Sciencemadness Discussion Board - Dezincification of gallium alloy

Dezincification of gallium alloy

yagoply - 24-1-2019 at 18:01

A few months ago, a collector friend gave me a small amount of this gallium-zinc alloy of unknown percentages from a big ingot of it. It melts before water starts to boil, so I suspect it having a significant amount of gallium in it. It becomes a grainy paste while solidifying, instead of creating nice crystals like a pure metal.

Those are some details about it, but what I'm looking to do is separate the gallium from the zinc and end up preferably with a purer sample of gallium.

My first guess is having the zinc protect the gallium from corrosion from a oxidizer such as bleach, but i'm not sure if that is even an option in alloys (i can always change the crystal size by re-melting if that is a variable) or if the zinc is more reactive than gallium or vice-versa.

Below is a blob of the alloy after being cooled in a warm water bath.

fusso - 24-1-2019 at 18:52

Not sure if Ga(OH)3 is soluble in NH3(aq). If it isn't then NH3 is probably the best way to separate the hydroxides.
Not sure if ZnCl2 is soluble in ether. If it isn't then this vid could help you: https://www.youtube.com/watch?v=NwLgL1dGuSM

[Edited on 190125 by fusso]

Tdep - 24-1-2019 at 18:59

Ga(OH)₃ is amphoteric so yes, it does dissolve in ammonia, as I have seen

j_sum1 - 24-1-2019 at 18:59

Pure speculation follows...

My first guess would be warm dilut acetic acid with lots of stirring. Check out solubility of GaAc3 to see if it is feasible and then do a small test run.

yagoply - 24-1-2019 at 19:06

Quote: Originally posted by j_sum1

Pure speculation follows...

My first guess would be warm dilut acetic acid with lots of stirring. Check out solubility of GaAc3 to see if it is feasible and then do a small test run.

Gallium acetate is moderately soluble. My question is, would the zinc protect it from the acetic acid? That's what I'm looking for. Zinc acetate doesn't need heating to form, but that would speed up the reaction which is nice.

fusso - 24-1-2019 at 19:17

Quote: Originally posted by yagoply

Quote: Originally posted by j_sum1

Pure speculation follows...

My first guess would be warm dilut acetic acid with lots of stirring. Check out solubility of GaAc3 to see if it is feasible and then do a small test run.

Both will react with acid to form the corresponding salts.

j_sum1 - 24-1-2019 at 20:30

I would think that Zn would react preferentially. The warm temperature is to melt the metal. The stirring is to continually expose fresh zinc. There will be some loss but then you could recover Ga by electrolysis.

fusso - 24-1-2019 at 20:39

But won't Zn also electrolyse out with the Ga, just like Na/Hg from chloralkali process?

j_sum1 - 24-1-2019 at 21:36

Quote: Originally posted by fusso

But won't Zn also electrolyse out with the Ga, just like Na/Hg from chloralkali process?

Well that bit is easy. Look up the reduction potentials for both. Ga will be produced at a lower potential than Zn. This is called electrorefining.

My point is that it is quite plausible that you could achieve separation with the right selection of acid. It would be easy to test.

BromicAcid - 24-1-2019 at 21:48

Distillation? There is a 1500°C difference in boiling points. With that much of a buffer it might be as simple as metal tube + fire.

fusso - 24-1-2019 at 22:19

Quote: Originally posted by BromicAcid

Distillation? There is a 1500°C difference in boiling points. With that much of a buffer it might be as simple as metal tube + fire.

But then you'll introduce more contaminants into the Ga...

yagoply - 25-1-2019 at 18:02

I attemped to remove the zinc through reaction with hot water with constant stirring. In the end I had the solid blob of gallium alloy at the bottom with a lot of black insoluble particulate that sank after a while. I retried the experiment diluting bleach into it, and was left with powdered gray metal that looked a lot like old powdered zinc and no particulate. The powdered metal was remelted back into the original thing with no change in properties. I'll try again with an acid to see if the result is different. This is getting fun

Edit: any ideas on what the black stuff was?

[Edited on 26-1-2019 by yagoply]

fusso - 25-1-2019 at 18:14

I don't think Zn/Ga will react with hot water, unlike Al/Ga...

yagoply - 25-1-2019 at 18:24

Quote: Originally posted by fusso

I don't think Zn/Ga will react with hot water, unlike Al/Ga...

They clearly reacted in both tries. And yes, zinc is supposed to react with hot water, but result in a clear solution, not black stuff. Maybe if the particles were REALLY coarse they could be black. Still, I won't know if this experiment will meet an end until I have some acid.

I don't know what the black stuff is, so I'll just label it as a contaminant reacting in the metal until someone finds out.

fusso - 25-1-2019 at 19:02

Found some ZnGa phase diagrams. Maybe you can determine the % from the MP?
https://www.google.com/search?q=ga+zn+phase+diagram&tbm=...

yagoply - 26-1-2019 at 04:07

Quote: Originally posted by fusso

Found some ZnGa phase diagrams. Maybe you can determine the % from the MP?
https://www.google.com/search?q=ga+zn+phase+diagram&tbm=...

That's interesting. I'll definitely make a comparison when I touch that thing again.

walruslover69 - 26-1-2019 at 15:44

place in water, add enough HCL to dissolve 1-5% of your Ga/Zn and stir until all the HCL has reacted. All of the zinc will react preferentially. take it out observe the properties and see if you need to react it with more HCL. You are looking at a 1-2% loss of gallium maximum.