DEVELOPMENT AND TESTING OF A SOLID-STATE CO2 GAS SENSOR FOR USE IN REDUCED-PRESSURE ENVIRONMENTS

A planetary instrument called the thermal and evolved gas analyzer (T/ EGA) is currently being developed, consisting of a combined differenti al scanning calorimeter (DSC) and evolved gas analyzer (EGA) to subjec t regolith samples to a temperature ramp and monitor gas-evolution eve nts. This paper reports the development and testing of a miniature car bon dioxide (CO2) solid-state electrochemical gas sensor (SSEGS) for u se in the EGA portion of the instrument. A miniature potentiometric CO 2 sensor has been developed that is configured in a planar geometry. T he sensor uses solid-state reference and measuring electrodes co-locat ed on one side of a beta alumina electrolyte substrate, and a thick-fi lm platinum heater on the opposite side. Experiments are performed und er reduced-pressure conditions to characterize the sensor response in terms of heater power, sensor temperature, total pressure, and gas-com position parameters. The sensor response to carbon dioxide (CO2) is fo und to be a complex function of these variables, and to act through tw o separate and independent mechanisms to influence the sensor output. The sensor oxygen sensitivity is also measured in the presence of CO2. A sensor temperature of 530 degrees C is found to result in an oxygen -response slope coefficient of zero. Operation of the sensor at this t emperature results in selective carbon dioxide response, and an output that is independent of oxygen partial pressure.