Thoughts On Anodes

Hi Xenoid... my initial attempts were with a commercial MMO anode offered by Northstar Pyro. The cross section of that Ti strap (gets calculator) is 22.3 mm squared. I have no idea if the strap was Ti or a Ti alloy, and I'm not sure if it makes a difference with regards to conductivity. Anyway, I used a quality Cu connector... everything was pretty optimal for carrying current, and those straps heated to well above 100C at 50 amps. I found out only after I attempted to clean a bit of salt creep with a water spray, and the water flashed to a boil.

Things were improved considerably when I mounted a heat sink on the strap. Interestingly, these were the cathode straps. The anode (MMO) straps were much cooler. I don't pretend to understand the mechanism there, but it was distinct... the all-Ti cathodes were hotter than the Ti + MMO. Anyway, I just wanted to throw that out as a consideration. Sometimes, commercial MMO cells are designed to carry less current than we are considering pushing through these setups, and the "choke point" seems to be the hanger cross section, between the Cu power cables, and the immersed electrode.

Dann2, I'm using a homemade spot welder now. Previously, I had been using a TIG welder on the all Ti cathodes that I had been making, and it was working fine, but I had not tried TIG welding MMO plate or mesh. When my mesh arrived, I dusted off the spot welder to see if it would work. I first tried it on two pieces of Ti and was stunned that it worked as well as it did. For the MMO mesh, I scraped the coating off the mesh junctions, the fat areas where the rows meet, on the areas under the strap; cleaned it a bit with alcohol, and fired away, and it worked very well. Just one weld was secure, and a typical strap to mesh interface is about 15 separate welds. It's clean and fast, no overheating, and appears to be a good way if an experimenter is doing a considerable quantity of these.

Here is the spot welder:



My talents lie more in fabrication than the chemistry behind this process, although I do have a chemistry background, and am trying to catch up on the many years of effort by dedicated hobbyists to produce a simple and cheap anode for perchlorate production.

Huh! Tried to edit my post and it was deleted!!!

Anyway the gist of it was;

I have a whole bunch of these 24V water inlet solenoid valves which I got from defunct electronic drive washing machines. They are rated at 60oC and 0.2 - 10 bar. They appear to be made from glass reinforced nylon. They are probably not suitable for concentrated acid but should be OK for dilute dosing, say in the pH range 3 to 7. The outlet (cell inlet) will need to be connected to some narrow bore tubing to restrict flow.

[Edited on 23-10-2008 by Xenoid]

[Edited on 23-10-2008 by Xenoid]

and again

@ Dann2

Geez! - I found one of those in the back paddock a while back! I wondered what it was - Ti, Nb you say!

Probably a good point. I'm usually pretty conscientious about stuff like that, but I honestly don't remember expending much effort on cleaning the Ti before mounting the Cu cables. I've been using this type of cable mount on most of my cells... this is from a very early cell:



These are nice assemblies from any home supply store, and need be bolted only once to a strap. Connections thereafter happen by sticking the bare Cu wire into the body of the assembly, and tightening a screw. With a bit of care, cleaning, etc before mounting one of these, it should last forever. IIRC these were #10 Cu cables, too light.

I switched to #4 Cu welding cable, which has really fine strands and makes for an awesome connection. They sell lugs sized to fit, requiring a crimp, and it's been this type for me:



#4 barely gets warm at 50 amps, negligible voltage loss.

Anyway, what you are saying makes some sense. Even with Ti being a worse conductor than Cu, with good cleaning, I'm guessing that the heating I saw will mostly disappear.

Hello,

There is a device here:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.ht...
for calculating resistances of wire and strips etc.

It is better to think in terms of the current the conductor is carrying.
The 'voltage we are working at' will not be 'seen' by the conductor in question if you know what I mean.
Only a small voltage (too much if it is getting hot of course) will appear accross the part getting hot/warm.

Taking a strip of Ti going to the anode that is 6 cm long by 1cm wide by 0.2cm thick.
It has a cross section area of 0.2cm squared and length is 6cm.
The (from Matweb.com) resistivity of Ti is 0.000000554 = 5.54 X 10^-7 ohm M
Copper is 1.7 X 10^-8 ohm M.
Using the page above gives a resistance of 0.00166 ohms for the Ti strip.
and 0.0000509 ohms if the strip was Copper.

@100amps you get I^2 R watts = 100 X 100 X0.00166 = 16.6 watts for the Ti
and 0.5 watts if the strip was Copper.
@150 amps you will get 37.4 watts with the Ti. (0.249 volts dropped accross strip)
with Copper you would get 1.14 watts.
How hot the thing will get will depend on how well insulated it is.

This assumes connections are perfect etc. Bad connection loads of heat.

Dann2

hope my calcs. are OK

[Edited on 24-10-2008 by dann2]

Haha! Dann2, my ability to do that sort of calculation on paper, while there, would require more effort than I was ready to give. To determine how much Ti cross section I'd need, I simply clamped various test pieces across my big power supply, and dialed in the current. With a small(ish) Ti cross section, it didn't take much current before it became smoking hot. I continued to add Ti until it was able to sustain 50 to 70 amps and not exceed maybe 60 C.

In the end, I settled on 2 straps, 1" wide by 0.062" thick, or 25mm X 1.6mm.



This was a worst-case scenario. The Ti did not have one end immersed in electrolyte, which would draw much of the heat away. But at the same time, the Ti was not encased or potted in plastic, as it would be with a cell.

I will do a test today. I'll mount a Ti strap across my power supply leads, apply current, and measure the temperature of the Ti. Then, I will thoroughly clean any oxides off the contact areas, both on the Ti and the Cu, and repeat the experiment, to see if there is any difference.

Trying to load the image

Here is corrosion caused by shunt current. You can see how the edge of the place was "chewed".

Edit: I should mention that this happened due to imperfection of the assembly. Error was made on the assembly line and overlooked during test's. In bad cases you can loose significant part it titanium mass and cause structural damage. At the same time you 'dilute" titanium in solution

[Edited on 25-10-2008 by simple]

Great! Now we have "shunt current erosion" to worry about... as if there weren't enough issues with this process.

I think what a lot of this boils down to is too much power. Many of us (me included) are taking 2" X 5" mesh anodes and jamming 60+ amps through them. If we either increase the size of our systems, especially electrode area, and/or decrease the current a bit, erosion, overheating, and other problems will be minimized.

@ Dann2 - is not 1960 "modern" enough for you!

The Djvu version of the Perchlorates Monograph, you yourself posted here a while back has tables (pp 74 - 75) and discussion (pp 85 - 86) on pH control. In general, slightly acid to neutral conditions are preferred, with pH 6.6 - 6.8 being used in commercial operations.

This is only for current efficiency reasons and is not a problem for amateurs using platinized Ti of PbO2 electrodes. Indeed, the stability field of PbO2 is expanded at higher pH. From memory, my assorted perchlorate cells approached pH 12 after extended running. I guess this is why my various baked MnO2 anodes performed very poorly in perchlorate (and less poorly in chlorate) cells. At high pH, MnO4- (permanganate) (recall Purple Haze) and MnO4= (manganate) are the stable (aqueous) species. pH would have to be kept below about 4 for an MnO2 anode to remain stable. I am not sure if a pH this low is feasible in a (per)chlorate cell. In a strongly acid solution an MnO2 anode would rapidly dissolve (Mn++) in the absence of the highly oxidising conditions on the anode surface.

All this assumes I am interpreting the Pb and Mn Pourbaix diagrams correctly!

Hello Folks,

@Xenoid. That clears up the pH thing in Perk. cells.
When I operated a Perk. cell with a LD anode the pH went to 10.8. Lots of Lead was depositing on the cathode. Perhaps this would not have happened if pH was kept at around 6 or 7.

@Splinky. If you are not controlling pH then there is no way Chlorine can escape from the cell after it has started to operate for an hour or so.

Regarding the shunt current problems (the new spanner in the works), I don't think it is a problem for us at all.
There are two types of cells used in Industry. Monopolar and Bipolar. The Bipolar cells use a row of electrodes 'in series' in the same cell. There are no seperate anodes and cathodes as such except the two end electrodes which have the + and - connected to them. All other electrodes are an anode on one side and a cathode on the other side (of the same MMO (or whatever) coated plate) with no actual electrical connection going to them! It is a set up we will never be using. I won't anyways.
All our cells are Monopolar and therefor will be very unlikely to get effected with this problem.
The electrodes pictured by Simple are (I think) from Bipolar set up's.
(I think it would be near impossible for the actual anode or cathode to get effected by shunt currents in a Monopolar cell. Perhaps some metal used as part of the cell construction might get eaten by a shunt current problem)
Bipolar cell pictured below.

Also the linked document explained it better than I can:
http://ifile.it/d342ftr

There is also a paper discussing the prediction of Shunt Currents in Bipolar cells in the References wanted in the Reference section. It is essential bedtime reading. A absolute must for all garage chlorate making Guru's.


Dann2


[Edited on 26-10-2008 by dann2]

Or perhaps by your horrible, corroded, twisted wire connections, Tim -

Would agree with Tentacles. If you were to (loosly) thermally attach the recharging chamber (which comes after ppt chamber) to the anode/cathode chamber this would keep it warmer than settling chamber. What you want IMHO.
A very small pump is required for the circulation, you may be better to have the pump set up on a timer that pumps every half hour for a few seconds (say).
What about a reaction chamber?? You are going to control pH I presume? If so it will be advantageous to have a large chamber (after anode chamber) that is warm/very warm to allow the chemical formation of Chlorate. You will add acid into this chamber. The anode/cathode chamber will be OK for a reaction chamber IMHO if you do not want to add (yet another chamber).

You could get rid of KCl addition chamber by adding finely powdered KCl to anode/cathode chamber and stirring gently.(magnetic stirrer) every day or so. The amount of KCl will be found out when you have discovered you current efficiency (how much KCl you are destroying) per day.
I presume there will be no evaporation from the system. If there is (say you have a reaction chamber (will be warm 60, 70C) with a fairly large surface area open to the air), then you can easly add KCl via a concentrated solution of the stuff to the anode/cathode chamber.

What will come out/stay/dissolve in the solution is depicted by ye old mutual solubility diagram.
Thanks to Watson.Fawks, who turned up an explanation of how to use (bloody) mutual solubility diagrams, you can educateyourself on how to interpret them here:
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...
See the first few pages of 'How to disign fractional crystalization processes'.
There is a mutual solubility diagram for KCl and KClO3 here:
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...
Unfortunately it is in mass ration, you want mass percent in order to figure out what will/will not stay in solution as per the Watson.Fawks article.
Does anyone know how to convert the graph? The axis are easy but it is difficlult to know where to draw the lines. Would need to sit down and study the thing. The table that Xenoid showed you has the data in mass % (and you could draw a (lovely ) graph).
There will be no problem getting the KClO3 out as it is less soluble and also has a large slope in it's solubility graph.
Me thinks that if you just set the system up and let it belt away for a day or two it will work as you require. It will take it a day or two to reach its 'working point' where K Chlorate comes out nicely and KCl goes in nicely. You may have to insulate the whole thing (or keep shed reasonably at the same temp.) as wildly varying outside temperatures may upset it.

Regarding efficiencys: The anode to cathode spacing debate has more to do with voltage drop accross cell which is related to power efficiency (very very important to the industrial Chlorate makers). Not very important to you.
The largest increase in current efficency (time efficiency) for the amateur can be got by pH control and (since pH control is being implemented) using a seperate chemical chlorate formation chamber which is hot or use a fairly large anode/cathode chamber (ie. the anode/cathode chamber is also the chemical chlorate formation chamber).

The next biggest step up for to get high CE is to keep the Chlorde level high.

From then on you will just be tweeking at the edges for little CE return.

My two cents worth on Cell chem. is here:
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...

Regarding reduction at the cathode:
From what I can figure out from all my bedtime reading adventures (read: sad fuck) Iron cathode are good at reducing Chlorate and hypochlorite back to Chloride. (What we don't want). Ti is not as good at converting Chlorate and Hypochloride back to Chloride. (that's good for us).
Therefor area of Cathode (large area gives low current density and this increases reduction, read this somewhere, can't remember where I'm afraid) is even less important to us when you use Ti. (I am not trying to say that area of Cathode is a really big deal anyways). Chromates are added to cell to stop reduction in industry. Perhaps you will get away with adding no Chromates if Ti cathode is used?????????
Perhaps if you use a very small Ti Cathode it would really reduce reduction without having to add Chromate etc.
Industry would NEVER use a very small cathode as it would raise voltage accross the cell a bit (they would'nt tolerate that at all).
The less additives the better. Then again Chromate also buffers the solution which is an advantage.



Well, I'm glad I got all that off my chest!!!!!!!!!!

Cheers,
Dann2

[Edited on 29-10-2008 by dann2]

cutting through the fog

Hello,

It is amazing the near absence of Graphite erosion that industry can achieve.
4kg Graphite per ton Chlorate produced, @30C. That's 4 grams per KG , and not all of the four grams will appear as black gunk. Some will have gone off as CO2.
We are doing something(s) very wrong when using Graphite. No pH control I guess is by far the biggest issue.

@Swede
Would you not need to mention the more aggressive species that the pH probe will be in contact with + the fact that the temperature will be up at 60C. These factors will be a pH probe killer, perhaps not?
It can be hard to extract the info. you need from people selling stuff.
While my suggestion will not be in line with your (to put it mildly) exacting standards, you could set up the system and just have a constant feed of acid into cell and check pH twice per day (or more at the start).
I did this with a cell before and the pH stayed in the wanted region remarkably well.
The rate of acid addition was 0.35ml per amp each hour. Acid was 12% hardware store (used for cleaning cement) HCl. pH stayed in the region of 6.7 to 7.
You would need 17.5ml per houre if your cell was running at 50 amps. Of course you cell might need more/less. 17.5ml per hour sounds alot. 0.42 liters per day.
You still need to get a pH probe and may neet to take a sample out of the cell both to let it cool and to stop voltage gradients in the cell from putting the pH reading haywire.

Which reminds me of another point for your pH probe in the actual tank. Will it operate with the voltage gradient that is in the tank?
Mine would not. Samples had to be removed. If you had a seperate 'chemical chlorate making vessle' (hot), there would be no voltage problem is this vessel and a permanently installed pH probe shoud work OK there.
You may also be able to shield the probel with a metal shield to keep voltage field from probe in anode/cathode chamber.

Dann2

[Edited on 29-10-2008 by dann2]

Quote:

Originally posted by dann2 Hello, It is amazing the near absence of Graphite erosion that industry can achieve. 4kg Graphite per ton Chlorate produced, @30C. That's 4 grams per KG , and not all of the four grams will appear as black gunk. Some will have gone off as CO2. We are doing something(s) very wrong when using Graphite. No pH control I guess is by far the biggest issue. Dann2

Hi Splinky - how did you harvest the chlorate? Did you start with potassium salts, or sodium? Either way, once you had your potassium salts, remember that they are VERY insoluble in cold water. If you used some sort of filter rig, once the potassium chlorate is sitting there in the filter basket, you can pour (wash) significant amounts of ice cold water on them, which will remove much clinging contaminants, and also residual chloride, while dissolving very little of the chlorate. I wash first with ice water, then with an alcohol/water mixture (also cold) as a final wash. The alcohol helps in the wetting of the crystals and also speeds drying. They should not smell like hypochlorites when dry.

It might have been your washing technique. Did you get the ice water to all of the crystals with a bit of mixing/stirring of the mass? If you simply pour cold water over the surface of the crystals, the water will follow a path of easiest flow, and may not access clumps of crystals in some parts of your rig.

I tested some potassium chlorate crystals washed in this manner, and they had a low chloride residual; they were 99.3% pure. Recrystallizing KClO3 is easy and will produce a quality product.

I like your thought of using the KCl crystal mass as some sort of heat sink! Interesting. Along those lines, I picked up what is called an "offline chlorinator" at a pool store today. Thes are cannisters designed to accept 3" chlorine tablets, and have water trickled through them to leach the chlorine, which is then injected back into the pool. This is what it looks like:



This sort of gadget can find all sorts of uses in (per)chlorate electrolysis. The plastic is designed to withstand wicked oxidizers. It is also engineered to be completely sealed. I can see something like this being a stand-alone cell (the volume is impressive, about 4 liters), an electrode cell, or a chloride replenishment cannister; any of these with just a bit of work. They can be had on eBay relatively cheaply. I'll take a look at it today and snap some pics.

@Tentacles: That sucks that the anodes have not arrived yet. Hopefully customs will release them soon. I'll bet they will be opened and inspected. Hopefully they'll repack them properly.

I am going to take my small test anode of this material and set up a perchlorate cell, starting with recrystallized chlorate, and rip some serious amperage/voltage through it to see how it stands up. Another one will do duty as a chlorate-only anode.

[Edited on 30-10-2008 by Swede]

Hmm, that would be one way to wash crystals, and it should have done so thoroughly, Make sure you save the was water for your next run... it'll carry chlorate with it. Replenish that water with chloride, and it'll give you a head start.

"Used" chlorate cell electrolyte is loaded with intermediate species, and significant quantities of chlorine as well. I have about 5 gallons in a poly jug over KCl crystals to replenish for the next run, and with the lid removed, it becomes unbearable in the vicinity of the jug. This is mainly due to the chlorine, but also the bleach.

Anyway, maybe someone else has some thoughts on washing. I used to use coffee filters, but when the batches approached a kilo, that was too slow, so I made a plastic filter/funnel rig. The entire batch gets dumped into this, then the cold water is applied with stirring; the holes allow the water to drain. I have never had a dried chlorate batch smell like anything at all.

I'm sorry, I meant to also post this: A doctoral thesis on the electrochemistry of the chlorate process. 119 pages of doctoral yumminess. First glance indicates it will be an excellent resource for the dedicated amateur.

www.diva-portal.org/diva/getDocument?urn_nbn_se_kth_diva-344...

I wish I had written it. Enjoy!

I was thinking that the easiest way to create the buffer would be to mix phosphoric acid and NaOH and adjust the ratios to achieve a pH of around 6.0, but it would be more economical to have the mono and disodium phosphate salts at hand, determine a correct ratio, and add the salts during preparation. Where one would obtain these salts at an economical price, I have no idea. Anyway, it'd definitely be for a future experiment.

I love the way these patents say things like "current efficiency dropped to 90%; unacceptable." I'd kill to get 90% efficiency!

I like the direction this discussion is taking... altenate methods to do what industry takes for granted. I found yet another patent (I hate reading patents because it's often hard to find good nuggets in them, but they are there) that makes use of a tungsten electrode set and appropriate electronics to measure chlorate concentration, much like watson.fawkes mentions. Further, I am confident that there are ways to determine chloride concentration (end of run) conditions based upon voltage/current plots, even when efficiency may not be known. Logic says that as the species change in the system, the voltage required to create a given current (with a good supply capable of constant current operation) will follow a predictable path. What I've seen with my own system, starting with potassium salts, is a concave voltage curve... it starts high, drops, then begins to rise once more as the chloride is depleted. As WF says, conductivity may be a useful measurement that is overlooked.

My point is, with enough research and some hands-on experimentation, things like quantitative analysis, pH control, and other pressing issues, can and will be overcome.

Dann2, I laughed when you pointed me towards the Reflex electrode. I have literally been researching poisoning-resistant pH electrodes for weeks without finding anything like that. I've come up with "Triple-junction, glass-domed, PTFE membraned, long life electrodes" stuff like that, but nothing that flat-out says "It cannot be poisoned." I am going to email or call them as well and see what they have. I will not hesitate to buy an expensive pH electrode if I know that it will survive. Worth every penny, IMO. Thank you for the resource.

But for setups without a controller, I like the concept of simply adding calculated quantities of HCl, and doing periodic checks with a pH meter. I did not realize that there was a calculable quantity of HCl consumed given a known current. Since we know our current (ammeters are cheap) then we should know how much HCl to trickle in. A dosing pump set up on a timer could administer X ml per hour, and all you have to do is check on it once in a while.

I am interested in efficiency... it tells me that I'm doing it correctly. The runs where I calculated my efficiency, it was at best 61%, maybe a tad bit higher. That was with no pH control at all beyond inadequate shots of HCl using a wash bottle. I think a well-run home chlorate cell can do 75% to 80%, and if I can get there I'd be delighted. The other good thing, if you know your efficiency, and it is reasonably constant batch to batch, you can use math rather than tedious chloride quantitative analysis to determine end-of-run.

I am going to finish plumbing today... I need to get more HCl from the pool store, and rig up some sort of drip system, before I fire it up. I don't want to proceed without at least a crude way to keep the pH in check.

Again, sorry for yet another "stream of consciousness" post, but I am delighted to find a bunch of smart guys here with a common interest. Wish me luck!

Oh yes, I finally figured out a good way to create a swappable anode "cartridge". This was baffling me for some time, but the end result is simple. I created a round slug of CPVC, slotted it 98% of the way through for the anode strap. I drilled 3 or 4 holes through the strap where the CPVC circle would fit, and then glued it in. The holes are critical... PVC cement does not stick at all to Ti. The holes form a PVC "bridge" between the hemispheres, and keep everything secure.

Next, the anode strap + CPVC slug was glued into a rimmed carrier that has a viton o-ring, not installed in the pics. This carrier is installed in the cell lid from below, and an aluminum block is clamped on the topside to fix the strap in place... it cannot move vertically. This will replace the "sculpey" PVC clay plug that I had tried earlier.

Hello,
One more figure for acid consumption in Sodium Chlorate process:
http://books.google.ie/books?id=_R00NqWST6MC&pg=PA233&am...
Encyclopedia of Chemical Processing and Design
Vol 51 page 184

50kg HCl per ton Sodium Chlorate.
It does not say if they mean 35% HCl acid (or perhaps 100% equivalent).

Thats 50 grams per KG Na Chlorate

What is the No. of the patent showing the set up for measuring Chlorate conc.?

I like that chunk of Al. It will be a great heatsink. If you really have a stubborn heat problem at this point you could cut slots in the block, just like a regular heat sink.

In regards to monitoring Cl2 coming from cell see pic. below. It is from E. of Chem Proc. and Design.
Perhaps in conjunction with this type of device it may do instead of pH monitoring.
http://cgi.ebay.co.uk/Industrial-Scientific-CL266-Chlorine-G...
Cl coming from cell may/will also be a function of things other that pH so you may have to keep cell parameters constant (eg. temp) when using this method.



Dann2

Hello Swede,

I agree with your calculations.
With '100%' acid you need 39.7ml acid per day.
If you used 12% acid you would need 331 ml per day. (hope I got that right).
A figure that I give (from my jamjar type cell that was pH controlled) is not too far (plus 25% ) from this figure. I calculated on post of 29-0-08 that you would need 420 ml 12% acid (from the jamjar data) for your cell running 50 amps.

If you have room in the cell for the extra water you would be better off using a lower % that 38%, as each time you drop a drop of the 38% stuff into the cell you will get an immediate reaction at the liquid surface and a smell of Cl2.
You could inject into bottom of cell and that would help. Perhaps it is a very minor issue.

Dann2

[Edited on 3-11-2008 by dann2]

Update: I promised in my blog that my "T-Cell" would be running... yesterday. It's still not running, for one primary reason. I had ordered a dosing pump off eBay, but I was not expecting it for several days yet. it arrived early, and now I am cramming, trying to integrate it. I don't think it's going to happen.

The pump: A Hanna BL5. http://www.hannainst.com/usa/prods2.cfm?id=018001

I made a big mistake. I placed the order before I really thought about the volume of acid to be delivered (low) and the fact that I was planning on automatic pH control, rather than semi-manual. This pump delivers FAR too much with each stroke.

Benefits: The BL pumps can be bought bew off eBay for a hundred bucks. Good dosing pumps are normally $300-$500. Everything wetted is either kynar, PTFE, or glass, good for darned near anything, chemical wise. And the interesting thing, with each stroke of the pump, exactly 1 ml is delivered. As far as I can tell, it is quite precise.

This means for 50 amps, I'll need about 4 strokes per hour. When the pump is set on it's slowest speed, it executes one stroke every 5 seconds. This means that each hour, unless I use a controller, the pump would need to come on for 20 seconds, then shut down. I don't have a timer that will do that. The average consumer timer would come on for at least one minute.

I could dilute the acid by three, OR, I could have it come on for a minute, overdose slightly, then shut down for three hours.

Anyway, I need to figure out how to do the acid additions. Maybe I should set up a drip while I figure out how to integrate the pump.

Lesson learned... if you shop for a dosing or chemical pump for a home chlorate system, get one that delivers very small dosages; or, one that can be minutely controlled.

I hope to get the system running tonight or tomorrow morning. I'll need at least 24 to 48 hours of nearly cotinuous monitoring and tweaking to ensure there are no leaks, the temps are good, and the system is behaving as it should.

It has really gotten more complicated than I had anticipated. Oh well! It's also been a lot of fun! I just hope all the work and materials are not going to go to waste.

My old system with no pH control was 60% efficient. I think I can get this to 80% or better, meaning at 80 amps (if it'll handle that without overheating, the projected yield would be 1.46 kilos per 24 hour period at 100%, and 1.10 kilos at 75%, with an estimated capacity of 25 liters.

My old system of 6 liters was doing 1 kg per batch from 14% down to 7% chloride, so this rig should do at least 4 kilos per run. If I can take it to 3% chloride, it should do 6.8 kilos. Since I am hopelessly optomistic with estimates, a more realistic value is in fact 3 to 4 kilos max. Can't wait to fire it up!

Sorry for the string of posts... it's running, and everything so far is perfect. No problems at all. 50 amps created a delta T (temperature differential) of 20 degrees within 15 minutes. The pump is barely ticking over right now. If the DT gets too large, I'll crank the pump up a bit.

pH within minutes was at 8.4. Until I can rig up a drip (probably tomorrow) I'm simply ging to inject some HCl using a syringe.

Electrode spacing and area looks good... 5V on the supply created a current of 55 amps. If everything goes well, and the system doesn't overheat, I may try 70 or 80 amps.

I'll get some pics up later.

Tentacles - The shank is identical, 0.041" thick by maybe 0.950" wide. It's doing 50 amps with ease. The aluminum block connector helps a bit. I may clamp a heat sink to the block, and later attach it permanently, but it's really not needed.

pH - when I bought the dosing pump from an eBay outfit called eSeasonGear

http://stores.ebay.com/eSeasonGear

I picked up the electrode as well. I'd say it is not a super-cheapie, but it is definitely low on the totem pole. $37. It is a double-junction electrode from Milwaukee instruments...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=28017...

It is the yellow one in the picture. The first thing I did was prepare a liter of electrode storage solution using KCl, and I soaked it overnight. The next day, I calibrated the Extech controller using pH 7.00 and 10.00 buffers. I was really happy to see 7.01 and 10.01 on the meter without having to touch the set screw.

The way I am measuring pH right now is simple. I draw off a few ml of liquor from the ball valve on the exit port of the EC... comes out quite hot.



The electrode is rinsed, goes into the liquor for maybe 2 seconds, I note the reading, and out it comes immediately into distilled water for a rinse. Then, right back into storage solution. With such limited contact to the liquor, I am betting it will last a long time.

One thing I've noticed in the 16 hours it's been running... the pH is not responding as well as I'd like to additions of HCl. I started by dosing 4ml conc. HCl per hour. The pH would go from 8.2 to 7.9, but fairly quickly go back up to 8.2. It seems to want to hang there at 8.2, as if it is buffered there.

Today I am going to force the issue with much larger HCl additions. If I can get it below 7.0, I am going to see how long it will stay there. If it climbs back quickly to 8.2, then I think I can conclude that manual, periodic acid additions, while helpful, probably won't be able to keep the pH at 6.6 or 6.8. That would require true control; or, a continuous drip or dosing setup.

This begs the question again of buffering with chromates, or the phosphate ions. I'd really like to give the latter a try. I will conclude this run with no buffers, but for the next one, I'd definitely like to find some sodium phosphate salts and try the buffering as described in the patent.

[Edited on 5-11-2008 by Swede]

Hello,

It's not really 'the bulk of the reactions' but rather 'the bulk' reactions. I know it sounds ridiculous to bring it up but there is a difference.
This is why, when we are controllig pH, it is good to have a seperate chamber where the 'chemical Chlorate formation reactions' (also called the 'bulk reactions') can take place, away from the electrodes. (Or you can have a single, large, chamber which contains the electrodes + this chamber will have volume away from the electrodes, known as the 'bulk').
When controlling pH is not great to have a small 'bulk' area in the electrodes chamber. Large chamber in relation to electrode size is best (or a seperate, very warm chamber).

When we are not controlling pH, it does not matter a toss about the size of electrode chamber in relation to electrode size (within reason) as there is NO 'Chemical Chlorate formation reactions' taking place. Chlorate is make by a reaction called 'Anodic Chlorate formation'. The vast majority of garage Chlorate cells (no pH control) make there Chlorate by 'Anodic Chlorate formation'.

'Anodic Chlorate formation' is avoided like the plague in industry (pH controlled used!) as it is considered an electricity robbing reaction.
Since you are doing pH control you should perhaps aim for this lofty ideal! (seperate 'chemical Chlorate formation' chamber)

I think you will agree that the above explanation of cell chemistry is an exquisitely clear and terse explanation of what is going on : ..........perhaps not!
The picture below explaines it better, I think.
The how, why and where of reactions A, B and C are really all you need to know about, in order to understand the vast majority (from our simple point of view anyways) of what is going on in the cell. (you may also like to look at the graph of distribution of species (HOCl & ClO-) in the cell at different (bulk of solution rem.) pH values, next post)



Dann2

[Edited on 6-11-2008 by dann2]

This diagram just about sums up what pH controll is all about.

perhaps straying off topic a bit but what the heck.

Hello Swede,

Looking at the diagram below, I think it is fair to assume that I would not cut it as a pilot. Moving swiftly along..................

Good to know there was a easily found problem.
Consider using your crystallization chamber as a 'chemical Chlorate formation' chamber. You will then have to add another chamber. I reckon your electrode chamber is a bit too small (in relation to electrode size).
That's not to say this device will not work. You may get CE that are high enough, and it may not be worth the extra effort. The crystallization chambe could be a bucket with a cloth in it just to see how things went. There would be litttle need for venting etc.
You could also consider drilling lots of holes in the cathodes to reduce surface area and putting plastic on the back sides of them where CD is probably very low. (will stop/minimize cathode reduction).

Regarding your system at the moment I would be inclined to meter in what ever acid you think is needed and leave for 24 hours. (if your pumping system allows that).

Why do you want to lower Chloride concentration down to 50 gpl or less? If you want to keep CE high you should keep it at 100 gpl or more.

MMO always seems to give good CE. You should be able to get 80 or 90% with pH control.

It is hard to give a figure on what the circulation rate of the whole system should be. I would guess if you pump the contents of the electrode cell once every hour. (Wild assed guess).

Keep it up!!
Dann2

[Edited on 6-11-2008 by dann2]

Before I can digest the evening input, I have a small situation to take care of... Why does bad stuff always happen when you are asleep?

I went to bed with everything looking good. This morning, the DT (Temp Diff) between the two had gone from 30 to 60. The temp of the EC was 90 Celsius! I found out why...

When I built the thing, I created two ports on the big vat, one at 1/3 height, the other at 2/3 height. I plugged the pump input into the 1/3 height port... which jammed solid with crystals in the evening chill. The EC flow ceased, and at 50 amps, the temperature soared. Hopefully no damage was done. I dialed the current down to 2 amp just to keep the electrodes charged. It's cooling right now.

Two things I did wrong. I placed the pump inlet source too low on the collection vat, and I selected tubing with way too small a bore for the pump. AND I should have installed some sort of prefilter for the pump. I'm lucky the pump didn't chew through the tubing and spring a leak. I should have known better on all of these issues.


I am convinced this concept is workable. Everything was going as planned with the exception of the pH. I am going to tear down what I have this morning, harvest what crystals exist, replumb, and fire it back up. It's going to be a noxious task.

My HCl dosing pump came with a beautiful mesh PVDF prefilter which I am going to cannibalize and use to protect the system pump; AND I'm going to plug into the port at 2/3 height. There's no way crystals are going to reach that port.

When I'm done with this chore, I'll come back and read the latest inputs. But it's going to be a busy morning!

[Edited on 6-11-2008 by Swede]

[Edited on 6-11-2008 by Swede]

Well, I've got some good news, plenty of bad news. Here's what happened...

The line leading to the pump was JAMMED with fine crystals. The crystals had not reached the port level in the collection vat; the liquor had simply cooled, and once the solution was saturated with chlorate, fine seed crystals formed in the tubing, and from there, they grew.

With the pump in a no-flow state, the temperature in the EC soared. I measured 90 degrees C in the thermowell!



I took it outside and opened it up. The bottom had a layer of very fine crystals about 2" deep. Good news: the materials (CPVC and PVDF) held up perfectly, which is remarkeable given those temperatures. The bad news - the cathodes. I have never sen anything like it, and I am at an utter loss. They are both warped HUGELY in a symmetrical pattern away from the anode, which looked fine.

Check this out:





What the f***? All I can think of is that perhaps the TIG welds set up some sort of stress, which was released by the current? More bad news - the cathodes are permanently installed, and the lid is ruined unless I don't mind warped cathodes. Really, really bizarre.

Continued; next post

I wheeled the collection vat outside... the cart IS the way to go for a heavy setup. I attempted to drain it from the side ports, but they too were clogged hopelessly.

I popped the lid. There was a small amount of chlorate in the bottom, some nice, fat crystals, but not much. I'm estimating the chloride level in the liquor went from 145 g/l to no less than 130, to deliver such a paltry yield. I expected this. the rig had not been running long enough for a big yield.



With the exception of the clogged ports, everything was perfect. The lid, with all it's vent ports and gadgets, was likewise good.





I had installed those CP Ti cathodes earlier. I had a hunch that something catastrophic might happen, and I want to be able to run the vat as a stand-alone cell. That's probably what's going to happen now.

I was forced to scoop out much of the liquor by hand, with a cup, to salvage what little chlorate there was.

Thoughts: Everything was going perfectly so long as the entire system was liquid. Sodium chlorate would not have given me this problem. Someone needs to talk me into using sodium salts.

I was surprised at the amount of crystals formed in the EC. BUT, and that's a big but, I suspect everything I saw in there happened AFTER the circulation stopped. I had 50 amps running in a relatively small cell, and it simply brute-forced a certain yield. If the liquor had been circulating, I would have expected crystallization in the big vat.

I'm not sure this concept is sound with potassium salts. If it can be done, it'll require careful monitoring of the pump lines, which need to be fairly wide-bore, and screening of the pump inlet. A thermostat needs to be set up to remove power if the temperature rises too high in the EC, which would indicate a stopped pump.

A pump capable of carrying a slurry, and the use of hard CPVC pipe instead of tubing might also help.

For the moment, I am going to shelve the EC, and execute a carefully-controlled run with just the collection vat. With my old, crude setup, I was getting a kilogram of fat, clean potassium chlorate crystals, and this vat is at least 4X the size. With no external plumbing beyond venting, the system is dead-simple.

I'm down but not out. I'll find a way to boost efficiency. And the big question, what in the HELL hapened to my cathodes?

No biggie. It's part of the research process. And Tentacles, you'll be happy to know that anode material looks like a winner for chlorate, so far.

[Edited on 6-11-2008 by Swede]