Liquid metals in a vacuum, electric control

[farmerben]

 

I was researching eutectic amalgams, such as mixtures of lead, bismuth, mercury, tin, etc. These make low melting point metal alloys.  It appears that most of the transition metals in small quantities can be dissolved in large quantities of heavy semi-conductor elements.

Unfortunately the information I'm finding online is contradictory.  Some people claim the metals vaporize, some people claim they release no gaseous metal.  

In air, toggling the voltage of an amalgam can toggle the oxidation properties of the surface.  And the liquid can be moved quite easily with electric fields.  

 

I'm interested in a device which contains liquid metal and high vacuum in a single chamber.  Or a chamber which opens to space without losing any metallic gas.  

[Cunjo Carl]

@farmerben, sorry I'm not quite following, but maybe I can provide some more information?

A common device containing liquid metal and high vacuum in a single chamber would be the "evaporator", which is designed to deposit thin films of metals onto things. There are two main kinds of evaporator, separated by how they heat up the metal: Thermal evaporators, which heat up the metal using electricity (typically going through a resistor in which the metal sits), and  E-Beam evaporators which use a beam of high voltage electrons to heat the metal. When heated, most metals will liquefy before they evaporate, and don't disturb the high vacuum. In fact, they often help the vacuum through a process called gettering, where the evaporated metal vapors react with the tiny amount of gas in the chamber (typically water at 1*10^-8 atm), and then stick the resulting compound as a metal oxide/hydroxide on the chamber wall.

There's many excellent metal amalgams. The most common one these days for being a room temp liquid is Galinstan, a mixture of Gallium Indium and Tin. It's quite expensive, but is much less toxic than most other options.

Transition metals can dissolve into semiconductors to varying amounts, where they're typically called dopants. They heavily effect the semi-conductor's conductivity. Some metals are highly mixable (like iron and silicon), and others not so much.

Molten metals and salts have all kinds of fun electrical properties. There's research done on molten metal spheres, doing a quick internet search (Youtube Video).

[farmerben]

Thanks, I found that helpful. 

The device I'm thinking about is a high flux isotope reactor with fissile material in an amalgam.  Like this only liquid.

https://en.wikipedia.org/wiki/High_Flux_Isotope_Reactor#/media/File:High_Flux_Isotope_Reactor_Simplified_Core.jpg

Using reflector based control rods like on a Nerva engine, we concentrate a "pit" of intense fast neutron flux.    If it is possible to control the amalgam to shape it into a hemi-sphere, like half a fruit. This would allow high vacuum for the other half of the sphere.  (other geometries are possible, I'm just going with sphere for simplicity).  

A vacuum allows us to send very high energy particle beams into the pit region.  Not simply to create spallation neutrons in a material, but also to collide with other beams from other directions.  

The amalgam is a continuous source of alpha particles and radical neutrons in the 10 keV range.  A cyclotron with a single magnet can get deutrons up to the 700 keV range.  In this environment both tritium helium fusion and tritium deuterium fusion can take place.  We do not even need a source of tritium because near the center neutron flux is very high.  

There are fission product gasses like xenon and krypton, so these must be removed.  But it would be undesirable to remove metals, or have them plate everything.

 

 

....

Another application of this vacuum technology is a safety feature for terrestrial fission reactors, independent of all the beams and fusion ideas.  

We maintain criticality by having some of the neutrons cross a vacuum, reflect, cross vacuum again, and produce a fission.  Any air that gets between the reflector and the core will increase neutron moderation and increase the cooling rate.  Many Gen IV designs use the concept of a drain tank for emergencies.  In this design, losing vacuum has a similar effect as draining the core, only way faster and easier to reset.  

 

....

High flux reactors are the best way to create RTG material, but they could be even better.  

700 keV proton or deutron beams will produce over 20 spallation neutrons when they hit lead or bismuth.  These are fast neutrons around 10 keV the same energy as released by fission.  More beam power raises the number of neutrons slightly (to about 26) but the energy of the neutrons considerably. 

Occasional fusion caused by particle collisions gives us one neutron (therefore our criticality factor doesn't change much if we create more fusions).  However the fusion will tend to give us alpha particles at 4MeV kinetic energy and a neutron at 14 MeV. 

In the MeV range we have the power to transmute super heavy elements, for use in RTG's.

 

On out reflector Be + a = C + n, so we have a third fusion reaction occurring.  We could also get D-D and T-T fusion.  All with low probability, and tending to increase the energy of radical neutrons without changing the number of neutrons significantly.  

 

.....

In space, fluid engines and fluid coolants are difficult.  Thermocouples are the most simple and reliable.  The lightest solution for coolant is not to have any.    Thermocouples in vaccuum outside the reflector generate electricity.  The temperature of the core can be ridiculously hot if it is all liquid metal.  (4000 K if you need graphite crucibles).  Control of spallation neutrons means you can go from subcritical to critical rapidly.  The amalgam could absorb massive amounts of heat, cool off for long periods of time and be restarted by beams.

Edited May 8, 2019 by farmerben

[Nuke]

might want to look up the feep thruster while you are at it. very low thrust, but with a very high isp. i think some satellites already use it. uses liquid metals as propellant.

[farmerben]

10 hours ago, Nuke said:

might want to look up the feep thruster while you are at it. very low thrust, but with a very high isp. i think some satellites already use it. uses liquid metals as propellant.

 

What I found implies that these metals cohere and adhere in vacuum.  I don't know for sure, but I think high frequency electricity of limited potential would cause liquid conductors to cohere more.  

 

Perhaps we could use high frequency electromagnetic radiation, and electron beams, to influence the alpha rays.  Given that some of the alpha particles are headed along a desired vector at over 5% the speed of light, it ought to be possible to eject or even boost these.  And at the same time catch more of the alpha rays along other vectors.

 

[Cunjo Carl]

On 5/9/2019 at 6:45 AM, farmerben said:

What I found implies that these metals cohere and adhere in vacuum.  I don't know for sure, but I think high frequency electricity of limited potential would cause liquid conductors to cohere more. 

Perhaps we could use high frequency electromagnetic radiation, and electron beams, to influence the alpha rays.  Given that some of the alpha particles are headed along a desired vector at over 5% the speed of light, it ought to be possible to eject or even boost these.  And at the same time catch more of the alpha rays along other vectors.

Liquid metals have exceptionally high cohesion, owing to their sea of electrons. From our perspective it means they have extremely high surface tension, even relative to water. Their adhesion depends 100% on what surface they're on. When we want low adhesion, we tend to use specific ceramics or sometimes vitreous carbon.

There's several forms of electric levitation that work on molten metals. The main one I'm familiar with uses eddy currents for levitation much like the standard Physicist's jumping ring trick. It's used very rarely in specialized 'inductive' evaporators. As far as I'm aware, it should work in the 1s of kHz region but the paper I link to suggests using RF. You can also use a quadrupole electric field if the molten metal is provided a net charge to ground (which in practice is fairly easy). About a decade ago I really wanted to build one, but fortunately discovered before starting they're a huge pain in the rear end. I think the version shown would be the preferred method.  Levitation paper

Directing alphas using the electric field is apparently very difficult. An old coleague of mine told me once that there was a lot of work done on this during the 70s to try harnessing electric power directly from alpha particles and initially the work looked quite promising, but in the end controlling them in large amounts in any meaningful way was just too difficult. Even with magnetic fields is quite tough apparently- I guess that's one of the reasons Tokomaks are so tricky.

[farmerben]

Very cool.  

I wonder if this still works when you have bismuth (the most diamegnetic metal) with neodymium (a fission product and the most ferromagnetic).  

The idea I'm talking about would be throwing alpha particles and neutrons radially outward all the time.  Some of those would interact with the beryllium.  Holes in the solid beryllium reflector provide some control.  

This thing could potentially cool off or even freeze and be capable of restarting.  The great thing is any particle beam that hits the metal will create 20 or so more neutrons and drive up the criciticallity and breed some heavy isotopes.  Beams hitting other beams, or hitting alpha particles from the natural decay of heavy elements can fusion.  Many of the fusion events lead to alpha particle banking by creating atoms like Curium and Californium

 

 

[farmerben]

This is almost too good to be true.

https://en.wikipedia.org/wiki/Muon-catalyzed_fusion

https://journals.aps.org/prab/pdf/10.1103/PhysRevSTAB.12.111301

 

One of the most exciting new technologies is the laser wakefield accelerator which can produce a pulsed beam of electrons at 1 GeV using a tabletop device (1m).  I couldn't see the application at first because it does not alter the neutron balance.  

However, these electron pulses on semiconductors can generate muons.  Muons can replace electrons in atoms, but with much smaller average distance from the nucleus.  Therefore they shrink the Coulomb barrier.  This makes duetrons and alpha particles way more susceptible to fusion.  And my intuition would be more likely to breed heavy elements as well, especially at the surface where metal and alpha particles meet.

[Cunjo Carl]

16 hours ago, farmerben said:

This is almost too good to be true.

https://en.wikipedia.org/wiki/Muon-catalyzed_fusion

https://journals.aps.org/prab/pdf/10.1103/PhysRevSTAB.12.111301

 

One of the most exciting new technologies is the laser wakefield accelerator which can produce a pulsed beam of electrons at 1 GeV using a tabletop device (1m).  I couldn't see the application at first because it does not alter the neutron balance.  

However, these electron pulses on semiconductors can generate muons.  Muons can replace electrons in atoms, but with much smaller average distance from the nucleus.  Therefore they shrink the Coulomb barrier.  This makes duetrons and alpha particles way more susceptible to fusion.  And my intuition would be more likely to breed heavy elements as well, especially at the surface where metal and alpha particles meet.

Nice connection! Looks like it's a thing:

Existing Source for Muon-Catalyzed Nuclear Fusion Can Give Megawatt Thermal Fusion Generator

They use a similar muon production method in conjunction with ultra dense Hydrogen-1 (some kind of condensed matter which is totally new to me), to get some pretty impressive looking power gains on paper. Will definitely be reading up more.

 

Edit: More reading on that ultra dense Hydrogen phase.. Several elements of this throw up hoax red flags for me, but honestly the bulk of it passes the smell test for good science done in good faith. As a whole, I'm inclined to believe it. Definitely going to run a copy over to a condensed matter group at work to see what they think. If even a quarter of what's presented is true, it's jaw droppingly amazing- Hydrogen at a density of 100, able to exist as a stable free phase! Too good to be true doesn't begin to cover it.

Edited May 12, 2019 by Cunjo Carl

[farmerben]

Well the muons have a lifetime of 2 x 10^-6 s.  Not stable at all.  

Wakefield accelerators typically shoot 50 femtosecond pulses at a rate of 50 Hz.  

 

https://www.popsci.com/science/article/2011-01/using-muons-disguise-chemists-fool-helium-thinking-its-hydrogen