Precipitation of Silver Powders in the Presence of Ethylenediamine Tetraacetic Acid

Silver powders can be produced by the reduction of a silver salt in an aqueous solution. The manipulation of the rates of the reaction allows the control of the properties such as size and size distribution of the produced particles. In the present work, we studied the addition of ethylenediamine tetraacetic acid (EDTA) as a complexation agent to moderate the rate of the reduction of silver cations with hydrazine as the reducing agent. The experiments were carried out in a batch reactor at different concentrations of the reactants. In the absence of EDTA, the reaction between hydrazine and the silver cations is extremely fast. It was found that, in the absence of seeds, the reaction starts by the precipitation of the free silver ions followed by a period where any reduced elemental silver forms sub -micrometer particles by nucleation. The addition of seeds promotes the growth of particles and suppresses nucleation. When the concentration seeds are greater than 5.4 × 10^-1 mM, no nucleation is apparent. This allows the determination of the reaction rate between hydrazine and silver cations. At 20 °C, the empirical rate law for the reduction of silver was rAg = 9.35 [Ag]1.3 [N2H4]0.7 [EDTA]-1.1 in mmol of Ag/L-min.