[Jotaro]

Dear all,

I am new to this forum and really glad this forum exists!
I am working with radiochemistry, with no chemistry background. Not the best introduction, but I have to be honest. Still, I manage to do my job.

I have a question regarding the Polonium instant deposition (plating) on Cu discs (also applicable on Ni and Ag discs).
The procedure I work with (after liquid-liquid extraction with TBP and Xylene) I dry the 8M HNO3 fraction that contains the Po. Change the media to about 2M HCL, my question is why is HCL used? I understand that HNO3 would eat away Cu and other metal discs, but does the HCL help to plate the Po on the Cu disc?

Thank you for your time

[Borek]

Hard to tell not knowing more details, but in general HCl is much more volatile so it is often used when we need strong acid that will be easy to remove by drying.

[Corribus]

Based on the information you provide, it's probably mostly due to the activity of nitric acid. Nitric acid reacts strongly with copper, but hydrochloric acid does not.

[Jotaro]

Thank you both for replying!

Hard to tell not knowing more details, but in general HCl is much more volatile so it is often used when we need strong acid that will be easy to remove by drying.

I can give you as many details as you need.

Actually, the solution is maintained in 2M HCL throughout the plating process, leading to my understanding that HCL (or acids in generals) "helps" plating the Po, but we can not use any acid, due to it dissolving the disc itself.
But I am not sure why or how this is. Maybe someone knows this detail? I could be completely wrong too. Could be to prevent something else to plate, like lead.

[Borek]

Apart from what Corribus has mentioned, Cl^- often shows complexing properties, which help maintain right concentration of the cations involved and help plate them at right potentials.

In my experience some of the recipes used for plating are partially magic - that is, it is "easy" to "explain" why the work once you experimentally find the right conditions, but these "explanations" have no predictive power that would make it easier to deal with other cases. No idea if that's the case.

[wildfyr]

In my experience some of the recipes used for plating are partially magic - that is, it is "easy" to "explain" why the work once you experimentally find the right conditions, but these "explanations" have no predictive power that would make it easier to deal with other cases.

Its a bummer how often this applies.

[Corribus]

Its a bummer how often this applies.

To chemistry in general.

[Enthalpy]

Its a bummer how often this applies.

To chemistry in general.

To many sciences and technologies. But outside chemistry, people often forget that their science is experimental.

[Jotaro]

Thank you all for your answers.

I know that my lack of chemistry knowledge is a challenge in my efforts to improve certain methods.
However, I try to compensate with common logic. E.g. when plating and for measurements of alpha particles, you don't want to plate other high Z elements due to attenuation of the alphas. So the solution should not have many high Z elements, not high molarity of anything really, and not too low so no reaction takes place. Ideally something that only plates the element of interests and does not readily plate other competing elements.

Would be great to find some literature explaining things in the manner as above, coming to the conclusion that a handful of elements/acids should be used for a particular element/purpose.

Key words, narrowing down the near infinite combinations through knowledge in reaction chemistry.

It is known that Ag discs give better yield for Po plating than Cu and Ni discs. Also, plating under 158 degree Fahrenheit is better than room temperature.
From these two observations, one should be able to extract favorable conditions that can be used to further improve the method.

1) What is the difference between Ag and Cu and Ni?
2) What would a higher temperature achieve? Keeping the solution in movement? Stirring the solution in room temperature is still not as good as 158 degree Fahrenheit. So that's not it. etc etc.

[Jotaro]

Hi again,

Was doing some late night research on this topic, found this article:
https://www.sciencedirect.com/science/article/pii/S1687850715000874#bib22

"  In HCl solutions, Po is assumed to be PoCl6⁻²"
"Spontaneous deposition of Polonium is more efficient (>99%) in 0.5N HCl medium at 97 °C"
"The interference in the spontaneous deposition of polonium is due to presence of Fe3+, Au, Hg, Pt, or Te. These impurities inhibit the deposition process and must be removed either by reduction"

The reference to these experiments dates back to early-mid 1900. Someone should really reproduce these experiments and document & publish them so that they can become available to researchers around the world.

[AWK]

Check this document from 1961
https://www.osti.gov/servlets/purl/4034029

[Borek]

Someone should really reproduce these experiments and document & publish them

Go on.