Preparation And Properties Of SrCe_0.9Yb_0.1O_3-α Proton Conductor Ceramics

With the approaching of energy crisis,it is urgent to develop and utilize hydrogen as clean energy.As a kind of hydrogen-related materials,proton conductor electrolyte ceramics play an important role in the production and utilization of hydrogen.Proton conductor electrolyte ceramics can be used in solid fuel cells,hydrogen sensors,separation and purification of hydrogen and ammonia synthesis at atmospheric pressure.In this paper,10%Yb doped SrCe O₃electrolyte with high proton conductivity and good high temperature stability was taken as the research object.The powder was prepared by solid phase synthesis method,and the SrCe_0.9Yb_0.1O_3-αceramics were obtained by dry pressing sintering molding method.The effects of molding pressure,sintering temperature and holding time on the phase composition and microstructure of SrCe_0.9Yb_0.1O_3-αceramics were studied by X-ray diffraction and scanning electron microscopy.Meanwhile,the effects of sintering temperature on the stability,hydrogen permeability flux and electrical conductivity of SrCe_0.9Yb_0.1O_3-αceramics were studied.The specific research results are as follows:（1）The effects of pressing pressure,sintering temperature and holding time on the phase composition and microstructure of the ceramics were studied.The results showed that when the pressing pressure was 10MPa,the sintering temperature was 1475℃,and the holding time was6h,the phase composition of the ceramics was a single perovskite structure,the microstructure of the ceramics was compact and smooth without holes,the grain boundary was clear,and there was no microcrack on the grain surface.The radial shrinkage rate and average grain size of SrCe_0.9Yb_0.1O_3-αceramics increase with the increase of sintering temperature.The apparent porosity and density of ceramics at different sintering temperatures were measured by Archimedes drainage method.With the increase of sintering temperature,the apparent porosity of ceramics showed a decreasing trend.According to the classical ceramic growth kinetics equation,the grain growth index of SrCe_0.9Yb_0.1O_3-αceramics was measured to be 4,and the activation energy of grain growth was about 61KJ/mol,which indicated that the average grain size growth of ceramics was mainly controlled by grain boundary diffusion during sintering under these conditions,and the grain growth was easier to overcome the potential barrier due to the low grain growth.（2）The effects of boiling water and supercritical environment（25MPa/650℃）on the phase composition and microstructure of SrCe_0.9Yb_0.1O_3-αceramics were studied.The results show that,when the sintering temperature of SrCe_0.9Yb_0.1O_3-αceramics is 1400℃,the pore structure on the surface of the ceramics is slightly increased after being treated with boiling water.However,the surface of the ceramic sintered at 1450℃has little change.After the ceramics sintered at 1500℃are treated with boiling water,the microcracks on the surface extend obviously.This is mainly because the specific surface area of the sintered dense ceramic body decreases in reaction with H₂O,inhibiting the reaction between SrCe_0.9Yb_0.1O_3-αand H₂O,so the ceramics has certain stability in high temperature aqueous atmosphere.However,there is no obvious change in the section morphology of the ceramics at three sintering temperatures.SrCe_0.9Yb_0.1O_3-αceramics sintered at 1400℃and 1450℃still maintain a single perovskite structure after being treated with boiling water for 24h.This indicates that it has certain stability in boiling water.Exposment experiments in supercritical environment showed that the sintered ceramics could not exist stably in this environment.After 12h,all the sintered ceramics were transformed into SrCO₃,Ce O₂and Yb₂O₃.（3）The electrical resistance and conductivity of SrCe_0.9Yb_0.1O_3-αceramics sintered at different temperatures were measured and analyzed.The results show that the conductivity of SrCe_0.9Yb_0.1O_3-αceramics sintered at different temperatures is as follows:σ（wet hydrogen）>σ（dry hydrogen）>σ（dry air）>σ（wet air）in different atmospheres at the test temperature of700-900℃.The conductivity of SrCe_0.9Yb_0.1O_3-αceramics in different atmospheres is the same,only the difference of conductivity exists.The conductivity of the ceramics sintered at 1475℃is the highest in the wet hydrogen at 900℃,reaching 0.0065S·cm^-1.The conductivity of ceramics sintered at different temperatures in the same test atmosphere isσ（1475℃）>σ（1400℃）>σ（1450℃）from high to low.The conductivity of ceramics sintered at1400℃has little difference with that sintered at 1475℃.