The detection and measurement of CO using ZnO single crystals

Abstract A gas sensor that is based on the electrical conductivity changes effected by the adsoprtion of gases on single crystals of ZnO has been developed. The behaviour of the sensor in CO-, CH4-, H2- and H2O-in-air mixtures is described. The effect of temperature in the range 300 – 500 °C on the characteristics of the sensor has been investigated in detail. Data are presented describing the variation of conductance with CO concentration, the response and the recovery times when the sensor is exposed to step changes in gas concentration and the long-term behaviour of the sensor. The results indicate that the sensors are sensitive to CO and to H2 but are insensitive to CH4 and water vapour, have good long-term stability and have response time ∼ 2 min.