Gas Sensors Based On Solid Electrolyte For Metallurgical Process

The traditional metallurgical processes such as sintering,ironmaking,coking and the newly developed hydrogen metallurgical process produce a large amount of industrial gases.The accurate detection and analysis of these gases components is of great significance to control and optimize the production process,ensure production safety and prevent environmental pollution.With the gradual upgrading of digitization and intelligence of metallurgical industry,industrial sensors which can automatically collect and process production status information will play an important role.Solid electrolyte based gas sensor exhibits characteristics such as simple structure,high detection sensitivity,high temperature resistance,on-line and continuous detection,which is very suitable for gas composition analysis in metallurgical process.Solid electrolyte based H₂,NO_xand NH₃sensors were designed and prepared respectively for hydrogen leakage detection and SCR denitration process control in metallurgical process.The performance of the materials was systematically characterized,and the response characteristics and mechanism of the sensors were studied,which laid a foundation for practical application.La_1.9Ca_0.1Ce₂O₇proton conductor was synthesized by solid-state reaction,which shows good sintering performance and high conductivity.The impedancemetric H₂sensor was fabricated by impregnation technique and in situ preparation of Sn O₂sensing electrode in porous layer using La_1.9Ca_0.1Ce₂O₇as electrolyte.The composition and morphology of solid electrolyte and sensing electrode were characterized,and the response performance of the sensor was tested at 550～700℃.Results show that in200～1000 ppm H₂concentration range,the response values(|Z|_base-|Z|_gas)/|Z|_baseexihibit a linear relation with the H₂concentration.The detection sensitivity of the sensor reached the maximum value of 0.003 ppm^-1at 650℃.The DRT method was used to analyze the impedance spectra of the sensor at different H₂concentrations.It is found that the P5peak related to gas diffusion at the three-phase interface in the DRT diagram is the highest,and increases with the increase of H₂concentration,which indicates that the diffusion process is the control step of the sensor.Non-self-heating and self-heating NO_xsensor were prepared by using Cr₂O₃as sensing electrode and 3YSZ as solid electrolyte.The sensitivity of the sensor to NO_xwas systematically studied.When the calcination temperature of the sensing electrode is1200℃and the test temperature is 500℃,the non-self-heating sensor shows good sensing performance.The self-heating sensor was prepared according to best parameters of the non-self-heating sensor.The optimal heating voltage（6.1 V）and the optimal working frequency（1 Hz）of the self-heating sensor were determined.The sensor can not only detect the respective content of NO and NO₂,but also the total amount of NO_x,and shows excellent reproducibility,stability and anti-interference performance,which lays a foundation for the commercial application of the sensor.The perovskite La_0.75Sr_0.25Mn O_3-δ,La_0.75Sr_0.25Cr O_3-δand La_0.75Sr_0.25Co O_3-δmaterials doped with 5 mol%Ag at A and B positions were prepared by impregnation method,respectively.The impedancemetric NO₂sensor was prepared by using the perovskite materials as sensing electrode and YSZ as electrolyte.The influence of the composition of sensing materials and Ag doping position on the sensor performance was studied.The results show that La_0.75Sr_0.25Co O_3-δ（0.05Ag-LSCo O）with Ag doped at the A position shows excellent sensitivity.The sensor with 0.05Ag-LSCo O-SE sintered at 900℃shows good response performance at 450～550℃,and exhibits the best sensing performance at500℃.The response process of sensor was analyzed by using DRT technology,the resistance to the diffusion process is found to decrease significantly with the increasing temperature.Cu V₂O₆sensing material was synthesized by sol-gel method.A mixed potential NH₃sensor was prepared by introducing Cu V₂O₆sensing material into porous layer of apatite La₁₀Si_5.5Al_0.5O_27-δelectrolyte by screen printing method.The sensor exhibits excellent response and recovery performance to NH₃in the concentration range of 25～300 ppm at350～500℃.The sensor shows the highest sensitivity(-83.4 m V·decade^-1)and best response performance at 400℃.However,the sensor exhibits interference response to NO_xgas.The Cu V₂O₆/Ag composite is used as the sensing electrode,which effectively reduces the interference of NO_xto NH₃.The interference caused by 150 ppm NO₂or NO to 100 ppm NH₃is reduced from 58%and 65%to 22%and 14%.TPD analysis indicates that Ag inhibited the adsorption of NO₂on the sensing electrode,which is the reason for the enhancement of the selectivity.The polarization curve shows that the response of the sensor follows the mixed potential mechanism.Figure 96;Table 8;Reference 175...