【作者】 杨华哲；

【导师】 祁阳；

【作者基本信息】 东北大学 ， 材料物理与化学， 2008， 博士

【摘要】 本文采用溶胶-凝胶(sol-gel)方法制备BSCCO超导带材,对溶胶-凝胶方法合成Bi-2212相的实验工艺、BSCCO超导带材的相成份和表面形貌进行了细致地研究。采用熔盐电化学方法在不同的阴极衬底上制备MgB2超导带材,重点讨论了温度对MgB2相成分的影响,并对带材的结构、形貌和超导特性进行了分析。本文主要研究了以下内容：1.研究了不同溶胶-凝胶工艺对Bi-2212相的影响。采用溶胶-凝胶方法,以金属硝酸盐作为反应物,以EDTA为络合剂制备了Bi-2212粉末。讨论了溶液浓度及溶液加热装置对最后成相的影响,并通过实验条件的改进提高了样品的Bi-2212相纯度。在制备工艺的探索中,开创性地提出并利用了传统凝胶工艺和二次凝胶工艺制备前驱粉末,再以不同的烧结时间烧结获得Bi-2212粉体。实验结果表明,对于传统凝胶工艺,最佳的烧结时间为10h。对于二次凝胶工艺,最佳的烧结时间为5h,且样品的质量略好于传统凝胶工艺中所获得的最佳样品,即二次凝胶工艺不仅能够缩短烧结时间,而且更有利于Bi-2212单相的形成。其原因在于二次凝胶与传统凝胶相比能更好的保持各组元成分的均一性,从而缩短了烧结时间,获得了相纯度更好的样品。2.研究了不同制备工艺的凝胶机制。从前面的实验结果出发,参考前人对凝胶模型的认识,设计了凝胶模型。同时,通过Materials Studio软件中的Dmol3模块优化了其结构,并计算了其能量。从目前的计算结果分析,二次凝胶的能量低于传统凝胶,因此二次凝胶中各组元的桥连强度要强于传统凝胶。该结果与实验检测中所得到的结论相符合。3.研究了BSCCO带材的制备。首先对衬底的处理方式和带材的热处理条件进行初步的摸索,然后采取两条路线制备BSCCO带材：(一)以前驱溶胶为旋涂液,在NiO/Ni衬底上制备前驱凝胶膜,并通过干燥和高温热处理条件制备出具有织构特性的BSCCO带材；(二)用sol-gel法制备出的Bi-2212粉末为原料,分别以溶胶、酒精和丙酮作为溶剂,混合后通过搅拌和超声振荡制备BSCOO粉末的悬浊液,在NiO/Ni衬底上通过旋转喷涂法制备BSCCO带材。XRD、SEM和光学显微分析结果表明对于路线(一)衬底的清洗方式能明显影响衬底氧化层的质量和润湿性,热处理条件对于制备具有高质量的BSCCO超导带材非常重要,通过研究已获得具有择优取向的Bi-2201单相和Bi-2212/Bi-2201混合相的带材。路线(二)中丙酮与Bi-2212粉体所形成的前驱液体系比其他两种体系更适合于NiO衬底上超导带材的制备。4.研究了MgB2超导带的制备。通过对熔盐体系和电解电压的研究,确定了实验的电解参数范围。在熔盐电解法制备MgB2带材的实验过程中,首先对于电解设备进行改进,降低了实验难度。然后采用石墨、不锈钢和铜作为阴极衬底,电解制备MgB2超导带。在制备过程中,重点讨论了不同电解温度对MgB2带材制备的影响。得到石墨、不锈钢、铜阴极衬底上合成了MgB2带的最佳电解温度。此外,在不锈钢衬底上初步尝试了脉冲电解,提高了MgB2的超导相纯度。更多还原

【Abstract】 In this dissertation, BSCCO superconducting tapes were prepared by sol-gel method. The experimental technique was studied. In addition, the phase composition and surface morphology were investigated in detail. Furthermore, MgB2 superconducting tapes were prepared on different substrates (cathodes) via molten salts electrochemical technique, and the influence of temperature on MgB2 was investigated. The main content of the dissertation are as follows:1. The influence of different sol-gel techniques on the formation of Bi-2212 phase. In the process to prepare Bi-2212 powders, Metal nitrates were used as starting materials and ethylenediaminetetracetic acid (EDTA) was used as chelating agent. The influence of concentration of precursor solution and the heating devices on Bi-2212 phase were studied, and thereby the phase purity of Bi-2212 was improved. Furthermore, a novel technique named the secondary gel technique was devised and settled, and Bi-2212 powders were obtained through conventional gel technique and secondary gel technique for different sintering time. Results reveal that the optimized sintering times for the conventional and secondary gel technique were 10h and 5h, respectively. Furthermore, the property of sample derived from the secondary gel technique is better than the one derived from the conventional gel technique. That is to say, the secondary gel technique can not only decrease the sintering time to form Bi-2212 phase, but also improve the Bi-2212 phase purity. The reason lies in the improvement of ingredient homogeneity of the secondary gel during the preparation of Bi-2212 powders.2. The mechanism of different gel techniques. According to the experimental results and the recognition of gel models, the models of gels in the experiment were devised. In the meanwhile, structures of the conventional and secondary gel were optimized and energies of them were calculated by the Dmo13 module of Material Studio software. According to the current results, energy of the secondary gel is lower than that of the conventional gel, and thereby the bridging ability of the secondary gel is stronger. The results derived are in accordance with the experimental results.3. The fabrication of BSCCO tapes. First of all, before the fabrication of BSCCO tapes, the treatment of substrates and the heat treatment conditions were investigated. Then, two routes were adopted during the experiment:(1) the precursor sol was spin-coated on NiO/Ni substrates, and BSCCO tapes with texture were prepared through the heat treatment; (2) Bi-2212 powders were used as solute, and sol, acetone and alcohol were used as solvent to prepare suspension via stirring and ultrasonic vibration. Then the suspension was spin-coated on NiO/Ni substrates to prepare precursor tapes, and the BSCCO tapes were derived through the process of heat treatment. The results of XRD, SEM and optical microscopy indicate that for route (1), the treatment of substrates can affect the surface wettability and thickness of NiO buffer layer. In addition, the sintering conditions are crucial to the preparation of tapes with good properties, and BSCCO tapes with Bi-2201 single phase and Bi-2212/Bi-2201 mix phases with preferential orientation have been obtained. For route (2), the suspension consisting of acetone and Bi-2212 powders are favorable to the preparation of BSCCO tapes on NiO/Ni substrates.4. Fabrication of MgB2 superconducting tapes. In the investigation, the system of the molten salts and the electrolytic conditions of the experiment were investigated in detail, and the ranges of electrolysis parameters were fixed. During the experiment, the electrolysis cell was simplified, and the difficulty to control the distance between the two electrodes was decreased. Then, MgB2 films were successfully prepared on graphite, stainless steel and copper cathodes. The influence of electrolytic temperature on the purity and crystallinity of MgB2 was investigated, and the optimized electrolytic temperatures for different cathodes were obtained. In addition, pulse power source was introduced on the stainless steel cathode, and the purity of MgB2 phase was improved.更多还原