The Fabrication Of Bi-based Superconducting Tapes By Sol-gel Method And Process Optimization

In this dissertation, BSCCO superconducting tapes were prepared by Sol-Gel method. In addition, the phase influence about differernt sol-gel techniques, NiO/Ni substrate, drying condition of the pre-sol are all studied and optimized. 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. 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.2. The preparation of BSCCO tapes. The texture character of Ni substrates, NiO sintering process and surface cleaning process were optimized. The results indicated that NiO/Ni substrate sintered in vacuum got better texture character, and NiO which through sintering optimizing have better wettability for pre-sol. Then, two routes were adopted during the experiment:(1) 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 pre-sor tapes, and the BSCCO tapes were derived through the process of heating treatment. (2) the pre-sol was spin-coated on NiO/Ni substrates, and BSCCO tapes with texture were prepared through the heat treatment; The results of XRD, SEM and optical microscopy indicate that indicate that for route (1), the suspension consisting of acetone and Bi-2212 powders are favorable to the preparation of BSCCO tapes on NiO/Ni substrates. For route (2), 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.3. The reason why the Bi-2212 single phase was not gotten. The probable reason was that the component became non-homogeneous when the pre-sol was spin-coated on NiO/Ni substrate. Through the investigation of pre-sol and its drying condition, the process of metal ions segregation, the reason of non-homogeneous component was confirmed and the experimental reproducibility is great.