Development Of Poisonious Gas Sensors Based On NASICON Solid Electrolyte

With the development of industry, compression of urban mass and sudden growth of coal and oil fuel, the atmospheric pollution procreant seriously threatens the existence and development of mankind. The principal pollutant of atmospheric pollution are the poisonous gases such as NOx, SOx, H2S, NH3, Cl2 and toluene. So that it is very important to develop sensors which could monitor and detect these poisonous gases. For this paper, the mixed potential type NASICON solid electrolyte gas sensors are developed in connection with these gases.With the synthesis and characterization of the NASICON solid electrolyte, six different gas sensors were fabricated with NASICON solid electrolyte as the substrate conducting layer and different metal oxides or compound metal oxides as the sensing electrode.1. The NASICON materials were synthesized by two kinds of sol-gel methods with different original materials. The synthesized NASICON materials were characterized by XRD, IR, Raman and XPS methods to investigated the crystalline structure, component, crystalline size and proportion of the element.(1) The optimal calcining temperature was 900°C for the NASICON material which was synthesized by the first sol-gel method with ZrOCl2, NaNO3, Si(OC2H5)4, (NH4)2HPO4 as the precursors. The monocline structure was found to be fit for the synthesized material and the mean crystalline size was 10-22 nm.(2) The optimal sintering temperature was 1100°C for the NASICON material which was synthesized by the second sol-gel method with C6H15O4P, Zr(OC4H9)4, Si(OC2H5)4, C2H5NaO as the precursors. Also the monocline structure was found to be fit for the synthesized material. The mean crystalline size was 28 nm.2. The NASICON solid electrolyte H2S gas sensor was fabricated with 5 wt% Pr6O11 doped SnO2 as the sensing electrode. And this type of sensor exhibited well sensing properties to H2S.The largest sensitivity (slope) for this sensor occurred at the operating temperature of 300°C and was 74 mV/decade. Also rapid response-recovery rate was found for this sensor, the response and recovery time of the sensor to 5, 20, 50 ppm H2S was 8, 6, 4 s and 12, 18, 30 s respectively. The sensor exhibited well selectivity and resistance against water vapor.3. The NASICON solid electrolyte Cl2 gas sensor was fabricated with CaMg3(SiO3)4 doped CdS as the sensing material. And this sensor showed well sensing characteristics to chlorine.Well sensing characteristics was found for the sensor which was calcined at 600°C. At 200°C, the largest sensitivity (slope) was found and was -392 mV/decade to 1-10 ppm chlorine. The sensor exhibited rapid response recovery rate, the response and recovery time to 5 ppm chlorine was 20 and 37 s respectively. And the sensor showed well selectivity and resistance against water vapor.4. The NASICON solid electrolyte SO2 gas sensor which exhibited well sensing properties to sulfur dioxide was fabricated with 5 wt% V2O5 doped TiO2 as the sensing electrode.The EMF value of the sensor which was sintered at 600°C showed well linear relationship with the logarithm of the concentration for sulfur dioxide. And the largest sensitivity (slope) occurred at the operating temperature of 300°C and was -78 mV/decade. And rapid response recovery rate was found for this type of sensor. The response and recovery time to 1-50 ppm SO2 was 25-10 and 30-40 s respectively. Also the sensor exhibited well selectivity to sulfur dioxide.5. The NASICON solid electrolyte NH3 gas sensor was fabricated with 10 wt% C doped Cr2O3 as the sensing electrode respectively. And the sensor showed well sensing properties to ammonia gas.The largest sensitivity (slope) occurred at 300°C and was -93 mV/decade. The response and recovery time to 50, 500 ppm ammonia was 35, 30 s and 60, 65 s respectively. Also well selectivity to NH3 was found for this sensor.6. Three different NASICON solid electrode nitrogen dioxide sensors were fabricated with NASICON as the conducting layer. The sensivitity of the sensor which was fabricated with NiO+Au as the sensing electrode as the electrode was large. The variety of the EMF value for the sensor to 50 ppm nitrogen dioxide was 159 mV. Thus the combined action of NiO and Au could account for the seriously increasing of the sensing characteristics. So that the selection of the sensing materials was of vital importance for the gas sensors with well characteristics. The response/recovery characteristics of the sensor is needed to be improved further.7. A kind of double functional incorporated NH3-C7H8 gas sensor was designed and fabricated with NASICON as the conducting layer and two kind of metal oxides (C-Cr2O3, ZnO-TiO2) as the sensing electrodes.This new type of sensor exhibited well sensing properties to ammonia and toluene. The EMF value of the sensor showed well linear relationship with the logarithm of NH3 (50-500 ppm) and C7H8 (5-50 ppm) concentration. The sensitivity of the sensor to ammonia and toluene was -91 and -60 mV/decade at 250-400°C. Also this type of sensor exhibited rapid response-recovery rate and well selectivity characteristic. This type of double functional gas sensor was the aggregation of two single gas sensors. Only one heater was public used for the two sensors. And the thermal efficiency was improved too.8. The mixed potential theory was found to be fit for the sensing mechanism of the six different gas sensors.