JPS60204810A - Method and device for producing ultrafine metallic particle - Google Patents

Abstract

PURPOSE:To produce ultrafine metallic particles having high quality at a high yield by introducing a small amt. of carbon dioxide into a vacuum chamber, forming a dry ice film on a capturing plate and sticking the ultrafine metallic particles generated from a heating furnace thereon. CONSTITUTION:The inside of a chamber 1 connected to a vacuum pump 6 is evacuated to a vacuum and a metal is melted to evaporate with a heating furnace 2 is said chamber to generate ultrafine metallic particles. On the other hand, a small amt. of carbon dioxide is introduced through a carbon dioxide introducing pipe 5 into the chamber and a capturing plate 3 disposed to face the furnace 2 is cooled by a refrigerant in a refrigerant conduit pipe 4 to form a dry ice film 7 thereon. The above-mentioned ultrafine metallic particles are stuck to and captured by said film 7 and thereafter the dry ice is sublimated to obtain the ultrafine metallic particles. The ultrafine metallic particles are stuck in laminated layers via the dry ice film by repeating plural times the formation of the film 7 and sticking of the ultrafine metallic particles by the above-mentioned method, by which the ultrafine metallic particles are recovered with the higher efficiency.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a method for producing ultrafine metal particles with a particle size of several microns or less for use as high-density magnetic recording materials, conductive paints, sintering promotion materials, catalysts, etc. The present invention relates to a method and apparatus for manufacturing at a high rate and with high quality.

(Prior art) A general method for producing the above-mentioned ultrafine metal particles is the in-gas evaporation method, in which an inert or reducing atmosphere gas such as argon, hydrogen, helium, etc. After being introduced at a pressure of 250 Torr, a metal such as iron is melted and evaporated in a heating furnace installed at the bottom of the chamber to eject ultrafine metal particles, which are cooled and decelerated by colliding with the atmospheric gas. The ultrafine metal particles are deposited on a collection plate provided above the heating furnace, and then collected by scraping the adhered ultrafine metal particles with a brush or the like.In this case, the particle size of the ultrafine metal particles is determined by the atmospheric gas It is controlled by the concentration.In other words, when the atmospheric gas concentration is low and the chamber is in a high vacuum, the ultrafine metal particles that fly out of the metal collide with each other while still in a high temperature state, and the particle size increases before colliding with the atmospheric gas. On the other hand, when the atmospheric gas concentration is high and the chamber is under low vacuum, the particles quickly collide with the atmospheric gas and adhere to the collection plate, resulting in a small particle size. Although ultrafine metal particles of various particle sizes can be produced using conventional manufacturing methods such as the evaporation method in gas, they have the following drawbacks and inconveniences.

[Problem that the invention seeks to solve]

That is, (1) The collision rate between the generated ultrafine metal particles and the atmospheric gas is low, and most of them do not collide with the atmospheric gas and reach the collection plate at high temperature and are deposited on the collection plate. The proportion (yield) of ultrafine metal particles from the raw metal is extremely low, at most 10%, even when the atmospheric gas concentration is high.
Therefore, in order to obtain the desired amount of ultrafine metal particles,
＋2
) If the atmospheric gas concentration in the chamber is increased to obtain small-diameter ultrafine metal particles, the evaporation rate of the metal will be significantly suppressed and the production speed will be reduced. If the concentration of the atmospheric gas is lowered, the drawbacks of (1) above will be further exacerbated and the yield will be reduced; and (4) ultrafine metal particles will be contaminated by containing atoms of the atmospheric gas in the process of colliding with the atmospheric gas. (5) Recovery of ultrafine metal particles is difficult due to the mechanical structure of scraping them off with a brush, etc., and complete recovery is difficult.

(Means for Solving the Problems) The present invention solves all of the drawbacks (1) to (5) of the in-gas evaporation method, improves the yield, and produces high-quality ultrafine metal particles. and its design.

The first aspect of the present invention is to form a dry ice coating on a collection plate above a heating furnace, evaporate metal in a vacuum, condense and adhere ultrafine metal particles to the coating, and then sublimate the dry ice coating. The second invention is a method for obtaining ultrafine metal particles by repeatedly forming a dry ice film on the ultrafine metal particles already attached during the method of the first invention to adhere the ultrafine metal particles. This is a method in which ultrafine metal particles are sequentially layered in a sandwich-like manner with a dry ice coating, and finally the dry ice coating is sublimated to obtain ultrafine metal particles.
The invention is an invention of an apparatus for carrying out the methods of the first and second inventions, in which a heating furnace is disposed below in a closed chamber communicating with a vacuum exhaust system, and a heating furnace is disposed above. A collection plate having a flat surface facing the heating furnace and provided with a cooling means, and a carbon dioxide gas introduction pipe for supplying and blowing carbon dioxide gas to the lower surface of the collection plate. It is characterized by:

(Example) The present invention will be described in detail below using FIGS. 1 to 4.

FIG. 1 is a sectional view showing an example of an ultrafine metal particle manufacturing apparatus that implements the manufacturing method of the present invention, FIG. 2 is a perspective view illustrating a collection plate and a carbon dioxide gas introduction pipe, and FIGS. 3 and 4 are 1st each. This is an explanatory diagram of the second method of the invention, and both diagrams show an enlarged view of the area around the dry ice coating.

In FIG. 1, a heating furnace 2 having an appropriate heating means such as resistance heating, induction heating, or an electron beam is located at the bottom of a chamber 1 formed airtight, and above the heating furnace 2 is a flat surface facing the heating furnace 2. A collection plate 3 is provided. In addition,
Although the collection plate 3 is shown in a disk shape in FIG. 2, it may have any shape. Then, a refrigerant conduction pipe 4 is installed in close contact with the upper surface of the collection plate 3.
Similarly, a ring-shaped carbon dioxide gas introducing pipe 5 is disposed close to the lower surface, and a large number of nozzles 51 are opened in the ring-shaped portion toward the lower surface of the collection plate 3.

Furthermore, the vacuum pump 6 is connected to the valve 61 . It is connected to the chamber 1 via an exhaust pipe 62.

To explain the first method of the invention using the above-mentioned apparatus, first, the vacuum pump 6 is operated, and the inside of the chamber 1 is brought to a high vacuum of about 10 to 1 O-6 Torr while removing moisture, dust, etc. Next, liquid nitrogen (boiling point -1
A low-temperature refrigerant such as 96° C.) is conducted to cool the lower surface of the collection plate 3, and a small amount of carbon dioxide is ejected to the bottom of the collection plate 3 through the nozzle 51 of the carbon dioxide gas introduction pipe 5 to trap it. to form a dry ice coating 117. Next, when the metal in the heating furnace 2 is melted and evaporated to eject ultrafine metal particles, the ultrafine metal particles collide with the dry ice coating 7 and are cooled, and the ultrafine metal particles 8 are absorbed into the coating 7 as shown in FIG. Condenses and adheres to surfaces. After a suitable amount of ultrafine metal particles 8 are deposited on the dry ice coating 7 in this manner, the evaporation of the raw metal is stopped, and the vacuum pump 6 is also stopped. Next, a saucer (not shown) is appropriately arranged below the collection plate 3, and heated gas is passed through the refrigerant polishing tube 4 instead of the refrigerant to sublimate the dry ice coating 87, and the dry ice coating 87 is sublimated. The ultrafine metal particles 8 fall and are collected in the tray.

In the above method, the particle size of the ultrafine metal particles 8 can be set to v4ftJ depending on the distance between the collection plate 3 and the heating furnace 2.

That is, when the distance between the heating furnace 2 and the collection plate 3 is long, the chance of collision between high-temperature ultrafine metal particles increases, and ultrafine metal particles with a large diameter can be obtained, and conversely, the shorter the distance, the smaller the particle size. The gas introduced into the chamber 1 is preferably a sublimation gas that solidifies at low temperatures and evaporates directly without liquefaction as the temperature rises; any gas having such properties may be used. Although gases can be used, carbon dioxide gas is generally preferred. In addition, since ultrafine metal particles adhering to the portion where the dry ice coating M7 is not formed cannot be recovered later, the carbon dioxide gas introduction pipe 5 is arranged such that the dry ice coating 17 is uniformly and quickly formed on the entire lower surface of the collection plate 3. It is preferable that the nozzle 51 of the introduction pipe 5 is placed close to the bottom surface of the collection plate 3 and the opening position of the nozzle 51 of the introduction pipe 5 is directed toward the bottom surface of the collection plate 3 so that carbon dioxide gas can be directly blown onto the entire bottom surface of the collection plate 3. Furthermore, if the carbon dioxide gas introduction tube 5 is configured to be movable, the entire lower surface of the collection plate 3 can be used for the attachment of ultrafine metal particles, which is more effective.

Furthermore, the amount of carbon dioxide gas to be introduced into the chamber 1 may be determined by considering the temperature and area of the lower surface of the collection plate 3, the vapor pressure of dry ice, the thickness of the dry ice coating 1117, etc. Regarding the thickness, based on my experience, it is 0.1
It is preferable that 1- to 100n.

Example 1 In an ultrafine metal particle manufacturing apparatus configured as shown in FIG.
After evacuating the chamber 1 with contents ff140Q to 10 Torr, a dry ice film 7 was formed on the collection plate 3, and then 4 g of iron was heated to about 2000°C in a heating furnace 2 using a molybdenum heater to remove the entire amount. It melted and evaporated.

Next, the dry ice was sublimed to obtain 1.5 g of ultrafine metal particles. From the above, the yield was 37%, and the produced ultrafine metal particles were of high quality.

Next, the second invention method will be explained with reference to FIG.

In this method, even after the metal has been evaporated and collected in the first invention method described above, the collection plate 3 is continued to be cooled and a second carbon dioxide gas is introduced, and the dry ice coating 7 has already been covered in the previous step. A new dry ice film 7A is formed on the metal ultrafine particles 8 adhering to the metal, the introduction of carbon dioxide gas is stopped, the second metal is melted and evaporated, and the metal ultrafine particles 8A are adhered thereon. . By repeating this process, the ultrafine metal particles are successively wrapped in multiple layers of dry ice in a sandwich-like manner to collect the ultrafine metal particles.

Finally, all of the dry ice coating is sublimated to collect ultrafine metal particles. In this way, the ultrafine metal particles that adhere one after another can be collected without adhering to each other, so it is possible to produce ultrafine metal particles in stripes using a collection plate of a constant area. J3. In the above explanation, it is preferable that the amount of carbon dioxide gas introduced each time is small because it can be introduced many times, but if it is too small, there will be parts where the dry eye film is not formed or the dry eye film is too thin, and in those parts, the ultrafine metal particles It goes without saying that the thickness of the dry ice coating must be taken into consideration, as in the first method of the invention, since this may cause problems such as adhesion of the dry ice to each other.

〔Effect of the invention〕

As described above, according to the first invention, (a) ultrafine metal particles generated by metal evaporation are cooled by a low-temperature dry ice coating and condense and adhere to the coating, and are not vapor-deposited as in the conventional method; is collected, resulting in a high yield. Therefore, the amount of raw material metal required for producing ultrafine metal particles is small, and the heating cost is low, making it economical.

(b) Also, since the metal is evaporated in a vacuum, the evaporation rate is fast and the production speed is also improved.

(c) Since the generated ultrafine metal particles have very few collisions with gas before reaching the collection plate, the ultrafine metal particles almost never contain gas atoms, and are therefore free of contamination and of high quality. You can get something.

(iv) Furthermore, the recovery of the ultrafine metal particles is simple and complete, as it is sufficient to simply heat the dry ice coating and sublimate it.

(e) Moreover, since the dry ice coating 7 is formed in a somewhat uneven shape, a larger number of ultrafine metal particles can be attached than on a mere flat surface.

In addition, according to the second invention, not only the effects of the first invention method are improved, but also the ultrafine metal particles are laminated in many layers with a dry ice coating, so that a fixed area can be captured. The efficiency of using the collecting board is increased and it is practical.

Furthermore, according to the third aspect of the invention, ultrafine metal particles can be easily produced by having the configuration as described above.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment of an ultrafine metal particle device embodying the present invention, and FIG. 2 is a perspective view of a portion of the configuration of FIG. 1. FIGS. 3 and 4 are explanatory views of the first and second methods of the invention, respectively, and both show the area around the dry ice coating 7 on an enlarged scale. 1 is a chamber, 2 is a heating furnace, 3 is a collection plate, 4 is a refrigerant conduit, 5 is a carbon dioxide gas introduction pipe, 6 is a vacuum pump, 61 is a valve, 62 is an exhaust pipe, 7 and 7A are dry Ice coating, 8,
8A is ultrafine metal particles. Figure 1 #b2 Figure

Claims (1)

[Claims] 1. A method for producing ultrafine metal particles, in which ultrafine metal particles produced by melting and evaporating metal in a heating furnace in a chamber are temporarily collected and recovered by a collection device provided above the heating furnace, After evacuating the inside of the chamber, a small amount of carbon dioxide gas is introduced and the collection plate is cooled to form a dry ice film on the collection plate, and then the metal is evaporated and a metal superoxide is added to the dry ice film. A method for producing ultrafine metal particles, which comprises adhering the fine particles and then sublimating dry ice to obtain ultrafine metal particles. 2. In a method for producing ultrafine metal particles, in which ultrafine metal particles are produced by melting and evaporating metal in a heating furnace inside a chamber, the ultrafine metal particles are collected on a collection plate provided above the heating furnace, and then recovered. After that, a small amount of carbon dioxide gas was introduced and the collection plate was cooled to form a dry ice film on the collection plate, and then the metal was evaporated to adhere ultrafine metal particles to the dry ice film. After that, a small amount of hydrogen carbon dioxide gas is introduced into the chamber at appropriate time intervals to form a dry ice coating on the ultrafine metal particles already attached on the dry ice coating, and the ultrafine metal particles are attached to the dry ice coating. 1. A method for producing ultrafine metal particles, which comprises sequentially repeating the steps to adhere ultrafine metal particles to a stack via a dry ice coating, and then sublimating the dry ice coating to obtain ultrafine metal particles. 3. A collection plate in which a heating furnace is disposed below and a flat surface facing the heating furnace is disposed above and a cooling means is disposed in a sealed chamber communicating with the vacuum exhaust iA unit. and a carbon dioxide gas introducing pipe for supplying and blowing carbon dioxide gas to the lower surface of the collection plate.