KR101699881B1 - Method for preparing monodisperse metal fine particles - Google Patents

Abstract

The present invention relates to a method for producing monodisperse fine particles of a metal selected from the group consisting of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) The present invention relates to a method for producing monodisperse metal microparticles by controlling the reaction conditions (reduction rate, gas flow rate, reactor composition, etc.) by a gas phase reaction without a surfactant It is possible to produce metal fine particles having a higher crystal quality and a higher purity and a uniform size.

Description

METHOD FOR PREPARING MONODISPERSE METAL FINE PARTICLES [0002]

The present invention relates to a method for producing monodisperse fine particles of a metal selected from the group consisting of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) More particularly, the present invention relates to a method for producing monodisperse metal fine particles having uniform shape and size through a gas phase reaction which does not require a surfactant.

(Fe), cobalt (Co), tantalum (Ta), molybdenum (Ta), tantalum (Ta), and the like are used for the production of electric and magnetic materials, conductive pastes, battery materials, high temperature materials and ceramic composite materials, Metallic fine particles such as molybdenum (Mo), tungsten (W), vanadium (V) and titanium (Ti) have been widely applied and their importance is gradually increasing.

Particle size in microparticles has a great effect on physical properties. Particularly, as the size distribution of microparticles is narrowed, it is more advantageous in expressing the characteristics of microparticles. Therefore, many studies have been made to synthesize monodispersed fine particles having uniform size.

For the synthesis of monodisperse fine particles, two conditions must be met. The first condition is that the nucleation step and the particle growth step are separated, and the second condition is that the aggregation is prevented.

Among these, the first condition, separation of nucleation and particle growth steps, can be achieved with high nucleation rate. If no additional nucleation occurs at the grain growth stage, the particles can grow into monodisperse particles because they lie under the same growth conditions. According to the literature of Park, J., et al., Nat. Mater., 2004. 3 (12): p. 891-895), instantaneous nucleation separates nucleation and particle growth , It has been known to successfully synthesize monodispersed fine particles of uniform shape. However, this method is limited to a liquid-phase process and can not be applied to gas phase synthesis because a surfactant is used to prevent aggregation of particles.

Gas phase synthesis of metal microparticles is a method of obtaining particles with high crystallinity and purity. However, in the gas phase synthesis, collision occurs frequently due to collision and aggregation due to reaction conditions at a high temperature without a surfactant. Therefore, there is a need for an additional process that requires a lot of time and cost to prevent agglomeration between particles in the conventional gas phase synthesis.

On the other hand, not only the size of the particles but also the shape of the particles in the fine particles are important factors for determining the properties of the fine particles. For example, spherical metal microparticles have a high packing density, and hexahedral metal microparticles have a much higher saturated magnetization compared to spherical metal microparticles of the same size. Since the characteristics vary depending on the shape, controlling the particle shape according to the application field is emerging as an important issue. However, in order to control the shape of such fine particles, a liquid phase synthesis method using a surfactant has also been used. In such a liquid phase synthesis method, there is a problem that impurity content and particle aggregation are inevitable.

 Park, J., et al., Nat. Mater., 2004. 3 (12): p. 891-895.

Accordingly, it is an object of the present invention to provide a process for the production of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium Ti) as a monodisperse fine particle having a uniform shape and size with high crystallinity and high purity.

According to the above object, the present invention provides a process for producing a reaction product comprising the steps of: (1) preparing a vertical reactor having a heating zone for a reduction reaction; (2) supplying metal precursor vapor and hydrogen gas to the heating zone; (3) reducing the metal precursor vapor with the hydrogen gas at a temperature of 400 to 1300 占 폚 to produce metal nuclei; And (4) growing the metal nuclei into metal microparticles and discharging the metal nanoparticles to the outside of the reactor, wherein the metal precursor, the metal nuclei, and the metal fine particles are selected from the group consisting of iron (Fe), cobalt (Co), tantalum (Ta) A precursor, a core and a fine particle of a metal selected from the group consisting of molybdenum (Mo), tungsten (W), vanadium (V) and titanium (Ti), wherein an isothermal section exists in the heating zone, (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) and titanium (Ti), wherein the metal fine particles are discharged in the isothermal section Ti). ≪ / RTI >

According to the method of the present invention, fine particles of a metal selected from the group consisting of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) Can be synthesized in the gas phase without a surfactant. Particularly, according to the method of the present invention, the reduction reaction for metal production is performed in a high temperature isothermal section, so that no additional nucleation occurs in the grain growth step, and thus it can grow into monodisperse particles. In addition, the method according to the present invention can prevent agglomeration between particles even though gas phase synthesis is performed without a surfactant since the vertical type reactor is used and the generated fine particles are discharged in an isothermal section. As a result, according to the method of the present invention, it is possible to produce monodisperse metal microparticles and to control further reaction conditions (reduction rate, gas flow rate, reactor configuration, etc.) Particles can be produced. Such monodisperse metal microparticles can be used in a variety of fields such as electrical and magnetic materials, conductive pastes, battery materials, high temperature materials and ceramic composites, medical materials, and defense industry products.

Figure 1 shows an exemplary cross-sectional view of a horizontal reactor and a vertical reactor.
Figure 2 shows the gas flow inside the horizontal reactor and the vertical reactor.
3 shows the temperature distribution inside the vertical reactor.
Figure 4 shows the hydrogen gas flow inside the reactor with various hydrogen gas injection positions.
5 is a simulation of the equilibrium crystal shape (ECS) of metal microparticles by software.
FIG. 6 is a graph showing changes in the shape of metal microparticles according to the vaporization rate and the reaction temperature of the metal precursor in the gas phase reaction of Example 3. FIG.
7 and 8 are FESEM (Field Emission Scanning Electron Microscope) images of the iron microparticles and the cobalt microparticles prepared in Example 4, respectively.

It is to be understood that monodisperse metal microparticles selected from the group consisting of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) The manufacturing method is

(1) preparing a vertical reactor having a heating zone for a reduction reaction;

(2) supplying metal precursor vapor and hydrogen gas to the heating zone;

(3) reducing the metal precursor vapor with the hydrogen gas to produce metal nuclei; And

(4) growing the metal nuclei into fine metal particles and discharging the metal fine particles to the outside of the reactor,

Wherein the metal precursor, the metal nuclei and the metal fine particles are selected from the group consisting of Fe, Co, tantalum, molybdenum, tungsten, vanadium and titanium. Precursors, nuclei, and fine particles of the metal being < RTI ID = 0.0 >

An isothermal section is present in the heating zone, and the reduction reaction and the discharge of the metal fine particles are performed in the isothermal section.

The term "metal", "metal microparticle", "metal precursor", "metal precursor vapor", and "metal nucleus" refer to metals such as iron, cobalt, tantalum, molybdenum Mo, tungsten, vanadium, and titanium, particles, precursors, precursor vapors, and nuclei thereof, respectively. On the other hand, the metal to be used in this specification does not correspond to the metal elements of groups 10 to 12 in the periodic table.

Each step will be described in detail below.

(1) Preparation of reactor

In this step, a vertical reactor to be used for the preparation of metal microparticles is prepared.

The vertical reactor may be a dry reactor as a gas phase reactor. Specifically, the vertical reactor may be a gaseous hydrogen reduction reactor. Also, the vertical reactor may be a tubular reactor.

The vertical reactor may have a reaction flow in the vertical direction. Preferably, the vertical reactor may have a bottom to top reaction stream.

The vertical reactor has a heating zone for a reduction reaction. Also, the vertical reactor may further include a heating zone for evaporating the metal precursor.

In this specification, the heating zone for evaporating the metal precursor is referred to as a "first heating zone ", and the heating zone for the reduction reaction is simply referred to as a" second heating zone ".

The heating zone (first heating zone) for evaporating the metal precursor may be surrounded by a tube. Specifically, the tube may have a cylindrical shape. At this time, the tube may have a hole at the top, and the hole may be located within the isothermal section. Accordingly, the vapor generated by evaporation of the metal precursor in the tube can be supplied to the isothermal section through the hole.

The vertical reactor may include a first hydrogen gas injection pipe at an upper end thereof and an inert gas injection pipe and a second hydrogen gas injection pipe at a lower end thereof.

When the first heating zone is surrounded by the tube, hydrogen gas is injected into the tube by the first hydrogen gas injection tube and the second hydrogen gas injection tube, and the inert gas is injected into the tube An inert gas may be injected, and the hydrogen gas and the inert gas may be supplied to the isothermal section.

1 (a) and 1 (b) are cross-sectional views showing examples of conventional horizontal type reactors.

The horizontal reactor may have, for example, a horizontal reaction vessel having a tube shape. The reactor has a heating zone (second heating zone) 7 in which a reduction reaction takes place. In addition, the reactor may have a heating zone (first heating zone) 6 where evaporation of the metal precursor takes place. The first heating zone 6 and the second heating zone 7 may be in the form of a tubular shape.

The first heating zone 6 may include a first heater. In addition, the second heating zone 7 may include a second heater. Specifically, the inner region of the reactor corresponding to the zone provided with the first heater and the second heater may be defined as a first heating zone 6 and a second heating zone 7, respectively.

The reactor may include insulating materials (3, 5) on the outer sides of the first heater and the second heater. Also, the reactor may include an insulating material 4 between the first heater and the second heater. The inner region of both ends of the reactor corresponding to the region where neither the insulating material 3, 4 or 5 nor the heater 6 or 7 is attached can be defined as the low temperature region 1 or 2

The first heating zone 6 in the reactor is provided with a crucible 8 to which a metal precursor is charged and evaporated. In the second heating zone 7, there is provided a substrate 9 to which the reacted metal microparticles are adhered .

At the left end of the reactor, injection pipes 11 and 12 for injecting hydrogen gas and inert gas are provided, and a discharge pipe 10 for discharging gas is provided at the right end.

1 (c) is an illustration of a vertical reactor (V-1) according to one embodiment.

The vertical reactor may have, for example, a vertical reaction vessel having a tube shape.

The reactor (V-1) has a heating zone (second heating zone) 7 in which a reduction reaction takes place. In addition, the reactor may have a heating zone (first heating zone) 6 where evaporation of the metal precursor takes place. The first heating zone 6 and the second heating zone 7 may be in the form of a tubular shape.

The first heating zone 6 may include a first heater. In addition, the second heating zone 7 may include a second heater. Specifically, the inner region of the reactor corresponding to the zone provided with the first heater and the second heater is defined as a first heating zone 6 and a second heating zone 7, respectively.

The reactor is provided with an insulating material (3, 5) on the outer periphery of each of the first heater and the second heater. Also, the reactor is provided with an insulating material 4 between the first heater and the second heater. The inner regions of the upper and lower ends of the reactor corresponding to the regions where neither the insulating material 3, 4 or 5 nor the heater 6 or 7 is attached can be defined as the low temperature regions 1 and 2.

The crucible 8 is provided in the first heating zone 6 inside the reactor to evaporate the metal precursor.

The second heating zone (7) inside the reactor is provided with a discharge pipe (10) through which the metal fine particles produced through the reaction are discharged. The outlet tube 10 may be located within an isothermal section of the second heating zone.

An inert gas injection pipe 11 is provided at a lower end of the reactor, and a hydrogen gas injection pipe 12 is provided at an upper end of the reactor.

Fig. 1 (d) is an illustration of a vertical reactor V-2 according to another embodiment.

The vertical reactor (V-2) similarly includes the vertical reactor (V-1) of FIG. 1 (c).

In addition, the reactor (V-2) is equipped with tubes 13 throughout the entire first heating zone 6 and a portion of the second heating zone 7 therein. The tube 13 surrounds the crucible 8, the lower end of the tube is fixed to the lower part of the reactor, and the upper end of the tube has a hole. The holes provided on the tube 13 are located in the second heating zone 7. More specifically, the holes provided on the tube 13 are located within an isothermal section of the second heating zone 7. Preferably, the hole is directed toward the discharge tube 10 and has a diameter that is narrower than the diameter of the lower end of the tube 13.

An inert gas injection pipe (11) provided at the lower end of the reactor is provided to inject inert gas into the tube (13). Accordingly, the inert gas may be injected into the lower end of the tube to transfer the vapor of the metal precursor to the upper portion of the tube.

In addition, the reactor has a hydrogen gas injection pipe 12 at a lower end as well as an upper end thereof, and the hydrogen gas injection pipe 12 at the lower end is adapted to inject hydrogen gas to the outside of the tube 13 do. Accordingly, the hydrogen gas injected to the lower end can rise to the second heating zone 7 along the outer wall of the tube 13 to participate in the reduction reaction.

As shown in FIG. 3, in the reactors, the second heating zone 7 has an isothermal section b, c inside. Preferably, the isothermal section is the hottest section in the second heating zone.

For example, the isothermal section may refer to a continuous section having a temperature deviation within 占 0 占 폚. That is, the temperature difference between the highest temperature point and the lowest temperature point within the isothermal section may be within ± 20 ° C. Specifically, the isothermal section may mean a continuous section having a temperature deviation within ± 10 ° C, more specifically within ± 5 ° C, more specifically within ± 1 ° C.

In the vertical reactor, the discharge pipe (10) may be disposed within the isothermal section. Specifically, the inlet of the discharge pipe 10 (that is, the hole through which the metal fine particles are sucked) may be disposed within the isothermal section.

1 (c) and 1 (d), the vertical reactor may include the first heating zone 6 and the second heating zone 7 at the lower portion and the upper portion, respectively. At this time, the first heating zone 6 and the second heating zone 7 are connected to communicate with each other. For example, the first heating zone 6 and the second heating zone 7 may have no boundary therebetween. Accordingly, the gas, particles, etc. in the first heating zone 6 can flow freely into the second heating zone 7. Or the first heating zone 6 is surrounded by the tube 13 so that the first heating zone 6 and the second heating zone 7 are opposed to each other by holes provided in the tube 13, I can go through.

As another example, although not shown in the drawings, the first heating zone may be located outside the reactor. For example, only the second heating zone is provided inside the reactor, and the first heating zone may be provided outside the reactor. In this case, the metal precursor vapor generated in the first heating zone may be supplied to the second heating zone inside the reactor through an injection tube or the like.

(2) Supply of metal precursor vapors and hydrogen gas

In this step, the metal precursor vapor and the hydrogen gas are supplied to the heating zone (second heating zone) for the reduction reaction.

2-1) Supply conditions of metal precursor vapor and hydrogen gas

The hydrogen gas is supplied from the outside of the reactor to the second heating zone in the reactor.

The flow rate of the hydrogen gas supplied to the second heating zone may be 30 to 600 sccm, and more specifically, 100 to 350 sccm. Alternatively, the flow rate of the hydrogen gas supplied to the second heating zone may be 0.005 to 40 cm / s, more specifically 0.005 to 1.5 cm / s.

As the metal precursor, a metal chloride (MCl _x ) may be used. Accordingly, the vapor of the metal precursor may be a vapor of a metal chloride.

At this time, since the metal in the present invention is selected from the group consisting of Fe, Co, tantalum, molybdenum, tungsten, vanadium and titanium, The metal may be selected from the group consisting of iron chloride, cobalt chloride, tantalum chloride, molybdenum chloride, tungsten chloride, vanadium chloride, and titanium chloride.

More specifically, the metal chloride is selected from the group consisting of iron chloride (FeCl ₂ ), iron chloride (FeCl ₃ ), cobalt chloride (II) (CoCl ₂ ), tantalum chloride (V) (TaCl ₅ ), molybdenum chloride (MoCl ₂ ), molybdenum chloride (III) (MoCl ₃ ), molybdenum chloride (MoCl ₄ ), molybdenum chloride (V) (MoCl ₅ ), tungsten chloride (WCl ₂ ), tungsten chloride ), WCl ₃ , WCl ₄ , WCl ₅ , WCl ₆ , VCl ₂ , VCl ₃ , and the like. ) (VCl _3), vanadium chloride (IV) (VCl _4), titanium chloride (II) (TiCl _2), titanium chloride (III) (from the group consisting of TiCl _3), and titanium chloride (IV) (TiCl ₄₎ Can be selected.

The flow rate at which the metal precursor vapor is fed to the second heating zone may be from 0.5 to 30 sccm, and more specifically from 0.5 to 10 sccm. Alternatively, the flow rate at which the metal precursor vapor is fed to the second heating zone may be 0.0001 to 2 cm / s, more specifically 0.0001 to 0.005 cm / s.

The temperature of the second heating zone may be 400 to 1300 ° C. Specifically, the temperature of the second heating zone may be 700 to 1300 ° C, more specifically 800 to 1200 ° C.

The vapor of the metal precursor may be generated outside the reactor and fed to the second heating zone in the reactor. Alternatively, the vapor of the metal precursor may be generated in the reactor and supplied to the second heating zone. Specifically, the reactor further includes a heating zone (first heating zone) for evaporating the metal precursor, so that the metal precursor is evaporated and the generated vapor can be supplied to the isothermal section.

The temperature of the first heating zone may be 300 to 1200 ° C. More specifically, the temperature of the first heating zone may be 700 to 1000 ° C, more specifically 750 to 950 ° C.

The metal precursor produced in the first heating zone in the reactor can be moved to the second heating zone by diffusion or carried by the carrier gas injected into the reactor. As the carrier gas, an inert gas may be used. For example, nitrogen gas, argon gas, helium gas, or the like may be used.

The carrier gas may be supplied to the first heating zone in the reactor from outside the reactor. The flow rate at which the carrier gas is fed to the first heating zone may be between 150 and 2000 sccm, and more specifically between 400 and 600 sccm. Alternatively, the flow rate at which the carrier gas is fed to the first heating zone may be from 0.01 to 125 cm / s, more specifically from 0.01 to 20 cm / s.

2-2) Gas flow in horizontal reactor and vertical reactor

Figure 2 (a) is a schematic representation of gas flow in a horizontal reactor. In view of the temperature distribution inside the horizontal type reactor, high temperature and low temperature gases coexist in the region where the heat insulating material 5 exists between the second heating zone 7 and the low temperature region 2. Hot gases, which are less dense than cold gases, are floated by buoyancy, and hot gases are cooled down by cold walls. Accordingly, as shown in FIG. 2 (a), the gas flows in a circulating (convection) manner. The gas flow to be circulated increases the residence time of the particles, thereby causing flocculation and also broadening the residence time distribution of the particles. This means that all the particles are not placed under the specific growth conditions, which can lead to degradation of the fine particles.

On the other hand, FIG. 2 (b) is a schematic representation of the gas flow in the vertical reactor (V-1). Referring to FIG. 2 (b), the hydrogen gas injected into the upper end of the reactor is filled in the reactor sequentially from the upper portion of the reactor, and reaches the second heating zone. In addition, the inert gas injected to the lower end of the reactor fills the inside of the reactor sequentially from the lower part of the reactor, and vapor of the metal precursor vaporized in the crucible is transferred to the second heating unit. Accordingly, the circulation (convection) of the gas flow does not occur in the vertical reactor (V-1), and the reaction of the hydrogen gas and the metal precursor vapor in the second heating zone can occur.

2 (c) is a graphical representation of the gas flow in the vertical reactor V-2. Referring to FIG. 2 (c), the hydrogen gas injected into the upper end of the reactor is sequentially filled into the reactor from the upper portion of the reactor, and reaches the second heating zone. The inert gas injected into the tube at the lower end of the reactor sequentially fills the inside of the tube from the lower portion of the tube, and the vapor of the metal precursor vaporized in the crucible is transferred to the second heating unit. In addition, the hydrogen gas injected to the outside of the tube at the lower end of the reactor flows from the lower portion of the reactor through the outer wall of the tube, and sequentially reaches the second heating zone. Accordingly, the circulation (convection) of the gas flow does not occur in the vertical reactor (V-2), and the reaction of the hydrogen gas and the metal precursor vapor in the second heating zone can occur. In particular, the tube allows the reaction between the hydrogen gas and the metal precursor vapor to be concentrated in a narrower region of the second heating zone.

For this reason, for the production of monodisperse particles, vertical reactors are preferred over horizontal reactors. Vertical reactors are capable of narrow residence time distributions and short mean residence times, so that the gas flow in the reactor can be axisymmetric. Horizontal reactors, on the other hand, are not suitable for achieving an axially symmetrical gas flow since the flow direction is perpendicular to gravity.

However, even in the vertical reactor, there may be a region where the low temperature gas and the high temperature gas coexist. Therefore, it is important that the particles do not stay in the region where the cold gas and the hot gas coexist. Therefore, it is preferable to inject hydrogen gas into the upper end of the vertical reactor and dispose the discharge pipe in the isothermal section of the heating zone.

(3) Reduction reaction - formation of metal nuclei

In this step, the metal precursor is reacted with the vapor of the metal precursor to produce metal nuclei. The reduction reaction may occur in a second heating zone. Accordingly, the metal nuclei can be generated in the second heating zone. The reduction reaction can be represented by the following reaction formula (1).

<Reaction Scheme 1>

MCl _{X (g)} + H _{2 (g)} M _(s) + x HCl _(g)

3-1) Reaction conditions for producing monodisperse metal microparticles

In order to obtain monodispersed particles, it is advantageous that the reaction takes place at a high temperature for a short time, which can be achieved by carrying out a reduction reaction in an isothermal section of the second heating zone.

3 shows the temperature distribution inside the vertical reactor. As shown in FIG. 3, the second heating zone includes a temperature rising section (a), an isothermal section (b, c), and a warming section (d) in order from the bottom.

As shown in FIG. 3, when the reactor has a vertical heater, and the second heating zone is defined as an area in the reactor corresponding to the zone where the heater is provided, the isothermal section b, (1/4 to 3/4 h) corresponding to 1/4 to 3/4 of the height h from the bottom, and more preferably, from 1/4 to 2/4 from the bottom May be present within a height (1/4 to 2/4 h).

In the temperature raising section (a) and the temperature raising section (d), the turbulence is generated in the section having a temperature gradient, and the moving path of the particles and the residence time become longer and irregular, so that agglomeration of the particles may be caused. Such particle agglomeration is a cause of increasing the degree of dispersion of the particle size.

Therefore, it is necessary to make it occur in the isothermal sections b and c through the reduction reaction. Particularly, the reduction reaction in the lower isothermal section (b) is more advantageous for formation of monodispersed particles.

In order to move the reaction zone to the isothermal zone, the location of the metal microparticle discharge tube, the metal precursor vapor flow rate, the reaction temperature, the hydrogen gas injection flow rate, and the like can be controlled.

3-1-1) Adjusting discharge position of metal fine particles

In order to obtain monodisperse metal microparticles, it is advantageous to discharge metal microparticles in an isothermal section of the second heating zone.

As the discharge position of the metal fine particles changes, the residence time of the generated metal fine particles in the reactor changes, and the retention time is minimized by discharging the metal fine particles in the isothermal section where the reduction reaction occurs, The particle growth time can be relatively reduced.

Particularly, it is possible to minimize the residence time of the metal microparticles by discharging the particles in the lower isothermal section (Fig. 3 (b)).

3-1-2) Regulation of hydrogen gas injection position

In order to obtain monodisperse metal microparticles, it is advantageous that hydrogen gas is injected into the upper end of the vertical reactor.

Figure 4 shows the hydrogen gas flow inside the reactor with various hydrogen gas injection positions.

4 (a) and 4 (b), when the hydrogen gas is directly supplied to the vicinity of the center of the second heating zone, gas is directly injected into the reaction region at a relatively high temperature, There is a possibility to escape to the discharge pipe after passing through the low-temperature region while circulating inside the reactor. In this case, not only the loss to the wall of the reactor but also the movement path of the particles increases, so that the probability of collision between the particles is increased, which is disadvantageous for synthesizing the monodispersed fine particles.

On the other hand, in the vertical type reactor of the present invention, as shown in (c) of FIG. 4, since the hydrogen gas fills the lower temperature region of the upper portion of the reactor and the metal fine particles produced through the reaction do not rise to the low temperature region, I can go out. Therefore, in the case of the vertical reactor according to the present invention, the loss of particles in the low-temperature region can be reduced, and the retention time and movement path of the particles are shortened and regular. Is advantageous.

3-1-3) Adjustment of supply position of metal precursor vapor

In order to obtain monodisperse metal microparticles, it is advantageous that the metal precursor vapor is fed directly to the second heating zone.

As shown in FIGS. 2 (b) and 2 (c), the metal precursor vapor can reach the second heating zone by the inert gas injected into the lower end of the reactor. Since the inert gas is injected into the lower end of the vertical reactor and supplied to the second heating zone in the reactor, the inert gas is supplied from the lower end of the vertical reactor to the isothermal section in the second heating zone Can be filled.

Accordingly, it is possible to control the point at which the metal precursor vapor transported by the inert gas meets with the hydrogen gas to be confined to the isothermal section of the second heating zone. In particular, when a tube is provided in the reactor as shown in FIG. 2 (c), it may be more advantageous to adjust the supply position of the vapor of the metal precursor.

3-2) Specific temperature condition by metal type

Since the equilibrium vapor pressure of the metal precursor and the Gibbs free energy for the hydrogen reduction reaction are different for each metal type, it is possible to control the preferable temperature condition for each type of metal considering this.

The preferred temperature conditions for each type of metal are shown in Table 1 below.

metal
Kinds metal
Precursor In the first heating zone
Temperature (℃) In the second heating zone
Temperature (℃) Fe FeCl ₂ 700 to 1050 750 to 1200 FeCl ₃ 300 to 500 400 to 1000 Co CoCl ₂ 700 to 1100 750 to 1300 Ta TaCl ₅ 300 to 1000 1000 to 1300 Mo MoCl ₅ 300 to 500 400 to 1300 W WCl ₅ 300 to 500 400 to 1300 WCl ₆ 300 to 500 400 to 1000 V VCl ₂ 300 to 1200 400 to 1300 VCl ₄ 300 to 800 900 ~ 1300 Ti TiCl ₄ 300 to 650 400 to 1300

3-3) Reaction conditions for controlling the shape of metal microparticles

In the reduction reaction, the shape of the metal fine particles can be controlled by controlling the reaction conditions.

The shape of the metal fine particles that can be produced by the reduction reaction is hexahedral (particularly, cubic), spherical, truncated octahedral (or truncated hexahedron), nanowire, and the like.

For the production of shape controlled metal microparticles selected from the group consisting of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) and titanium , The reduction reaction may be carried out,

When the volume of the second heating zone is VR (cm ³ ), the flow rate of the metal precursor vapor to the second heating zone is FR (sccm), and the reduction reaction temperature is RT (° C)

i) 0 <FR (sccm) / VR (cm ³ ) <1/636 (min ^-1 ), or

ii) 1/636 (min ^-1 )? FR (sccm) / VR (cm ³ ) and the following equation:

&Quot; (1) &quot;

X (℃) / 636 (cm 3) <[RT (℃) / VR (cm)] - 25 (℃ / sccm) x [FR (sccm) / VR (cm 3)] <Y (℃) / 636 ( cm ³ )

In the above equation (1)

X = 600 (占 폚) and Y = 850 (占 폚), or

X = 900 (占 폚) and Y = 1500 (占 폚).

According to an example of a specific reaction condition for the production of hexahedral metal microparticles, the reduction reaction is carried out under the condition of 2/636? FR / VR and the equation (1), and X = 650? And Y = 850 ° C. According to an example of a more specific reaction condition for the production of hexahedral metal fine particles, the reduction reaction is carried out under the conditions of 3/636? FR / VR and the equation (1), where X = 700 Deg.] C and Y = 850 [deg.] C. At this time, the metal microparticles may have a shape of a cube or a rectangular parallelepiped, and preferably a shape of a cube.

According to an example of specific reaction conditions for the production of spherical metal microparticles, the reduction reaction is carried out under the condition of 2/636 FR FR / VR and the equation (1), wherein X = 900 캜 and Y = 1200 ° C. According to an example of a more specific reaction condition for the production of the spherical metal microparticles, the reduction reaction is carried out under the condition of 2/636 FR FR / VR and the above-mentioned formula (1), and X = 900 캜 And Y = 1100 ° C.

According to an example of specific reaction conditions for producing truncated octahedral metal microparticles, the reduction reaction is performed under the condition that 0.5 / 636 < FR / VR < 1/636 is satisfied.

The volume VR of the second heating zone may be the volume of the region in the reactor defined by the region in which the second heater is provided. Alternatively, the volume VR of the second heating zone may be the volume of the region in the reactor corresponding to a high temperature isothermal section in the second heating zone.

(4) Growth and emission of metal microparticles

In this step, the metal nuclei are grown into fine metal particles and discharged to the outside of the reactor. Specifically, the metal nuclei generated in the previous step grow as fine particles through continuous reduction reaction. Preferably, the growth of the fine particles can be performed in the isothermal section.

The grown metal microparticles can be discharged to the outside of the reactor through a discharge pipe of the reactor. The discharge of the metal microparticles is performed in an isothermal section of the second heating zone. That is, the inlet of the discharge pipe of the reactor (i.e., the hole through which the metal fine particles are sucked) may be positioned within the isothermal section of the second heating zone.

The resulting metal microparticles may have an average size of from 1 nm to 900 nm. Preferably, the metal microparticles may have an average size of 10 nm to 400 nm.

The metal microparticles may have a size distribution that exhibits a geometric standard deviation of from 1.0 to 1.5. Preferably, the metal microparticles may have a size distribution that exhibits a geometric standard deviation of 1.0 to 1.3, more preferably a geometric standard deviation of 1.0 to 1.2.

The metal microparticles may have a shape such as a hexahedron (especially a cube), a sphere, a truncated octahedron (or a truncated hexahedron), a nanowire, or the like. Preferably, the metal microparticles can be obtained only in any one of the shapes exemplified above.

Since the reduction reaction for metal formation is performed in a high-temperature isothermal section, the method for producing metal microparticles according to the present invention can have a high nucleation rate, so that nucleation and grain growth steps can be separated. Thereby, no additional nucleation occurs in the grain growth step, so that all the grains can grow into monodisperse grains because they are under the same growth conditions. In addition, the method for producing the metal microparticles according to the present invention can prevent agglomeration between particles even though the gas phase synthesis is performed without a surfactant since a vertical reactor is used and the generated fine particles are discharged in an isothermal section. As a result, according to the production method of the present invention, it is possible to produce monodisperse metal microparticles and to control further reaction conditions (reduction rate, gas flow rate, reactor configuration, etc.) Particles can be produced.

Hereinafter, the present invention will be described in more detail by way of examples. The following examples are illustrative of the present invention, but the present invention is not limited to the following examples.

Preparation of reactor

Hereinafter, the construction of a horizontal type reactor and a vertical type reactor used for producing the metal fine particles of the present invention are illustrated.

Horizontal reactor H-1

Figure 1 (a) shows an exemplary cross-section of a horizontal reactor H-1.

The reactor is equipped with a horizontal reaction vessel having a tubular shape of 4.5 cm in inner diameter and 120 cm in length in quartz.

A first heater having a length of 30 cm and a second heater having a length of 40 cm are attached to the outer wall of the reactor. The inner region of the reactor corresponding to the zone to which the first heater and the second heater are attached is defined as a first heating zone 6 and a second heating zone 7, respectively.

The reactor is provided with insulating materials (3, 5) on the outer surfaces of the first heater and the second heater, and an insulating material (4) is also provided between the first heater and the second heater. The internal regions of both ends of the reactor corresponding to the regions where neither the insulating material (3, 4, 5) nor the heater (6, 7) are attached are defined as the low temperature region (1, 2).

The first heating zone 6 in the reactor is provided with a quartz crucible 8 in which a metal precursor is charged and evaporated. In the second heating zone 7, a substrate 9 to which the reacted metal fine particles adhere is provided Respectively.

At the left end of the reactor, there is provided an injection pipe 11 into which hydrogen gas and inert gas are injected, and a discharge pipe 10 through which gas is discharged at the right end.

Horizontal reactor H-2

Figure 1 (b) shows an exemplary cross-section of a horizontal reactor H-2.

The reactor is equipped with a horizontal reaction vessel having a tubular shape of 4.5 cm in inner diameter and 120 cm in length in quartz.

A first heater having a length of 30 cm and a second heater having a length of 40 cm are attached to the outer wall of the reactor. The inner region of the reactor corresponding to the zone to which the first heater and the second heater are attached is defined as a first heating zone 6 and a second heating zone 7, respectively.

The reactor is provided with insulating materials (3, 5) on the outer surfaces of the first heater and the second heater, and an insulating material (4) is also provided between the first heater and the second heater. The inner regions of both ends of the reactor corresponding to the regions where neither the insulating material 3, 4, 5 nor the heater 6, 7 are attached are defined as the low temperature regions 1, 2.

The first heating zone 6 in the reactor is provided with a quartz crucible 8 in which a metal precursor is charged and evaporated.

An inert gas injection pipe 11 and a hydrogen gas injection pipe 12 are provided at the left end of the reactor and a discharge pipe 10 through which metal microparticles generated through the reaction are exhausted at the right end.

Vertical reactor V-1

Fig. 1 (c) shows an exemplary cross-section of the vertical reactor V-1.

The reactor has a quartz vertical reaction vessel having a tube shape with an inner diameter of 4.5 cm and a length of 120 cm.

A first heater having a length of 30 cm and a second heater having a length of 40 cm are attached to the outer wall of the reactor. The inner region of the reactor corresponding to the zone to which the first heater and the second heater are attached is defined as a first heating zone 6 and a second heating zone 7, respectively.

The reactor is provided with insulating materials (3, 5) on the outer surfaces of the first heater and the second heater, and an insulating material (4) is also provided between the first heater and the second heater. The inner regions of both ends of the reactor corresponding to the regions where neither the insulating material 3, 4, 5 nor the heater 6, 7 are attached are defined as the low temperature regions 1, 2.

The first heating zone 6 in the reactor is provided with a quartz crucible 8 in which a metal precursor is charged and evaporated.

The second heating zone (70) inside the reactor is provided with a discharge pipe (10) through which gas is discharged from the metal fine particles generated through the reaction.

An inert gas injection pipe 11 is provided at a lower end of the reactor, and a hydrogen gas injection pipe 12 is provided at an upper end of the reactor.

Vertical reactor V-2

Figure 1 (d) shows an exemplary cross-section of a vertical reactor V-2.

The vertical reactor V-2 is similar to the vertical reactor V-1. Further, the vertical reactor V-2 is provided with a tube 13 over the entire first heating zone and a part of the second heating zone inside. The tube 13 surrounds the quartz crucible 8, the lower end of the tube is fixed to the lower part of the reactor, and the upper part has a hole. The holes provided on the tube 13 are located in the second heating zone 7.

The vertical reactor V-2 is also provided with a hydrogen gas injection pipe 12 at its lower end. The hydrogen gas injection tube 12 is provided to inject hydrogen gas to the outside of the tube 13 and the inert gas injection tube 11 is provided to inject inert gas into the tube 13.

Example 1: Preparation of monodisperse metal microparticles using a vertical reactor

This embodiment was carried out using the vertical reactor V-1 shown in Fig. 1 (c). Further, as a comparative example, the horizontal type reactor H-2 shown in Fig. 1 (b) was used.

As the metal fine particles, particles of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) or titanium (Ti) As the metal chloride, iron chloride, cobalt chloride, tantalum chloride, molybdenum chloride, tungsten chloride, vanadium chloride, or titanium chloride was used.

The carrier gas (nitrogen gas) and the reducing gas (hydrogen gas) were injected into the reactor through the injection tubes 11 and 12 at flow rates of 500 and 125 sccm, respectively. The metal chloride powder was charged into a quartz crucible and placed in the center of the first heating zone 6. The metal chloride was reduced by hydrogen gas at the center of the second heating zone 7.

The temperature (evaporation temperature) of the first heating zone was set at 850 ° C and 900 ° C in the vertical reactor V-1 and the horizontal reactor H-2, respectively. The temperature of the second heating zone was set at 950 ° C or 1050 ° C for the vertical reactor V-1 and 950 ° C for the horizontal reactor H-2. In the vertical type reactor V-1, the discharge pipe was arranged at the center of the second heating zone or at a height of -10 cm above this.

The temperature at the point where the reduction occurred during the reaction was measured by a thermocouple thermometer.

Particulate capture was carried out for 30 minutes by a filter connected to the discharge pipe while performing the reaction. The microstructure of the metal microparticles prepared by using the horizontal type reactor and the vertical type reactor was observed. Specifically, the sizes of the particles were examined by roughly measuring the edge or sphere diameter of the hexagonal particles. Using the measured values, the geometric standard deviation (GSD) and the average size of the particles were calculated.

First, as a comparative example, metal fine particles were prepared by setting the temperatures of the first and second heating zones in the horizontal reactor H-2 at 900 ° C and 950 ° C, respectively. As a result, it was analyzed that all of the metal microparticles produced had a cuboid shape. The average size was about 205 nm and the GSD was 1.46.

As Example (1-1), in the vertical reactor V-1, the temperatures of the first and second heating zones were set at 850 캜 and 1050 캜, respectively, and the discharge pipe was disposed at the center height of the second heating zone, . The resulting metal microparticles were analyzed to have a cubic and spherical shape. The ratio of the number of cube-shaped particles to spherical particles was less than 0.5. The average sizes of the cubic and spherical particles were approximately 308 and 237 nm, respectively. The GSDs of the cubic and spherical particles were 1.23 and 1.15, respectively.

As the embodiment (1-2), in the vertical type reactor V-1, the temperatures of the first and second heating zones were set at 850 ° C. and 1050 ° C., respectively, and the discharge pipe was arranged at a height of -10 cm from the center of the second heating zone Metal fine particles were prepared. As a result, all of the metal microparticles showed a cubic shape. The average size was approximately 114 nm and the GSD was 1.17.

As the embodiment (1-3), in the vertical type reactor V-1, the temperatures of the first and second heating zones were set at 850 캜 and 950 캜, respectively, and the discharge pipe was disposed at the center height of the second heating zone, . As a result, all of the metal microparticles showed a cubic shape. The average size was about 172 nm and the GSD was 1.21.

The XRD diffraction patterns of the metal microparticles on the cube thus prepared were consistent with the reflection of the single crystal metal, so that the particles on the cube were pure single crystal metal microparticles.

The simultaneous observation of the cube-shaped and spherical metal microparticles in Example (1-1) appears to be due to the reduction rate of the metal chloride. As the rate of reduction of the metal chloride is high or low, metallic fine particles on the spherical or cubic, respectively, can be produced, because the metal chloride is adsorbed on the {100} faces of the metal fine particles during the CVD process. Considering this, the metal microparticles of these two shapes mean that the reduction rate is too high or the vapor pressure of the metal chloride is insufficient to synthesize the metal microparticles on the cube. Therefore, in order to synthesize only cubic-phase particles, the reduction rate should be decreased or the vapor pressure of the metal chloride should be increased.

In Examples (1-2) and (1-3), the rate of the reduction reaction was adjusted by moving the position of the discharge tube or lowering the temperature of the second heating zone as compared with Example (1-1) Particles. These results are summarized below.

Reduction reaction rate control according to discharge pipe position

The point where the metal chloride and hydrogen gas are mixed and the reduction occurs depends on the position of the discharge pipe. For example, when the discharge tube position is lowered, the point at which the reduction occurs is also lowered. In this case, the point where the reduction occurs can be roughly estimated by observing the metal thin film deposited on the inner wall after the particle synthesis.

In addition, the temperature in the reactor decreases sharply as it goes away from the high-temperature region as described above. Therefore, when the discharge pipe 10 located at the center of the second heating zone 7 is moved to the position of the heat insulating material 4 in FIG. 1 (c), the reduction point is also lowered.

In Example (1-2), the reduction rate was reduced by adjusting the reduction temperature by moving the discharge tube position as compared with Example (1-1).

Specifically, in the embodiment (1-2), the position of the discharge tube is moved to a height of -10 cm higher than the center of the second heating zone as compared with the embodiment (1-1) The metal fine particles on the cube were synthesized by lowering the reduction point. Therefore, it is concluded that these conditions, together with the reduction temperature and the particle residence time, are suitable for the synthesis of cubic-phase particles.

Since the high nucleation rate is a necessary condition for monodispersed particle synthesis, the particle size distribution can be further improved by placing the discharge tube position in the isothermal section, or more specifically, in the lower isothermal section.

Adjusting the reduction rate according to the second heating zone temperature

In Example (1-3), the temperature of the second heating zone was lowered to 950 占 폚 to synthesize metal microparticles on a cubic body, as compared with Example (1-1). The temperature at which the actual reduction reaction occurred was approximately 916 ° C.

Since all of the metal microparticles obtained in the above Example (1-3) have a cubic shape, it is judged that these conditions are bonded to the synthesis of the cubic particle. The reason why the average sizes of the cubic-phase particles in Examples (1-2) and (1-3) are different from each other seems to be due to the difference in the residence time of the particles under these conditions.

In the above comparative example, the geometric standard deviation of the metal fine particles on the cube synthesized by the horizontal reactor H-2 was far from the geometric standard deviation (less than 1.25) of the monodisperse particles. On the contrary, the geometric standard deviations of the metal fine particles of Examples (1-1) to (1-3) synthesized by the vertical reactor V-1 all showed less than 1.25.

Therefore, it has been confirmed that the vertical reactor for the synthesis of metal microparticles is suitable for the synthesis of monodisperse and non-aggregated metal microparticles.

Example 2: Size control of spherical monodisperse metal fine particles

1 (a) to 1 (d), the vertical reactor (V-1 or V-2) shown in Fig. 1 (c) Fine particles were prepared.

As the metal precursor, iron chloride, cobalt chloride, tantalum chloride, molybdenum chloride, tungsten chloride, vanadium chloride, or titanium chloride were used.

As a result, monodisperse spherical metal microparticles were obtained, and the average size of these monodisperse particles was measured and summarized in Table 2 below.

Sample
number H ₂ flow rate (sccm) N ₂ flow rate
(sccm) 1st
Heating zone
Temperature (℃) Second
Heating zone
Temperature (℃) Outlet location
(cm)
(Second heating zone
Central standard) Metal precursor
Evaporation position (cm)
(Based on the center of the first heating zone) Reactor
Kinds Average
size
(nm) a 125 500 1050 850 0 0 V-1 400 b 125 500 1000 850 +10  +10 V-1 300 c 600 200 1050 800 5 0 V-2 150 d 45 250 1000 850 5 0 V-2 50

Particularly, monodispersed particles were obtained through the vertical reactor, and it was found that monodispersed particles with finer sizes could be obtained by using a vertical reactor (V-2) having a tube. This is because the tubes provided in the vertical reactor V-2 could limit the nucleation and particle growth and discharge due to the reduction reaction to a narrower region.

Reference Example 1: Shape change of metal microparticles according to hydrogen gas

In this reference example, the horizontal reactor H-1 shown in Fig. 1 (a) was used as a reactor.

As the metal fine particles, particles of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) or titanium (Ti)

First, cube-shaped metal fine particles having an average size of 185 nm were prepared by CVD, and the metal fine particles were dispersed by ultrasonic vibration on a sapphire single crystal substrate (C-plane (0001), Crystal Bank). It was confirmed that the initial metal microparticles dispersed on the sapphire substrate were observed to have a cube shape.

The substrate in which the metal fine particles were dispersed was placed in the center of the second heating zone of the horizontal reactor H-1. While the hydrogen gas was injected into the reactor at a flow rate of 1000 sccm, the second heater was operated to heat the metal microparticles at a temperature of 950 ° C for 30 minutes

As a result of observation of the shape of the metal microparticles after the heat treatment, it was found that the shape was changed compared to that before the heat treatment. Specifically, it was clearly observed that the shape of the metal microparticles changed from a cubic shape to a nearly spherical polyhedral shape. Of these, nearly spherical particles appear to have reached an equilibrium shape. On the other hand, some of the metal microparticles were observed to have a shape slightly deviated from the sphere (e.g. oval). These particles seem to be still in equilibrium, probably because the heat treatment time or temperature applied to these particles is not sufficient to reach equilibrium shape.

However, when compared with the initial metal microparticles before the heat treatment, it was clear that the hydrogen gas atmosphere destabilizes the {100} plane and causes the spherical shape to change on the cubic plane.

The numerical value of energy on each facet of the metal microparticles after the heat treatment was input by Wulffman software to simulate the equilibrium crystal shape (ECS) of the metal fine particles, and the results are shown in FIG. 5 (a) . As shown in FIG. 5 (a), the {100}, {111} and {210} planes of the metal microparticles were developed. According to ECS, it was found that the relative sizes of the surface energies were γ ₁₁₁ <γ ₂₁₀ <γ ₁₀₀ <γ ₁₁₀ (where subscripts 100, 111 and 210 denote the Miller index).

Reference Example 2: Shape change of metal microparticles according to metal precursor vapor

In this reference example, the horizontal reactor H-1 shown in Fig. 1 (a) was used as a reactor.

As the metal fine particles, particles of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V)

As the metal chloride, iron chloride, cobalt chloride, tantalum chloride, molybdenum chloride, tungsten chloride, vanadium chloride, or titanium chloride was used.

The metal microparticles dispersed on the sapphire substrate were preliminarily heat-set in a hydrogen gas atmosphere for 30 minutes and placed in the center of the second heating zone of the horizontal reactor H-1.

The metal chloride powder was charged into a quartz crucible and placed in the center of the first heating zone. In order to prevent reduction of the metal chloride, the inside of the reactor was purged with nitrogen gas for 30 minutes. Thereafter, while the hydrogen gas was injected into the reactor at a flow rate of 1000 sccm, the first heater was activated to evaporate the metal chloride. At this time, the vapor pressure of the metal chloride was controlled by controlling the temperature condition of the first heating zone to 750 ° C, 800 ° C or 850 ° C (the chloride vapor pressure exponentially increases with the heating temperature). The reaction time was changed to 0, 15, 45 or 75 minutes.

After completing the reaction, the shape of the heat-treated metal microparticles on the sapphire substrate was observed, from which the relative surface energies of each side of the metal microparticles were calculated via Wulffman software.

The initial shape of the metal microparticles (0 min of heat treatment) showed spherical shape, but after the heat treatment at 950 ° C for 15 min in a metal chloride atmosphere, the shape changed to a cuboctahedral shape. Experimental ECS of the metal microparticles heat-treated for 15 minutes was generated by software and is shown in Fig. 5 (b). It can be seen that the {100} and {111} planes are developed. The relative size of the surface energy was analyzed as γ ₁₀₀ = γ ₁₁₁ <γ ₁₁₀ .

As a result of observing the metal microparticles heat-treated at 950 ° C. for 45 minutes in a metal chloride atmosphere, the metal microparticles having relatively small sizes changed to a cubic shape while the metal microparticles having relatively large sizes were not cubic , Which appears to be due to the relatively slow reaction rate of large particles.

As a result of observing the metal microparticles heat-treated for 75 minutes in a metal chloride atmosphere, it was confirmed that all of them turned into a cube shape. Experimental ECS of the heat-treated metal microparticles for 75 minutes was generated by software and is shown in Fig. 5 (c). The developed sculptured facets were {100} and {111} facets. The surface energy was analyzed to be not equal to γ ₁₀₀ <γ ₁₁₁ <γ ₁₁₀ .

It was confirmed that the surface energy was reversed from {100} to {111} after the heat treatment in a metal chloride atmosphere. From this, it can be confirmed that the metal chloride vapor stabilizes the {100} surface of the metal fine particle. This is presumably because the adsorption of metal chloride molecules occurs preferentially on the {100} plane.

Reference Example 3: Shape variation of metal microparticles according to the vapor pressure of a metal precursor

In this reference example, the thermodynamic / dynamic relationship of the shape change of the metal microparticles according to the vapor pressure of the metal chloride was experimented.

Adsorption is explained by many isotherm curves. It is expected that when the Langmuir adsorption isotherm curve, known as the simplest and most accurate model, is applied to adsorption of metal chloride, the fraction of surface area covered with metal chloride is expected to increase as the partial pressure of the metal chloride increases. This means that the partial pressure of the metal chloride may affect the degree of stabilization of the {100} plane. In other words, if the partial pressure of the metal chloride is not sufficiently high, the {100} plane may not be sufficiently stabilized to produce a cubic shape.

This possibility was examined by examining the influence of partial pressure of metal chloride on the shape of metal microparticles.

In this reference example, particles of iron (Fe), cobalt (Co), tantalum (Ta), molybdenum (Mo), tungsten (W), vanadium (V) Iron chloride, cobalt chloride, tantalum chloride, molybdenum chloride, tungsten chloride, vanadium chloride, or titanium chloride were used.

First, as a result of heat treatment at 950 ° C for 45 minutes in a hydrogen gas atmosphere, most of the metal microparticles were observed to be spherical or elliptical, so that hydrogen gas did not stabilize the {100} plane and caused an almost spherical equilibrium shape I could.

Subsequently, these spherical metal microparticles were further heat-treated for 45 minutes at various evaporation temperature conditions.

For example, as a result of further heat treatment of the metal chloride at the evaporation temperature of 750 ° C for 45 minutes, the shape of the metal microparticles was observed to be spherical not greatly different from the previous one. The reason that the particles maintain their spherical shape is because the low chloride vapor pressure has thermodynamically / dynamically influenced.

On the other hand, as a result of additional heat treatment at a temperature of 800 ℃ for 45 minutes, the shape of some particles changed to truncated cube, which means that the {100} plane developed. This shape is due to the somewhat higher vapor pressure of the metal chloride.

Further, as a result of further heat treatment at a vaporization temperature of 850 캜 of the metal chloride, the metal microparticles having a size of less than 500 nm changed into a cube shape, which corresponds to ECS in a metal chloride atmosphere. The {100} plane dominates because of the high rate of reaction that turns into a cuboid, which is due to the high metal chloride vapor pressure.

Example 3: Shape variation of metal microparticles according to the vapor flow rate and reaction temperature of a metal precursor

Using the vertical reactor V-1 shown in Fig. 1 (c), metal microparticles were prepared under various conditions.

As the metal precursor, iron chloride, cobalt chloride, tantalum chloride, molybdenum chloride, tungsten chloride, vanadium chloride, or titanium chloride were used.

Specifically, the metal chloride powder was charged into a quartz crucible and placed in the center of the first heating zone. Hydrogen gas was introduced into the reactor at a rate of 125 sccm, and nitrogen gas at a flow rate of 500 sccm. The first heating zone temperature, the second heating zone temperature, the outlet tube position, and the sample position were performed under the respective conditions (Sample Nos. 1 to 12) shown in Table 3 below.

During the reaction, the vapor flow rate of the metal precursor, the reaction temperature, and the shape of the fine metal particles were measured. At this time, the vapor flow rate (sccm) of the metal precursor was calculated by dividing the reduction amount (g) of the solid metal precursor powder by the time, by the density of the metal precursor. The reduction reaction temperature (the actual reaction temperature at the point where the reduction occurs) was measured by a thermocouple thermometer. The shape of the generated fine metal particles was observed with an electron microscope.

Sample The first heating zone
Temperature (℃) Second heating zone
Temperature (℃) Discharge tube position (cm)
(Second heating zone
Central standard) Metal precursor evaporation position
(cm) (first heating zone
Central standard) One 850 1000 0 0 2 850 1000 0 0 3 850 1050 +10 9 4 850 1050 +10 -5 5 850 1100 0 0 6 800 1050 +10 0 7 750 950 0 0 8 850 1000 0 0 9 850 950 0 0 10 800 950 0 0 11 850 950 +10 0 12 900 950 0 0

Based on the results of the above experiment, graphs of the relationship between the shape of the metal microparticles according to the vapor flow rate of the metal precursor and the reaction temperature are shown in FIG.

As shown in FIG. 6, it can be confirmed that various shapes of metal microparticles were produced according to the metal precursor vapor flow rate and the reaction temperature. In addition, it can be seen that the relationship between these reaction conditions and the shape of the fine metal particles also conforms to the range of the above-mentioned formula (1).

Example 4: Preparation of spherical monodisperse metal fine particles

Spherical monodisperse metal microparticles were prepared using a vertical reactor.

First, a powder of iron chloride (FeCl ₂ , 98%, STREM Chemicals) was charged into a quartz crucible and placed in the center of the first heating zone of the vertical reactor V-1 shown in Fig. 1 (c). Hydrogen gas was introduced into the reactor at a rate of 125 sccm, and nitrogen gas at a flow rate of 500 sccm. The first heating zone temperature was 950 占 폚, the second heating zone temperature was 820 占 폚, and the discharge tube position was the center of the second heating zone to produce iron microparticles. An FESEM image of the iron microparticles is shown in Fig.

Next, cobalt chloride (CoCl ₂ , 98%, Sigma-Aldrich) The powder was charged into a quartz crucible and placed in the center of the first heating zone of the vertical reactor V-2 shown in Fig. 1 (d). Hydrogen gas was injected into the reactor at a flow rate of 22 sccm respectively, and nitrogen gas was injected at a flow rate of 250 sccm. The first heating zone temperature was 950 占 폚, the second heating zone temperature was 850 占 폚, and the discharge tube position was the center of the second heating zone to produce cobalt fine particles. An FESEM image of the cobalt microparticles is shown in FIG.

As shown in FIGS. 7 and 8, it was found that spherical monodisperse metal fine particles were produced by the manufacturing method of the present invention.

1, 2: low temperature region, 3, 4, 5:
6: first heating zone, 7: second heating zone,
8: crucible, 9: base material,
10: discharge pipe, 11, 12: inert and hydrogen gas injection pipe,
13: Tube.

Claims (10)

(1) preparing a vertical reactor having a heating zone for a reduction reaction;
(2) supplying metal precursor vapor and hydrogen gas to the heating zone;
(3) reducing the metal precursor vapor with the hydrogen gas at a temperature of 400 to 1300 占 폚 to produce metal nuclei; And
(4) growing the metal nuclei into fine metal particles and discharging the metal fine particles to the outside of the reactor,
Wherein the metal precursor, the metal nuclei and the metal fine particles are selected from the group consisting of Fe, Co, tantalum, molybdenum, tungsten, vanadium and titanium. Precursors, nuclei, and fine particles of the metal being &lt; RTI ID = 0.0 &gt;
An isothermal section is present in the heating zone and the reduction reaction and the discharge of the metal microparticles are performed in the isothermal section,
Wherein the reactor further comprises a heating zone for vaporizing the metal precursor therein,
Wherein the heating zone for vaporizing the metal precursor is surrounded by a tube,
Said tube having a hole in its upper portion,
The hole is located within the isothermal section,
Characterized in that the metal precursor is evaporated in the tube and the generated vapor is supplied to the isothermal section through the hole.
Wherein the metal is selected from the group consisting of Fe, Co, tantalum, molybdenum, tungsten, vanadium and titanium.
The method according to claim 1,
Wherein the hydrogen gas is injected into the upper end of the vertical reactor and supplied to the heating zone.
3. The method of claim 2,
Wherein the vertical reactor is filled with the injected hydrogen gas from an upper end to an isothermal section in the heating zone.
The method of claim 3,
Characterized in that the metal precursor vapor is transported by an inert gas and supplied to the heating zone, and the inert gas is injected into the tube at the lower end of the vertical reactor and supplied to the heating zone. / RTI &gt;
The method according to claim 1,
Wherein the isothermal section is a continuous section having a temperature deviation within 占 0 占 폚.
The method according to claim 1,
Wherein the heating zone includes a vertical heater,
Characterized in that the isothermal section is present in a height (1/4 to 3/4 h) corresponding to 1/4 to 3/4 from below with respect to the height (h) of the heater. Way.
The method according to claim 6,
Characterized in that the isothermal section is present in a height (1/4 to 2/4 h) corresponding to 1/4 to 2/4 from below with respect to the height (h) of the heater. Way.
delete The method according to claim 1,
Wherein the reactor has a first hydrogen gas injection tube at an upper end thereof,
An inert gas injection pipe and a second hydrogen gas injection pipe at a lower end,
Hydrogen gas is injected to the outside of the tube by the first hydrogen gas injection tube and the second hydrogen gas injection tube and an inert gas is injected into the tube by the inert gas injection tube, Is supplied to the isothermal section.
The method according to claim 1,
Characterized in that the monodisperse metal microparticles have an average size of from 10 nm to 400 nm and a size distribution that exhibits a geometric standard deviation of from 1.0 to 1.2.

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