The Bucket Cell Adapter
Entry posted by Swede
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In my adventures with the (per)chlorate process, I have run the gamut from a plastic cup with no lid, to the T-cell, a dual-celled beast with a pump designed to produce vast amounts of chlorate crystals in a collection chamber. The T-Cell failed spectacularly (see older blog entries for the story) due to the tenacious clogging of tubing and pipes with potassium chlorate. I have since simplified the T-Cell into the T-Cell Jr., a single (but large) cell that works in the traditional manner... power on, convert, power off, lid off, harvest.
The making of the T-Cell was lengthy, difficult, and in the end, expensive. At about this time, Tentacles and I kicked around an idea we called the "Bucket Cell Adapter." Essentially, any decent hardware store has plastic paint buckets in a variety of sizes, with the normal sizes being 2.5 and 5 gallons, or approximately 10 to 20 liters. These are almost universally made of HDPE, High Density Polyethylene plastic. HDPE is an excellent plastic that is resistant to the bulk of chemicals that a pyrotechnician may be interested in, but unfortunately, it is not in the same league as PVC, PET, or any of the fluorinated resins. Regardless, a heavy HDPE bucket would last for many runs, and the price is right, with a 5 gallon bucket and lid costing maybe $5.
Our thought was, "Why not make a set of hardware that is durable and resistant to the cell's contents that is easily mounted to a typical HDPE bucket? When the bucket croaks, move the hardware to the next bucket?" The idea we came up with was a gasketed or O-ringed sandwich using two PVC plates, with the essential hardware (anode, cathode, fittings) mounted in the upper plate.
Since I am about ready to test my Lead Dioxide anode, and not wanting to fire up the 25 liter T-Cell for this, I decided to pursue the bucket cell adapter, or BCA.
The first step was to create blocks of PVC that would firmly hold the Ti sheet metal straps, and separate the anode and cathode by a fixed amount. The design I came up with was simple... a plain central block, and two end clamp blocks that are slotted for the electrode shanks. The entire sandwich is pulled together with two sections of 316 stainless threaded rod and nuts:
The second picture shows the block assembly together with the two clamp rods, and a section of Ti sheet to simulate an electrode.
The idea was that this central block would be cemented or bolted to the upper PVC sandwich. The early concept was that these sandwich pieces would be disk-shaped, and as anybody knows, making disks can be a real pain. Finally, I decided "Why not make the pieces rectangular?", and I could see no reason not to. So I cut out two pieces of 1/2" thick PVC plastic of exactly 6.4" X 3.4" dimension, and began work on them to create the BCA.
One of the things I learned from the T-cell was that you could not have too many clamping bolts or studs. The pressure exerted by the sandwich on the viton O-ring stock needs to be both even and quite firm. I played around a bit with the fasteners I had on hand to determine the best pattern. The bolts in this picture are not stainless... they are titanium, and if any portion of these bolts is exposed to the liquor, titanium is far and away the best material to use. Even 316 SS will corrode, whereas Ti will come through with flying colors.
Ti fasteners are expensive. If these were purchased new, they would probably cost about $5 to $8 each. On eBay, they were 30 cents apiece.
Once I had determined an effective clamping arrangement, I calculated the hole locations, and drilled the upper sheet through for the bolts (they are 10-32) and tapped the lower sheet.
The next step was to cut the channel for the viton O-ring stock, and this was done in the same manner as the channel cut for the T-cell, although on a much smaller scale.
This O-ring channel was cut in the UPPER sandwich piece, on the outer perimeter, but inside the bolt pattern. As it is set up, there are only two places the electrolyte can creep out of the cell, assuming the O-ring stock seals, which I have confidence it will... it could potentially creep up the threaded Ti hold down bolt holes (extremely unlikely); or, it could creep up the electrode shanks (more likely). This will hopefully be limited with a well-engineered set of electrode shank clamp blocks on the upper sandwich piece.
The O-ring channel was cut and relieved at the corners, and the next step was to cut slots in the upper sandwich piece for the electrode straps. I decided to make these quite a bit oversized, and am counting upon the clamp blocks to seal. To cut the slots in this 1/2" thick material, it first had to be relieved with a larger end mill. I cut a pair of V-slots on the lower side, then finished the slot with a 1/16" (0.062") end mill. The slots match exactly the edges of the fixed central clamp block on top.
The underside:
The top of the upper sandwich piece:
I decided to drill and tap the upper piece for the central clamp block:
On the lower side, the O-ring channel can be seen, filled with viton O-ring stock. Viton is an excellent plastic that has proven itself to be exceptionally resistant to the aggressive electrolyte, and is flexible enough to form a good seal. The Ti strap seen here is obviously not connected to any sort of electrode - it was used only for planning and fitting purposes.
All that remains now is to drill and tap the remainder of the upper sandwich piece for essential ports. The most important is, of course, the vent. I learned the hard way that it is almost impossible to have too many ports on a cell. Everything from sampling, temperature, to pH control, requires a port, and it is always easier to add them at the beginning, rather than to add them at a later date. I decided to drill and tap the upper piece for no less than four threaded ports. Any of them that are not actively used are easily capped.
When drilling and tapping for such ports, obviously their location needs to be recorded so that corresponding holes can be drilled in the lower sandwich piece. In the end, the lower piece does nothing more than provide a clamping device to apply pressure to the viton o-ring stock, creating a quality seal, so I may simply remove the bulk of the central area rather than drill specific holes that correspond to upper port locations.
To use the BCA, I plan on creating a "cut template" which will be placed on a bucket lid, and the necessary holes and cuts can be made so that the BCA can be mounted on the HDPE bucket lid. I hope to put this to work very soon in a test with the Lead Dioxide anode I made last winter, using a 2.5 gallon bucket cell with saturated potassium chlorate.
I realize that this particular adapter requires some specialized tools, but something similar could easily be made with nothing more than a drill press, and the ability to make use of cheap and available HDPE buckets is a big plus! Maybe this will give guys some ideas on something similar.
KISS is a philosophy that is particularly suitable to the (per)chlorate process. 
Now that the cool autumn is here, I plan on a few runs using both the data-collection system, and the lead dioxide anode. My fingers are crossed! Also, I am hard at work on what I call my "Opus"... an illustrated user's guide to making chlorate and perchlorate at home. I am using information from my blog and other sources to create a document that will hopefully set the standard for home electrolysis of (per)chlorate. It is at 60 pages now, and will probably be 100+ pages before I am done. Check back later for this document. I hope to be done by the end of November, and I also hope it will be something that hobbyists will find useful.
The Green Man:
In European mythology, he rules the forests. In Pyrotechnology, he keeps us safe. Stay green, friends.
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