JPH0647447B2 - Method for producing aluminum nitride powder - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing aluminum nitride powder.

[Technical background of the invention and its problems]

Aluminum nitride (AlN) sintered body has high thermal conductivity,
It is a substance that is drawing attention as a high-temperature material because of its properties such as corrosion resistance and high strength.

By the way, the following two representative methods have been conventionally known as a method for synthesizing an AlN powder as a raw material of the AlN sintered body. That is, there are a method of directly nitriding the metal Al powder and a method of firing a mixed powder of alumina and carbon in an atmosphere containing nitrogen gas.

However, in the former method, impurities are mixed in the step of pulverizing the raw material Al to increase the nitriding rate and the step of pulverizing the generated AlN to a particle size of several μm or less in order to adapt it as a raw material for firing. Secondary pollution is unavoidable. Further, since Al remains, it becomes an AlN powder containing metal impurities of approximately several weight%. On the other hand, according to the latter method, AlN powder having a relatively fine particle size can be synthesized. However, it is difficult to carry out the nitriding reaction completely, and a few wt% of unreacted alumina remains. In addition, in order to obtain a fine powder having a particle size of several μm or less even by such a method, pulverization is required in many cases, which causes secondary contamination such as mixing of metal impurities and oxygen.

Therefore, the AlN powder obtained by the above-mentioned synthesis method has a large amount of metal oxides and oxygen content, and the AlN sintered body produced using these AlN powder as a raw material has low purity and sufficiently exhibits the original characteristics of AlN. There was a problem that was not done. Also,
Since these AlN powders also have difficulty in sinterability, it was necessary to add a sintering aid and sintering conditions of high temperature and high pressure. Therefore, it has been difficult to obtain an AlN sintered body by a method that is industrially satisfactory.

[Object of the Invention]

The present invention is intended to provide a method for producing a high-purity AlN powder that is in the form of ultrafine powder and has a low content of impurities and oxygen.

[Outline of Invention]

In the present invention, an alumina powder or aluminum hydroxide powder having an average particle size of 5 μm or less and a carbon powder having an average particle size of 1 μm or less are mixed in the presence of an aqueous medium to form a slurry-like mixture, and the mixture is spray-dried to obtain the above-mentioned mixture. Aluminum nitride powder characterized by being formed by agglomerating the fine carbon powder on the surface of alumina powder or aluminum hydroxide powder, and then firing at a temperature of 1400 to 1700 ° C. in an atmosphere of nitrogen or ammonia. Is a manufacturing method.

It is desirable to use the alumina powder or aluminum hydroxide powder having a purity of 99.0% by weight or more, preferably 99.9% by weight or more. Further, it is desirable to use carbon powder having a purity of 95% by weight or more, preferably 99% by weight or more.

The reason why the average particle size of the alumina powder or aluminum hydroxide powder is limited to 5 μm or less and the particle size of the carbon powder is 1 μm or less is that when the particle size exceeds 5 μm and 1 μm, respectively, in the presence of an aqueous medium. This lowers the mixing and dispersibility of the compound (1), which leads to a decrease in reactivity during firing and carbon residue.

The mixing ratio of the alumina powder or aluminum hydroxide and carbon is preferably specified in the range of 1: 0.35 to 0.37 (where aluminum hydroxide is converted to alumina). The reason for this is that if the mixing ratio thereof deviates from the above range, alumina or carbon may remain in the AlN powder obtained by firing and impede purification. The mixing ratio of aluminum hydroxide powder and carbon powder is in the range of 1: 0.22 to 0.24.

The greatest feature of the present invention is to disperse alumina powder or aluminum hydroxide powder and carbon powder in the presence of an aqueous medium. That is, when mixing and dispersing amphoteric raw materials in an aqueous medium, the use of a surface modifier that controls the characteristics of the particle surfaces of the amphoteric raw materials in water makes it possible to form fine particles on the surface of alumina or aluminum hydroxide powder having a large particle diameter. It is possible to agglomerate various carbon powders and spray-dry in that state to form granules. Therefore, by firing such a granular material, the reduction of alumina or alumina converted from aluminum hydroxide proceeds completely with the minimum necessary carbon powder. As a result, the required amount of carbon powder is almost the theoretical amount, so there is almost no carbon as an impurity in the AlN powder after firing, which leads to an increase in oxygen content and eliminates the need for a decarburization process, which is a complicated process. Become.

In the dispersion and mixing with the above aqueous medium, the production advantage is not impaired even if a binder which is convenient for making the granules later is used. Needless to say, it is necessary to take care not to reduce the purity of the raw materials in the mixing, dispersion and drying steps.

The granular mixture is calcined in the range of 1400 to 1700 ° C, preferably 1450 to 1650 ° C. If the firing temperature is lower than 1400 ° C, the reaction does not proceed smoothly, but if the temperature exceeds 1700 ° C, the particle size of the produced AlN powder becomes coarse.

Example of Invention

 The embodiments of the present invention are described above.

Example 1 100 g of alumina powder having a purity of 99.9% by weight and an average particle size of 0.5 μm, ash content of 0.1% by weight or less, and an average particle size of 0.02
35.4 g of carbon powder of μm was placed in a plastic pot containing a plastic ball, pure water, a surfactant and a binder were added to the pot and mixed for 1 hour.
Dispersed. Subsequently, the obtained slurry was spray-dried with a spray dryer to prepare a granular material having an average particle size of 70 μm. Next, this granular material was loaded into a graphite tray and baked in nitrogen gas at 1550 ° C. for 5 hours to obtain a white powder.

Example 2 The same alumina powder and carbon powder as in Example 1 were placed in a plastic pot containing a plastic ball at a mixing ratio shown in Table 1 below, and 5 kinds of granules were prepared by the same method as in Example 1 below. Was prepared. Next, these granular materials were loaded into a graphite tray and fired under the conditions shown in Table 1 to obtain 5 types of white powder.

Comparative Example 1 Alumina powder and carbon powder similar to those in Example 1 were used in a ratio of 1:
The mixture was mixed at a ratio (weight ratio) of 0.353, charged in a graphite tray, and then fired in nitrogen gas at 1550 ° C. for 5 hours to obtain a powder.

Therefore, the powders of Examples 1 to 6 and Comparative Example 1 were examined for oxygen content, carbon content, average particle size and constituent phase.
The results are also shown in Table 1 below. The oxygen and carbon contents in the powder were determined by an instrumental analyzer, and the constituent phases were determined by the powder X-ray diffraction method.

Example 7 100 g of aluminum hydroxide (Al (OH) ₃ ) powder having a purity of 99% by weight and an average particle size of 0.8 μm and 23 g of carbon powder having an ash content of 0.2% by weight or less and an average particle size of 0.02 μm were used as plastic balls. After being stored in a plastic pot containing, the pure water, the surfactant and the binder were added to the pot and mixed and dispersed for 1 hour. Then, the obtained slurry is spray-dried with a spray dryer to obtain an average particle size of 80.
A μm granular material was prepared. Next, this granular material was loaded into a graphite tray and fired in nitrogen gas at 1550 ° C. for 5 hours to obtain a white powder.

Examples 8 to 12 The same aluminum hydroxide powder and carbon powder as in Example 7 were housed in a plastic pot containing a plastic ball in the mixing ratio shown in Table 2 below, and then, in Example 7 below.
Five kinds of granular materials were prepared by the same method as described in (1). Next, these granular materials were loaded into a graphite tray and fired under the conditions shown in Table 2 to obtain 5 kinds of white powders.

Comparative Example 2 The same aluminum hydroxide powder and carbon powder as in Example 7 were mixed at a ratio (weight ratio) of 1: 0.23, and this was loaded on a graphite tray, and then, at 1550 ° C. in nitrogen gas,
The powder was obtained by firing for 5 hours.

Then, the oxygen content, the carbon content, the average particle size and the constituent phases of the powders of Examples 7 to 12 and Comparative Example 2 were examined. The results are also shown in Table 2 below.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to produce a high-purity aluminum nitride powder that is ultrafine and has a low content of impurities and oxygen in a simple process, and by using the aluminum nitride powder as a raw material. By carrying out molding and firing, there are remarkable effects such as high sinterability and the ability to obtain an aluminum nitride sintered body having excellent characteristics inherent to aluminum nitride.

Claims (2)

[Claims] 1. Alumina powder or aluminum hydroxide powder having an average particle size of 5 μm or less and carbon powder having an average particle size of 1 μm or less are mixed in the presence of an aqueous medium to form a slurry mixture, and the mixture is spray-dried. Aluminum nitride characterized in that the fine carbon powder is agglomerated on the surface of the alumina powder or aluminum hydroxide powder to form a granule, which is then fired at a temperature of 1400 to 1700 ° C. in an atmosphere of nitrogen or ammonia. Powder manufacturing method. 2. Alumina powder or aluminum hydroxide powder (calculated as alumina) and carbon powder in a weight ratio of 1:
The method for producing the aluminum nitride powder according to claim 1, wherein the aluminum nitride powder is mixed in a ratio of 0.34 to 0.37.