High density and connectivity of a MgB₂filament made using the internal magnesium diffusion technique

Abstract

In order to allow precise and detailed physical studies of an MgB2 filament made by the internal magnesium diffusion process (IMD), a modified approach (MIMD) using a Mg tube filled with boron powder deformed into wire was introduced. The MIMD process allows easy extraction of the MgB2 filament after the final heat treatment and performance of four-probe resistive measurements and density estimation, which is not possible for standard IMD wires. The Rowell approach has been applied for the grain connectivity from R(T) data of extracted MgB2 for the first time. The filament’s density has been estimated from the precise volume measured by x-ray micro-tomography and mass. The high connectivity and density of the MgB2 filament made by the diffusion process are discussed and compared with those of filaments made by other processes.

Reverse advance internal magnesium diffusion process to produce dense MgB2 bulks and high JC wires through high pressure heat treatment

“…Unlike the green wire, the heat-treated wire does not show regions with different composition (contrast) meaning reactions took place homogenously throughout the whole B core. The high magnification images (b) and (c) reveal high grain connectivity, typical of the diffusion technique [12]. The images show also defects caused by grain removed during metallographic preparation by grinding and polishing it is still difficult to find some regions with different chemical composition.…”

“…In order to overcome the issues associated with the Mg rod centering, in the present paper we report the development of an inverse architecture to the AIMI route, called reversed-AIMI (r-AIMI), in which the Mg rod surrounded by B is replaced with a Mg tube filled with B powder inside a metal sheath. Design of the starting billet is related to the process previously proposed by Kulich et al [12] for bulk extraction from a metal sheath and the performed connectivity measurements on the extracted core. This configuration permits an easier tubefilling procedure, avoiding issues related to Mg rod centering, resulting in a versatile process for manufacturing different typologies of conductor or samples including bulk, wire and tape.…”

Superconducting MgB2 Wire Drawing Considering Anisotropic Hardening Behavior and Hydrostatic Effect

“…In the current study, the I c factor, defined as a value of the final packing density multiplied by the area of the powder mixture, was used to indirectly estimate the critical current (I c ) of the multi-filamentary MgB 2 wire. Generally, the I c can be enhanced by increasing the J c or a superconducting area ( ∵I c = J c A sc , where A sc is the superconducting area) [46][47][48]. It is well known that an increase in J c can be Fig.…”

İki farklı metot ile üretilen oleik asit katkılı külçe MgB2 süperiletkenlerin süperiletkenlik özellikleri üzerine bilyeli öğütme etkisinin araştırılması

“…Due to the absence of inherent flux pinning centres, and the presence of high porosity and poor connectivity between the grains, the critical current density decreases so fast under a high field in MgB2. The simplest and most effective ways to overcome this problem are adding or doping of chemicals to the MgB2 structure and fabrication of MgB2 with different methods such as hot pressing (Naito et al, 2020), ball milling (Liu et al, 2020), internal Mg diffusion technique (Kulich et al, 2016) and laser irradiation (Erdem & Yanmaz, 2017). Since the MgB2 structure is resistant to many chemicals, the selection of the chemical powder to be used as an additive is very important.…”