Uniform Dispersion and Exfoliation of Multi-Walled Carbon Nanotubes in CNT-MgB2 Superconductor Composites Using Surfactants

Abstract

We developed a novel yet commercially viable strategy of synthesizing superior high-TC superconducting composites by dispersing fully exfoliated carbon nanotubes (CNTs) uniformly throughout the grain of CNT-MgB2 composites. First, we optimized the amount of the surfactant required to produce a highly stable and homogeneous colloidal suspension of CNTs. This amount was found to be 1/8th of the amount of CNTs. Second, we prepared a homogeneous CNT-B mixture by adding amorphous nano-boron (B) to the colloidal CNT suspension. Next, two different MgB2 synthesis routes were explored. In one case, we mixed an appropriate amount of Mg in the CNT-B mixture and carried out sintering. In the second case, the CNT-B mixture was heat treated at 500 °C, prior to mixing with Mg and sintering to form CNT-MgB2. Both kinds of samples were rigorously characterized to obtain an insight into their properties. The direct synthesis route shows a clear exfoliation and uniform dispersion of CNTs with a critical current density (JC) of 104 A/cm2 at 3.5 T and 20 K, which is useful for the application in magnetic resonance imaging MRI magnet operating with a cryogen free cooler. Our JC(H) result is 10 times higher than that of the pure sample. By contrast, the performance of the sample subjected to heat processing before sintering was severely compromised given the formation of MgO. Despite its simplicity, the direct synthesis route can be used for the cost-effective fabrication of CNT–MgB2 superconducting composites.

Reinforcing Increase of ΔTc in MgB2 Smart Meta-Superconductors by Adjusting the Concentration of Inhomogeneous Phases

“…Chemical doping is often used to study superconductivity. Unfortunately, many experimental results confirm that this method reduces the T c of MgB 2 [ 25 , 26 , 27 , 28 , 29 , 30 ]. Thus far, no useful strategy for improving the T c of MgB 2 is yet available.…”

Investigation of Layered Structure Formation in MgB2 Wires Produced by the Internal Mg Coating Process under Low and High Isostatic Pressures

“…However, PIT MgB 2 wires have several disadvantages, such as a large number of voids, poor connections between grains, low density of pinning centers, low irreversible magnetic field, and large grains [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. Current research has shown that doping allows for increasing the density of pinning centers [ 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Heating under pressure increases the number of connections between grains, reduces the amount of voids, and creates pinning centers [ 22 , 23 , 24 ].…”

Effect of Low Annealing Temperature on the Critical-Current Density of 2% C-Doped MgB2 Wires Used in Superconducting Coils with the Wind-and-React (W&R) Method—High-Field and High-Temperature Pinning Centers

“…Further studies showed that doping allowed for an increase in J c in middle and high magnetic fields [ 6 ]. Currently, many admixtures have been used for MgB 2 wires and bulks, e.g., SiC [ 15 ], rare earths [ 16 ], rare earths and carbon [ 17 ], copper [ 18 ], carbon nanotubes [ 15 , 19 ], graphene [ 20 ], and TiB 2 [ 21 ]. However, studies have shown that the admixture of carbon most effectively increases the critical parameters [ 22 , 23 ].…”