Swede - 10-10-2008 at 12:27
Hello everybody - I've been lurking here for quite some time. Like many, I have become heavily invested in time, $$, and effort, investigating the
chloride --> chlorate --> perchlorate process. It has become almost an obsession.
I am making a miniature (per)chlorate "factory", the details of which can be found in my blog on the APC site. Summary: it will have two "cells", a
small, hotter cell of mostly CPVC which will carry the electrodes and instrumentation, and a much larger crystallization chamber, which will hopefully
collect the vast bulk of the product. I am using potassium salts throughout.
It will eventually have a heat exchanger and possibly a chloride ion replenishment rig. A pump will circulate the electrolyte.
The anode will be swappable. The cathodes are titanium. My question for you guys... I am a bit concerned about the complexity, and if for some
reason the circulation concept does not pan out, I will at the very least have a huge, deluxe cell by simply using ONLY the big chamber. I would like
to permanently install a large sheet titanium cathode in that cell. When the rig is in the original (intended) recirculation mode, the Ti plate would
simply sit there, immersed in hot and noxious electrolyte.
Will this Ti plate be OK without cathodic protection, without being energized at all? I'd really like to permanently install the plate (it'd be much
less work), but if it needs to be removeable, I could go that route as well.
Thanks!
12AX7 - 10-10-2008 at 16:33
I think it'll be fine.
Tim
Picric-A - 11-10-2008 at 01:48
yep should be fine, nice cell btw!
what is your intended use of all the chlorate/perchlorate you manufacture?
Swede - 11-10-2008 at 06:11
Thank you guys, that is a relief... it makes things much simpler.
For me, the chlorate is an intermediate step to perchlorate. I have been interested in crafting "serious" fireworks (crysanthemum/peony shells, other
aerial fireworks) since I was a kid, and now I have the chance. I don't have the experience (yet) to safely use chlorate in my displays. Perchlorate
is so expensive, and used in so many compositions, this rig will hopefully pay for itself pretty quickly. I am also concerned that sooner, rather
than later, (per)chlorates will be very difficult to obtain.
I also find myself drawn to the process for the challenge of purification, the analysis of the product(s), and the chemistry behind it. I started my
adult life as a chemist, but went down another path, and I want to get back into it a bit.
dann2 - 12-10-2008 at 17:07
THAT is one tidy cell!!
The only two cents worth I can throw is that it may be advantageous to use smaller cathodes.
When current density is low on Cathodes (in a Chlorate cell, don't know about Perchlorate cell) the reactions (Cathodic reduction) that convert
Hypochlorite and Chlorate ion back to Chloride are more prevelant than when a higher current density is used.
It would be a pity to have to cut them, perhaps covering with pvc strip would reduce area and keep current carrying capacity as before.
It is a relatively minor point IMHO.
Perhaps DiChromate additive eliminates the unwanted reactions anyways.
It is interesting to see that K Perchlorate can be made directly from K Chlorate. I though that the K Perchlorate would accumulate on the Anode at it
was formed. No so obviously.
Cells used in Industry, made from plastic (PVC or CPVC) have run temperatures below 60C to stop the plastic from being damaged.
Also, if you intend to pH control a good yoke for the job is a syringe pump as per:
http://cgi.ebay.co.uk/LIFECARE-4100-PCA-PLUS-II-INFUSER-SYRI...
Dann2
Heard a quote today.
(From someone who got divorced)
I'm not going to get married again.
I'll just meet and befriend a woman I don't like and buy her a house.
[Edited on 13-10-2008 by dann2]
Swede - 13-10-2008 at 07:50
Thank you Dann2, and the info on cathode current density is something that I was not aware of... very interesting. The good part: There are two
cathodes that make a sandwich of the anode, but they are connected externally. By removing the heavy Cu jumper between them, I can remove one of them
from the circuit. If necessary, I will definitely do that. I wanted excess cathode surface area so the cell can handle any conceivable anode.
As for perchlorate physically accumulating on the anode, I have been using some serious agitation/circulation in my later runs. I think it not only
keeps the anode physically clean, I believe it also makes for a better electrochemical environment, especially for chlorate, keeping evolved gasses
mixed.
I was hoping to get higher working temps from the CPVC... we'll find out one way or another. Some damage or erosion is inevitable, just need to keep
it reasonable.
My dream "tank" is one welded from sheet Ti, and used as a cathode. That would last for years.
Swede - 16-10-2008 at 11:58
Rather than start a new thread, I'd figure I'd post this here...
I have a huge sheet of MMO over Ti mesh that I am going to cut and equip with shanks, thus creating custom anodes of any size. I've done a bit of TIG
welding with good results on Titanium, but haven't dealt with the MMO coating yet.
I plan on laying the solid shank onto the mesh in a typical manner, and placing some small and neat tack welds that will connect portions of the mesh
with the shank.
Two schools of thought... Clean off the MMO first, by scraping, grinding, sanding, etc. unless there is a spot chemical method to strip the MMO
coating. Degrease, clean, and weld. The other method, given that MMO is conductive, is to simply weld away with no scraping or grinding. The MMO
will probably be dispersed throughout the weld.
Since this is not a structural, NASA-grade weld, but just one to make good electrical contact, that may not be so bad.
Anyway, has anyone welded this stuff? Any hints to pass along before I botch it?
[Edited on 16-10-2008 by Swede]
12AX7 - 16-10-2008 at 19:05
Oxides plus titanium equals caca. Best to grind.
Tim
Xenoid - 16-10-2008 at 19:38
Hi Swede, beautiful work, I enjoyed reading your blogs, the trials and tribulations of a (per)chlorate cell builder! I really will have to get a lathe
and welder. Your Sorenson power supply was a wonderful purchase, I just wish such things were available as cheaply here in NZ.
Just a couple of points, hopefully not turning this into another (per)chlorate cell thread!
With regard to your T-cell cathodes, (and anode) if you are able to weld Ti would it not have been simpler to weld, say, 5-6mm Ti rod (assuming you
can source it) onto them instead of the straps. This would have enabled you to bring all three connections straight up through the lid via drilled
holes and "O" ring seals.
Are you not worried about not being able to see what is going on inside your cell? I considered a similar design using 100mm drain PVC drain fittings,
a bit like my pressure filter:
http://www.sciencemadness.org/talk/viewthread.php?tid=9630&a...
but with an end-cap glued on the bottom. All my cells have been glass, except the 10 litre "paint bucket" cell. With that bucket cell it was a little
frustrating not knowing what was going on inside. I have 4 glass "pickle jars" which hold about 5 litres each, which I got from a delicatessen. If I
built another cell using MMO or Pt anodes I think I would use one of them. A PVC lid is easily attached because the top openings are flanged rather
than threaded so simple clips are all that is required to hold the lid on.
My Pt coated and MMO pool chlorinator mesh anodes appear to be simply spot welded onto the Ti connection strap. Obviously, large mesh sheets are
coated with MMO or Pt, then cut up in a guillotine and spot welded 2 - 5 times, straight through the MMO and Pt onto the Ti strap. The MMO coating
goes right up to the weld, there doesn't appear to have been any cleaned or ground off!
Anyway, good luck and keep us informed of your progress!
Swede - 17-10-2008 at 07:12
Hi Xenoid, I agree that Ti tubing would have made excellent shanks for a cathode. You could take a tube, slot the end for maybe an inch, install the
cathode plate into that slot, then "smoosh" that joint in a vise or press. After squishing the area flat, a few welds on both sides would have
finished the job.
The only reason I didn't do that was because I had no tubing, and I was impatient! 
It is definitely easier to seal a round shank in a system like this than those flat straps, and if I ever build another (I've got lots of 4" CPVC
pipe to do so) that will be the way I'll go.
It bugs me a little that I can't see what's going on, but I've done enough chlorate runs at least to know what sorts of efficiencies I can expect, and
being able to quantitatively measure chloride ion is really all that's needed. Perchlorate is a different matter. I don't have as much experience
there, and I need to come up with a reliable way to detect "end of run" conditions, either by measuring remaining chlorate concentration, or some
other means such as voltage.
I've thought about incorporating a clear PVC window in some part of the system, and if necessary I can always add one. But I wonder how long it would
truly remain clear... I suspect it would fog fairly quickly, and if that happens, it'd be a lot of work gone for nothing. It's something that could
be tested by simply dropping a small section of clear PVC pipe into a cell and see what happens.
Your big flanged glass cells sound awesome... I wish I could find something like that.
Power supplies... since I've started this obsessive project, I have picked up no fewer than SEVEN power supplies off eBay! It's amazing how cheaply
they go. I know you are in NZ and the choices may be fewer, or the shipping would be prohibitive, but there ARE some amazing bargains, every day, for
eBay power supplies. The really cheap ones are the high-amperage, 5V fixed switching supplies. I picked of a 400 (!) amp 5V supply for $30, and
three matched 5V 120A supplies for $15 each. The good part, these supplies can be run in series quite easily, especially if they are identical units.
They also usually have screw adjustments to take the voltage from 4 to 6 or so, so a pair of these can deliver 8 to 12V at 120 amps. A 5V supply
would be good for chlorate, and perhaps more voltage might be needed for perchlorate.
I'm going to cut and weld some of the mesh today, we'll see how it goes. Thanks!
Swede - 17-10-2008 at 15:24
The spot-welding of the MMO mesh went off without a hitch. In fact, it worked far better than I could have dared hope for. The "dimples" on the
shank side are depressions created by the spot welder pincers. The fact that the Ti is cratered is a very good sign... it indicates the Ti softened
and melted, and the weld should be a good one.
This small anode, 3" X 2", will be tested to destruction to finally answer the question, just how low a chloride concentration will these things
process before there are real problems?