Preparation And Performances Of Perovskite Structure Of Mixed Ionic-electronic Conducting Oxygen Separation Membrane Materials

The mixed-conducting perovskite-type materials have a wide range of technicalapplication in fuel cells, sensors and oxygen preparation and so on. Specially, it showsconsiderable oxygen permeation at high temperature, with a theoretical selectivity of100%,which draws a lot of attention of its potential application on producing pure oxygen and ascathode materials for SOFC. For practical applications, the mixed conducting oxygenpermeable membranes need high oxygen permeability as well as good stability to withstandharsh conditions. Presently, research on oxygen permeable membrane materials mainlyfocused on mixed-conducting perovskite-type oxides. Despite a lot of achievements havebeen made, there are still some problems to be solved, such as the poor stability ofCo-based materials, even having high oxygen permeability. Thus, in practical applications,improving the stability and oxygen permeability of permeable membrane materials isurgent. In the dissertation, by doping Sr, Fe at site A and B respectively, LaGaO3-basedoxygen ionic conductor materials, which show mixed electron conductivity, were prepared.It was found that the materials have a low coefficient of thermal expansion and highstability. By now, there has lack of a detailed study about their performance, and we chooseLa1-xSrxGa0.6Fe0.4O3-δ(x=0.1,0.3,0.5) materials to investigate their structure andproperties.In the experimental, La1-xSrxGa0.6Fe0.4O3-δpowders were prepared by the solid statemethod and glycine-nitrate process using La2O3、SrCO3、Ga2O3、Fe2O3、La(NO3)3·9H2O、Sr (NO3)2·3H2O、Ga (NO3)3·3H2O、Fe (NO3)3·9H2O、C2H5NO2as main raw materials withsuitable organic binder. Effects of the sintering temperature on the microstructure, theelectrical conductivity and the thermal expansion coefficient of the sintered body weresystemically investigated. The iron valence state changes were tested by iodine titrationmethod and the oxygen permeability of material were tested by the device of homemade.The main results of the full text are as follows:La1-xSrxGa0.6Fe0.4O3-δpowders were prepared by the solid state method usingcorresponding oxide as raw materials. the powders were sintered at different temperatures.Electrical conductivity and thermal expansion coefficient of the sinteredLa1-xSrxGa0.6Fe0.4O3-δsamples were tested. The highest conductivity was obtained forsamples with doping amount of x=0.3at sintering temperature for1450℃, and an average thermal expansion coefficient of11.25×10-6K-1was achieved with doping amount ofx=0.1at test temperature of400-800℃.Fine La1-xSrxGa0.6Fe0.4O3-δpowders with perovskite structure were prepared by theGNP method using corresponding nitrates as raw materials and calcining at700℃for5h.Sintered La1-xSrxGa0.6Fe0.4O3-δsamples with different doping amount, have electricalconductivity of4.09S·cm-1,4.42S·cm-1and4.33·cm-1for x=0.1,0.2and0.3, respectively, attest temperature of800℃, and the average thermal expansion coefficient at400-800℃are10.74×10-6K-1,11.12×10-6K-1and11.55×10-6K-1, respectively.The δ values of the non-stoichiometry and the average valence of Fe in theLa1-xSrxGa0.6Fe0.4O3-δ（x=0.1，0.3，0.5） materials were investigated by iodine titrationmethod. The results showed that the average valence of Fe reaches3.17for x=0.3, and the δvalues of the non-stoichiometry with La1-xSrxGa0.6Fe0.4O3-δis in the range of0.0356-0.228,at test temperature between600-900℃.The oxygen permeability of La0.7Sr0.3Ga0.6Fe0.4O3-δmembranes synthesized by both thesolid-phase method and the GNP method, increases with test temperature. Besides, underthe same test conditions, the oxygen permeability of La0.7Sr0.3Ga0.6Fe0.4O3-δmembranesynthesized by the GNP method is higher than that synthesized by the solid phase method.the permeability of La0.7Sr0.3Ga0.6Fe0.4O3-δmembrane is mainly controlled by the surfaceoxygen exchange. With the treatment of H2, the oxygen permeability ofLa0.7Sr0.3Ga0.6Fe0.4O3-δmembrane is significantly improved.