JP2680681B2 - Method for producing aluminum nitride powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an aluminum nitride powder having a small degree of aggregation of primary particles.

(Prior Art) Recently, aluminum nitride powder has a high thermal conductivity and has been in the spotlight as a raw material of an aluminum nitride sintered body which is extremely useful as an electronic material. Aluminum nitride powder is known, for example, from JP-A-59-50008. The aluminum nitride powder described in the above publication is 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 light transmittance. That is, in the above publication, an aluminum nitride powder having an average particle size of 2 μm or less, an oxygen content of 1.5% by weight or less, and a cation impurity content 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 is a raw material of an aluminum nitride sintered body having excellent properties because it is highly pure and fine particles. However, when the above aluminum nitride powder is molded into a sheet or the like and then sintered, the shrinkage rate due to the sintering is large, and the dimensional stability is not sufficiently satisfactory.

(Means for Solving the Problem) Therefore, the inventors of the present invention have conducted repeated studies for the purpose of obtaining an aluminum nitride powder having a relatively small shrinkage factor during sintering and good dimensional stability. As a result, the average particle size converted from the specific surface area, the average particle size measured by the sedimentation method, aluminum nitride powder obtained as a raw material alumina powder having a specific relationship, it was found that achieve the above object, The present invention has been completed.

That is, according to the present invention, (a) the particle size (D ₁ ) calculated from the specific surface area and the average particle size (D ₂ ) measured by the sedimentation method are 0.1 μm ≦ D ₁ ≦ 1.0 μm D ₂ / D ₁ A method for producing an aluminum nitride powder, characterized in that a mixed powder of alumina and (b) carbon both satisfying ≦ 8 is fired at 1300 to 1700 ° C. in an atmosphere containing nitrogen.

The specific surface area of the alumina powder in the present invention is that obtained by nitrogen gas adsorption by the BET method. From this specific surface area, the particle diameter (D ₁ ) can be obtained by converting into a true sphere.
The particle size (D ₁ ) obtained by this method represents the primary particle size of the alumina powder.

On the other hand, the sedimentation method, for example, the average particle size (D ₂ ) measured using an automatic particle size distribution analyzer CAPA-500 manufactured by Horiba, Ltd. represents the average particle size of aggregated particles formed by aggregating primary particles.

In the present invention, the particle size (D ₁ ) calculated from the above specific surface area must be within the range of 0.1 μm ≦ D ₁ ≦ 1.0 μm. When an alumina powder having a D ₁ of less than 0.1 μm is used as a raw material, the mutual dispersion of alumina and carbon becomes poor, and the alumina agglomerates during the nitriding reaction, and the intended aluminum nitride powder cannot be obtained. When the alumina powder having D _{1 of more} than 1.0 μm is used as the raw material, the aluminum nitride powder is remarkably agglomerated, though the cause is unknown, and is not suitable for obtaining the intended aluminum nitride powder. The above particle size (D ₁ ) may be in the range of 0.1 μm ≦ D ₁ ≦ 1.0 μm, but is preferably in the range of 0.1 μm ≦ D ₁ ≦ 0.8 μm.

Next, in the alumina powder as a raw material, the particle size (D ₁ ) calculated from the specific surface area and the average particle size (D ₂ ) measured by the sedimentation method must be D ₂ / D ₁ ≦ 8. When alumina having a D ₂ / D ₁ value of more than 8 is used as the raw material, the degree of agglomeration of the produced aluminum nitride powder is significantly increased,
It is not possible to obtain an aluminum nitride powder having a sufficiently small shrinkage rate during sintering. D ₂ / D ₁ is preferably 6 or less, and more preferably 5 or less from the viewpoint of suppressing agglomeration of the produced aluminum nitride powder.

In the present invention, if the above-mentioned D ₁ and D ₂ are specific alumina, known ones can be used without any limitation. For example, alumina obtained by firing aluminum chloride, aluminum sulfate, aluminum nitrate, deuterium oxide, aluminum hydroxide or the like may be any one that satisfies the above particle size conditions.

Further, even alumina which does not satisfy the above-mentioned particle diameter condition can be adopted as a raw material for aluminum nitride powder as long as the above particle diameter condition can be satisfied by classification or mixing. Further, by performing the pulverization treatment, alumina satisfying a predetermined particle size condition can be obtained, and such alumina can also be used as a raw material.
As the pulverization method, any method generally known as an industrial method can be adopted without any distinction. For example, ball mill grinding, air flow grinding (jet mill grinding), attritor grinding, etc. can be used.

Moreover, by subjecting the raw material alumina to the above-mentioned pulverization treatment, the effect that the impurity content of the aluminum nitride powder greatly falls below the estimated value calculated from the impurity content in the alumina is also obtained.

In the present invention, known carbon can be used without limitation as a raw material carbon. In particular, in order to make the obtained aluminum nitride powder highly pure and suppress its agglomeration, the ash content is 0.3% or less, the average particle size is 1 μm or less, and the specific surface area is 60 m ² /
Carbon having g or more and oil absorption of 80 cc / g or more is preferably used.

The impurities in aluminum nitride can be reduced from the estimated amount calculated from the amount of impurities in alumina by pulverizing the raw material alumina, but the impurities in alumina and carbon are at least partly contained as impurities in aluminum nitride. Since it remains, in order to obtain a high-purity aluminum nitride powder, the purity of alumina is 99% by weight or more, preferably 99.5% by weight or more, and the ash content of carbon is 0.3% by weight or less, preferably 0.2% by weight or less. Preferably.

The mixing ratio of alumina and carbon in the method of the present invention is generally in the range of 1: 0.4 to 1: 3, preferably in the range of 1: 0.4 to 1: 0.7 in order to reduce the amount of impurities mixed from carbon ash. is there.

The mixing may be either dry type or wet type. Usually, it is preferable to use a ball mill as the mixing means. However, the container, balls, etc. used at this time are made of high-purity alumina, zirconia, aluminum nitride, or plastic, and the inclusion of impurities should be prevented as much as possible. preferable. Examples of the ball mill include known ones, for example, a rotary ball mill, a vibro ball mill and the like. Mixing with an attritor may also be employed. Further, it is preferable to perform sufficiently uniform mixing in order to increase the reaction rate and minimize the amount of unreacted alumina. Mixed powder is 1300 ~ 1700 by firing furnace
The aluminum nitride powder is obtained by firing at a temperature of ℃, preferably 1450 to 1650 ℃ for 3 to 10 hours. If the sintering temperature is lower than the above lower limit temperature, the nitriding reaction does not sufficiently proceed and the desired aluminum nitride powder may not be obtained, which is not preferable. Further, at a high temperature where the firing temperature exceeds the above-mentioned upper limit temperature, the nitriding reaction sufficiently proceeds, but the particle size of the aluminum nitride powder that is often formed becomes large or agglomeration becomes remarkable, and the desired fine powder of aluminum nitride is obtained. May not be obtained, which is not preferable.

At the time of the firing, it is preferable to consider the materials of the firing furnace material and firing balls so as not to cause impurities. The firing atmosphere is preferably an atmosphere containing nitrogen, usually a high-purity nitrogen gas or a gas obtained by adding an ammonia gas thereto, and the amount of these reaction gases is usually sufficient to allow the nitriding reaction to proceed sufficiently. Alternatively, firing may be performed while intermittently supplying.

Since the mixture after firing contains unreacted carbon in addition to the aluminum nitride powder, the mixture is generally 550 ° C.
It is preferable to calcine in air or oxygen at a temperature of up to 750 ° C. to oxidize and remove residual carbon. If the oxidation temperature is too high, the surface of the aluminum nitride powder will be excessively oxidized, and the desired powder tends to be difficult to obtain. Therefore, it is preferable to select an appropriate oxidation temperature and time.

It can be said that the aluminum nitride powder obtained by the method of the present invention is a powder in which the degree of aggregation of primary particles is relatively small. That is, assuming that the particle size calculated from the specific surface area of the aluminum nitride powder is D ₃ and the average particle size measured by the sedimentation method is D ₄ , an aluminum nitride powder with D ₄ / D ₃ ≦ 2.60 is obtained.

(Effect) In the present invention, the aluminum nitride powder obtained by using alumina and carbon as raw materials under specific particle diameter conditions has a small degree of aggregation of primary particles. Therefore, when the aluminum nitride powder is used for sintering, the linear shrinkage can be 20% or less, further 17% or less, and further preferably 15% or less. As described above, the aluminum nitride powder obtained by the method of the present invention has good dimensional stability, and in particular, a simultaneous firing method in which a paste of a refractory metal is printed on the surface and fired, or in the production of laminated packages. In this case, it is preferably used because it can reduce the difference in shrinkage rate with metal.

Furthermore, when aluminum nitride powder having a low oxygen content and a small amount of cationic impurities is used as a raw material, it is possible to obtain an aluminum nitride sintered body having high thermal conductivity and translucency in addition to the above effects. it can.

(Examples) Examples and comparative examples are given below to more specifically describe the present invention, but the present invention is not limited to these examples.

Various physical properties in the following examples and comparative examples were measured by the following methods.

1) Carbon ash content: 75 according to JIS K-6221-1970
It was determined from the weight after ashing at 0 ° C.

2) Carbon oil absorption: determined from the amount of dibutyl phthalate added in accordance with JIS K-6221-1970.

3) Specific surface area: determined by BET method by N ₂ adsorption. (Using "Flowsorb 2300" manufactured by Shimadzu Corporation) 4) Average primary particle size of powder 5) Average agglomerated particle size of powder: Determined by a centrifugal sedimentation method.
(Using "CAPA500" manufactured by Horiba, Ltd.) 6) Impurity amount in powder Cation impurity amount: The powder was alkali-melted, neutralized with an acid, and quantified by ICP emission spectroscopic analysis of the solution. (Using "ICPS-1000" manufactured by Shimadzu Corporation) Impurity carbon amount: The powder was burned in an oxygen stream and quantified from the generated CO and CO ₂ gas amounts. (Using "EMIA-110" manufactured by Horiba Ltd.) Impurity oxygen amount: Determined from the amount of CO gas generated by the high temperature thermal decomposition method of the powder in the graphite crucible. (Using "EMGA2800" manufactured by Horiba, Ltd.) 7) Density (d (g)) of sheet compact: AlN powder and dispersant are dispersed in an organic solvent to form a slurry, which is shaped by the doctor blade method. The green density was obtained from the dimensions and weight of the obtained molded product, and the molding density of only the AlN powder was calculated from this value.

8) AlN sintered body density (d (s)): determined by Archimedes method. (Toyo Seiki Co., Ltd. “High-precision hydrometer D-
H ”is used) 9) Thermal conductivity of AlN sintered body: Obtained by a laser flash method, and the thickness was corrected by a calibration curve. (Using "Gakugaku Denki Co., Ltd." thermal constant measuring device PS-7 ") 10) Shrinkage rate during sintering: Determined by dimensional measurement before and after sintering.

Example 1 Purity 99.9%, average particle diameter (D ₂ ) measured by sedimentation method 0.
94 μm, specific surface area 7.7 m ² / g, particle size calculated from specific surface area (D ₁ ) 0.21 μm, D ₂ / D ₁ = 4.5 Al ₂ O ₃ 500 g and ash content 0.08
Carbon 500 with weight%, specific surface area 138m ² / g, oil absorption 120cc / g
g was mixed using a nylon pot and a ball. The mixed powder was placed in a high-purity graphite crucible, and it was heated to 1550 under N ₂ gas flow.
The mixture was heated at ℃ for 6 hours, and then unreacted carbon was removed by oxidation. The X-ray diffraction pattern of the obtained powder showed only the AlN peak. The characteristics of the obtained powder are as shown in Table 1.

Next, 400 g of the obtained AlN powder, 24 g of Ca ₃ Al ₂ O ₆ , 4 g of sorbitan trioleate, 132 g of toluene and 108 g of ethanol were placed in a nylon pot having an internal volume of 4.8 and mixed with a nylon-coated ball for 24 hours. To the mixed slurry, 28 g of polyvinyl butyral, 28 g of benzylbutyl phthalate, 44 g of toluene and 36 g of ethanol were added, and the mixture was further ball-milled for 24 hours. The obtained slurry has a viscosity of 20000 cps (at 25
Vacuum degassing was performed until the temperature reached (° C.). The defoamed slurry was molded by a doctor blade sheet molding method to obtain a molded body having a thickness of 1 mm. This molded body was punched out with a 34 mm die to obtain a sample for a sintering test. Sheet compact density (d
(G)) was 19.1 (g / cm ³ ). The stamped compact was degreased in a muffle furnace in air at 600 ° C for 3 hours.
Then, the molded body was put into a graphite crucible having an inner wall coated with BN slurry, and a sintering test was performed. Sintering was performed in a N ₂ stream at a temperature rising rate of 5 ° C / min from room temperature to 1800 ° C, and
After holding at 00 ° C. for 7 hours, it was performed under the condition of natural cooling. The obtained sintered body was subjected to measurement of thermal conductivity, size and density.

The density of the obtained sintered body was 3.26 g / cm ² , and the shrinkage rate during sintering was 16.3%. The thermal conductivity was 163 W / mK.

Example 2 Various types of alumina powder and the carbon used in Example 1 were mixed in the same manner as in Example 1 and then calcined. The X-ray diffraction patterns of the obtained powders were all AlN single phase. Next, molding and firing are performed in the same manner as in Example 1,
The physical properties of the sintered body and the shrinkage rate during sintering were measured. Table 2 shows the results.

Example 3 Alumina powder having a purity of 99.9% (Fe76ppm, Si130ppm) and an average particle diameter (D ₂ ) of 1.83 μm measured by a sedimentation method and a particle diameter (D ₁ ) of 0.20 μm calculated from a specific surface area was used as an alumina ball medium. Lighter crushed. The pulverized alumina thus obtained has a purity of 99.9% or more, Fe80ppm and Si127ppm, the particle size (D ₁ ) calculated from the specific surface area is 0.19μm, and the average particle size (D ₂ ) measured by the sedimentation method is 0.65μm. there were. 500 g of this ground alumina and 0.08% by weight of ash (Fe23ppm, Si
4ppm), specific surface area 138m ² / g, oil absorption 120cc / g carbon 500
g and a nylon pot and balls were used to mix the mixed powder into a high-purity graphite crucible, and 1550 under N ₂ gas flow.
The mixture was heated at ℃ for 6 hours, and then unreacted carbon was removed by oxidation. Table 3 shows the physical properties of the obtained powder.

Next, molding and firing were performed in the same manner as in Example 1 to measure the physical properties of the sintered body and the shrinkage rate during sintering. The results are shown in Table 4.

Comparative Example The alumina powder used in Example 3 was used as a raw material without being crushed, and mixed and fired in the same manner as in Example 3 to obtain a white powder. Table 5 shows the physical properties of the obtained powder.

Next, molding and firing were performed in the same manner as in Example 1, and the physical properties of the sintered body and the shrinkage rate during sintering were measured. The results are shown in Table 6.

Claims (1)

(57) [Claims] 1. A particle diameter (D ₁ ) calculated from (a) specific surface area
And the average particle diameter (D ₂ ) measured by the sedimentation method both satisfy the following formula 0.1 μm ≦ D ₁ ≦ 1.0 μm D ₂ / D ₁ ≦ 8, and (b) a mixed powder of carbon and nitrogen. A method for producing an aluminum nitride powder, which comprises firing at 1300 to 1700 ° C. in an atmosphere containing.