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 (Jc) 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.