Synthesis and characterization of nanocrystalline ZnO powders by a novel combustion synthesis method

Nanocrystalline ZnO powders have been synthesized by means of a novel, quick and simple combustion synthesis method using glycine as fuel and zinc nitrate as oxidant. The starting materials were directly mixed and a slurry precursor with high homogeneity was formed due to the hygroscopicity of the reactants. The precursor could be ignited at room temperature, resulting in dry, loose and voluminous ZnO powders. An interpretation based on the measurement of maximum combustion temperature (Tc) and the amount of gases produced during reaction for various fuel-to-oxidizer molar ratios (ψ), has been proposed for the nature of combustion and its correlation with the characteristics of as-synthesized product. The variation of adiabatic flame temperature (Tad) with the ψ value was calculated theoretically according to the thermodynamic concept. The reaction process of the precursor was investigated by TG-DTA, IR and XRD techniques. The as-synthesized ZnO powders, characterized by XRD, SEM, TEM and BET, show high specific surface area and possess small primary crystallite size. Additionally, using doped-ZnO powders obtained via this combustion synthesis method after sintering in air at 1050 °C for 1.5 h, the varistor can be produced having a sintered density ∼92% of its theoretical density with grain size of ∼5 μm and a nonlinear coefficient of ∼42.