JPS6278103A - Production of aluminum nitride powder - Google Patents

Abstract

PURPOSE:To produce AlN powder having fine particle size, high purity and low impuritya and oxygen contents, by calcining granules containing alumina powder or Al(OH)3 powder and carbon powder in N2 or NH3 atmosphere. CONSTITUTION:Alumina powder or Al(OH)3 powder having an average particle diameter of <=5mum and a purity of >=99.0wt% is mixed with carbon powder having an average particle diameter of <=1mum and a purity of >=95wt% at a weight ratio of 1:(0.34-0.37) and the mixture is dispersed in the presence of an aqueous medium to obtain a slurry mixture, which is spray-dried to form granules. The granules are calcined at 1,400-1,700 deg.C in N2 or NH3 atmosphere.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a method for producing aluminum nitride powder.

[Technical background of the invention and its problems]

Sintered bodies of aluminum nitride (AtN) are attracting attention as various high-temperature materials because they have properties such as high thermal conductivity, corrosion resistance, and high strength.

By the way, the following two typical methods are conventionally known as methods for synthesizing AtN powder, which is a raw material for the above-mentioned AtN sintered body. That is, there are two methods: one is to directly nitride metallic At powder, and the other is to sinter a mixed powder of alumina and carbon in a nitrogen gas-containing atmosphere.

However, in the former method, impurities are mixed in in the process of pulverizing the raw material At to increase the nitriding rate and in the process of pulverizing the produced AtN to a particle size of several μm or less in order to make it suitable as a raw material for firing. Secondary contamination cannot be avoided. Also, since kl remains, the scattered form i
The result is an AtN powder containing metal impurities of close to 50%. on the other hand,
According to the latter method, AtN is relatively fine and has uniform particle size.
Can synthesize powder. However, it is difficult to carry out the nitriding reaction completely, and 1% of unreacted alumina remains. Moreover, even with this method, in many cases pulverization is required to obtain fine powder of several μm or less, which leads to secondary contamination such as metal impurities and oxygen. The AtN powder obtained has a high content of metal oxides and oxygen, and the AtN sintered body produced using these AtN powders as raw materials has a low purity (AtN
There was a problem in that the original characteristics were not fully exhibited.

In addition, these AtN powders have difficulty in sinterability, so
This required the addition of sintering aids and high temperature and high pressure sintering conditions. For this reason, it has been difficult to obtain an AtN sintered body in an industrially satisfactory manner.

[Object of the Invention] “The present invention aims to provide a method for producing high-purity AtN powder that is ultrafine and has a low content of impurities and oxygen.

[Summary of the invention]

In the present invention, alumina powder or aluminum hydroxide powder with an average particle size of 5 μm or less and carmen powder with an average particle size of 1 μm or less are mixed in the presence of an aqueous medium to form a slurry mixture, and this mixture is spray-dried. It is characterized in that it is made into granules and then fired at a temperature of 1,400 to 1,700° C. in an atmosphere of elementary or ammonia.

The alumina powder or aluminum hydroxide powder preferably has a purity of 99.0 weight or more, preferably 99.9 weight or more. Further, it is desirable to use carbon powder having a purity of 95% by weight or more, preferably 99 weight fjks 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 to 1 μm or less is that if the particle size exceeds 5 μm or 1 μm, it will not work in the presence of an aqueous medium. This is because the mixing and dispersibility of the resin decreases, resulting in decreased reactivity during firing and cargane residue.

It is desirable that the mixing ratio of the alumina powder or aluminum hydroxide and carbon is set in the range of 1:0.35 to 0.37 (aluminum hydroxide is equivalent to alumina). The reason for this is that if the mixing ratio of these components deviates from the above range, alumina and carbon may be present in the AtN powder obtained by firing. This is because there is a risk that the particles may remain and impede high purity. The mixing ratio of aluminum hydroxide powder and carbon powder is in the range of 1:0.22 to 0.24.

The most important feature of the present invention is that alumina powder or aluminum hydroxide powder and carbon powder are dispersed in the presence of an aqueous medium. That is, when mixing and dispersing the pixel raw material in an aqueous medium, fine carbon particles are added to the surface of the large particle size alumina or aluminum hydroxide powder by using a surface modifier that controls the characteristics of the particle surface of the pixel raw material in water. The powder can be agglomerated and then spray-dried into granules. Therefore, by firing such granules, the reduction of alumina or alumina converted from aluminum hydroxide can proceed completely with the minimum necessary amount of carbon powder. As a result, the required amount of carbon powder is almost the theoretical amount, so there is almost no carbon that becomes an impurity in the AtN powder after firing, leading to an increase in the amount of oxygen (as well as decarburization that requires a complicated process). No processing required.

During the dispersion mixing using the aqueous medium, the manufacturing advantages are not impaired even if a binder that is convenient for forming the product into granules is used. Also mixed.

Needless to say, care must be taken not to reduce the purity of the raw materials during the dispersion and drying steps.

The temperature of the granular mixture is 1400-1700°C.

Preferably, the temperature is 1450 to 1650°C.

If the firing temperature is lower than 1400°C, the reaction will not proceed smoothly, but if the temperature exceeds 1700°C, the particle size of the AtN powder produced will become coarse.

[Embodiments of the invention]

The present invention will now be described in detail.

Example 1 100% aluminum powder with a purity of 99.9% by weight and an average particle size of 0.5 μm. F and ash content 0.1% by weight or less, average particle size 0.0
2μm car? After placing 35.4 g of the powder in a plastic pot containing 1 bottle of plastic, pure water, a surfactant, and a binder were added to the pot, and the mixture was mixed and dispersed for 1 hour. Subsequently, the obtained slurry was spray-dried using a spray dryer to prepare granules having an average particle size of 70 μm. Next, this granular material was loaded into a graphite tray and calcined 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 container at the mixing ratio shown in Table 1 below, and the following procedure was carried out in the same manner as in Example. Five types of granules were prepared. Next, these granules were loaded into a graphite tray and fired under the conditions shown in Table 1 to obtain five types of white powder.

Comparative Example 1 The same alumina powder and carden powder as in Example 1 were mixed in l:o
, 353 (weight ratio), loaded onto a graphite tray, and fired in nitrogen gas at 1550° C. for 5 hours to obtain a powder.

Therefore, the oxygen content, carbon content, average particle size, and constituent phases of the powders of Examples 1 to 6 and Comparative Example 1 were examined.

The results are also listed in Table 1 below. The oxygen and carbon contents in the powder were determined using an instrumental analyzer, and the constituent phases were determined by X-ray diffraction of the powder.

S1 Example 7 100 I of aluminum hydroxide (AA(OH)3) powder with a purity of 99% by weight and an average particle size of 0.8 μm and 23 g of carden powder with an ash content of 0.2 weight or less and an average particle size of 0.02 μm were made into plastic. After storing the mixture in a plastic pot containing a bottle, pure water, surfactant, and binder were added to the pot and mixed for 1 hour.

Dispersed. Subsequently, the obtained slurry was spray-dried using a spray dryer to prepare granules having an average particle size of 80 μm. Next, this granular material was loaded into a graphite tray and calcined in nitrogen gas at 1550° C. for 5 hours to obtain a white powder.

Examples 8 to 12 Aluminum hydroxide powder and carden powder similar to those in Example 7 were placed in a plastic pot containing a plastic ball at the mixing ratio shown in Table 2 below.
Ninety-five types of granules were prepared in a similar manner. Next, these granules were loaded into a graphite tray and fired under the conditions shown in Table 2 to obtain five types of white powder.

Comparative Example 2 As in Example 7, aluminum hydroxide powder and carden powder were mixed at a ratio of 1:0.23 (weight ratio), and after loading this into a graphite tray, the mixture was heated at 1550°C in nitrogen gas.
A powder was obtained by firing for 5 hours.

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

〔Effect of the invention〕

As described in detail above, according to the present invention, ultrafine, highly pure aluminum nitride powder with low impurities and oxygen content can be produced in a simple process, and the aluminum nitride powder can then be molded as a raw material.

Firing has remarkable effects such as being able to obtain an aluminum nitride sintered body with high sinterability and excellent properties inherent to aluminum nitride.

Claims (2)

[Claims] (1) Alumina powder or aluminum hydroxide powder with an average particle size of 5 μm or less and carbon powder with an average particle size of 1 μm or less are mixed in the presence of an aqueous medium to form a slurry mixture, and this mixture is spray-dried to form granules. 1. A method for producing aluminum nitride powder, which comprises baking at a temperature of 1400 to 1700° C. in an atmosphere of nitrogen or ammonia. (2) Alumina powder or aluminum hydroxide powder (alumina equivalent) and carbon powder in a weight ratio of 1:0.34~
The method for producing aluminum nitride powder according to claim 1, characterized in that the aluminum nitride powder is mixed at a ratio of 0.37.