JPH0456768B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing aluminum nitride (AlM), more specifically NH ₄ Al (OH) ₂ CO ₃ (aluminum ammonium carbonate hydroxide (hereinafter referred to as AACH)).
This invention relates to a method for producing fine aluminum nitride powder with few agglomerates from aluminum nitride powder.

[Conventional technology]

Sintered bodies of aluminum nitride have characteristics such as high thermal conductivity, corrosion resistance, and high strength, and are therefore attracting attention as electronic materials such as ceramic substrates for semiconductors and various high-temperature materials.

Generally, in order to obtain a dense ceramic sintered body, it is necessary to use a raw material powder of high purity and made into single particles with a fine primary particle size. However, no conventional aluminum nitride powder has been developed that satisfies this point, and there has been a strong desire to develop a fine aluminum nitride powder that is made into single particles, that is, has fewer aggregates.

Conventionally, methods for producing aluminum nitride powder include using alumina powder as a starting material and heating it together with carbonaceous powder in a nitrogen or ammonia atmosphere, and using metallic aluminum powder as a starting material and directly nitriding it with nitrogen or ammonia. A method is generally known in which aluminum hydroxide powder is used as a starting material and heated together with carbonaceous material in a nitrogen or ammonia atmosphere.

[Problem that the invention seeks to solve]

Among the above-mentioned methods for producing aluminum nitride powder, the method using alumina powder as a starting material includes 1600
Since high firing temperatures of ℃ or higher are required, the primary particle size of the resulting powder is large and strongly agglomerated aggregates are likely to be formed in the powder.Also, it is difficult to carry out the nitriding reaction completely, so unreacted alumina remains and it is necessary to further refine the hard alumina, resulting in problems such as increased grinding energy consumption and contamination of impurities during grinding.

On the other hand, the method using aluminum hydroxide powder as a starting material improves the low aluminum nitride production efficiency, which is a drawback of the above method, but
It does not improve the primary particle size or aggregation state.

Furthermore, in the method using metallic aluminum powder as a starting material, in order to increase the nitriding rate, there is a step of pulverizing the raw material metallic aluminum, and the obtained
There are problems in that impurities are mixed in during the process of pulverizing AlM into fine powder as a raw material for sintering, and unreacted metallic aluminum remains and aggregates.

This invention has been made based on the above-mentioned technical background, and its purpose is to provide a method for producing fine aluminum nitride powder with few agglomerates by solving the problems of conventional methods. be.

[Means for solving problems]

The inventor has found that using AACH as a starting material for producing aluminum nitride powder is effective in achieving the objectives of the present invention.

That is, the method for producing aluminum nitride powder of the present invention involves combining an aluminum compound represented by the chemical formula NH ₄ Al(OH) ₂ CO ₃ with a carbonaceous substance and/or a substance that produces a carbonaceous substance at a temperature below the calcination temperature. It is characterized by firing in a non-oxidizing atmosphere containing nitrogen.

As a starting material in the production method of this invention,
AACH and a carbonaceous material and/or a compound that converts to carbonaceous material below the calcination temperature is used.

AACH can generally be obtained by the reaction of ammonium hydrogen carbonate with aluminum salts such as aluminum chloride and ammonium alum (for example, Japanese Patent Publication No. 56-9447). AACH synthesis conditions, e.g. pH of reaction solution,
The concentration of the solution and the reaction temperature may be changed as appropriate depending on the form required for AACH.

Carbonaceous substances as starting materials are substances mainly composed of carbon, and include natural substances such as anthracite and natural graphite, as well as artificial substances such as coke, carbon black, oil coke, activated carbon, charcoal, and graphite. . In this invention, the material is not limited to carbonaceous materials, and any substance that produces the above-mentioned carbonaceous materials at a temperature below the firing temperature (for example, 1200 to 1650° C.) can be used in place of carbonaceous materials or together with carbonaceous materials. Substances that generate this carbonaceous substance include hydrocarbons such as anthracene and naphthalene, and other organic substances.

The purity of starting materials such as AACH and carbonaceous materials used in this invention can be changed as appropriate depending on the purity of aluminum nitride, and if high purity aluminum nitride powder is to be obtained, high purity starting materials are used. This is desirable. Furthermore, the starting material is preferably in the form of powder in order to promote the reaction. For carbonaceous substances that are easy to crush, it is desirable that the average particle diameter be, for example, 0.5 μm or less, preferably 0.1 μm or less. On the other hand, since AACH has weak aggregation and is brittle, it does not require pulverization and can be used in the present invention in its synthesized form.
AACH generally does not have a constant shape depending on the synthesis conditions; for example, it is chestnut-like, rice-grain-like, or irregularly shaped.

In this invention, each starting material can be used as a mixture and subjected to the reaction, but each starting material can also be introduced simultaneously or sequentially and used for the reaction. In order to carry out the reaction completely, in the former case it is preferable to mix each starting material uniformly, and in the latter case it is desirable to introduce each starting material so that it is evenly dispersed. In this invention, the amount of each starting material to be used is 0.1 to 1.0 parts by weight, preferably 0.2 to 0.5 parts by weight of the carbonaceous material per 1 part by weight of AACH. This is because if the amount of carbonaceous material is less than 0.1 part by weight, the nitriding reaction does not proceed sufficiently and the product is
- This is because alumina will be mixed in, and if more than 1.0 parts by weight is used, carbonaceous substances will remain in the product, impairing its purity.

In this invention, the starting materials are heated (calcined) in a non-oxidizing atmosphere containing nitrogen. In addition to nitrogen, this atmosphere can also contain non-oxidizing gases such as ammonia gas, argon, hydrogen, etc., and the atmosphere can be allowed to stagnate or flow during the reaction. The firing at this time is carried out at a temperature range of 1200 to 1650°C, preferably about 1300 to 1600°C.
This is because aluminum nitride is difficult to form at temperatures below 1200°C, and grain growth becomes noticeable at temperatures above 1650°C. This firing time can be changed as appropriate depending on the temperature, particle size, etc., and a short firing time is sufficient at higher firing temperatures.

In the manufacturing method of this invention, the aluminum nitride obtained after firing usually has an average particle size of 0.5 μm.
It is a fine powder with less agglomerates.

[Action and effect of the invention]

Although the reaction mechanism of this invention is not necessarily theoretically clear, it is thought to be as follows.
Note that this is for the purpose of understanding the invention more clearly, and is not intended to limit the scope of the invention.

When AACH is thermally decomposed alone, amorphous alumina with an extremely high non-surface area is produced, which undergoes α-aluminaization through θ-alumina. In this case, the transition proceeds at a lower temperature than in other aluminum salts, and even finer α-alumina crystal nuclei are uniformly generated.

Therefore, even within the reaction system of this invention, in the low temperature region, it is likely that
AACH decomposition products adsorb a large amount of nitrogen gas,
This is considered to be a factor that causes the subsequent nitriding reaction to proceed rapidly. As described above, the fact that AACH generates uniform and fine crystal nuclei in a low temperature region is the biggest factor in easily generating fine aluminum nitride, which is the target substance in the nitriding reaction of the present invention. This is the most important point. Furthermore, it is speculated that the fact that the carbon material is uniformly mixed with AACH from the beginning prevents agglomeration between the generated particles and is a contributing factor to the generation of fine aluminum nitride particles.

In any case, the following effects can be obtained by this invention.

(a) In the conventional method using alumina as a starting material, the hard starting material (alumina) is finely divided, for example, 1 μm.
Since there is no need for further pulverization, it is possible to reduce extra preparation steps, significantly reduce the pulverization energy cost during production, and prevent the contamination of impurities during the pulverization process.

(b) In the method using alumina as a starting material, firing was performed at a temperature of 1600°C or higher in order to increase the nitriding rate, but the method of this invention can obtain a high nitriding rate at a lower firing temperature, so it requires significantly less energy. This is a huge savings.

(c) In the method using alumina as a starting material, aluminum hydroxide or aluminum salt is thermally decomposed in advance, but in this invention,
Since a direct nitriding reaction is carried out simultaneously with the process of thermally decomposing AACH, aluminum nitride can be obtained at a lower cost.

(d) Since AACH is easy to purify, if a high purity carbonaceous material is used as the starting material, an aluminum nitride powder of unprecedented purity can be obtained.

(e) Therefore, the problems in the conventional method can be solved and fine aluminum nitride with few aggregates can be easily obtained.

(Example) The present invention will be specifically explained using the following example.

Example 1 6.75 g of AACH with a purity of 99.99% or more and 2.5 g of carbon black with an ash content of 0.2% and an average particle size of 0.023 μm
(0.37 parts by weight based on AACH) were wet mixed for 2 hours in a nylon ball mill using ethyl alcohol as a medium. After drying the mixture, it was placed in an alumina container and heated at 1550° C. for 5 hours in an electric furnace while supplying nitrogen gas at 200 ml/min. Next, in order to remove unreacted carbon in the product, it was heated at 850℃ in air.
Heating was performed for 2 hours. The powder obtained weighed 1.80 g.

The X-ray diffraction pattern of the obtained powder is shown in FIG. From FIG. 1, it was confirmed that this powder was aluminum nitride, and it was also found that no alumina remained.

Furthermore, in the scanning electron micrograph (Figure 5) of this aluminum nitride powder, it was observed that the uniform spherical particles with an average particle diameter of about 0.5 μm hardly aggregated, and even if they did aggregate, the cohesive force was weak. It was done.

Example 2 Aluminum nitride powder was synthesized in the same manner as in Example 1, except that heating was performed at 1500°C for 5 hours. The X-ray diffraction pattern of the obtained powder was
As shown in the figure. Furthermore, in the scanning micrograph of this aluminum nitride, uniform spherical particles with an average size of about 0.5 μm were observed.

Example 3 Aluminum nitride powder was synthesized in the same manner as in Example 1 except that the carbonaceous material was activated carbon. The X-ray diffraction pattern of the obtained powder showed no alumina diffraction line and only aluminum nitride peaks. Further, in a scanning electron micrograph of this aluminum nitride powder, uniform spherical particles with an average size of about 0.5 μm were observed.

Example 4 0.55g of carbon black (relative to AACH)
Aluminum nitride powder was synthesized in the same manner as in Example 1 except that 0.08 parts by weight) was added. The X-ray diffraction pattern (Fig. 3) of the obtained powder shows the following:
Although alumina diffraction lines were present, the amount of alumina remaining was small despite the small amount of carbon black.

Comparative Example 1 Aluminum hydroxide obtained by Bayer method
7.64 g and 2.82 g of carbon black (0.37 parts by weight based on aluminum hydroxide) having an ash content of 0.2% and an average particle size of 0.023 μm were wet mixed for 2 hours in a nylon ball mill using ethyl alcohol as a medium. Thereafter, aluminum nitride powder was synthesized by the same operation as in Example 1. The X-ray diffraction pattern of the obtained powder is shown in FIG. This figure shows that even though a large amount of carbonaceous material was used, alumina remained. Further, in the scanning electron micrograph (FIG. 6) of this aluminum nitride, slightly agglomerated particles with an average particle diameter of 1.0 μn were observed.

[Brief explanation of the drawing]

Figures 1, 2, 3 and 4 are
FIG. 5 is a diagram showing the X-ray diffraction patterns of Examples 1, 2, and 4 and Comparative Example 1, respectively, and FIG. 6 is an electron micrograph at 10,000 times magnification showing the particle structure of AlN obtained in Comparative Example 1.

Claims (1)

[Claims] 1. Calcining an aluminum compound represented by the chemical formula NH ₄ Al(OH) ₂ CO ₃ and a carbonaceous material and/or a substance that produces a carbonaceous material below the calcination temperature in a non-oxidizing atmosphere containing nitrogen. A method for producing aluminum nitride powder, characterized by: