JPS62270707A - Production of metallic powder - Google Patents

Abstract

PURPOSE:To efficiently produce fine metallic powder having a low oxygen content by melting a metal having ductility or malleability at room temp., cooling drops of the molten metal with a gas or liq. at a specified solidification rate and subjecting the resulting powder to oxidation, mechanical fine crushing and heat treatment in a reducing atmosphere. CONSTITUTION:A metal having ductility or malleability at room temp., e.g., an alloy consisting of 13wt% Cr, 1wt% Si and the balance Fe is melted to make drops. Drops of the molten metal is cooled with a gas or liq. at <=10<4> deg.C/sec solidification rate so as to regulate the grain size of the resulting powder to <=30mum. The resulting powder is oxidized, mechanically finely crushed and heat treated in a reducing atmosphere. Thus, metallic powder having <=0.5% oxygen content and <=30mum particle size is produced.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for easily producing fine metal powder.

[Conventional technology]

Fine metal powder is required for powder metallurgy, filters, electromagnetic materials, paints, etc.

Conventionally, fine metal powder has been produced by an atomization method or a pulverization method, and then sieved.

When producing powder by the atomization method, the spray pressure is high and the amount of spray water or gas is increased to finely crush ductile or malleable metal droplets (by doing so, it is possible to form spherical or irregular particles with a low oxygen content). The hui of the state.

A fine metal powder is obtained. However, the yield of powder of 30 μm or less is about 30%, which is not an economically preferable method.

When producing powder by a pulverization method, since brittle metals have low plastic deformability, pulverization can destroy grain boundaries or inside grains to obtain angular powder. However, thin sheets of ductile or malleable materials or metal powders can be ground into fine metal powders by mechanical grinding with stamp mills or vibrating mills. A flaky metal powder with a large aspect ratio is obtained. However, the yield of powder of 30 μm or less is 20 to 30%, which is not an economically preferable method.

[7.1 Problems to be Solved by the Present Invention] The present invention has been made in consideration of the problems of the prior art, and
As a result of various studies on how to easily and easily produce fine metal powder from ductile or malleable metals, we found that by oxidizing and crushing metal powder with crystal grains of 30 μm or less, fine angular metal can be produced. The present invention was completed based on the knowledge that the powder could be produced in a high yield.

[Means for Solving the Problem] That is, the present invention uses a gas or liquid to melt droplets of a metal that is ductile or malleable at room temperature, so that the crystal grains of the obtained powder are
The powder is cooled at a solidification rate of 104°C/sec or less so that the size becomes 0 μm or less, the resulting powder is oxidized and mechanically pulverized, and heat treated in a reducing atmosphere to reduce the amount of oxygen to 0.5 μm. % or less and metal powder with a diameter of 30 μm or less.

[Operation] In the present invention, it is important to control the crystal grain size of the powder before pulverization. It is known that the size of crystal grains in powder is influenced by the material and solidification rate. Among these, the solidification rate is a particularly important factor.

Since the purpose was to obtain a powder having fine crystal grains of 30 μm or less, the solidification rate was set to be faster than the droplet solidification rate of 104° C./sec. The powder obtained in the above step, which is a material that is ductile or malleable at room temperature and has fine crystal grains, is heated at a high temperature to promote diffusion of metal and oxygen and oxidize the powder. Oxygen diffuses into the oxide film formed on the powder surface through grain boundaries. Moreover, oxides are formed along grain boundaries by reacting with metal ions diffused from inside at the grain boundaries, causing volume expansion. This volumetric expansion generates compressive stress inside the powder, causing cracks to occur.

Even when heating is used to accelerate the oxidation reaction, the degree of oxidation loss differs between dry air and humid air, and oxidation tends to be accelerated by H2O. However, for single metals, 0□
Alternatively, in air oxidation, the influence of H2O tends to be small.

Oxidized powder hardly undergoes plastic deformation, so even if it is crushed by a crusher such as a stamp mill, vibration mill, jet mill, or attritor, it will not form into flakes and will not form into a shape, but will continue along the grain boundaries. Shattered.

In addition, metals containing oxygen as a solid solution are generally hard and brittle,
Because of this, even the inside of the crystal grains can be pulverized to obtain fine powder.

Since the fine powder is in an oxidized state due to the reaction with oxygen, the next step is heat treatment in a reducing atmosphere. For example, by using a hydrogen atmosphere, CO gas atmosphere, etc., a powder with a low oxygen content can be obtained. .

If the solidification rate is slower than 10'C/sec, it is difficult to reduce the grain size to 30μ or less. Even if this is pulverized at grain boundaries, powder of 30 μm or less cannot be obtained. 3
In order to obtain powder of 0 μm or less, it is necessary to destroy the inside of the crystal grains. This is difficult for ductile or malleable materials. This is because in the case of mechanical pulverization to obtain a powder with a particle size of 30 μI or less, compressive stress is repeatedly applied, resulting in flaky powder with a high asbestos-to-tok ratio, and fine powder cannot be obtained in good yield.

〔Example〕

Hereinafter, typical examples of the present invention will be shown.

Example (1) Cr 13. Owt%, Si 1. OwL%, balance Fe
The molten metal at 1600°C was flowed out from a hole with a diameter of 10 mm at the bottom of a refractory container, and the solidification rate of the droplets was 10'.
Spray pressure cuff 0kg/cd so that it is below ℃/sec,
The molten metal stream was pulverized with a water spray amount of 10 It/sec, and was cooled by dropping into water to produce a powder. The average particle size of the obtained powder was 70 μm, and the crystal grain size was 5 to 20 μm.

The powder obtained in the above step was placed in a container and charged into an electric furnace. Humid air containing 0.3% 020 was introduced into the electric furnace, and the temperature was maintained at 1000° C. for 10 hours to oxidize the powder. 3 kg of the oxidized powder was put into a crusher and crushed for 3 hours. After adding and mixing 2.8% of carbon, which is the same amount as the amount of oxygen in the pulverized powder, the mixture was placed in a container and placed in a vacuum furnace, where it was maintained at a temperature of 1200° C. for 4 hours. The amount of powder of 30 μm or less obtained by reduction was 2.7 kg, and the yield was 9.
It was 0%. Further, the oxygen content of the powder was 0.25%, and the average particle size was 15 μI.

Example (2) Ni 12. Owt%, Cr 16. Owt%, Si
An alloy of 1.0 wt% and the balance Fe was melted, and the molten metal at 1600°C was flowed out from a hole with a diameter of 10 mm at the bottom of a refractory container.
The molten metal stream was pulverized with a spray pressure cuff of 0 kg/d and a spray water amount of 101/sec so that the solidification rate of the droplets was 104° C./sec or less, and the powder was cooled by dropping into water to produce a powder. The average particle size of the obtained powder was 60 μm, and the crystal grain size was 3 to 20 μm.

The powder obtained in the above step was placed in a container and charged into an electric furnace. The atmosphere in the electric furnace was humid air containing 0.5% H20. The powder was oxidized by maintaining the temperature at 1000° C. for 10 hours. 2 kg of the oxidized powder was placed in a vibration mill and pulverized for 2 hours. After adding and mixing 3.3% of carbon, which is the same amount as the amount of oxygen in the pulverized powder, the mixture was placed in a container and placed in a vacuum furnace, where it was maintained at a temperature of 1200° C. for 4 hours. The amount of powder of 30 μm or less obtained by reduction was 1.8 g, and the yield was 90%. The oxygen content of the powder was 0.35%, and the average particle size was 10 μm.

Example (3) A 100% Cu metal was melted, and the molten metal at 1300°C was flowed out from a hole with a diameter of 8m1W at the bottom of a refractory container, and sprayed so that the solidification rate of droplets was 10'°C/sec or less. The molten metal stream was pulverized with a pressure cuff of 0 kg/cj and sprayed water at IJ51/sec, and was cooled by dropping into water to produce a powder. The average particle size of the obtained powder was 60μ, and the crystal grain size was 2 to 1.
It was 5 μm.

The powder obtained in the above step was placed in a container and charged into an electric furnace. The atmosphere of the air furnace is dry air flowing in, and the temperature is 600℃.
℃ for 6 hours to oxidize the powder. 3 kg of the oxidized powder was put into a pulverizer and pulverized for 3 hours. The crushed powder was placed in a container and charged into a furnace in a hydrogen atmosphere, and the temperature was 720°C.
It was kept at ℃ for 2 hours.

30 μl or less of powder obtained by reduction is 2.7 K
The yield was 90%. Also, the amount of oxygen in the powder is 0.1
5%, and the average particle size was 11 μm.

Example (4) An alloy of Sn 10.0 and the balance Cu was melted to 1250
°C molten metal is flowed out from a hole with a diameter of 8 mm at the bottom of the refractory container, and the spray pressure is 4 kg/cflI and the spray gas amount is 3001/cm so that the solidification rate of the droplets is 104 °C/sec or less.
A powder was produced by crushing the molten metal stream at 100 sec and cooling it by dropping it into water.The average particle size of the obtained powder was 80 μm, and the crystal grain size was 3 to 25 μm.

The powder obtained in the above step was placed in a container and charged into an electric furnace. Humid air containing 0.5% H20 was introduced into the electric furnace, and the temperature was maintained at 600° C. for 5 hours to oxidize the powder. 2 kg of the oxidized powder was placed in a vibration mill and pulverized for 2 hours. The pulverized powder was placed in a container, placed in a furnace in a hydrogen atmosphere, and maintained at a temperature of 750° C. for 2 hours. The amount of powder of 301 Jm or less obtained by reduction was 1.7 kg, and the yield was 85%. The oxygen content of the powder was 0.35%, and the average particle size was 15 μm.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to easily obtain fine metal powder with good yield in which the amount of oxygen contained in the alloy or metal powder is 0.5% or less.

The metal powder of the present invention is suitable for powder metallurgy, filters, electromagnetic materials, paints, etc.

Claims (1)

[Claims] A droplet of a metal that is ductile or malleable at room temperature is cooled with a gas or liquid at a solidification rate of 10^4°C/sec or less so that the crystal grains of the obtained powder have a size of 30 μm or less. The obtained powder is oxidized, mechanically pulverized, and heat treated in a reducing atmosphere to reduce the amount of oxygen to 0.
A method for producing metal powder of 30 μm or less with a content of 5% or less.