JPS5943962B2 - Method for producing ultrafine metal powder - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing ultrafine metal powder.

More specifically, the present invention relates to a method for producing ultrafine metal powder that suppresses oxidation of the powder surface during pulverization and produces less oxides.

Ultrafine metal powders have attracted attention for various uses, and various methods for producing them have been studied.

For example, methods using chemical reactions, evaporation methods, dry pulverization methods such as jet mills, wet pulverization methods, etc. are known.
Both methods have drawbacks such as difficulty in obtaining uniform and ultrafine powder, and the surface being susceptible to oxidation during grinding.

As a result of various studies on methods for obtaining ultrafine metal powder stably and with good yield, the present inventors found that a wet pulverization method is advantageous because it can easily obtain a fine powder.

However, like other crushing methods, it is not possible to suppress the formation of oxides due to oxidation of the new metal sand cross section.

Furthermore, even if crushed in an inert gas or inert solvent, the fractured surface remains active, and there is a risk of an explosive reaction if it comes into contact with air or an active solvent.

Therefore, as a result of intensive research in order to further suppress the oxide formation during wet grinding and obtain ultrafine metal powder in a stable and high yield, the method of the present invention was arrived at.

That is, the present invention involves adding 0.1 to 100% by weight of a vinyl compound to the coarse metal powder and performing wet pulverization when producing fine metal powder by pulverizing coarse metal powder by a wet pulverization method. It is characterized by

When the method of the present invention is used, oxidation of the powder surface is suppressed, and ultrafine powder can be obtained which has a small metal oxide content and is extremely stable against air and the like.

In addition, ultrafine powder can be used as a raw material for metal carbide fibers with excellent performance by firing a metal carbide precursor obtained by spinning a polyacrylonitrile dope in which ultrafine powder is dispersed, or by mixing it with carbon and firing it. When pulverized, it exhibits excellent effects as a raw material for producing ultrafine metal carbide powder.

The metal coarse powder used in the present invention includes Ti, Si, Zr, and B, especially in consideration of the uses described later.
.

Fe, V, W, Ta are preferred, especially Ti, Si,
Those containing Zr and B as main components are preferable.

Coarse metal powder may be used alone or in combination of two or more.

Normally, ductile metals such as AA are difficult to pulverize.

Furthermore, there are no particular limitations on the vinyl compound used in the present invention, and the vinyl compound polymer to be mixed into the ultrafine powder does not pose an obstacle to the use of the ultrafine powder obtained by the present invention. All you have to do is choose.

For example, when used for metal carbide synthesis, vinyl compounds mainly composed of acrylonitrile, acrylic esters, and methacrylic esters are particularly suitable.

Examples of acrylic esters include methyl acrylate, ethyl acrylate, and butyl acrylate, and examples of methacrylic esters include methyl methacrylate, ethyl methacrylate, and butyl methacrylate.

Vinyl compounds may be used alone or in combination of two or more.

The amount of vinyl compound used is 0.1~
It is 100% by weight, preferably 3 to 70% by weight.

If the amount used is too small, sufficient effects cannot be obtained.

In addition, if there is a large amount of unreacted monomer remaining in the system, this may cause problems when using the ultrafine metal powder after pulverization, and the polymer produced in large amounts may make pulverization difficult or cause agglomeration of the fine powder. adverse effects appear.

To explain the wet pulverization method of the present invention in more detail, the wet pulverization method is particularly preferably a wet forced stirring ball mill method.

The wet forced stirring ball mill method is a method in which hard balls, coarse metal powder to be crushed, and a solvent are placed in a certain container, and the balls are forcibly stirred to crush the metal and disperse it in the solvent. be.

Although the particle size of the obtained powder largely depends on the size of the balls, the grinding time, etc., the addition of a vinyl compound in the present invention can also suppress agglomeration of the fine powder and promote grinding.

The smaller the size of the ball, the greater the crushing effect, but it is more expensive, and the longer the crushing time, the greater the energy loss, so these conditions should be determined depending on the target particle size of the powder.

The solvent used in the present invention is not particularly limited, but examples include hydrocarbon compounds that are liquid at room temperature, inert amides such as dimethylformamide and dimethylacetamide, dimethyl sulfoxide, sulfolane, and tetramethylurea.

When a hydrocarbon compound with a low boiling point is used, it vaporizes due to the rise in temperature during pulverization, so it is necessary to cool the threads during pulverization.

In order to grind efficiently, it is necessary to consider the amount of solvent and coarse metal powder.

The amount of coarse powder to be charged is preferably about the same weight or less as the solvent used.

This amount varies depending on the shape of the container, the stirring state of the ball, the specific gravity of the metal used, etc., but good results will not be obtained if at least the solvent is less than the top surface of the ball.

Further, the vinyl compound may be added by any method as long as it is normally carried out before the start of pulverization of the metal coarse powder (before the start of stirring of the ball).

The ultrafine metal powder obtained by the method of the present invention can be used as a raw material for producing metal carbide fibers and ultrafine metal carbide powder, as described above, to obtain metal carbide with high performance and high yield. can.

In other words, the content of metal oxides that tend to evaporate or generate other compounds (impurities) during firing is small, and the particle size of the metal powder is small, so a high yield and high performance metal carbide can be obtained. be.

In addition, carbon fibers having a metal carbide surface layer can be manufactured by coating the fine powder dispersion with a binder added as necessary on the surface of carbon fibers and firing, or carbon fibers such as cellulose fibers, polyacrylonitrile fibers, and pitch fibers can be manufactured. Carbon fibers having a metal carbide surface layer can also be produced by coating the fiber precursor fiber surface in the same manner and firing.Furthermore, by dispersing ultrafine metal powder in a polymer solution or dispersion, various types of carbon fibers can be produced. It can also be used as a surface coating agent that is applied to the surface of molded products to impart electrical conductivity, thermal conductivity, radiation absorption properties, etc.
It can also be used as a filler for plastics, a raw material for sintered bodies, etc.

The reason why the method of the present invention provides such excellent effects is unknown, but the vinyl compound is polymerized by the radicals generated on the surface of the pulverized metal, and the radicals are annihilated, and the generated polymer adheres to the surface of the powder. It is thought that this prevents oxidation.

Therefore, in addition to vinyl compounds, radical scavengers and the like are also effective.

The present invention will be explained below with reference to Examples, but the present invention is not limited to the Examples.

Note that the percentages in the examples are percentages by weight unless otherwise specified.

Example 1 A 500m1 stainless steel container with a stirrer, 5mm in diameter
Add 700g of stainless steel bowl.

Next, add 30 g of 200-mesh metal silicon powder, and then add 800 g of balls.

After injecting 15g of distilled acrylonitrile into this,
Add toluene until it reaches 5mm above the top of the ball.

After pulverizing this in a ball mill at 230 mm for 50 hours, the silicon powder dispersion was separated from the ball, and the dispersion was concentrated to obtain 42 g of solid content.

More than 95% of the solid particles had a particle diameter of 0.5 μm or less.

Further, the 5i02/(Si+5iO2) value was 0.092.

30 g of the solid content was redispersed in 150 g of dimethylformamide, and 14 g of polyacrylonitrile (5% by weight methyl acrylate copolymer) was dissolved in the dispersion at 90°C to produce a dope.

#2300 gold steel, hole diameter 0.15mm, number of holes 1
The dope was spun into water using a spin tank equipped with No. 5 nozzles.

There were no problems such as filter clogging.

After oxidizing the obtained yarn at 260°C in air for 20 minutes,
Calcination was performed at 1350° C. for 15 minutes in argon.

The yield was 70%. Based on Si analysis, X-ray analysis, and free carbon analysis using a thermobalance, the composition of the fired product was found to be 6.5% free carbon.
5%, silicon carbide 93.5%.

Example 2 The same experiment as in Example 1 was conducted except that the solvent used during pulverization and the vinyl compound in Example 1 were changed.

The results obtained are summarized in Table 1.

However, the spinning was carried out so that the result was S i 02 + S i/PAN + vinyl polymer (produced by polymerization of the vinyl compound added during crushing) -50150.

Comparative Example 1 The same experiment as in Example 2 was conducted except that no vinyl compound was used.

The results obtained are summarized in Table 1.

As is clear from Table 1, when a vinyl compound is used during pulverization, the amount of SiO□ produced is very small, so the yield of silicon carbide increases.

Claims (1)

[Scope of Claims] 1. When producing fine metal powder by pulverizing coarse metal powder by a wet pulverization method, 0.1 to 100
A method for producing ultrafine metal powder, which comprises adding a vinyl compound in an amount of % by weight and wet grinding. 2. The method according to claim 1, wherein the wet pulverization is performed by a wet forced stirring ball mill method. 3 Metal is Ti, Si, Zr1B, Fe, V
, W, and Ta. 4. The method according to claim 1, which comprises wet grinding in a non-aqueous, inert organic solvent. 5. The method according to claim 1, wherein the vinyl compound is a vinyl compound mainly containing at least one selected from acrylonitrile, acrylic esters, and methacrylic esters.