| MgB2 superconductor with simple crystal structure has stimulated comprehensive attention because of its remarkably high critical temperature (Tc) of 39K and high critical current densities (Jc) (an order of 105Acm-2) comparing to the known intermetallic compound superconductors and its good processing and synthesizing performance comparing to the cuprate superconductors. Currently, Physical or chemical vaper deposition are mature technology for preparing MgB2 films. Those methds not only need expensive equipments but also has low production efficiency, so there are not suitable for large scale application. However, molten salt electrochemical method is a desirable method for the preparation of MgB2 film. Because this method not only can significantly reduce the cost of production, but also has high productivity, meanwhile it is applicable to substrates with arbitrary shapes and sizes. And the technique of molten salt electrochemical method to prepare MgB2 films is still at the experimental stage, many experimental parameters are uncertain, and the theory investigation about this are also scare. In this paper, the method for preparation of MgB2 films was discussed. In this paper, the impact of five different molten systems including MgB2O4 and B2O3 on preparation of MgB2 films with molten salt electrochemical technique has been researched from the point of view of the character of the molten salt. The specific details are as follows.First, before the electrolysis experiment, the improvement of the electrolysis equipment has been executed. The electrolytic device with a water cycle cooling system through our independent research has been used, and then the samples can be cooled quickly and efficiently under the protection of Ar atmosphere. So this method is economical and time saving. Second, refering to previous research, a fused mixture with a molar ratio of MgCl2:NaCl:KCl:MgB2O4=10:5:5:2 has been used for contrast experiment about different cathode, cooling method and electrolysis time, and the optimized process parameters of these have been find out. Third, under those optimized process conditions, five different molten salt systems M01(MgCl2+KCl+NaCl+ MgB2O4), M02(KCl+NaCl+MgB2O4), M03(MgCl2+KCl+MgB2O4), M04(MgCl2+ KCl+B2O3) and M05(MgCl2+B2O3) have been researched and optimized for good MgB2 films' preparation. And the advantadges and disadvantages of those different molten salt systems and the causes of problems in existence have been discussed. The compositions and crystal performance of samples have been analyzed and charactered by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The results demonstrate that graphite cathode has better adhesion between cathode and film compare to copper cathode, so graphite cathode is more suitable for growth of MgB2 film. And the best electrolysis time is 2h. M03 and M04 molten salt systems are better choices among the five molten systems, and their corresponding best molten salt compositions are the molar ratio of MgCl2:KCl:MgB2O4=3:2:0.8 and MgCl2:KCl:B2O3=3:2:0.8. The XRD patterns and SEM images of the best samples show that the films are flat and compact and including MgB2.So our choices of molten salt are preferable. However, the conductivity of films are not well due to the existence of non-conductive materials such as molten salt. The existence of problems in the course of molten salt electrolysis have been discussed, and the conclusion that the ways of improving film's performances is to find an electrolyte system with high decomposition voltage that can lower the melting point and viscosity of the molten systems or a system including Mg and B that also can lower melting point and viscosity of the molten systems and with low decomposition voltage has been proposed. |
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