Morphology and particle size of micro spherical silver fabricated by multistep reduction

Sodium borohydride was used as reducer to prepare silver seed, and then the silver nitrate was reduced step-by-step in aqueous solution to fabricate micron silver powder. The effects of reducing agent, the amount of silver seed, the concentration of reducer and silver nitrate on the size and morphology of the silver particles were studied. SEM and X-ray diffraction were used to characterize the surface morphology and crystal structure of silver particles. The results show that the silver powder prepared with strong redusing agent agglomerates seriously and the particle size is non-uniform; when reduction agent concentration is too low (0.05 mol/L) or too high (0.25 mol/L), the silver particle is very small and agglomerates seriously; when adding fewer volume of crystal seeds (1 mL), the silver particle is non-uniform, and when adding more volume of seeds (3 mL), the silver powder is fine and agglomerates seriously; spherical silver particles with better dispersibility and uniform particle size can be obtained by using 2 mL of silver seed and weak reducing agent (ascorbic acid) when the concentration of ascorbic acid is 0.15 mol/L. With the increase of concentration of silver nitrate from 0.05 mol/L to 0.20 mol/L, the particle size of silver particle increases first and then decreases. When the concentration of silver nitrate is 0.15 mol/L, the spherical silver particle with average size of 1.5 μm has smooth surfaces, better dispersibility and uniform particle size.