A few things about Gallium

[TARDISgirl]

Ok, I've never done this before (use a forum website). I'm in school and we have to conduct our own demonstrations for 4th graders. I am using liquid gallium an I want to pass an electric current through it using immersed electrodes. However I don't know what electrodes to use as I know gallium isn't exactly "friendly" with most other metals. I don't know what materials it might be friendly with.

So what electrodes should I be using.

I'm in middle school and very new to this.

[rktpro]

You want to show that gallium conducts? I wonder where you picked the idea. There are better projects to do at your level. You need inert electrodes like platinum, though.

That info is not all to actually carry out the work.

[John Cuthber]

It's true that gallium attacks some other metals.
however, in most cases the attack is slow.

In the sort of timescale that schoolwork takes place over I think the only metal that would be really susceptible would be aluminium.

I think copper or stainless steel would be fine. It's not as if you will be using the electrodes in some load-bearing safety critical application afterwards so who cares if they fall apart?

 

Also, I'm pleased to see that you thought about it and checked before getting underway.

With a bit of effort, you might be able to show that solid gallium is a rather better conductor than the liquid.

 

If Rktpro thinks you need platinum electrodes then he needs to do a bit more research. For a start, gallium attacks platinum.

[Enthalpy]

What about graphite? Could that work?

Though, if copper works, it's of course the best choice.

[John Cuthber]

Graphite would be OK, but its resistivity is a bit high.

Edited March 10, 2014 by John Cuthber

[rktpro]

John, how do I predict that gallium reacts with platinum? From the electrode potentials?

Edited March 11, 2014 by rktpro

[John Cuthber]

I doubt you could sensibly aspire to predict it.

 

On the other hand, you could do what I did and google the phrase "gallium attacks platinum".

But that's hardly the point.

Why did you post something as a fact when you hadn't checked it was right and, as you say, you had no way to know if it was correct?

[rktpro]

I googled 'gallium reacts with platinum' and got no info about the reaction. That is why I asked you whether you predicted the reaction yourself. I admit that in my knowledge Platinum is nobel and I don't know of any reaction between it and metal like aluminium. Please post the reaction in your next post.

[John Cuthber]

What reaction?

[Enthalpy]

Platinum is nobel and I don't know of any reaction between it and metal like aluminium.

 

It's just a liquid solution. Not a reaction in terms of oxidation or reduction or anything similar. That's why potentials aren't expected to help pick a metal. Each metal keeps its electron count, and the solid one diffuses in the liquid.

 

Generally, liquid metals are good solvents for other metals. For instance mercury, sodium-potassium eutectic and the like use to dissolve many metals. So if handling any liquid metal, including gallium (which is forbidden in airliners for that very reason), one should have a warning lamp go on in his mind, and remember that few metals don't dissolve.

 

In semiconductor processes, we used tungsten and sometimes platinum as a barrier between silicon and gold (yes, some time ago!) because warm solid gold woud dissolve other materials, even silicon. Such choice would be a weak hint that refractory metals resist dissolution better - but nothing more than a weak hint. And our gold wasn't even liquid.

Why did you post something as a fact when you hadn't checked it was right and, as you say, you had no way to know if it was correct?

 

Could that possibly be a cultural difference ? As a plain boring old European, it surprises me every time too.

Edited March 12, 2014 by Enthalpy

[John Cuthber]

 

 

Could that possibly be a cultural difference ? As a plain boring old European, it surprises me every time too.

If he answers I guess we will both get to find out.

[rktpro]

 

Over-confidance, Sir. Certainly. I have a habbit of establishing the logic behind inorganic reactions. Reaction mechanisms are not quite common in books and sources and when I see a reaction I try to establish its identity. I do it with redox, quite easy, with reaction between oxides etc. Ignorance of the fact that Enthalpy points out, I might have failed considering that.

But, both copper and platinum have ccp lattice. If Enthalpy is right, then gallium diffuses equally well in both.Isn't it?

Edited March 13, 2014 by rktpro

[John Cuthber]

I suspect (but can't cite evidence for it) that the work function or the melting point might be a better indicator of how well the metals resist gallium.

 

I'm also rather inclined to doubt that the Xtal structure makes that much difference (except indirectly) because i think the attack takes place at Xtal boundaries.

[TARDISgirl]

John, thanks for the information on the type of electrode.

 

Thank you everyone for your input.

Also, I didn't think to mention that the electrodes were simply to allow an electric flow so that I would be able to show the effects of a magnetic field on conducting fluids. My hypothesis is that the gallium should cool down after being exposed to the magnetic field. It wasn't to show the 4th graders that gallium conducts. I usually think outside the box before I know what is inside it, and it didn't occur to me. Too late now.

Thanks.

Maybe if this works out well I will post some of my final project on here.

[rktpro]

I suspect (but can't cite evidence for it) that the work function or the melting point might be a better indicator of how well the metals resist gallium.

 

I'm also rather inclined to doubt that the Xtal structure makes that much difference (except indirectly) because i think the attack takes place at Xtal boundaries.

You mean it is adsorption and not absorption or say sorption? If it is physisorption, which is pointed out, then it shouldn't be much of a trouble.

[Enthalpy]

Dissolution of a solid metal into a liquid one must be very little more than individual atoms at the surface that happen to concentrate at one time enough thermal energy to leave the solid.

 

Anyway, these surface atoms already share delocalized electrons with both the solid and the liquid, hence have strong links to both.

 

The vapour pressure of the hot solid, which indicates how strong surface atoms bind with the solid, could suggest which metals dissolve less. That would mean: Mo < Nb < Ta < W. Though, how well the dissolved atom binds (radius? valence?) with the liquid may play a role.