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| NIRE Annual Report | 
| 1998 |
Development of an Opto-chemical Gas Sensor using
Safety Monitoring and Control Division |
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Objectives
This study aims to develop new type CO gas detector that is an opto-chemical gas sensor using fine metallic-oxide film. Although CO gas detector of element type is used, this type is often influenced by electric noise. Moreover, this type consume much electric quantity and the detection precision of this type is no good. Therefor, we studied the new type CO gas detector using optical measurement and chemical reaction. We reported the light irradiated from a p-type semiconductor metallic-oxide film is changed by CO gas or reduction gas atmosphere and the light transmission factors depend on the gas concentration.
Apparatus and procedure
Fig.1 shows optical measurement system used in our experiment. First, a metallic-oxide film plate set in a test quartz cell, and heat by a heater until an arbitrary temperature. Then, after air was blown to the cell for about 1 hour, CO gas of 1 vol.% is blown for 30 min. This cycles are repeated in each experiment. A halogen lamp is used as a light source and an optical power meter and an optical spectrum analyzer is used for measurement of transmission light intensity.
Results
Table 1 shows an example of measured result for the difference in light transmission factor depending on types of metallic-oxide film. For the NiO film, a oxide film of 6 vol.% solution exhibited greater light intensity change than that of 3 vol.% solution. However, the change ratios were approximately same. NiCo2O4 film indicated the highest change of about 50nW in oxide films tested. This value is about three times that of NiO, which is a typical p-type semiconductor. For double oxide layer films, SnO2/NiO 3 vol.% (Upper/Lower) film showed the maximum change in light intensity of about 1.5 times that of one layer film. It is pointed out that doubling of layer results in increased light intensity change. Fig.2 shows an example of gas response test (90% response time) result. It is confirmed that NiCo2O4 exhibits superior result to other films. When CO gas is replaced with air, NiO 3 vol.% film results in a special behavior comparing with that of 6 vol.% film.
