A novel sintering protocol to enhance the connectivity of ex situ MgB2 bulks in an open system by using Mg vapor

In this paper, we establish a novel sintering protocol for ex situ MgB₂ bulk in an open system by using Mg vapor. The Mg vapor successfully restrains both the continues oxidation and decomposition of MgB₂, even after 96 h at 900 °C. Such robust protection given to the ex situ MgB₂ bulk at high temperature provides the possibility of improving the superconducting connectivity and critical current density (J_c) using long-term sintering at high temperatures. The effect of sintering time on phase formation, microstructure, superconducting properties, and the mechanical properties of ex situ MgB₂ bulk are systematically investigated. A comparison of our novel protocol and the most successful ex situ MgB₂ bulk sintering process—the powder-in-closed-tube method (PICT)—is also discussed. Our novel protocol can improve superconducting properties to the same level as with the PICT method but allows MgB₂ bulk to be used in an open system. This makes dealing with ex situ MgB₂ bulk for engineering applications feasible.