Preparation of silver spheres by the reduction of silver polyamine complexes
View Patent ↗Dispersed uniform spherical silver particles were prepared in the absence of a protective colloid by rapidly mixing concentrated iso-ascorbic acid and silver-polyamine complex solutions.
1. A method for the formation of dispersed, uniform, smooth surface, spherical silver particles without the use of a protective colloid comprising the sequential steps of :
(a) dissolving a silver salt in a solvent and mixing this solution with a polyamine to form a solution of a silver-polyethylene amine complex;
(b) preparing a reducing solution comprising iso-ascorbic acid or ascorbic acid dissolved in a solvent;
(c) adding the reducing solution to the silver-polyethylene amine complex solution to form finely divided, dispersed, uniform shaped spherical silver particles;
(d) separating the silver particles from the solution of step (c);
(e) washing the silver particles with a solvent; and
(f) drying the finely divided, dispersed, uniform shaped spherical silver particles.
2. The method of claim 1 wherein said silver salt is silver nitrate.
3. The method of claim 1 wherein step (c) is performed in the temperature range 20° C. to 80° C.
4. The method of claim 1 wherein the polyethylene amine is a linear poly-amine or a substituted linear poly-amine.
5. The method of claim 1 wherein the polyethylene amine is selected from the group consisting of: ethylenediamine, diethylenetriamine, triethylenetetraamine, and tetraethylenepentamine.
6. The method of claim 5 where the polyamine is ethylenediamine.
7. The method of claim 1 where the reducing solution includes one of the following: L-ascorbic acid, D-ascorbic acid, and their salts.
8. The method of claim 1 where the reducing solution comprises isoascorbic acid.
9. The method of claim 1 where the particles are dried at 220° C. to remove residual organic material and increase the crystallinity.
10. The method of claim 1 where the ratio of Ag/polyethylene amine is equal to or greater than 1:1.
11. The method of claim 10 where the ratio of Ag/polyethylene amine is equal to or greater than 4:1.
12. The method of claim 1 where the solvent of step (a) is water.
13. The method of claim 1 where the solvent of step (a) is a polyol.
14. The method of claim 13 where the solvent is diethylene glycol.
15. The method of claim 1 where the solvent of step (a) is a mixture of a polyol and water.