JPS5910342A - Manufacture of ultrafine particle - Google Patents

Abstract

PURPOSE:To manufacture ultrafine particles having uniform grain sizes and crystal habits with good reproducibility, by providing an auxiliary heating atmosphere using an IR lamp near a vapor source. CONSTITUTION:The air in an evaporation chamber 1 is evacuated with a diffusion pump 2, the valve 3 of the chamber 1 is closed, and an inert gas having a prescribed pressure is introduced from a gas bomb 4 through a valve 5 into the chamber 1. Evaporation is accomplished while the temp. is controlled by regulating adequately the position 14 where an IR lamp 13 for providing an auxiliary heating atmosphere near the vapor source is focussed, the irradiation range 15 thereof and the voltage to be impressed to the electrodes 18 of the IR lamp, whereby ultrafine particles are manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for evaporating materials in an inert gas atmosphere.
The present invention relates to a method for producing ultrafine particles.

The general method for evaporating metal in an inert gas atmosphere to produce ultrafine metal particles (1 μm or less) is to evaporate the metal in a vacuumed container using helium.

Introducing an inert gas such as argon or quinanone at a specified pressure,
By heating the target metal to a specified temperature and evaporating it by means such as resistance heating method, laser heating method, electron beam heating method, etc., creating metal smoke consisting of ultrafine metal particles, and collecting the smoke. , using a method to obtain metallurgical particles.

In the conventional method described above, the produced metal smoke moves due to the convection of inert gas in the container due to the influence of the local temperature distribution near the evaporation source, and the metal particles evaporate as they move through the space. Due to the heat from the source, growth due to fusion occurs to different degrees depending on the position of the smoke from the evaporation source, and the particle size and crystal habit of the collected metal particles are not constant and the variation is wide (this has the disadvantage of being be.

Hereinafter, an example of a conventional method for producing ultrafine metal particles will be explained with reference to the drawings, and the problems of the conventional technique will be clarified. In this example, the metal ultrafine particles are magnesium and the inert gas is helium, which is evaporated by resistance heating in a tungsten boat.

Figure 1 is a schematic diagram of the apparatus, and the procedure for producing ultrafine particles is as follows:
It is as follows. First, the evaporation chamber 1 is heated to 4X10-4Pa.
Then, the valve 5 of the evaporation chamber is closed, and inert gas at a predetermined pressure of 5 x 101 to 3.3 x 10'Pa is introduced from the gas cylinder 4 through the valve 5. A predetermined voltage is applied to both ends of the tungsten board 1o, which is fixed to a conductive support 9 through the filament lead wire 8 vacuum-sealed to the Pelger wall 7 by B, and resistive heating evaporates, and the ultrafine particles generated at that time are evaporated. The smoke 11 adhering to the wall of the evaporation chamber 1 is collected.

Figure 2 shows magnesium and helium fs65X10”P
1 with a tungsten boat 10 fixed to a support 9 in
A graph showing the distribution of particle size in the horizontal direction of a cross section of smoke at each position of the vertical distance from the evaporation source for smoke 11 made of ultrafine magnesium particles produced when resistively heated to 350 ° C. It is. In this case, not only the particle size differs at each position of the smoke, but also the crystal habit also varies greatly. For example, the central part A of the smoke shows a spherical or polyhedral crystal habit with a small grain size, and the part B near the outside of the smoke shows a polyhedral crystal habit with a large grain size. In case of C, fine particles of magnesium having a hexagonal thin plate crystal habit with a large particle size are formed.

FIG. 3 shows the temperature distribution in the vicinity of the tungsten boat 10 during evaporation, as measured by a platinum-platinum-rhodium thermocouple.

A qualitative explanation of the generation mechanism of ultrafine particles due to heating evaporation in the inert gas revealed by the above experimental results is as follows.
As follows: When a metal is evaporated in an inert gas, near the evaporation source, the metal vapor displaces the inert gas, creating a region of metal vapor that is repelled by the surrounding inert gas molecules. As the metal atoms collide with each other, their kinetic energy decreases, and the mutual collisions generate clusters.Next, at the boundary between the metal vapor and the inert gas molecules, mutual diffusion occurs and they mix, and the metal atoms collide with each other. , further condensation occurs.

To describe these growth step by step: (1) In the metal vapor region, nucleation occurs from the metal vapor, and particles with a critical medium diameter or larger exist at a high degree. (2) Due to the presence of metal vapor and gold particles, nucleation and growth as well as fusion growth between particles occur together. (
3) Outside the area of metal vapor, fusion growth between particles occurs in the high temperature range. (4) In the upper part of the smoke, the temperature is low (
Then, growth stops.

Considering the above-mentioned growth process in this method, the distribution of supersaturation degree of metal vapor due to convection of inert gas near the evaporation source and temperature distribution have a large influence on the causes of variations in particle size and crystal habit of ultrafine particles. It is clear that it is given.

Especially, near the boat, the vapor density is extremely high, and the vapor is rapidly cooled in the boat's helicopter, reaching a degree of supersaturation sufficient for nucleation. Therefore, the number of nuclei (particles) generated there is extremely large (and the mass per unit volume of the generated particles is large (and the temperature is high, so the probability of fusion is large).

In this way, in the helicopter of a tungsten boat, the growth in metal vapor and the fusion growth between metal particles occur rapidly, which causes the grain size to rapidly increase (become thicker) and cause variations in grain size and various crystal habits. It has become.

In order to take advantage of the fact that the physical, chemical, electrical, and optical properties of materials are different from those of bulk materials by making them into ultrafine particles, it is necessary to use ultrafine particles with uniform particle size and crystal habit. A method is needed to produce fine particles with good reproducibility.

The present invention provides a method for producing the above ultrafine particles with uniform particle size and crystal habit with good reproducibility.

In a method of producing ultrafine particles by evaporation in an inert gas, an auxiliary heating atmosphere is provided near the evaporation source using an infrared lamp, and the target material is heated during evaporation depending on the evaporation source temperature or evaporation rate. Then, by bringing the heating atmosphere to an appropriately high temperature state using the infrared lamp and controlling the supersaturation degree and temperature distribution of the vapor near the evaporation source, ultrafine particles with uniform particle size and crystal habit can be obtained.

The method for producing ultrafine particles according to the present invention includes providing an auxiliary heating atmosphere near the evaporation source using an infrared lamp while the target material is being evaporated in a container filled with inert gas at a specified pressure.
By appropriately controlling the temperature of the heating atmosphere according to the inert gas pressure, evaporation source temperature, and evaporation amount, the distribution of vapor supersaturation degree and temperature distribution, which are factors that determine grain size and crystal habit during crystal growth, can be controlled. to be closer to steady conditions,
This method makes it possible to reduce the deviation in vapor density, and as a result, it is possible to produce ultrafine metal particles with uniform particle size and crystal habit.

An example of the method for producing ultrafine metal particles with uniform particle size and crystal habit according to the present invention will be described below with reference to the drawings.

The procedure for producing ultrafine particles may be carried out by the conventional method described above up to the step immediately before evaporating the particles. For example, the first
First, the evaporation chamber 1 is heated to 4X10-'P using the device shown in the figure.
The pulp 3 in the evaporation chamber is closed, and an inert gas at a predetermined pressure of 3.times.10" to 3.3.times.104 Pa is introduced into the evaporation chamber 1 from the gas cylinder 4 through the pulp 5.

During the evaporation, an infrared lamp 13 for providing an auxiliary heating atmosphere near the evaporation source is installed at the focal point 14 of the infrared lamp, the irradiation range 15 and the electrode 1 of the infrared lamp.
By appropriately adjusting the voltage applied to 8, ultrafine particles may be produced while controlling the temperature.

An example of the method for producing the above ultrafine particles will be described below with reference to FIG. 4 and WJ5.

4K, in order to provide an auxiliary heating atmosphere surrounding the spiral type evaporation source 16, the infrared lamp 13 is placed so that the focus 14 is directed from directly below the evaporation source 16 to near the evaporation source.
The cross-sectional view shows an example of the installation. Furthermore, in order to provide an auxiliary heating atmosphere near the tungsten boat type evaporation source 20, as shown in FIG. A cross-sectional view of an example is shown. In either production method, an auxiliary heating atmosphere is provided near the evaporation source by using the infrared lamp 13 moderately while evaporating the evaporation material 21 using the evaporation source 16. supersaturation degree and temperature distribution can be created. As a result, ultrafine particles with uniform particle size and crystal habit can be obtained.

Furthermore, as an application of Fig. 5, multiple auxiliary heating atmospheres can be provided near the evaporation source depending on the evaporation material by using multiple infrared lamps and individually controlling the focus position and temperature. Accordingly, it is also possible to obtain more constant conditions for producing fine particles.

By changing the auxiliary heating atmosphere provided near the evaporation source, the vapor density of the evaporation material near the evaporation source is reduced, the evaporation rate can be increased, and it is also possible to increase the yield of ultrafine particles. .

As described above (1) According to the present invention, in a method for producing ultrafine particles by evaporation performed in an inert gas, the target material is Accordingly, an auxiliary heating atmosphere is provided near the evaporation source using an infrared lamp, and the heating atmosphere is appropriately heated by the infrared lamp to control the supersaturation degree and temperature distribution of the vapor near the evaporation source, thereby reducing the particle size. And ultrafine particles with uniform crystal habit can be easily obtained.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the equipment used in the conventional ultrafine particle production method, and Figure 2 shows the distribution of particle sizes in the horizontal direction of the cross section of the smoke produced by the equipment in Figure 1. The graph, Figure 3 is a diagram showing the temperature distribution near the boat during resistance heating of a tungsten boat, and Figure 4 is a diagram showing the temperature distribution in the vicinity of the boat during resistance heating of a tungsten boat. An example of a cross-sectional view, FIG. 5, is a cross-sectional view of an example in which an auxiliary heating atmosphere is provided in the vicinity of a tungsten boat type evaporation source by a plurality of infrared lamps. 1... Evaporation chamber 2... Diffusion pump 3...
Main pulp 4...Inert gas cylinder 5...Pulp for inert gas introduction 6...Crow hermetically sealed lure...Pel jar wall 8...) Lead wire for lament 9. ... Strut 10 ... Tungsten boat 11 ... Smoke made of ultrafine particles 12 ... Vacuum side 13 ... Infrared lamp 14 ... Focus of infrared lamp 15 ... Irradiation range of infrared lamp 16 ... Evaporation source filament 17...Evaporation source filament electrode 18...Infrared lamp electrode 19...Infrared lamp reflector 20...Evaporation source tungsten boat 21...Evaporation material 11. Figure 1 ? Figure 3: ↑ In the direction of the heavy remains of the baby 1 shot and α6 [v 4 Sowing 5 Figure

Claims (1)

[Claims] 1. A method for producing ultrafine particles by evaporating a material in an inert gas atmosphere, which is characterized by providing an auxiliary heating atmosphere near the evaporation source using an infrared lamp.