JPS6241704A - Synthesis of aluminum nitride - Google Patents

Abstract

PURPOSE:To efficiently synthesize high-purity ultrafine aluminum nitride particles, by using ammonia and hydrogen, etc., at a given flow rate ratio as raw materials in the high-frequency induction heating plasma method. CONSTITUTION:Nitrogen gas and argon gas are introduced from a gas feed inlet of a synthesis apparatus and aluminum is introduced from a raw material feed inlet. High-frequency induction heating plasma is then generated to convert the above-mentioned argon and nitrogen into a plasma flame. A mixed gas of NH3 and H2 at 0.1-70 (NH3/H2) flow rate ratio is then introduced into the lower part of the flame to completely nitride aluminum melted and vaporized in the plasma flame.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention describes a method for synthesizing aluminum nitride using high-frequency induction thermal plasma and a plasma reaction using gold, aluminum, argon, nitrogen, hydrogen, and ammonia gas. related.

(Prior art and its problems) Aluminum nitride has excellent insulating properties and good thermal conductivity, so it has become increasingly important as a heat dissipation substrate for electronic circuits in recent years.

Various methods have been tried to synthesize aluminum nitride. That is, alumina is used as a starting material, carbon black or graphite is mixed therein, heated to 1500°C to 1900°C in a steady air flow, and At, 03
A method of synthesis using the reaction +N2+3C-2AzN+3CO is known. Although this method has the advantage of being able to synthesize aluminum nitride in large quantities at low cost, impurities such as oxygen and carbon remain in the synthesized aluminum nitride, which is a problem in synthesizing high-purity aluminum nitride. There is.

That is, oxygen contained in alumina (A4t03), which is a raw material, becomes a solid solution in aluminum nitride and cannot be reduced to a certain amount or less. Another problem was that unreacted carbon could not be completely removed.

Also known is a method of synthesizing aluminum nitride using a thermochemical reaction of aluminum halides using the method expressed by the following reaction. .

2AA+ 2HC1-2AtCt+H, high temperature section 2At+
In other words, gold and aluminum are converted into chloride gases in a high-temperature section, and then transported to a low-temperature section where they are precipitated as AtN. Although this method has the advantage that oxygen and carbon are not mixed, there is a problem that unreacted aluminum metal and aluminum chloride are mixed into the AtN. There is also the drawback that the synthesized ktN contains amorphous materials.

There are reports that unreacted aluminum and aluminum chloride can be reduced by mixing ammonia gas into the above reaction system, but in this case, a large amount of ammonium chloride is produced.
There is also the problem that some AtN gets mixed in with the generated AtN.
There are problems as a method that can be manufactured in large quantities at low cost.

Further, as a direct nitriding method of aluminum, a method is known in which aluminum nitride is synthesized by heating residual aluminum to 1500° C. to 2000° C. in nitrogen or in an air stream containing a mixture of nitrogen and ammonia. in this way,
However, there is the following problem. That is, even if the metal surface is covered with aluminum nitride, the metal inside is difficult to nitride, and the reaction does not proceed to the inside. For this purpose, a method is adopted in which the aluminum surface is nitrided, then crushed and nitrided again. However, according to this method, contamination of impurities due to pulverization cannot be avoided.

Further, there are problems such as the particle size of the produced A t N powder is difficult to control, and impurity contamination due to the reaction between the crucible and golden brown aluminum is unavoidable.

On the other hand, the method using high-frequency induction thermal plasma is an excellent method that eliminates the problem of contamination from the electrode because it uses a non-electrode discharge.
It is known that ultrafine particles such as SiC can be obtained by the reaction of rCt4 and CH. When used in the synthesis of aluminum nitride by the reaction of aluminum and nitrogen,
A similar problem was occurring as mentioned above. That is, since the temperature of high-frequency thermal plasma is usually 20,000°C to 30,000°C, even if it is once nitrided and becomes aluminum nitride, it will be decomposed again at high temperatures, resulting in the problem of contamination of metal aluminum and the problem of the surface 2 of metal aluminum. When is nitrided and aluminum nitride is synthesized on the surface, the inside is not nitrided, so there is a problem that aluminum nitride cannot be synthesized in a single phase.

Furthermore, in the conventional synthesis method using high-frequency induction thermal plasma,
Since only argon gas for discharge and nitrogen gas are used, there is a problem that not only does the nitriding reaction of aluminum not proceed completely, but also that the particle size cannot be controlled. Generally, it is said that the smaller the grain size of the powder raw material is, the smaller the size of the grain, the clearer the crystal planes, and the narrower the grain size distribution, the lower the sintering temperature and the higher the density of the sintered body. Argon gas and
In the method using only nitrogen gas, the AtN particles synthesized tend to be acicular, and only particles with particle diameters of 02 μm or more were obtained. Also, the specific surface area is 3
I couldn't get more than 0.

(Object of the Invention) An object of the present invention is to provide a method for synthesizing aluminum nitride fine particles using high-frequency induction thermal plasma, which can eliminate the various drawbacks described above.

(Structure of the Invention) The present invention provides a method for synthesizing aluminum nitride using a high-frequency induction thermal plasma method.
This is an aluminum nitride synthesis method characterized by nitriding metal aluminum using nitrogen, hydrogen, and ammonia gas.

(Detailed explanation of configuration) The synthesis apparatus according to the present invention will be explained below based on the drawings.

FIG. 1 schematically shows a synthesis apparatus according to the present invention.

The high-frequency coil 1 is placed outside a quartz plasma generating tube 2 which is water-cooled by flowing cooling water from a cooling water port 3 to a cooling water outlet lower, and argon and nitrogen gas are introduced from a gas supply port 4, and a raw material supply port 14, metal powder or aluminum wire is introduced. Alcon and nitrogen gas are made into a plasma flame 5 by high frequency induction. It was effective to flow hydrogen gas along the tube wall from hydrogen gas inlet/6 to control the particle size of the synthesized aluminum nitride.

A mixed gas of ammonia and nitrogen or hydrogen is introduced into the lower part of the plasma flame 5 through a gas mixer 13 from mixed gas ports 8 and 8I. The metal aluminum powder or wire rod introduced from the upper part of the plasma generation tube is melted and vaporized in the plasma flame, a part of which is nitrided, and transported to the lower part and the space of the reaction vessel 9, where it is further passed through the ammonia gas atmosphere where it is gasified into high-temperature plasma. Complete nitriding is completed by passing it through. The generated fine powder is collected by a powder collector 10 and separated from the gas, and then sent to an exhaust device 11. , 12, the gas is exhausted.

Needless to say, prior to the reaction, the quartz plasma generating tube and the reaction vessel 9 are sufficiently evacuated to 1.0-' or less by a separate exhaust device 12 to remove internal air, moisture, etc., and replace with nitrogen.

For the water-cooled plasma generator tube 2, quartz was used because it is heat resistant and allows the state of plasma generation to be easily observed. You can use anything as long as you can do it. The reaction vessel 9 is suitably made of stainless steel or quartz from the viewpoint of workability as an apparatus. As the plasma gas, argon is used as it is a gas that easily becomes plasma, but nitrogen gas alone may be used as long as the high frequency power is sufficiently large. The desired result was that the amount of ammonia in nitrogen or hydrogen or a mixed gas of nitrogen and hydrogen was 1% or more. When ammonia is introduced into high temperature plasma,
This creates a non-equilibrium excited gas state such as NH, NH, etc., which has the effect of promoting the nitriding reaction.

This ammonia mixed gas is supplied to the mixed gas supply ports 8 and 8.
Introduced from I.

Although only two locations are shown in FIG. 1, it is natural that gas uniformity can be improved and favorable results can be obtained by simultaneously supplying gas from three or more locations.

Any device may be used as the exhaust device 11 as long as it can achieve an exhaust speed higher than the flow rate of the gas to be introduced.

The aluminum laminated raw material used may be in the form of particles of 3o mesh or less, or may be wire rods of about 1.0flφ. Aluminum raw material purity is at least 99.99
% or more is desirable.

Examples using this device will be described below.

(Example) Using the apparatus shown in FIG. 1, the apparatus was evacuated to 10-' Torr using the exhaust device 12 and then filled with nitrogen gas. Argon gas flow rate 40/, 7 minutes/N,
Gas was introduced from the supply port 4 at 10 t/min, and high frequency power of 20 I (W) was applied to generate plasma.

NI (3) and H2 were each introduced from the mixed gas inlet 8.8I at 201/min or less. H7 for particle size control was introduced at 5t/min.
The flow rate was set to less than 1 minute.

Thereafter, 100 g/min of aluminum powder (30 mesh or less) with a purity of 99.99% was introduced from the raw material supply port and reacted. As a result, the ratio of NH, flow rate and HA amount NH
A nitriding rate of 100% was obtained with s/'H2 in the range of approximately 01 to 70. The specific surface area of the obtained powder is 3orMy
That was it. , while when NH, is not mixed, about 3
Only 0% of AzN was used, and the rest was metal aluminum.

The amount of aluminum nitride depends on the amount of metal aluminum supplied and the high frequency power, but was up to 500 y/L at a high frequency power of 20 KW.

The amount of impurity metal ions in aluminum nitride was investigated by emission spectroscopy, and was found to be less than 'toopprri'. Oxygen was analyzed by activation analysis and was found to be extremely pure with less than 1% by weight. The best results were obtained when the degree of vacuum during plasma generation was 100 to 250 Torr. When the vacuum level is increased to below 1oOTor,
We were also able to synthesize aluminum nitride with a smaller particle size.

(Effects of the Invention) As described above, according to the present invention, aluminum metal is introduced into plasma, melted and evaporated, and the aluminum metal vapor is subjected to a nitriding reaction in a mixed gas of nitrogen and NH excited by the plasma. The present invention provides a method for synthesizing ultrafine aluminum nitride particles with extremely high efficiency, and has extremely high practical value.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a high frequency plasma reaction device. 1st
In the figure, 1 is a high frequency coil, 2 is a quartz plasma generation tube, 3 is a cooling water inlet, 4 is a gas supply port, 5 is a plasma flame, 6 is a hydrogen gas inlet, 7 is a cooling water outlet, 8 is a mixed gas inlet , 92 reaction vessel, 10: powder collector, 11:
Exhaust device 512: vacuum exhaust device, 13 is a gas mixer, 1
4: Raw material supply port.

Claims (2)

[Claims] (1) A method for synthesizing aluminum nitride using a high-frequency induction thermal plasma method, which is characterized in that argon, nitrogen, hydrogen, and ammonia gas are used as a raw material mixed gas. (2) The flow rate ratio of ammonia and hydrogen NH_3/H_1 is 0
．． 1 to 70. The method for synthesizing aluminum nitride according to claim 1.