Dense Diffusion Barrier Limiting Current Oxygen Sensor Based On LSGM Solid Electrolyte

Dense diffusion barrier limiting current oxygen sensor based on solid electrolyte is a novel oxygen sensor,which plays a significant role and extensive application in the industrial boils in Metallurgical and Petrochemical industry and automobile engine system to control the Air/Fuel ratio in the combustion process.La0.8Sr0.2(Ga0.8Mg0.2)1-xCrxO3-?(LSGMC,x=0.1,0.3,0.5,0.7,0.9)and La0.8Sr0.2(Ga1-xCox)0.8Mg0.2O3-?(LSGCM)mixed oxide/electron conductor and La0.8Sr0.2Ga0.8Mg0.2O3-?(LSGM)solid electrolyte were synthesized by high-temperature solid-state reaction method.The crystal structure,chemical compatibility,thermal expansion properties,micro-morphology,total conductivity,ion conductivity,and density of LSGM and LSGMC 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,and Archimedes method,respectively.The study not only focused in matching physical and chemical compatibility of LSGM and LSGMC,but also in different manufactured method of oxygen sensor with LSGM and LSGMC materials.The oxygen sensor with LSGMC(x=0.5,0.7),LSGM,and LSGCM were fabricated by Pt sintered-paste method,the output performance of oxygen sensor was discussed.The oxygen sensor with LSGMC(x=0.7)was manufactured by co-pressed and co-sintered method,the output performance of oxygen sensor was discussed.The oxygen sensor with LSGM as substrate(or cladding layer),LSGMC(x=0.7)as cladding layer(or substrate)were prepared,the effect of microstructure,element composition and bonding properties by laser cladding process and the comparison of processing parameters were investigated.The results are as follows:(1)The XRD results indicate that both the LSGM and LSGMC have the cubic perovskite structure.The total conductivity of LSGMC(x=0-0.9)grows with the rising temperature and the doping concentration in air,all the total conductivity values are higher than 0.011 S/cm over 500 ?.The conductivity with ac method and dc method of LSGM shows closed values.Both of the LSGM and LSGMC(x=0.5,0.7)are dense body,the relative density and volume density of LSGM,LSGMC(x=0.5)and LSGMC(x=0.7)are 97.6%,96.4%and 95.7%,6.49 g/cm3,5.01 g/cm3 and 5.12 g/cm3,respectively.LSGM and LSGMC have the similar average linear thermal expansion coefficient,the average linear thermal expansion coefficient of them in the room temperature-1000? are 11.58×10-6/K?11.37×10-6/K and 11.76×10-6/K,respectively.(2)The dense diffusion barrier limiting current oxygen sensor fabricated by Pt sintered-paste method show good performance,the oxygen detecting range,operation temperature and operation voltage.are 1.92%-21%,800 ?-850 ? and 1.26 V-1.34 V,respectively.Limiting current is proportional to oxygen concentration,the sensibility of oxygen sensor is highest at 850 ?,which is 5.48 mA.The response time of oxygen sensor decreases with rising temperature,the response time is from 0.74 s to 2.58 s in 800 ?-850? and 1.92%-21%.The polarization resistance declines with the increasing temperature and rising temperature from 39.73 ? to 13.77 ? in 800 ?-850 ?and 1.92%-21%.The oxygen sensor with LSGM diffusion barrier shows a great output performance,the oxygen detecting range,operation temperature and operation voltage are 1.92%-21%,0.67 V-0.98 V and 700 ?-850 ?.Limiting current is proportional to oxygen concentration,the sensibility of oxygen sensor is highest at 850 ?,which is 2.20 mA.The response time of sensor decreases with rising temperature,the response time is from 0.35 s to 1.37s in 800?-850 ? and 1.92%-21%.The oxygen sensor with LSGCM diffusion barrier shows a good output performance,the oxygen detecting range,operation temperature and operation voltage are 0%-3.31%,0.96 V-1.35 V and 750 ?-850 ?.The relationship between limiting current and oxygen concentration is linear,where the slope increases with the temperature.The polarization resistance declines with the increasing oxygen concentration from 37.47 ? to 16.21 ? at 850 ?.(3)The dense diffusion barrier limiting current oxygen sensor fabricated by co-pressed and co-sintered method show good performance,the measured oxygen concentration is 1.92%-21%at 800 ?,the limiting current platform is occurred at 600 ?-850?;The relationship between limiting current and oxygen concentration is linear.(4)Expositing LSGM on LSGMC(x=0.7)substrate shows a good metallurgical bonding between LSGM cladding layer and LSGMC(x=0.7)substrate.The suitable optimal process parameters are:29W(laser output power),0.3mm(spot diameter),and 0.5mm/s(scanning speed),respectively.The low pulse duration,the high scanning speed and the low pulse frequency are suggested in order to avoid the formation of crack.