| Under the urgent requirement for real-time monitoring of polluted gas in industrial production,environment,medical fields and so on,much research is focused on gas sensors.The coatings are the core of gas sensors,yet cost-effectively preparation of the gas sensors remains challenging.Furthermore,the gas sensing mechanism is insufficiently known.In this paper,the tungsten oxide coating was prepared by liquid phase plasma spraying to prepare the nanostructured tungsten oxide coating.The preparation process of the coating was optimized.The microstructure of the tungsten oxide coating was observed.The microstructure and properties of the WO3 composite coating and the pure WO3 coating prepared by the inclusions;the gas sensing mechanism of the tungsten oxide coating was explained.The main conclusions of this paper are as follows:The effect of TiO2 metal dopants and spraying power on WO3 coating was studied and compared with pure WO3 coating prepared under the same conditions(spray power is33k W).After doping with Ti O2,it is found that the grain length in the coating is limited to a certain extent,so that the specific surface area of the coating is increased,and it is easier to contact the test gas.The coating prepared at a spraying power of 33 k W was used as the research object to characterize the gas sensing properties of the coating.During the gas sensitivity test,it was found that the Ti O2-WO3 composite coating had a short response and recovery time for 100 ppm of NO2 regardless of the temperature conditions.When the temperature is at 100?,the sensitivity of the Ti O2-WO3 sensor is significantly better than that of the WO3 coating,and the sensitivity of the former is order of magnitude higher than that of the latter.In the study of the gas sensing mechanism of the coating,it is found that Ti O2 and WO3 are uniformly distributed in the Ti O2-WO3 composite coating.Since both Ti O2 and WO3 belong to the n-type semiconductor,the close contact will form the n-n type Heterojunction at the interface.Since the work function of WO3 is smaller than the work function of Ti O2,electrons are transferred from the Ti O2 conduction band to the vicinity of WO3.As the electron transfer occurs,an electron accumulation region appears at the WO3conduction band to form an aggregation layer,so that the band can be bent downward.The corresponding depletion layer is formed in the vicinity of Ti O2,so that the band can be bent upwards,and it is more likely to be in contact with the oxygen in the adsorption state,and the material will have a certain degree of decrease in the electrical conductivity,so that the two form a contact barrier at the contact point.The presence of a contact barrier limits the transfer of electrons between Ti O2-WO3,resulting in improved gas sensing properties of the coating.This is why the Ti O2-WO3 composite coating exhibits superior gas sensitivity compared to the pure WO3 coating under the same conditions.The effect of Au metal dopants and spray parameters on WO3 coatings was studied and compared with pure WO3 coatings prepared under the same conditions(spray power is33k W).In this paper,170mm is determined as the optimum spraying distance.Under this spraying distance,the crystallinity of WO3 particles in the obtained coating is intact,and the grain size is still in the nanometer scale,which meets the requirements of good gas sensitivity of the coating.When the operating temperature of the gas sensor is 100?,150?and 200?,respectively,it is found that the response resistance of the Au-WO3 composite coating decreases significantly as the test temperature increases,which will result in a decrease in the sensitivity of the coating.The gas sensitivity performance is deteriorated.Therefore,the Au-WO3 gas sensor coating prepared in this paper has better sensitivity at lower temperature (100?). |
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