Pentaborane
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References on Downs' Cell Design/Construction
I have come across some very interesting blueprints for the original Downs' cells while digging through some archives in my (professional) research,
including blueprints of the original single anode cells built at Niagara Falls, NY by Downs and decided to have them digitized. They are big
industrial cells, but I've seen a couple of people here attempting to build small versions in the past so I wanted to make them available to the
community if anybody wants them. The files are too big to upload, so if anybody wants to take a look (for non-commercial/amateur/historical purposes),
please let me know and I will find a way to get them sent as a dropbox link or something of that nature. These are old and not proprietary (the new
versions with four anodes are, but they are probably impractical as references for the amateur anyway).
As a word of caution, I will say that the process is incredibly hazardous in just about every way, please use extreme caution if you ever attempt to
build one of these, even on small scale. To give an idea of what they look like during operation and what the the associated hazards are like (modern
four anode versions), see here
There is nearly no way to avoid some amount of burning sodium/calcium and associated air quality and fire hazard issues, even on small scale. Also
keep in mind that you're dealing with very hot chlorine and material compatibility is a major issue (a chlorine-metal fire is not something you want
to deal with). The plants that did this were basically always in some sort of trouble for safety issues. Barium chloride (used in the cell bath) is
also quite toxic. Because of the requirements to access the cell components regularly, they are not under inert gas, so sodium that misses the
collector will be continually burning (called "fireflies" in the industry).
The salt must be quite dry when fed into the cell, as any moisture adds oxygen and promotes corrosion of the graphite anodes. Same with sodium oxides.
Another issue to be aware of is the deposition of calcium dendrites on the steel mesh diaphragm. These eventually short circuit the cell and burn
holes in the diaphragm. In industrial operation, you usually get about three months before the diaphragms need to be replaced completely. You can
shake them to try to break them off, but only if something is ensuring proper alignment and preventing the diaphragm from hitting both the anode and
cathode, which would short circuit violently (as compared to the calcium dendrites, which are reasonably small). They do not like being shut down, as
it damages the refractory and the salt freezes (maybe there is a clever way to get around this for amateur use?). I suspect for small ones, you will
need external heating as well. Electrolyte circulation is important. In industrial cells, convection combined with the gas lift effect (from Cl2
bubbles) promote good circulation. Modern cells have hollow anodes and slits cut in them to aid in circulation.
If anybody has other additional information/operating experience with Downs' cells, maybe this thread could become a nice repository? Producing sodium
is a common theme on this forum.
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markgollum
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I have been tempted to make one at several different times in the past as my metalworking skills improved. I always wondered about the materials
compatibility and the temperature limits. For example, the mesh diaphragm and “chimney” guiding the chlorine out is steel, how hot before the
chlorine directly reacts with the steel? And what is a good mesh size? And what about the formation of a finely divided sodium “fog” in the melt
as can occur in an overheated castner cell.
I once -nearly two decades ago- made something like one but without a divider, where I was shielding the sodium and consuming the chlorine by
maintaining a capping gas of propane over the melt (huge propane consumption and constant flames). The propane prevented the sodium from burning and
also was instantly reacting with the chlorine and being swept away. I was able to isolate a very small amount of sodium (and also calcium when I
switched to calcium chloride, but it was more difficult to get a granule of calcium) messing about with that contraption.
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EF2000
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Quote: Originally posted by Pentaborane  | The files are too big to upload, so if anybody wants to take a look (for non-commercial/amateur/historical purposes), please let me know and I will
find a way to get them sent as a dropbox link or something of that nature. These are old and not proprietary (the new versions with four anodes are,
but they are probably impractical as references for the amateur anyway).
If anybody has other additional information/operating experience with Downs' cells, maybe this thread could become a nice repository? Producing sodium
is a common theme on this forum. |
If these files are not proprietary, then you can try uploading it on the Internet Archive (archive.org), they are happy to host anything with right
copyright status.
Wroom wroom
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