How different electrically are liquid conductors, like molten metals, vs solid ?

[MathWizard]

I was thinking of if all the solder in a circuit was molten, ignoring it's heat or gravity, how different would the circuit behave. I should read something on wikipedia, but I'm just wondering if any cool stuff could be done with liquid metals, in a circuit, besides mercury switches or something like that.

And then I wonder farther about if other stuff was molten or liquid, I guess that get get's into chemical reactions tho too, a lot more areas.

I'm sure the high temperature of most molten metals makes this unpractical, but I'm just wondering if any have cool or useful effects that we miss out on for now, due to the high temperature that would be needed.

[LinuxHata]

Well, since it is in liquid form, ions would move more freely, so as current passes, electrolysis will go on, leading to undesirable results...

[Jwillis]

Some metals as your know are liquid at around room temperature. Mercury being the most well know. Gallium and Cesium are two lesser known metals that are liquid at room temperature. Others include Francium and Rubidium.

[MarkT]

Unconfined liquid metal as a conductor would be a problem - the self magnetic field would push it around, squeezing the "wires" and expanding any current carrying loops till they disintegrated.   At signal current levels this is probably negligible compared to surface tension (which itself is another issue).

In practical terms gallium is a safe material to experiment with, but it sticks to almost everything and becomes a complete mess.  Even in polythene bottles (which it is supposed not to wet), it sticks to the sides a bit.  It has a strong tendancy to super-cool, so once its melted at 30C or whatever it may stay molten at room temperature for ages.

And gallium is like mercury in being able to destroy large amounts of aluminium so you've got to be careful with it (completely forbidden on aircraft for instance).  So can't use it with electrolytic caps(!)

[nfmax]

Gallium is fun! Like water, it expands on freezing, which can cause problems. 'Gallinstan', a (non-eutectic) alloy of Gallium, indium, and tin remains liquid down to -19˚C. A sensor application I worked with once used it as a pressure coupling medium, where the medium had to be completely free of hydrogen, for material compatibility reasons.

[ejeffrey]

I don't think a liquid metal should have any significant ionic movement or electrolysis.  The electric field inside is extremely well screened by the conduction electrons, the metal nucleii are so much more massive than the electons they will hardly move at all, and I think the ability of the free electrons to cross the boundary with any electrode prevents any potential drop that would support a redox reaction.

Mercury of course has been used as an electrical conductor for ages in switches, thermostats, and relays.  At low current or when wetting solid contacts it doesn't do much interesting.  If you get into situations where the magnetic field induced force is significant (like in motor wingdings) then it would do probably weird things.

[MrAl]

I was thinking of if all the solder in a circuit was molten, ignoring it's heat or gravity, how different would the circuit behave. I should read something on wikipedia, but I'm just wondering if any cool stuff could be done with liquid metals, in a circuit, besides mercury switches or something like that.

And then I wonder farther about if other stuff was molten or liquid, I guess that get get's into chemical reactions tho too, a lot more areas.

I'm sure the high temperature of most molten metals makes this unpractical, but I'm just wondering if any have cool or useful effects that we miss out on for now, due to the high temperature that would be needed.

It's an interesting idea.

Imagine a circular pipe full of mercury where the mercury was being pumped around in the circle at normal water flow rates.  There would have to be a lot of electrons going around in that circle.  Could it be used to make a special kind of motor.  In regular wires the electrons move very slowly around the wire.  The question is, will the moving electrons in the pipe generate a field.
The best example I can think of is the moving metal core of the Earth which gives us our huge magnetic field, although it is weak by our magnetic standards for use in electronics.  Many orders of magnitude weaker.
So we know it would create a field, the question then is how strong, or at least how useful.

[coppercone2]

this is a studied area of electronics related to self heating circuits. you use silicone to make fluidic pathways for metals used for conductors. Some say its the future of low power and flexible electronics.

[MathWizard]

Yeah I've seen video's of Gallium, but never had a sample, I didn't think it would stick to stuff.

Yeah I never considered the magnetic effects that can happen with moving charges. The flexible metal pathways, yeah that sounds like cell biology stuff. I lot of bio-chemistry I think of as slow, but if you can engineering nano pathways to act as switches and maybe add other effects like amplification, yeah maybe that can be really small and fast.

[coppercone2]

well more like just instead of a PCB. That is another realm of some kinda fluidic mems stuff.

The idea is if you can replace kapton with something flexible you can get much better medical devices, wearables, etc.

[CatalinaWOW]

In some ways you can think of much like conducting electricity through plasma.  The standard ohms law kind of stuff doesn't change much.  But containing liquid and potentially very hot conductors, especially in the presence of significant magnetic fields adds a whole world of fun.  Defining the boundaries of conductors for discrete element analysis gets interesting.

[JustMeHere]

Generally you want your conductors cold not warm.

https://simple.m.wikipedia.org/wiki/Superconductor

[joeqsmith]

I was thinking of if all the solder in a circuit was molten, ignoring it's heat or gravity, how different would the circuit behave.

I've seen first hand various examples where solder became molten on a PCB.   I ran a small, controlled demonstration  showing how copper expands when vaporized.  The circuit in that case was about an inch of small gauge wire and about 600J applied to it. 

[HarryDoPECC]

You might also be interested to look at https://en.wikipedia.org/wiki/Electromagnetic_pump
Used for example in nuclear reactors to drive the primary cooling loops

[T3sl4co1l]

As mentioned, electrons are by far the dominant charge carriers; atomic motion is dominated by thermal energy, that's all.

Resistance does increase suddenly on melting, though by how much, or with what tempco once molten, isn't very oft-studied.  I think you can find a few tables of data somewhere, but it's not common knowledge.  (And no, not like it's controversial or anything. It's just almost no one needs to know it.)

So, you'd expect the resistance to be high due to the chaotic environment versus a nice smooth crystalline matrix, and that's true, but the temperature is high in general so there's plenty of electron-phonon interaction and such to dissipate kinetic energy and contribute all that resistance.

Lorentz forces are negligible for signal levels as you'd have on a PCB, not to mention solder joints are so small compared to the better conductors (mostly copper or brass, sometimes steel) that are usually smooshed together -- most PCB joints are lap joints and the solder fills the mere capillary space between/around them.

At higher induction levels, depending on size and frequency, Lorentz or convection forces will tend to dominate.  Lorentz force is higher at low frequencies (more flux density for a given power dissipation), while convection is dominant at larger dimensional scales (like a bath of molten metal in a furnace).  With enough field intensity, and a divergent geometry, you can levitate metal in space; depending on resistivity, it will get quite hot in the process though, so that for example a copper sphere might levitate for tens of seconds, maybe minutes, in air, but eventually get too hot (resistivity too high) to support, at least at the same field intensity; beyond which it might get yellow or white hot to continue supporting it.  On the other hand, if you're doing something like melting refractory metals in vacuum, let alone something truly exotic like plutonium... the high temperature is quite suitable.

Tim

[coppercone2]

i am working for a english lighting systems developer and I wanted to know about the conductivity parameters of boiling plutonium used to cool our over loaded dc/dc converters (we think its causing our installations to break in nottingham). the manufacturer won't send us a data sheet

[Berni]

Molten metal in circuits is used commonly in the form of mercury weted switches. But they can also work well as slip rings or seals.

Another use of liquid metal is as thermal interface material to bond CPUs to heatsinks, since metals have a very good thermal conductivity (much higher than any regular thermal paste). But in all these cases care must be taken for the metal not to escape and unintentionally short things out.

Metals don't care if they are solid or liquid when it comes to being conductive. In either case they are full of free electrons that can move around and carry charge. This gets more problematic once you heat metals up enough to be a gas, this brings atoms too far apart for electrons to just roam from atom to atom, but that state makes it easier to knock electrons off it, ionizing the gas and this making it conductive (This is how mercury vapor lamps work, and the reason they need a high voltage pulse to start up).

The opposite actually tends to happen when melting stuff!
Quite a few insulating materials actually become conductive once they are molten. Prime example of this is salts. They typically an ionic crystal in solid form, the crystal structure holds the ions in place, so they can't act as charge carriers. If you measure table salt crystals with a multimeter they wont conduct at all, however once you dissolve it in water it becomes very much conductive, since that allows the ions to move once suspended in water.

However that has nothing to do with water. If you heat up table salt to a high enough temperature to melt it, it will also become very conductive since the liquid form is just a jumbled mess of ions that can move around. This even works for glass since some components of most types of glass form ions. Since glass doesn't have a sharp eutectic melting point it means that it will slowly become conductive as you heat it up even before it looks like it is melting at all. So in theory you could use a glass rod with wires attached to the ends as a NTK thermistor temperature sensor for high temperature.

[SeanB]

Yes have seen the molten glass become conductive, ans this can actually handle enough current to keep the glass molten. Have done it using a blown light bulb, using the broken glassbase , and the lead wires as current carriers, to apply current, via another lamp in series, and on heating the end with a torch to red heat, the other lamp lit, and it was passing enough current to keep the glass molten.

[Stray Electron]

  I wonder if the CRC Handbook has a table of the conductivity of molten metals? It has just about every other chemical and physical characteristic that I can think of.  I don't know how common that book is outside of the US but in the US, it is a standard Referernce book. https://archive.org/details/CRCHandbookOfChemistryAndPhysics97thEdition2016