【作者】 黄伟钱；

【导师】 祁阳；

【作者基本信息】 东北大学 ， 材料物理与化学， 2009， 硕士

【摘要】 由于超导体MgB2与同类的金属间化合物相比具有高的转变温度(Tc=39K)和高的临界电流密度(可达105A/cm2),与氧化物超导体相比具有易加工,易合成的优点,使其有可能得到比较广泛的应用。目前较成熟的MgB2膜制备技术大多是采用物理或化学气相沉积法,这些方法不仅设备昂贵,而且生产效率不高,不适合大规模推广应用。而熔盐电化学法则可以大大降低成本,且生产效率高,同时不受衬底形状、尺寸的限制,因而是一种非常值得研究推广的制备方法。但熔盐电化学法制备MgB2膜的工艺尚处于实验研究阶段,一些工艺参数也未能确定,相关的理论研究也极少,因此本文用该法对MgB2膜制备进行了探讨。本文主要从熔盐特性的角度出发,研究了分别含有MgB204和B203的五种不同熔盐体系对MgB2膜熔盐电化学法制备的影响,其具体内容如下：在电解实验前,首先对电解设备进行了改进,采用了自主研发的电解装置,加入了循环水冷却系统,使样品得以在Ar保护气氛下快速有效地冷却,既经济又省时；其次,以前人的研究作为参考,采用摩尔比MgCl2:NaCl:KCl:MgB2O4=10:5:5:2的熔盐组成进行了不同阴极材料、冷却方式、电解时间等对比实验,并对这些参数进行优化；然后在此优化的工艺条件下,对M01(MgCl2+KCl+NaCl+MgB2O4)、M02(KCl+NaCl+MgB2O4)、M03(MgCl2+KCl+MgB2O4)、M04(MgCl2+KCl +B2O3)、M05(MgCl2+B2O3)的五种不同熔盐体系均作了最佳熔盐组成的优化研究,并探讨了各熔盐体系的优缺点以及存在问题的原因。样品的物相及结晶性能由X射线衍射仪(XRD)进行检测分析,表面形貌由扫描电子显微镜(SEM)进行表征。结果表明,石墨阴极比铜阴极具有更好的粘附性更利于膜的生长,而实验最佳的电解时间为2h。五种熔盐体系中M03和M04熔盐体系是较优的选择,其对应的最佳熔盐组成分别为摩尔比MgCl2:KCl:MgB2O4=3:2:0.8和摩尔比MgCl2:KCl:B2O3=3:2:0.8。最优样品的XRD图谱及SEM图像表明,我们制得的膜含有目标相MgB2且较致密而平整,说明我们的熔盐选择具有积极意义。然而由于非导电物质熔盐等的存在导致膜的导电性能并不佳。本文从熔融体系自身特性方面,提出了提高膜性能的方案是要寻找出能有效降低熔盐体系熔点和粘度同时分解电压又较高的电解质体系或低熔点、低粘度及低分解电压的Mg和B元素的物质体系的结论。更多还原

【Abstract】 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.更多还原