JPH0912308A - Method for nitriding aluminum - Google Patents

Abstract

PURPOSE: To provide a method for nitriding Al by which pulverization is easily carried out. CONSTITUTION: A granular, strip-or foil-shaped Al or Al alloy material of 0.1-5mm diameter or minor side length is mixed with 5-40% Al or Al alloy powder of <=0.3mm diameter and the resultant powdery mixture is nitrided in an atmosphere of pure gaseous nitrogen at 500-900 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for nitriding aluminum, and particularly to a method for nitriding aluminum which is easy to grind.

[0002]

2. Description of the Related Art Aluminum nitride obtained by nitriding aluminum by 100% is used as a substrate material because it has excellent thermal conductivity and good electric insulation. This aluminum nitride is produced by carbon reduction of alumina or direct nitriding of aluminum powder.
In the direct nitriding method of aluminum powder, a method of using aluminum powder having a particle size of 400 μm or less, nitriding at a temperature of 900 to 1400 ° C., and then crushing to make it fine has been industrially put to practical use.

Further, in order to enhance its nitriding property, a method in which aluminum powder is crushed to form flakes and a mixture of this and aluminum nitride powder is used as a raw material, particle size 250 μm
After nitriding metallic aluminum powder of m or less once below the melting point of aluminum and crushing it to an average particle size of 15 μm or less, further 130
Method of nitriding at 0 to 1400 ° C. (Japanese Patent Laid-Open No. 61-8360)
8) 、 Metallic aluminum powder mixed with fluorine-containing ammonium compound and aluminum nitride powder.
After nitriding by nitriding, a method of nitriding in a temperature range of 900 to 1300 ° C (Japanese Patent Laid-Open No. 62-3007) is known.

[0004]

When the aluminum nitride material obtained by nitriding aluminum by the above-mentioned conventional method is manufactured, there is a problem that it is difficult to pulverize the obtained nitride. An object of the present invention is to provide a nitriding treatment method for aluminum, which is easy to grind.

[0005]

Means for Solving the Problems The inventors of the present invention have found that a mixed powder obtained by mixing metal aluminum having a large size with fine metal aluminum has a large surface area of 400 μm.
It has been found that the sintering of the powder particles is smaller, the purity is higher, and the powder is more easily crushed than the metal aluminum powder of less than less than. The present invention is based on this finding.

That is, in the aluminum nitriding method of the present invention, the diameter or the length of one side (short side) is 0.1 mm or more,
Granular, strip-shaped or foil-shaped aluminum or aluminum alloy material of 5 mm or less is mixed with 5 to 40% of aluminum or aluminum alloy powder having a diameter of 0.3 mm or less, and the resulting mixed powder is pure nitrogen of 500 to 900 ° C. It is characterized by nitriding in a gas atmosphere.

The mixed powder to be nitrided of the present invention has a diameter or a length (short side) of 0.1 mm or more and 5 mm or less of granular or strip-shaped or foil-shaped aluminum or aluminum alloy material and a diameter of 0.3 mm or less. Of aluminum or aluminum alloy powder. Granules having a diameter or a side length (short side) of 0.1 mm or more and 5 mm or less,
The strip-shaped or foil-shaped aluminum or aluminum alloy material constitutes particles of large size, and the chips produced by machining such as a saw can be used as they are. For example, chips such as aluminum sash can be used as this raw material. The aluminum or aluminum alloy powder having a size of 0.3 mm or less constitutes particles having a small size, and atomized powder can be used.

The aluminum metal to be nitrided may be pure aluminum particles or aluminum alloy particles alloyed with other metals. In particular, an alloy containing 0.5% by weight (hereinafter,% means% by weight unless otherwise specified) of magnesium is preferable. The aluminum material is a metal that is very easily oxidized, and usually has a slight natural oxide film on its outermost surface, and this oxide film interferes with nitriding. In this case, the problem can be solved by using a material containing 0.5% or more of magnesium as the aluminum nitride material. Magnesium is a metal that easily evaporates and has a vapor pressure reduction of about 300 Pa at 540 ° C. under atmospheric pressure, and it is considered that this magnesium vapor acts as an oxygen target and promotes nitriding.

The compounding amount of the large-sized granular, strip-shaped or foil-shaped particles constituting the mixed powder occupies 60 to 95% when the whole is 100%. And the small size powder occupies the remaining 40 to 5%. If the size of the particles is less than 60%, the crushability after treatment is poor, which is not desirable. On the other hand, if it exceeds 95%, the reactivity of nitriding is poor, which is not desirable.

Aluminum nitride powder can be added to the mixed powder. This aluminum nitride powder has the function of preventing aluminum powder from sticking together and preventing sintering. The aluminum nitride powder is preferably blended in an amount of about 5 to 20% when the entire amount is 100%. The mixed powder is nitrided in a state where the inflow path of nitrogen is secured. Nitriding is performed in a pure nitrogen gas atmosphere. Here, pure nitrogen gas has a purity of 99.9%.
Above, and most importantly, there is no inflow of air from piping or the like, which is managed by measuring the dew point of the atmosphere in the furnace. The dew point is usually controlled at -20 ° C or lower.

The nitriding temperature is 500 to 900 ° C. If the nitriding temperature is lower than 500 ° C., the nitriding rate may be slow and the reaction may not substantially occur. On the other hand, if the temperature exceeds 900 ° C., a rapid nitriding reaction occurs, causing sintering between the raw materials and lowering the nitriding rate. It is known that the lower the processing temperature, the finer the particles. The nitriding time is about 3 to 15 hours.

Nitriding is performed at a temperature of 500 to 900 ° C.
It may be carried out stepwise, or may be carried out in two steps of first nitriding at a temperature below the melting point of the aluminum or aluminum alloy material, followed by second nitriding at a temperature higher than the first nitriding and lower than 900 ° C. . The first nitriding is 6
Nitriding is preferably performed at a temperature of 00 ° C. or lower. According to the aluminum nitriding method of the present invention, aluminum nitride having a nitriding ratio of 40 to 100% and excellent in crushability or aluminum nitride containing metallic aluminum can be obtained. Aluminum nitride is present in the aluminum matrix as aluminum nitride particles or needles having a diameter of 1 μm or less.

The obtained aluminum nitride or aluminum nitride containing metallic aluminum may be pulverized in dry air to make the oxygen content of the obtained powder 0.4% or more. Moisture in the air is easily adsorbed on the produced aluminum nitride material, which impairs corrosion resistance. In order to prevent this, it is effective to immediately perform crushing treatment in a dry air with a ball mill, a vibration mill or the like after the nitriding treatment so that the oxygen content of the obtained powder is 0.4% or more. This also prevents the conductivity of the material.

[0014]

In the aluminum nitriding method of the present invention, 50
Along with nitriding under a pure nitrogen gas atmosphere of 0 to 900 ° C., a mixed powder is constituted by an aluminum material having a large size that delays nitriding and an aluminum powder having a small size that promotes nitriding, and mild nitriding proceeds. Therefore, it is possible to obtain aluminum nitride that is easily crushed.

[0015]

EXAMPLES Hereinafter, the nitriding method of the present invention will be described in more detail with reference to examples. As a raw material for nitriding, chips generated by saw shaving of aluminum sash, which is industrially produced in large quantities, were used. As shown in FIG. 1, the outer shape of this swarf is 0.1 to 0.5 mm, mainly consisting of granules of 0.1 to 3 mm.
mm, thickness strips and foils. The material of this chip is JIS 6063 (0.6% M
g, 0.4% Si).

The aluminum powder used as a mixture with this raw material has a particle size of 10 to 150 produced by a rapid solidification method.
and a material containing 2.5 wt% of magnesium was used. Further, 5 to 20% of aluminum nitride powder having a particle size of 5 to 100 μm was added to prevent sintering. Table 1 shows the composition of the mixed powder and the treatment amount.

[0017]

[Table 1]

For the nitriding, a heat-resistant steel muffle electric furnace (Erema furnace) was used. This electric furnace is usually used for sintering iron-gas sintered materials. This electric furnace has a structure that is not completely sealed and has an intermediate shutter in the center. The introduced gas enters the furnace from above the central part, blows sideways at the inner part of the muffle, and is discharged from the insertion port. The furnace volume is about 16 liters.
Although this electric furnace is not the most suitable as an experiment for intermediate treatment of aluminum, we thought that it would not be industrially feasible if it could not treat even this level of furnace, so we used this electric furnace.

The mixed powder shown in Table 1 was thinly and evenly spread on a stainless square pad (17 × 21 cm ² , height 3 cm). Then, after inserting the pad into the furnace, the inside of the furnace was replaced with nitrogen gas (gas introduction amount: 30 L /
Minutes, required time: 5 hours). Then 10 per hour
It was heated to a predetermined nitriding temperature at a rate of 0 ° C. and nitrided under the nitriding conditions shown in Table 1. The amount of pure nitrogen gas introduced during nitriding is 3 for 1 minute.
It was set to 0 liter. After nitriding, it was cooled in a furnace to obtain a nitride.

The obtained nitride was tested with the test NO. Except for No. 7, it was roughly crushed by hand and then crushed to a predetermined particle size in a mortar (made of alumina). As an example, FIG. 2 shows the particle size distribution of the crushed material (test No. 2) crushed in a mortar for 7.5 minutes. In addition,
In the aluminum nitriding method of the present invention, the obtained nitride is extremely easy to grind. Therefore, a very simple crushing method was adopted in which the material was roughly crushed by hand and then crushed to a predetermined particle size in a mortar (made of alumina). When nitriding only fine aluminum powder, crushing such as crushing with a hammer is required.

The test NO. After the 7 materials were taken out of the furnace, they were immediately placed in a ball mill purged with dry air at 150 ° C. and pulverized for 10 minutes. Test No. 1 to
In No. 5, following the first nitriding treatment at 540 ° C. × 3 Hr,
In this example, the second stage nitriding is performed at 580 to 900 ° C.
Unlike nitriding of aluminum powder alone, when the second stage nitriding was carried out at 650 to 900 ° C, all nitriding was 100%. When only aluminum powder is nitrided, the nitriding rate is 60 to 95%.

Test No. Nitriding rate of 62% in 5 and 6
3% is obtained. In addition, the test NO. : Test No. 3 in which aluminum powder was removed from the treated material of No. 3: The nitriding ratio of 31 is as low as 19%, and the significance of adding aluminum powder is recognized. Test No. 31 is easily crushed because the nitriding rate is low. Test No. 7 is NO. The same mixed powder as in No. 2 was treated under the same nitriding conditions, cooled in a furnace, immediately put in a ball mill purged with dry air at 150 ° C., and ground for 10 minutes. NO. 2 oxygen amount 0.30%,
NO. The oxygen content of No. 7 increased to 0.65% and had no conductivity. Note that NO. 50 pieces in a furnace after crushing 2 pieces in a mortar
Oxygen content of the powder subjected to oxidation treatment at 0 ° C for 15 hours is 0.37
%Met. From this, the effect of surface oxidation by the grinding treatment with a ball mill, a vibration mill, etc. can be seen. It should be noted that the presence of water in the air causes surface adsorption and impairs corrosion resistance.

[0023]

The nitride obtained by the aluminum nitriding method of the present invention is extremely easy to grind. Therefore, a nitride having a predetermined grain size can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a photograph showing the outer shape of the particle structure of aluminum chips used in Examples.

FIG. 2 is a test NO. It is a figure which shows the particle size distribution of 2 nitride.

[Procedure amendment]

[Submission date] July 12, 1995

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

Claims (3)

[Claims] 1. The diameter or the length of one side (short side) is 0.1.
mm or more and 5 mm or less in granular, strip or foil aluminum or aluminum alloy material with a diameter of 0.3 m
5 or less aluminum or aluminum alloy powder
-40% is mixed and the resulting mixed powder is 500-900 ° C.
Nitriding treatment method for aluminum, which comprises nitriding in a pure nitrogen gas atmosphere. 2. Nitriding comprises first nitriding performed at a temperature below the melting point of the aluminum or aluminum alloy material followed by second nitriding at a temperature higher than the first nitridation and lower than 900 ° C. A method for nitriding aluminum as described. 3. The method for nitriding aluminum according to claim 1, wherein, following nitriding, the powder is pulverized in dry air to have an oxygen content of 0.4% or more.