(183u) Preparation and Characterization of Hollow Flower-like Nickel Nanoparticles

Hollow nickel spheres with unique morphology have much potential applications in catalysts，chemical sensors, and photonic crystals. Generally, metal nanopowders are synthesized by the reduction of metal ions in aqueous or organic solution. Polyol reduction method is usually used to fabricate varies metal nanoparticles in different shapes like nano wires, nano sheets, nano flowers and so on. However, this method remains limited for the issues of agglomeration and instability.

In this work, we developed a facile polyol method to prepare hollow flower-like nickel nanoparticles and applied them in solid propellant as combustion promoter. In this method, complex Ni[C₂H₄(NH₂)₂]₃(COOH)₂ was synthesized first as redox precursor in ethylene glycol(EG). PVP was also been added as dispersant, the complex was transformed to an Ni(II)-intermediates after heating at 180℃ for 30min, with the protection of N₂. The intermediates, which was already formed the hollow flower-like structure, was then calcined at 300^oC for another 30min in N₂. The Ni(II)-intermediates decomposed to nickel(0) and other gases. Then, the hollow flower-like nickel spheres were obtained. The effects of reaction and calcination conditions were investigated.

The hollow particles` shell thickness is about 100nm, and the petals` thickness of the flower structure is about 10nm. Importantly, the hollow spheres` diameter can be accurately controlled from 200nm to 2um by adjusting the concentration of complex Ni[C<sub>2</sub>H<sub>4</sub>(NH<sub>2</sub>)<sub>2</sub>]<sub>3</sub>(COOH)<sub>2</sub> in the reaction solution.The growth mechanism of the hollow flower-like particles was illustrated by analyzing the intermediates` morphologies at different reaction time in an individual experiment. The results elucidated an extraordinary growth-shrink-collapse process.

By adding a certain amount (typically 5wt%) of the prepared nickel powders into ammonium perchlorate (AP, base of propellant), the ammonium perchlorate`s decomposition exothermic performance was well promoted. The decomposition temperature was decreased, and the high temperature exothermic peak shifted to low temperature range.