Preparation, Structure And Properties Of The α-Fe₂O₃-Based Gas-Sensing Nanomaterials

Ferric oxides have been used as the third series of gas-sensing materials following SnO2 and ZnO, especially a- Fe₂O₃ nanomaterials with high chemical stability and unnecessarily doping the noble metal have attracted much attention. So far, the systematic research on the relativity of composition-structure-property is scarce. In this dissertation, on the basis of measurements and characterizations of α-Fe₂O₃ based nano-powders and gas sensitive sensors, the correlativity between the synthesis and structure of powders and the characters of sensors was deeply studied and the sensitive mechanism was discussed.1. During the preparation of a- Fe2O3 based nano-powders, the effects of pH value and drying methods on the grain-size and dispersal of powder and the gas-sensitivity of sensors were studied. The results showed that Controlling pH value and increasing ?potential can improve the dispersal of powders and finally enhance the gas-sensitivity of a- Fe2C3 sensor. The study of the microstructure and properties of gas-sensitivity for the prepared powders also exhibited that azeotropic distillation and Sol-Gel method can competently prevent the formation of hard agglomeration, and so good sensitivity is obtained. In addition, The method of microemulsion reaction can play a significant role in the preparation of a- Fe2Os nanoparticles.2. hi order to obtain good sensitivity, the effects of the sintering conditions on the crystal size and specific surface area of the powders and the sensitivity of the sensors were studied. The proper sintering condition of thick film sensors doped with Sn4+ is 450'C> 3h.3. A series of characterizations and measurements were done on the basis of good gas-sensitivity of a- Fe2O3 materials doped with Sn4+.(1) Investigations of TG> DSCU XRI^ TEM, XPS> gas-sensitivity, revealed that Sn4+ may be substituted for Fe3+ in the corundum structure of a- Fe2O3 between 0.5mol% and 1.5mol%. The high sensitivity for CO is intimately correlated with the amount of Sn4+ replacing Fe3+ of a-Fe2O3.(2) The results of DRS showed that doping Sn4+ can't effectively change the band-gap breadth of a- Fe2O3. XPS measurement results exhibited that no detectable Fe2+ existed in the compound of a Fe2Os doped with Sn4+, which suggest that oxygen anions or cation vacancies not only can compensate the charge balance but alsosignificantly enhance the gas-sensitivity of a- Fe2O3 based gas sensors. (3) Conductive type of a-Fe2O3 doped with Sn4+ is showed in the n -type by HALL measurement and gas-sensitivity measurement. The results of measurements and characterizations suggest that the sensitive mechanism of the a- Fe2O3 based nano-materials prepared by this work be the surface resistance controlled mode.