The Optimization Design And Trial Manufacturing For SnO₂ Methane Gas Sensor

Gas sensor is a very important component of sensors.With enhanced living conditions and increased attention on environment protection,the demand for gas sensors has expanded greatly.In the past,gas sensors were mostly applied in the gas detection and warning for houses or mines.Now,the application of gas sensor has turned to the areas such as detection for various kinds of poisonous and harmful gas, supervision and control of air pollution and industrial air waste,and the quality inspection of food and living environment.To realize the above purpose,it is necessary to research and develop new type of gas sensor and corresponding inspection techniques,which ensures that the gas inspection devices have higher sensitivity and selectivity as well as good repeatability and stability.Metal oxide has the longest history of development and application among semiconductor gas sensors.Because the easy production techniques and low cost,the related production developed very fast and has become one type of sensors that has the greatest production quantity,most various families,and most expanded applications.SnO₂ was the first developed metal oxide gas sensitive semiconductor material. Gas sensors that use SnO₂ gas-sensitive ceramics,which do not have any noble metal catalysts added,offers advantages such as higher sensitivity,longer life-cycle,and lower prices.SnO₂ gas sensor can be widely applied to the inspection,supervision, control,and warning of flammable gas,and has very great potential as a new type of gas-sensitive element。 Because the sensing mechanism of SnO₂ gas sensor is not totally clear,an effective way of developing this kind of sensors,which is of moderate sensitivity, promising selectivity,and good long-term stability,is to work on the basics of current SnO₂ sensing theory,fully draw lessons from the existing knowledge,experiences and research results,and select new raw material formulations as well as optimizing industrial conditions though systematic and through scientific experiments.SnO₂ methane gas(CH₄) gas sensor,which is produced using pure SnO₂ under proper conditions,also has certain gas-sensitive effect.To product SnO₂ CH₄ gas sensor of excellent performance,it is required to select SnO₂ raw material of high purity,great specific surface area,comparatively even granularity distribution.This is because that such material can produce sensing material of higher activity,more pores, and greater specific surface area.Mixing SnO₂ with PdCl₂ and SiO₂ can enhance the methane gas sensitivity of the SnO₂ CH₄ gas sensor.Especially,the mixture ratio of PdCl₂ and SiO₂ significantly influence the methane gas sensitivity.The principle of mixing SnO₂ with PdCl₂ to increase methane gas sensitivity has close relationship with the Fermi level pinning effect of PdCl₂.Comparing with mixing with Pd,mixing with PdCl₂ not only enhance the methane gas sensitivity of SnO₂ CH₄ gas sensor,but also increase the selectivity of other gas types,which can not be realized by mixing with Pd.Adding SiO₂ plays an important role in increasing the catalyzing effect of PdCl₂ in the gas sensors. Besides,SiO₂ is a very effective cementing compound,which can moderately increase the mechanical strength of gas sensors.Mixing SnO₂ with Sb₂O₃ can significantly decrease the inherent resistance R₀ of SnO₂ CH₄ gas sensor.The rule is the inherent resistance R_0s decreases when the Sb₂O₃ mixture ratio increases.However,it should be noted that the SnO₂ CH₄ gas sensor sensitivity K_V also decreases when the Sb₂O₃ mixture ratio increases.Therefore.when using Sb₂O₃ to decrease the inherent resistance R₀ of the SnO₂ CH₄ gas sensor,it is necessary to pay attention on balancing the sensitivity K_V.When the material formulation is decided,the technological indicators of SnO₂ CH₄ sensor,especially the sensitivity K_V,have close relationship with sintering temperature.The regulation is that with the increasing sintering temperature,the sensitivity soon approaches the peak value and then drops down rapidly.On the basis of systematic experiment and scientific optimization,we got a set of material formulation and parameters which can yield heater type SnO₂ gas sensor of good performance quality and application values.SnO₂ CH₄ Gas Sensor FormulationSnO₂ raw material:purity 98.8%,good crystal grain consistency,and specific surface area 56.50 m²/gMixture:SnO₂,SiO₂,PdCl₂,and Sb₂O₃.Mixture ratio:SnO₂:SiO₂:PdCl₂:Sb₂O₃=100:3:10:10Technical parametersAgglomeration temperature:580℃Agglomeration time:45 minutesAging time:72 hoursUsing the above formulation and parameter as guidelines,a batch quantity of SnO₂ CH₄ gas sensors were put through try production and test.The test result proved that the key technique indicators,such as inherent resistance,sensitivity,and selectivity,all meet the practical application standard.The sensors have been put into batch production and sold in market,and received good social and economical benefits.