Ybco Element Substitution And Oxygen Permeability Of The Surface Modification Research

Firstly, the conception, the category, the research progress, the oxygen permeation mechanics and theoretical calculation formula of oxygen permeation flux of mixed ionic and electronic conductivity membranes (MIEMC) are presented in this thesis. In addition, preparing methods, properties characterizing, application and some problems in development of MIECM are reviewed. The structure character and some oxygen behavior of the high temperature superconductor material YBa₂Cu₃O_7-δ (abbreviation, YBCO) are described too.Iodometric titration was used to determine the oxygen content in Fe substituted YBa₂Cu_3-xFe_xO_7-δ samples. The result shows that the oxygen content increases with the increase of Fe content. With the increasing of Fe content, oxygen desorption content decreases gradually when measured by thermogravimetry (TG) method, which indicates that more oxygen will remains in crystal lattice.YBa₂Cu_3-xFe_xO_7-δ samples have been characterized by X-ray diffraction (XRD) and steady state permeation method (gas chromatography analysis). Combining with the case of oxygen content change we conclude that Fe doping not only effect the crystal lattice structure, but also introduces more oxygen deficiency which results in the increase of oxygen permeation flux at high temperature (T>875 °C ). The oxygen permeation flux of YBa₂Cu₂.7Fe_0.3O_7-δ at 950°C is fifty percent more than that of YBCO. However, when the Fe content is larger, the oxygen permeation flux decreases because Fe begins to substitute Cu(2) site.The crystal lattice structure ofYBa2Cu_1-x,Zn_xO₍7-δ(x=0.1,0.2,0.3)and La_1-xCa_xBa₂Cu₃O_7-δ (x=0.1, 0.3, 0.7) have been analyzed by X-ray diffraction (XRD) and the dependence of oxygen permeation flux on temperature and time has been measured by steady state permeation method. It is found that the oxygen permeation flux decreases with the increase of Zn content due to the reduction of lattice parameter by Zn doping. The oxygen permeation flux of YBa₂Cu_2.9Zn_0.1O_7-δ can reaches 0.6ml.cm^-2.min^-1, but the oxygen permeation flux is not steady under the oxygen chemical potential gradient. Because there coexists La_1-xCa_xBa₂Cu₃O_7-δ and Ba₂Cu₃O_5+x, we speculate that the oxygen permeation flux increase with the increasing Ca is caused by the increases of oxygen vacancies concentration which is resulted in by the substitution of bivalent Ca for trivalent Y.The experiment of surface modification of YBa₂Cu_3-xFe_xO_7-δ indicates that deposition of porous layers of the same material seems to improve the oxygen permeation flux. The...