Effect Of Synthesis Route On The Ethanol Sensing Characteristics For LaFeO₃ Nanoparticles By Citric Sol-gel Method

Recently due to the application in the high temperature superconductivity,giant magneto resistance effect,catalysis and gas sensing,ABO₃ perovskite rare earth oxides have attracted more and more attention.Many studies have shown that the gas sensor based on perovskite type rare earth oxides has the characteristics of low cost,selectivity and stability,and can detect a variety of gases.This type of material is very active in the field of gas sensitive research,LaFeO₃ is the most typical receives more and more attention.The gas sensitive properties of perovskite type rare earth oxides have direct relationship with the physical and chemical properties,morphology and structure of the materials themselves.This paper starts with the preparation process of LaFeO₃nanomaterials and gas sensitive components.The preparation process of LaFeO₃nanomaterials and the influence of the preparation process of the gas sensor on the gas sensitivity of the gas sensor were studied.In this paper,LaFeO₃ particles were prepared by using citric acid sol-gel method.The main work and conclusions are as follows:The choosing of polyethylene glycol instead of ethylene glycol as raw material and additional pre-calcination at 400^oC rather than direct calcination at600^oC could result in the decrease of resistance due to the reduction of activation energy Ea.Meanwhile,the choosing of ethylene glycol as raw material and additional pre-calcination leads to the enhancement of sensitivity to ethanol.Comprehensive analysis on the sensitivity and XRD,SEM,TEM,XPS results indicates that the sensing performance of LaFeO₃ should be mainly determined by the adsorbed oxygen species on Fe ions,with certain contribution from native active oxygen.The best sensitivity of 46.1 to 200 ppm ethanol at prime working temperature of 112^oC is obtained by the sample using ethylene glycol as raw materialwithadditionalpre-calcination,whichoriginatesfromits uniformly-sized and well-dispersed particles as well as high atomic ratio of Fe/La at surface region.The as-prepared sensors were either sintered at 200^oC-500^o C for 2 h or at200^oC for 1.5 h-2.5 h to study the sintering effect on the electrical and ethanol sensing characteristics.At the prime working temperature of 128^oC,the sensor sintered at 200^oC for 2 h showed the lowest resistance,highest gas response of95.5 towards 100 ppm ethanol and best selectivity among the sensors sintered at different temperatures for 2 h,which also exhibited medium resistance,the highest gas responses to ethanol,acetone,DMF,CH₂Cl₂ and NH₃?H₂O among the sensors sintered at 200^oC for the different time.Consequently,sintering at200^oC for 2 h was considered as the prime sintering condition for LaFeO₃nanoparticle-based thick film sensors to achieve the best ethanol sensing performance.When the gas sensor is produced,LaFeO₃ nanoparticles were mixed with terpineol to form a paste.Three different amounts of E-glass fiber with weight ratios of x%?0,15,30 and 45?with respect to LaFeO₃ nanoparticles were added.The primary objective of the present work is to elucidate the effect of E-glass fiber,which is composed of alumino-borosilicate and added during the sensor fabrication,on the ethanol sensing characteristics of La FeO₃ nanoparticle-based thick film sensors.The prime working temperature?Tp?is 132?for x=0 and 15,while it is 140?for x=30 and 45.Increased addition of E-glass fiber from x=0to 30 leads to decreased gas response to ethanol,while the gas response is close for x=0 and x=45 at each own Tp.The gas selectivity towards ethanol was enhanced by decreased gas response to acetone.For the LaFeO₃nanoparticle-based thick film sensors,addition of E-glass fiber could lead to the increment of electrical resistance,the activation energy of small polarons and the prime working temperature.Appropriate amount of addition could result in faster dynamic response as well as better selectivity towards ethanol at the prime working temperature.