Process for making highly dispersible spherical silver powder particles and silver particles formed therefrom

• US 20080028889A1
• Filed: 05/31/2007
• Published: 02/07/2008
• Est. Priority Date: 06/02/2006
• Status: Active Grant

• Current Assignee: Du Pont China Limited (DuPont de Nemours, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Irizarry-Rivera, Roberto, Alvarado, Victor, Glicksman, Howard
• Granted Patent: US 7,648,557 B2
• Time in Patent Office: Days
• US Class Current: 75/371
• CPC Class Codes: B22F 1/00 Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• CPC Class Codes: B22F 1/065 Spherical particles
• CPC Class Codes: B22F 1/068 Flake-like particles
• CPC Class Codes: B22F 9/24 starting from liquid metal compounds, e.g. solutions

Abstract

Disclosed is an improved process for making highly dispersible, spherical silver particles. In particular, the invention is directed to a process for making silver particles, which are very high solids and highly ordered. The silver particles formed are particularly useful in electronic applications.

Claims

1. A method for the formation of very high solids, highly ordered, finely divided, and controlled morphology silver powder particles comprising the sequential steps of:

(a) preparing an aqueous nitric acid solution of a silver salt wherein said aqueous nitric acid solution comprises a silver salt;

(b) preparing a reducing solution comprising;

(i) a reducing agent ascorbic acid;

(ii) one or more surface modifier(s); and

(iii) a particle size modifier; and

(c) mixing together the aqueous nitric acid solution of silver salt and said reducing solution to form silver powder particles in a final aqueous solution wherein said final aqueous solution has a pH of less than or equal to 6.

2. The method of claim 1 further comprising the steps of:

(a) separating said silver powder particles from said final aqueous solution;

(b) providing deionized water;

(c) washing the silver powder particles with said deionized water; and

(d) drying said silver powder particles.

3. The method of claim 1 wherein said silver salt is silver nitrate.

4. The method of claim 1 wherein step (c) is performed at a temperature in the range of 10°

C. to 35°

C.

5. The method of claim 1 wherein step (c) is performed at a temperature in the range of 36°

C. to 44°

C.

6. The method of claim 1 wherein step (c) is performed at a temperature of greater than 45°

C.

7. The method of claim 1 wherein said particle morphology modifier is potassium sulfate.

8. The method of claim 1 wherein said particle size modifier is a metal colloid.

9. The method of claim 1 wherein said the surface modifier for making finely divided silver particles is gum arabic.

10. The method of claim 1 wherein the pH of said final aqueous solution is less than or equal to 2.

11. The method of claim 6 wherein said silver powder particles formed are particles that are two-dimensional flakes.

12. The use of the silver powder particles formed by the method of claim 1 in thick film applications.

13. The use of the silver powder particles formed by the method of claim 1 in flat panel display applications.