Development of Solid Electrolyte Sensors Operative at Ordinary Temperature

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This project has aimed at developing new solid state gas sensors operative at ordinary temperature using solid electrolyte, i.e., <H_2> and CO sensor using proton conductors and oxygen sensor using La <F_3> . The results obtained are as follows.1. Proton conductor sensor: Sensor elements were essentially based on the electrochemical cell (Pt black !proton conductor!Pt black) in which antimonic acid was mainly used as proton conductor. The sensors developed in this project were found to be sensitive to small amounts of <H_2> and CO in air at room temperature and could be classified in the following three categories according to the out-put signals used.(1) Potentiometric sensor; An electromotive force ultilized as sensor signal of the potentiometric sensor was proportional to a logarithum of <H_2> and CO concentration in air and thus this type of sensor was fit for detecting sample gases in a wide-ranging concentration.(2) Amperometric sensor; A short circuit current ultilized as sensor … More signal of the amperometric sensor was in direct proportion to the sample gas concentration under the constant humidity. The amperometric sensor had an advantage over potentiometric one in precise measurement of gas concentration.(3) Four-probe type sensor; Under the short circuit condition, the potential difference which could be detected by Ag probes inserted in the proton conductor was produced in the proton conductor by the contact of the sensing Pt electrode with the sample gas. The potential difference was a linear function of <H_2> concentration independent of humidity in an ambient atmosphere.2. Lanthanum fluoride oxygen sensor; The sensor composed the electrochemical cell (Sn,Sn <F_2> !La <F_3> !Pt, <O_2> )and an electromotive force of the cell was found to change in proportion to a logarithum of oxygen partial pressure even at room temperature.(1) Single crystal sensor; While the newly fabricated elements showed very slow response, exposure to water vapor at 150 ゜C followed by the repetition of response to oxygen reduced the 90% response time to about 2 min at 25 ゜C. This sensor could also respond sensitively to dissolved oxygen in water.(2) Spputered film sensor; By using the sputtered La <F_3> film ( 5 <micro> m thick), the 90% respnse time could be decreased to ca. 30 sec after water vapor treatment. Less