Preparation And Characterization Of Ferrite Complex Metal Oxides And Their Gas Sensitivity

A gel-gridding method was developed for the large-scale synthesis of nanocrystalline ferrite MFe₂O₄ (M=Cd, Cu) and MFeO₃ (M=La, Al). And synthesis, characterization and gas sensitivity of powders were studied systematically in this paper, as well as the gas sensitive mechanism of sensors.1. Synthesis, characterization and gas sensitivity of nanopowders CdFe₂O₄ and CuFe₂O₄ were studied.(1). Nano- powders CdFe₂O₄ and CuFe₂O₄ were obtained by a gel-gridding method. And the best synthesis conditions of these powders were also gotten.(2). The crystal structure and surface morphology were examined by means of X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Nanopowders CdFe₂O₄ were made by a gel-gridding method (3wt%, 4wt%, 5wt% agar solution), respectively. And the average diameters of these three kinds of powders were different. As-prepared ferrite powders were made into thick film gas sensors for gas sensitivity tests. The results of tests to CH3SH demonstrated that CdFe₂O₄ nanopowder which prepared by 5wt% gel-gridding method showed remarkable sensitivity and good selectivity to CH3SH.(3). The results showed that the gas sensitivity of nanopowders CdFe₂O₄ was better than CuFe₂O₄ which was synthesized by the same way, 5wt% gel-gridding method. The possible reason of the results was also investigated.2. Synthesis, characterization and gas sensitivity of nanopowders LaFeO₃ and AlFeO₃ were studied.(1). Nanopowders LaFeO₃ and AlFeO₃ were obtained by a gel-gridding method. Andthe best synthesis conditions of these powders were also gotten.(2). The mean grain size of the powders LaFeO₃ and AlFeO₃ which had been calcinedat the optimal temperature was gained using X-ray powder diffraction (XRD).As-prepared powders LaFeO₃ and AlFeO₃ were made into thick film gas sensors andgas sensitivity tests were also carried out.(3). It could be seen from the results to the gas tests that the gas sensors based onLaFeO₃ nanopowder showed better sensitivity than that of AlFeO₃. In addition, thepossible reason for this was also discussed in this paper.3. The gas sensitivity mechanism of ferrite compound oxides was investigated.4. Different materials for gas sensitivity have been synthesized by doping different metal oxides such as SnO₂, Ag₂O,La₂O₃ and by different doping ways. The results demonstrated that doped ZnO showed better sensitivity and good selectivity to HCHO than ZnO undoped. Especially, the sensitivity of ZnO doped by La₂O₃ was much better than the others. And doped ZnO prepared using a gel-gridding method showed higher sensitivity to HCHO than that prepared using soakage. Furthermore, gas sensitivity mechanism was also discussed.