KR20100081510A - A method for producing ultrafine nickel powder by chemical reduction - Google Patents

Abstract

PURPOSE: A manufacturing method of minute Ni powder by chemical reduction is provided to shorten process time by adding hydrazine and sodium hypophosphite as a reducing agent. CONSTITUTION: First solution is made of hydroxide nickel by adding pH adjusting agent into nickel sulfate. Hydrazine and sodium hypophosphite are injected into the distilled water to make second solution. First solution and second solution are mixed and stirred to make Ni powder. The Ni powder is separated from solution. The separated Ni powder is cleaned and dried.

Description

A method for producing ultrafine nickel powder by chemical reduction

The present invention relates to a method for producing fine nickel powder by chemical reduction method, and more particularly, nickel sulfide (NiSO ₄ ) and sodium hydroxide (NaOH) by reacting nickel hydroxide (Ni (OH)) in order to facilitate a reduction reaction. ₂ ) to prepare a reaction solution, the sodium hypophosphite and hydrazine at the same time by reducing the reaction to prepare a fine nickel powder, and by adding an organic solvent to prepare a fine nickel powder that can grow the particle size of the nickel powder It is about a method.

Nano-sized nickel powders are being actively researched for use in batteries, multilayer ceramic capacitors (MLCC), catalysts, and high alloy phases. In particular, high-purity spherical nickel powders ranging from 100 nm to several μm in size have attracted much attention. In line with the trend of miniaturization of applications using red ceramic capacitors, the thickness of each ceramic layer and the thickness of the inner conductor layer are further reduced to form a multilayer structure of components and substrates of the multilayer ceramic capacitor. The number of floors is increasing. As a result, the specific gravity of the internal electrode is gradually increased so that the internal electrode material of the multilayer ceramic capacitor is expensive noble metal, palladium (Pd), platinum (Pt), and inexpensive metal, nickel (Ni) or copper (Cu). It is being replaced.

Nickel powder production methods include sonochemistry, microemulsion method, chemical reduction method, gas phase reaction method, ball mill method, hydrothermal synthesis method and the like. According to Chen, nanosized nickel powders were obtained by reducing nickel chloride (NiCl ₂ ) through hydrazine in emulsion ( Chem . Mater , 2000, 12, 1354), and Prozorov used an acoustic chemical reaction of volatile organic precursors. Nickel and cobalt-nickel compounds were studied ( J. Mater . Chem , 1998, 8, 769). They controlled the composition of the nickel-cobalt compound by varying the concentration of initial precursors in the solution. Toneguzzo prepared micrometer-sized nickel, cobalt-nickel and iron-cobalt-nickel compounds by polyol method ( J. Mater. Sci , 2000, 35, 3767). As disclosed in Korean Patent Application No. 1999-7009697, there is a gas phase reduction method of reducing and depositing nickel powder by contacting a reducing gas such as hydrogen with vapor of nickel chloride. However, these methods require a variety of devices and high-risk hydrogen gas is used as the reducing agent in the process of obtaining powder. In addition, in the case of the gas phase reduction method, since the particles are formed by instantaneous reaction, it is difficult to control the size, shape, and particle size of the particles, and because the reaction is performed at a high temperature of 1000 ° C. or more, the cost of the manufacturing process itself is expensive.

According to the chemical reduction method ( Korean Ceramic Society , 2005. 42 (6), 432-436), nickel powder was prepared by the liquid reduction method, and a method using hydrazine as a reducing agent is known. However, this method is not economical because the particle size of the nickel powder is generally large, about 2 μm, and a reduction reaction is required for a long time at a high temperature.

Nickel powders are important not only for small particle size but also for chemical uniformity and crystallinity. Among the various manufacturing methods, coprecipitation is a manufacturing method that satisfies these needs, and is advantageous in forming a final structure through a dynamic equilibrium process.

In order to solve the above problems, the present invention provides a method for economically producing nickel powder in a liquid phase at room temperature by a chemical reduction method in a short time, the particles of the nickel powder has a size of 100 ㎛ to several ㎛, lamination It is to provide a method that can control the particle size of the nickel powder to have a particle size suitable for use as a material for the internal electrode of the ceramic capacitor.

Thus, the method for producing the fine nickel powder of the present invention provides a method prepared by a chemical reduction reaction consisting of (nickel sulfate (II) + sodium hydroxide)-(hydrazine + sodium hypophosphite)-water system.

EMBODIMENT OF THE INVENTION Hereinafter, the content of this invention is demonstrated in detail.

In the method for producing fine nickel powder by the chemical reduction method of the present invention,

a) nickel sulfate (Ⅱ) was dissolved was added a pH adjusting agent nickel hydroxide (Ni (OH a) ₂₎ Making a first solution to be produced; Preparing a second solution by adding hydrazine (N ₂ H ₂ ) and sodium hypophosphite (NaH ₂ PO ₂ ) to distilled water; b) mixing the first solution and the second solution and stirring to produce nickel powder; c) obtaining the resulting nickel powder by separating it from the filtrate and washing with water to remove impurities to provide a method for producing a fine nickel powder.

Hereinafter, the content of the present invention will be described in more detail.

In the method for preparing fine nickel powder according to the present invention, for preparing the first solution of step a), nickel (II) sulfate (NiSO ₄ ) or nickel sulfate (II) hydrate (NiSO ₄ 6H ₂ O) as a starting material The silver is dissolved by stirring in distilled water for a certain time, and basic compounds such as sodium hydroxide, ammonia water, potassium hydroxide and sodium carbonate may be used, and it is preferable to use sodium hydroxide. The amount of the pH adjusting agent is advantageously added until the pH of the nickel sulfate solution is 8 to 13, preferably 10 to 13. When the pH of the first solution is less than 8, the production time of nickel hydroxide becomes long and the particle size is not dense. If the pH of the first solution exceeds 13, the expected effect of increasing the process cost may not be achieved.

In the preparation of the first solution, mixing nickel sulfate (II) and sodium hydroxide requires a method of dissolving nickel sulfate (II) and slowly dropwise adding an aqueous sodium hydroxide solution rather than mixing them simultaneously. When mixing nickel (II) sulfate and sodium hydroxide at the same time, a jelly type mixture may be formed.

In the present invention, a method of simultaneously using hydrazine and sodium hypophosphite as a reducing agent for producing fine nickel powder was adopted. As a reducing agent, hydrazine has been described in the invention for preparing a fine nickel powder by a known chemical reduction method, but by using hydrazine alone, a result of obtaining a nickel powder by stirring at a high temperature for a long time is obtained. However, in the present invention, by using hydrazine and sodium hypophosphite at the same time as the reducing agent can be expected to obtain a high-purity fine nickel powder in a fast time at room temperature without applying heat.

Determination of the dosage of hydrazine and sodium hypophosphite for the preparation of the second solution of step a) is determined according to the effect of the concentration of nickel sulfate (II), sodium hydroxide, hydrazine and sodium hypophosphite on the particle formation of nickel powder In order for the nickel powder particles to have a particle size of 100 μm to several μm, the molar ratio of nickel sulfate (II): sodium hydroxide: hydrazine: sodium hypophosphite is (0.1 to 1.5): (2.4 to 3.75): (1.5 to 7.5). ): (0.1 to 0.8) is preferred, and 1: 1: (2.4 to 3.75): (1.5 to 7.5): (0.4 to 0.62) is most preferably mixed.

In step b), sodium hypophosphite is not reduced by itself. However, by using a proper combination of hydrazine and sodium hypophosphite it causes a reduction reaction at a high speed at room temperature. The molar ratio of nickel sulfate (II): sodium hydroxide: hydrazine was dissolved in 1: 3.75: 7.0, and sodium hypophosphite relative to 1 mol of nickel (II) sulfate was added in an amount of 0.1 to 0.8 mol, preferably 0.4 to 0.62 mol. It is advantageous. As the concentration of sodium hypophosphite increases, it can be observed that the particle size decreases and has a spherical shape (FIGS. 4 and 5), and the time until the nickel reduction reaction starts is shortened from 5 minutes to 1 to 2 minutes. Can be observed. This may be because the rate of nucleation increases as the concentration of sodium hypophosphite increases. However, when the concentration of sodium hypophosphite is less than 0.1 mole, the reduction effect by hydrazine is significantly reduced, and when the concentration of sodium hypophosphite exceeds 0.8 mole, the particle size of the nickel powder is no longer small.

From what described above, the nickel divalent cation reduction mechanism of the (Ni ^{+ 2)} is a nickel-it can be seen that the particles formed by the (Ni-P). That is, nickel divalent cations together with hypophosphite ions (H ₂ PO ₂ ⁻ ) form a nickel-phosphorus compound, which is an amorphous activation catalyst, and is reduced to nickel by dropping a potassium borohydride (KBH ₄ ) solution. In the present invention, the reduction process of (nickel sulfate (II) + sodium hydroxide)-(hydrazine + sodium hypophosphite)-water system is shown in Scheme 1 below.

Scheme 1

However, the X-ray diffraction analysis did not find the structure of the Ni-P compound and after calcination at 400-500 ° C. In other words, it can be expected that these compounds exist for a short time and eventually change to nickel.

As described above, hydrazine shows superior reducing ability in temperature conditions and reaction times by using together with sodium hypophosphite than when used alone as a reducing agent. When the concentration of sodium hypophosphite was 0.8 mol or more, the nickel powder particle size did not become small anymore. For this reason, the molar ratio of nickel sulfate (II): sodium hydroxide: sodium hypophosphate is dissolved at 1: 3.75: 0.62, and the hydrazine relative to 1 mol of nickel sulfate is 1.25 mol to 7.5 mol, preferably 1.5 mol to 7.0 It is advantageous to react with moles. When the concentration of hydrazine is less than 1.25 moles, nickel hydroxide, which does not complete the reduction reaction and does not react with the nickel powder particles, is found together. It is believed that the proper amount of reducing agent is a major factor in the production of nickel powder. As a result, as the concentration of the hydrazine is changed from 1.5 mol to 7.0 mol, the average particle size of the nickel powder is formed in the range of 0.07 µm to 0.15 µm.

In the process of reducing the nickel divalent cation together with the hydrazine and sodium hypophosphite, the addition of the organic solvent affects the growth of the particles. The organic solvent here is at least one selected from the group consisting of ethylene glycol, diethylene glycol, polyethylene glycol and butadiene, preferably diethylene glycol is advantageous. In the present invention, the organic solvent added to the reduction reaction of nickel divalent cation has a weight ratio of nickel sulfate (II) / organic solvent in the range of 0.1 to 0.6, preferably 0.1 to 0.3, which is advantageous for grain growth of nickel powder. Do. As the input amount of the organic solvent increases, the particle size of the nickel powder increases from 0.3 μm to 2.0 μm and a nickel powder having good dispersibility can be obtained. It is considered that the relatively high boiling point of the organic solvent raises the viscosity of the entire solution, thereby increasing the energy required for nucleation, thereby reducing the number of nucleation and increasing the particle size.

In the mixed solution of step b), the reaction temperature is at room temperature, the reduction reaction time is 0.5 to 6 hours, preferably 0.5 to 2 hours, the reaction is completed. As the progress of the reaction proceeds, the color of the initial mixed solution becomes green, and gradually decreases to black as the reduction reaction proceeds, and the colloidal form of nickel collides.

The nickel powder prepared after the completion of the reduction reaction in step c) is separated from the filtrate and washed several times with distilled water to remove impurities in the reactant and dried in a vacuum dryer at 70 ° C. for at least 24 hours.

Characteristic of the production method of the fine nickel powder of the present invention can control the particle size of the nickel powder within the range of 100nm to 2㎛ according to the concentration of nickel sulfate (II), hydrazine, sodium hypophosphite and organic solvent, Depending on the concentration of sodium phosphite, the reduction reaction time can be shortened. More specifically, the higher the concentration of nickel (II) sulfate, the thinner the hydrazine concentration, the higher the concentration of sodium hypophosphite, the smaller the particle size of the nickel powder, and the thinner the concentration of nickel (II) sulfate As the concentration of hydrazine increases, the concentration of sodium hypophosphite decreases, and as the amount of organic solvent added increases, the particle size of the nickel powder increases. This is summarized in Table 1.

[Table 1] Nickel Powder Particle Size and Concentration Correlation

The present invention relates to a method for producing fine nickel powder by chemical reduction method, and compared to other known methods, by adding not only hydrazine but also sodium hypophosphite as a reducing agent, the process time can be significantly shortened without adding heat. In addition, it is an economical process that can control the particle size of the nickel powder from 100nm to 2㎛.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are not intended to limit the invention only.

As a method for evaluating the physical properties of the nickel powder in Example, the crystal phase was investigated by X-ray diffraction analysis (XRD: X-ray diffraction, SIEMENS, MODEL: D5000), to observe the size and shape of the nickel powder A scanning electron microscope (SEM: scanning electron microscopy, JEOL, MODEL: JSM-5410) was used.

The types and properties of the reagents used in the examples of the present invention are shown in Table 2.

[Table 2] Types and Characteristics of Reagents

Example 1

To obtain nickel hydroxide (II), 131.43 g (0.5 mole) of nickel sulfate (II) hydrate was dissolved in 1 L of distilled water, and 96 g (2.4 mole) of NaOH was added thereto, followed by stirring at room temperature for 10 minutes to adjust the pH to 10 or more. Here, 145.77 g (2.24 mole) of hydrazine hydrate and 35.20 g (0.4 mole) of sodium hypophosphite hydrate were stirred and slowly added to the solution to react. At this time, the solution was changed from green to black to form a nickel colloid and stirred until the reduction reaction was completed. The precipitate prepared after completion of the reduction reaction was separated from the filtrate, washed several times with distilled water to remove impurities in the reactant, and dried in a vacuum dryer at 70 ° C. for 24 hours.

[Example 2]

Under the same conditions as in Example 1, only 262.86 g (1.0 mole) and 394.29 g (1.5 mole) of nickel sulfate hydrate were dissolved.

Nickel powders obtained in Examples 1 and 2 are shown in FIG. 2 through X-ray diffraction analysis. As a result, it could be seen that the particles of the nickel powder were nickel of a typical FCC structure, and no peaks other than the peak of nickel appeared, and it was confirmed that high purity nickel powder was obtained through this.

Example 3

Dissolve 131.43 g (0.5 mole) of nickel sulfate (II) hydrate in 1 L of distilled water in two beakers, add 96 g (2.4 mole) of NaOH, and stir at room temperature for 10 minutes to adjust the pH to 10 or more. 50g (0.47mole) of diethylene glycol (DEG) was put, and 200g (1.88mole) of diethylene glycol was put into the other beaker. Here, 145.77 g (2.24 mole) of hydrazine hydrate and 35.20 g (0.4 mole) of sodium hypophosphite hydrate were stirred and slowly added to the solution to react. At this time, the solution was changed from green to black to form a nickel colloid and stirred until the reduction reaction was completed. The precipitate prepared after completion of the reduction reaction was separated from the filtrate, washed several times with distilled water to remove impurities in the reactant, and dried in a vacuum dryer at 70 ° C. for 24 hours.

As a result of observing the obtained nickel powder through a scanning electron microscope, as shown in FIG. 3, when 200 g of diethylene glycol was added, the average particle size of the nickel powder was 0.3 μm to 0.5 μm, and diethylene glycol was obtained. When 50 g was added, a micro-sized spherical nickel powder having good dispersibility was obtained.

Comparative Example 1 Influence of Sodium Hypophosphite Concentration

The molar ratio of nickel (II) sulfate: sodium hydroxide: hydrazine: sodium hypophosphite is 1: 3.75: 7.0: 0.1-0.8, and the molar ratio of nickel (II) sulfate, sodium hydroxide, hydrazine is fixed and the concentration of sodium hypophosphite I've only changed. The same process as in Example 1 was performed. And the obtained nickel powder was observed with the scanning electron microscope, and the relationship between the sodium hypophosphite and the particle size of nickel powder is shown graphically.

As shown in Figures 4 and 5, it can be observed that the particle size decreases as the concentration of sodium hypophosphite increases. In addition, the experiment confirmed that as the concentration of sodium hypophosphite increases, the time until the nickel reduction reaction starts is shortened from 5 minutes to 1 to 2 minutes.

Comparative Example 2 Influence of Hydrazine Concentration

The molar ratio of nickel (II) sulfate: sodium hydroxide: hydrazine: sodium hypophosphite is 1: 3.75: 0.88 to 7.5: 0.62, and the molar ratio of nickel (II) sulfate, sodium hydroxide and sodium hypophosphite is fixed and the concentration of hydrazine I've only changed. The same process as in Example 1 was performed. The obtained nickel powder was observed by scanning electron microscopy and X-ray diffraction analysis.

As a result, as shown in Figures 6 and 7, the average particle size appeared in the range from 0.07㎛ to 0.15㎛ as the concentration of hydrazine is changed from 1.5mol to 7.5mol. When the hydrazine concentration was less than 1.25mol, the complete reduction reaction was not completed. Nickel particles and nickel hydroxide particles were found together, and when the hydrazine concentration was more than 7mol, the crystallinity tended to decrease little by little. This confirmed that the proper addition amount of the reducing agent is a major factor in the production of nickel powder.

Comparative Example 3 Thermodynamic Analysis

Ni (OH) ₂ -αN ₂ H ₄ -H ₂ O, Ni (OH) ₂ -αNaH ₂ PO ₂ -H ₂ O, Ni (OH) ₂ -2.0N ₂ H ₄ -αNaH ₂ PO ₂ -H ₂ O In order to determine the optimal composition of the three reaction systems, a thermodynamic analysis program was used. The concentration of hydrazine in the third system was set to 2.0 mol, referring to the literature ( Korean Ceramic Society , 2005, 10, 649), and the results analyzed by the 'thermodynamic analysis' program under T = 298K and P = 1.0 atm are shown in FIG. 8. It is shown in. As a result, it can be seen that nickel powder can be produced when the molar concentration of hydrazine is higher than 2.0 mol when the nickel hydroxide is reduced by hydrazine, and N2 and NH3 are generated together with the nickel powder (FIG. 8A). When the molar concentration was lower than 2.0 mol, it remained in the form of nickel monoxide (NiO). Unlike the Ni (OH) ₂ -αNaH ₂ PO ₂ -H ₂ O system, it can be seen from Figure 8b that the nickel powder can not be obtained. In this reaction system, P ₄ O ₁₀ , together with NaOH was reduced to form a nickel compound was found to require a separate treatment. Finally, when a reducing agent is used together with N ₂ H ₄ + NaH ₂ PO _2, it is as shown in FIG. 8C. According to the concentration of NaH ₂ PO ₂ , Ni ₃ P and Ni ₅ P ₂ compounds appeared with pure nickel powder. When NaH ₂ PO ₂ was α> 0.4, nickel was completely Ni ₃ P and Ni ₅ P ₂ It can be seen that the compound changes.

Precious metal powders such as palladium (Pd) and platinum (Pt) are mostly used as internal electrodes of multilayer ceramic capacitors. The situation is being switched to the spherical nickel powder of 1.0 μm or less. In addition, nano-sized nickel powder can be used as a catalyst, a magnetic material, an anode material for SOFC, and the like, and its use is expected to be extensive.

1 is a flowchart showing a process for producing a fine nickel powder by the chemical reduction method of the present invention,

Figure 2 shows the concentration of nickel (II) sulfate (a) 0.5 mole, (b) 1.5 mole; The particle shape of the nickel powder according to the observation was observed through a scanning electron microscope,

Figure 3 shows the concentration of diethylene glycol when diethylene glycol is added to the reaction solution (a) 90:10; (b) 70:30; Particle growth of the nickel powder was observed by scanning electron microscope,

Figure 4 is a graph showing the particle size change of the nickel powder with the concentration of sodium hypophosphite at room temperature,

Figure 5 shows the concentration of sodium hypophosphite at room temperature (a) 0.078 mol; (b) 0.156 mol; (c) 0.31 mol; (d) 0.47 mol; The particle size change of the nickel powder was observed by scanning electron microscope,

Figure 6 shows the concentration of hydrazine (a) 1.5 mol; (b) 7.5 mol; The particle size change of the nickel powder was observed by scanning electron microscope,

7 shows the concentration of hydrazine (a) 0.88 mol; (b) 1.25 mol; (c) 1.75 mol; (d) 3.5 mol; (e) 7 mol; The composition of nickel powder was observed by X-ray diffraction analysis.

FIG. 8 shows (a) Ni (OH) ₂ -αN ₂ H ₄ -H ₂ O, at 25 ° C. and 1 atmosphere; (b) Ni (OH) ₂ -αNaH ₂ PO ₂ -H ₂ O; (c) Ni (OH) ₂ -2.0N ₂ H ₄ -αNaH ₂ PO ₂ -H ₂ O; The reaction mechanism of nickel according to the change is classified through the thermodynamic analysis method.

Claims (10)

a) Nickel sulphate (II) (NiSO ₄ ) is dissolved and a pH regulator is added to form nickel hydroxide (Ni (OH) ₂ ). Making a first solution to be produced; Preparing a second solution by adding hydrazine (N ₂ H ₂ ) and sodium hypophosphite (NaH ₂ PO ₂ ) to distilled water; b) mixing the first solution and the second solution and stirring to produce nickel powder; And c) obtaining the resulting nickel powder from the filtrate and washing with water to remove impurities, followed by drying. Method for producing a fine nickel powder containing. The method of claim 1, A molar ratio of nickel sulfate (II): hydrazine: sodium hypophosphite is added at a concentration of 1: 1.5 to 7.5: 0.4 to 0.62 to produce fine nickel powder. The method according to claim 1 or 3, pH adjusting agent is a method for producing fine nickel powder to be added at least one selected from the group consisting of ammonia water, potassium hydroxide and sodium hydroxide. The method of claim 1, Method for producing a fine nickel powder to a pH adjusting agent of step a) so that the pH of the first solution is 10 to 13. The method of claim 1, Method of producing a fine nickel powder comprising the step of controlling the particle size of the nickel powder by adding an organic solvent to the mixed solution of step b). The method of claim 5, The organic solvent is a method for producing fine nickel powder, characterized in that at least one selected from the group consisting of ethylene glycol (ethylene glycol), diethylene glycol (diethylene glycol), polyethylene glycol (polyethylene glycol) and butanediol. The method of claim 5, A method for producing fine nickel powder in which the amount of the organic solvent added to the mixed solution is 0.1 to 0.6 in weight ratio of nickel sulfate (II) / organic solvent. The method according to claim 1 or 5, Method for producing a fine nickel powder, characterized in that to control the particle size of the nickel powder to 0.07㎛ to 2.0㎛. The method of claim 1, The reduction reaction time of the mixed solution is a method for producing fine nickel powder to be 0.5 ~ 2 hours.  The method of claim 1, Reduction temperature of the mixed solution is a method for producing a fine nickel powder, characterized in that the room temperature.

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