Research On Preparation Of Composite Solid Electrolytes In Planar SO₂ Sensor

An electrochemical gas sensor based on a solid-state bi-electrolyte couple of YSZ and NASICON doesn't need to measure the partial pressure of oxygen and both electrodes are exposed to the same test gas eliminating the need for isolating the electrode compartments that will simplify the fabrication of sensor. Reportedly, a solid-state bi-electrolyte couple of CO2 sensor of this kind had been successfully fabricated and SO2 sensor of this kind had been preliminarily studied. As a foundation of these work referred to above, this dissertation had carried out an intensive study of the preparation process of a solid-state bi-electrolyte couple used in planar SO2 sensor. Detailed work is as following.Solid electrolyte natrium super ionic conductor (NASICON) was prepared by the polycondensation of silica sol and polyvinyl alcohol via a sol–gel route which were then compared with the Nasicon powders prepared by the hydrolysis-polycondensation of tetraethyl orthosilicate. It was found that the higher purity of phase and 80～100 nm of homogenous round grains could be obtained by the method of silica sol and polyvinyl alcohol. This provided insights into the preparation of gas sensors with better performance in the future.To prepare the composite electrolytes, NASICON powders were coated on one side of YSZ solid electrolyte. Four different ways had been tried to make composite electrolytes. It had drawn the conclusion that mixtures including NASICON powders, EC and alcohol with screen printing method were coated on YSZ sheet and the coatings were sintered at a high temperature. This method could get a dense structure, low gap and good combined with the substrate.Composite solid electrolytes were prepared by screen printing method and sintered at three different temperatures. The conclusions were that coatings prepared under sealing situation and sintered at 1200℃for 3 hours had perfect crystals and contained more Na content than other sintering temperatures. The ionic electrical resistivity of composite solid electrolytes was tested by electrochemical impedance spectroscopy and electrical properties of electrolytes working under different temperatures had been analyzed. Conclusions were that the conductivity working at the temperature of 600℃was 4.6×10-4 S/cm. The results were much lower as that after sintering at a high temperature, the contents of Nasicon had been changed and its structures of course were changed. But its number had reached the order of magnitude of 10-4, the electrolyte working at the temperature of 600℃could be used in the preparation of sensors.