The Research On Process Of NiO Powder Prepared By Microwave-assisted Combustion Synthesis

As one of important inorganic function material, NiO has been widely used in such areas as catalysts, electrode, gas sensors and magnetic materials owing to its particular properties. In this paper, principles and applications of low temperature combustion synthesis, microwave-assisted combustion synthesis and glycine-nitrate process are studied, meanwhile various preparation ways and applied characteristics of NiO are inspected. NiO powder is successfully synthesized by microwave-assisted combustion method by using nitrate as oxidizer,urea and glycine as fuel, respectively. The influences of molar ratio of fuel to oxidizer, power of microwave and the mositure contenets in hybrid on the phase constitution, morphology of products have been researched. The products are characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscope(TEM),laser particle size analyzer (LPSA) and so on. The results are as follows:When the molar ratio of urea to nickel nitrate (expressed by U/N) are 1.5 and 1.67, the outcomes are pure NiO, moreover, grain sizes d are in the range of 6～10nm with spheric shape particle. When U/N are 3,4,4.5,5,5.1,5.2, 5.3,5.4,5.5,6,7, respectively, Ni and NiO coexist. The relative amount and grain size of NiO descend as the increase of molar ratio and the products have different morphologies. When U/N is 5, four different output power of microwave(30%,50%,70%,100%) is set for reaction and the product have the highest purity and the least grain size in four samples. Besides, concentration of precursor and volume of beaker influence the reaction more or less. The TEM and corresponding electron diffraction diagram show that the reactant first forms amorphous particles, then these amorphous particles are broken and have the tendency to convert crystalline as the combustion reaction and gas output, in the end polycrystaline NiO powder forms. XRD analysis of impurities show that middle product of ammonium nitrate occurs during the combustion processing.The products are also pure NiO powder with grain size d of 4.8nm and 6.2nm when the molar ratios of glycine to nickel nitrate (expressed by G/N) are 0.37 and 0.61, respectively. While the molar ratio is 1.6, the product is Ni powder with good crystallization with d value is 31.1nm. When the molar ratios are 1, 1.1, 1.23, 1.84 and 2.44, Ni and NiO coexist. But G/N=1.23 is a inflection point because when G/N is less than 1.23, relative amount and grain size of NiO continuously descend as the increase of G/N but they increase when G/N is bigger than 1.23. Particle size analysis results show that the initiated grain size is bigger but particle size is smaller of synthesized power as the increase of G/N molar ratio.