bereal511 - 15-6-2008 at 10:14
Hey, I was curious as to whether or not calcium aluminate will dissolve in liquid calcium chloride. I'd like to build an electric furnace to melt
calcium chloride and electrolyze it to calciu metal, but I'm not sure what suitable refractory material would work. If you guys have any inputs as to
what to use, that would be great.
12AX7 - 15-6-2008 at 12:02
Sure, why not.
I've heard magnesium chloride is unusually corrosive, requiring stuff like inconel to hold it. Calcium chloride is more ionic, but it's probably
still troublesome. Fortunately there's nothing wrong with a steel crucible, which you can use as cathode.
Tim
garage chemist - 15-6-2008 at 14:22
In the production of calcium by electrolysis, an eutectic of CaCl2 with another salt (I think it was BaCl2, not sure- don't have the book at hand) is
used as the electrolyte to lower the required temperature to a point where the calcium is produced in solid form at the cathode. This would be ideal
for a steel crucible as the cathode, giving the calcium as an adherent layer instead of it rising to the top and burning in the air.
Anode must be graphite, of course.
Originally, the cathode was a thin steel rod on which the solid calcium collected while the rod was gradually lifted upwards, slowly producing a thick
rod of crude calcium metal.
The problem here is probably the high required temperature.
Have you thought about electrically heating the crucible from the outside? Putting a layer of refractory concrete around it, coiling nichrome or
Kanthal wire around that, coating this again with concrete and wrapping it in kaowool or, cheaper, rockwool?
Remember, len1's highly successful castner cell used electrical heating of the NaOH container as well!
[Edited on 16-6-2008 by garage chemist]
bereal511 - 17-6-2008 at 08:23
Ah, steel would not be a problem in this situation? Is there a type of steel most suitable for this operation?
I assume that the anode would have to be placed in such a way to avoid the evolving chlorine from attacking the metal. But let's just say that
oxygen is also evolving from the anode. Would there be alternatives to graphite as an anode, or would I have to just settle with replacing it every
so often as it burns up from oxygen?
I know that sodium chloride will form a eutectic to 550 degrees Celsius, but I'm not sure if sodium metal would be preferentially produced even if the
voltage were much higher than the standard potential of calcium.
Hmmm, I'd forgotten about len1's castner cell, thank you for reminding me, I'll look into that thread. I'll probably refer back to the older threads
on electric furnaces and electrochemical alkali production, but thank you for your help 12AX7 and garagechemist.
A note: My goal will not be to collect the calcium metal. I want the metal to dissolve in calcium chloride and run a preliminary test on the so
called FFC Cambridge Process because I'm interested in applying the electrochemical process to armour production. My idea isn't particularly novel,
but it'd be nice to be able to do some small scale work on refractory metals and ceramics that would otherwise require much larger setups. I'd like
to be able to submit my results to the DARPA Armor Challenge. Anyone familiar with DARPA should know about the DARPA Grand Challenge (driverless
cars).
[Edited on 17-6-2008 by bereal511]
not_important - 18-6-2008 at 17:14
If you're looking at FFC - the oxygen content of calcium aluminates seems to contribute to oxygen contaminate in the metals produced, as well as being
attacked to some degree by the bath.
Small scale experimentation seems to use alumina containers, although they too can contribute oxygen. Stainless steel is the other material. Also
I've read of a suggestion to line the vessel with TiO2 , with a buried conductive grid if needed, and reduce that at the start of production, making
the container interior be metallic titanium.
bereal511 - 19-6-2008 at 10:25
Interesting. I haven't come across any articles suggesting lining the vessel with the material to be reduced to protect it. Would you happen to have
the paper or a link?