JPH0563406B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an aluminum nitride powder in which the degree of agglomeration of primary particles is small, and a method for producing the same. (Prior Art) Aluminum nitride powder has recently been in the spotlight as a raw material for aluminum nitride sintered bodies, which have high thermal conductivity and are extremely useful as electronic materials. Aluminum nitride powder is, for example,
It is known from the publication No. 59-50008. The aluminum nitride powder described in the above publication has high purity and fine particles, and is used as a raw material for an aluminum nitride sintered body having excellent properties such as high thermal conductivity and translucency. That is, the above publication describes an aluminum nitride powder that has an average particle size of 2 μm or less, has an oxygen content of 1.5% by weight or less, and contains cationic impurities of 0.3% by weight or less when the aluminum nitride composition is AlN. It is shown. (Problems to be Solved by the Invention) The above-mentioned aluminum nitride powder has high purity and fine particles, and thus serves as a raw material for an aluminum nitride sintered body having excellent properties. However, when the above aluminum nitride powder is sintered after being formed into a sheet etc., the shrinkage rate due to sintering is large.
The dimensional stability was not fully satisfactory. (Means for Solving the Problems) Therefore, the present inventors have conducted research with the aim of obtaining aluminum nitride powder that has a relatively small shrinkage rate during sintering and has good dimensional stability.
As a result, it was discovered that an aluminum nitride powder having a specific relationship between the average particle size calculated from the specific surface area and the average particle size measured by the sedimentation method achieves the above object, and the present invention was completed. Ivy. That is, in the present invention, the average particle diameter (D ₁ ) calculated from the specific surface area and the average particle diameter (D ₂ ) measured by the sedimentation method are determined by the following formula: 0.2 μm≦D ₁ ≦1.5 μm D ₂ /D ₁ ≦2.60 This is an aluminum nitride powder that satisfies both of the following. The specific surface area in the present invention is obtained by nitrogen gas adsorption using the BET method. The average particle diameter (D ₁ ) can be determined from this specific surface area by converting it into a true sphere. Average particle diameter (D ₁ ) determined using this method
represents the primary particle size of aluminum nitride powder. On the other hand, the average particle size (D ₂ ) measured using a sedimentation method, for example, Horiba's automatic particle size distribution analyzer CAPA-500, represents the average particle size of aggregated particles formed by agglomeration of primary particles. . In the present invention, the average particle diameter (D ₁ ) calculated from the above specific surface area must be in the range of 0.2 μm≦D ₁ ≦1.5 μm. Aluminum nitride powder with a D ₁ of less than 0.2 μm has a large specific surface area and accordingly an excessively large oxygen content, making it impossible to obtain a sintered body with excellent physical properties. Aluminum nitride powder with D ₁ exceeding 1.5 μm cannot be sintered to a sufficient degree, making it impossible to obtain a dense sintered body. The above average particle size (D ₁ ) is 0.3 μm≦D ₁ ≦1.0 μm
The range is preferably 0.3 μm≦D ₁
More preferably, the range is ≦0.7 μm. Next, the average particle size (D ₁ ) calculated from the specific surface area and the average particle size (D ₂ ) measured by the sedimentation method are as follows:
D ₂ /D ₁ must be 2.60. If the value of D ₂ /D ₁ exceeds 2.60, aluminum nitride powder with a sufficiently small shrinkage rate during sintering cannot be obtained. D ₂ /D ₁ is preferably 2.50 or less, and more preferably 2.40 or less from the viewpoint of dimensional stability. When aluminum nitride powder is produced by the method described below, generally 2.00≦
Powders in the range D ₂ /D ₁ ≦2.60 can be obtained. Incidentally, the aluminum nitride powder described in JP-A-59-50008 mentioned above has a specific surface area (4.2
The average particle diameter (D ₁ ) calculated from m ² /g) is 0.44 μm.
and the average particle size (D ₂ ) measured by the sedimentation method.
is 1.22 μm, and D ₂ /D ₁ =2.77. The aluminum nitride powder of the present invention has D ₂ /D ₁ ≦
2.60, it can be said that the powder has a relatively small degree of aggregation of primary particles. The aluminum nitride powder of the present invention only needs to satisfy the above conditions, but in order to obtain an aluminum nitride sintered body with further excellent thermal conductivity, it is necessary to have a low oxygen content and cationic impurities. preferable. That is, when AlN has an aluminum nitride composition, the oxygen content as an impurity is 1.5% by weight or less,
Aluminum nitride powder containing 0.3% by weight or less of cationic impurities is preferred. Furthermore, aluminum nitride powder having an oxygen content of 0.4 to 1.3% by weight and a cationic impurity of 0.2% by weight or less is more suitable. Note that aluminum nitride in the present invention is a 1:1 compound of aluminum and nitrogen, and anything other than this is treated as an impurity. However, the surface of aluminum nitride powder is inevitably oxidized in the air.
Al-N bonds are replaced by Al-O bonds,
This bonded Al is not considered a cationic impurity.
Therefore, metal aluminum that does not have Al--N or Al--O bonds is a cationic impurity. The aluminum nitride powder in the present invention may be obtained by any method. A typical method for producing aluminum nitride powder that is generally suitably employed will be described below.
Carbon, which is a raw material in the present invention, has a specific specific surface area and oil absorption amount. That is, the specific surface area is 60
m ² /g or more, preferably 100 to 300 m ² /g.
In addition, the oil absorption amount is 80c.c./g or more, preferably 100c.c./g or more.
~200c.c./g. If the specific surface area and oil absorption amount are out of the above range, the aluminum nitride powder of the present invention described above cannot be obtained. Furthermore, the apparent density of carbon often affects the degree of aggregation of the resulting primary particles of aluminum nitride powder. Among the above-mentioned aluminum nitride powders of the present invention, in particular when obtaining one in which D ₂ /D ₁ ≦2.50, the apparent density of carbon is preferably 1.90 to 2.10 g/cc. As for the alumina which is one of the raw materials, one represented by Al ₂ O ₃ can be used without any restriction. It may also be alumina obtained by firing an aluminum compound that can be turned into alumina by firing as described below, such as aluminum chloride, aluminum sulfate, aluminum nitrate, alum, or aluminum hydroxide. That is, an aluminum compound that can be turned into alumina by firing is mixed with carbon,
The present invention can also adopt a method in which the aluminum compound is decomposed into alumina by firing under the conditions described below, and then the aluminum compound is further fired to perform a nitriding reaction. The average particle diameter of alumina is preferably 2 μm or less, preferably 1 μm or less, as measured by a sedimentation method, in view of the ease with which the nitriding reaction progresses. Most of the impurities contained in the raw materials carbon and alumina described above remain in the aluminum nitride powder as impurities. Therefore, in order to obtain high purity aluminum nitride powder, the ash content of carbon should be 0.3% by weight or less, preferably 0.2% by weight or less, and the purity of alumina should be 99.0% by weight or more, preferably 99.5% by weight or more. It is preferable that there be. The mixing ratio of alumina and carbon is generally 1:0.4
~1:3 range, preferably 1:0.4~1: to reduce the amount of impurities mixed in from carbon ash.
A range of 0.7 is preferred. Mixing may be done either dry or wet, but wet mixing is usually preferred in order to achieve sufficient mixing. Generally, it is preferable to use a ball mill as the mixing means, but it is preferable that the containers, balls, etc. used in this case be made of high-purity alumina or plastic to prevent contamination with impurities as much as possible. Examples of the ball mill include known ones, such as a rotary ball mill and a vibroball mill. Mixing by an attritor may also be employed. Further, in order to increase the reaction rate and minimize the amount of unreacted alumina, it is preferable to perform sufficiently uniform mixing. The mixed powder is fired in a firing furnace at a temperature of 1300 to 1700°C, preferably 1450 to 1650°C, for usually 3 to 10 hours to obtain the aluminum nitride powder of the present invention. If the firing temperature is lower than the above lower limit temperature, the nitriding reaction will not proceed sufficiently and the desired aluminum nitride powder may not be obtained, which is not preferable. In addition, when the firing temperature is higher than the above-mentioned upper limit temperature, the nitriding reaction proceeds sufficiently, but the particle size of the aluminum nitride powder that is produced often becomes large or the agglomeration becomes significant, making it difficult to obtain the fine powder of the present invention. This is not preferable because it may not be possible. During the firing, it is preferable to take care to ensure that the materials of the firing furnace and the firing boat do not cause impurities. In addition, the firing atmosphere is preferably an atmosphere containing nitrogen, usually high-purity nitrogen gas or a gas in which ammonia gas is added to it.Usually, these reaction gases are continuously supplied in sufficient quantities to allow the nitriding reaction to proceed. Alternatively, baking may be performed while feeding intermittently. Since the above-fired mixture contains unreacted carbon in addition to the aluminum nitride powder, it is generally preferable to sinter the mixture at a temperature of 650 to 750°C in air or oxygen to oxidize and remove the remaining carbon. If the oxidation temperature is too high, the surface of the aluminum nitride powder will be excessively oxidized, making it difficult to obtain the desired powder, so it is preferable to select an appropriate oxidation temperature and time. (Effects) The aluminum nitride powder of the present invention has a small degree of aggregation of primary particles. Therefore, when sintering is performed using the aluminum nitride powder of the present invention, the linear shrinkage rate can be reduced to 20% or less, and further to 18% or less. As described above, the aluminum nitride powder of the present invention has good dimensional stability, and can reduce the difference in shrinkage rate with metal, especially in the simultaneous firing method in which a high-melting point metal paste is printed on the surface and fired. It is preferably used because it can. Furthermore, when aluminum nitride powder with low oxygen content and cationic impurities is used as a raw material, in addition to the above effects, it is possible to obtain an aluminum nitride sintered body that has high thermal conductivity and even translucency. can. (Examples) In order to explain the present invention more specifically, Examples and Comparative Examples are listed below, but the present invention is not limited to these Examples. In addition, measurements of various physical properties in the following Examples and Comparative Examples were performed by the following methods. (1) Carbon ash content: Calculated from the weight after ashing at 750°C according to JIS K-6221-1970. (2) Oil absorption amount of carbon: determined from the amount of dibutyl phthalate dropped according to JIS K-6221-1970. (3) Specific surface area: Determined by the BET method using N ₂ adsorption.
(Using "Flowsorb 2300" manufactured by Shimadzu Corporation) (4) Apparent density: Determined by helium displacement pressure comparison method. (Using “Autopycnometer 1320” manufactured by Shimadzu Corporation) (5) Average primary particle diameter of AlN powder (D ₁ ) D ₁ (μm) = 6/S×3.26 S: Specific surface area of AlN powder (m ² / g) 3.26: AlN powder true density 6: Constant (6) Average agglomerated particle size (D ₂ ) of AlN powder: Determined by centrifugal sedimentation method. (Manufactured by Horiba, Ltd. "CAPA 500"
(7) Amount of impurities in AIN powder Cation impurities: The powder was melted in alkali, neutralized with acid, and quantified by ICP emission spectrometry analysis of the solution. (Using "ICPS-1000" manufactured by Shimadzu Corporation) Amount of impurity carbon: Powder was burned in an oxygen stream and determined from the amount of CO and CO ₂ gas generated.
(Using ``EMIA-110'' manufactured by Horiba, Ltd.) Impurity oxygen content: Determined from the amount of CO gas generated by high-temperature pyrolysis of powder in a graphite crucible. (Manufactured by Horiba, Ltd.) “EMGA
2800") (8) Sheet compact density (d (g)): Disperse AlN powder and dispersant in an organic solvent to form a slurry, and mold this using the doctor blade method. Calculate the green density from the dimensions and weight,
From this value, the compacted density of only the AlN powder was calculated. d(g) = (Green density of green body) x (AIN weight in slurry) / (Slurry weight) - (Paid solvent weight) (9) AlN sintered body density (d(s)): Obtained by Archimedes method . (Manufactured by Toyo Seiki Co., Ltd.) “High precision hydrometer D
-H") (10) Thermal conductivity of AlN sintered body: Determined by the laser flash method, and thickness correction was performed using a calibration curve. (manufactured by Rigaku Denki Co., Ltd. "Thermal constant measuring device PS-7"
(11) Shrinkage rate during sintering: Determined by measuring dimensions before and after sintering. Shrinkage rate = (1 - sintered body size / molded body size before sintering) x
100 Example 1 500 g of Al ₂ O ₃ with a purity of 99.99%, an average particle diameter of 0.52 μm measured by a sedimentation method, and a specific surface area of 8.1 m ² /g,
500 g of each type of carbon shown in Table 1 was mixed using a nylon pot and a ball. The mixed powder was placed in a high-purity graphite crucible and heated at 1600℃6 under a flow of _N2 gas.
heated for an hour. The reaction mixture was heated in air at 700 °C for 10
The mixture was heated for a period of time to oxidize and remove unreacted carbon.
The X-ray diffraction pattern of the obtained powder showed only the AlN peak in all experimental examples except Experiment No. 9, and no α-Al ₂ O ₃ diffraction line was observed.
In Experiment No. 9, a slight α-Al ₂ O ₃ peak was observed. Next, 400 g of each of the obtained powders, 24 g of Ca ₃ Al ₂ O ₆ , 4 g of sorbitan triolate, 132 g of toluene, and 108 g of ethanol were charged into a nylon pot with an internal volume of 4.8 g, and mixed for 24 hours using a nylon-coated ball. Add polyvinyl butyral to the mixed slurry
28g, benzyl butyl phthalate 28g, toluene
44 g and 36 g of ethanol were added, and the mixture was further mixed in a ball mill for 24 hours. The resulting slurry has a viscosity of
Vacuum defoaming was carried out until the pressure reached 20,000 cps (at 25°C). The defoamed slurry was molded using a doctor blade sheet molding method to obtain a molded product with a thickness of 1 mm. This molded body was punched out using a 34 mm□ mold to be used as a sample for a sintering test. The punched compact was degreased in air at 600°C for 3 hours in a Matsufuru furnace. This molded body was then placed in a graphite crucible whose inner wall was coated with BN slurry, and a sintering test was performed. Sintering is
The heating rate was 5°C/min from room temperature to 1800°C in a N ₂ stream, and the temperature was maintained at 1800°C for 7 hours, followed by natural cooling. The obtained sintered body has thermal conductivity,
It was subjected to measurements of dimensions and density. The results are summarized in Table 1. In Table 1, Experiments No. 9 and No. 10 are comparative examples.

[Table] Example 2 AlN powders with mainly different particle sizes were synthesized in the same manner as in Example 1, and then sheet molded, degreased, and
Sintering was performed and various evaluations were performed. The results are shown in Table 2. In the table, Experiment Nos. 6, 7, and 8 are comparative examples.

【table】

Claims (1)

[Claims] 1. The average particle diameter (D ₁ ) calculated from the specific surface area and the average particle diameter (D ₂ ) measured by the sedimentation method are expressed by the following formula: 0.2 μm≦D ₁ ≦1.5 μm D ₂ /D ₁ ≦ 2.60 Aluminum nitride powder. 2. A mixed powder of carbon and alumina having a specific surface area of 60 m ² /g or more and an oil absorption of 80 c.c. / g or more is fired at 1300 to 1700°C in an atmosphere containing nitrogen. A method for producing aluminum nitride powder according to claim 1.