Technique Research On The Preparation Of Mgb₂ Film Via Molten Salts Electrochemical Method

Since the discovery of superconductivity of MgB2 in 2001, the new style superconducting material with simple crystal structure has stimulated comprehensive attention owing to not only 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, but also its good processing and synthesizing performance comparing to the cuprate superconductors. However, it is still a problem to.connect two parts to form closed loop circuit through ordinary method. The molten salts electrochemical technique is a new way to product MgB2 films with a thickness of several micrometers on cathode with various shapes and size, which can connect two parts to form closed loop circuit easily. The development of this technique, however, is hindered in the industrial implementation owing to the uncertainty of experimental parameter as well as the immaturity of the theoretical research. In this thesis, we tried to prepare MgB2 films on different cathodes via the molten salts electrochemical technique.In the experiment, based on the calculation of electrolytic voltages as well as the analysis of phase and fusibility diagram, the range of electrolysis parameters were set. Then, under constant dc, MgB2 films were prepared on graphite, stainless steel and copper cathodes at different temperature. X-ray diffraction (XRD) analysis was adopted to analyze the constituent and integrity of phases. The sample was also characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The electrical resistivity and magnetization measurements of the specimen were measured by conventional four-probe method and SQUID, respectively.The results demonstrate that MgB2 films have been prepared on different cathodes successfully, and the optimized electrolysis temperatures are 620℃for graphite cathode,598℃for stainless steel and 601℃for copper, respectively. Moreover, the electroplated MgB2 films on copper cathode undergo a superconducting transition with the critical temperature (Tc, onset) at about 50K. However, the phase purity and crystallinity of the samples need to be improved and weak link exist among crystal grain. In the end, the melting salts system (density, surface tension and viscosity) are investigated theoretically, and modification scheme of the system is proposed.