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Author: Subject: More on PbO2 electrodes
nitro-genes
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[*] posted on 10-8-2020 at 15:50


Probably, gasses formed from electrolyte reaching the LD/graphite interface produce enough pressures to crack it eventually. Funnily, never seen any of the composite LD coated anodes crack like that...apart from the higher electrical resistance it is also likely the composite substrate anodes (or LD itself) were probably porous enough to let most of the gas pressure escape without catastropic failure like that. Might be interesting for forming solid LD anodes.

A thicker coat of better quality LD and pH control will probably also help...Since the part of the GSLD anode that is not submersed in the electrolyte is hardly eroded at all at the LD/graphite interface, I wonder if you could design an almost solid lead dioxide lower (submersed) part, which is attached to a almost complete graphite "base", which itself is not submersed, and mostly used as electrical connection. Something like that should be possible using 2 separate LD coating runs. Maybe using this scheme, even a relatively porous LD coating would prove quite durable, even with no pH control. Due to the very low surface area of the lower graphite part, a catastrophic failure would probably be unlikely.

GSLD design - Copy.jpg - 28kB

Having read about some GSLD anodes having been gone through 2 years of continuous operation before failing...wonder if the LD coating and pH control were really good enough to protect the underlying graphite substrate for that long. A crazy thought would be that they were running an empty shell of very porous LD, still holding on to the unsubmerged upper part of the intact graphite substrate. :D

[Edited on 11-8-2020 by nitro-genes]
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markx
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[*] posted on 11-8-2020 at 00:14


Yeah, I would kind of take such claims (2 years of continuous operation) with a slight grain of salt :) All the experience collected so far suggests that such durability is rare at best, if not totally impossible on most instances.



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yobbo II
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[*] posted on 17-10-2020 at 14:15



Thickness of coating was probably around 5mm of a proper coat.
They used them in the Henderson plant in Navada in the sixties.
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mysteriusbhoice
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[*] posted on 6-11-2020 at 04:53


I have also included a pic of my lead ion perchlorate cell here with the lead ion feeder to buildup more PbO2 by continuous leeching of Pb(ClO3)2 via a second lead anode of smaller surface area than the immersed graphite.

lead ion perch cell.jpg - 67kB
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mysteriusbhoice
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[*] posted on 12-11-2020 at 13:20


so I first plated PbO2 onto EDM graphite and got a uniform coating that had lots of pits due to this membrane sucking hard!!.
I notice this PbO2 was unlike my one made with lead acetate which had really bad conductivity as the thickness grew up to like 3mm when it literally had electrical conductivity of 100 ohm or some crap.
This lead chlorate made PbO2 is highly conductive giving 0.3 ohm resistance when probed with multimeter.

This was plated at room temp with Pb(ClO3)2 and Pb(ClO4)2 solution made with membrane although this membrane isnt like my others which was properly constructed for ion exchange electrolysis for making exotic chlorates/perchlorates, this one is for a chloro alkali cell its more permeable to the solution and PVA would fuck off due to the strong acids involved.

anyway I added superglue to support the initial layer and it seemed to have helped stabalize the coating and after sometime the PbO2 grew around the superglue and made a nice thick coating that doesnt peel off.

the dragon electrode.jpg - 18kB

[Edited on 12-11-2020 by mysteriusbhoice]
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mysteriusbhoice
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[*] posted on 17-11-2020 at 12:05


made another one of these this time plated with ultrasound and very low current density of 6ma/cm^2
flaky was from previous plating attempt which sucked cuz I used too high current density.
It was extremely hard to remove the old plating that was all bumpy because even while running it in NaCl at 300ma/cm^2 it just wouldnt come off.
I had to run it as a cathode which finally took out most of it away and then plated only using ultrasonic bath with low current for this currently nice even coating.

IMG_20201118_000157.jpg - 74kB

[Edited on 17-11-2020 by mysteriusbhoice]
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