Method for preparing silver powder by using micro-nano bubbles as crystal seeds

Abstract

A preparation method using micro-nano bubbles as crystal seeds to induce spherical or spherical-type silver power production, said method specifically comprising the steps of: pre-adding a prepared dispersing agent solution to a reaction vessel, within the reaction vessel, simultaneously adding a prepared oxidizing solution (an aqueous solution containing silver ions or a silver ammonia solution) and a reducing solution (an aqueous solution containing one or a plurality of hydroxylamine compounds, vitamin C, formaldehyde or hydrazine hydrate), performing a reduction reaction under vigorous stirring, and using the pre-generated micro-nano bubbles within the dispersing agent solution as crystal seeds, the micro-nano bubbles crystal seeds effectively controlling the particle size of reduced silver particles throughout the reduction reaction. The method effectively controls the particle size of the silver powder during production, and also controls the crystal nucleus growth rate and dispersibility.

Claims

1. A method for preparing silver powder, comprising the following steps: (1) preparing an oxidant solution, the oxidant solution including silver nitrate or silver sulfate, having a silver concentration of 0.1-10 mol/L, and being kept at 10° C. to 50° C.; (2) preparing a reductant solution, the reductant solution including a reductant selected from the group consisting of a hydroxylamine compound, vitamin C, a 37% to 40% formaldehyde solution, and hydrazine hydrate, having a reductant concentration of 0.1-10 mol/L, and being kept at 10° C. to 50° C., a volume of the reductant solution being 0.5-5 times a volume of the oxidant solution; (3) preparing a dispersant solution, the dispersant solution including a dispersant selected from the group consisting of polyvinylpyrrolidone (PVP), poly(ethylene glycol) 400 (PEG), polyoxyethylenesorbitan monopalmitate, and glycerol and being kept at 10° C. to 50° C., a weight of the dispersant in the dispersant solution being 0.01-5 times a weight of the silver in the oxidant solution; (4) preparing a flocculant solution, the flocculant solution including alcohol and a flocculant selected from the group consisting of oleic acid and an oleate, a weight of the flocculant is 0.01% to 10% of the silver in the oxidant solution; (5) adding the dispersant solution in a reaction vessel, generating controllable micro-nano bubbles in the dispersant solution by using a micro-nano bubble generator, the micro-nano bubbles being introduced as crystal seeds, adding the oxidant solution and the reductant solution simultaneously to the dispersant solution at a flow rate of 0.1-100 L/min; and (6) discharging a mixture of the dispersant solution, the oxidant solution and the reductant solution from step (5) into a flocculation sedimentation tank, adding the flocculant solution, stirring for 1-60 min, and standing for precipitation to obtain nearly spherical silver powder having an average particle size of 0.1-10 μm, wherein in step (5), the oxidant solution and the reductant solution are simultaneously sprayed through micropores into the dispersant solution at a flow rate of 50 L/min and stirred at 120 rpm.

2. The method of claim 1, wherein the reductant is the hydroxylamine compound is selected from the group consisting of hydroxylamine, hydroxylamine sulfate, and hydroxylamine nitrate.

3. The method of claim 1, wherein the silver powder particles have an internal loose structure that aids an activity of the silver powder particles.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a flow chart of the method of the present invention.

(2) FIGS. 2A, 2B and 2C are schematic views showing detection of the particle size of the silver powder prepared by the method of the present invention.

(3) FIG. 3 is an SEM electron micrograph of the spherical silver powder prepared by the method of the present invention, wherein: FIG. 3A is an SEM electron micrograph of a spherical silver powder magnified 20,000 times; FIG. 3B is an SEM electron micrograph of a spherical silver powder magnified 5000 times; FIG. 3C is an SEM electron micrograph of a spherical silver powder magnified 5000 times; FIG. 3D is an SEM electron micrograph of a spherical silver powder magnified 20000 times; FIG. 3E is an SEM electron micrograph of a spherical silver powder magnified 2000 times; and FIG. 3F is an SEM electron micrograph of a spherical silver powder magnified 2000 times.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) The present invention will be described in conjunction with the preferred solutions of the present invention; however, it should be understood that the descriptions are only to further illustrate the features and advantages of the present invention, rather than limiting the claims of the present invention.

(5) The micro-nano bubble generator applied in the present invention is an ordinary commercially available instrument.

Example 1 (Silver Powder S001)

(6) (1) Preparation of an oxidant solution containing silver nitrate: silver nitrate salt solid or equivalent silver nitrate liquid is dissolved in deionized water, the molar concentration of silver ions in the solution [silver ion] is kept at 0.3 mol/L, and the solution is kept at a constant temperature of 20° C. to 30° C.;

(7) (2) preparation of a reductant solution containing hydrazine hydrate: a hydrazine hydrate solution is added to deionized water, the molar ratio of [silver ion]:[hydrazine hydrate] in the solution is kept at 1:0.1-5 according to the silver content in the silver-containing oxidant solution, and the solution is kept at a constant temperature of 10° C. to 50° C.;

(8) (3) preparation of a dispersant solution: one or more kinds of PVP or polyethylene glycol 400 are dissolved at a content of 50-100 g/L in deionized water to obtain a dispersant solution, and the solution is stirred well and kept at a constant temperature of 10° C. to 50° C.; and

(9) (4) the dispersant solution containing the compound of PVP or polyethylene glycol 400 is pre-dispensed into the reaction vessel by using a metering pump, and simultaneously a micro-nano bubble generator is turned on to generate controllable micro-nano bubbles in the dispersant solution in the reaction vessel, and then the oxidant solution containing silver and the reductant solution containing hydrazine hydrate are quantitatively sprayed into the reaction vessel through micropores (flow rate: 10-20 L/min); the reduction reaction is carried out under vigorous stirring (300 rpm) and, after completion of the reaction, silver powder of various ranges of particle size is obtained by precipitation through addition of a flocculant.

Example 2 (Silver Powder S002)

(10) Preparation of an oxidant solution: 500 mL of silver nitrate solution containing 180 g/L of silver is prepared in a jar of 2000 mL, and 200 mL of ammonia water with a concentration of 18% by mass is added to the jar to obtain a silver-ammonia solution, which is heated to 45° C. and kept constant for future use;

(11) preparation of a reductant solution: 50 g of hydroxylamine sulfate and 50 g of vitamin C are dissolved in 500 mL of deionized water in another jar of 2000 mL to obtain a solution containing vitamin C and hydroxylamine sulfate, and the solution is heated to 45° C. and kept constant for future use;

(12) preparation of a dispersant solution: 65 g of PVP and 40 mL of Tween 40 are dissolved in 250 mL of deionized water in a jar of 500 mL to obtain a dispersant solution, and the solution is heated to 35° C. and kept constant for future use;

(13) a metering pump is used to pump the dispersant solution in advance into a jar of 5000 mL, and a micro-nano bubble generator is turned on simultaneously to generate controllable micro-nano bubbles in the dispersant solution in the reaction vessel, and then the above prepared oxidant solution and reductant solution are simultaneously added dropwise quantitatively to a jar of 5000 mL through micropores and mixed, with the flow rate of the two solutions controlled at 150 mL/min; stirring is started at a stirring rate of 400 rpm; after completion of the reaction, the flocculant is added and stirred for 10 min, and the solution is allowed to stand for precipitation, so that spherical or nearly spherical silver powder is obtained by separation.

Example 3: Mass Production (Silver Powder S003)

(14) 250 kg of silver nitrate solid is added to a preparation tank of 1000 L, 800 L of deionized water is added and stirred well, and 250 L of ammonia water of 23% is added to the solution to obtain a silver-ammonia solution, which is heated to 35° C. and kept constant for future use (oxidant solution);

(15) 500 L of deionized water is added to another preparation tank of 1000 L, then 150 kg of vitamin C and 55 kg of hydroxylamine sulfate are added and fully dissolved, and the solution is heated to 35° C. and kept constant for future use (reductant solution);

(16) 35 kg of PVP is dissolved in 400 L of deionized water in a preparation tank of 500 L and stirred well, and the solution is heated to 35° C. and kept constant for future use (dispersant solution); and

(17) a metering pump is used to pump the dispersant solution in advance into a jar of 3000 L, and a micro-nano bubble generator is turned on simultaneously to generate controllable micro-nano bubbles in the dispersant solution in the reaction vessel, and then the above prepared oxidant solution and reductant solution are spray-mixed quantitatively in the reaction vessel through micropores, with the injection flow rate of the two solutions controlled at 50 L/min; stirring is started at a stirring rate of 120 rpm; the dispersant solution is added dropwise during the reaction and, after completion of the reaction, the reaction liquid is discharged into a flocculation sedimentation tank of 5000 L, a flocculant is added, and stirring is started at a stirring rate of 300 rpm; and the mixture is rapidly stirred for 30 min and then allowed to stand for precipitation, so that the spherical or nearly spherical silver powder having an average particle size of 0.1-10 um is obtained by separation.

(18) Table 1 shows the detection data of three groups of silver powder prepared according to the method of the present invention.

(19) TABLE-US-00001 Silver powder index Silver powder Silver powder Silver powder S001 S002 S003 Powder D100 <1.0 μm <10 μm <6 μm parameter D90 0.8 ± 0.2 μm 3.5 ± 0.2 μm 3.0 ± 0.2 μm D50 0.6 ± 0.2 μm 2.5 ± 0.2 μm 1.7 ± 0.2 μm D10 0.4 ± 0.2 μm 1.8 ± 0.2 μm 1.0 ± 0.2 μm Specific surface 0.8-1.1 m.sup.2/g 0.2-0.5 m.sup.2/g 0.3-0.6 m.sup.2/g area Tap density ≥3.5 g/cm.sup.3 ≥5.5 g/cm.sup.3 ≥5.0 g/cm.sup.3 Burning loss <0.7% <0.5% <0.6% (530° C.) Morphology Spherical Spherical Spherical

(20) The electron micrographs of the silver powder S001 are shown in FIGS. 3A and 3D, the electron micrographs of the silver powder S002 are shown in FIGS. 3B and 3E, and the electron micrographs of the silver powder S003 are shown in FIGS. 3C and 3F.

(21) The technical content and the technical features of the present invention have been disclosed as above, but those skilled in the art can still make various substitutions and modifications without departing from the spirit of the present invention based on the teachings and disclosures of the present invention. Therefore, the scope of protection of the present invention should not be limited to the disclosure of the examples, but should include various substitutions and modifications without departing from the present invention, which are covered by the claims of the patent application.