I posted previously about a lot of work that went to waste... a new acrylic lid for a proposed "super-cell." With the homemade lid cracked to hell, I was forced to modify the original lid to this device. The slots went well, and the three threaded ports were either plugged, or put to use. Liberally glued with silicone sealant, the lid is just about ready:

One of the lessons learned from the previous cell is to not underestimate the volume of gasses that the cell will generate. The old cell used a 1/4" tube to carry the gasses away, and this tube ended up carrying spattered liquid as well. I could see it creeping along the tube. I already had a stock of 1/4" OD Teflon tube that I was determined to use, being so expensive, so I conceived of a "riser" tube of much greater diameter that would limit the ammount of spatter that is injected into the smaller tube:

Into this goes an all-plastic (look for PE rather than nylon) compression fitting for the small tube. This routes the gasses outside my workshop.

The previous cell used #8 copper line, and the cables warmed at 20 amps. Warm copper cables equates to voltage drop and inefficiency, so I replaced them with #4 welding cable, crimped to a copper connector. Don't even think about alligator clips above 15 amps or so. The contact they make is poor.

The acrylic tower was filled with 1/2 old electrolyte, and 1/2 saturated KCl solution. The spare holes in the lid were plugged, and the system energized.

I warmed it up at 20 amps, then dialed in 30 amps for about 2 hours. Right away I noticed a problem. This cell is very tall and skinny, not an optimum shape at all. The upper area near the electrodes was opaque with evolved gasses, while the lower section, probably 85% of the height, remained clear. I was hoping that it would thermally stabilize with an even heat, but no such luck. In fact, it wasn't even close. The area of the cell near the electrodes has hot, probably 60 C, while the lower was near ambient. Not good. Circulation was nonexistent. I pondered this for a while... how to circulate the liquor? Industrial setups probably use expensive teflon-bodied pumps. These are a mere $2,000+ for the cheapest version. Then I had an idea... I have plenty of teflon tube. Why not drop a teflon tube line to the bottom of the cell, and gently bubble clean air through the cell? This should circulate the electrolyte just fine.

Years ago, I threw away probably 3 air pumps from my reef aquarium. Lesson - throw nothing away. If it feels wrong tossing it in the trash, it is wrong! Now I had to drive to the pet store and buy an air pump. While I was at it, I bought a filter...

And a dual air valve to modulate the amount of air pumped into the cell...'

The PTFE tube was routed through a special, all-plastic bulkhead fitting, terminating at the bottom of the cell. The air pump was turned on, and as expected, the bubbling was too vigorous. By opening the valve on the left (to the cell) fully, and slightly opening the one on the right, which acts as a bleed valve, I was able to reduce the air entering the cell. The electrolyte was now opaque throughout; chlorine gas, which needs to dissolve to maintain the pH at the correct level, was being retained in the tall column. It was working perfectly!

At 40 amps, it was humming along. New problem: while the heat was even, it was still too high. I placed the cell in a big plastic tub, and added 60 liters of clean water to surround it. This water acts as a big heat sink, and finally, at 40 amps, the heat was not excessive.

Not quite... fiddling with the electrodes, I heard and felt my skin sizzle on something very hot. The cathode, which is pure Ti, and not the greatest conductor of electricity, was screaming hot, so hot that the copper connector was discolored! A bit of water sprayed on it flashed to a boil. it was probably pushing 150C. All I could do there was to clamp a heat sink with a small pair of vise grips to the shank of the cathode. Oddly enough, the anode was barely warm at 40 amps. The only difference between the anode and cathode is that the anode is electroplated with a mixed metal oxide coating; the coating alone improved the conductivity of the anode dramatically, enough so that it did not heat up like the cathode. Valuable lesson: At these current levels, you must keep the electrode spacing as tight as possible. The heat comes from the wattage of the system, current (squared) times resistance. High current is desireable, so get the resistance DOWN with tight electrode spacing. When this batch is complete, I will add a second cathode in parallel with the first, which will drop the current through a given cathode in half, and keep them a lot cooler.

I think that the circulation brought about by the air pump will dramatically improve the efficiency of this cell. At 40 to 50 amps, if I can keep the cathode cool enough, I should be able to produce at least a pound, perhaps two, per day of cell operation.

I hope you guys are enjoying these blog entries. I know I have fun writing them and sharing some lessons learned in this process. How about some of you pros start blogging? I'd love to see some 4" and up spherical shells being made, some big rockets, stuff like that. We've got a nice opportunity here with this new software, and I don't want to be the only one doing this. The water's fine, maybe a little contaminated with chlorate. Come on in!

The Next Morning... After less than 24 hours of operation at 40 amps, I have a layer of KClO₃ about 3" deep! Almost no salt creep, it is sealing well. The bubbler had ceased overnight, as the tip was buried in crystals. I raised it up above the xtal level, and tweaked the valves. Back in business, and looking awesome!