| As the gradually expand of industry scale, the gas type and quantity of raw gases and produced gases are growing. Some of these gases are flammable or explosive, some of them are poisonous. Their leakage not only causes environmental pollution problems such as the greenhouse effect, acid rain, ozone depletion et al. but also harms to people’s personal and property security, prone to explosions, fires or biological poisoning. At the same time, as the rise of people’s living standard, liquefied petroleum gas, natural gas and city fuel gas are also rapidly popularized as domestic fuel. These can also cause the leakage of gas explosion, fire and poisoning accidents. It is the necessary premise to solve the problem of environmental pollution to effectively detection and alarm these toxic, pollution gas.There have been several types of CO2 sensors such as infrared, surface acoustic wave, solid electrolyte, capacitive, resistive and MOS have been found. The measurement accuracy of infrared absorption sensor is high, though meanwhile, the device is large, the price is high, and then the popularization is difficult. Electrochemical Severinghaus electrode sensor, which is susceptible to electromagnetic interference, mainly applied to measure the carbon dioxide in the blood. The NASICON solid electrolyte CO2 sensor is also difficult to use widespread because of its actual manufacturing difficulty. The conductance or resistance type CO2 gas sensing materials are mainly concentrated in the p-n type composite oxide materials, such as CuO-BaTiO3 composites or mixed silver CuO-BaTiO3 composites. Because of involving two substances (CuO and BaTiO3),the composite materials need complex preparation technics. In addition, BaTiC>3 needs higher temperature to crystallize, and the best working temperature of Cu0-BaTiO3 composites CO2 gas sensor is 400℃ or more. It has been shown tfiat some composite or single phase oxides can be used as the resistive CO2 sensors, where there is a change in the electrical resistance of semiconductor upon exposure to CO2 in air. The composite oxide films (such as CuO-BaTiO3,La2O3-BaTiO3 and ZrO2-BaTiO3) and single phase semiconductors (such as LaOCl, Nd2C2CO3, SmCoO3, GdCo03 and Lai.xSrxFeO3) present an increase of resistance to CO2 gas. So far, the gas-sensing mechanism of the single and composite oxides to CO2 is still not very clear. There are a lot of controversies.Compared with the single metal oxide, ABO3 perovskite oxide as gas-sensing material has some advantages, not only showed better selectivity and sensitivity of gases but also had higher stability. In addition, the sensitivity, selectivity and stability of ABO3 perovskite gas sensing material can be adjusted and controled not only by changing the element in A or B site, but also by partly replacing the element in A or B site with other elements. The structure of ABO3 perovskite oxide is so stable that doping will not change its original structure.The studies of this paper mainly include the following results:1. HoFeO3 nanopowders prepared by sol-gel method can exhibit considerable sensing response to CO2 gas. The resistance of the GdFeO3 sensor increases with increasing concentration of CO2. At 700℃, the responses of the sensor to2000,4000 and 6000 ppm CO2 are 1.842,2.195 and 2.47.2. GdFeO3 nanopowders prepared by sol-gel method can exhibit considerable sensing response to CO2 gas. The resistance of the GdFeO3 sensor increases with increasing concentration of CO2. At 220℃, the best response of the sensor to 2000ppm CO2 is 1.453.3. YFeO3 nanopowders prepared by sol-gel method can exhibit considerable sensing response to CO2 gas. The resistance of the YFeO3 sensor increases with increasing concentration of CO2. Al 220℃, the best responses of the sensor to 2000ppm CO2 is 1.626.4. The possible CO2 sensing mechanism was discussed. |
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