The Research Of Humidity Tolerance Of Hot-wire Gas Sensor Based On SnO₂

With the advance of science and technology, better performance is needed for gas sensor. Since the gas sensor works in ambient air environment, the changes in humidity have a significant impact on gas sensor response. It is one of the problems how to improve the humidity tolerance of gas sensor. In this paper, It is studied how to improve the humidity tolerance of gas sensor. Pure SnO₂ and doped SnO₂ were prepared, and were characterized by FT-IR, XRD and SEM. the gas-sensing and humidity tolerance of SnO₂-based hot-wire gas sensor were measured. And the sensing mechanism of the hot-wire gas sensor was discussed according to the structure and experimental results.Pure SnO₂ and Sb doped SnO₂?ATO? sensitive material were prepared by nitric acid oxidation and co-precipitation method, and the materials were characterized by FT-IR, XRD and SEM. Comparative analysis showed that 6% Sb doped SnO₂ did not produce a new crystalline phase and still were the quartet rutile structure. The gas sensitivity and humidity tolerance of SnO₂-based hot-wire gas sensor was measured. With 6% ATO as the material of sensitive element, the results showed that the maximum response value of the sensor was 435 mV. With Al2O3 or SnO₂ as the material of reference element, the response to 1000 ppm H2 and humidity tolerance of the sensor was quite different. When the material of reference element was Sn O₂, due to the sensitive element and the reference element were the same with SnO₂-based material, the response of the sensor to the H2 was reduced from 435 mV to 170 mV. However, as the materials of two elements were the same base material, the sensor was showed a good humidity tolerance when the relative humidity changed between 20% and 90%. The relative deviation of sensitivity caused by humidity changed from ± 14.0% to ± 7.3%.In order to improve the situation of the sensor response decrease that was caused by the material of the reference element replaced by SnO₂. According to the special structure of the hot-wire gas sensor and sensing mechanism, Zn, Mg, Cu and Si doped of SnO₂ material were discussed in this paper. Under the conditions of low humidity tolerance, the response of the sensor was greatly improved. The Zn, Mg, Cu and Si-doped SnO₂-based material were prepared by co-precipitation method, and the materials were characterized by FT-IR, XRD and SEM. The results showed that, compared with the pure SnO₂ material, 5% Zn, 2% Mg, 0.8% Cu and 0.7% Si-doped SnO₂-based composite materials did not produce a new crystalline phase and still were the quartet rutile structure. The gas sensitivity and humidity tolerance of SnO₂-based hot-wire gas sensor were measured, and the results showed that when the material of sensitive element was 6% ATO and the materials of reference element were different SnO₂-based composite materials, the sensor response had greatly improved to 1000 ppm H2. With 0.8% Cu-doped SnO₂ as the material of reference element, gas sensors had the best response to 1000 ppm H2, and the sensitivity was 479 mV. In addition, when the relative humidity changed between 20% and 90%, compared with the 20 ? and 50% RH conditions, zero drift of the sensor in the air was less than ±15 mV. And the change of sensor response value was small in the H2. So the sensor showed low humidity tolerance. With 0.8% Cu-doped SnO₂ as the material of reference element, gas sensors had the optimal performance, and the relative deviation of sensitivity caused by humidity was ± 4.3%. Based on the special structure of the hot-wire gas sensor, it is provided a new idea to solve the problem of the important impact to gas sensor by environmental humidity.