JPH0465003B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing highly pure, fine, easily sinterable aluminum nitride powder. [Prior Art] Aluminum nitride (hereinafter referred to as AlN) is not only used as a heat-resistant material because of its excellent mechanical properties and chemical durability, but also because of its high thermal conductivity, high electrical insulation, and low dielectric constant. For these reasons, it is also expected to be used as a heat dissipation material for semiconductors. Although AlN is sometimes used in the form of a thin film, it is often used in the form of a sintered body. The sinterability and properties of such AlN sintered bodies are
It is known that this is strongly influenced by the properties of the starting material AlN powder and the sintering aid. That is, it is desirable that the AlN powder has high purity, uniform and fine particle size, and that an appropriate sintering aid is uniformly dispersed in the AlN powder. AlN powder has conventionally been produced by direct nitriding of metal aluminum or reductive nitriding of alumina. In the direct nitriding method, by using high purity alumina with fine and uniform particle size as the starting material, it is easier to obtain a slightly better AlN powder by the direct nitriding method, but it is difficult to say that it is the desired powder. As a method to improve the above method and obtain AlN powder with high purity, fine, and uniform particle size, water is added to a dispersion of aluminum alkoxide and carbon to cause hydrolysis of the alkoxide, and a mixture of aluminum hydroxide and carbon is produced. A method for obtaining a mixture of aluminum hydroxide and carbon by adding an alkali to an aqueous solution containing a water-soluble aluminum salt and carbon and using a neutralization precipitation method has been proposed (Japanese Unexamined Patent Application Publication No. 1983-1999).
6105, Special Publication Showa 61-26485). The mixtures obtained by these methods are more uniformly mixed than the alumina and carbon mixtures described above, so by firing them in a non-oxidizing atmosphere containing nitrogen, they can be made more uniform and finer than before. Na
It is now possible to obtain AlN powder. However, even in the above improved method, when water or alkali is added dropwise for hydrolysis or neutralization precipitation, precipitates are locally generated and immediately coagulate. For this reason, many aggregates of aluminum hydroxide with a size of 1 μm or more that do not contain fine carbon powder are formed, and the resulting mixture of aluminum hydroxide and carbon has insufficient uniformity. The particle size of the AlN powder obtained by firing such a heterogeneous mixture in a non-oxidizing atmosphere containing nitrogen tends to be irregular, and even after firing, the alumina remains without being nitrided, and the particle size is 1 to 5 μm.
The result was a tendency to form coarse-grained AlN. In order to solve the above problems, the present inventors proposed in Japanese Patent Application No. 61-05863 that they used boehmite (AlOOH) or coagulated boehmite powder, which has excellent dispersibility and stability of the dispersion liquid, and used boehmite (AlOOH) or coagulated boehmite powder to uniformly combine with the carbon source material. We have disclosed a method for obtaining fine AlN powder with a narrow particle size distribution range by preparing a dispersion, solidifying it while maintaining this uniformly dispersed state, drying and firing it. In the above disclosure, when solid carbon is used as a carbon source, the particle size distribution of the obtained AlN powder tends to vary depending on its particle size and dispersion state.
For example, if the particle size exceeds 1 μm, or if the dispersion is insufficient, the particle size may aggregate more than 1 μm.
Many AlN grains were observed, and in extreme cases, nitriding was insufficient and alumina remained. [Problems to be solved by the invention] The present invention provides highly pure and fine particles with excellent sinterability.
The purpose is to further develop the above-mentioned disclosure regarding the method for producing AlN powder, to further improve the quality of the excellent AlN powder, and to provide a method for stably and reproducibly producing fine AlN powder with a narrow particle size distribution range. It is something to do. [Means to solve the problem] AlN with high purity, fine, and excellent sintered body
As a method for producing powder stably and with good reproducibility,
The present invention consists of the following technical means. (1) A boehmite sol in which boehmite is stably dispersed is prepared in advance by adding boehmite or coagulated boehmite powder, which has excellent dispersibility in water, to water and adjusting the pH to a range of 1.2 to 4.5. The boehmite particle size in the boehmite sol is
It is 500 Å or less. Precipitated boehmite has an X-ray diffraction peak at the same position as boehmite crystal, but the peak width is broader than that of boehmite crystal.
Boehmite is poorly crystallized, but it is not much different from boehmite crystals in terms of dispersibility in water. (2) As a carbon source material to be added to the boehmite sol, carbon obtained from a water-soluble organic carbon source material and solid carbon powder are mixed so that the weight ratio of the organic carbon source material and solid carbon powder is in the range of 0.05 to 0.5. A carbon source material blended with is used. This solid carbon powder preferably has a particle size of 0.5 μm or less. After uniformly mixing the total amount of carbon in this carbon source material and boehmite at a weight ratio of 0.4 to 3.0, solidifying while maintaining this uniform mixing state and drying, the mixture is dried in a non-oxidizing atmosphere containing nitrogen. Fire inside. (3) In the step (2) above, in order to maintain the homogeneous mixed state of the boehmite sol and carbon source material dispersion and solidify it, water was removed by evaporation etc. and the boehmite sol was made to coexist with carbon. It is preferable to gel the mixture as it is, then dry it, and then sinter it in a non-oxidizing atmosphere containing nitrogen. Here, the water-soluble organic carbon source material is preferably one that does not affect the dispersibility of the boehmite sol and has a high carbon residual rate at high temperatures, such as a water-soluble resin or lignin sulfonic acid. [Function] The present invention will be specifically explained along with its function. First, boehmite powder or coagulated boehmite powder is added to water, and the pH is adjusted to a range of 1.2 to 4.5 so that the boehmite sol is optimally dispersed. Next, a carbon source material is prepared by blending carbon obtained from a water-soluble organic carbon source material and solid carbon fine powder so that the weight ratio thereof is in the range of 0.05 to 0.5,
The boehmite sol and the carbon source material are uniformly mixed so that the total carbon content in the carbon source material and the boehmite powder are in a weight ratio of 0.4 to 3.0.
This mixture is solidified while maintaining a uniformly mixed state, dried, and then fired at 1350 to 1700°C in a non-oxidizing atmosphere containing nitrogen to obtain AlN powder. The following three methods are used to solidify the above mixture.
A typical example is the street. b) Continue kneading for a long time. Since gelation of the boehmite sol progresses gradually during kneading, the viscosity of the mixture gradually increases and solidifies over time. b) While kneading, water is forcibly volatilized by heating etc. to form a gel state. c) Gelation is promoted by adding acids, alkalis, various ions, polymer flocculants, etc. When making boehmite sol, adjust the pH to 1.2 to 4.5.
The reason for limiting the range is as follows. PH is
If it is less than 1.2, the gelation of the boehmite sol will proceed rapidly, making it virtually impossible to perform the mixing operation with the carbon source material. When the pH exceeds 4.5, boehmite powder is not dispersed in water and remains as an aggregate of 1 μm or more, making it difficult to mix uniformly with the carbon source material. The reason why carbon obtained from a water-soluble organic carbon source material and solid carbon fine powder are blended as the carbon source material so that the weight ratio thereof is in the range of 0.05 to 0.5 is as follows. The effects of the present invention can be maximally achieved by mixing the carbon source material and boehmite sol as uniformly as possible. In order to uniformly mix them, it is first necessary to create a state in which boehmite and carbon are uniformly dispersed. A good dispersion of boehmite can be obtained by adjusting the pH of water as described above. On the other hand, methods for obtaining a good dispersion of a carbon source material include a method of peptizing and dispersing finely powdered solid carbon in a solvent, or a method of dissolving an organic carbon source material in a solvent (in the case of the present invention, the solvent is water). There is a method to use. When only solid carbon powder is used as the carbon source material, the particle size is usually 200 Å even if only fine powder solid carbon is used.
This is the above, and this finely divided carbon is deflocculated to the utmost.
Difficult to disperse. Therefore, an extremely large amount of solid carbon is required to cover the boehmite grains with solid carbon, and the production efficiency of AlN powder becomes extremely low. In addition, if the peptization and dispersion of solid carbon are even slightly insufficient, boehmite may not be reduced and nitrided and may remain as alumina, or the particle size of the resulting AlN powder may become irregular, resulting in poor quality stability and reproducibility. It is also undesirable from a sexual standpoint. In order to solve this problem, it is effective to use a water-soluble organic carbon source material that can easily disperse carbon uniformly. However, if a large amount of organic carbon source material is used, strong bonds between carbons are formed during the high temperature process during AlN powder synthesis, and after the ring element nitridation reaction of boehmite, extremely hard lumps of AlN and carbon are formed. It becomes a thing. That is, in order to treat a mixture of AlN and carbon in an oxidizing atmosphere and decarburize the AlN powder while suppressing oxidation, it is important to crush the above-mentioned lumps as finely as possible in advance. If the lumps are harder than necessary, not only will it take a long time to crush them, but also impurities will inevitably be mixed in during the crushing process.
The residual carbon content also increases. For the above reasons, if the ratio of carbon obtained from the organic carbon source material to solid carbon powder is less than 0.05, the effect of addition is so small that it is virtually unrecognizable, and if this ratio exceeds 0.5, reduction occurs. After the reaction, the lumps of AlN and carbon become extremely hard.
It is regulated between 0.05 and 0.5. The reason why the mixing weight ratio of the total carbon content in the carbon source material to the boehmite powder was limited to a range of 0.4 to 3.0 is as follows. When the weight ratio is less than 0.4, alumina remains even after reductive nitriding, and the particle size also becomes large. If the weight ratio exceeds 3.0, the production efficiency of AIN powder becomes extremely low and is not practical. According to the present invention, fine (1 μm or less) AlN powder with an extremely narrow particle size distribution can be stably produced with good reproducibility. The present invention further improves the prior art in the following two points. (a) By incorporating an appropriate amount of water-soluble organic carbon source material,
The average particle size was smaller and the particle size distribution was narrower, resulting in improved formability and sinterability. (b) AlN that allows carbon to be dispersed in an earlier application
It is extremely sensitive to the properties of the powder and greatly affects it. In contrast, in the present invention, manufacturing variations are small. The AlN powder of the present invention can be easily purified by using high-purity raw material boehmite, for example, the total amount of metal ion impurities can be
It can easily be obtained with a purity of 200 ppm or less. Furthermore, in the present invention, fine boehmite powder and carbon powder are uniformly mixed, so during reductive nitriding,
Impurities such as F ₂ O ₃ and SiO ₂ are easily reduced and volatilized, and as a result, even higher purity AlN powder can be obtained. Further, by using the AlN powder of the present invention, a highly pure and dense sintered body (density of 99% or more) can be easily obtained. [Example] A mixture for producing AlN was prepared using the formulations shown in Table 1, and the mixture was fired at 1450°C for 5 hours in a nitrogen atmosphere, and then decarburized at 650°C for 3 hours.
Got the powder. In Table 1, ... are examples that meet the manufacturing conditions of the present invention, and ... are comparative examples. Mixtures were prepared for all of these using the following procedure. 20% by weight boehmite sol dispersed at PH = 3.0, a dispersant and water were added to solid carbon, and mixed in a pot mill for 10 minutes.
A 15% by weight carbon dispersion obtained by kneading for hours is prepared in advance. After mixing both, a predetermined amount of a water-soluble organic carbon source substance is added. After the addition, the mixture is heated to remove water while stirring, gelatinized, and then dried. The particle size distribution of the above nine types of AlN powders is shown in FIG. 1, and the Al ₂ O ₃ and carbon contents after the nitriding reaction and after decarburization are shown in Table 2. ~ in Figure 1 and Table 2 correspond to ~ in Table 1, respectively. From Figure 1 and Table 2, we were able to confirm the following. Comparative example, the particle size is coarse and _AlBO3 in AlN
The remaining amount is also larger compared to the examples. Furthermore, the particle size distribution and Al ₂ O ₃ content of the obtained AlN powder tend to vary between production lots. The example is compared to the comparative example.
The particle size is fine, the particle size distribution is narrow, and the variation between lots is small. The amount of Al ₂ O ₃ remaining after decarburization and the amount of carbon remaining are also small. In the comparative example, since the lumps after the nitriding reaction were too hard, impurities were likely to be mixed in during pulverization. Even when alumina porcelain is used, the Al ₂ O ₃ content increases due to crushing (Table 2). In addition, the comparative example had a large amount of carbon remaining after decarburization. In the comparative example, a large amount of Al ₂ O ₃ remains after the nitriding reaction, and the particle size of the AlN powder is also coarse.

【table】

[Table] ** Decarburized after being crushed using an alumina crusher.
[Effects of the Invention] The present invention provides high purity, fine and uniform particle size.
It has become possible to produce AlN powder extremely stably and with good reproducibility. By using this AlN powder, high density,
This makes it easy to produce AlN sintered bodies with high thermal conductivity and high strength, which greatly contributes to their use in high-temperature structural materials, IC substrates, etc.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the particle size distribution of AlN powder synthesized by various methods.

Claims (1)

[Claims] 1 Add boehmite powder to a liquid containing water and adjust the pH.
Aluminum nitride powder is produced by preparing a boehmite sol with the boehmite powder adjusted to 1.2 to 4.5, mixing the boehmite sol with a carbon source material, drying, and then firing in a non-oxidizing atmosphere containing nitrogen. In the manufacturing method, a carbon source material containing carbon obtained from an organic carbon source material and solid carbon powder is blended in a weight ratio of 0.05 to 0.5, and the total carbon amount in the carbon source material and the boehmite powder are and in weight ratio
A method for producing aluminum nitride powder, characterized by mixing at a ratio of 0.4 to 3.0.