Development of carbon dioxide sensor using semiconductive oxide

Our efforts have been devoted to the development of a compact, inexpensive, durable, and reliable CO2 sensor by using semiconductive metal oxide, sinc e the other types of CO2 detection methods such as infrared or solid electr olyte methods are expensive or unreliable. Although it was well known that the conductivity of SnO2 was not altered by the change in CO2 concentration , we have first found that the addition of lanthanum onto SnO2 resulted in the induction of CO2-detecting ability. The addition of yttrium onto the La /SnO2 element much improved the durability of the sensor. Mounting of a fil ter with Pt-supporting silica gel over the sensor decreased the inhibitory effects of alcohol and water in air. The interference by the temperature ch ange was diminished by introduction of a disk with a pinhole between the se nsor and the filter. The combination of these improvements with newly devel oped computer software for controlling the sensor enabled us to commerciali ze the CO2 sensor systems in 1997.