Optimization And Applications Of γ-Fe₂O₃ Methane Gas Sensors

Metal oxide semiconductor gas sensors have the longest history in thedevelopments and applications of semiconductor gas sensors. Since the simpledevice process and low cost, now the sensors have been developed as one ofthe sensors of the largest mass production, the most various types and thebroadest applications in the world.Following SnO₂, γ-Fe₂O₃ gas sensitive ceramic is a new type of oxidesemiconductor materials for gas detection. Because the high sensitivity, longusage time and low prices, γ-Fe₂O₃ gas sensors are widely used for flammablegas monitoring, alarming and detection. Therefore the sensors certainly have agood application prospect.One effective way to develop the γ-Fe₂O₃ gas sensors with moderatesensitivity and high stability is: draw on the successful experience andtechnology based on the gas sensitivity mechanisms, then do lots ofexperiments to study new materials and optimize device processes. And basedon the analysis of experimental data, further understand the gas sensitivitymechanisms of γ -Fe₂O₃ metal oxide gas sensors.This dissertation discussed the structures and mechanisms of the metaloxide semiconductor sensors, then by means of the side-heat device processesfor metal oxide gas sensors and advanced testing equipments to study theeffect factors on the γ-Fe₂O₃ gas sensor characteristics. These factors includethe selection of γ--Fe₂O₃ raw materials, γ -Al2O3 structure reagents, La2O3electronic reagents, sintering temperature and aging times.The γ-Fe₂O₃ raw materials with high-purity, large surface andgranularity uniformity can produce excellent performance γ-Fe₂O₃ gas sensors,because of its much more active characteristics, considerable pores and largesurface.The sensitivity and response speed of gas sensors and the sinteringtemperature can be improved by adding moderate γ-Fe2O3. This may be due toγ-Al2O3 and γ-Fe2O3 can form a solid solution and evenly mutual dissolved,and stabilized the lattice.Moreover, the sensitivity and response speed of gas sensors can besignificantly improved by adding La2O3. The improvement degree was muchmore significant than adding γ-Al2O3. Adding La2O3 had little effect on thesintering temperature. At low the sintering temperature, the sensors showedthe highest sensitivity. Experimental results demonstrated that the addingvolume of La2O3 should be 0.5-5mol%.As sintering temperature increasing, the sensitivity increased quickly tomaximum point and then rapidly declined. The highest sensitivity appeared at550℃ and about 700℃ for the contents of γ-Al2O3 are 6mol% and 20mol%,respectively. Evidently, adding moderate γ-Al2O3 can increase sinteringtemperature.According to the above experimental results, we obtained anappropriate recipe and optimize device processes for γ--Fe2O3 methane gassensors. The parameters of sensors reached the predetermined performance.Therefore, the route by combined analysis of experimental and theoretical datato obtain new recipes and optimize device process techniques was feasible forγ -Fe2O3 gas sensors.With 89C2051 SCM and double γ-Fe2O3 gas sensors, the designedmethane gas detectors have the functions to detect and display theconcentration of methane gas, alarm and failure detection etc, and accordinglypower on the exhaust fans and shut the valves. The overall design makes thegas detectors work stably with high measurement precision and low powerconsumption for different application fields...