KR101336702B1 - Metal nanopowder agglomerate with excellent compactability and the manufacturing method the same - Google Patents

Abstract

In one aspect of the present invention, a method for preparing a metal nanopowder agglomerate having excellent moldability may include grinding a metal oxide into a nanopowder (a powder having a size of 100 nm or less), and manufacturing the nanopowder into a spherical agglomerate using a spray dryer. Step, the heat treatment of the spherical aggregates to produce a spherical metal nano-powder aggregates and the spherical metal nano-powder aggregates comprising the step of coating with an organic binder. In addition, the metal nanopowder agglomerates having excellent moldability are spherical metal nanopowder agglomerates having a network structure, the diameter of the spherical metal nanopowder agglomerates is 20 µm or less, and the organic binder is formed on the surface of the spherical metal nanopowder agglomerates. A coating layer is formed.

Description

Metal nanopowder aggregate with excellent moldability and manufacturing method thereof {METAL NANOPOWDER AGGLOMERATE WITH EXCELLENT COMPACTABILITY AND THE MANUFACTURING METHOD THE SAME}

The present invention relates to a metal nanopowder agglomerate that can be used for precision sintered parts and the like and a method of manufacturing the same.

Nano-sized particles exhibit unique physicochemical properties when compared to bulk materials. Metal nanopowders with sizes of several hundred nanometers or less have enormous specific surface areas. This results in very high interpowder friction during die molding, resulting in low molding densities of less than 50% under normal molding conditions.

Since nano powders have high sinterability, high density can be secured during sintering to sufficiently overcome the low molding density mentioned above, but high shrinkage rate generated from low molding density to full densification can make product dimensional stability It is a big factor.

In addition, the metal nano powder having the specific surface area as described above is generally limited in the powder preparation operation due to the explosive oxidizing property.

Due to such a reduction in molding density, dimensional stability of the product, and difficulty in handling, there is a problem in processing into parts. Therefore, it is time to develop a metal nano powder having excellent moldability applicable to precision sintered parts.

One aspect of the present invention can provide a metal nano-powder aggregates excellent in formability applicable to precision parts and the like and a manufacturing method thereof.

In one aspect of the present invention, a method for preparing a metal nanopowder agglomerate having excellent moldability may include grinding a metal oxide into a nanopowder (a powder having a size of 100 nm or less), and manufacturing the nanopowder into a spherical agglomerate using a spray dryer. The method may include preparing the spherical metal nanopowder aggregates by reducing heat treatment of the spherical aggregates and coating the spherical metal nanopowder aggregates with an organic binder.

It is preferable that the metal of the said metal oxide is 1 type, or 2 or more types of Fe, W, Cu, Mo, and Ni.

The reduction heat treatment is preferably carried out by one of hydrogen reduction or electrochemical reduction.

The reduction heat treatment is preferably carried out at 200 ~ 800 ℃.

In addition, another aspect of the present invention, the metal nanopowder agglomerates having excellent moldability are spherical metal nanopowder agglomerates having a network structure, and the diameter of the spherical metal nanopowder agglomerates is 20 µm or less, and the spherical metal nanoparticles are aggregated. The organic binder coating layer may be formed on the surface of the powder aggregate.

The metal of the metal nanopowder aggregate is preferably one or two or more of Fe, W, Cu, Mo, and Ni.

The metal nanopowder aggregate may include a metal nanopowder having a size of 100 to 500 nm and a metal nanopowder having a size of 1 to 30 nm.

According to the metal nanopowder agglomerates of the present invention and the manufacturing method thereof, precision parts can be easily and safely manufactured by using the agglomerates with excellent moldability. Due to the excellent moldability, it is possible to produce a molded body having a molding density required according to product characteristics in a wide range of pressure ranges. In particular, high molding density of more than 80% can be secured, and together with a fine sintered structure after sintering, it is possible to prevent product damage due to severe shrinkage rate of nanopowder during sintering, and dimensional deviation is reduced, so that a healthy sintered product can be obtained.

Due to the organic binder coating, it is possible to prevent the formation of oxide during the process and to ensure the fluidity of the powder aggregate during molding.

It can be synthesized in a relatively simple process by performing heat treatment simultaneously with reduction.

Various metal oxides can be prepared with metal powder aggregates, and can be applied to various industrial fields.

1 is a flowchart illustrating a method of manufacturing a metal nanopowder aggregate, which is an aspect of the present invention.
Figure 2 is a side view of the present invention, a photograph of agglomerates prepared using a spray dryer.
Figure 3 is an embodiment of the present invention, a graph showing the weight loss rate with time during the reduction heat treatment.
4 is a graph showing a temperature change with time according to an embodiment of the present invention.
5 is a graph showing the results of X-ray diffraction analysis of aggregates as an embodiment of the present invention.
Figure 6 (a) to (d) is an embodiment of the present invention, is a photograph observing the microstructure of the aggregates heat-treated at 450 and 550 ℃.
7 is a graph showing molding densities of Inventive Examples 1 and 2 and Comparative Example 1 according to molding pressure as an example of the present invention.
8 is a graph showing molding densities of Inventive Example 2 and Comparative Examples 2 to 4 according to molding pressure as an example of the present invention.

The present inventors conducted a study on the method to secure a high formability when manufacturing a metal powder from a metal oxide, as a result of pulverizing the metal oxide into a nano-sized powder to produce a spherical aggregate, by reducing heat treatment By controlling the nanostructure of the nanopowder and then applying an organic binder coating, the present inventors have realized that high moldability and antioxidant properties can be ensured.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Hereinafter, the manufacturing method of the metal nano powder aggregate which is excellent in the moldability which is one side of this invention is demonstrated in detail. In the present invention, the nanopowder means a powder having a size of 500 nm or less.

As shown in FIG. 1, first, a metal oxide is pulverized to prepare a nano-sized metal oxide (S11). Here, the metal oxide is a compound in which a metal and oxygen are bonded, and the bonding form may be any bond. In addition, although any kind of metal can be applied, it is preferable that one or two kinds of Fe, W, Cu, Mo, and Ni are used. One kind of metal oxide may be used, but two or more kinds of metal oxides may be used.

Here, in order to produce a nano-sized metal oxide, any method can be used as long as it can produce a nano-sized metal oxide, but it is preferable to use a mechanical grinding method. It is more preferable to carry out through ball milling, and for this purpose, it is most preferable to carry out an attribution mill or a circulating horizontal bead mill.

As an embodiment of the present invention, when using the attrition milling method, by using a steel ball and methyl alcohol, acetone, water and the like of 3mm or less as a process control agent (PCA) for 10 hours milling at 300 rpm 20 ~ 20 ~ A 30 nm powder can be obtained, and in the case of using a cyclic horizontal bead milling method, a zirconia bead of 0.65 mm, methyl alcohol, acetone, and water are used as a PCA and milled for 10 hours at 1800 to 2400 rpm for 20 to 30 minutes. nm powder can be obtained. Although the said PCA is not specifically limited, The thing containing surfactant and a dispersing agent in methyl alcohol, ethyl alcohol, acetone, water, or these can be applied.

The nano-sized metal oxide powder prepared as described above is prepared into a spherical aggregate using a spray dryer (S12). After inject | pouring the slurry which mixed metal oxide powder and PCA into the spray dryer, it is preferable to manufacture in spherical aggregates. In addition, when wet ball milling is used, the slurry material immediately after ball milling can be directly injected into the spray dryer, and then spherical aggregates can be produced.

Depending on the operating conditions and the collecting position of the spray dryer, it is possible to secure porous aggregates of various sizes. In one embodiment of the present invention, the slurry injection speed of 2500 cc / h, injection pressure of 80 kPa, 15 ~ 20 microns in the bottom of the drying tank at 30 ℃ temperature inside the tank (Fig. 2 (a)), 2 in the middle of the exhaust pipe Spherical aggregates of ˜5 micron size (Fig. 2 (b)) were obtained.

Then, the spherical aggregates are subjected to reduction heat treatment (S13). Metal oxides can be thermally and electrochemically reduced. In the case of iron oxide, it is preferable to produce reduced iron by hydrogen reduction. At this time, it is preferable to reduce the said spherical aggregate in a hydrogen atmosphere, heating up at 200-800 degreeC. By performing a sufficient heat treatment, by inducing bonding (sintering) between the powder, and by forming a network structure, it is possible to prevent the aggregates from being broken during molding, through which plastic deformation can be induced. At this time, when the temperature is less than 200 ° C., it is difficult to exert sufficient heating effect, and when the temperature exceeds 800 ° C., the above-described reduction heat treatment effect is saturated, so it is preferable to control the temperature at 200 to 800 ° C. However, the present invention is not limited to the heat treatment temperature, and various applicable temperature ranges can be set according to the type of metal.

However, at this time, the heat treatment temperature is more preferably controlled to 550 ~ 700 ℃. In the above temperature range, smaller nano-sized powders are positioned between the larger nano-sized powders, thereby greatly increasing moldability. It is possible to secure the compactness of the aggregates and increase the bonding force by placing small nano-sized powders in the pores between the large nano-sized powders inside the aggregates. This will greatly increase the molding density. At this time, it is possible to set various applicable temperature ranges according to the type of metal.

Thereafter, the surface of the reduced metal aggregate is coated using an organic binder (S14). The organic binder is not particularly limited and can be subjected to ordinary coating treatment. By reducing the exposed surface area, the aggregates can be prevented from being oxidized, thereby controlling the handling in the air. Here, the organic binder is not particularly limited, it is possible to apply a low density binder, such as stearic acid, wax-based, it is preferable to apply a binder that can be easily decomposed at 200 ~ 300 ℃.

The thickness or volume of the coating layer is not particularly limited, but is preferably formed to coat all surfaces of the aggregate, and may be coated at 5 vol% or less with respect to the volume of the metal nanopowder aggregate.

The spherical coated metal nanopowder agglomerates manufactured by the above-described manufacturing process can secure high molding density, thereby, along with a fine sintered structure after sintering, to prevent product damage due to severe shrinkage of the nanopowder during sintering. It can prevent and reduce the dimensional deviation can produce a healthy sintered product.

Hereinafter, a metal nanopowder agglomerate excellent in moldability as another aspect of the present invention will be described in detail.

The metal nanopowder agglomerate, which is one side of the present invention, has a network structure, and the diameter of the spherical metal nanopowder agglomerates is preferably 20 μm or less. In addition, it is preferable that the organic binder coating layer is formed on the surface of the spherical metal nanopowder aggregates.

Here, the metal may be applied to any kind of metal, but preferably corresponds to one or two kinds of Fe, W, Cu, Mo, and Ni. It may be one kind of metal, or two or more kinds of metals.

The spherical aggregates are networked, porous forms containing pores. At this time, the metal powder of several hundred nanoscale and the metal powder of several tens of nanoscale may be included. Smaller nano-sized powders are placed between the larger nano-sized powders, which can greatly increase moldability. It is possible to secure the compactness of the aggregates and increase the bonding force by placing small nano-sized powders in the pores between the large nano-sized powders inside the aggregates. This will greatly increase the molding density. The hundreds of nano-size metal powder is preferably 100 ~ 500nm size, the tens of nano-size metal powder is preferably 1 ~ 30nm size.

The thickness or volume of the coating layer is not particularly limited, but is preferably formed to coat all surfaces of the aggregate, and may be coated at 5 vol% or less with respect to the volume of the metal nanopowder aggregate.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

(Example 1)

After ball milling Fe ₂ O ₃ to powder of 10-30 nm, Fe ₂ O ₃ powder and PCA mixture were injected at a rate of 2500 cc / h. The air jet pressure for pulverizing the slurry droplets was controlled to 80 kPa to prepare spherical aggregates, and heated to 450 ° C. under a hydrogen atmosphere and maintained for 1 hour for reduction heat treatment. Thermogravimetric analysis was performed and the measured values are shown in FIG. 3.

As shown in FIG. 3, the weight loss was stopped after 40 minutes after the start of the heat treatment, from which it was found to be reduced to pure Fe. That is, it was confirmed that the reduction of the metal oxide may sufficiently occur when the reduction heat treatment is performed at 450 ° C.

(Example 2)

After ball milling Fe ₂ O ₃ to powder of 10-30 nm, Fe ₂ O ₃ powder and PCA mixture were injected at a rate of 2500 cc / h. The air jet pressure for pulverizing the slurry droplets was controlled to 80 kPa to prepare spherical aggregates, and heated to 550 ° C. under a hydrogen atmosphere and maintained for 1 hour for reduction heat treatment. A graph of temperature versus time is shown in FIG. 4.

After dissolving 3 vol% of stearic acid to act as a surfactant and an antioxidant organic binder in an ethyl alcohol solvent, the reduced metal aggregate was charged and wet-coated. The mixture was mixed for 5 minutes without milling media and then dried to minimize breakage of aggregates in the coating. In addition, X-ray diffraction analysis was performed in the air to confirm the oxidation resistance of the aggregate in which the antioxidant film was formed, and is shown in FIG. 5.

As shown in FIG. 5, no phase of Fe oxide due to reoxidation other than reduced Fe was not identified. Through this, it was confirmed that the reoxidation resistance is excellent when coating the organic binder.

(Example 3)

After ball milling Fe ₂ O ₃ to powder of 10-30 nm, Fe ₂ O ₃ powder and PCA mixture were injected at a rate of 2500 cc / h. The spherical aggregates were prepared by controlling the air injection pressure to crush the slurry droplets at 80 kPa, and the reduction heat treatment was performed by heating up to 450 ° C. and 550 ° C. under hydrogen atmosphere for 1 hour.

Micrographs observing the microstructure of each aggregate are shown in Figs. 6 (a) to (d), respectively. As shown in Figure 6 (a) and (b), it can be confirmed that when the reduction heat treatment at 450 ℃ some 200 ~ 300nm size powder and a large number of particles 1 ~ 20nm size was formed. In addition, as shown in Figure 6 (c) and (d), when the reduction heat treatment at 550 ℃ 20 to 30nm size particles are located between the particles of 200 ~ 500nm, the connection structure between the powder more precisely It was confirmed that it was formed.

(Example 4)

After ball milling Fe ₂ O ₃ to powder of 10-30 nm, Fe ₂ O ₃ powder and PCA mixture were injected at a rate of 2500 cc / h. The air jet pressure for crushing the slurry droplets was controlled to 80 kPa to prepare spherical aggregates, and the aggregates were heated to 450 ° C. and 550 ° C. under a hydrogen atmosphere and maintained for 1 hour for reduction heat treatment.

In addition, Fe ₂ O ₃ was subjected to reduction heat treatment at 450 ° C. Molding was performed for each example, and the molding density of each molding pressure was measured and shown in Table 1 and FIG. 7.

division Heat treatment temperature
(℃) Powder size
(nm) Aggregate size
(탆) Molding density (% T.D.) 250 MPa 500 MPa 1250 MPa Inventory 1 450 1 to 100 2 to 5 49.17 53.06 65.21 Inventory 2 550 10-200 2 to 5 64.27 73.4 85.83 Comparative Example 1 450 10-20 5-100 43.41 47.34 53.97

As shown in Table 1 and Figure 7, it was confirmed that the powder of Comparative Example 1 (direct reduction without pulverizing with nano powder) did not increase the molding density significantly even if the molding pressure was greatly applied. On the contrary, inventive example 1 subjected to reduction heat treatment at 450 ° C. was confirmed to have an increased molding density compared to comparative example 1. FIG. Inventive Example 2, which was subjected to reduction heat treatment at 550 ° C., showed that the molding density was greatly increased as compared with Comparative Example 1.

(Example 5)

FeNi agglomerates known to have excellent moldability were measured in accordance with molding pressure, and are shown in Table 2 and FIG. 8. As shown in Table 2, Comparative Example 2 is 50% Ni, the aggregate size is 20 ~ 70nm (powder size 10 ~ 30㎛), Comparative Example 3 Ni content is 40%, the size of the aggregate Is 30 nm (powder size: 30 µm), Comparative Example 4 has a Ni content of 40%, and the size of the aggregate is 100 nm (powder size: 5 µm and 500 µm). In order to compare the molding density of Inventive Example 2 described in Example 4, it is shown together in Table 2 and FIG.

division Powder size
(nm) Aggregate size
(탆) Molding density (% T.D.) 250 MPa 500 MPa 1250 MPa Inventory 2 10-200 2 to 5 64.27 73.4 85.83 Comparative Example 2 20-70 10 to 30 55 65 - Comparative Example 3 30 30 50 55 72 Comparative Example 4 100 5, 500 - - 75

As shown in Table 2 and FIG. 7 below, it was confirmed that the moldability of Inventive Example 2 was superior to Comparative Examples 2 to 4, which are generally known to have excellent moldability. In addition, it was confirmed that the molding density is highly dependent on the molding pressure irrespective of the size of the nanopowder or the size of the aggregate.

Claims (7)

Grinding the metal oxide into nanopowders (powder having a size of 100 nm or less);
Preparing the nanopowder into spherical aggregates using a spray dryer;
Reducing heat treatment of the spherical aggregates to produce spherical metal nanopowder aggregates having a network structure; And
Coating the spherical metal nanopowder aggregate having the network structure with an organic binder,
A spherical metal nanopowder aggregate having a network structure has a diameter of 20 μm or less, and a method for producing a metal nanopowder aggregate having excellent moldability including a metal powder having a size of 100 to 500 nm and a metal powder having a size of 1 to 30 nm.
The method according to claim 1,
The metal of the metal oxide is Fe, W, Cu, Mo and Ni, one or two or more of the metal nano-powder agglomerates excellent in formability.
The method according to claim 1,
The reduction heat treatment is a method for producing a metal nanopowder agglomerates excellent in formability performed by one of hydrogen reduction or electrochemical reduction.
The method according to claim 1,
The reduction heat treatment is a method for producing a metal nano-powder agglomerates excellent moldability is carried out at 200 ~ 800 ℃.
Spherical metal nanopowder aggregates having a network structure,
The spherical metal nanopowder agglomerate has a diameter of 20 μm or less, and includes a metal powder having a size of 100 to 500 nm and a metal powder having a size of 1 to 30 nm, and an organic binder coating layer is formed on the surface of the spherical metal nanopowder aggregate. Metal nano powder aggregates with excellent properties.
The method according to claim 5,
The metal nanopowder aggregate of the metal nanopowder aggregate is excellent in formability of one or two or more of Fe, W, Cu, Mo and Ni.
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