Fabrication Of The Formaldehyde Gas Sensor And Study Of Its Sensitivity

In this paper, the method about the fabrication of the formaldehyde gas sensor and the study of its sensitivity property were introduced. The SnO2 nanocrystalline material was prepared by chemical co-deposit method, La_xSr₁-xFeO₃ and NiO nanocrystalline material were prepared by citrate method respectively. The comparison between the different sensing materials has been taken. The sensing property of the SnO₂ gas sensor was better than the others, and the sensitivity of the SnO₂ gas sensor was the highest. Different structure has been compared, including the thick-film gas sensor and the indirect-heat gas sensor, the experiment results showed that the indirect-heat gas sensor was better than the thick film under the current techniques.The sensitivity of the formaldehyde gas sensor that we fabricated has been measured. It was showed that the heating power corresponding to the highest sensitivity was about 0.4W. The response time is about 25 seconds, and the recover time is about 40 seconds. Along with the increase of the gas concentration, the sensitivity of the gas sensor increased. The influence of ethanol to the formaldehyde gas sensor has also been tested. The results shows that the sensitivity of the gas sensor to ethanol is higher than its sensitivity to formaldehyde when the gas concentration is high, but when the gas concentration is much lower, the sensitivity trend towards higher for formaldehyde than for ethanol. This means the gas sensor we made is suitable for the detection of formaldehyde in lower concentration. The influence of the humidity was weak and may be neglected.An automatic test system for gas sensors was designed. D/A card was used to control the Mass Flow Controller (MFC), so that the flow and the concentration of the gas could be controlled automatically. During the afflux of the gas, the total flow of the gas remains invariable, so that the influence of the flow to the gas sensor can be eliminated. A/D card was used to collect the real-time response signals.Due to disturb of ethanol to formaldehyde, we try to analysis the reason theoretically. Using the La₀.7Sr₀.3FeO₃ gas sensor as an example, an equivalent circuit model was built to analysis the adsorption theory of the formaldehyde gas.