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γ-Fe_2O_3气敏材料的特点是无需贵金属掺杂即可获得实用化的灵敏度。其缺点是选择性差,稳定性不好。γ-Fe_2O_3是氧化铁的一种介稳状态,高温下会不可逆地转变为灵敏度低的α-Fe_2O_3.研究表明,采用化学共沉淀物还原氧化的方法,在γ-Fe_2O_3中掺入了Y,Ce,Eu和Tb的氧化物后,γ-Fe_2O_3的结晶度有所降低,颗粒尺寸减小,气孔率增加,气体灵敏度升高。经热分析表明,Ce-γ-Fe_2O_3,Eu-γ-Fe_2O_3的相变温度都在600℃以上,比纯γ-Fe_2O_3580℃的转变温度有所提高,即稀土氧化物掺杂后增加了γ-Fe_2O_3的相稳定性。另外选择合适的工作温度和稀土添加剂,还可使γ-Fe_2O_3材料实现对C_2H_5OH,C_2H_2和LPG的选择性检测。γ-Fe_2O_3的气敏机理属体控制型,稀土催化,陶瓷微结构等均对气敏效应有一定影响。
Gamma-Fe 2 O 3 gas-sensitive material is characterized by practicality without the need for precious metal doping. The disadvantage is the poor selectivity, poor stability. γ-Fe_2O_3 is a metastable state of iron oxide and irreversibly transformed into low-sensitivity α-Fe_2O_3 at high temperature. The results show that γ-Fe_2O_3 is doped into γ-Fe_2O_3 by chemical coprecipitation reduction oxidation, After the oxides of Ce, Eu and Tb, the crystallinity of γ-Fe 2 O 3 decreased, the particle size decreased, the porosity increased and the gas sensitivity increased. The results of thermal analysis show that the transformation temperatures of Ce-γ-Fe_2O_3 and Eu-γ-Fe_2O_3 are both above 600 ℃, which are higher than the transition temperature of pure γ-Fe_2O_380 ℃, Phase stability of Fe_2O_3. In addition, the suitable operating temperature and rare earth additives are selected, and the selective detection of C_2H_5OH, C_2H_2 and LPG can also be achieved in γ-Fe_2O_3 materials. The gas sensing mechanism of γ-Fe_2O_3 is controlled by the genus, the catalysis of rare earth and the microstructure of ceramic all have certain influence on the gas-sensing effect.