JPH08109011A - Increase in reactivity in nitriding of aluminum - Google Patents

Abstract

PURPOSE: To improve the reactivity between Al and nitrogen and enable efficient production of AlN by etching the Al surface. CONSTITUTION: In the reaction of Al with nitrogen, the reaction heat emits, when the nitriding starts form the Al surface. Thus, the Al surface is etched as a pretreatment to increase the Al surface area and improve the reactivity. Thus, a large amount of heat is emitted on the initial nitriding, and the remaining Al is allowed to react with nitrogen with this reaction heat whereby AlN is produced efficiently. Thus, the nitriding of Al of a large size becomes possible in spite that such nitriding has been impossible because of their low reactivity, thus an AlN powder of high purity can be produced at lower cost than the conventional process.

Description

Detailed Description of the Invention

[0001]

[Field of Industrial Application] Sintered bodies of aluminum nitride (hereinafter referred to as "AlN") are used in metal melting crucibles and the like because of their high strength at high temperature, thermal shock resistance, and high temperature corrosion resistance. Recently, it has begun to be put into practical use as a semiconductor substrate (heat sink) because of its high thermal conductivity, electrical insulation, and the coefficient of thermal expansion close to that of silicon. Currently, in order to produce AlN by reacting aluminum with N ₂ , finely powdered aluminum is required as highly reactive aluminum. However, when compared at the same degree of purity, fine powder aluminum is more expensive than large aluminum, and the use of fine powder aluminum increases the manufacturing cost of AlN. The present invention uses, as a raw material, larger aluminum which is less expensive than conventional raw materials and has low reactivity. The present invention provides a method for producing high-purity AlN at low cost by nitriding it without adding a reaction aid.

[0002]

2. Description of the Related Art When AlN is produced by direct nitriding of aluminum, fine powdery aluminum having a particle size of 10 μm or less, that is, atomized powder is indispensable as active aluminum because of its low reactivity. Furthermore, recently, with the demand for high-purity AlN, high-purity atomized powder has been used as a raw material. However, high-purity atomized powder is expensive, and the use of atomized powder causes the price of AlN to rise. On the other hand, there is no example of succeeding in producing AlN by direct nitriding without adding a reaction auxiliary agent, using a large amount of aluminum, which has high reactivity and is relatively inexpensive and has low reactivity.

[0003]

In direct nitriding of aluminum, when nitriding starts from the surface of aluminum particles, a nitride film is formed on the surface of the particles. It is considered that the formation of this nitride film has two positive and negative effects on the subsequent reaction. The negative effect is that it inhibits the diffusion of nitrogen into the aluminum inside the nitride film, and the positive effect is that reaction heat is generated during the formation of the nitride film, and the nitrogen inside the aluminum inside the nitride film is generated. Is the effect of promoting the diffusion of. In the case of nitriding aluminum in the form of fine powder, since the specific surface area is large, sufficient reaction heat is generated during the initial nitriding and nitriding proceeds, but in the case of large aluminum, the reaction heat during the initial nitriding Is not sufficiently generated, and the reaction almost stops only by nitriding the surface.

In contrast, the present invention activates the surface by increasing the specific surface area of large aluminum in order to enhance the above-mentioned positive effects. Then, by generating a large amount of reaction heat in the initial nitriding and nitriding all of the aluminum inside the nitride film by this heat, the purpose is to nitrid 100% of the large aluminum that was rarely nitrided in the past in one operation. I am trying.

[0005]

In order to achieve the above object, an attempt was made to nitride the raw material by roughening the surface of aluminum by etching to activate the surface.
AlN was manufactured in the process of etching aluminum → nitriding.

The nitriding operation is preferably performed as follows.
Since the nitriding reaction starts during heating, it is better to completely remove oxygen from the inside of the electric furnace before starting heating.

Further, before the full-scale nitriding reaction starts, the melting point of aluminum (660 ° C.) because the specific surface area is not reduced by the melting of aluminum and the activity is not lost.
Up to the following, it is necessary to slow the temperature rising rate to form a thin film of AlN on the surface of aluminum.

Then, after forming a thin film of AlN, 100
Nitriding is preferably performed at a temperature of 0 ° C. or higher.

[0009]

As described above, a high nitriding rate can be obtained by one nitriding operation by performing the etching treatment as a pretreatment when nitriding large aluminum. This is because the large specific surface area of aluminum increases and the surface is activated, so that a large amount of reaction heat is generated during the initial reaction and the subsequent nitriding is promoted.

Further, by forming a thin film of AlN on the surface of aluminum below the melting point of aluminum,
The active shape of the surface is maintained, and then a full-scale nitriding reaction can occur at high temperature.

[0011]

[Example 1] Aluminum 2 mm in diameter and 50 mm in length
The aluminum wire rod (purity 99.99%) was used. this,
As a pretreatment, it was immersed in 25 wt% NaOHaq and 20 wt% HClaq for 30 seconds each and washed with water. After that, electrolytic etching was performed at room temperature at a current density of 1000 A / m ² for 60 seconds in 1.0 N-HClaq using aluminum as an anode and graphite as a cathode. 4g of this aluminum wire
Was filled in a Si ₃ N ₄ reaction tube (length 60 mm, inner diameter 14 mm) and set in a horizontal tubular electric furnace. And N ₂ gas is 400 ml / mi
While supplying n, the temperature was raised at 5 ° C / min, and the temperature was kept at 1300 ° C for 2 hours to prepare AlN having a nitriding rate of 99.3%.

[0012]

[Example 2] In Example 1, the temperature rising rate was set to 7 ° C / mi.
As n, all other operations were the same, and the nitriding rate was 98.
8% AlN could be obtained.

[0013]

Since the present invention is configured as described above, it has the following effects.

High-purity AlN can be manufactured at a lower cost than in the conventional case by using a large aluminum as a raw material, which has been conventionally impossible to be nitrided.

Claims (2)

[Claims] 1. The reactivity of aluminum and nitrogen is improved by etching the surface of aluminum.
Next, a method for producing aluminum nitride, which comprises using this aluminum as a raw material and heating it in an atmosphere containing nitrogen or ammonia. 2. The method according to claim 1, wherein the form of aluminum is not particularly limited as long as it can be etched.