Optimization of the experimental conditions for the synthesis of micro-size monodisperse spherical silver powders using Box–Behnken design

Monodisperse and spherical micro-size silver powder, which has narrow size distribution and high purity, was prepared by using silver nitrate as metal source, L-ascorbic acid as reductant and sodium sulfate as dispersant. The aim of this paper was to study the simultaneous effects of pH (2–6), silver nitrate concentration [AgNO3] (0.25–0.75 mol/L), dropping time td (5–15 min) and their interactions on properties of silver particles. In order to detect factor interactions and optimize these parameters, Box–Behnken design of experiments (a response surface methodology) was used. Synthesized silver powders were characterized by a laser particle size analyzer (LPSA), a scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). After surveying the experiment data and regression analysis of the data, a mathematical model was derived for optimizing particle size. The optimum condition was: [AgNO3], 0.75 mol/L; pH, 6; and td, 5 min. The predicted particle size was 1.39 μm and the experimental particle size was 1.38 μm at the optimum condition, which showed that the model agreed well with the experimental data. It is found that the [AgNO3] and dropping time have a positive effect and the pH value has a negative influence on the particle size. The possible mechanism for the formation of novel spherical silver particles is explored.