JP2000178610A - Production of metallic hyperfine particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of producing an aggregated body and a dispersed body of hyperfine particles of the group 1B and 8A metals in the Periodic Table and the alloys thereof. SOLUTION: As to this method, from an alloy in which 1st metal as a solute is formed a super-saturated solid solution into a matrix of 2nd metal, the 2nd metal is extracted to form a hyperfine particle aggregated body in which the hyperfine particles of the 1st metal are aggregated to a skeleton shape, the stage in which this aggregated body of the hyperfine particles is cleaned is included, and the hyperfine particles of the 1st metal are produced. In this case, (1) a liq. alloy composed of the 1st metal consisting of Cu, Au, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and/or Pt and the 2nd metal consisting of Al or (2) a liq. alloy composed of the 1st metal consisting of Ag-Pd or Ag-Cu and the 2nd metal consisting of Al is rapidly solidified to form into an alloy in which the 1st metal is formed the super-saturated solid solution into the 2nd metal, and an aq. soln. of the hydroxide of alkali metal is acted on this super-saturated solid solution alloy to extract the 2nd metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ultrafine metal particles, and more particularly, to a method for forming a group 8A and a group 1B of the periodic table.
The present invention relates to a method applicable to ultrafine particles of a group III metal and an alloy of two or more of these metals. Metal powders are used in many fields in industry. For example, conductive paints and conductive adhesives in the electronics field include Ag, A
powder such as u, Pt, Pd, Ag-Pd, Ag-Au, and powder such as Ni, Ag for the electromagnetic wave shielding material.
Ag powder is used for the cathode material of the secondary battery, Pt powder is used for the oxygen electrode of the fuel cell, and Fe, Co,
Powders such as Ni, Ru, Pd, Pt and Ag, Ag powders for antibacterial agents, Co powders for WC-Co cemented carbides, and Ag- powders for electrode materials of multilayer ceramic capacitors.
Pd and Ni powders, and powders of Fe, Co, Ni, and Cu are used as raw material powders for MIM (metal injection molding). Accordingly, a method for producing various metal powders used for various applications will be described below.

[0002]

2. Description of the Related Art The above-mentioned metal powder can be powdered by a conventional technique such as a mechanical pulverization method, a chemical salt decomposition method, an electrochemical plating method, and a molten metal atomization method. However, it is not easy to produce so-called ultrafine particles of about 100 nm or less by these methods. Various methods such as a gas evaporation method can produce ultrafine particles of various metals, but have low productivity and high cost.

USS issued on July 16, 1970
R Inventor Certificate No. 267079 and JP-A-8-30
In the method disclosed in Japanese Patent No. 2405, in order to produce Ag ultrafine particles with high productivity, an Ag-Al alloy ingot containing 40% by weight of Ag is melted, and this alloy ingot is 1.5 to 2 mm in size. Rolled into a strip foil having a thickness of
This temperature is maintained for 2 hours to form a homogeneous supersaturated solid solution of Ag in Al, then quenched in water to fix the structure, and then to remove the KOH from the strip to perform chemical surface cleaning of the strip foil. Soak in 15% aqueous solution, then water, then H
It is immersed in a 30% aqueous solution of NO ₃ , immersed again in water, and then immersed in a 25% aqueous solution of KOH at 30 ° C. for 12 hours in order to extract Al. Transfer to a new tank, pour a new 35% aqueous solution of KOH, perform thorough stirring for 15 minutes, further apply ultrasonic vibration of 40 KHz frequency to the tank for 25 minutes, separate the resulting powder from the alkaline aqueous solution, and wash ,dry. It is described that ultrafine Ag particles having an average particle size of about 85 nm can be produced by this method.

The metallurgical significance of this known technique is
One is that the Ag solute is made into a "solid solution" alloy in the Al matrix in order to obtain high purity ultrafine particles, and the other one is to increase Ag yield in pursuit of high productivity. In this case, a solution heat treatment is performed to form a solid solution in which Ag is “supersaturated” in Al. This "supersaturated solid solution" is described in the specification as being useful for producing high-purity ultrafine particles. The metallurgy of this usefulness
Considering the chemical meaning, the Al matrix in the alloy forming the supersaturated solid solution retains the property of pure Al, which is soluble in an aqueous alkaline solution, and its A
l Solute Ag atoms present without regularity in the crystal
It is interpreted that when Al is extracted, it is liberated as Ag atoms, which are aggregated to form ultrafine particles.
By the way, regarding the corrosion of the alloy, the corrosion (melting) of the alloy is generally affected by the constituent elements of the alloy, as in the case of a corrosion suppressing means, for example, by adding an element for increasing the potential of the anode. Therefore, the above-described interpretation is based on the idea of exclusively extracting Al and releasing Ag from the aspect of the metal structure, and it is possible to explain the phenomenon occurring in the Al-Ag alloy by such an idea. However, since the above publication does not specifically show other alloys, it cannot be immediately determined that this interpretation can be extended to alloys other than Al-Ag.

According to the Ag-Al equilibrium diagram, this "supersaturated solid solution" is, for example, an Ag-Al containing 40% by weight of Ag.
A mixed phase of Al phase and Ag ₂ Al phase the Al liquid alloy matches the equilibrium diagram and slow cooling solidification at a cooling rate 5 × 10 ⁰ ℃ / s. When this mixed phase alloy is treated with an alkaline aqueous solution, only Al is extracted, and Al in the Ag ₂ Al intermetallic compound is not extracted. That is, after extraction, Ag ₂ A
(1) The intermetallic compound remains in the shape and size of the crystal formed during solidification, and high-purity Ag ultrafine particles cannot be obtained. Therefore, in order to avoid the formation of Ag ₂ Al, if the aim is to reduce the amount of Ag to form a solid solution of Ag in Al, an example in which a solute Ag atom that is not supersaturated and solid-solved is separated is disclosed in the aforementioned publication. It is not known whether it is possible to extract Al because it is not available. However, even if it is possible, the amount of Al that forms a solid solution with Ag in an equilibrium state at room temperature is a very small amount of 1% by weight or less. Absent.

In order to dissolve a large amount of Ag in Al, a solution heat treatment method is adopted in the above-mentioned conventional technology. That is, in the Ag-Al alloy, when the temperature of the alloy is increased, the solid solubility limit of Ag in an equilibrium state is increased, and
In this case, the amount of solid solution increases to 55% by weight of Ag. Therefore, if the state in which a large amount of solid solution is dissolved at a high temperature is quenched in water to fix the structure, an Ag-Al alloy in which a large amount of Ag is supersaturated is obtained.

[0007]

However, Japanese Patent Application Laid-Open No. Hei 8-3
The method of 02405 has three disadvantages. The first disadvantage is the type of metal that can be applied. This method is Al-A
It is unknown which combination of metals other than g can be applied. Assuming that the interpretation described in paragraph 0004 can be extended, the metals that can be extracted with an aqueous alkali solution are Al, S
In a combination of three types of i and Zn, in which the target ultrafine particles are a metal that does not dissolve in an aqueous alkaline solution, a practical value of 1% by weight or more is obtained at the same time as supersaturated solid solution by solution heat treatment. According to the known phase diagram, the combination expanded to a certain amount is an Ag-Al alloy and C
There are only two types of u-Al alloys. That is, high-purity ultrafine particles other than Ag and Cu cannot be produced. The second disadvantage is that the production of a supersaturated solid solution by heat treatment requires many steps, including casting, rolling, solution treatment, and water cooling, resulting in high costs. The third disadvantage is that, as means for purifying the ultrafine particles, the aggregate is carefully stirred in an alkaline aqueous solution to promote the extraction of Al, and ultrasonic vibration is applied. When this is carried out, the aggregation collapses and a part thereof becomes ultrafine particles, which are dispersed in the alkaline aqueous solution. The dispersed state is disadvantageous in that sedimentation and filtration for separating the alkaline aqueous solution and the ultrafine particles in the subsequent washing step become industrially very difficult.

[0008]

SUMMARY OF THE INVENTION The present invention provides means for solving the above three disadvantages. That is, an object of the present invention is to provide a method capable of producing ultrafine particle aggregates and dispersions of metals of Groups 1B and 8A of the periodic table and alloys thereof.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention is directed to a method of extracting a second metal from a supersaturated solid solution of a first metal as a solute in a matrix of a second metal to form ultrafine particles of the first metal. Generating ultrafine particles aggregated in a skeleton form, and washing the ultrafine particles aggregate, wherein the method of producing ultrafine particles of the first metal comprises Cu, A
u, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir
And a liquid alloy consisting of at least one first metal selected from the group consisting of Pt and Pt, and a second metal consisting of Al, which is rapidly solidified to form an alloy in which the first metal is supersaturated and dissolved in the second metal. The method is characterized in that an aqueous solution of an alkali metal hydroxide is allowed to act on the solid solution to extract the second metal. In a second embodiment according to the present invention, an ultra-fine particle in which the first metal is extracted as a solute from a supersaturated solid solution in a matrix of the second metal and the ultrafine particles of the first metal are aggregated in a skeleton form is extracted. A method for producing ultrafine particles of a first metal, comprising the steps of: producing a fine particle aggregate and washing the ultrafine particle aggregate, wherein a first metal comprising Ag-Pd or Ag-Cu and a second metal comprising Al A liquid alloy comprising a metal is rapidly solidified to form an alloy in which a first metal is supersaturated in a second metal, and an aqueous solution of an alkali metal hydroxide is applied to the supersaturated solid solution to extract a second metal. And An important advantage of the present invention is that a super-saturated solid solution is obtained in a cast state by applying a rapid solidification technique as a new technique without performing a solution heat treatment which is a known technique. With this new technology, ultrafine particles can be produced even with metals other than Ag.

The fact that a supersaturated solid solution can be obtained by rapid solidification even in an alloy system in which a solid solution cannot be obtained in an equilibrium state is described in, for example, Midson, S., 1981;
P, & Jones, H .; Is Proc. 4th, Int.
Conf. on Rapidly Quenched
At METALS, "ON THE ABSOLUTE STABILI" was compiled and presented a large number of paper data.
TY CRITERION IN RELATION
TO PREDICTING EXTENSION O
F SOLID SOLUBILITY ”. According to this document, 2 of the periodic table that forms a supersaturated solid solution in Al
A, 3A, 4A, 5A, 6A, 7A, 8A, 1B, 3
The 25 types of elements belonging to groups B and 4B and their supersaturated solid solution amounts are shown. In this specification, arithmetic notation is used for notation of a group in the periodic table, not Roman numeral.

Here, the terms used in the present invention will be explained. The "first metal" is a metal or an alloy which does not dissolve in an alkaline solution.
u, Fe, Co, Ni, Ru, Rh, P
It is used as a metal of d, Os, Ir, Pt or an alloy of two or more of these. The second metal is a metal or an alloy which forms a crystal as a matrix and is dissolved in an aqueous alkaline solution, and Al is used.

The amount of solid solution of an alloy system which satisfies the requirements of the first metal and the second metal and forms a supersaturated solid solution by rapid solidification is as follows:
For example, when the first metal is Cu and the second metal is Al, Cu
Can be supersaturated with Al in the range of 34% by weight or less. Similarly, when the second metal is Al, the first metal is Ag
= 72% by weight or less, Au = 2.5% by weight or less, Fe = 1
Supersaturated solid solution in the range of 1% by weight or less, Co = 10% by weight or less, Ni = 15% by weight or less, Ru = 10% by weight or less, Pd = 0.4% by weight or less, and Pt = 15% by weight or less. it can.

In the second embodiment of the present invention, the desired ultrafine Ag—Pd alloy is Ag: Pd: A
l = 18: 2: 80% by weight can be supersaturated solid solution. That is, the alloy of Ag: Pd = 9: 1 has a maximum A of 20% by weight.
1 to form a supersaturated solid solution. Similarly, Ag-Cu
Ag: Cu: Al = 20: 20: 60% by weight of the alloy can be supersaturated solid solution.

When the cooling rate of rapid solidification decreases, the proportion of the first metal which forms a supersaturated solid solution decreases. For example, when the cooling rate is 1 × 10 ² ° C./s or less and the second metal is Al, the amount of each of the various first metals to form a solid solution does not exceed 1% by weight, and is of no practical value. At a cooling rate or an equilibrium state lower than the preferable lower limit of the cooling rate, there is no first metal that forms a solid solution in which Al, Si, and Zn as the second metals are 1% by weight or more at room temperature. In the range where a supersaturated solid solution is formed, the higher the cooling rate, the higher the solid solubility limit, and there is no upper limit for the cooling rate.

An industrial process for rapidly solidifying a liquid alloy is possible in a number of ways. For example, the alloy droplet is dropped into water at 20 ° C. by a water dropping method and rapidly solidified to a diameter of about 3 m.
m, the cooling rate is estimated to be about 3 × 10 ² ° C./s, and the cooling rate is about 7 × for spherical particles with a diameter of 50 μm when argon is used as the atmospheric gas by the centrifugal spray method. It is estimated to be 10 ² ° C / s, and the peripheral speed is 6 by the single roll method.
The cooling rate is said to be about 1 × 10 ⁶ ° C./s for a 20 μm thick and 6 mm wide ribbon made by continuously supplying a liquid alloy to the outer periphery of a water-cooled copper roll rotating at 5 m / s and rapidly solidifying. ing. In the present invention, the method of rapid solidification and the shape of the rapidly solidified alloy are not limited. The cooling rate changes depending on the shape and size of the rapidly solidified alloy.

[0016] 1 × 10 ⁰ ℃ / s measurement of a cooling rate of about described herein are possible in methods using a thermocouple, a cooling rate of moderate about 1 × 10 ² ℃ / s Is estimated by using an Al-4.5 wt% Cu alloy described in "Dendrite arm spacing and cooling rate measurement method for aluminum" issued by the Japan Institute of Light Metals, and a relational expression d = 50.
× C ^-0.41 enables estimation with high accuracy. here,
d is the interval between the secondary arms and is measured by a microscope in units of μm. C is the cooling rate and the unit is ° C / s. 1
Fast cooling rates, on the order of × 10 ⁶ ° C./s, lack accuracy of estimation with current technology. However, the cooling rate defined by the present invention is a value of about 1 × 10 ² ° C./s, and there is no problem because the estimation accuracy is high. As described above, to produce a supersaturated solid solution, the present invention can be performed at a low cost in one step.

In order to extract the second metal from the supersaturated solid solution, an aqueous solution of an alkali metal hydroxide is applied. Alkali metal hydroxides are, for example, lithium hydroxide, sodium hydroxide, potassium hydroxide, alone or as a mixture, particularly preferably sodium hydroxide alone,
Alternatively, potassium hydroxide is used. The extraction operation can be repeated with a new alkaline aqueous solution. In order to increase the amount of extraction, it is preferable that the extraction is repeated two to three times with a new alkaline aqueous solution. The extraction temperature can be arbitrarily selected according to the size of the target ultrafine particles and the strength of aggregation. When relatively small ultrafine particles are used for weak cohesion, the extraction temperature is lowered. For example, extraction is performed at a temperature of 10 ° C. Conversely, when relatively large ultrafine particles are intended for strong cohesion, the extraction temperature is increased. For example, temperature 6
Extract at 0 ° C. Since the extraction reaction is an exothermic reaction, it is necessary to provide a cooling vessel jacket or the like in the reaction vessel when extracting at a low temperature. In order to avoid sudden heat generation, do not add a large amount of supersaturated solid solution to the alkaline aqueous solution.Do not add a small amount at a time, or add the entire amount to water, and then gradually add the alkaline aqueous solution to a predetermined concentration. Is preferred. The concentration of the aqueous alkali solution is 1 to 50
% Can be arbitrarily selected, but considering the heat generated by the above-mentioned extraction reaction, the concentration is preferably low, especially in the case of extraction at a low temperature, and is 3% in Examples described later. The amount of the alkali metal hydroxide used for the extraction must be at least 1 times in molar ratio to the amount of the second metal in the supersaturated solid solution,
Desirably, it is 1.5 times or more.
More than double.

In the alkaline aqueous solution after extraction, for example, when aluminum is used as the second metal and sodium hydroxide is used as the extractant, sodium aluminate is dissolved. In this liquid, an aggregate of the desired ultrafine particles is settled. In order to produce ultrafine particles, it is necessary to separate the ultrafine particles from the alkaline solution. Since the ultrafine particles are aggregates having an average particle size of 10 μm, the separation can be easily performed by general industrial means such as filtration.

The operation of washing a small amount of the alkaline solution attached to the separated ultrafine particle aggregate can be easily performed by general industrial means. For example, in filtration, a method of adding an excessive washing liquid to the ultrafine particle aggregate remaining on the filter paper or the like can be performed, or the ultrafine particle aggregate is placed in a container containing a new cleaning liquid, and filtered after stirring. May be repeated. When the application in which the ultrafine particles are used is preferably in a state of being wetted with water, for example, as in the case of a certain Ni catalyst for a chemical reaction, the ultrafine particles may be stored and supplied in fresh water.

On the other hand, when the dried state is preferable,
In the case of ultrafine particles of an element such as u, Ag-Pd, and Pt, which hardly form an oxide, drying can be performed by general industrial means. For example, the ultrafine particle aggregate containing the cleaning liquid can be transferred to a container of a rotary evaporator, heated, dried under reduced pressure, and taken out into the air. Alternatively, drying may be performed in a stream of dry air. F
In the case of ultrafine particles of an element which easily forms an oxide, such as e, Co, and Ni, the particles are dried in an inert gas stream and stored in an inert gas. The ultrafine particles in this form are used as a catalyst for non-aqueous chemical reaction. Further, a stabilization treatment for oxidizing ultrafine particles in an inert gas to which a trace amount of O ₂ has been added can be performed to enable handling in general use.

According to a third embodiment of the present invention, there is provided a method of dispersing ultra-fine particle aggregates of the cleaning liquid obtained in the first or second embodiment into individual ultra-fine particles. The method of dispersing the aggregates of ultrafine particles can be performed by applying ultrasonic vibration to the aggregates in the liquid or by applying strong stirring. It can be implemented by adding. As the ultrasonic vibration device, a general industrial device can be used.
The frequency of the ultrasonic vibration can be applied in a wide range, but is 28 kHz in the embodiment described later. It is desirable that the output density of the ultrasonic vibration generating surface is large, and in the embodiment described later, 5 W
/ Cm ² . The time for applying the ultrasonic wave is desirably 10 minutes or more, and is 5 hours in the embodiment. The ultrasonic vibrator can be inserted into the liquid containing the aggregate, or the ultrasonic vibrator may be attached to the bottom or the side of the container. Furthermore, a liquid containing an aggregate can be put in the second container, and this can be installed in a container equipped with an ultrasonic vibrator via an intermediate liquid.

The dispersion by vigorous stirring can be carried out by a mechanical method. Water, alcohols, ketones, hydrocarbons, and the like can be used as the dispersion medium used for ultrasonic vibration or strong stirring. In the case of water, 0.01% by weight to 1% by weight of sodium hexametaphosphate or a surfactant which is a main component of a household detergent can be added as a dispersant.

[0023]

EXAMPLE 1 In a graphite crucible of an electric furnace, 20 g of Ni (purity 99.99) was prepared.
%) And 180 g of Al (99.99% purity)
200g Ni-Al liquid alloy (10% by weight N
i) is melted and cooled in a graphite crucible at 780 ° C.
Liquid alloy. An Ar gas pressure was applied to the surface of the liquid alloy, and the liquid alloy was continuously discharged into an Ar gas atmosphere from a nozzle diameter of 0.5 mm. The continuously flowing liquid alloy is 500 m in diameter, which is provided directly below the nozzle and rotates at 2500 rpm.
m, and rapidly solidified on the outer peripheral surface of one water-cooled copper roll having a width of 30 mm to produce a thin strip having a thickness of 20 μm and a width of 6 mm.
The above operation was repeated to produce a ribbon of 1 kg in total.
In the same manner as the production of this ribbon, the Cu-Al
A ribbon was made from a liquid alloy (4.5% by weight Cu). As a result of examining the metal structure with a microscope, the interval between the secondary dendrite arms was observed to be smaller than 1 μm. Therefore, from the relational expression d = 50 × C ^−0.41 , the cooling rate was 1.4 × 10 ^4.
It was estimated to be faster than C / small.

As a result of examining the crystal phase of the Ni—Al alloy ribbon with an X-ray diffractometer, there was no peak corresponding to NiAl ₃ but only a diffraction peak corresponding to Al. The ribbon was cut into a length of 10 mm to obtain a thin section. In the first extraction, 1 kg of a slice was used, poured into 7 liter of a 30% aqueous solution of NaOH, and extracted at 60 ° C. for 3 hours with stirring.
After the first extraction, the first extraction liquid is removed by filtration,
The filtration residue was poured into 1 liter of a fresh 30% aqueous solution of NaOH, and the second extraction was performed at 60 ° C. for 3 hours with stirring. After the second extraction, 0.1 kg of the remaining Ni aggregates were repeatedly subjected to filtration and stirring and washing in water to remove NaOH, and the obtained Ni aggregates were stored in water. The shape of the Ni agglomerate wet with water is the original shape of 20 μm × 6 m
It was a powder without leaving a shape of mx 10 mm. A very small amount of the powder wet with water was taken on a sample stage, dried in vacuum, and observed with a high-resolution scanning electron microscope.
An aggregate in which 00 nm primary particles aggregated was detected. The shape of the agglomerate was irregular, with the face of the original flake partially remaining. As a result of examination by X-ray diffraction, it was a very broad peak corresponding to Ni. In the chemical analysis of the Ni aggregate, the Al content was 0.23%.

Example 2 200 g of Pt-Al liquid alloy (Pt: Al = 10: 90)
% By weight) and cooled to 700 ° C.
Similarly to the above, a thin strip having a thickness of 20 μm and a width of 6 mm was produced by a single roll method. This operation was repeated to produce a ribbon of a total of 1 kg, which was cut into a 10 mm slice. As a result of examining the crystal phase of the produced Pt-Al alloy flake using an X-ray diffractometer, only a peak corresponding to A1 was detected. Using 1 kg of this slice, extraction and washing were performed in the same manner as in Example 1, and 100 g of the obtained Pt aggregate was stored in water.
As a result of processing in the same manner as in Example 1 and observation with an electron microscope,
Aggregates in which primary particles of about 50 nm aggregated were detected.

Example 3 200 g of a Cu-Al liquid alloy (Cu: Al = 20: 80)
% By weight) and cooled to 650 ° C.
Similarly to the above, a thin strip having a thickness of 20 μm and a width of 6 mm was produced by a single roll method. This operation was repeated to produce a ribbon of a total of 1 kg, which was cut into a 10 mm slice. As a result of examining the crystal phase of the produced Cu-Al alloy flake using an X-ray diffractometer, only a peak corresponding to A1 was detected. Using 1 kg of the slice, extraction and washing were performed in the same manner as in Example 1, and 200 g of the obtained Cu aggregate was stored in water.
As a result of treatment in the same manner as in Example 1 and observation with an electron microscope, an aggregate in which primary particles of about 70 nm were aggregated was detected.

Example 4 200 g of Ag-Pd-Al liquid alloy (Ag: Pd: Al
= 18: 2: 80% by weight), and then cooled to 750 ° C.
m, a ribbon having a width of 6 mm was produced. By repeating this operation, a ribbon of a total of 1 kg is produced, cut and cut to a length of 10 m.
m. As a result of examining the crystal phase of the produced Ag-Pd-Al alloy flake using an X-ray diffractometer, only a peak corresponding to Al was detected. 130 L of a 3% aqueous solution of KOH is placed in a container having a cooling jacket, and the KOH
1 kg of Ag-Pd-Al alloy flakes were gradually added to the aqueous solution with stirring, and the first extraction was performed for 20 hours while controlling the temperature of the KOH aqueous solution at 10 ° C. ± 3 ° C. The second extraction uses 5 liters of a fresh 10% aqueous KOH solution and
This was performed for 3 hours while controlling the temperature to 0 ° C. ± 3 ° C. After the second extraction, the same washing as in Example 1 was performed, and the Ag-Pd aggregate was stored in water. Next, 28KH with temperature control function
The Ag-Pd aggregate was transferred to a z, 5 W / cm ² ultrasonic vibration container, and the aggregated particles were dispersed for 5 hours while controlling the temperature at 10 ° C. ± 3 ° C., followed by drying in air. Observation of the obtained ultrafine particle powder with a high-resolution scanning electron microscope revealed that Ag
-The size of the Pd particles was about 30 nm. The particle shape was rounded and irregular. Chemical analysis revealed that the Al content of the Ag-Pd aggregate was 0.25%.

Example 5 An Ag-Pd-Al alloy (Ag: Pd: Al =) in which the compounding ratio (20% by weight) of Ag-Pd was smaller than in Example 4.
7.2: 0.8: 92% by weight), and then cooled to 750 ° C.
m, a 2.5 m high disc filled with Ar gas and poured into a tundish provided at the center of the upper part, and a disk rotating at 60000 rpm at a position 10 mm downward from a 1.2 mm diameter nozzle below the tundish Was discharged toward the center of the sample, sprayed using the centrifugal force of the disk, and rapidly solidified to prepare an Ag-Pd-Al alloy powder. The disc has a diameter of 40 mm and is 60
It is made of boron nitride having a funnel-shaped top surface shape whose inner angle formed by rotating an inclined straight line is opened upward by 120 degrees. The average diameter of the obtained powder was 50 μm, and the shape was spherical. In this case, the cooling rate was estimated by observing a 50 μm diameter particle of an Al-4.5 wt% Cu alloy produced under the same conditions with a microscope, and using the relational expression d = 50 × C ^−0.41 from the interval between the secondary dendrite arms. As a result, 7 × 10
² ° C./s, and the cooling rate was lower than that of Example 4. As a result of examining the crystal phase of the produced Ag-Pd-Al alloy powder with an X-ray diffractometer, there was no diffraction peak of Ag ₂ Al,
There was only a diffraction peak corresponding to. Extraction of Al and dispersion by ultrasonic vibration were performed in the same manner as in Example 4 and dried to obtain a powder. Observation of the obtained powder with a high-resolution scanning electron microscope revealed that the size of the Ag-Pd particles was about 25 nm.
Met.

Comparative Example 1 An Ni-Al liquid alloy having the same composition as
mm and a length of 200 mm in a ceramic mold.
The cooling rate at this time, a result of the thermocouple was measured by attaching the inner space of the mold was about 2 × 10 ⁰ ℃ / s. The round bar was cut with a lathe, and a minute chip was used as a sample to examine by X-ray diffraction. As a result, peaks corresponding to NiAl ₃ and Al were obtained. As a result of the structure observation, dendrites of NiAl ₃ were recognized. Extracting the chips in the same manner as in Example 1, washed, results the residue was examined by X-ray diffraction, only peaks very broad corresponding to Ni, NiAl ₃ and Al
Could not be confirmed. Chemical analysis revealed that the Al content was 2.9% and the purity was poor. As a result of observation with a scanning electron microscope, a large number of particles that retain the shape of the original chip were observed. The interior of the particles was composed of a complex shape of the same shape as the NiAl ₃ dendrite before extraction, and a space was formed between the shapes, and the whole was porous. There were no fine particles of 1 μm or less.

[0030]

As described above, according to the present invention, aggregates and dispersions of high-purity ultrafine particles of metals and alloys belonging to groups 8A and 1B of the periodic table, which can be applied to various applications, are provided.
It can be provided at low cost.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K001 AA41 DB17 4K017 AA04 BA02 BA03 BA05 BA06 BB02 BB05 CA08 EB01 EC02 ED01 EK08 FA21

Claims (3)

[Claims] 1. An ultra-fine particle aggregate in which ultra-fine particles of a first metal are aggregated in a skeleton form by extracting a second metal from an alloy in which a first metal as a solute is a supersaturated solid solution in a matrix of a second metal. Then, the method for producing ultrafine particles of the first metal, which includes the step of washing the ultrafine particle aggregates, comprises: Cu, Au, Fe, Co, Ni, Ru, Rh, P
A liquid alloy consisting of at least one first metal selected from the group consisting of d, Os, Ir and Pt and a second metal consisting of Al was rapidly solidified and the first metal became a supersaturated solid solution in the second metal. A method for producing ultrafine metal particles, wherein an alloy is used, and an aqueous solution of a hydroxide of an alkali metal is allowed to act on the supersaturated solid solution alloy to extract a second metal. 2. An ultrafine particle aggregate in which ultrafine particles of the first metal are aggregated in a skeleton form by extracting a second metal from an alloy in which the first metal is a solute in a supersaturated solid solution in a matrix of the second metal. And a method of producing ultrafine particles of a first metal, which comprises a step of washing the aggregate of ultrafine particles, wherein the first metal comprising Ag—Pd or Ag—Cu;
1 is rapidly solidified to form an alloy in which the first metal is supersaturated in the second metal, and an aqueous solution of an alkali metal hydroxide is acted on the supersaturated solid solution alloy to form the second metal. A method for producing ultrafine metal particles, characterized by extracting water. 3. The cooling rate of the liquid alloy is 100 ° C./s.
The method for producing ultrafine metal particles according to claim 1 or 2, which is the above.