Sciencemadness Discussion Board

Plutonium reactions - how'd they figure this stuff out?

j_sum1 - 29-9-2023 at 15:17

Side topic from Finding small amounts of Pu or U235
That thread is likely destined for Detritus but it did raise some questions for me.

I posted this video which shows how Pu(NO3)4 is reduced to metallic plutonium. (The video presents a flow diagram of the process in the first 3 minutes then repeats the same information showing the actual equipment.)
Plutonium Metal Preparation

Two reactions interest me. One is the formation of a peroxide complex to precipitate plutonium nitrate.
The second is the use of elemental calcium and elemental iodine together to reduce PuF4 to Pu.

How did anyone figure out these were feasible routes?
Why would you expect the peroxide complex to be insoluble (and selective)? Why would you choose Ca and I2 for the reduction? I can't imagine anyone had a significant amount of raw material to develop these processes. It must have been more than a hunch to derive the methodology.
And that second reaction seems a strange choice. I am guessing the reaction is
PuF4 + Ca + I2 --> Pu + CaF2 + 2IF
But other stoichiometries are possible.


(Placed in general chem because I am interested in the reactions and the mode of discovery.)
And, on second thoughts, moving to Radiochemistry.

[Edited on 29-9-2023 by j_sum1]

pantone159 - 29-9-2023 at 18:49

Part of the answer, was working with extremely small amounts of Pu in the early days, to study Pu chemistry and figure out purification that would work. It was a triumph of nano-scale chemistry, especially with 1940's technology.

The Ca+I2 sounded strange to me also, but late in that video there was a comment that this heated up the Ca to where it worked for the reduction. I wasn't sure what to make of that comment.

UC235 - 29-9-2023 at 20:06

Uranium and thorium form insoluble peroxides, so it seems like a good place to start.

[Edited on 30-9-2023 by UC235]

wg48temp9 - 29-9-2023 at 20:12

It seemed unlikely that any interhalogen compound would form, as it would combine with the plutonium metal.

Apparently, the plutonium is reduced by the calcium to form calcium fluoride. Additional calcium combines with the iodine to heat up the reaction, and the formed calcium iodide reduces the melting point (fluxes) of the calcium fluoride to allow the plutonium to form a button at the bottom of the crucible.

See Attachment: 4438226.pdf (894kB)
This file has been downloaded 84 times

Pumukli - 29-9-2023 at 21:02

j-sum, Ca as reducing agent seems fairly logical for me. Reductions by metals were widespread in those early days. The "tendency" of Ca2+ to combine with F- and yield practically insoluble CaF2 makes this choice attractive.
Maybe, they tried these reactions on other "model compounds" previously and found them "worthwhile".

j_sum1 - 29-9-2023 at 21:41

So, I2 is there as an energy boost and to create a flux
Makes sense.

Still, there is a lot of creative thinking to devise such a process.

I really am in awe.
Even determining MP would have been a challenge. If I was to guess, I would have gone a lot higher.

unionised - 30-9-2023 at 02:53

Fluorine gets its name from fluorspar which is essentially naturally occurring calcium fluoride.
Fluorspar gets its name from its use in metallurgy as a flux- very loosely it means "flow stone".

So roughly 1500 years before anyone knew about plutonium, they knew that calcium fluoride was a useful flux.
Hardly shocking that they chose to use it.

[Edited on 30-9-23 by unionised]