| In this thesis, a NASICON solid-electrolyte material CO2 gas sensor with tube-type is introduced. NASICON is coated reelingly on a hollow Al2O3 ceramics tube and sintered at the high temperature, then a base-layer is formed. The sensitive and contact electrode are prepared on each side of the exterior, respectively. A carbonate mixture BaCO3-Li2CO3 (1:1, in the ratio of mol) is formed as the auxiliary phase by melting and quenching method. In order to heat the element, a small heater coil penetrates through the tube.In the experiment, NASICON is synthesized by sol-gel technique. The raw materials are ZrOCl2·8H2O,NaNO3,Si(OC2H5)4,(NH4)2HPO4,C2H5OH and NH3·H2O, as well as HNO3 is used as the resolving solution. The material has been analyzed by XRD, IR, RAMAN, XPS and resistance analysis. From the XRD of the samples sintered at different temperature, it is concluded that the sample sintered at 900℃ has already been monoclinic structure and the crystal is tending to perfection. The infrared ray absorption peaks of the samples are simple, which are different from that of the mul-polymer phosphate, it is known that the phase structure is pure. Observing the XPS charts, we know that each element has a single electrovalence. The calculated molecular formula is similar to the theoretic Na3Zr2Si2PO12. Na+ moves slowly and the resistance of the material is very high when the temperature is under 250℃, once the temperature is higher than 300℃, Na+ moves quickly and the resistance decreases obviously, which is shown in the resistance analysis.Several structures of the NASICON solid-electrolyte CO2 sensors are introduced. The tube-type sensor with inner heater is designed based on the plate-type and the tube combustion-type sensor. Fabrication technics and process are described by figures.The output electromotive force (EMF) of the sensor is chosen as the performance parameter. Firstly, the essential capabilities of tube-type element are tested. These capabilities include the relation of EMF and the heating current (temperature), the sensitivity of the element to CO2, the response and recovery time, the influence of humidity, the property of resistance to other gases and the stability in 30 days. It is concluded that the absolute values of EMF increase with the augment of the heating current and the values are linear to the square of the current. In the CO2 volumetric ratio concentration range from 200 to 2000×10-6, the linear of EMF to the logarithm of concentration is excellent, as fits well with the Nernst equation. With the increase of the current, the sensitivity of element increases. At 180mA current, the sensitivity is 55mV/decade. This current is used as the operate current. The response and recovery properties change with the concentration. Higher is the concentration, shorter are the response and recovery time, and the 65% response and recovery time from the atmosphere to 1000×10-6 are 9.6s and 55s, respectively. EMFs move with the influence of humidity, but the sensitivity hardly changes. The property of resistance to CH4,CO,H2S,H2,C2H5OH is measured. In the co-existing gases range from 200 to 4000×10-6, above five gases affect the element differently, especially CH4,H2S,C2H5OH. In 30 days, the EMF values of the same element are tested every five days. It is shown that EMFs fluctuate and the change in the first 5 days is the largest. To 1000×10-6 CO2, the most change of EMF is 8.8mV in 25 days, which is within 10%. At the same time, the dispersion between 500×10-6 and 1000×10-6 fluctuates 3.8mV.The thermal field of tube-type element is different from that of the plate-type element because of their different heating mode. The former is symmetrical and the later is asymmetrical, relatively. Especially, the tube-type element is more ascendant than the plate-type element in the sensitivity, resistance to humidity and stability.The element's performance depends on the thickness of NASICON base-layer, as well as the sintering temperature and time. It is presumed that temperature has ef...
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