Using X-ray diffraction (XRD) and field emission scanning electron microscope (SEM) analysis the phase composition and microstructure of samples; SQUID (superconducting quantum interferometer with) to measure samples of the superconducting transition temperature; At 4.2 K under standard four wire method was used to measure short sample of critical current Ic with the change of magnetic field, the loss in excess of the criterion of 1 v/cm, in the measurement process and direction of magnetic field parallel to the axis of the wire; And according to the critical current Ic and MgB2 superconductor core cross-sectional area calculation of the critical current density Jc.

The results and discussion after 950 after annealing MgB2 / Fe superconducting wire core scanning electron microscopy (sem) picture of cross section. From at high magnification (b) you can see in the images, superconducting less core porosity, core material density is higher, this may be due to the high temperature heat treatment to enhance the grain due to connectivity; From low power (a) you can see in the picture has a larger MgB2 grain size, this is mainly because of the not original powder for ball mill, there are also some can be sintered in the high temperature heat treatment process.

As you can see, the center main each other into MgB2 superconducting core samples, in addition to containing MgO style and MgB4 impurity phase; Sample the stronger MgB4 is contained in the XRD diffraction peak, it may be because of the wire for high temperature heat treatment < 16 >; Also because of the way with mechanical polishing to apart from the surface of the superconducting cores, so not found in the diffractogram Fe content.

MgB2 / Fe superconducting wire core XRD after annealing at 950 annealing treatment of MgB2 / Fe wire magnetic susceptibility curve along with the change of temperature. Can be seen from the figure in the superconducting transition temperature Tc initial about 38.3 k. can also be seen from the figure, the curve of the transition width is large, this may be due to superconducting cores of MgO style and MgB4 < 16 >, but it did not enter the MgB2 lattice; On the other hand, high temperature annealing can effectively reduce the stresses produced during cold working, at the same time improve the connectivity of grain < 7 >. Can also be seen from the figure, the curve of the transition width is large, this may be because of MgB2 superconductor core caused by the uneven grain size, it can be seen from the SEM low power in the photo.

MgB2 / Fe wire magnetic susceptibility curve along with the change of temperature 4.2 K is given under the first bit line of MgB2 / Fe strip of critical current density (Jc) curve along with the change of magnetic field. Can be seen from the diagram, when the magnetic field range of 47 t, homemade MgB2 / Fe wires superconducting properties than Nakane et al. Preparation of MgB2 < 15 > / Fe strip performance is high; Under the 4.2 K / 4 t homemade the critical current density of pure MgB2 / Fe wire for 104 a/cm2, and Nakane et al. Preparation of < 15 > strip the critical current density of less than 103 a/cm2.

This experiment to the first bit of MgB2 / Fe wire 950 high temperature heat treatment, effectively reduced the stress occurring in the process of cold working, to improve the connectivity of MgB2 grain, increase the density of the sample, to improve the magnetic flux pinning characteristics, thus improved its superconducting properties. And Nakane et < 15 > the first bit of of strip annealing temperature on the low side (600), which is leading to a lower strip superconducting properties of the main reasons.

4.2 K under a line strip which was prepared first JcB curve: homemade MgB2 / Fe wire Nakane et al. Preparation of MgB2 < 15 > / Fe strip Flukiger people such as < 7 > special emphasis on the initial powder granularity (ball mill) for a first the importance of preparation of high performance wire strip Lezza < 17 > points out that the ball mill, 100 h is better than 3 h, and Takano et < 9 > points out that the ball mill time shoulds not be too long. Visible, ball grinding time needs further research to find the appropriate to the size of the powder particle size to increase the density of core superconducting materials, improve grain connectivity and magnetic flux pinning characteristics, so as to improve the superconducting properties of a normal strip first. In addition, Nakane et al. < 15 > points out that the use of MgB2 powder prepared by in situ as a method of the initial powder can obviously increase the first critical current density of a legal system for strip first. If in this way, with in situ prepared method of nanometer powder doping MgB2 powder as a first initial sintering powder, and can effectively increase magnetic flux pinning center and improve the connectivity of grain, this will likely greatly increase a normal first strip superconducting properties.

Conclusion based on the first bit of MgB2 / Fe superconducting wires, and the phase composition, microstructure, and superconducting properties was tested. Experimental results show that the superconducting wire of MgB2 / Fe critical transition temperature is about 38.3 K, 4.2 K / 4 t under the critical current density for 104 a/cm2. The study shows that the high temperature heat treatment reduced the stress occurring in the process of cold working, to improve the grain connectivity, increase the density of core material, improve the magnetic flux pinning characteristics, effectively improve the MgB2 / Fe superconducting properties of wire rod. In short, by improving the initial powder granularity, and effectively high temperature heat treatment can significantly improve a line strip which was prepared first superconducting properties, is expected to make a normal first strip to meet application requirements.