JP2683704B2 - Manufacturing method of aluminum nitride - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing aluminum nitride (hereinafter referred to as AlN).

Conventional technology and its problems AlN has recently attracted attention as a material for high temperature containers, IC substrates, LSI substrates, etc. because it has excellent heat resistance and thermal conductivity. These materials are generally manufactured by mixing AlN powder with a sintering aid and a binder and sintering the mixture at a temperature of about 1800 to 2000 ° C. The AlN powder is produced by a reducing nitriding method of heating a mixed powder of AlN ₂ O ₃ and C in a N ₂ or NH ₃ stream, a method of nitriding aluminum halide in an NH ₃ stream, N ₂ or NH ₃ A direct nitriding method in which aluminum powder is heated in an air stream is known. Among these methods, the direct nitriding method is widely adopted because it can mass-produce high-purity products at low cost.

However, in the direct nitriding method, since the reaction is performed at a temperature significantly higher than the melting point of aluminum, the Al powders are fused to each other, and the nitriding reaction does not proceed sufficiently. Various measures have been taken to solve this problem. For example, by crushing the partially nitrided fused mass and then renitriding it, or by mixing the raw aluminum powder with AlN powder,
Attempts have been made to prevent fusion of aluminum powder. However, in the former case, there is a risk of contamination with impurities and in an increase in energy consumption, and in the latter case, productivity is lowered, and both are solutions to the fundamental problems. I don't get it.

Means for Solving the Problems The inventors of the present invention have conducted extensive research in view of the problems of the prior art as described above, and as a result, the surface of the raw material aluminum powder to be subjected to the nitriding reaction is preliminarily prepared as a precursor of the sintering aid. It has been found that when the above is coated with and heated at a temperature equal to or higher than the melting point of aluminum in an air stream containing N ₂ and / or NH ₃ , this problem is substantially eliminated.

That is, the present invention relates to a "method for producing aluminum nitride by nitriding aluminum powder under heating, wherein the raw material aluminum powder is coated with a precursor of a sintering aid. Is provided.

The shape and particle size of the aluminum powder used in the present invention are not particularly limited, but spherical or teardrop-shaped ones obtained by an atomizing method or the like are preferable, and usually a particle size of 5 to 20.
Those having a size of about 0 μm are used.

As described above, when sintering the AlN powder to obtain various materials, a sintering aid is used. In the present invention, a compound that can serve as a sintering aid under the reaction conditions for producing AlN from aluminum powder (this is referred to as a precursor or simply a precursor of the sintering aid in the present specification) is used to convert the aluminum powder into a powder. Cover. By using the raw material aluminum powder having such a specific structure, the nitriding rate of the raw material is increased and the sinterability of the generated AlN is improved. Such precursors are compounds of alkaline earth metals and rare earths, which are lower alcohols (methanol, ethanol, isopropanol, n-butanol, etc.) and ketones (acetone, methyl ethyl ketone, etc.) alone or in a mixed organic solvent. Those that can be dissolved in. The condition of being soluble in the organic solvent is necessary for the coating operation on the raw material aluminum.
Examples of the precursor include inorganic compounds such as nitrates, chlorides and bromides of alkaline earth metals and rare earths; organic compounds such as alkoxides of alkaline earth metals and rare earths. More specific examples include yttrium nitrate, yttrium chloride, cerium nitrate, lanthanum chloride, calcium bromide, magnesium bromide, yttrium-n-butoxide, calcium methoxide, magnesium isopropoxide and the like. The amount applied to the aluminum powder is preferably such that the coating amount of the produced AlN powder surface as an oxide is 0.1 to 5% by weight (hereinafter simply referred to as%). If this amount is less than 0.1%, the nitriding ratio of the aluminum powder and the sinterability of the produced AlN are not sufficiently improved. On the other hand, if it exceeds 5%,
The nitriding rate of aluminum powder is reduced.

The application of the precursor to the aluminum powder can be performed by any method such as immersing the aluminum powder in a solution in which the precursor is dissolved in an organic solvent, or spraying the solution on the aluminum powder.

The aluminum powder coated with the precursor is heated in a stream containing N ₂ and / or NH ₃ at a temperature equal to or higher than the melting point of aluminum according to a conventional method. At this time, since the precursor coating the aluminum powder is decomposed before the start of the nitriding reaction and changed into an oxide that should serve as a sintering aid, fusion of the aluminum melted inside thereof, agglomeration, etc. To be prevented. When the nitriding reaction begins to proceed in earnest, molten aluminum flows out from the cracks formed in the oxide film and is immediately nitrided to obtain the desired AlN powder containing the sintering aid.

EFFECTS OF THE INVENTION According to the present invention, when AlN is produced by the direct nitriding method, it is possible to almost completely carry out the nitriding reaction while preventing fusion or agglomeration of aluminum powder.

In addition, the reaction product is a soft AlN mass, so it can be easily crushed, and fine AlN
A powder is obtained.

Furthermore, since the obtained AlN powder already contains the sintering aid in a uniformly dispersed state, it is not always necessary to mix the sintering aid, and moreover, a sintered body using this as a raw material The warpage and dimensional accuracy are improved.

EXAMPLES Examples are shown below to further clarify features of the present invention.

Example 1 Ethanol 100ml to dissolve the _{Y (NO 3) 3 · 6H} 2 O 1.46g, this aluminum powder (trademark "AC2500", Toyo Aluminum Co., Ltd., 250 mesh pass 95% or more, 350
Mesh pass 80% or more, the oxygen content of 0.309%) after the dispersing 57 g, the ethanol was removed using an air pump in a _{thermostat, Y (NO 3) 3 ·} 6H 2 O 2.5% containing aluminum powder Got This amount corresponds to 0.5% as the amount of Y ₂ O ₃ based on the finally obtained AlN. From the scanning electron microscope photograph and the electron probe microanalyzer photograph, it was observed that a precipitate consisting of a compound containing Y was present on the surface of the obtained powder.

Then, the obtained Y compound-coated aluminum powder was treated with N ₂
900 at a heating rate of 15 ° C / min in an electric furnace under gas flow
The temperature was raised to 0 ° C. and the temperature was maintained for 2 hours for nitriding.

The relative density of the AlN mass after the reaction was about 50%.
Moreover, it was confirmed from the scanning electron micrograph of the fracture surface that the particles in the agglomerated product all had a diameter of 2 μm or less, and many of them were submicron. In addition, this agglomerated product, because the fine particles are loosely bound,
It was easily crushed, and AlN fine powder could be easily obtained.

Table 1 shows the average particle diameter of the obtained AlN fine powder, the nitriding ratio, and the relative density of the HIP compact obtained by using the AlN fine powder.

In the same manner as in Examples 2-3 Example 1, referenced to aluminum powder (the finally obtained AlN containing 5% YCl ₃ · 6H ₂ O Y
As ₂ O ₃ amount, equivalent to 1.35%) and _{Ce (NO 3) 3 · 6H} 2 O
To obtain an aluminum powder containing 7.5% (corresponding to 2% of CeO ₂ amount based on AlN finally obtained).

Using these Y compound- or Ce compound-coated aluminum powders, AlN fine powders were obtained in the same manner as in Example 1.

Table 1 also shows the average particle diameter of the obtained AlN fine powder, the nitriding ratio, and the relative density of the HIP compact obtained by using the AlN fine powder.

Comparative Example 1 AlN fine powder was obtained in the same manner as in Example 1 except that coating with the Y compound was not performed.

Table 1 also shows the average particle diameter of the obtained AlN fine powder, the nitriding ratio, and the relative density of the HIP compact obtained by using the AlN fine powder.

Table 1 Average particle size Nitriding rate Relative density (μm) (%) (%) Example 1 0.85 99.8 98 2 0.83 99.3 97 3 0.90 99.0 99 Comparative example 1 2.0 5.9 − Note: (a) Average particle size is HORIBA It was measured by a "CAPA700" type particle size measuring instrument manufactured by Seisakusho.

(B) The nitriding rate was measured by the Kjeldahl method.

(C) Relative density is temperature 1600 ℃, pressure 2000kg / cm ² , time
Hot isostatic press method (HI
P) The value of the molded product.

Example 4 By the same method as in Example 1, an aluminum powder containing 3% of CaBr ₂ .6H ₂ O (the amount of CaO based on AlN: 2.
Equivalent to 7%).

Using this Ca compound-coated aluminum powder, AlN fine powder was obtained in the same manner as in Example 1.

The average particle size and nitriding rate of the obtained AlN fine powder and the relative density of the HIP compact obtained by using the AlN fine powder were as follows.

Average particle size 0.77μm Nitriding rate 99.5% Relative density 97%

Claims (2)

(57) [Claims] 1. A method for producing aluminum nitride, which comprises nitriding aluminum powder under heating to produce aluminum nitride, wherein raw material aluminum powder is coated with a precursor of a sintering aid. 2. The method for producing aluminum nitride according to claim 1, wherein the precursor of the sintering aid is a nitrate of an alkaline earth metal and a rare earth.