JPH0459610A - Production of readily sinterable aluminum nitride powder - Google Patents

Abstract

PURPOSE:To obtain readily sinterable AlN powder with hardly any coarse and aggregated particles by mixing alumina powder with carbon powder and specific amounts of a nonionic surfactant and an anionic surfactant in water dispersing medium, regulating the pH and thermally reacting the mixture in a nitrogen-containing atmosphere. CONSTITUTION:(A) Alumina powder is mixed with (B) carbon powder, (C) a nonionic surfactant (e.g. polyoxyethylene nonyl phenyl ether) in an amount of 5-20 pts.wt. based on 100 pts.wt. component (B) and (D) an anionic surfactant (e.g. ammonium salt of a polycarboxylic acid) in an amount of 1-10 pts.wt. based on 100 pts.wt. component (A) in water dispersion medium. The pH of the water dispersing medium is subsequently regulated within the range of 9-13. The regulated mixture is then thermally reacted in a nitrogen-containing atmosphere (e.g. nitrogen gas) to afford readily sinterable aluminum nitride powder. An AlN sintered compact, having a high density and thermal conductivity and hardly containing pores cane readily be obtained by using the aforementioned powder.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing easily sinterable aluminum nitride powder. The present invention relates to a method for obtaining aluminum nitride powder with few particles and a sharp particle size distribution.

[Conventional technology]

Alumina has traditionally been widely used for highly reliable IC substrates or paracane materials. High integration of LSI etc.
With the increase in speed and output, the amount of heat generated from semiconductor chips increases, and the need to efficiently dissipate heat outside the system increases.Therefore, there is a demand for a material that has better thermal conductivity and better heat dissipation than alumina. has been done.

Aluminum nitride has high thermal conductivity and excellent electrical properties such as insulation resistance, dielectric strength, dielectric constant, and mechanical properties such as strength, and is attracting attention as an IC substrate and paracane material with excellent heat dissipation. .

Methods for producing aluminum nitride powder include direct nitriding, in which metal aluminum powder is heated in a nitrogen-containing atmosphere to nitride it, and a mixture of alumina or alumina hydrate and carbon is heated in a nitrogen-containing atmosphere to nitride it. There are two representative methods known in the past: the reduction nitridation method.

The former method usually uses high-purity aluminum powder or foil as a raw material, or an oxide film is present on the surface of these, and is contained in aluminum nitride as an oxygen impurity after the nitriding reaction. Furthermore, due to the exothermic reaction, lumpy products are likely to be produced due to aluminum welding, and it is necessary to grind the product to adjust the particle size after the nitriding reaction.

For this reason, impurities are easily mixed in, making it difficult to obtain highly pure aluminum nitride powder. Therefore, as a method for obtaining high purity aluminum nitride powder to obtain high thermal conductivity,
The latter reductive nitriding method is seen as promising.

[Problem to be solved by the invention]

It is already known that this reductive nitriding method uses high-purity fine powder alumina as a raw material to obtain high-purity aluminum nitride powder that retains the characteristics of the raw material.

However, sintering of alumina occurs during the nitriding reaction process, and as a result, the current situation is that only aluminum nitride powder with a broad particle size distribution containing coarse or agglomerated particles compared to the raw material alumina powder is obtained.

When sintering is performed using a powder with a broad particle size distribution including many coarse particles or agglomerated particles, sinterability is generally poor and a sintered body containing many pores is likely to be obtained. In the case of aluminum nitride, in particular, pores cause a decrease in thermal conductivity, so a raw material powder with few coarse or aggregated particles and a sharp particle size distribution is desired.

In the production of aluminum nitride powder by the alumina reduction nitriding method, it is necessary to sufficiently mix and disperse raw materials alumina powder and carbon powder. By nature, alumina powder has a hydrophilic surface, while carbon powder has a lipophilic surface. It is very difficult to uniformly mix and disperse powders having these contradictory surface characteristics in a dispersion medium.

Generally, in an aqueous dispersion medium, alumina powder is highly dispersed in an acidic region, while carbon powder is highly dispersed in an alkaline region, so the dispersibility of alumina powder is usually prioritized and manufactured in an acidic region. .

Therefore, there was a problem in that the aluminum nitride powder obtained by this method contained a large amount of coarse particles or agglomerated particles. In order to improve this point, Japanese Patent Application Laid-Open No. 60-60910
A method using an organic solvent as a dispersion medium as disclosed in the above publication has also been proposed, but the method was not always satisfactory.

In addition, in order to improve sinterability, a method is known in which aluminum nitride powder is coated with a sintering aid in advance, and in this case, Ca(NO3)2
or Y(NO3)1 etc. to make Ca(OH)+ or Y(
Since we use a method of precipitating as Ca(OH)3, Ca(OH)3 is precipitated as
).

There is a demand for production in an alkaline region where 0 and Y(0 old) are stably present.

[Means to solve the problem]

In view of these circumstances, the inventors of the present invention have conducted extensive studies and found that in order to improve the mixing and dispersion state of alumina powder and carbon powder in an alkaline region when water is used as a dispersion medium, a nonionic surfactant and a nonionic surfactant have been developed. By using both anionic surfactants, we have discovered a method to prevent alumina from sintering with each other during the nitriding reaction process, and to produce easily sinterable aluminum nitride powder with a uniform particle size distribution and few coarse or agglomerated particles. , which led to the completion of the present invention.

That is, the present invention provides a method for producing aluminum nitride powder by mixing alumina powder and carbon powder in an aqueous dispersion medium and heating and reacting the mixture in a nitrogen-containing atmosphere. Add 5 to 20 parts by weight of anionic surfactant to 100 parts of alumina powder, and adjust the pH of the aqueous dispersion medium to a range of 9.0 to 13.0. The present invention provides a method for producing easily sinterable aluminum nitride powder, which is characterized by the following.

The present invention will be explained in detail below.

The purity and particle size of the aluminum nitride powder obtained in the present invention approximately correspond to the purity and particle size of the alumina powder used as the raw material. Therefore, the purity and particle size of the raw material alumina powder can be appropriately selected in consideration of the intended purity and particle size of the aluminum nitride powder.

However, when a large alumina powder with a center particle size of 10 μm or more is used as a raw material, heating at a high temperature for a long time is required to allow the nitriding reaction to proceed sufficiently. In addition, when using alumina powder containing coarse particles or aggregated particles as a raw material, it is inevitable that coarse particles or aggregated particles will be mixed in the aluminum nitride powder produced even if the raw materials are thoroughly mixed and dispersed. .

In addition, metal impurities such as iron, magnesium, silicon, and titanium are known to have a negative effect on the thermal conductivity of sintered bodies, so in order to obtain aluminum nitride powder with excellent sinterability, it is necessary to It is preferable to select alumina powder as the raw material, which has a particle size of 10 μm or less, preferably 5 μm or less, and contains metal impurities such as iron, magnesium, silicon, titanium, etc., or 1100 pp or less.

Such alumina powders include low soda alumina,
High-purity alumina and easily sinterable alumina of commonly sold grade can be used. Also,
As the carbon powder, use is made of highly pure, finely graded carbon powder, preferably having a secondary particle diameter of 1 μm or less and an ash content of 0.3% by weight or less.

As such carbon powder, acetylene black, furnace black, channel black, thermal black, etc. are known, and among these, acetylene black is preferable in terms of higher purity. Further, from the viewpoint of ease of handling, it is advantageous to use granular products granulated to a size of 0.3 to 1.5 mm or press-compressed granular products if dispersion is easy.

Polyethylene glycol type surfactants are used as nonionic surfactants, such as polyoxyethylene alkylphenyl ethers such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, or polyoxyethylene. Polyoxyethylene alkyl ethers such as olein ether and polyoxyethylene lauryl ether are known.

The amount added is 5 to 100 parts by weight of carbon powder.
A range of 20 parts by weight is appropriate. If the amount is less than 5 parts by weight, the dispersibility of the carbon powder is insufficient, and only aluminum nitride powder with many agglomerated particles can be obtained.

On the other hand, if it exceeds 20 parts by weight, the dispersibility of the carbon powder becomes saturated, and the cost also increases, which is not preferable.

As the anionic surfactant, carboxylate type surfactants are used, and higher fatty acid sodium salts, polycarboxylic acid ammonium salts, and the like are known.

The amount added is 1 to 100 parts by weight of alumina powder.
A range of 10 parts by weight is suitable. If it is less than 1 part by weight, the dispersibility of the alumina powder will be insufficient, and only aluminum nitride powder with many aggregated particles will be obtained.

On the other hand, if it is more than 10 parts by weight, the dispersibility of the alumina powder becomes saturated, and the cost also increases, which is not preferable.

The above nonionic surfactant and anionic surfactant are added when alumina powder and carbon powder are mixed and dispersed in an aqueous dispersion medium.

The amount of water added is in a weight ratio of 0.5 to 6, preferably 1 to 5, based on the solid components of alumina powder and carbon powder.

Further, it is necessary to adjust the pH of the aqueous dispersion medium to a range of 9.0 to 13.0, and the pH is adjusted using sodium hydroxide, aqueous ammonia, or the like as appropriate. The pH of the aqueous dispersion medium is 9.
If it is less than 0 or more than 13.0, the anionic surfactant will not work sufficiently and the dispersibility of the alumina powder will be insufficient, which is not preferable.

By adjusting the pH of the aqueous dispersion medium to a range of 9.0 to 13.0, alumina powder is highly dispersed, and carbon powder is similarly highly dispersed due to the action of the nonionic surfactant. Uniform mixing of powder and carbon powder,
A dispersed state is obtained, sintering of alumina powders is suppressed in the subsequent nitriding reaction step, and aluminum nitride powder containing no agglomerated grains or coarse grains is obtained.

The mixing ratio of alumina powder and carbon powder is preferably in the range of 3 to 10 in carbon/alumina molar ratio. When the molar ratio is less than 3, unreacted aluminum remains;
Exceeding 1O is not preferable because the amount of unreacted carbon remaining increases, making it difficult to remove and increasing costs.

Mixing and dispersion methods include general methods such as ball mills and ultrasonic dispersion machines, particle granulators,
Although it is possible to use various types of mixers such as a Unilunar mixer, it is preferable to use a device whose parts that come into direct contact are made of a material that does not contain metal impurities.

As such a mixer, it is desirable to use one made of synthetic resin such as polyethylene, nylon, urethane, natural or synthetic rubber, alumina or aluminum nitride, or one lined or coated with these materials.

Normal industrial methods can be used to dry the mixture, but if the viscosity of the slurry during mixing is low and there is a risk of separation of alumina powder and carbon powder during drying, spray drying or freeze drying may be used. It is preferable to use a method such as a rotary evaporator method or the like.

In addition, if necessary, we can also mix and dry 20 μm to 3 mm.
Since it can be granulated into particles of a certain size, granulation has the advantage of making subsequent handling easier.

The powder or granulated mixture thus obtained is heat-treated in an atmosphere containing nitrogen to perform a reductive nitriding reaction, or the atmosphere may be nitrogen, ammonia, nitrogen-ammonia mixed scum, nitrogen- Hydrogen mixed gas, nitrogen-argon mixed gas, etc. can be used.

The heat treatment temperature is usually in the range of 1450 to 1700°C, preferably in the range of 1500 to 1600°C. 14
If it is less than 50°C, it will take a long time for the reduction-nitriding reaction to proceed sufficiently, and if it exceeds 1700'C, coarse particles will be produced in large quantities, which is not preferable. As an economical range, it is most appropriate to maintain the temperature at 1500 to 1600°C for 2 to 6 hours. Furthermore, heat treatment is performed in an oxidizing atmosphere for the purpose of removing excess carbon remaining after the reduction nitriding reaction, and the treatment temperature is 600 to 7500C and 1
~4 hours is appropriate.

For the heat treatment, commonly used equipment such as an oven-type box furnace or a rotary kiln-type rotary furnace can be used.

〔Effect of the invention〕

The aluminum nitride powder obtained in the present invention is an easily sinterable aluminum nitride powder with few coarse grains or agglomerated grains and a sharp particle size distribution. It is possible to easily obtain a sintered body with excellent properties, and it is useful as a raw material powder for producing an aluminum nitride sintered body with excellent thermal conductivity.

〔Example〕

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

In addition, the particle size distribution described in the examples was measured by Sedigraph 5000ET manufactured by M Noho Seisakusho, and the sintered density was measured by a solid specific gravity measuring device using the Archimedes method manufactured by Nohho Seisakusho. The thermal conductivity was measured using a thermal conductivity measurement device T using the laser flash method manufactured by Shinku Riko ■.
Measured using C-7000.

Example 1 255 g of low soda alumina powder with a purity of 99.9% and a center particle size of 0.7 μm and 1 μm or less or 80% and an ash content of 0.00
5% acetylene black (Denki Kagaku Kogyo (ready made 100
% pressed product) 120g, polyethylene glycol (Wako Pure Chemical Industries (ready made #1000) as a viscosity modifier)
．． 8 g (12 parts by weight) of polyoxyethylene alkyl phenyl ether (Daiichi Kogyo Yakuhin (ready made Noigen EA-137) as a nonionic surfactant, 14.4 g (12 parts by weight) of polyoxyethylene alkyl phenyl ether (Daiichi Kogyo Yakuhin (ready made by Noigen EA-137)) as a nonionic surfactant, and ammonium polycarboxylate (Sannopco (produced by Sannopco) as an anionic surfactant). Kiki-made SN Dispersan h 5020,
7.65g (solid content: 40% by weight) converted to solid content
(3 parts by weight) and ion-exchanged water as a dispersion medium.
00g was added and placed in a polyethylene pot of 51 along with 200 urethane balls with a diameter of 25mm, 0.5g of concentrated ammonia water was added to adjust the I)H of the water dispersion medium to 10.5, and the rotation speed was 40 rpm. Mixing was carried out for 10 hours.

After drying the mixed slurry thus obtained in a dryer, 300g of it was packed into a graphite tray and heated at 1550°C for 8 hours using an electric furnace with nitrogen gas flowing at 201/ml. Then, a reductive nitriding reaction was performed. Next, this reaction product was heated to 7008 mL in dry air.
After heating at C for 3 hours, 130 g of aluminum nitride powder was obtained.

The particle size distribution curve of this aluminum nitride powder according to a Sedigraph is shown in FIG. 1 (1).

The center particle size is 1.4 μm, and 92% of the particles are 3 μm or less.
The powder had a sharp particle size distribution with almost no coarse particles or agglomerated particles.

To this powder, 3% by weight of Y2O3 (Japan Yttrium (ready made)) was added as a sintering aid, and the green molded body obtained by press molding at 1500 kg/cm was buried in a mixed powder of aluminum nitride and boron nitride. 180 in nitrogen atmosphere
Sintering was carried out at normal pressure at 0°C and 1850°C for 5 hours.

Table 1 shows the sintered density and thermal conductivity of the obtained sintered body.

Table-1 Sintering temperature Sintering density Thermal conductivity 1800°C3
,16g/cm' 189W/mK1850°C3
, 26g/am' 205W/mK Comparative Example I 0.765g (0.3 parts by weight) of ammonium polycarboxylate as an anionic surfactant in terms of solid content
Aluminum nitride powder was obtained in the same manner as in Example 1 except that the powder was used.

The particle size distribution curve of the obtained powder by Sedigraph is
This is shown in Figure (2).

The center particle size is 2.4 μm, and 66% of the particles are 3 μm or less.
It was a powder with many aggregated particles.

This powder was sintered in the same manner as in Example 1, and the sintered density and thermal conductivity of the obtained sintered body are shown in Table 2.

Table-2 Sintered density Thermal conductivity 2, 86g/am” 135W/mK3.19g/
cm' 189W/mK Sintering temperature 1800°C 1850'C Comparative Example 2 Aluminum nitride powder was obtained in the same manner as in Example 1 except that no anionic surfactant was used.

The particle size distribution curve of the obtained powder by Sedigraph is
It is shown in Figure (3).

The central particle size is 2.2 μm, and 69% of the particles are less than 3 μm.
It was a powder with many aggregated particles.

This powder was sintered in the same manner as in Example 1, and the sintered density and thermal conductivity of the obtained sintered body are shown in Table 3.

Table-3 Sintering temperature Sintering density Thermal conductivity 1800'c
2.95g/cm' 149W/mK18
50°C3,24g/cm' 195W/mK

[Brief explanation of drawings]

FIG. 1 is a graph showing particle size distribution curves of aluminum nitride powders obtained in Examples and Comparative Examples measured using a Sedigraph, and shows the relationship between cumulative weight and particle size. Cumulative mff1 (%) Agent Patent attorney Kokuro Moroishi (and 1 other person) Procedural amendment (voluntary) April 30, 1991 1. Display of case 1990 Patent Application No. 173141 2. Name of invention Easy to burn Relationship with the manufacturing method case for condensed aluminum nitride powder Patent applicant address: 4-5-33 Kitahama, Chuo-ku, Osaka Address: Apparatus 5, 4-5-33 Kitahama, Chuo-ku, Osaka; 'Detailed explanation' column. 6. Contents of the amendment (1) "r 1100pp" on page 7, line 15 of the specification is corrected to "10,100pp for each." (2) "Preparation Co" on page 10, line 4 of the specification is corrected to "adjustment J. (3) In the specification, page 1, line 6, "preparation" is corrected to "adjustment." (4) “Preparation” on page 10, line 10 of the specification is “adjustment”
Correct to. (5) "12 parts by weight" on page 14, line 9 of the specification is corrected to "12 parts by weight J for 100 parts by weight of carbon powder." (6) "12 parts by weight" on page 14, line 12 of the specification 3 parts by weight J is corrected to 3 parts by weight J for 100 parts by weight of alumina powder. (7) "Preparation" on page 14, line 16 of the specification is changed to "adjustment"
Correct to. (8) "8 hours" in the first line of page 15 of the specification is corrected to "5 hours". (9) "0.3 part by weight" on page 16, line 3 of the specification is replaced with "
Corrected to 0.3 parts by weight per 100 parts by weight of carbon powder. that's all

Claims (1)

[Claims] In a method for producing aluminum nitride powder by mixing alumina powder and carbon powder in an aqueous dispersion medium and heating the mixture in a nitrogen-containing atmosphere, 5 to 5 parts by weight of a nonionic surfactant is added to 100 parts by weight of carbon powder. 1 to 10 parts by weight of anionic surfactant is added to 100 parts by weight of alumina powder, and the pH of the aqueous dispersion medium is adjusted to 9.
．． A method for producing easily sinterable aluminum nitride powder, characterized in that the particle diameter is within the range of 0 to 13.0.