Research On Dense Diffusion Barrier Limiting Current Oxygen Sensor

There are a variety of combustion furnaces in the metallurgical industries.In order to improve combustion efficiency and reduce environmental pollution,it is necessary to strictly control the air/fuel ratio.Electrochemical oxygen senser technology based on solid electrolyte is an effective analytical method.Solid electrolyte material of La0.8Sr0.2Ga0.8Mg0.2O3-?(LSGM),and mixed conductor materials of La0.8Sr0.2(Ga0.8Mg0.2)1-xCoxO3-?(LSGMCo)and La0.8Sr0.2Ga1-xCoxO3-?(LSGCo)(x=0.1?0.9)were prepared by a high temperature solid-state reaction method.The crystal structure,thermal expansion properties,chemical compatibility,micro-morphology,total electrical conductivity and ionic conductivity were characterized by X-ray diffraction,thermal expansion instrument,scanning electric microscopy(SEM),Van Der Pauw dc four-probe method and ac electrical impedance spectroscopy(EIS)method.The results showed that:(1)The crystal structures of LSGM,LSGMCo and LSGCo were all perovskite.With increasing x,the crystal structure of LSGMCo is transformed from cubic perovskite structure(x=0.1)to single oblique perovskite structure(x=0.3,0.5,0.7 and 0.9),while the crystal structures of LSGCo were single oblique perovskite structure.(2)The thermal expansion coefficient(TEC)of LSGM in the temperature range of 300?1000? was 12.51× 10-6 K-1.The TECs of LSGMCo(16.33×10-6-20.76×10-6K-1)and LSGCo(14.98×10-6?21.58×10-6K-1)were large different from that of LSGM.(3)The conductivities of LSGMCo and LSGCo increased with increasing x,and a transition from semiconductive conduction to metallic conduction was observed with the temperature rise.(4)The LSGMCo and LSGCo ceramics are relatively densification and meet the requirements of the dense diffusion barrier.The dense diffusion barriers of LSGMCr and LSGMFe were prepared by a high temperature diffusion method,respectively.The crystal structure,chemical compatibility,micro-morphology,total electrical conductivity and ionic conductivity were characterized by X-ray diffraction,scanning electric microscopy(SEM),Van Der Pauw dc four-probe method and ac electrical impedance spectroscopy(EIS)method.The results showed that:(1)The crystal structures of LSGMFe were stable perovskite structure.(2)The conductivities of LSGMCr dense diffusion barrier were 0.22 S·cm-1 at 800? and 0.24 S·cm-1 at 850?.The activation energies of conductivity were 0.083 eV at 300?550 ? and 0.151 eV at 550?850?.The conductivity of LSGMFe dense diffusion barrier was as high as 8.73 S·cm-1 at 800?.The activation energies of conductivity were 0.183 eV at 300?550? and 0.338 eV at 550?850?.(3)LSGMCr and LSGMFe dense diffusion barriers with a thickness of about 60 ?m and 40 ?m,respectively,were well attached to the LSGM solid electrolyte.(4)The polarization resistance of the sample decreased with the temperature rise.The oxygen sensors with LSGMCo(x=0.9)and LSGCo(x=0.9)dense diffusion barrier,respectively,were prepared by the Pt sintered-paste method.The influences of temperature and oxygen content on sensing performance were investigated.The results showed that the limiting current oxygen sensors exhibited good limiting current plateaus in a wide range of oxygen content and temperature.IL depended linearly on the oxygen contents,while logIL depended linearly on 1000/T.The limiting current oxygen sensors with LSGMCr and LSGMFe dense diffusion barrier,respectively,prepared by high temperature diffusion method exhibited good limiting current plateaus in the temperature range of 700?850 ? and 800?850 ?,in the oxygen content range of 0.4 mol%?8.4 mol%and 0.1 mol%?4.9 mol%,respectively.IL depended well linearly on the oxygen contents.