Calibration Design And Structural Modification Of Current Ammonia Sensor Based On YSZ

The number of motor vehicles in China is increasing year by year,and NOx emissions are becoming more and more prominent,and emission standards are becoming stricter.As an important component,NH₃ sensors are required to monitor the NH₃ concentration downstream of the SCR system in real time to prevent secondary pollution caused by NH₃ leakage.At present,domestic research on NH₃ sensors is still at the experimental stage,limited by signal stability,durability and selectivity,and other factors,the currently researched NH₃ sensors in China have not been put into use.Considering several types of NH₃ sensors,the amperometric NH₃ sensor developed from the amperometric NOx sensor has more prospects for development,so this paper selects the amperometric NH₃ sensor for research.In this paper,a calibration and detection system for the amperometric NH₃ sensor is built to simulate the working atmosphere and to collect the response signal in real time.In order to avoid the deactivation of NH₃-sensitive materials under the co-sintering temperature,we design a step-by-step NH₃ sensor chip,which is coated with ammonia-sensitive catalytic slurry after the first sintering and sintered twice with glass-bonded slurry,and the sensor chip measures ammonia content based on the limit current principle,which can achieve high measurement accuracy and the unity of compact structure.The process optimization tests were carried out for the designed new NH₃sensor chip.The organic solvent system used for the cast slurry needs to be optimized because of its toxicity,while the glass bonding slurry used for the stepwise sintering of the sensor chip needs to be tested for the optimal ratio.The test results showed that the solvent system of 50%ethanol+50%cyclohexanone has suitable viscosity and moderate drying time,and can replace the original solvent system of methylbenzene;the best bonding performance of the glass bonding paste is achieved when the ratio of zirconia powder to glass powder is about 1.0:9.0.The performance of the amperometric NH₃ sensor with GdVO₄ as the sensitive electrode was investigated.The results show that at the secondary sintering temperature of the step-formed NH₃ sensor,the microstructure of GdVO₄ sensitive electrode is loose and porous with a large specific surface area,and the sensitivity can reach 0.30638μA/ppm at the working temperature of 700℃,while the selectivity of the sensor is good.When mixed with different contents of YSZ powder,the microscopic morphology showed that the crystals gradually developed toward agglomeration until agglomeration,and the control powder high-temperature sintering experiment showed that the quality of sensitive electrode powder did not change,i.e.,the sensitive electrode powder did not sublimate at high temperature,which combined with the change of sensitivity of the sensor led to the conclusion that the crystal growth agglomeration of sensitive material at high temperature was the main reason for the loss of activity of NH₃ sensitive material.