US 8,574,338 B2Granted

Reactor and continuous process for producing silver powders

AssigneeE. I. Du Pont de Nemours and Company

InventorsRoberto Irizarry, Kalyana C. Pyada

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Abstract

Disclosed herein is a continuous process for producing silver powders comprising silver particles. Each powder is comprised of silver particles that have a specific morphology that is determined by the process conditions and the use of one or more particle modifiers in the process. A reactor for carrying out the process is also disclosed. The silver powders produced are particularly useful in electronic applications.

Claims16

Dependent claims

A continuous process for preparing a silver powder comprising silver particles, said process comprising the steps of:

(a) preparing an acidic aqueous silver salt solution comprising a water soluble silver salt dissolved in deionized water;
(b) preparing an acidic reducing solution comprising:
(i) a reducing agent selected from the group consisting of an ascorbic acid, an ascorbate and mixtures thereof dissolved in deionized water;
(ii) nitric acid;
and
(iii) one or more particle modifiers;
(c) maintaining said acidic aqueous silver salt solution and said acidic reducing solution at the same temperature TM, wherein TM is in the range of 10° C. to 90° C.;
(d) providing a flow reactor, wherein said reactor has an axis along the length of said reactor and said axis is vertical, said reactor sequentially comprising:
(1) a cylindrical shell-shaped first zone of length l and inner diameter d and having an upper end and a lower end, wherein d is in the range of 0.25 to 6 inches (0.6 to 15 cm), said first zone positioned at the top of said reactor and comprising a mixing tee that provides a first inlet of diameter d at the upper end of said first zone to enable injection of a first reactant solution into said first zone along said axis of said reactor and a second inlet of inner diameter a positioned at an angle of 30° to 90° to said axis to enable injection of a second reactant solution into said first zone at said angle to said axis, wherein said first zone has means to control temperature and wherein the ratio o/d is in the range of 0.1 to 1;
(2) a second zone in the form of a truncated circular conical shell and having an upper end and a lower end, wherein said second zone serves as a transition zone and has an inner diameter d at said upper end of said second zone that is connected to said lower end of said first zone and an inner diameter D at said lower end of said second zone;
(3) a cylindrical shell-shaped third zone of length L, inner diameter D and having an upper end and a lower end and means to control temperature, wherein the upper end of said third zone is connected to the lower end of said second zone and wherein the ratio D/d is in the range of 1.2 to 6, the ratio l/L is in the range of 0.05 to 0.5 and L is in the range of 2 to 30 feet (0.9 to 9 m);
and
(4) a fourth zone in the form of a truncated circular conical shell and having an upper end and a lower end with an inner diameter D at its upper end and an inner diameter less than D at its lower end and a valve to control flow rate and keep said reactor pressurized, wherein said upper end of said fourth zone is connected to said lower end of said third zone;
(e) continuously feeding said acidic aqueous silver salt solution into one inlet of said first zone of said flow reactor and continuously feeding said acidic reducing solution into the other inlet of said first zone of said flow reactor to form a reaction mixture in said first zone and maintaining said reaction mixture in said first zone at the temperature TM of (c), wherein the reaction mixture flows through said first zone into said second zone of said flow reactor, wherein the residence time of the reaction mixture in said first zone and said second zone is up to and including 5 minutes and wherein upon completion of said residence time said reaction mixture exits said second zone and enters said third zone of said flow reactor;
(f) maintaining said reaction mixture in said third zone of said flow reactor at temperature TR as said reaction mixture flows through said third zone, wherein TR is in the range of 10° C. to 90° C. and wherein the residence time of said reaction mixture in said third zone of said flow reactor is from 1 to 20 minutes and results in the production of said silver powder particles in a final aqueous solution that enters said fourth zone of said flow reactor upon completion of said third zone residence time;
and
(g) collecting said silver powder particles in said final aqueous solution as said final aqueous solution exits said fourth zone of said flow reactor.

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Dependencies are inferred from the claim text.

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Abstract

A continuous process for preparing a silver powder comprising silver particles, said process comprising the steps of:

(a) preparing an acidic aqueous silver salt solution comprising a water soluble silver salt dissolved in deionized water;
(b) preparing an acidic reducing solution comprising:
(i) a reducing agent selected from the group consisting of an ascorbic acid, an ascorbate and mixtures thereof dissolved in deionized water;
(ii) nitric acid;
and
(iii) one or more particle modifiers;
(c) maintaining said acidic aqueous silver salt solution and said acidic reducing solution at the same temperature TM, wherein TM is in the range of 10° C. to 90° C.;
(d) providing a flow reactor, wherein said reactor has an axis along the length of said reactor and said axis is vertical, said reactor sequentially comprising:
(1) a cylindrical shell-shaped first zone of length l and inner diameter d and having an upper end and a lower end, wherein d is in the range of 0.25 to 6 inches (0.6 to 15 cm), said first zone positioned at the top of said reactor and comprising a mixing tee that provides a first inlet of diameter d at the upper end of said first zone to enable injection of a first reactant solution into said first zone along said axis of said reactor and a second inlet of inner diameter a positioned at an angle of 30° to 90° to said axis to enable injection of a second reactant solution into said first zone at said angle to said axis, wherein said first zone has means to control temperature and wherein the ratio o/d is in the range of 0.1 to 1;
(2) a second zone in the form of a truncated circular conical shell and having an upper end and a lower end, wherein said second zone serves as a transition zone and has an inner diameter d at said upper end of said second zone that is connected to said lower end of said first zone and an inner diameter D at said lower end of said second zone;
(3) a cylindrical shell-shaped third zone of length L, inner diameter D and having an upper end and a lower end and means to control temperature, wherein the upper end of said third zone is connected to the lower end of said second zone and wherein the ratio D/d is in the range of 1.2 to 6, the ratio l/L is in the range of 0.05 to 0.5 and L is in the range of 2 to 30 feet (0.9 to 9 m);
and
(4) a fourth zone in the form of a truncated circular conical shell and having an upper end and a lower end with an inner diameter D at its upper end and an inner diameter less than D at its lower end and a valve to control flow rate and keep said reactor pressurized, wherein said upper end of said fourth zone is connected to said lower end of said third zone;
(e) continuously feeding said acidic aqueous silver salt solution into one inlet of said first zone of said flow reactor and continuously feeding said acidic reducing solution into the other inlet of said first zone of said flow reactor to form a reaction mixture in said first zone and maintaining said reaction mixture in said first zone at the temperature TM of (c), wherein the reaction mixture flows through said first zone into said second zone of said flow reactor, wherein the residence time of the reaction mixture in said first zone and said second zone is up to and including 5 minutes and wherein upon completion of said residence time said reaction mixture exits said second zone and enters said third zone of said flow reactor;
(f) maintaining said reaction mixture in said third zone of said flow reactor at temperature TR as said reaction mixture flows through said third zone, wherein TR is in the range of 10° C. to 90° C. and wherein the residence time of said reaction mixture in said third zone of said flow reactor is from 1 to 20 minutes and results in the production of said silver powder particles in a final aqueous solution that enters said fourth zone of said flow reactor upon completion of said third zone residence time;
and
(g) collecting said silver powder particles in said final aqueous solution as said final aqueous solution exits said fourth zone of said flow reactor.

14 more elements