KR101252057B1 - METHOD OF MANUFACTURING Co POWDER USING SLURRY REDUCTION METHOD WITH EXCELLENT REACTION VELOCITY - Google Patents

Abstract

Disclosed is a method for producing cobalt powder having a high reaction rate capable of producing a dendritic high purity cobalt powder from a Co (OH) ₂ slurry using a slurry reduction method.
Cobalt powder manufacturing method according to the present invention comprises the steps of (a) dissolving the cobalt salt and NaOH in a solvent in a weight ratio of 1: 8 ~ 1: 24 to form a Co (OH) ₂ slurry; (b) injecting said Co (OH) ₂ slurry into a reaction vessel; (c) stirring the slurry introduced into the reaction vessel while heating; It characterized in that it comprises a and (d) by reduction reaction of the Co (OH) ₂ slurry to supply a reducing agent to the above-stirred Co (OH) ₂ slurry to obtain a cobalt powder.

Description

METHODS OF MANUFACTURING CO POWDER USING SLURRY REDUCTION METHOD WITH EXCELLENT REACTION VELOCITY

The present invention relates to a cobalt powder production technology widely used in high-tech industries such as electronics, precision industry, batteries, and more particularly to producing a high-purity cobalt powder of dendritic type from Co (OH) ₂ slurry using the slurry reduction method. It relates to a cobalt powder production method excellent in the reaction rate.

Cobalt powder is widely used in materials such as metallurgy industry, magnetic alloys, electronics, tools, chemical catalysts and dyes. Recently, with the development of high-tech industries such as electronics, precision industry, batteries, etc., it is required to miniaturize and high performance of the product, and to meet these demands, research on the production of fine and ultra-fine metal powder particles is actively underway.

Conventional cobalt powder production methods include a hydrogen reduction method, a wet reduction method and a pyrolysis method. At this time, the hydrogen reduction method is a method of producing a powder by adding hydrogen gas at a high temperature and high pressure process conditions of about 800 ℃ it is possible to manufacture micro-sized cobalt particles with less impurities. However, such a hydrogen reduction method has a problem that a classification process and a crushing process are required due to the fusion and aggregation between particles in the reduction reaction.

On the other hand, the wet reduction method is a method for producing a powder by using a reducing agent in an organic solvent such as ethylene glycol (Ethylene glycol) at a relatively high temperature of 150 ℃, spherical shape by controlling the shape of cobalt particles, control of a uniform reduction reaction rate The advantage is that particles and uniform particle size control are possible. However, the wet reduction method has a lower purity than the hydrogen reduction method due to unnecessary wastes generated during the filtration and washing process of cobalt particles and unreacted compounds.

The pyrolysis method involves spraying a solution and then injecting the droplets into a high temperature reactor by a carrier gas, causing precipitation of the solute as the concentration is increased by evaporation of the solvent in the droplet, thereby producing particles through pyrolysis of the dried solute. It is a way.

As such, the conventional cobalt powder manufacturing method has a problem in that a large process cost is required when preparing the cobalt powder, as a relatively high temperature, high pressure, and an organic solvent are required.

An object of the present invention is to produce a cobalt powder using a slurry reduction method at a low temperature and low pressure, and to improve the reaction rate to produce a cobalt powder of dendritic type having an average diameter of 1 ~ 10㎛ within a short time To provide.

Cobalt powder production method using a slurry reduction method excellent in the reaction rate according to an embodiment of the present invention for achieving the above object is (a) cobalt salt and NaOH dissolved in a solvent in a weight ratio of 1: 8 ~ 1: 24 Co ( OH) ₂ slurry; (b) injecting said Co (OH) ₂ slurry into a reaction vessel; (c) stirring the slurry introduced into the reaction vessel while heating; It characterized in that it comprises a and (d) by reduction reaction of the Co (OH) ₂ slurry to supply a reducing agent to the above-stirred Co (OH) ₂ slurry to obtain a cobalt powder.

The cobalt powder manufacturing method according to the present invention is excellent in the reaction rate by increasing the concentration of NaOH, and appropriately controlling the type, reaction time, reaction temperature and reducing agent concentration of the cobalt salt, dendritic type having an average diameter of 1 ~ 10㎛ Cobalt powder of can be prepared.

In addition, the cobalt powder prepared by the cobalt powder manufacturing method may have a yield of 95 to 99% and a purity of 99.9% or more.

1 is a process flowchart schematically showing a cobalt powder manufacturing method using a slurry reduction method with excellent reaction rate according to an embodiment of the present invention.
2 and 3 are graphs and photos showing the cobalt powder prepared according to NaOH concentration measured and taken by XRD and SEM.
4 and 5 are graphs and photographs showing the cobalt powder prepared according to the type of the solvent measured and taken by XRD and SEM.
6 and 7 are graphs and photographs showing the cobalt powder prepared according to the type of cobalt salt measured and photographed by XRD and SEM.
8 and 9 are graphs and photos showing the cobalt powder produced by reaction time at a NaOH concentration of 3.6M by XRD and SEM.
10 and 11 are graphs and photos showing cobalt powders produced by reaction time at 7.2 M NaOH concentration by XRD and SEM.
12 and 13 are graphs and photographs of the cobalt powder prepared according to the reaction temperature measured and photographed by XRD and SEM.
14 and 15 are graphs and photos showing the cobalt powder prepared according to the concentration of the reducing agent measured and photographed by XRD and SEM.
FIG. 16 is a SEM photograph of cobalt powder prepared according to an addition rate of a reducing agent. FIG.
17 and 18 are graphs and photos showing cobalt powders prepared according to the concentration of NaBH ₄ during the reduction reaction in cobalt ions by XRD and SEM.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments and drawings described in detail below. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.

Hereinafter, a method of preparing cobalt powder using a slurry reduction method having an excellent reaction rate according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a process flowchart schematically showing a cobalt powder manufacturing method using a slurry reduction method with excellent reaction rate according to an embodiment of the present invention.

Referring to Figure 1, the cobalt powder manufacturing method according to the present invention includes a slurry forming step (S110), the input step (S120), the stirring step (S120) and the cobalt powder obtaining step (S140).

Slurry formation step

In the slurry forming step (S120), the cobalt salt and NaOH are dissolved in a solvent in a weight ratio of 1: 8 to 1:24 to form a Co (OH) ₂ slurry.

In this case, the cobalt salt may be selected from CoCl ₂ , CoSO ₄ and Co (OH) ₂ . If CoCl ₂ is used as the cobalt salt, CoCl ₂ and NaOH are dissolved in a solvent, where CoCl ₂ and NaOH undergo the chemical reaction of Scheme 1 below.

Scheme _{1: CoCl 2 + 2NaOH → Co} (OH) 2 + 2Na + + 2Cl -

As described above, the cobalt salt and NaOH are preferably added in a weight ratio of 1: 8 to 1:24.

If the weight ratio of the cobalt salt and NaOH is less than 1: 8, since the content of NaOH is too small compared to the cobalt salt, there is a limit in providing OH ⁻ required to reduce the Co (OH) ₂ slurry. There is a problem that cannot be exercised properly. On the contrary, when the weight ratio of cobalt salt and NaOH exceeds 1:24, there is a problem of only increasing the cost without the effect of adding NaOH.

In this case, the Co (OH) ₂ slurry precipitated from CoCl _{2 in the} cobalt salt is very well dispersed, and when used as a precursor, there is an advantageous effect in preparing mono-modal dendritic cobalt powder. .

On the other hand, it is preferable to use distilled water (H ₂ O) as the solvent. When distilled water was used as the solvent, dendritic crystals were formed due to a change in anisotropy of certain properties such as interfacial energy between solid and liquid and kinetic effects of attracting atoms. In addition, since the solubility of Co (OH) ₂ has a very low solubility in distilled water, it is possible to grow into a dendritic type having a low material transfer rate when reduced to powder.

Input stage

In the input step (S120), Co (OH) ₂ slurry prepared through the slurry forming step (S110) is injected into the reaction vessel (not shown).

At this time, the Co (OH) ₂ slurry is supplied at a height and concentration set in the reaction vessel. The reaction vessel provides a sealed space with the outside, it may be made of a ceramic material.

Stirring step

In the stirring step (S130) is stirred while heating the Co (OH) ₂ slurry introduced into the reaction vessel through the input step (S120).

In this stirring step (S130), for example, a reaction vessel containing a Co (OH) ₂ slurry is heated to an appropriate temperature using a heating means (not shown) such as a heater, and then a thermocouple It is possible to maintain the desired set temperature by measuring the temperature of the Co (OH) ₂ slurry using.

At this time, the Co (OH) ₂ slurry to be introduced into the reaction vessel is preferably stirred at a stirring speed of 60 ~ 1500rpm using a stirrer (not shown) so as to be properly mixed.

Cobalt Powder Obtaining Step

In the cobalt powder obtaining step (S140), a cobalt powder is obtained by reducing the Co (OH) ₂ slurry by supplying a reducing agent to an appropriately stirred Co (OH) ₂ slurry through the stirring step (S130).

N ₂ H ₄ or NaBH ₄ may be used as the reducing agent, of which N ₂ H ₄ is preferable.

At this time, the cobalt powder may be obtained through the following Scheme 2 by adding N ₂ H ₄ as a reducing agent to the Co (OH) ₂ slurry obtained by the reaction scheme 1.

Scheme 2: 2Co (OH) ₂ + N ₂ H ₄ → 2Co + N ₂ + 4H ₂ O

Here, N ₂ H ₄ may be supplied in the form of hydrazine monohydrate (N ₂ H _{4 ·} H ₂ O). The reducing agent N ₂ H ₄ is preferably supplied in a semi-continuous manner using a dropwise method of dropping dropwise in the reaction vessel in the form of hydrazine monohydrate.

As a result, when dropwise supplying one drop of redox reaction semi-continuously rather than batch method of supplying hydrazine monohydrate at once, it is possible to obtain a uniform, ie mono-modal, cobalt powder. It was confirmed that the particle size is also easy to adjust.

At this time, the reducing agent is preferably added at a rate of 1ml / min ~ 7ml / min. If the rate of addition of the reducing agent is less than 1 ml / min, there is a problem that the nucleation is small and the nuclear growth is long, resulting in coarse particle sizes. On the contrary, when the rate of addition of the reducing agent exceeds 7 ml / min, nucleation is constant, but the aggregation of particles is intensified, making it impossible to produce fine dendritic cobalt powder. At this time, the aggregation is intensified because an increase in the addition rate requires an excess of reducing agent rather than the rate of dissolution and reduction, so that the reaction occurs on the surface of the previously generated particles.

Here, the CoCl ₂ and the reducing agent is preferably added in a weight ratio of 1: 1 to 1: 3. If the weight ratio of CoCl ₂ to the reducing agent is less than 1: 1, the addition amount of the reducing agent is too small to properly exhibit the addition effect. On the contrary, when the weight ratio of CoCl ₂ and the reducing agent exceeds 1: 3, the coagulation of the particles is intensified due to the excessive addition of the reducing agent to CoCl ₂ , thus making it difficult to produce fine dendritic cobalt powder.

Here, when reducing the Co (OH) ₂ slurry by supplying the reducing agent, the reaction temperature is preferably carried out at 40 ~ 80 ℃.

If the reaction temperature is less than 40 ° C, there is a problem that the reduction reaction does not occur because the temperature is too low. On the contrary, when the reaction temperature exceeds 80 ° C., there is a problem of only increasing the process cost and time without any further temperature increase effect.

At this time, it is preferable to perform reaction time for 1 to 60 minutes. If the reaction time is less than 1 minute, since the reaction time is too short, a portion of the Co (OH) ₂ slurry may not be reduced, which may make it difficult to prepare a fine dendritic cobalt powder. On the contrary, when the reaction time exceeds 60 minutes, there is a problem in that the cost of adding a large amount of NaOH in order to activate the reduction reaction.

Although not shown in the drawings, after the cobalt powder production step, the reduced cobalt powder may be solid-liquid separated, washed with ethanol and distilled water, and the washed cobalt powder may be further dried at 50 to 70 ° C.

As described above, the cobalt powder manufacturing method according to the embodiment of the present invention may be terminated.

Cobalt powder prepared by the above-described cobalt powder manufacturing method has an average diameter of 1 ~ 10㎛, it may be made of a well-dispersed dendritic type. In addition, the cobalt powder prepared by the above production method may have a yield of 95 to 99% and a purity of 99.9% or more.

Experimental sample

The samples used to prepare the cobalt powder using the slurry reduction method are as follows.

Solvent: Ethylene Glycol (HOCH ₂ CH ₂ OH), Ethanol (C ₂ H ₅ OH) and Distilled Water (H ₂ O)

Cobalt salts of cobalt chloride hexa hydro light (CoCl _· 6H ₂ O), cobalt hydroxide (Co (OH) ₂₎ and cobalt sulfide hepta hydrate (CoSO _{4 ·} 7H ₂ O)

Reducing agent: Hydrazine monohydrate (N ₂ H _{4 ·} H ₂ O) and sodium borohydride (NaBH ₄ )

At this time, sodium hydroxide (NaOH) was used to slurry the cobalt salt.

Effect of NaOH Concentration

Figure 2 is a graph showing the cobalt powder prepared according to the NaOH concentration measured by XRD, Figure 3 is a photograph taken with SEM SEM cobalt powder prepared according to the NaOH concentration.

Experimental conditions using distilled water as a solvent, fixed cobalt salt 0.3M, NaOH 3.6M, N ₂ H ₄ 1.2M, temperature 60 ℃, reaction time 60 minutes, NaOH concentration 0.6M, 1.2M, 2.4M , 3.6M, 4.8M and 7.2M were tested.

NaOH plays an important role in producing Co (OH) ₂ slurry as well as providing OH ⁻ for reduction of hydrazine (N ₂ H ₄ ).

In this experiment, the concentration of cobalt ions was 0.3 M, which was 0.6 M NaOH for converting cobalt ions into Co (OH) ₂ slurry and 0.6 M NaOH to provide the OH ⁻ needed to reduce the slurry of Co (OH) ₂ . In theory, a total concentration of 1.2M is required. However, as shown in (a) to (f) of FIG. 2, the XRD results show that the Co (OH) ₂ slurry could not be reduced to cobalt powder at the NaOH concentration of 1.2M, which is twice that of NaOH 2.4M. Co (OH) ₂ was all reduced to cobalt powder. This suggests that an excess of NaOH is required when the reduction to the actual cobalt powder is theoretical.

On the other hand, Co (OH) ₂ slurry is observed in FIG. 3 (a), and Co (OH) ₂ slurry in FIG. 3 (a) is fine Co just before reducing the cobalt powder. It can be seen that (OH) ₂ slurry is observed. And (c) to (f) of Figure 3 it can be seen that the dendritic cobalt powder of about 3 ~ 5㎛ reduced to the cobalt powder was produced. At this time, the particle size and shape of the cobalt powder at a concentration of NaOH 2.4M or more did not change significantly.

Solvent effect

Figure 4 is a graph showing the cobalt powder prepared according to the type of solvent measured by XRD, Figure 5 is a photograph taken by SEM of the cobalt powder prepared according to the type of the solvent.

Experimental conditions were fixed with CoCl ₂ 0.3M, NaOH 3.6M, N ₂ H ₄ 1.2M, temperature 60 ℃, reaction time 60 minutes, the solvent was ethylene glycol (HOCH ₂ CH ₂ OH), ethanol (C ₂ H ₅ OH ) And distilled water (H ₂ O) was tested.

As shown in (a) of FIG. 4, when ethylene glycol is used as the solvent, the cobalt powder is not completely reduced to the cobalt powder, as a small amount of Co (OH) ₂ is present as a result of XRD measurement. At this time, as shown in Figure 5 (a), when using ethylene glycol as a solvent, it can be seen that the cobalt powder has a spherical powder having a 0.5 ~ 1.0 ㎛.

In addition, as shown in (b) of FIG. 4, when ethanol is used as the solvent, the cobalt powder shows that a large amount of Co (OH) ₂ was not reduced to the cobalt powder as a result of XRD measurement. At this time, as shown in (b) of Figure 5, when using ethanol as a solvent, it can be seen that the cobalt powder has a large powder form before changing to a dendritic crystal and a dendritic crystal.

On the other hand, as shown in Figure 4 (c), when distilled water is used as the solvent, as a result of the XRD measurement it can be seen that both Co (OH) ₂ reduced to the cobalt powder. At this time, as shown in Figure 5 (c), when using distilled water as a solvent, it can be seen that the cobalt powder is reduced to a dendritic type of about 5㎛.

The reason why the powder is different depending on the solvent is that ethylene glycol (ethylene glycol) has the ability to reduce metal salts although the reducing power varies depending on the temperature. As a result, cobalt nuclei are generated before the reducing agent is added, and the cobalt powder produced after the reducing agent is added is grown around the nucleus that has been previously formed to form spherical powder.

Ethanol and distilled water formed dendritic powders, which are due to changes in the anisotropy of certain properties such as interfacial energy between solid and liquid and kinetic effects of attracting atoms. to be. The dendritic crystal refers to a shape in which the main body of the crystal grows to (110), for example, and the main body of the crystal grows to (100), which is the other side of the crystal like a twig. The reason for the growth of dendritic crystals is that the ethylene glycol is nucleated or the viscosity of the solvent acts as a protective agent for the cobalt powder produced earlier. This is because there was no main substance, and the atmosphere grew easily in the direction of crystal growth different from that of the main axis in the nuclear growth stage, and grew in the direction of crystal like branches.

The other reason is that Co (OH) ₂ has a very low solubility in distilled water, so it has grown to a dendritic type due to the low rate of mass transfer when reducing to powder.

Based on the above experimental results, it was confirmed that pure cobalt powder having a particle size of about 5 μm was obtained when distilled water was used as a solvent when preparing cobalt powder by slurry reduction.

Effect of Cobalt Salts

Figure 6 is a graph showing the cobalt powder prepared according to the type of cobalt salt measured by XRD, Figure 7 is a photograph taken by SEM of the cobalt powder prepared according to the type of cobalt salt.

Experimental conditions using distilled water (H ₂ O) as a solvent, cobalt salt 0.3M, NaOH 3.6M, N ₂ H ₄ 1.2M, temperature 60 ℃, reaction time 60 minutes fixed, cobalt salt CoSO ₄ , CoCl ₂ and Co (OH) ₂ was divided into experiments.

As shown in (a) to (c) of Figure 6, irrespective of the type of cobalt salt, XRD measurement results show that all of the Co (OH) ₂ slurry was reduced to cobalt powder.

On the other hand, as shown in Figure 7 (a), when using CoSO ₄ as the cobalt salt, the cobalt powder can be confirmed that the small dendritic crystals of 2 ~ 3㎛ aggregated to have a relatively large particles of 10㎛. In addition, as shown in Figure 7 (b), when using CoCl ₂ as the cobalt salt, it can be seen that cobalt powder is well dispersed 3 ~ 5㎛ dendritic molds. And, as shown in Figure 7 (c), when using Co (OH) ₂ as the cobalt salt, it can be seen that the cobalt powder is a large dendritic crystal of 10㎛.

According to the above experimental results, it can be seen that the shape and size of the cobalt powders produced according to the cobalt salt is different, due to the difference in the crystallinity and the shape of the precursor Co (OH) ₂ . In general, reagent grade Co (OH) ₂ has good crystallinity and is not homogeneous in shape or particle size distribution because it is dried for several hours at a high temperature of 110 ° C. or higher. However, the Co (OH) ₂ slurry precipitated from the cobalt salt is in a well dispersed state. Therefore, when Co (OH) ₂ slurry is precipitated using CoCl ₂ as a cobalt salt and used as a precursor, it becomes possible to prepare a dispersed dendritic cobalt powder.

Effect of response time

Cobalt powders produced at reaction times of NaOH concentrations of 3.6M and 7.2M, respectively, were analyzed. The reason for dividing the NaOH concentration by 3.6M and 7.2M was based on the assumption that the reaction time required for the reduction would also change if the concentration of OH ^- involved in the reduction reaction changed.

8 is a graph showing the cobalt powder produced by reaction time at NaOH concentration of 3.6M by XRD, and FIG. 9 is a photograph taken by SEM of cobalt powder produced by reaction time at NaOH concentration of 3.6M.

Experimental conditions were tested using distilled water as a solvent, the reaction time was changed to 0, 5, 10, 15, 30 minutes at CoCl ₂ 0.3M, NaOH 3.6M, N ₂ H ₄ 1.2M, temperature 60 ℃.

FIG. 10 is a graph illustrating XRD of cobalt powder generated by reaction time at NaOH concentration of 7.2M, and FIG. 11 is a SEM photograph of cobalt powder produced by reaction time at NaOH concentration of 7.2M.

Experimental conditions were tested by changing the reaction time to 5, 10, 15, 30, 60, 120 minutes using distilled water as a solvent, CoCl ₂ 0.3M, NaOH 7.2M, N ₂ H ₄ 1.2M, temperature 60 ℃. .

As shown in Figure 8 (a) ~ (e), XRD results show that the initial Co (OH) ₂ slurry was reduced to cobalt powder with the reaction time and all the reaction time was reduced to cobalt powder over 30 minutes Can be.

As shown in (a) to (e) of FIG. 9, SEM image shows that the Co (OH) ₂ slurry having a reaction time of 0 minutes is decomposed into a fine powder at a reaction time of 5 minutes in one large slurry, and the reaction time. It can be seen that the finely divided powder is reduced to the dendritic cobalt powder as it passes.

As shown in (a) to (f) of FIG. 10, the XRD results showed that the Co (OH) ₂ slurry was present at the reaction time of 5 minutes, but all were reduced to the cobalt powder from the reaction time of 10 minutes.

(A) to (d) of FIG. 11 are SEM photographs when the reaction time is 5, 10, 15, and 20 minutes, and Co (OH) ₂ is present at the reaction time of 5 minutes, and the shape of the powder is about A spherical powder of 0.5 μm is shown. On the other hand, in the reaction time of 10 minutes or more, about 2㎛ dendritic powder, 15 minutes of reaction time, about 3㎛ dendritic powder, and the reaction time 30 minutes, about 3.5㎛ dendritic powder was formed.

At this time, comparing the XRD results of Figure 8 and Figure 10, it can be seen that the effect of NaOH concentration on the reaction time. In NaOH 3.6M, the reduction was terminated at 30 min reaction time, and in NaOH 7.2M the reduction was terminated at 10 min reaction time. As a result, it was proved that NaOH concentration assumed at the beginning of the experiment influences the reaction time, and it can be seen that the reaction time decreases as the NaOH concentration increases.

Meanwhile, referring to FIGS. 11A to 11D, as the reaction time increases, the cobalt powder changes from a spherical powder to a dendritic powder, and the size and agglomeration of the powder increase.

Effect of reaction temperature

In order to know the effect of the reaction temperature on powder manufacturing, experiments were conducted according to the change of reaction temperature. Experimental conditions were tested by changing the reaction temperature to room temperature, 40, 50, 60, 70 and 80 ℃ in CoCl ₂ 0.3M, NaOH 3.6M, N ₂ H ₄ 1.2M, reaction time 1 hour.

12 is a graph showing the cobalt powder prepared according to the reaction temperature measured by XRD, and FIG. 13 is a photograph taken by SEM of the cobalt powder prepared according to the reaction temperature.

As shown in (a) to (f) of FIG. 12, the reduction reaction of the Co (OH) ₂ slurry did not occur at a reaction temperature of room temperature. On the other hand, it can be seen that the Co (OH) ₂ slurry was reduced to cobalt powder at a reaction temperature of 40 ° C. or higher. From this it can be seen that the minimum temperature required for the reaction is 40 ℃ or more.

As shown in (a) to (f) of FIG. 13, a powder in the form of a slurry of Co (OH) ₂ is seen at a reaction temperature of room temperature, and a powder of about 20 μm or more is formed at a reaction temperature of 40 ° C. Can be. The size of the powder at the reaction temperature of 50 ° C. was about 15 μm, and the dispersion degree of the powder was better than 40 ° C. The size of the powder at the reaction time of 60 ° C. was about 10 μm smaller than the reaction temperature of 50 ° C., and the dispersion degree was excellent.

Therefore, it can be seen that as the reaction temperature increases, the size of the powder decreases and the dispersion degree of the powder is excellent. In this case, as the reaction temperature increases, the size and agglomeration of the powder decreases, and as the reaction temperature increases, the Co (OH) ₂ dissolved in the solution increases, and the increased cobalt ions increase more at the beginning of the reduction reaction. This is because it produces a nucleus.

Effect of Reducing Agent Concentration and Addition Rate

Hydrazine (N ₂ H ₄ ) serves as a reducing agent to provide a redox energy to reduce the Co (OH) ₂ slurry to cobalt powder. In order to know the effect of the powder produced according to the concentration of hydrazine to play this role, the following experiment was performed.

14 is a graph showing the cobalt powder prepared according to the concentration of the reducing agent by XRD, and FIG. 15 is a photograph taken by SEM of the cobalt powder prepared according to the concentration of the reducing agent.

Experimental conditions were tested by changing the concentration of N ₂ H ₄ to 0.15M, 0.3M, 0.6M and 0.9M at CoCl ₂ 0.3M, NaOH 7.2M, reaction temperature 60 ℃, reaction time 60 minutes.

As shown in FIGS. 14A to 14D, the hydrazine theoretically required for the reduction of the Co (OH) ₂ slurry into the cobalt powder as a result of XDR At 0.15M, it can be seen that a small amount of Co (OH) ₂ remains without being reduced. It can be seen that all of the excess hydrazine 0.3M or more than the theoretical formula was reduced to cobalt powder.

As shown in (a) to (d) of FIG. 15, the SEM size of the powder was about 4 μm at the hydrazine concentration of 0.15M, and the powder size was all about the hydrazine concentrations of 0.3M, 0.6M, and 0.9M. Although it is similar to about 4 ~ 5㎛, it can be seen that as the concentration of the hydrazine increases, the aggregation of the particles becomes more severe. The reason why the aggregation of the particles increases as the concentration of the hydrazine increases is that the surface reduction reaction of the hydrazine on the surface of the resulting powder increases.

FIG. 16 is a SEM photograph of cobalt powder prepared according to an addition rate of a reducing agent. FIG.

Experimental conditions were tested by changing the addition rate of reducing agent to 1, 5, 10ml / min and direct addition at CoCl ₂ 0.3M, NaOH 7.2M, N ₂ H ₄ 1.2M, reaction temperature 60 ℃, reaction time 60 minutes.

As shown in (a) to (d) of FIG. 16, the cobalt powder has a size of about 7 to 10 µm at an addition rate of 1 ml / min, and a powder size of 5 ml / min, 10 ml / min and a direct addition at 5 ml / min. It was similar to about 7㎛. However, when looking at the cohesion of the cobalt powder it can be seen that the aggregation of the particles is increased as the rate of addition of the reducing agent increases. This is because the particle size increases due to the low nucleation of the solution and the long nuclear growth when the addition rate is slow.

On the other hand, when the addition rate is 5ml / min or more, nucleation is constant, but the particles are agglomerated, when the cobalt ions dissolved in the solution are reduced to the cobalt powder, the Co (OH) ₂ slurry is dissolved. This is because an excess of reducing agent increases rather than the rate at which it is reduced and reacted and agglomerated at the surface of the previously produced particles.

Evaluation of Reduction in Cobalt Ions

FIG. 17 is a graph showing XRD of cobalt powder prepared according to the concentration of NaBH ₄ during reduction in cobalt ions, and FIG. 18 is a SEM of cobalt powder prepared according to the concentration of NaBH ₄ during reduction in cobalt ions. This picture was taken.

This experiment was performed to compare with the powder prepared by the slurry reduction method when the cobalt ions reduced to cobalt powder. At this time, hydrazine was not used as a reducing agent, because most of the solutions in which cobalt ions are dissolved are present in an acidic solution, but hydrazine in the acidic solution reacts as in Scheme 3 below.

Scheme ^{_{3: N 2 + 5H + +}} 4e - = N 2 H 5 + (-0.27V)

As shown in Scheme 3, hydrazine having a redox potential of -0.27V in an acidic solution cannot be reduced to cobalt powder because it falls short of the -0.277V redox potential required for reduction from cobalt ions to cobalt powder. Therefore, in this experiment, cobalt ions were reduced to powder using NaBH ₄ rather than hydrazine as the reducing agent.

As shown in (a) to (e) of FIG. 17, no peak was observed at the NaBH ₄ concentration of 0.15M theoretically required and excess NaBH ₄ 0.3M. An amorphous peak of cobalt was seen at a NaBH ₄ concentration of 0.6M or higher.

As shown in (a) to (e) of Figure 18, the size of the cobalt powder prepared in NaBH ₄ 0.6M was very fine 60n. It can be seen that the size and dispersion of the powder at NaBH ₄ 1.2M and 1.8M show little change at NaBH ₄ 0.6M.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

S110: slurry formation step
S120: Input Step
S130: stirring step
S140: cobalt powder obtaining step

Claims (12)

(a) dissolving cobalt salt and NaOH in a solvent at a weight ratio of 1: 8 to 1:24 to form a Co (OH) ₂ slurry;
(b) injecting said Co (OH) ₂ slurry into a reaction vessel;
(c) stirring the slurry introduced into the reaction vessel while heating; And
Method cobalt powder produced, characterized in that it comprises a; (d) to obtain the above Co (OH) by reacting cobalt powder reduced the _second slurry by supplying the reducing agent to the above stirred Co (OH) ₂ slurry.
The method of claim 1,
The cobalt salt is
CoCl ₂ , CoSO ₄ And Co (OH) ₂ Cobalt powder manufacturing method characterized in that one selected from.
The method of claim 1,
The solvent
Method for producing cobalt powder, characterized by using distilled water (H ₂ O).
The method of claim 1,
The reducing agent
Process for producing cobalt powder, characterized in that N ₂ H ₄ or NaBH ₄ .
5. The method of claim 4,
N ₂ H ₄ is
It is supplied in the form of hydrazine monohydrate (Hydrazine monohydrate), the hydrazine monohydrate (Hydrazine monohydrate) is a cobalt powder manufacturing method characterized in that the supply in a dropwise (dropwise) method.
The method of claim 1,
The cobalt salt and reducing agent
A method for producing cobalt powder, which is added in a weight ratio of 1: 1 to 1: 3.
The method of claim 1,
The rate of addition of the reducing agent is
A method of producing cobalt powder, characterized in that it is carried out at 1ml / min ~ 7ml / min.
The method of claim 2,
CoCl ₂ and NaOH
Process for producing a cobalt powder, characterized in that the chemical reaction of Scheme 1.
Scheme _{1: CoCl 2 + 2NaOH → Co} (OH) 2 + 2Na + + 2Cl -
9. The method of claim 8,
The cobalt powder is
The method for producing cobalt powder, which is obtained through the following Scheme 2 by adding N ₂ H ₄ to the Co (OH) ₂ slurry obtained by the above Scheme 1.
Scheme 2: 2Co (OH) ₂ + N ₂ H ₄ → 2Co + N ₂ + 4H ₂ O
The method of claim 1,
Cobalt powder obtained by the step (d)
It has a mean diameter of 1-10 micrometers, The manufacturing method of the cobalt powder characterized by the above-mentioned.
The method of claim 1,
In the step (d)
The reduction reaction is
Cobalt powder production method characterized in that the reaction temperature: 40 ~ 80 ℃ and reaction time: 1 to 60 minutes.
The method of claim 1,
After the step (d)
(e) solid-liquid separation of the reduced cobalt powder and washing with ethanol and distilled water;
(F) drying the washed cobalt powder at 50 ~ 70 ℃; method of producing a cobalt powder further comprises.

Images