# US 2014/0196772 A1 · Process for making silver powder particles with small size crystallites

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- Number: US 2014/0196772 A1
- Document ID: US20140196772A1
- Status: Published application
- Kind: A1
- Application number: 14/217,826
- Filed: 2014-03-18
- Published: 2014-07-17
- Earliest claimed: 2011-03-08
- Assignees: E. I. Du Pont de Nemours and Company
- Applicants: E I Du Pont De Nemours and Company
- Inventors: ROBERTO IRIZARRY-RIVERA; Haixin Yang
- Web page: https://patentgrep.com/patent/US20140196772A1

## CPC

- B22F 9/24: starting from liquid metal compounds, e.g. solutions
- B22F 1/05: Metallic powder characterised by the size or surface area of the particles
- B22F 1/07: Metallic powder characterised by particles having a nanoscale microstructure (nanosized particles B22F1/054)
- C22C 5/06: Alloys based on silver
- C23C 24/087: {Coating with metal alloys or metal elements only}
- H01B 1/02: mainly consisting of metals or alloys
- H10F 77/211: {for photovoltaic cells}
- B22F 2301/255: Silver or gold
- B22F 2304/10: Micron size particles, i.e. above 1 micrometer up to 500 micrometer
- Y02E 10/50: Photovoltaic [PV] energy
- B22F: WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER (making alloys by powder metallurgy C22C); APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- H01B: CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES (selection for magnetic properties H01F1/00; waveguides H01P {; printed circuits H05K})
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

The process for making silver powder particles with small size crystallites uses a combination of gum arabic and maleic acid with the reduction of a silver salt with ascorbic acid, Silver thick film paste containing these silver powder particles can be used in electronic applications to form electrodes for semiconductor devices and, in particular, solar cells.

## Claims

### Claim 1

Silver powder particles made by a process comprising:
(a) preparing an acidic aqueous silver salt solution comprising a water soluble silver salt dissolved in deionized water;
(b) preparing an acidic aqueous reducing and particle modifier solution comprising:
(i) a reducing agent selected from the group consisting of ascorbic acid, ascorbates and mixtures thereof dissolved in deionized water;
(ii) nitric acid;
(iii) gum arabic;
(iv) maleic acid; and
(v) deionized water;
(c) maintaining said acidic aqueous silver salt solution and said acidic reducing and particle modifier solution at the same temperature, wherein said temperature is in the range of 10° C. to 65° C., while stirring each said solution during and after preparation;
(d) adding said acidic aqueous silver salt solution to said acidic aqueous reducing and particle modifier solution while stirring to make a reaction mixture and maintaining the temperature of said reaction mixture at said temperature of (c), wherein said silver powder particles precipitate and are contained within the resulting final aqueous solution; and
(e) increasing the temperature of said final aqueous solution to a temperature in the range of 65° C. to 80° C. while continuing stirring;
said silver powder particles comprising crystallites between 30 and 47 nm in size as determined by X-ray diffraction and the Scherrer formula; and said silver powder particles having d50 in the range of 0.5 to 3.5 μm.

### Claim 2 (depends on 1)

The silver particles of claim 1, said process further comprising:
(f) separating said silver powder particles from said final aqueous solution;
(g) washing said silver powder particles with deionized water; and
(h) drying said silver powder particles.

### Claim 3 (depends on 1)

The silver particles of claim 1, wherein said water soluble silver salt is silver nitrate and said reducing agent is ascorbic acid.

### Claim 4 (depends on 1)

The silver particles of claim 1, said acidic aqueous reducing and particle modifier solution further comprising a metal colloid selected from the group consisting of gold colloid and silver colloid.

### Claim 5 (depends on 1)

The silver particles of claim 1, wherein the temperature in process step (c) is in the range of 10° C. to 35° C. and the temperature in process step (e) is in the range of 65° C. to 75° C.

### Claim 6 (depends on 1, 2, 3, 4, 5)

A silver thick film paste comprising said silver powder particles of any of claims 1-5.

### Claim 7 (depends on 6)

The silver thick film paste of claim 6, said silver thick film paste comprising 65 to 90 wt % said silver powder particles and further comprising 0.1 to 8 wt % glass frit and 5 to 30 wt % organic medium, wherein the wt % are based on the total weight of the silver thick film paste.

### Claim 8 (depends on 7)

A semiconductor device comprising an electrode, said electrode, prior to firing, comprising said silver thick film paste of claim 7.

### Claim 9 (depends on 8)

The semiconductor device of claim 8, wherein said semiconductor device is a solar cell.