CN1219617C - Method of preparing nano metal nickel powder - Google Patents

Abstract

The present invention relates to a method for preparing nanometer metal nickel powder. The method comprises: firstly, nickel sulfate is matched with a water solution of 0.2 to 1.0 mol/l; secondly, potassium borohydride of which the weight permillage is 2 to 5 is added in a hydrazine hydrate water solution to obtain a second solution; thirdly, a first solution is heated up to 50 to 80 DEG C, the second solution is added, a charging rate is controlled at 20 to 40 ml/s, and after reacting, the nanometer metal nickel powder is prepared. The method has fast reaction ratio, percent reduction achieves 100%, nickel powder granules are smaller than 100 nm through distribution, and the purity of the nickel powder is larger than 98%.

Description

Method for preparing nano metal nickel powder

Technical Field

The inventionrelates to a method for preparing nano metal nickel powder.

Background

The nanometer superfine nickel powder has great volume effect and surface effect, and thus has excellent magnetic performance, heat resistance, chemical activity and other features and wide application foreground. For example, ultrafine nickel powders can be made into conductive pastes to replace precious metals; can be used as combustion improver of solid propellant and engineering blasting explosive; it can be used as catalyst for high-performance chemical and metallurgical industry, and magnetic recording material.

The production method of metallic nickel powder has been the focus for a long time, and the nickel powder produced by the traditional method is usually micron or submicron grade, such as nickel carbonyl pyrolysis method, hydrogen catalytic reduction method, chemical reduction method. In recent years, with the rise of nanotechnology heat, new methods have been developed for the preparation of nano nickel powder, among which physical methods, such as plasma sputtering; physical chemical methods such as microwave plasma chemical synthesis, ball milling chemical reaction; while chemical methods such as chemical vapor deposition, sol-gel methods, hydrothermal methods, carboxylate pyrolysis methods, and the like are still used more frequently. The applicant has prepared ultrafine nickel powder with an average particle size of 5nm by reducing nickel halide with zinc in an alkaline aqueous solution by forming a nano nickel powder coating layer on the surface of zinc powder particles by using a displacement reaction, and then dissolving out excessive zinc by alternately using dilute acid and concentrated alkali to obtain the nano nickel powder. The method has the advantages that the prepared nickel powder is fine and is generally below 30nm, but the reaction yieldis low and the purity is not high enough.

Disclosure of Invention

The invention aims to provide a method for preparing nano metallic nickel powder, which has the advantages of high reaction rate, high reduction rate and particle size distribution of the nickel powder of less than 100 nm.

In order to achieve the purpose, the invention adopts the following technical scheme: the method for preparing the nano metallic nickel powder comprises the following steps:

(1) preparing 0.2-1.0mol/l aqueous solution of nickel sulfate, adjusting the pH value to 8-10 by using ammonia water and dilute sulfuric acid respectively, and adding a dispersing agent to obtain a solution I, wherein the adding amount of the dispersing agent is 2-5 per mill of the weight of the solution I;

(2) adding potassium borohydride into a hydrazine hydrate aqueous solution to obtain a solution II, wherein the potassium borohydride accounts for 2-5 per mill of the weight of the solution II;

(3) heating the solution I to 50-80 ℃, adding the solution II under vigorous stirring, wherein the feeding speed of the solution II is 20-40ml/s, and obtaining black powder after reaction, namely the nano metal nickel powder.

In the step (3), the reaction time is 15-30 min.

In the step (3), the weight ratio of hydrazine hydrate to nickel sulfate is controlled to be 2-3: 1.

In the above step (2), the hydrazine hydrate aqueous solution is used in a concentration of 20 to 25% by weight, which is generally used.

In the step (2), the optimal range of potassium borohydride in the solution II is 3-4 wt%.

Inthe step (1), the addition amount of the dispersing agent is 2-5 per mill of the weight of the solution I.

Hydrazine hydrate is a commonly used reducing agent for preparing metal powder, and the reduction reaction with nickel sulfate is as follows:

ΔG°＝-262.4KJ

the reaction is thermodynamically feasible, but the kinetic properties are poor by using hydrazine hydrate alone as a reducing agent, and the reaction is difficult to carry out initially. Potassium borohydride is a strong reducing agent, and reacts with nickel salt to generate fine crystal nuclei firstly, so that the whole reduction reaction is promoted, the reaction is completed in a short time, and the superfine nickel powder with the particle size distribution of less than 100nm is favorably generated.

Drawings

FIG. 1 is a graph showing the effect of nickel sulfate concentration on the average particle diameter of nickel powder

FIG. 2a is a TEM photograph (X5000) of a nickel powder obtained under the condition that the concentration of nickel sulfate is 0.2mol/l

FIG. 2b is a TEM photograph (X5000) of a nickel powder obtained under the condition that the concentration of nickel sulfate is 1.0mol/l

FIG. 3 is a graph showing the effect of potassium borohydride on reaction rate

FIG. 4 is a graph showing the effect of potassium borohydride on average particle size

FIG. 5a is a TEM photograph of the nickel powder with 2% by weight of potassium borohydride (magnification:. times.50000)

FIG. 5b is a TEM photograph of the nickel powder with potassium borohydride in an amount of 3.5 wt.% (× 50000)

FIG. 6 is a graph showing the effect of reaction temperature on reaction rate

FIG. 7 is a graph showing the effect of reaction temperature on average particle diameter

FIG. 8a is a TEM photograph of nickel powder at a reaction temperature of 50 ℃ (X50000)

FIG. 8b is a TEM photograph of nickel powder at a reaction temperature of 70 ℃ (X50000)

FIG. 9 is a graph of the effect of feed rate on reaction rate

FIG. 10 is a graph of the effect of feed rate on average particle size

FIG. 11a is a TEM photograph (5000) of nickel powder at a feed rate of 20ml/s

FIG. 11b is a TEM photograph (5000) of nickel powder at a feed rate of 30ml/s

FIG. 12 is EDS spectrum of nano metallic nickel powder

Detailed Description

Example 1

Preparing 0.2mol/l aqueous solution of nickel sulfate, adjusting the pH value to 9 by using ammonia water and dilute sulfuric acid respectively, and adding 3 per mill of dispersant by weight to obtain solution I; wherein, the weight thousandths of the dispersant is the weight thousandths of the dispersant in the solution I, and the following examples are the same. Preparing 50 wt% hydrazine hydrate aqueous solution into 20 wt% hydrazine hydrate aqueous solution, and adding 3 wt% potassium borohydride to obtain solution II; the weight of potassium borohydride is the weight of potassium borohydride in solution II, and the following examples are all the same. And (3) heating the solution I to 70 ℃, adding the solution II into the solution I at a feeding speed of 30ml/s under vigorous stirring, wherein the weight ratio of hydrazine hydrate to nickel sulfate is controlled to be 2.5: 1, reacting for 20min to obtain black powder, washing for several times by secondary water, and drying for 8h at low temperature in an argon atmosphere to obtain the nano nickel powder.

Examples 2 to 5

The conditions of examples 2 to 5 were the same as those of example 1 except that nickel sulfate was prepared in aqueous solutions of different concentrations. Wherein, the nickel sulfate in the embodiment 2 is prepared into 0.4mol/l aqueous solution; the nickel sulfate in the embodiment 3 is prepared into 0.6mol/l aqueous solution; the nickel sulfate in the embodiment 4 is prepared into 0.8mol/l aqueous solution; the nickel sulfate in the embodiment 5 is prepared into 1mol/l aqueous solution;

in the above 5 examples, the effect of the concentration of nickel sulfate on the average particle diameter of the nickel powder is shown in FIG. 1. The morphology and particle size of the nickel powder at two different nickel sulfate concentrations of 0.2mol/l and 1mol/l are shown in TEM photographs in FIGS. 2a and b.

As can be seen from fig. 1, 2a and b, the average particle size of the nickel powder increases with the increase in the concentration of nickel sulfate, and it is generally considered that the formation of nanoparticles should be performed in a relatively dilute solution, because the probability of the formation of large particles due to aggregation of nuclei by collision is reduced when the concentration is low. Experiments show that the concentration of nickel salt is less than 1.0mol/l to obtain the nano nickel powder with the particle size distribution of less than 100 nm.

Example 6

Preparing 0.25mol/l aqueoussolution of nickel sulfate, adjusting the pH value to 9 by using ammonia water and dilute sulfuric acid respectively, and adding 3 per mill of dispersant by weight to obtain solution I; preparing 50 wt% hydrazine hydrate aqueous solution into 20 wt% hydrazine hydrate aqueous solution, and adding 1 wt% potassium borohydride to obtain solution II; and (3) heating the solution I to 70 ℃, adding the solution II into the solution I at a feeding speed of 35ml/s under vigorous stirring, wherein the weight ratio of hydrazine hydrate to nickel sulfate is controlled to be 2.5: 1, reacting for 20min to obtain black powder, washing for several times by secondary water, and drying for 8h at low temperature in an argon atmosphere to obtain the nano nickel powder.

Examples 7 to 10

The conditions in examples 7-10 were the same as in example 6 except that different amounts of potassium borohydride were used. Wherein the addition amount of potassium borohydride in example 7 is 2 weight ‰; the addition amount of potassium borohydride in example 8 was 3 weight ‰; the amount of potassium borohydride added in example 9 was 4% by weight; the amount of potassium borohydride added in example 10 was 5% by weight.

The amount of added potassium borohydride has a great influence on the reaction rate and the average particle size of the extra-fine nickel powder, as shown in fig. 3 and 4. FIGS. 5a and b are TEM photographs of the nano nickel powder prepared under the conditions that the potassium borohydride is added in an amount of 2 wt% and 3.5 wt%, respectively. It can be seen that within a certain range, the reaction speed increases with the increase of the addition amount of the additive, and the average particle size tends to decrease, but the more the potassium borohydride is, the better the average particle size is, the more the potassium borohydride. If the additive is used in a larger amount, more crystalnuclei are generated instantaneously but not dispersed, and the crystal nuclei are likely to aggregate and grow.

Example 11

Preparing 0.3mol/l aqueous solution of nickel sulfate, adjusting the pH value to 9 by using ammonia water and dilute sulfuric acid respectively, and adding 3 per mill of dispersant by weight to obtain solution I; preparing 50 wt% hydrazine hydrate aqueous solution into 20 wt% hydrazine hydrate aqueous solution, and adding 3 wt% potassium borohydride to obtain solution II; and (3) heating the solution I to 50 ℃, adding the solution II into the solution I at a feeding speed of 30ml/s under vigorous stirring, wherein the weight ratio of hydrazine hydrate to nickel sulfate is controlled to be 2.5: 1, reacting for 20min to obtain black powder, washing for several times by secondary water, and drying for 8h at low temperature in an argon atmosphere to obtain the nano nickel powder.

Examples 12 to 14

The conditions in examples 12 to 14 were the same as in example 11 except that the reaction temperature was changed. In examples 12 to 14, the reaction temperatures were 60 ℃, 70 ℃ and 80 ℃, respectively.

The reaction temperature has a large influence on the reaction speed, the reaction speed is accelerated with the increase of the reaction temperature, but the solution may be subjected to bumping if the reaction temperature is too high, so the reaction temperature is preferably controlled to be 50-80 ℃. FIGS. 6 and 7 are graphs showing the influence of the reaction temperature on the reaction rate and the average particle diameter, respectively, and FIGS. 8a and b are TEM photographs of nickel powder at a reaction temperature of 50 ℃ and 70 ℃. It can be seen that the reaction temperature is increased and the average particle size of the nano nickel powder is decreased.

Example 15

Preparing 0.3mol/l aqueous solution of nickel sulfate, adjusting the pH value to 9 by using ammonia water and dilute sulfuric acid respectively, and adding 3 per mill of dispersant by weight to obtain solution I; preparing 50 wt% hydrazine hydrate aqueous solution into 20 wt% hydrazine hydrate aqueous solution, and adding 3 wt% potassium borohydride to obtain solution II; and (3) heating the solution I to 70 ℃, adding the solution II into the solution I at a feeding speed of 10ml/s under vigorous stirring, wherein the weight ratio of hydrazine hydrate to nickel sulfate is controlled to be 2.5: 1, reacting for 20min to obtain black powder, washing for several times by secondary water, and drying for 8h at low temperature in an argon atmosphere to obtain the nano nickel powder.

Examples 16 to 18

The conditions in examples 16-18 were the same as in example 15 except that different feed rates were used. In examples 16 to 18, the feed rates were 20ml/s, 30ml/s and 40ml/s, respectively.

The feeding speed of the solution II has great influence on the reaction speed and the average particle size of the nano nickel powder. Within a certain range, the reaction speed is accelerated and the average particle size of the nickel powder is reduced with the increase of the feeding speed, but if the feeding speed is too high, the reducing agent cannot be dispersed, so that the reaction speed is reduced, and the particle size is not uniform and the particle size distribution is widened due to the high local concentration, so that the feeding speed is strictly controlled. The effect of the feed rate on the reaction rate and the average particle diameter are shown in FIGS. 9 and 10, respectively. FIGS. 11a and b are TEM photographs of nickel powder at different feed rates of 20ml/s and 30ml/s, respectively. As can be seen from the figure, the feed rate is preferably 20 to40 ml/s.

FIG. 12 is an EDS spectrum of nano nickel powder prepared by the method of the present invention. In the figure, 0.9, 7.5, and 8.2KeV are characteristic peaks of Ni, 8.0 and 8.9KeV are Cu peaks of copper mesh, 0.2 and 0.4KeV are C, O peaks of organic film, respectively, and no other impurity peaks, and it can be seen that the purity of the prepared nano nickel powder is more than 98%.

The preparation method of the invention has the following advantages:

1. usually, hydrazine hydrate is used as a reducing agent to prepare the superfine nickel powder, the reaction speed is slow, the reduction rate is low, after the potassium borohydride is added, the reaction speed is obviously improved, the reduction rate reaches 100 percent, and the particle size distribution of the nickel powder is less than 100 nm.

2. The ideal process conditions for preparing the nano nickel powder are that the reaction temperature is 50-80 ℃, the feeding speed is 20-40ml/s, the concentration of nickel salt is less than 1.0mol/l, and the dosage of potassium borohydride is 2-5 per mill by weight.

3. The nano nickel powder prepared by TEM observation has the particle size distribution of 30-70nm and is approximately spherical. EDS analysis shows that the purity of the nickel powder is more than 98 percent.

Claims (2)

1. A method for preparing nanometer metallic nickel powder is characterized in that: the method comprises the following steps:

(1) preparing 0.2-1.0mol/l aqueous solution of nickel sulfate, adjusting the pH value to 8-10 by using ammonia water and dilute sulfuric acid respectively, and adding a dispersing agent to obtain a solution I, wherein the adding amount of the dispersing agent is 2-5 per mill of the weight of the solution I;

(2) adding potassium borohydride into a hydrazine hydrate aqueous solution to obtain a solution II, wherein the potassium borohydride accounts for 2-5 per mill of the weight of the solution II;

(3) heating the solution I to 50-80 ℃, adding the solution II under vigorous stirring, wherein the feeding speed of the solution II is 20-40ml/s, and obtaining black powder after reaction, namely the nano metal nickel powder.

2. The method for producing nano-metallic nickel powder according to claim 1, wherein: in the step (2), potassium borohydride accounts for 3-4 per mill of the solution II by weight.

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