| Gas leakage may cause a series of safety accidents.In order to protect people's life and property,it is highly desirable for people to develop gas sensors with extraordinary gas sensing capabilities and highly promising practical application.Among various gas sensors,metal oxide semiconductor(MOSs)gas sensors is more attractive.Due to the advantages of durability,sensitivity,robustness,and simplicity in function,long life-time,small-size device,the MOS sensors are especially attractive for continuous monitoring and alarm systems.However,at present,the commercial metal oxide semiconductor gas sensors must work at high temperatures(300?400 ?).However,the high working temperature means the demand of electric heating equipment,and also leads to high power consumption,safety hazards and short lifetime.Therefore,it is an urgent task to develop MOSs gas sensors which work at low temperatures or even room temperature.It is now well accepted that the gas sensing responsibility of metal oxide semiconductor gas sensors is a kind of surface effect,the higher surface-to-volume ratio is,the lower temperature we will get.Therefore,more and more researches focus on the development of various kinds of nanostructured gas sensing materials.However,the gas sensors with low-dimensional MOS materials have many shortcomings such as complex preparation technology,low mechanical robustness,low thermal stability,and strong adsorption of vapor.For these reasons,it is difficult for the gas sensors with low-dimensional MOS materials becoming commercial product.In fact,people pay little attention to ceramic bulk materials.Our group has made research on composite nanoceramic bulk materials made from traditional sintering process.In this paper,two kinds of composite nanoceramics are studied,both Fe2O3 and SnO2 composite nanoceramics materials exhibit extraordinary outstanding room-temperature gas sensing capabilities.However we found composite nanoceramics made from the traditional sintering process have extraordinary outstanding room-temperature gas sensing capabilities.By analyze SEM results,we found that porous nanoceramics have the advantages of high surface-to-volume ratio just like low-dimensional materials.At the same time,porous nanoceramics have the advantages of high stability of block materials.Through the study on real-time gas sensing results of Fe2O3 and SnO2 composite nanoceramics in different gas atmospheres,the details are as follows:The SEM results of Pt-Fe2O3 composite nanoceramics show that there are a large number of nano-sized holes in the materials,and the grain size of Fe2O3 is only 30nm.Pt-Fe2O3 composite nanoceramics has a significant response to hydrogen at room temperature.The sensor was performed at different concentration of hydrogen from 5%to 0.1%.Results showed that the sensor exhibited excellent sensitivity and reproducibility at room temperature.The sensitivity of 5%hydrogen in nitrogen is as high as 90,and the response and recovery time are around 20s and 30s respectively.In order to reveal the mechanism of hydrogen sensitivity at room temperature,the concentration of hydrogen in nitrogen was reduced from 5%to 0,and the resistance of the ceramic was not changed with the decrease of hydrogen concentration in nitrogen.The results show that the hydrogen sensing response is caused by electron transfer between hydrogen molecule and chemical adsorbed oxygen on surface.Compared with TiO2 materials,the mechanism of hydrogen sensing response of Fe2O3 composite nanoceramics were significantly different.Therefore,it is necessary to systematically study on hydrogen sensing mechanism of various metal oxide semiconductor ceramic materials.The microscopic characterization of Pd-SnO2 composite nanoceramics also shows that there are many nano-sized holes.It has a significant gas sensing capabilities to CO at room temperature,and the response is related to palladium concentration.The resistance of samples with 1.Omol%and 5.0mol%palladium increased when encountered with CO.And the sample with 0.2mol%palladium has a reduction in the resistance when meeting CO,showing a good room temperature response.The gas sensing response of samples with 1 mol%Pd is as follows:for 100ppm CO,the sensitivity is about 15,the response and recovery time is about 20s and 60s.Compared with the response of the H2,it presents a significant CO selectivity.And combined the results of gas sensing response with XPS analysis,it indicates that when the Pd-SnO2 composite nanoceramics encountered CO,the resistance was increased by Pd2+,and the resistance was reduced by Pd4+. |
PDF Full Text Request