A novel gas–solid reaction process to synthesize low oxygen MgB₂ powder using Mg vapour

Abstract

We have established a novel reaction process using Mg vapour and B powder (a gas–solid reaction) to synthesize MgB2 powder with a low oxygen content. For the first time, we tried to eliminate the oxygen in Mg powder with a specially designed furnace tube that can keep the sample under an inert atmosphere throughout the entire synthesis process. The duration of heat treatment has a conspicuous effect on the phase formation of MgB2 which differs greatly from the conventional solid state reaction method. At short durations such as 1 h, unreacted B powder is ubiquitous in the sample. Full formation of MgB2 is achieved at 3 h. At longer times such as 4 h, MgB2 decomposes to form MgB4. It is deduced that the main reason for the unstable MgB2 phase formation in the gas–solid reaction is the Mg vapour present during the entire process. A feasible chemical reaction model of the novel gas–solid reaction has been established. This work provides an important foundation to obtain almost oxygen-free MgB2, which can finally resolve the mystery of the effect of oxygen on superconductivity in this system.

Exploration of the Effect of Oxygen on Superconductivity in MgB2 Bulk by Using Boron Powder with Different Particle and Purification

“…At the same time, the morphology of the different B powders was nearly the same. It allows us to investigate the effect of the particle size of B powder on the purification results solely and test our former speculations [10].…”

“…These powders react with Mg during synthesis. Only a few groups have tried to eliminate the oxygen in Mg powder [10,11].…”

Review on high-performance bulk MgB2 superconductors

“…Two primary oxygen sources involve MgO, which is present in the Mg precursor, and B 2 O 3 found in the B precursor. During synthesis, these powders react with Mg. Only a few groups have succeeded in removing oxygen from Mg powder [87,88]. MgB 2 films voluntarily pick up oxygen from the ambient atmosphere, forming numerous oxides (BO X , MgO, MgBO, BO X MgO Y etc) [89,90].…”

A novel sintering protocol to enhance the connectivity ofex situMgB2bulks in an open system by using Mg vapor

“…Commercial MgB 2 powder (Alfa Aesar 99.9%) was pressed into a pellet with a diameter of 10 mm and height with 1.65 mm using a uniaxial hydraulic press machine in air. The pellet was put in a homemade furnace tube firstly described in [23]. As shown in figure S1 is available online at stacks.iop.…”