PVP Protective Mechanism of Ultrafine Silver Powder Synthesized by Chemical Reduction Processes

Abstract Polyvinyl pyrrolidone (PVP) as a protective agent plays a decisive part in controlling superfine silver particle size and size distribution by reducing silver nitrate with hydrazine hydrate. The particle size and particle aggregation decrease with the PVP/AgNO3mole ratio. Mechanisms of PVP protection were divided into three stages. First, PVP donates loan pair electrons of oxygen and nitrogen atoms tosporbitals of silver ions, and thus the coordinative complex of Ag ions and PVP forms in aqueous solution. Second, PVP promotes the nucleation of the metallic silver because the Ag ions–PVP complex is more easily reduced by hydrazine than the pure Ag ions owing to Ag ions receiving more electronic clouds from PVP than from H2O. Third, PVP prohibits silver particle aggregation and grain growth as a result of its steric effect. All of the hypotheses were supported by ultraviolet spectra, infrared spectra, and heterogeneous nucleation and grain growth by addition of silver nuclei.