Synthesis Of Doped/Composite Metal Oxides Nanocrystallites By Mechanochemical Reaction And Research Of Gas Sensing Property

Semiconductor metal oxides nanomaterials, with special physico-chemical properties, have been widely applied in many fields including environmental protection, catalyst, medicine, ceramics, chemical engineering and photoelectric materials. Synthesis of nanomaterials have attracted a worldwide attention and have made great progress. The different preparation methods show direct influence on the microstructure and properties of the as-synthesized materials. Mechanochemical processing, a novel and effective method to synthesize nanomaterials, has many advantages including simple process, cheap, convenient, easy to control process and suitable for large-scale production of composite nanocrystallites.This work used the mechanochemical technology to prepare doped/composite metal oxide nanocrystallite such as In₂O₃, CdO, In₂O₃/CuO, Co₃O₄/CuO, In₂O₃/SnO₂ and CdO/SnO₂. The precursor was first formed from the mechanochemical reaction of the dichloride and sodium carbonate (or sodium hydroxide) with sodium chloride as diluent. Thermal treatment of the precursor and subsequent washing and drying to remove NaCl resulted in the formation of nanocrystalline metal oxides. The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), differential thermal analysis (DTA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDAX). The gas sensing properties of the sintered thick film organ prepared using the as-synthesized nanocomposite oxides were investigated. The sensitive properties were tested in the way of static ambience.The results indicate that NaCl diluent can effectively prevent grain agglomeration. The crystal size of the product was 20⁵0nm, varying with the calcination temperature. The lattice parameter and crystal size of the nanomaterial would change with different doped elements, the radius of doped ion was bigger than that of primary material. The sensitivity of SnO₂ were greatly improved with doped/composite other oxides. The sensing property of 10wt% CdO/SnO₂ was better than that of 30wt% CdO/SnO₂. Under the atmosphere of alcohol (1000ppm), acetone (1000ppm), gasoline (2000ppm) and hydrogen (2000ppm), the sensitivity of 10wt% CdO/SnO₂ was 276.9, 95.4, 68.7 and 36.3, respectively, which increased 5.3, 2.1, 5.7 and 14.5 compared with that of pure SnO₂. The selectivity of alcoholto methane was 131.8, improved 3 times than that of pure SnC>2 with the time of response and comeback of 1 and 5 seconds in 200ppm alcohol, respectively.The activation energies of nanocrystallite growth of the doped/composite metal oxides during the thermal treatment of the precursor were calculated using Kissinger and Ozawa equations. The kinetics equations for the nanocrystallite growth were determined for the activation energies of 10¹00kJ/mol. It shows that the calcination temperature has remarkable effect on the growth of nanocrystallites. It can be concluded that the nanocrystallite grows primarily by means of an interfacial reaction during the thermal treatment of the precursor. Otherwise, the mechanochemical behavior has been analyzed, such as collision, transfer of energy, superficial objection and local temperature. The mechanism for the mechanochemical synthesis of metal oxide nanocrystallites was primarily discussed. The synergistic effects between correlative oxides were researched and the sensing mechanism of In2O3(CdO) doped SnO2 have been thoroughly investigated.