Day 2 of LD anode test
Entry posted by Swede
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If you haven't been keeping up, (and if you care... 
) I have been blogging fast and furious while the LD anode is undergoing its first real test. If you'd like, it might be worth going back about a week to catch up. This entry will be more pictures, less text.
Basically, a few of the warts on one edge had broken off and fallen to the bottom of the cell. While not catastrophic, this had me concerned, as it hinted that the integrity of the anode was not what I had hoped for. A greater concern was the voltage. To obtain a decent amperage of only 15 amps, the system was requiring almost 10V, which is simply too high. Usually 6 to 7 is about the maximum that you would normally see. Part of the problem was that I had selected a very small cathode; supposedly, the current density on the cathode should be high for best efficiency. Well, efficiency can kiss my a** when it takes 10V to run the cell. Excess voltage is never good for either a chlorate or a perchlorate cell... it tends to stress the anode and create more heat than it would otherwise.
Additionally, the anode was gathering significant amounts of crystalline perchlorate on the surface. Interestingly, the side of the anode AWAY from the cathode was the one gathering crystals... the side facing the cathode was clean. I decided to replace the dinky cathode with one a bit larger, and also have a cathode area on both sides of the anode. While the system was down, I could also take a look at the anode and try to find out what was going on with it, mechanically.
The first step was to create a titanium box that would act as a pair of cathodes:
After this was made, the test cell was taken apart, temporarily. This is the anode inside the cell, away from the cathode. Note the loss of several of the edge "warts" on the left side, and the accumulation of perchlorate crystals:
The anode was removed, washed in warm water, and then I gently manipulated the remaining warts to see if they were adhering well. The warts on the bottom were quite strong. Those on the sides popped free easily. I decided to go ahead and remove all of the side warts, and it didn't take long.
These nuggets of lead dioxide were interesting. They are very dense, and similar to pure lead in their mass.
They reminded me of fossil teeth. Arranged in their original pattern, they look a bit like molars!
The good news - wherever the LD had adhered to MMO, which included the faces of the anode, and the bottom edge, the adhesion was very strong. I tried about 3X the manipulation on the bottom warts, which had an MMO edge (as opposed to a sawcut edge) and they didn't budge, so I left them there. The system was reassembled with the box cathode:
With the power applied, I was very happy to see the voltage drop by about 1.5V for a given amperage. I set the unit up to deliver 15 amps, and for now it is humming along. The perchlorate is accumulating fairly quickly... for a given amount of current, the conversion of chlorate to perchlorate is more than twice as fast as chloride to chlorate.
The anode in its current state wasn't what I started with, but at least I verified one thing - the lead dioxide plated over the MMO areas yielded a strong adhesion which is very promising. If I had popped those warts free after the anode had been initially plated, it'd look as it does now. A bit neutered, but what remains appears strong and functional.
So the news is, I'd say, about 75% good, and 25% bad. Properly prepared, it appears that LD does in fact plate over MMO very effectively. The real test will come in a day or four. If there is no additional erosion at the edges, where the warts were popped free, then I'd say I have a smaller, but strong and functional LD anode that should give good service.
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