Heat Treatment of MgB2 Superconductors With Different Metal Sheaths

The superconductors based on magnesium diboride have a lot of advantages in comparison with the traditional ones, such as relative simplicity of the superconducting compound synthesis process, small weight of the finished product, possibility to manufacture superconductors in the form of wires and tapes, and absence of superconducting properties anisotropy. In this paper, the results of manufacture and study of MgB
₂
superconductors with metal sheaths differing by mechanical and physical-chemical properties were presented. Inside of sheath there was Mg and B powders mixed in required proportion. The series of annealings of produced superconductor samples has been carried out at temperatures from 650 °C to 700 °C and duration from 0.25 to 1 h. After heat treatment, the microstructure of the formed compound has been studied by the scan electron microscopy method and critical temperature of superconductors has been also measured. It was established that the minimal temperature of superconducting MgB
₂
compound synthesis depends on physical-chemical properties of the metal sheaths. It is necessary to increase the heat treatment temperature up to 700 °C for the wires whose sheaths material has low value of thermal conductivity but heat treatment temperature can be 650 °C if the sheath material has thermal conductivity value close to one of the copper. Critical temperature of the produced superconductors after heat treatment by optimal regime was 38.5 K that is close to theoretical value-39 K.