked up the cell approx. two days ago and am waiting for the cell to stabalize (to come to the point where a steady (known) rate of acid addition keeps pH where we want it).
After one day with small Ti Cathodes I decided to put in the large Iron Cathode to age it a bit for the study proper. I am not 100% sure but it seems that the pH actually started to drop too much when the Cathode went in and when I stopped acid additions the pH stayed at approx. 5.9.
Can anyone comment on what might be going on. If a large amount of reduction is taking place at the Cathode will this cause the cell pH to go lower or stay lowish?
I will have to look up some cell chem. equations I guess.

On a slightly different note, since stainless steel has Chromium in it, perhaps it is not as bad a material for reducing wanted product back to starting products as compared to mild steel. Did I read somewhere that it does form a (somewhat poor) anti reduction film. Not too sure.

@Swede
Did you come to any conclusions regarding end of cell run detection with your data gathering?
I was thinking of making something like the attached pic. A sample would be taken from the cell and measure at zero degrees (nothing special about zero degrees it's just easy to do with ice). This would eliminate temperature problems. The distance between the probes would be fixed and could be quite large is this was an advantage.
Pt is compatable with soda glass and you would only need a cm or two of Pt wire as it can be soldered to Copper like here.

Dann2





PtProbes.GIF - 5kB

Swede - 31-1-2010 at 07:43

dann2: I like that concept that you have diagrammed, and I think it would work. I still have reams of data from the run, and I saw the exact same phenomenon seen before - at CC; an intitially higher voltage requirement which dips within a short time, but then gradually climbs as chloride is depleted. But then as we noted, it was strongly temperature-dependent, which really gums up the works as far as simply monitoring a cell's voltage and current as compared to the initial conditions. If I was more of a mathematician, I'll bet I could come up with a crude but workable mathematical model that relates voltage, current, temperature, to chloride, with a "constant" in there which will be derived via calibration, and which will vary with cell geometry and materials, since each cell is wildly different.

I was thinking about this the other day when we were talking about conductivity or other simple measurements. I am tempted to mix up several small samples, starting with, say, 15% KCl salt, and then introducing chlorate salt and reducing the KCl. Picture a series of about 5 small samples that would be representative of a cell during production. A set of electrodes very similar to what you have pictured. Then measure... what do we measure? Can it be as crude as resistance in ohms? And would this resistnace vary horribly with temperature, or could it successfully be ignored? Given the very high (saturated, but varying species) salt content of the liquor, you would no doubt get an ohm reading depending upon the size and spacing of your electrodes. Then, here comes pH to throw yet another variable.

If the temperature did not play a big role, it might yet be possible to get a reasonable idea of chloride based upon some very simple measurement, but pH...

Anyway, I like the idea of removing temp from the equation by doing it at 0, as you suggest.

On the use of stainless as a cathode - the thought that the chromium content might reduce or eliminate unwanted reduction at the cathode is a good one. But would the cathode be subject to erosion? Powered on, in theory, it would be cathodically protected and hopefully the liquor would remain free of chromium, nickel, moly, and Fe.

[Edited on 31-1-2010 by Swede]

12AX7 - 31-1-2010 at 10:52

The most useful measurements are measurements around the most useful operating point. That includes transient species like hypochlorite and all the active stuff around an electrode (H2 and OH- at the cathode, H+ and Cl2 at the anode), things that can't be measured with two salts in water at zero current.

Tim

Swede - 31-1-2010 at 13:57

Tim, I agree, and my understanding and general P-chem and electrochemical knowledge is painfully weak... but I'm thinking of a very simple method to determine rough end of run conditions. If it can get to within 1 to 2% chloride in terms of accuracy, I think that'd be successful, and since a potassium cell (at least) only goes from 16% to perhaps 6% Cl-, it is a margin of error of 10% or more.

It'll be a simple ratio of chloride to chlorate, and I'm wondering if that ratio changes, is there a simplistic method to measure it using conductivity? There are a few options now to measure or predict Cl- : you can titrate frequently or use expensive Hach Cl- titration strips; you can create a mathematical model that is based upon current delivered and starting chloride; or, you can again create a mathematical model expressed as a function of voltage, current, and temperature, and at a given temp, how the former two change in a given cell.

pH is a whole nuther ballgame. But these are starting thoughts.

@dann2: I re-read your cathode experiment, and am wondering - did you consider the differing environments when you do the cathode swap? CE isn't a constant thing, it doesn't stay at 85% for the entire run, but varies. I'd guess CE is at its very best at probably the 1/5th point - the cell chemistry is relatively mature, yet the Cl- is still high. If you swap cathodes through the run, each cathode is going to see a different Cl- concentration. Still, it's infinitely better than anything I've tried, which is to simply stick with Ti in a size "that looks about right." The only problem I ever had with Ti was the "banana" cathodes from the 95 C, zero chloride, near boil-out of my jammed electrode cell in the failed 2-cell system. Those cathodes never did straighten out, despite heating with a propane torch, and plain old aging.

The question is minimization of reduction at the cathode. How to control it? We don't want Cl- attacking Pt. Choices are materials, additives, current density, maybe temperature, maybe pH. pH control in a perc cell is problematic, and most simply don't bother.

Additives - different additives can wreck LD especially. I don't mind moderate toxicity like NaF but carcinogenics like chromium bug me personally.

Current density - high current density at the cathode is supposed to minimize reduction there, true? One method might be to try a run with a ridiculously small Ti cathode. There will probably be a point where the protection vanishes and the Ti is eroded. A small-scale bench-top setup could be run with a moderate MMO anode, very small Ti cathode, and progressively dial up amperage, giving each amperage a period of time, say 6 hours. Then, weigh closely and/or visually inspect for erosion. Perhaps titrate for Cl- using a sensitive test. At some or perhaps multiple points, you'd see a spike in Cl- concentration, visual Ti erosion, or both. That would be a limit for current density.

I'd expect low current + large cathode = reduction of ClO3 to Cl-, and higher current + small cathode = erosion. The sweet spot will be somewhere towards the latter. I'd rather erode a $5 Ti cathode than a $150 Pt anode.

Enough babbling for now. I've got "T-Cell III" ready to go with some excellent improvements. It'll do another run with chlorate, then a perc run using the tin-filled Ti shank welded to Pt. It has mechanical stirring using a PTFE rod + Ti paddles, and the previously mentioned HCl drip system. I'll get some pics up. :D

dann2 - 31-1-2010 at 20:57

Hello,

What I am doing with the Cathodes is not going to show a 'best' CD for Cathodes but (hopefully) show that it important to have a fairly sensible Cathode size. Large 'stupidly big' Cathodes will seriously effect CE (I think).
See Ullman page 24 (and 9) at this link:
http://oxidizing.110mb.com/chlorate/further/ullman.pdf
The presence of Chromate film on Cathode effectively raises Cathode CD. We can do the same using a small Cathode and covering the backs (the part of the Cathode away from the Anode) with plastic. A coaxial Cathode is going to have a very very low CD on it's back side (rude!). If a coxial Cathode must be used it would be important to have it drilled (ie. a mesh) so that surface area will be smaller and also current will be higher on it's back side as there will be a more direct line of site (as it were) to the Anode.

The different CE's I am going to get will be superimposed on the changing CE you obtain with changing Chloride but I am hopeing that I will get a good indication of the effect of very large Cathode versus small (sensible) size.

Large or very large CD on a Cathode is not a problem and it will not erode it at all IMO.

Corrosion in the head space is a problem unless using Ti (or Lead or Graphite?). I am getting rusting of the mild Steel Cathode in the head space (its very thin metal) so I am going to coat it with solder in the headspace area to protect it. I presume solder will not corrode?
Often wondered about a Lead Cathode. It would be easy to fabricate and cheap and non corroding.

Ti does not reduce Hypochlorite and Chlorate much I have read so a large Ti Cathode does not really matter (I think!), except for expence. (read this in a Thesis somewhere or other).

Regarding the probes I guess it's going to be a case of suck it and see :D
I am not to sure what exactly we are measuring and what is having the most effect at causing the cell voltage to rise. Less Chloride? More Chlorate?
I had not thought of pH. Perhaps it will not effect the reading much? Don't know myself.

I have splashed out on a one cm piece of Pt wire some time ago so I might try making the probes sometime and see. Small pieces of MMO might do instead or even two pieces of Graphite.

Dann2

Swede - 1-2-2010 at 07:55

Might niobium wire (reasonably cheap) form the basis of probes, or would it too passivate? Iridium is another metal that is not outrageous. Au? Fine Gold wire is significantly cheaper than platinum. It could be mechanically twisted with Cu leads, and all except a tiny Au portion encased - glass as mentioned, or possibly a polymer of some sort to keep the liquor off the Cu.

Swede - 1-2-2010 at 07:58

Ti CD: I have been corresponding with another hobbyist who apparently wrecked a Pt anode with excess current in an attempt to go from chlorate to perchlorate. He used a CP Ti cathode, and declared he saw "Heat traces" on the Ti. I don't know if he is referring to the strap above the liquor, where I too have seen heat discolor the Ti, or some other sort of traces or markings on the Ti working surface, but that could not be heat due to immersion.

I am tempted to immerse several small wire samples in a full chlorate run to see if the wires suffer in any fashion.

[Edited on 1-2-2010 by Swede]

watson.fawkes - 1-2-2010 at 08:12

Quote: Originally posted by Swede  
I'm thinking of a very simple method to determine rough end of run conditions.
Would a charge-meter work? Charge is just the integral of current, and you're already sampling and recording current values. Pick an upper bound on current efficiency, and it gives you a stop point. It won't run a liquor batch to completion, but it will keep the apparatus safe within its operating envelope. If you're reusing the liquor, you'd want to characterize it between batches, but this doesn't require new gear. If you're not reusing it, the loss is a bit of chloride feedstock and perhaps bath additives; this would trade off against the convenience of unattended operation and lower initial cost of monitoring sensors.

dann2 - 1-2-2010 at 17:29

Hello,

Regarding the charge meter IMO when you are using a CC supply it is very easy to know the amount of charge that has entered the cell. It's just time by the CC. The charge meter would be good for the person with a Voltage supply where the current is inclined to vary as the cell progresses. But either way you are back to guessing the CE in order to guess the end of run of cell.

Niobium (like Ti, W, Ta, Hf, Zr) is a Valve metal and will passivate when used as an Anode.
Gold will corrode but you may have 100's or 1000's of measurements done before it gives up. Iridium would work IMO. It's not as 'Noble' as Pt but the electrodes are only going to spend minutes in the samples.
A few cm of Pt will only cost a few dollars. The piece I have is actually 3cm!!! long which is plenty for two probes. I will have a row of sample soon taken from the Chlorate cell I have going at the moment and it would be easy to put them into ice water and 'measure' them all if I make the probes. Exactly what Voltage (or current density) to put onto the probes is anyone guess. When I put approx. 3.0 Volts or more on the probes I will have the worlds smallest Chlorate cell:cool: Since the cell is pH controlled all the samples will have similar pH. Some of them will have been sitting there for days which may lead to 'wrong' readings?

Dann2



watson.fawkes - 1-2-2010 at 18:50

Quote: Originally posted by dann2  
Regarding the charge meter IMO when you are using a CC supply it is very easy to know the amount of charge that has entered the cell. It's just time by the CC. The charge meter would be good for the person with a Voltage supply where the current is inclined to vary as the cell progresses. But either way you are back to guessing the CE in order to guess the end of run of cell.
I'm suggesting that the cell stops before it hits its end state. You're losing some yield on a per-batch basis, obviously. You're gaining unattended operation. This trade-off might be just fine for some people.

This idea does require some amount of calibration for the cell and its operating profile. You'd want a first run whose duration is calculated according to, say, 30% CE. When the cell stops, sample the contents and do a bit of quantitative analysis about what's in it. Start up again and sample at, oh, 40% and 50%. You can extrapolate where end conditions are. Now back off 5-10% of where you'd stop the cell if you were continuously monitoring. You're losing some per-batch yield, but it's not more that 15% or so. You'd be doing an extra batch for every five or six batches for similar yield. If that extra work is worth it to avoid building a continuous monitor, then the trade-off is worth it.

quicksilver - 2-2-2010 at 15:29

You guys got me hooked on this. - An unbelievable amount of great ideas!

The computer PSU was fun to build and I got some really good ideas from the concepts.

Pt probes

dann2 - 2-2-2010 at 17:54

Hello,

Good to see you hooked QuickSilver! I have lots and lots of Salt (it's very expensibe but you WILL want to buy it) for sale to start you off :D

I constructed two Pt probes that may or may not be of use. The glass tubes are 5mm in diameter. I had only 4cm of Pt wire (approx. 0.5mm diameter). Made one probe OK. The next one had the soldered connection to the Copper wire too close to the end of the Soda glass tube and also rubbing against the side of the tube and the solder melted again to a high temperature for some time as I melted the tube shut. This seemed to dissolve the Pt wire as it broke as soon as I moved the Copper wire (at the other end of tube) to bend it. Had to make it again and the bit of Pt sticking out of the end is very short (half cm, as opposed to one cm on first probe). If making one of these keep the soldered joint in the middle of the tube, not lying against the side of the glass tube where the solder will melt and damage the Pt (or use a longer piece of Pt so that the soldered joint is up the tube out of the way).
I poured some candle wax into the tubes at the opposite end of the Pt to steady the Copper connecting wires.

What Voltage/current/waveform to put on the probes for to see a usable signal telling us of the cell stage?

Dann2




probes.jpg - 13kB

Lambda - 2-2-2010 at 21:26

Quote: Originally posted by Swede  

... It'll be a simple ratio of chloride to chlorate, and I'm wondering if that ratio changes, is there a simplistic method to measure it using conductivity? ...


Hi @Swede,

Wonderful work !, ... I love reading your posts, and seeing your progress !

The easiest way to measure Ions (Cl, ClO3, ClO4 etc.) is done in the same way as with a regular ION-SELECTIVE PH Meter, ... and yes, ... a PH Electrode is an ION-SELECTIVE Electrode !

You can use a regular PH Meter for the readout, only now with different Electrodes (the principle stays the same though) that must be calibrated according to the Ions that you intend to measure via an Ion Selective Electrode.

And this is what I am referring to:

Ion selective electrode:

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

Just a few examples of what I am referring to (random examples):

Ion-Selectieve Electroden (Dutch):

http://www.rhombus.be/contents/nl/d151.html

Ion-Selectieve Electroden (Dutch) - Google Translation (Dutch to English):

http://translate.google.com/translate?js=y&prev=_t&h...

Technical Specifications for the Perchlorate Ion-Selective Electrode (ELIT 8061):

http://www.nico2000.net/analytical/perchlorate.htm

Ion Selective Electrodes : Ammonium (NH4+), Barium (Ba2+), Bromide (Br-), Cadmium (Cd2+), Calcium (Ca2+), Carbonate (CO32-), Chloride (Cl-), Cupric (Cu2+), Cyanide (Cn-), Fluoride (F), Iodide (I-), Lead (Pb2+), Mercury (Hg2+), Nitrate (NO3-), Perchlorate (CIO4-), Potassium (K+), Silver (Ag+), Sodium (Na+), Sulphide (S2-), Thiocyanate (SCN-), Water Hardness:

http://www.rmprocesscontrol.co.uk/Electrochemical-sensors/IS...

I hope that this info may be of assistance to your very interesting Chlorate/Perchlorate Project !

Lambda

Lambda - 3-2-2010 at 08:34

Here you have a book, and two articles on Ion-Selective Electrodes:



Ion-Selective Electrodes for Biological Systems - By Christopher H. Fry & Stephen E.M. Langley (Harwood Academic Publishers - 2001) 157s - Including Bookmarks.pdf

Ion-Selective Electrodes - By Mark A. Arnold & Mark E. Meyerhoff (Analytical Chemistry, Vol.58, No.5, pp20-48, April 1984).pdf

The Theory of Ion-Selective Electrodes - By Erno Pungor (PINSA-A, 64, pp53-65, January 1998).pdf

as

Ion.rar

iFile.it Download Link (8.69 MB):

http://ifile.it/u9ox3tz

No Password Required !

Enjoy !

Lambda

dann2 - 3-2-2010 at 13:14

Hello,

I obtained a paper entitled:
Simultaneous flow-injection measurement of hydroxide,
chloride, hypochlorite and chlorate in Chlor–alkali cell
effluents.
Some may be interested in taking a gauk.
It is in the ref. section under Wanted References and Needed Translations(6), post of 3 Feb 2010
Thanks to jokull.
I do not think its contents are of much use to us as the amounts of Chlorate are very low and the Chloride is measured using a conductivity cell but the NaOH (main interference) is already known and thus can be eliminated.
They have an interesting way of measureing Chlorate with KI that is readable using a photo detector and a led.

Dann2

quicksilver - 3-2-2010 at 13:52

I secured a supply of carbon cutting rods and they were coated (as some of you know) with a layer of copper. This copper is no joke to take off. It's perhaps a 1/2 mm in thickness and needed a a fine tip torch to cut a line in to peal off. But once they are off the graphite rode are well made. but that copper has to come off and the rods need to be cleaned of copper left behind of one's product will be green as grass.

dann2 - 3-2-2010 at 14:32

Hello,

@quicksilver
I found that the best way to peel of the Copper was to start at the top and put a small nick the Copper to lift a small part of it. Pincers were then used to start off the peeling by rotating the rod and moving down the rod as the Copper peels off. You end up with a big long piece of Copper (all in one piece) not unlike a spring.
Perhaps that is what you are doing.
If you controll cell pH (just add acid, no need for fancy pH meters etc) you should be able to get a few KG's of Chlorate made per rod. Without acid you will be lucky to get one KG of Chlorate per few rods!

Attached is a read on conductivity of solutions.
Each ion has a specific condutcivity factor which may be useful. These devices seem to use an AC between two (blackened) Pt probes.
Cheap circuit to build one is here:
http://pubs.acs.org/doi/abs/10.1021/ed074p572

They can be bought on ebay too.

Dann2

Attachment: 12Chapter12.pdf (55kB)
This file has been downloaded 1072 times

quicksilver - 5-2-2010 at 13:44

@ dann2:

Thank you.

I had been reading this thread till I feel a bit up to speed on some of the more basic issues. Cutting Rods were said to have some iron: obviously some more, some less; as all welding electrodes - how does one tell if you have a sweet brand or not? Or is this REALLY an issue? My agenda is to re-crystallize, etc thus clean up my yield anyway.

I also read about cleaning up the Cu with HNO3 2% and linseed oil impregnation - these sound like a good thing. Have you done this also?

Tungsten is easily acquired via TIG electrodes...I have some - are they of any use in some electro-chemical format?

[Edited on 5-2-2010 by quicksilver]

dann2 - 13-2-2010 at 12:34

Hello,

I attempted to coat W (Tungsten) with Tin Oxide (some time ago) using a similar procedure to Ti but could not get it to work.
It is very hard to etch with HCl too. I think a few W rods would make an everlasting Cathode for a small cell if you cannot get Ti.

There is a article on a cheap conductivity meter over in ref. section in the 'Wanted refs. and need translations (6)' thread, post of 5 Feb 2010, if anyone is interested. I think the solution conductivity idea will definately work with a K cell because the Chlorate (or Perchlorate) is constantly falling out of solution and the conductivity of the solution will be getting less and less (large signal) unlike a Sodium cell. The range of conductivity is way off from what is usually measured with conductivity meters though. Far too much ions in solution. Most conductivity measurements are performed on solutions with much less ions in them.

Dann2

quicksilver - 13-2-2010 at 13:29

I was reading back through this and other threads and had come across the concept that KCL does not dissolve well in cold water. I tried it and sure enough, in water about 70-80C I was getting super saturated solutions. However I have a chlorate cell with spacing at 2.5" (MMO and Ti), with this I have trouble with a super saturated solution. It will occasionally simply stop. I have check electrical issue so many times that I am confident that it is not a PSU issue. The brine is saturated well over what I have tried in the past. When it's running at 4.5 -5v at 3A everything is fine (starting at 12v via a PSU from a computer) but with most other voltage/current situations, it will not start. Is the highest level of saturation -something to avoid?

I found a 5v 30A premium PSU at a surplus electronics store in town (was used by Raythion) for $30 but I don't see how I can overcome the heat issue without a more sophisticated supply. I can also pick up a Lamda but I'm not sure if I want to gamble on it as they want $70 and that is a rack mount high end 1970's power unit.

dann2 - 14-2-2010 at 07:03

Hello,

Definitely an electrical issue. The computer power supply is probably going over the Amps that the 12V output is capable of supplying.
They can be fickle to get to come on and off too if you have no load on the 5V supply. Put a small bulb on the five Volts supply side. Use a switch between the green and black wire to turn supply on and off as the supply will 'behave' better using this method.
Look up the solubility of KCl on Wiki. Saturated solutions are OK. Supersaturated solution are pointless as you will get KCl coming out of solution as a small amount of time passes unless you heat some more.

Dann2

quicksilver - 14-2-2010 at 09:02

@ Dann2

Thank you.

I realize that salt will fall out so I wait approx 2 hours (perhaps that really is not enough?) but have come to think that I might be getting chlorate at the 8 hour mark, if the current is high enough. In a 2 liter cell 15A is enough to make that thing almost boil. I tied an experiment along those lines last night and am waiting to see what will happen after a week. I'm recording every detail so that I can simply measure out what will be the highest level of KCl the bring can handle.

Swede - 15-2-2010 at 13:34

2 liters is a pretty small cell, so I am not surprised you are overheating it with 15 amps. You can lower the current, create some form of external cooling, or change out into a larger cell.

Immersion of the 2 liter cell into a large pan of water, and directing a fan over the surface of the water, is a crude but surprisingly effective way to drop the cell temp probably 20 to 30 degrees. But I think your best answer is to make a larger cell.

My technique lately for getting good saturation is to mix my liquor at 60 degrees, but add only enough salt that would dissolve at 50. After the salt dissolves, get it going quickly, and it will never get below 55 degrees, and there will be no chloride precipitate. But this method only works if you know SPECIFICALLY what temperature you maintain at X working amps. I've known for a long time that my setup will run at 60 degrees at my standard 50 amps.

This sort of maneuver can easily double the yield over a room temp KCl solution.

Lambda - TY for the kind words! But I am simply following the lead of many who have been here before.

dann2 - 15-2-2010 at 15:44

Hello,

There is some KCl solubility info at this address:
http://www.oxidizing.110mb.com/chlorate/potassiu.html

I have been running my Na Chlorate cell (2.2 litres) with different sized Cathodes to find out if that makes a difference to CE. I am particularly interested in very large Cathodes (low CD on Cathode) with no additive to see if they drastically reduce CE.
The results are a bit of a mess. The times I am allocating to the different Cathodes is far too short to see a trend. It's all rather confusing. I will have to run the whole thing again using larger (6 days or so) times for different Cats.
Anode is Graphite, approx. 34mA per cm squared, pH is controlled at around 7 (with 0.6cc 12% HCl per hour), four Amps steady into cell (CC supply)

%CE was like this:
Start to day two CE = 72% (small and large steel Cat's used during this time as I was 'weathering' the large steel Cathode and not really trying to monitor anything and also waiting for cell to come to steady state as far as acid addition is concerned)
Day three (small Ti cat) 43% CE
Day four (large Ti cat) 0% CE
Day five and six (small Ti cat) 0% CE !!!!!
Day seven (large steel cat) 95% CE
Day eight and nine (still large steel) 46% CE
Day 10, 11, 12, 13, 14 (small Ti cat) 48% CE

Chloride concentration now at 192 grams per litre.
Day 15 to 20, MMO Anode with small Ti cats inserted giving 73% CE (and cell still going). I increased the Current to 8 Amps too when MMO inserted BTW.

The cell is possessed!
I will check some of the more daft looking figures/titrations.
The only useful figure I will get out of this cell run is:
What concentration of Chloride an MMO Anode will take Chloride to when let run and run?

Dann2



[Edited on 15-2-2010 by dann2]

quicksilver - 16-2-2010 at 10:52

@ Swede:
Yes, 15 was complete over-kill. But I was so curious to see how the PSU would handle it (fed it through a 75W resistor because the PS is a 30!) I watched as gas fairly flowed out of the vent hose! But since it did not appear to get over 80C I gave it a few hours, it seemed to calm down a bit.
The technique you described is helpful. That's something I have realized was appropriate: to get the solution started at 50-60 and -with haste; get it in a 5gal. Bucket Cell. One serious problem is not being able to see well into a large non-transparent cell while it's running.

@Dann2:
You've taken it ( a 2L cell) to 20 days? The information is very interesting. I've also wondered if there is a point of diminishing returns: just as I've often thought of what would be optimum current for what volume and saturation point. I haven't been doing this long enough to even formulate some of the idiosyncratic elements, but a lot of the questions have been touched upon. Thanks for the solubility link. This is pretty interesting stuff.

[Edited on 16-2-2010 by quicksilver]

dann2 - 17-2-2010 at 02:00

Hello,

@Quicksilver
Don't pay much heed to the efficiency figures above as they are not really of any use.
If you are getting 54% current efficiency (cell not pH controlled) you will get 1 gram of Sodium Chlorate per Amp every 167.76 minutes, or if you like, 0.00596 grams Chlorate formed per minute per amp which is the same as saying that 0.00327 grams Sodium Chloride is used up per minute per Amp.




Got back to testing Lead Dioxide plating solution for Nitrites. The aquarium test kit works OK. The blue colour of Copper Nitrate (if you have Cu Nitrate in solution) does not interfere as it is too diluted and not a strong enough blue.
It turns out my old plating solution (sitting for years AFIAK) has (evil) Nitrites in it as can be seen from picture. I added Nitrites to some of the old plating solution and got positive tests but then decided to do a 'blank' (no actual Nitrites added) and still got a positive result.
I had to make up a small amount of new plating solution with Lead Nitrate and Cu Nitrate. I added approx. 0.003 grams Nitrite to 1.5cc of plating solution (0.2%, figures very rough BTW) and got a clear immediate positive. The new plating solution on its own (no Nitrites added) gives a negative for Nitrites (RHS of picture).
The drops of test solution stay at the top of the Plating solution unlike when they are put into pure water where they sink to the bottom.

Made some Bismuth Nitrate. Added 70% Nitric acid to Bismuth and heated a bit to hurry up reacting the larger lumps and then evaporated away the Nitric acid.

Dann2

[Edited on 17-2-2010 by dann2]

nit_tests.jpg - 24kB

ninefingers - 17-2-2010 at 07:10

This is probably old hat to you guys, but:

I worked on switching power supplies for years; most need at least 1/3 their rated output just to start (that can be removed when the cell is connected.)

Computer p/s need a "power good" wire connected to ground to start. This is usually green--look up the mfgr/model on the web and see. They need the main +5v loaded to about 30% start, also. (I've had poor luck with these).

No matter what P/S you use, use heavy wires and distance it from the cell unless it has a Good lid (The salty/chlorate spray is Very corrosive)

Ti anodes seem to corrode right at where they touch the air. That DMV can be painted and they will then work well. Even the copper rods I use to hold my anode and cathode get corroded, so I paint everything above the water level except exactly where I need electrical contact. That gets graphite grease.

My graphite electrodes I got from a salvage yard. They are cut to about 1" square by 12"long; I use two of them. I soak 'em 3 days in Linseed oil (I have a gallon of it). At all hardware/paint/home stores. I think old motor oil or vegetable oil would work too, but messier.

Lead Peroxide has an extremely high resistance unless you use an old car battery grid. I haven't tried an old battery yet; I was going to run about 30 volts to it and have a trough of electrolyte above the cell vents, with plastic tubes sealed to it and the cells. Just pasting PbO2 to a plastic tube or lead doesn't seem to work well--it takes 60 volts to push 1 amps thru it; it gets Hot. A plastic tube Melts. I was using a 100W light bulb as a current limit; it glowed Brightly. I used lab grade PbO2; it still Sucks.:mad:

My old battery is a bit sulfated; be careful of that. Charge an old battery a good week; then dump the electrolyte (or use for H2SO4) and replace with distilled water. Always keep cells Wet with distilled Water Only. If exposed to air, the cells may get badly oxidized and not ever work. I have a de-sulfator circuit I need to finish and try on this old battery before I get the plastic trough/tubes sealed so they Stop Leaking--this is a Pain.:mad: When this is ready, of course, then the water may be dumped and the salt water or whatever you are electrolysing added.

Just plain Lead works pretty well. I also use it in electroplating.

I don't see why Gold won't work. I am trying to get some gold- filled chains to try. (Gold-filled is much thicker than plated; it is forced over the base metal.)

I tried a so-called Pt "wire" I got on eBay; it was a rip off.:mad: That guy got a lot of complaints--be careful buying precious metals now. A Pt/Ir plated Electrode was the same price ($55). A friend uses a Pt anode AND Cathode to make chlorates. It is Very Clean; can take enough current to make perchlorate directly and burn all the NaCl/KCl out. What is left is clean and Pure. No freezing and filtering to purify.:)

(We now together have about 20 Pounds of chlorates/perchlorates of varying quality. We can't use it all in 5 years. He is now attempting hydrogen fuel for his car with his cell. Making chlorates electrolytically is messier and a much longer process than boiling Bleach; but the raw materials (salt) aren't as suspicious or expensive as, say, 10 gallons of bleach. Perhaps tablets for a pool is a better idea, I haven't tried it.

dann2 - 17-2-2010 at 07:36

Quote: Originally posted by ninefingers  
This is probably old hat to you guys, but:

Ti anodes seem to corrode right at where they touch the air. That DMV can be painted and they will then work well. Even the copper rods I use to hold my anode and cathode get corroded, so I paint everything above the water level except exactly where I need electrical contact. That gets graphite grease.


Hello Ninefingers, (one assumes you were born with the extra one and still have your two thumbs? :P)

Can you explain what your "Ti Anodes" consist off?

I will be giving the Lead and Gold Anodes a miss. They have been suggested 1001 times.

Cheers,
Dann2

Perchlorate from LaserReds MMO!!

dann2 - 22-2-2010 at 15:37

Hello,

I have been running an MMO Chlorate cell for some time.
The MMO used here was 'LaserReds' MMO as sold on EBAY. Exact type of MMO coating in not known.
MMO was inserted when Na Chloride concentration was 180 grams per liter and Na Chlorate concentation 240 grams per litre.
Current density on MMO was approx. 200mA per square cm. 2.2 litre cell with 8 Amps current from constant current supply.
Voltage accross cell varied from 4.3 Volts @ at start of MMO run to approx. 4.5 Volts (before Anode passivation). pH was
maintained at around neutral with acid addition required all the time. This contrasts with Graphite where the cell does not need
acid additions when coming up the the Perchlorate point. The temperature was around 60C.
CE figures are calculated by using Chlorate production as ascertained with titrations.
First 61 hours (492 Ah) CE was 65%. (Seems rather low.) Next 81 hours (652 Ah) CE was 55%. Next 39 hours (312 Ah) CE was 33%. The Na Chloride concentration at this point was 21 grams per liter. There was no Perchlorate present.
Twenty four hours later the current was still flowing OK. Twenty hours later the Anode was discovered passivated with a test for Perchlorate being positive. CE was not measured for the last 44 hours.
Moral of the story is don't be trying to make Perchlorate with LaserReds MMO! or any other type of MMO IMO.
It is probably not wise to be lowering the Chloride concentration of a Chlorate cell much below 100 grams per litre or perhaps 150g/l if you want to keep CE high when using MMO.
At what point the MMO starts to wear or if that wear starts suddently at a certain point is not known.
It may be a bit like Graphite where large erosion starts fairly abruptly at approx. 30 grams per litre Na Chloride (pH controlled cell).
There is very little difference to see between the passivated part of the MMO Anode and the part that is not passivated at the top where the connection was (outside the cell).

On a slightly different note. I tested my Lead Dioxide plating solution some days ago and it tested positive for Nitrites.
I added approx. 10ml 35% H2O2 into two litres of solution and left it sitting for approx. 4 days. When tested for Nitrites they
were gone so I guess H2O2 done the job.

Dann2

Aqua_Fortis_100% - 23-2-2010 at 14:34

Dann2, the anode just 'passivated', didnt some of the MMO layer flaked off?

Some experiments I did on high concentrated chloride solutions (NaCl, KCl) for chlorate, on low-to-moderate current density, revealed some almost undetectable tiny black ppt that was not from solution (because when using MMO I always filter the solution prior to feed the cell with it) nor from cathode (Ti will produce at best a tiny white cloud of TiO2). Maybe just a natural wear of laserred MMO anode.

Is good to see that this is able to produce perchlorate. Bad enough, the mother nature dont keep it to produce a decent amount, without being destroyed.

quicksilver - 23-2-2010 at 15:54


@ Dann2

Awhile back there was some discussion about a high grade of aluminum as a cathode. Is this workable or a poor choice? I have been having a tough time finding Ti and high grades of stainless has been a hit or miss thing. I have found that very fine stainless steel screen made in either the US or EU seems to be copper free.

dann2 - 23-2-2010 at 17:43

Hello,

I think just all types of Aluminium will corrode. I don't recall it being discussed up the thread or anywhere else. I have never tried it myself. Woulter Vissers page says it will corrode. Try just about any type of Stainless Steel. It should be OK. If you are going to get corrosion it will be above the water line. You could perhaps try covering the part above the water line with plastic or epoxy, etc. Dont leave it in the cell when it is turned off.


@AF100%
I cannot see any MMO flaking off. The MMO mesh is slighty less black than it was at the start. This cell had a mild steel Cathode in it for a while so there is brown stuff (Fe compound) at the cell bottom which will hide any small amounts of MMO that may be there.

Swede ran this MMO in a Perchlorate cell for quite some time and the MMO Anode did not passivate. His cell had not much Chloride in it, a 'pure' Perchlorate cell. (I cannot for the life of me find the account, can you help Swede?).
He did NOT get any Perchlorate to form BTW.
The MMO may be a bit like Pt. The absolute NO NO zone is where there is some Chloride still in the cell and the cell is starting to make Perchlorate. Both Oxygen and Chlorine are being produced at this stage and this is bad for a Pt Anode and perhaps the same applies to MMO?

Dann2

[Edited on 24-2-2010 by dann2]

Aqua_Fortis_100% - 24-2-2010 at 13:35

Hello dann2

I dont know if this is feasible task or even a dumb question, but how about 'regenerating' at home fully used (passivated) MMO anodes like from lassered with ruthenium chloride/ tetrabutil titanium (both from e.g. university lab) and a heat gun? Do you really need to completely etch the used anode to put a new MMO layer or you could just decompose the salts on the old layer with good results?

If ones have acess to little Ru chloride I think this could be interesting to test..


[Edited on 24-2-2010 by Aqua_Fortis_100%]

dann2 - 24-2-2010 at 15:48

Hello,

Once the Ti has passivated it means the TiO2 is present and you will definitely have to etch the Ti to get rid of it.

Dann2

Aqua_Fortis_100% - 25-2-2010 at 07:45

Sorry, it seems was really a dumb question :(

I just wondered if most of the MMO layer dont flake but rather suffer any kind of modification that dont allow it to conduct current, and if there was any other way than etching to bring life again to the MMO.

One of my MMO laserred anode for example have some rusty spots on it (Ive used this same part of the mesh a couple of times) but keeps working. Wonder what can be this.



[Edited on 25-2-2010 by Aqua_Fortis_100%]

dann2 - 25-2-2010 at 11:24

Hello,

Laserreds MMO is second hand (afaik) and will be of unknown quality. It may vary from shipment to shipment. Perhaps the stuff I have has a very thin coat which is why it wore off so quickly.
Swede was cleaning up some of his Laserred MMO using HCl to remove the brown stuff.

Dann2

dann2 - 26-2-2010 at 16:19

Hello Folks,

Probing into the great unknowns of a Chlorate cell (as one does) may be easier than thought based on Swedes higher Voltage=less Chloride observation.
I put together a circuit to work with my two Pt probes and it seems to work OK. I have only tried it on pure salt solution (cell start) and liquor from a finished Chlorate cell (just at the Perchlorate point from the last MMO run).
The sample is placed into a glass U tube that is one cm inside diameter and 230 cm total length untill the tube is full. The probes are then placed into the top ends of the U tube.
There is an advantage in cooling down the test solutions as you get a large 'signal' between the start and end conditions of cell run.
At 19&degC the device gives a reading of 6.2 for start and 7.8 for end of run, a difference of 1.6.
At 0&degC the device gives a reading of 7.4 for start and 9.6 for end, a difference of 2.2.
The Zero degreese is also easier to replicate as opposed to some arbitary temperature.
The circuit puts a constant current between probes. The probes are not exactly equal as I made a blunder when constructing them. One is 1 cm long Pt by 0.3mm wire and the other is 0.5cm long my 0.3mm wire. Current into probes is approx. 37mA (steady). This gives a CD on probes of 785mA per square cm and 392mA per square cm.
This high CD gives a better 'signal' as I tried lower CD and got less 'signal'.
I also tried different wave forms etc into porbes using a signal generator and a scope to see the results but the good old DC seems to be the best. Also the use of a U tube gives a better signal as opposed to simply using a small container to hold the sample. A longer U tube may help more but you will have to use a higher Voltage on the CC source which is 12V for my circuit. This can be run from the Computer power supply powering the actual cell.
The actual Voltages read above from the probes are 1.18 * meter-readings Volts approx. as the meter in picture reads from 0 to 11.8 Volts (0 to 10 on meter).

It may not be a proper solution to solving what stage a cell is at because if you are adding slops from previous runs this may complicate matters but it seem to give a clear read out of a new cell from start to finish.

Dann2


prober.jpg - 25kB probe_cir.gif - 5kB

[Edited on 27-2-2010 by dann2]

WSM - 1-3-2010 at 20:17

Hi Swede,

I was trying to reach you on APC but either I can't get there or it's gone :o :( ! I really hope all your blogs are safe! Please E-mail me sometime or leave a message here. Thanks, old friend.

WSM

Bikemaster - 2-3-2010 at 05:46

Try this www.amateurpyro.com you will be happy:D

[Edited on 2-3-2010 by Bikemaster]

WSM - 2-3-2010 at 15:51

Quote: Originally posted by Bikemaster  
Try this www.amateurpyro.com you will be happy:D

[Edited on 2-3-2010 by Bikemaster]


Yes!!! Truly happy. :D Thank you.

WSM

Thoughts on Cathodes

dann2 - 11-3-2010 at 17:28

Hello,

I have been running a cell for the last 13 days or so to see if using a very large Cathode effects current efficiency (CE).
I started with a small Cathode for the first three days to let the cell stabilize so that acid additions would be steady.
A Graphite Anode was used. It was a cell I ran many times before. Current into cell was 4 Amps (constant current supply). Cell is 2.2 litre's in size. Temperature was around 48C.
I got a CE of 47% for the first three days. Then I added the large Cathode made of mild Steel. It is very large with a total surface area of 714 square CM (counting front and back) and are coaxial to the Anode. (see picture above on 29 Jan 2010).

I got a CE for the first three days of 47%. CE is inclined to be low at cell start in my experience.
I let the cell run for a further 10.4 days and got a NEGATIVE ! CE.
Chlorate in cell at start of 10.4 day time run was 78.5 grams. Chlorate in cell at end of 10.4 days run was 59.4 grams (using titrations).
I checked my samples again as I thought I had made a mistake.
The cell is going in reverse.
KEEP CATHODES SMALL
I suppose if you are using additives to stop Cathodic reduction they it may not matter so much but with 'green' cells (no additives) it is very important to keep Cathodes small.

The cell demanded acid at a rate above the normal (+17% more) in order to keep the pH at around neutral. I was also trying out the 'probes' (for probing the great unknowns of all Chlorate cells throughout the land) with little success(or so it seemed). The Voltage was going the wrong way. I guess they may be working OK after all.

Dann2

PS. Where is Swede? Hope he has not run foul of the Texas law, 'No beakers allowed........'

[Edited on 12-3-2010 by dann2]

quicksilver - 12-3-2010 at 08:31

Question

Experiment: 2 cells operating in similar circumstances
2.5 Liter cell KCl solution 320gr per L
2.25 L in both. One MMO anode / Ti cathode
The other: Gouging Rods both anode/cathode
Both exposed to 6A via computer PS for 13 days
Gouging Rod cell had better yield @ 169 gr / MMO cell 148 gr
* Could the graphite in the brine play a part in greater conductivity if current were that low?

In another situation large cell (5gal bucket filled 2.5 gal similar brine solution) MMO anode, Ti cathode 60A: Yield weight UNK - but much greater than similar configuration with Graphite.

Smaller cell w/ lower current gave better results with graphite than MMO/Ti - Larger cell, higher current levels did much better with MMO/Ti - Water temp in larger cell approx 50 C smaller cell - temp 60 C (+ or -)

Wear on rods similar in both; thus smaller cell had higher concentration of conductive material: conductivity of brine would change as time goes on.
Can the addition of a steady conducive material (graphite) in the brine make for higher efficiency w/ a concentrated environment such as the smaller cell?

* Note that SOME tracking of Voltage was attempted (switching supply: voltage not constant). Generalized construct, Start 4.50Vdc, day 8 5.10Vdc Finish 5.20Vdc in graphite cell. MMO cell, Start 4.25v Finish 5.85Vdc. Greater variation on MMO cell.



[Edited on 12-3-2010 by quicksilver]

dann2 - 12-3-2010 at 11:21

Hello Quicksilver,

The conductivity of the electrolyte has nothing to do with current efficiency.
What are the current densitys on the Anode materials that you are comparing?


Graphite works best around 34 - 44 mA per square cm.
MMO (I am not too sure actually) works around 200mA per square cm.(these are the figures industry uses)
Don't get too 'hung up' on the Voltage appearing accross the cell. It does not really tell you a whole lot. Most beginners (don't know if you are a beginner) seem to take it into their heads that it's all about 'the Voltage accross the cell'.
If you want a lower Voltage accross the cell place the Anode and Cathode closer together. This will give greater power efficiency, which is not the same thing as greater Current efficiency.
Regarding the Voltage accross cells, in extreme cases I have heard it argued like this:
The Voltage accross my cell is 4 Volts-------------> Therefor I am making Chlorate.
The Voltage accross my cell is 7 Volts-------------> Therefor I am making Perchlorate.
This is simply rubbish.

If you want to attempt comparing Anode materials think in terms of current density on Anodes and also have a similar cell-volume to current-into-cell ratio for each comparison. Thats really the best you can do.

Graphite is a very good Chlorate maker. MMO is only slightly better with only a very small lower Voltage needed to get Chlorine to be evolved. These small Voltage levels are levels that you WON'T be measureing unless you place a third electrode (reference electrode, satureted Calomel bla bla bla) in the cell.

Dann2

quicksilver - 12-3-2010 at 12:43

Quote: Originally posted by dann2  
Hello Quicksilver,

The conductivity of the electrolyte has nothing to do with current efficiency.
What are the current densitys on the Anode materials that you are comparing?

*************snipped for brevity*********
Dann2



Hello Dann2:

Thank you for your reply.

The info:
"Graphite works best around 34 - 44 mA per square cm.
MMO (I am not too sure actually) works around 200mA per square cm.(these are the figures industry uses)"
was quite valuable.
I was comparing MMO & Graphite - current: same, MMO of the perforated commercial type available via eBay 2x6". Rods were 5/8" diameter and contact with brine 8" depth. Due to the perforations I had no way to really assess the total of area in contact. Measurement was with a DIMM as I had no "amp clamp" at that time but it popped up at 6amps on both Computer PS held steady but when I did manage to borrow an amp meter they had both held at 6.12- 6.36a. but I had to do one after another. There were many flaws in my comparison. But when I weighed the yield on the 2 liter cells I did so when dry. {The larger cell was a visual comparison & for the most part valueless as data.}
Illustrating the possibility of the defused conductive particulate within the brine as a boon to yield.
You answered my query. Generally because of the resultant I had thought that the conductivity of the graphite that there MAY be an advantage to the hassle and time spent in clean-up of this black mess :-)

When I was quite young and children had "shop" classes in school & could work with "dangerous" things (& learn to love science etc.) I had been told that if one could obtain "pure" water that there would be no conductivity but rather it was the materials with water that would conduct electricity. There I had thought that if one had a STABLE conductor within water (the brine 's conductivity must change as the electro-chemical action takes place) that there MAY be a slight advantage to it's efficiency.
That my yield was slightly greater with a graphite anode gave rise to this question. What's more, I have no logical premise to base the fact that my yield was slightly better. I could go wild & guess that slight differences in anode-cathode separation could account for this or that water temp played a part - but I have no answer.
I DO take notes however my recording would need to be much more meticulous for me to do anything but grasp at straws. The fact this this occurred in ONE experiment leads me to believe I have no real basis for any belief in that direction. If it occurred in four or more straight shots in a row....& my accuracy was much keener than it had been - perhaps then I could develop a premise that there is some superiority in conductive particulate within the water making a difference.
The fact that industry does NOT use graphite punches holes in that.
However the loss of time in processing, disposal of waste, extra steps could make such a thing (IF possible) of little importance. Even the gain of 10-12% consistently would be outweighed by such an expense.

Of interest was when you used the statement "keep cathodes small" - by what percentage? Many if not most cells appear to have same size or in some cases much larger Cathodes.




[Edited on 12-3-2010 by quicksilver]

dann2 - 12-3-2010 at 14:22

Hello Quicksilver,

There is a page here:
http://www.oxidizing.110mb.com/chlorate/chlorate.html
that may help expain the chemsitry going on in the cell. Perhaps you seen it before.

I find the best way to get rid of the Graphite powder is to give the finished electrolyte a good boil to get rid of dissolved gasses and let the contents sit for a few days. All the Graphite goes to the bottom and you can siphon or decant off the 100% clear liquid and leave a small amount of black liquid behind. You can filter this small amount of liquid if you so wish. This will not work for K Chlorate only Na Chlorate.
If you don't boil the cell contents the gas seems to keep bubbling up and keeps cell agitated and thus keeps Graphite in suspension.

Stupidly large Cathodes are a disaster if you do not have additives in the cell (Chromate etc) to stop reactions at the Cathodes turning wanted products back to Chloride. Try to keep total 'active' Cathode area similar to Anode area or perhaps better down to 50% of Anode area. I say 'active' area to distinguish between the side of the Cathodes facing the Anode and the 'inactive' side which is the side away from the Anode. It would be great to cover the 'inactive' side with plastic but perhaps that's being too exacting. The small Cathodes will give a higher Voltage accross cell but that's no big deal IMO.
In my opinion there should be two Cathodes for flat Anodes, one each side so that the current on the Anode is distributed fairly evenly. Use three or four for rods.
I used to think that a great way to make a cell would be to obtain a large SS bucket and simply suspend an Anode in it. The bucket would be the Cathode. This would be a very very bad design if you had no additives and it might even make NO Chlorate.

Industry (monopolar cells) has equal Anode and Cathode area in Chlorate cells and they do not have much 'inactive' Cathode area because the Anodes/Cathodes are usually arranged in banks. The relatively small 'inactive' areas of Cathodes (at the ends of banks) may (guess) be covered to stop small currents leaving the surface. In bipolar cells it's not an issue at all.
The current density on the 'inactive' surface (the surface not facing Anode) will always be quite low. It is low current density areas on the Cathodes that are commiting the sins (read in Ullman) so there may always be a small advantage in covering 'inactive' areas even if Cathodes are relatively small.

Most cells that you see (amateur) may have a Cathode the 'same' size and the Anode on each side of the Anode. But that a total of twice the area of the Anode if you count the (sinning) 'inactive' side. Most of us don't like adding additives.

Just one note. The Cathode I used above was mild steel that was well rusted. This is the worst type of material for converting products back to Chloride. Ti would not be as bad but I don't know how much better it would be. You are not going to use big monster Ti Cathodes anyways.$$$

Dann2

[Edited on 12-3-2010 by dann2]

quicksilver - 13-3-2010 at 07:53

Dann2:

Again, thanks - your suggestions have consistently been valuable and appreciated.

dann2 - 14-3-2010 at 15:39

Hello,

Just when you though the subject of Cathodes was at an end........

Link here:
http://www.faqs.org/patents/app/20080230381
which describes using Phosphates in conjunction with Fe-Mo alloy coated Cathodes for to buffer Chlorate electrolyte and stop Cathodic reduction thus eliminating Chromates.

ONLY HARD CORE, 'GREEN' CELL RUNNING FOLKS CAN GET INTO THIS STUFF :cool:
(I will be giving it a miss)

Dann2

ninefingers - 19-3-2010 at 08:13

Quote: Originally posted by dann2  
Quote: Originally posted by ninefingers  
This is probably old hat to you guys, but:

Ti anodes seem to corrode right at where they touch the air. That DMV can be painted and they will then work well. Even the copper rods I use to hold my anode and cathode get corroded, so I paint everything above the water level except exactly where I need electrical contact. That gets graphite grease.



Quote:
Can you explain what your "Ti Anodes" consist off?


They are pure titanium . Right where air contacts them they burn (DMZ, not DMV, sorry.) I'd still like to try gold filled chains before investing in Pt. I got ripped of by a Pt scam on eBay; there went my budget.:mad:

JohnWW - 19-3-2010 at 09:53

Quote: Originally posted by dann2  

They are pure titanium . Right where air contacts them they burn (DMZ, not DMV, sorry.) I'd still like to try gold filled chains before investing in Pt. I got ripped of by a Pt scam on eBay; there went my budget.:mad:
Can you please tell us how the Pt $cam on eBay was operated? Who was the culprit?

Gamal - 28-3-2010 at 13:51

Quote: Originally posted by dann2  
Hello,

Just when you though the subject of Cathodes was at an end........

Link here:
http://www.faqs.org/patents/app/20080230381
which describes using Phosphates in conjunction with Fe-Mo alloy coated Cathodes for to buffer Chlorate electrolyte and stop Cathodic reduction thus eliminating Chromates.

ONLY HARD CORE, 'GREEN' CELL RUNNING FOLKS CAN GET INTO THIS STUFF :cool:
(I will be giving it a miss)

Dann2


Interesting reading!
Looks like they use mmo-anodes with chromates in the electrolyte. I though that wasn't possible. Have I missed something?

If I get it right, they get a ph stabilized cell only by the addition of phosfate to the cell.
"The hypochlorite concentration was quickly stabilised at a value of 0.06 mol/l for the cell with activated cathodes, and of 0.07 mol/l for the cell with non-activated cathodes."
Maybe I'm mixing things up here.

/Gamal

Gamal - 8-6-2010 at 15:43

Is this thread dead or what?
This is my favourite thred for now, as I'm planning my cell configuration.
I hope there will be some more interest in this topic in the future.
I'm thinking about using an aquarium as the cell. Do you think it's a good idea?
Does the silicon seals withstand the cell environment?

/Gamal

[Edited on 8-6-2010 by Gamal]

hashashan - 10-6-2010 at 03:38

I noticed that in quite a short time all the adhesives degrade therefore my recommendation is to use a plain plastic container .. you can get those in quite large sizes so that it would fit you.

hissingnoise - 10-6-2010 at 03:53

I'd go for glass every time - a large glass jar; doesn't degrade or opacify over time.

Na Perchlorate

dann2 - 11-6-2010 at 09:51

Hello Folks,

It's been a while. I have have silicon sealer at the top of my cells and it does not seem to have degraded but it was NOT holding in any liqued. Just a seal to stop gases from getting out round the rim.
If you just a want a small (2 liter cell) you can cut a glass 'demijohn' using a glass cutter and a hot wire to crack it.

@Gamal. It is OK to use Chromated with MMO. Lead Dioxide does not like the stuff as it reduces CE.

Some Sodium Perchlorate 'cakes' attached for you pleasure!
The stuff is just about impossible to crystallize. I can't imagine how they do it in industry in a normal crystallizer (they probably do not). I heated the solution untill it just about all evaporated away and then drained off the small amount of solution that was left on cooling from the solid. I then vacuum filtered the stuff (Buchner funnel) and obtained the pictured cakes (wet hydrates of some description). I put the these cakes in an oven at 120 degrees C and they turned to pools of liquid. They dried eventually and the cakes were found to contain 22% water.

Getting around to trying out a Bi doped Tin Oxide Anode for Perchlorate. Don't hold your breath.

Dann2


Na_perk.jpg - 67kB

mnick12 - 11-6-2010 at 14:01

Good job on the perchlorate, what was your anode material?

I have just been getting into chlorate synthesis and it is very neet. I am using a cobalt oxide/ nickel oxide with V2O5 on titanium for my anode and a iron cathode. I have had 3 cells so far two potassium chlorate and one sodium chlorate. The cells were powered by a cpu power supply. I have not weighed everything, but I would guess I have 700gr of KClO3 and mabe 300gr of NaClO3. The only trouble I have had is with the cathode corroding so I had to add about 200mg of CrO3, which seemed to stop it. The anode has not correded at all, so I hope some time try it in a perchlorate cell. Cool stuff though.


I have been wondering what do most of you do with your chlorates and perchlorates? My pyro days are over so I have been using my chlorate as an oxidizer for some organic chemistry rections, like oxidizing hydroquinone to benzoquinone. But what do you guys use it for?

thanks

12AX7 - 12-6-2010 at 13:51

I have a bag (a few pounds) of what I expect is crude NaClO4. As I recall, the bag was leaky and humidity was getting in, causing it to turn to mush again. Last I checked, I double bagged it...

The last thing I used chlorate for was speeding up the etching of circuit boards. I regularly use CuCl2 + HCl and it goes several times faster with chlorate. Be careful not to add too much or you'll gas yourself!

Tim

Gamal - 13-6-2010 at 14:12

@12AX7
That's interesting!
Do You use only chlorate or a mix of CuCl2 + chlorate?
What concentrations do you use?

It's nice to see this thread coming to live again!

/Gamal

12AX7 - 14-6-2010 at 05:30

I use a solution of bright green CuCl2 + HCl. There is probably a considerable amount of sodium in solution by now. Heat to about 50C, add NaClO3 periodically. More than a large pinch will result in chlorine fumes, which needless to say is unpleasant to the operator.

Tim

white rabbit - 15-6-2010 at 20:08

I have found that the platinum clad niobium electrodes from Anomet work exceptionally well. After well over a 1000 hours it appears unchanged. I use 304L stainless steel for the cathode and a rewound Mot for the supply. I run 25 amps at 6.2 volts measured at the electrodes. A run of 2.5 lbs KCl to chlorate takes 6 days to complete. 2.5lbs of NaCl to NaClO4 takes 180 hours minimum and complete conversion takes almost twice that. Solution temp runs a steady 85*C. The stainless cathode needs to be cleaned before every run. I do not adjust pH or run any chromates.

Here is a pic of the anodes.

Platinum Electrodes 002.jpg - 50kB

Here is the stainless cathode with the section not in solution protected with heat shrink tubing
Cathode 2 small.JPG - 67kB

Here, the direct conversion of KCl, is almost complete
Direct Conversion of Chloride to Chlorate small.JPG - 54kB


Here is the power supply. A rewound microwave transformer with a Pi filter. The secondary windings are 10 gauge and center tapped to use 2 diodes. There is 44,000Mfd on one side of the inductor and 85,000 on the other. Ripple is less than 1/10 volt at load.
rewound MOT small.JPG - 86kB


980 grams KClO4 (1/2 of one run)
Perchlorate small.JPG - 45kB

Alexein - 18-6-2010 at 09:29

Holy smokes!

How much did those anodes cost you? and do they sell to individuals?

hissingnoise - 18-6-2010 at 10:04

Quote: Originally posted by white rabbit  
I have found that the platinum clad niobium electrodes from Anomet work exceptionally well. After well over a 1000 hours it appears unchanged.

Nice work white rabbit. . .
The Pt plating on the anode will erode completely, though, given time.
A way around this is to use a second Pt-plated electrode as a cathode.
Pt lost from the anode will plate onto the cathode and this can be replated back by reversing the polarity of the cell every few hundred hours or so.
As it is, Pt is plating onto the ST cathode and is lost when cleaning.
I know it means double expense, but electrode life can be prolonged almost indefinitely. . .

white rabbit - 18-6-2010 at 13:30

@ Alexein/The electrodes were very reasonable, I think, at about $135 each including the shipping. I bought 4 for $540. They save a great deal of time on filtering and washing.


Thanks,Hissingnoise
It seems if the anodes are going to eventually corrode I will probably be long dead by then. There is absolutely no sign of wear as of now. ( I've run of over 20 lbs so far)

I have tried the platinum cathode and I can tell you that it is a very bad thing to do. I completely destroyed, (turned to powder), one of the 4 electrodes I bought, which leads me to believe that your idea of the platinum plating onto the cathode in normal operation is incorrect. It seems the plating goes from negative to positive, this is why, it seems, my platinum cathode completely dissolved in about 150 hours. Have you noticed the extremely vigorous action at the cathode and almost no activity at the anode during the normal electrolysis? When I have finished a run of perchlorate, the cathode looks extremely corroded and the platinum looks just like new. I think the best combination is a Ti cathode and platinum anode. (the anodes are actually platinum clad niobium)

Btw,I have 6 videos on youtube of these electrolysis. Just search "ytmachx"

white rabbit - 18-6-2010 at 13:48

Here is something that you probably don't come across too often.It appears to be a sodium chlorate crystal that I found in the bottom of my electrolyte one day.
Sodium Chlorate Crystal small.JPG - 46kB







NaCL03 small.JPG - 77kB



[file]10743[/file]

12AX7 - 18-6-2010 at 23:27

Strange, I get differently shaped crystals, never cubic.

Tim

hissingnoise - 19-6-2010 at 09:41

Quote: Originally posted by white rabbit  

I have tried the platinum cathode and I can tell you that it is a very bad thing to do. I completely destroyed, (turned to powder), one of the 4 electrodes I bought, which leads me to believe that your idea of the platinum plating onto the cathode in normal operation is incorrect. It seems the plating goes from negative to positive, this is why, it seems, my platinum cathode completely dissolved in about 150 hours. Have you noticed the extremely vigorous action at the cathode and almost no activity at the anode during the normal electrolysis?

For someone producing perchlorate by the pound you seem to know little about electrolysis. . .

12AX7 - 19-6-2010 at 10:41

I would think the large quantity of hydrogen would have a noticable effect on the cathode. Certainly it isn't plating across, and I find the theory suspect, that platinum will plate reversibly between anode and cathode. Foaming hydrogen is not conducive to bright, dense deposits.

Tim

hissingnoise - 19-6-2010 at 11:11

Quote:
Foaming hydrogen is not conducive to bright, dense deposits.

That would certainly be true in normal plating processes, but in this case the loss from the anode is really very small, so small that the rate of plating on the cathode would be so slow that effects from the evolution of H2 should be negligible. . .

white rabbit - 19-6-2010 at 16:42

Quote: Originally posted by hissingnoise  
Quote: Originally posted by white rabbit  

I have tried the platinum cathode and I can tell you that it is a very bad thing to do. I completely destroyed, (turned to powder), one of the 4 electrodes I bought, which leads me to believe that your idea of the platinum plating onto the cathode in normal operation is incorrect. It seems the plating goes from negative to positive, this is why, it seems, my platinum cathode completely dissolved in about 150 hours. Have you noticed the extremely vigorous action at the cathode and almost no activity at the anode during the normal electrolysis?

For someone producing perchlorate by the pound you seem to know little about electrolysis. . .












As I have already stated, and proved, your theory is incorrect.

You may have noticed, I do the work and then share the information, not just type theories. I may not have book smarts, but I have experience. I learned long ago, doing is better than talking and experience is a better teacher.

I've seen Tim's work and for that I have a great deal of respect for him.

Have you got anything to put on the table, or are you just going sit there and wiggle your fingers?

avi66 - 20-6-2010 at 01:55

if i run my sodium chloride cell with access sodium chloride on the bottom ... the access sodium chlorate will form pure crystal on the bottom in some stage?
i read that the crystallization of chlorate is selective ... so the crystals which i collect from the bottom of the cell are pure naclo3 which only need little surface purification?
if i use mno2 anode with non-controlled ph chlorate cell... i will not get hcl in the cell ... i get naoh ... so the anode corrosion will form only insoluble black mno2 powder?

hissingnoise - 20-6-2010 at 04:42

Quote: Originally posted by white rabbit  
As I have already stated, and proved, your theory is incorrect.

What?
My theory that metals from an electrolyte or anode plate onto the cathode of an electrolytic cell. . .
It's only the fundamental process in electrolysis - not a "theory"!
And you've now, already stated and proven that it is not correct?

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