Development of magnetic liquid metal suspensions for magnetohydrodynamics

Abstract

We demonstrate how to suspend various magnetic and non-magnetic particles in liquid metals and characterize their properties relevant to magnetohydrodynamics (MHD). The suspending method uses an acid as a flux to eliminate oxidation from both metal particles and liquid, which allows the particles to be wetted and suspend into the liquid if the particles have higher conductivity than the liquid. With this process we were able to suspend a wide range of particle materials and sizes from 40 nm to 500 µm, into three different liquid metal bases, and volume fractions φ up to the liquid-solid transition φc. By controlling the volume fraction of iron particles in liquid eGaIn, we increased the magnetic permeability by a factor of 5.0 and the electrical conductivity by 13% over that of the pure liquid metal, which gives these materials the potential to exhibit strong MHD effects on the laboratory scale that are usually only observable in the cores of planets and stars. By adding non-magnetic zinc particles, we increased the viscosity by a factor of 160 while keeping the magnetic and electrical properties nearly constant, which would allow independent control of MHD effects from turbulence. We show that the suspensions flow like Newtonian fluids up to the volume fraction of the liquid-solid transition φc.

Magnetically‐ and Electrically‐Controllable Functional Liquid Metal Droplets

“…The surface of the Galinstan immediately oxidized when exposed in the air, forming an oxide skin and making the surface much less reflective. [26,[29][30][31] (2) Next, we added 50 mg Cu-Fe NPs (Cu:Fe = 3:2) and shook the beaker until the surface of Galinstan was coated with a uniform layer of Cu-Fe NPs (Figure 1b). Due to the oxide layer on both of the Galinstan and the Cu-Fe NPs, the NPs can only stick to the oxide skin of the liquid metal and cannot break through the oxide layer to be suspended within the bulk liquid metal.…”

“…Due to the oxide layer on both of the Galinstan and the Cu-Fe NPs, the NPs can only stick to the oxide skin of the liquid metal and cannot break through the oxide layer to be suspended within the bulk liquid metal. [29] Figure 1. Production of the FLM.…”

“…[1,2] Such liquid metals possess many extraordinary properties including high surface tension, favorable flexibility, high electrical/ thermal conductivities, and much less toxic in comparison to mercury. Motivated by the process demonstrated for making magnetic liquid metal, [29] we first obtained the liquid metal marble by coating copper-iron (Cu-Fe) NPs on a Galinstan droplet and remove the oxide layer using hydrochloric acid (HCl) solution. Motivated by the process demonstrated for making magnetic liquid metal, [29] we first obtained the liquid metal marble by coating copper-iron (Cu-Fe) NPs on a Galinstan droplet and remove the oxide layer using hydrochloric acid (HCl) solution.…”

“…[3][4][5][6][7] Particularly, the mobility and deformability of liquid metal in aqueous environment have been verified to be of a great significance to develop diverse applications In this study, we developed a novel method for producing FLM that can be manipulated using both magnetic and electric fields, and yet, the FLM still exhibits similar appearance, mobility, and deformability to those of pure liquid metal. Motivated by the process demonstrated for making magnetic liquid metal, [29] we first obtained the liquid metal marble by coating copper-iron (Cu-Fe) NPs on a Galinstan droplet and remove the oxide layer using hydrochloric acid (HCl) solution. The FLM contains magnetic NPs was later separated from the solid shell and collected after applying an external potential gradient within a sodium hydroxide (NaOH) solution.…”

Effective magnetic susceptibility of suspensions of ferromagnetic particles

“…These properties suggest the suspensions behave as linear paramagnetic materials in this range, which is simpler for both modeling and control, despite the fact that the particles themselves are ferromagnetic. The suspensions are known behave like a ferrofluid such that after an applied magnetic field is removed, the particles separate and flow like a liquid [7]. This allows the ferromagnetic particles to move around in the liquid and reorient more freely than magnetic domains in a solid to avoid hysteresis and remnant magnetization.…”