JPH0421702A - Fine metal powder and its manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to magnetic powder for producing so-called plastic magnets by kneading with plastic materials and molding, or metal powder for producing sintered cores. The present invention relates to fine metal powders used for various purposes and methods for producing the same.

(Background technology) The particle size of magnetic powder for plastic magnets, metal powder for sintered cores, etc. can be changed to improve fluidity, improve compactness of molded products and sintered crystals, and improve magnetic field orientation. It is desirable to make it as small as possible.

However, the smaller the particle size of metal powder, the smaller the surface area
It increases in proportion to the power of oxidation, making it easier to oxidize. This tendency is particularly strong in magnetic powders used to manufacture rare earth alloy magnets.

Furthermore, when a metal is crushed to an average particle size of 10 microns or less, there is a probability that several percent of the particles are mixed with ultrafine particles of 1 micron or less, and as a result of pulverization, a new metal surface with extremely high activity is generated. Therefore, in the process of pulverizing metals, the problem of metal oxidation cannot be avoided.

If it is crushed to a particle size of 5 microns or less, it will spontaneously ignite and become a dangerous situation.

(Prior art) Conventionally, in order to improve the heat resistance of metal powder, a surface film of an organic substance was formed on the surface of the metal powder, but in this case, after the pulverization process, the metal powder was After the metal powder is removed, the metal powder is coated. Therefore, when taking out the metal powder from the crusher, there was a problem that the metal powder inevitably came into contact with the atmosphere and spontaneously ignited.

Previously, the applicant made fine powder from metal particles in an inert atmosphere, and before taking out the fine metal powder into the atmosphere, put a phosphate ester solution in the inert atmosphere to coat the surface of the fine metal powder with phosphoric ester. proposed a method for forming a thin film of an organometallic compound (Japanese Unexamined Patent Publication No. 1-234502). This method avoids the problem of spontaneous ignition of fine metal powder because the metal crushing and powder coating treatment are carried out in an inert atmosphere before taking out the fine metal powder from the metal crushing equipment. I was able to turn it into

The surface of this fine powder is covered with a thin film of phosphoric acid ester, which makes it extremely beautiful and has a heat resistance temperature of up to 300°C.If the temperature is raised above this temperature, the thin film will thermally decompose and the underlying metal fine powder will be destroyed. There was a problem with oxidation starting.

Therefore, in the applicant's proposal mentioned above, a metal powder with a thin film of a phosphate ester-based organometallic compound formed on the surface is further added.
A step was added in which the thin film was made into a thin film of a phosphoric acid-based metal compound that was stable even at high temperatures by heating to 00 to 450°C. As a result, the organic components in the thin film were removed, and the slightly exposed metal surface was then combined with oxygen in the atmosphere, and the powder particle surface was covered with a phosphoric acid-based metal compound, improving the heat resistance of the powder. However, by adding a heating process,
There was a problem with the product's high cost.

Moreover, even though the particle surface of the product is covered with a phosphoric acid-based metal compound from which organic components have been removed, this is either a thin film of an organometallic compound or is formed by being changed by heat treatment. -, and therefore the oxidation resistance was still not sufficient.

(Problems to be Solved) When fine metal powder is kneaded with a resin and molded, the kneading is carried out at a temperature considerably higher than the melting temperature of the resin (50 to 100°C). Since high temperatures are often generated locally in the kneading machine during cross-talk, it has been empirically shown that the thin film of fine metal powder has a temperature of 4.
It is necessary to have a heat resistance temperature of 00'C or higher, preferably 500'C or higher.

Many conventional phosphoric acid-based or other organic surface-coated metal fine powders cannot withstand high temperatures of 300°C or higher, especially 500°C or higher, as mentioned above, because they are mainly made of thin film coating layers made of organic compounds. Because I did.

In the process of continuing research on improving the heat resistance temperature of fine metal powder, the inventor used a phosphoric acid ester solution to be added to fine metal powder, which was a novel solution made by mixing phosphoric acid and alcohol. In this case, the fine metal powder has a high temperature resistance, but when a phosphate ester solution that has been prepared and left for several weeks is used, the temperature resistance of the fine metal powder tends to decrease. As a result of investigating the cause of this, it was discovered that in the case of a new phosphoric acid alcohol solution, most of the phosphoric acid was not yet esterified and existed in a mixed state in the alcohol, and the present invention was completed.

(Purpose) The present invention provides heat resistance of 500'C or more by simply carrying out a surface coating treatment process on fine metal powder in the same inert atmosphere following a metal grinding process in an inert atmosphere. The purpose of the present invention is to provide a fine metal powder having a high temperature and a method for producing the same.

Furthermore, since the present invention does not use an organic solvent, it effectively suppresses the organic conversion of phosphoric acid, and causes a phosphorylation reaction with the new surface of the highly active fine powder obtained in the metal crushing process. , provides a method for obtaining fine metal powder with excellent oxidation resistance.

In this application, "metal" refers to ferromagnetic alloys such as RCos, RCO+7 (R is Sm, Pr, Ce, L
(rare earth elements such as a), Nd-Fe-B-Co alloys, alnico alloys, ferromagnetic metallic iron, and other metals and alloys. "Phosphoric acid J includes not only phosphoric acid (H, PO,) but also inorganic phosphorus groups, metal phosphoric acid compounds, and other inorganic phosphorus compounds.

"Organic solvent" means alcohols such as methanol, ethanol, isopropyl alcohol, and other solvents having an organic group and dispersing phosphoric acid.

(Structure) The present invention is a fine metal powder whose surface is uniformly covered with a thin film of an inorganic phosphoric acid compound containing no organic group.

Further, in the present invention, a fine metal powder is produced in an inert atmosphere, and before the fine metal powder is taken out into the atmosphere, a mixture of phosphoric acid and an organic solvent, which is an organic phosphoric acid compound, is prepared in an inert atmosphere. A metal fine powder is brought into contact with fine metal powder in a state in which almost no generation occurs, and the highly active metal surface obtained by crushing the fine metal powder is covered with a thin film of an inorganic metal phosphate compound. This is a powder manufacturing method.

(Effects) The fine metal powder of the present invention uniformly covers the surface with an inorganic phosphoric acid compound and does not contain organic components, so its heat resistance is significantly improved, and it can withstand high temperatures of 500°C or more on average. I was able to do it.

Further, in the present invention, the metal pulverization process and the coating process are carried out in the same inert atmosphere, and the coating process is completed in a short time in one process, so that the manufacturing cost is low.

Incidentally, it is also possible to separate the pulverizing step and the coating step and perform the processing in separate apparatuses in a series of inert atmospheres.

(Example) FIG. 1 shows an oxidation-preventing coating treatment apparatus for metal powder used in carrying out the method of the present invention.

The apparatus of the embodiment also serves as a pulverizer for pulverizing metal particles, and a water-insoluble inert organic solvent that does not dissolve water, such as a hydrocarbon solvent such as toluene, hexane, or heptane, is used as a pulverizing aid. The coating treatment can be carried out immediately after the metal particles are powdered by wet grinding in the grinding aid and under an inert atmosphere.

Airtightly attach a lid plate (13) to the cylindrical stirring tank (1) with its top open.
The agitation body (2) is placed in the agitation tank and suspended inside the agitation tank.

The stirring body (2) has a plurality of scraping rods (22) protruding in the radial direction inside the stirring tank (1) on a rotating shaft (21) that freely and airtightly penetrates the center of the lid (13). A variable speed rotary drive device (23) is connected to the upper end of a shaft (21) that projects outward from the cover plate (13).

The stirring tank (1) has a double structure, with a cooling water filling chamber (10) between the inner wall and the outer wall, and a cooling water supply port (11) and a discharge port (12) are connected to this chamber. ing.

In addition, an inert gas supply pipe (4) passes through the cover plate (13),
and a gas pressure gauge (5) are connected.

The configuration of the above-mentioned apparatus is similar to a known wet metal grinding apparatus for powdering metal particles, and a stirring tank (1) contains metal particles to be ground, steel balls with a diameter of about 5 mm, toluene, benzene, n- A water-insoluble organic solvent such as hexane or a mixture of one or more of these is added as a grinding aid and the mixture is covered. The stirring tank (1) is filled with an inert gas such as N2 or Ar from the inert gas supply pipe (4).
) is maintained a little higher than atmospheric pressure to reliably prevent outside air from entering, and in this state, the agitator (2) is rotated.

The steel ball and the metal particles repeatedly collide, and the metal particles are crushed.

A feature of this device is that a coating treatment liquid supply pipe (61) is connected to the stirring tank (1).

In the embodiment, a coating liquid supply pipe (
61) is inserted into the stirring tank (1), and the processing liquid tank (6) is connected to the supply pipe (61).

A lid (62) is airtightly attached to the top opening of the tank (6), and an inert gas filling pipe (
63) The air layer between the tank (6) and the lid is constantly filled with inert gas to maintain it above atmospheric pressure, and outside air is allowed to flow into the tank (6). The inflow is reliably prevented.

Further, a liquid thermometer (7) for measuring the temperature of the liquid in the stirring tank (1) is provided through the lid plate (13).

The surface treatment solution is prepared by quickly stirring and mixing the necessary amount of phosphoric acid with an alcoholic solvent in a separate container within about 10 minutes just before the metal particles are crushed to the desired particle size and the coating is applied. The esterification of phosphoric acid was suppressed as much as possible and then transferred to the tank (6).

If the metal powder is used in a temperature range from room temperature to about 200° C., even fine metal powder treated with a treatment liquid with advanced esterification exhibits sufficient oxidation resistance.

However, for applications in which the fine metal powder is kneaded with resin and molded at high temperatures of 200°C or higher, it must be treated with a liquid that avoids phosphoric acid esterification and covered with an inorganic phosphate-based thin film. must be used.

When the metal particles are pulverized to the desired particle size, without continuing stirring the fine metal powder and the steel balls, the coating solution is pumped from the tank (6) through the supply pipe (6) using the injection valve (64).
1) into a stirring tank (1) and react with the newly formed surface of the fine metal powder with phosphoric acid, so that the surface of the fine metal powder is coated with a strong inorganic phosphoric acid-based oxidation-resistant material whose main component is a phosphate metal compound. Forms a thin film. Since the thin film forming reaction is carried out in a stirring tank with stirring, the reaction is preferably carried out within a very short time of 2 minutes or less. If stirring is continued for too long, the thin film will be destroyed and the bare metal will be exposed and will react with the treatment liquid again, but the phosphoric acid in the treatment liquid will have already been consumed and the coating treatment liquid will become insufficient.

As will be explained later, the amount of coating solution to be fed is strictly determined to the minimum necessary amount according to the average particle size of the fine metal powder, so if there is a shortage of coating solution, the color of the thin film of the coating solution will turn brownish. heat resistance decreases. Therefore, the stirring reaction between the metal powder and the coating solution needs to be completed in a short time without damaging the formed thin film.

As mentioned above, after the reaction between the coating treatment liquid and the metal powder is completed in a short time, the lid plate (13) is removed, the metal powder liquid is taken out of the apparatus by the pump, and the crushing aid and the coating treatment are immediately carried out. After removing the residual liquid, place it in a drying device with explosion-proof measures, and heat and dry it in the atmosphere at room temperature or at 70°C or lower, which is lower than the flash point of the organic solvent used, under normal pressure or reduced pressure to produce phosphoric acid. The coating process is completed.

In the case of a large-scale device for mass production, an inlet for the powder is provided on the top cover plate, and an outlet that can be opened and closed is provided on the outer periphery of the bottom of the tank (6), so that the metal powder and coating solution can be mixed together using pumps. It is also possible to input and discharge the liquid.

In the treatment method of the present invention, the metal powder is not exposed to the atmosphere until the phosphoric acid-metal layer is formed on the surface of the metal powder, so the particle size of the metal powder to be coated is 5 microns or less (for example, 1 micron). However, the problem of spontaneous combustion due to oxidation does not occur, the particle size of the powder can be made as small as possible, and the fluidity of the powder is also good.

The color of the thin film layer obtained by the reaction of the surface treatment liquid with the active surface of the fine metal powder varies depending on the method of phosphorylation with the metal of the multi-component alloy, and is blue-purple (heat resistant temperature 500℃ or higher) or gray-black. It is formed from a dense inorganic phosphoric acid metal compound or an inorganic phosphorus metal compound exhibiting a heat resistance temperature of 600'C or more.

In the industrial production of fine metal powders, for ease of operation and economy, it is necessary to specify the amount of phosphoric acid relative to the average particle size of the fine metal powders.

If phosphoric acid is in excess relative to the metal powder, the residual phosphoric acid in the treatment solution will react with the alcohol solvent during the drying process after coating, resulting in esterification, which will have an adhesive effect and cause the metal to A layer of fine powder may solidify or adhere firmly to containers being handled, making cleaning of equipment and containers difficult. Therefore, the amount of phosphoric acid to be added must be strictly defined according to the amount of fine metal powder to be treated and the average particle size, and the amount of alcohol solvent to dissolve this phosphoric acid must also be determined according to the amount necessary to uniformly disperse the phosphoric acid. It is important to limit it to a minimum.

Generally, the average particle size of the metal powder is around 10 microns, and the weight of phosphoric acid is 0.1 to 5.0% based on the weight of the fine metal powder.
The best oxidation-resistant film can be obtained within this range. As the metal fine powder approaches ultrafine powder with a particle size of 1 micron or less, the phosphoric acid weight percentage should be increased to approach 50%.

This avoids the troubles associated with esterification of phosphoric acid, and instead of having extremely smooth and fluid properties after drying, a phosphoric acid-based metal compound close to a monomolecular layer is formed on the surface of the fine metal powder. It can be held in place and the magnetic properties can be improved.

Since the surface film of the fine metal powder formed by the treatment method of the present invention is extremely thin and in a small amount, when this fine metal powder is pressure-molded and then sintered, various types of sintered crystals obtained after main sintering are required. There is no possibility that the characteristics will be significantly affected.

In addition, since metal particles can be pulverized, sintering can be performed at a temperature 100 to 200°C lower than conventional temperatures, which saves thermal energy and reduces the purchase cost of the sintering furnace itself and furnace materials. Many economic benefits can be expected as the lifespan of the equipment used will be extended.

Furthermore, by using the manufacturing method of the present invention, rare earth magnet products (both sintered molds and resin molded molds), which were conventionally manufactured using particle sizes of 5 microns or more, will now be manufactured using ultrafine particles of 1 to 3 microns. Powder can be used, and it is possible to obtain many effects such as not only improved moldability but also remarkable improvements in various properties of the resulting product, and furthermore, a beautiful appearance of the product.

As mentioned above, the coating method of the present invention is highly effective as a coating method for fine metal powder, but it is also fully applicable to coating general metal materials such as plates and pipes. It is something.

(Experimental Example) In the table below, Samples 1 to 3 are fine metal powders produced by the method of the present invention.

Samples 4 to 7 are comparative examples, and the coating treatment was performed after the completion of crushing.
The powder is taken out from the crushing device, the crushing media is removed, the powder is transferred to the stirring device, and a coating treatment liquid is added to perform the coating treatment.

(Margin below) For samples 1 to 3, the grinding time was 3 kg for the amount of balls.

Samples 4 to 7 show cases where a ball amount of 2 kg is used.

The oxidation start temperature is the temperature at which the weight of the fine metal powder increases by 0.15% when the fine metal powder is gradually heated.

The surface treatment solution for sample 4 is a mixture of phosphoric acid and methanol.
It was left alone for a week.

The surface treatment solutions of Samples 5 to 7 are commercially available products, all symbols are trade names, and are organic solutions.

GAFACLM400: Phosphate ester solution (manufactured by Toho Chemical Co., Ltd.) ZISNET BN-40:) Riazinethiol (manufactured by Sankyo Kasei Co., Ltd.) RMIOIA: (Shin-Etsu Chemical Co., Ltd. side) As is clear from this table, the metal fines of the present invention The powder showed high heat resistance up to 580°C or 5900C.

(Manufacturing example and measurement method of sample 1) Nd-based rare earth magnet alloy raw material powder having a composition of N d +2F e 78C04B6 in atomic weight % (rMQP-BJ average particle size 25 μm manufactured by General Motors) 500
Weigh gr.

In advance, 3 kg of steel balls, 300 gr of organic solvent n-hexane as a grinding aid, and 100 gr of toluene were placed in the stirring tank (1) shown in Figure 1.
After adding the mixed solution of gr, the lid plate (13) is fixed and sealed via an O-ring.

Next, the above raw material powder is introduced from the raw material inlet (8) using a funnel, this inlet is sealed, and N2 gas (purity 9
99% or more) was injected from the gas supply pipe at a flow rate of 217 m1n, and the stopcock of one outlet was opened to purge the air in the tank for about 5 minutes.

After the N2 gas replacement was completed, the stirring motor was started and wet pulverization was performed for 9 minutes at a rotation speed of 205 rpm until the average particle size was 1.
A fine grind of 1.7 μm is obtained.

Before this fine pulverization, the phosphoric acid solution is adjusted.

That is, 4g of orthophosphoric acid is weighed and dissolved in 40g of methanol and stirred for about 5 minutes using a stirrer to prepare a uniform phosphoric acid alcohol solution. After putting this surface treatment liquid into the treatment liquid tank (6) and performing the same N2 substitution,
When the above-mentioned pulverization is completed, the injection valve (64) is opened to apply N2 pressure (16 kg/cm2), and the injection is completed within a few seconds. On the other hand, the stirring rod is rotated at the same rotation speed (205 rpm) following the crushing to stir and disperse the treatment liquid, and after 30 seconds, the rotation is stopped to complete the coating treatment.

Next, open the lid, take out the lid plate and stirring rod together from the tank, and then put the coated fine powder, steel balls, and liquid into a container with a stainless steel wire mesh attached, and first put the steel balls in the wire mesh. After removing the powder, the fine powder precipitated in the receiver was transferred to a drying vat, and after removing the supernatant liquid, it was placed in a dryer equipped with an exhaust fan and dried by heating at 50 to 70'C for about 3 hours. Appears purple. Nd-based rare earth magnet alloy fine powder (Sample 1) is obtained.

Note that under the conditions of this example, there was little adhesion of the fine powder to the steel balls and containers, and there was almost no adhesion phenomenon of the coated fine powder to each other. Weighed 30 mg of the fine powder from the heel with a precision balance 7, put it in a platinum cup, put it into a Shimadzu TG meter, and heated it at a temperature of 5° from room temperature 20°C to 650°C while flowing air at a flow rate of 40 ml/min. The sample is heated at C/min and the change in weight of the sample is automatically recorded.

Based on this recorded data, the temperature at which 0.15% of oxidation weight increases is defined as the oxidation start temperature, and in the case of the above sample, it is 580'C.
showed that. This shows that this sample is hardly oxidized even when heated to 580° C. in the atmosphere.

(Manufacturing example of sample 2) For samples 1.3 to 7, the average particle diameter is adjusted to 11 to 12 μm for injection molding plastic mag combination, or for sample 2, the average particle size is adjusted to around 14 μm for compression molding. Therefore, the main conditions were that the grinding time was 6 minutes, and the surface treatment liquid was also 25g of phosphoric acid and 25g of methanol. Other operating procedures are exactly the same as Sample 1. The coated fine powder (sample 2) obtained had a blackish-purple color and had acid resistance of ↓, 5.
80'(':f;-1.1), no stagnation phenomenon was observed, and good results were obtained.

(Manufacturing Example of Sample 4) The raw material powder was the same as above, the sample weight was 250 gr, and the grinding time was adjusted to 8 minutes in order to suppress the average particle size to 11 to 12 μm for injection molding.

Therefore, the operating procedure is the same as sample 1, but as a surface treatment liquid, orthophosphoric acid is heated in advance to dehydrate it by about 18%, and after cooling, it is poured into a methanol solution, stirred and dissolved in Starcy for 30 minutes, and further esterified. In order to proceed with the process, a stock solution (5% phosphoric acid) was prepared by leaving it for one week. 20% of the stock solution just before pulverization
g, diluted with 400g of methanol, stirred with Starcy for about 5 minutes, put it into a processing liquid tank, and poured it with N2
Perform a replacement. Other operating procedures are the same as for sample 1. The obtained surface-treated fine powder (sample 4) exhibits a beautiful golden color, but its oxidation resistance is up to 320°C, and even if the amount of phosphoric acid is increased, this oxidation resistance temperature does not improve and the adhesion phenomenon increases. However, good results cannot be obtained from the handling point of view.

This tendency was also observed in other comparative examples.

That is, Comparative Examples 5 to 7 all form thin films containing organic substances, and even when the amount of surface treatment liquid (especially the main agent) is increased,
As mentioned above, the heat resistance did not improve, only the adhesion increased, and the expected effect was not obtained.

[Brief explanation of drawings]

FIG. 1 is a front view of a coating processing apparatus used in carrying out the present invention. (1)... Stirring tank (2)... Stirring body (4)
... Inert gas supply pipe (6) ... Processing liquid tank

Claims (1)

[Claims] 1. Fine metal powder whose surface is uniformly covered with a thin film of an inorganic phosphoric acid compound containing no organic groups. 2. Fine metal powder is produced by crushing metal particles in an inert atmosphere, and before the fine metal powder is taken out into the atmosphere, a mixture of phosphoric acid and an organic solvent is prepared, which is an organic phosphoric acid, in an inert atmosphere. A metal characterized by contacting fine metal powder in a state where almost no compound is generated, and covering the highly active metal surface obtained by crushing the metal particles with a thin film of an inorganic phosphate metal compound. Manufacturing method of fine powder.