JPH10245207A - Production of aluminum nitride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce aluminum nitride exhibiting small shrinkage in sintering. SOLUTION: Granules having a density of >0.9g/cm<3> and <=2.0g/cm<3> in dried state, a breakage strength of >=10g and <2,000g per one granule and a diameter of 2-30mm are produced from a powdery mixture of alumina or an alumina precursor and carbon or a carbon source. The granules are placed in a crucible and brought into contact with a reaction gas to effect the reducing nitriding reaction and obtain aluminum nitride exhibiting small shrinkage in sintering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved method for producing aluminum nitride powder. Specifically, this is a method for efficiently producing aluminum nitride powder having good dimensional accuracy during sintering using alumina powder as a raw material.

[0002]

2. Description of the Related Art Aluminum nitride ceramics generally have excellent industrial characteristics such as high thermal conductivity, high insulation, high corrosion resistance, and high strength. Attention has been paid to ceramic raw materials for various industrial materials such as HIC substrates.

[0003] The characteristics of these aluminum nitride ceramics depend on the characteristics of the raw material powder, and the dimensional accuracy during sintering depends on the molding density of the raw material powder. There is a need for a possible fine powder.

[0004] Aluminum nitride powder can be synthesized by direct nitriding of aluminum metal, reduction nitriding of alumina,
There are thermal decomposition methods of organic aluminum compounds containing nitrogen such as imides and gas phase reaction methods using chlorides, etc., but as a method for industrially obtaining inexpensive high-quality fine powders, the reduction nitriding method of alumina is excellent. I have.

[0005] As a method of performing the above-mentioned reduction nitriding method of alumina, there is a method in which a mixed powder of alumina and carbon as raw materials is filled in a multi-layered flat plate, and the reduced nitriding reaction is carried out in a tunnel type pusher furnace. JP-A 1-2905
62 and the like. In these methods, the nitrogen required for the reaction is supplied to the mixed powder only by diffusion because the mixed gas, which is a reaction gas, is ventilated above the surface of the mixed powder. The heat required for the reaction is
It is supplied only by radiation from the furnace wall. for that reason,
The reaction required a long time. As a method of performing the reduction nitriding method of alumina to compensate for this problem, a method of granulating a mixed powder of alumina and carbon in advance to form a granulated body and performing a reduction nitriding reaction in a moving bed of a vertical furnace, JP-A-62-2
No. 07703, JP-A-7-81912, JP-A-7-81913 and the like. In these methods, a reaction gas containing nitrogen gas or ammonia in a gap between granules (hereinafter referred to as a reaction gas)
Can be forcibly aerated, so that the heat required for the nitridation reaction is given to the raw material by radiation and sensible heat of the gas, and nitrogen is also efficiently given to the raw material. As a result, the reaction time can be reduced.

[0006]

However, in this reaction, when the granules to be used are broken by the shearing stress when moving in the furnace, the fragments in which the granules are broken in the furnace are formed. In order to block the gap between the granules and the granules, prevent a uniform flow of the reaction gas, or block the inside of the furnace, the granules need to have a strength that does not break due to the shearing stress during movement. Therefore, the above-mentioned publication states that a breaking strength of 2000 g or more is required.

On the other hand, a method for producing an aluminum nitride sintered body from aluminum nitride powder is as follows: 1) A predetermined amount of aluminum nitride powder, a sintering aid, a binder, and a solvent are mixed by a ball mill or the like to prepare a slurry. The slurry is formed into granules by spray drying or the like, and the granules are formed into a compact by press molding or the like. A method of removing a binder and the like in the molded body by degreasing and firing the molded body after degreasing to obtain a sintered body.

[0008] 2) The slurry composed of the aluminum nitride powder, the sintering aid, the binder, and the solvent prepared as described above is formed into a sheet-shaped formed body (green sheet) by a doctor blade method, etc., and then degreased and fired. To obtain a sintered body.

And the like.

[0010] These methods of sintering aluminum nitride include:
Aluminum nitride powder produced by using a strong granulated body composed of alumina and carbon as obtained in the moving bed is formed into a green body (a compact) and sintered to form an aluminum nitride powder. When a sintered body is manufactured, there is a problem that the shrinkage ratio during sintering is increased, and the dimensional accuracy of the obtained sintered body is deteriorated.

[0011]

Means for Solving the Problems First of all, the inventors of the present invention considered that the density of a green body (compact) manufactured from aluminum nitride powder was reduced due to a decrease in dimensional accuracy of the obtained sintered body. We noticed that it greatly affected the dimensional accuracy of That is, since the aluminum nitride powder produced from the above-mentioned granules of strong alumina and carbon has a large secondary agglomeration particle size, and since the agglomerates are formed firmly,
It is presumed that the density of the green body using the obtained aluminum nitride powder decreases, and as a result, the shrinkage ratio during sintering increases, and the dimensional accuracy of the sintered body decreases.

Based on the above idea, as a result of repeated studies, a mixed powder comprising alumina and carbon was granulated to a specific density and strength to produce a granulated body, and the granulated body was placed in a crucible. The resulting aluminum nitride powder is obtained with an appropriate cohesive force by performing a reduction nitridation reaction by allowing it to stand, and by molding this, a green body having a high density can be manufactured, and the dimensions at the time of sintering are obtained. It has been found that the accuracy can be significantly improved, and the present invention has been completed.

That is, according to the present invention, the density in a dry state exceeds 0.9 g / cm ³ from a mixed powder comprising alumina or an alumina precursor and carbon or a carbon source.
Granules having a breaking strength of 0 g / cm ³ or less and a breaking strength per piece of 10 g or more and less than 2000 g are granulated, and the granules are allowed to stand in a crucible and reduced under a reaction gas atmosphere. A method for producing aluminum nitride, comprising performing a nitriding reaction.

In the present invention, the density of the above-mentioned granules in a dry state is determined by the shape of the granules in a state (dry state) in which a solvent used in a later-described granulation method is dried as necessary. A value calculated from the dimensions and the weight. Also,
The breaking strength per granule refers to the weight value when the granule is broken by a Kiya hardness meter.

[0015]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, alumina, alumina precursor, alumina, aluminum hydroxide,
Any alumina or alumina precursor that can become aluminum nitride by a reductive nitridation method such as aluminum nitrate and aluminum sulfate is used without any limitation. Among them, alumina is preferred. For example, for alumina, α
Any known materials such as -alumina and γ-alumina can be used without any limitation, but α-alumina is usually used. Further, its purity is 99.0% by weight or more, preferably 99.0% by weight.
It is preferable that the content is 5% by weight or more, and the average particle size is 5 μm.
Below, preferably 3 μm or less is suitable. Further, the specific surface area is 1 to 30 m ² / g by a nitrogen adsorption method,
It is preferably 5 to 15 m ² / g.

In the present invention, carbon or a carbon source that does not remain as impurities in the obtained aluminum nitride is preferable as the carbon or carbon source.
For example, furnace black, channel black, thermal black, carbon black such as acetylene black, carbon such as graphite, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, vinyl resin such as vinyl acetal resin, polyethylene terephthalate, alkyd resin, A carbon source that produces carbon that can be a reducing agent in a reaction gas atmosphere described below, such as maleic acid resin, urethane rubber, and other polyester, polypropylene, polyethylene, polystyrene, phenolic resin, and urea resin, can be employed without any limitation. Among them, carbon black is preferable from the viewpoint of the amount of carbon per weight and stability of physical properties. For example, carbon black having an ash content of 1.0% by weight or less, preferably 0.5% by weight or less, and an average particle diameter of 1 μm or less is suitably used. The specific surface area is 20 to ²⁰⁰ m ² / g, preferably 70 to 150 m ² / g by the nitrogen adsorption method.
m ² / g is preferred. Further, when the DBP oil absorption is 50
~ 150ml / 100g, preferably 80 ~ 130m
1/100 g is preferred.

In the present invention, alumina or an alumina precursor (hereinafter, simply referred to as alumina) and carbon or a carbon source (hereinafter, simply referred to as carbon) are:
Any mixing ratio may be used as long as it is equal to or higher than the equivalent ratio.
Preferably, carbon is added to alumina (Al ₂ O ₃ ) in an amount of 1 to 3 times the equivalent of carbon in terms of carbon, more preferably 1.3 to 2 times the equivalent of carbon in terms of carbon to alumina. good.

As a method of mixing alumina and carbon,
There is no particular limitation on the method as long as they can be uniformly mixed. For example, wet and dry ball mill mixing using a rotary ball mill mixer, a vibrating ball mill mixer, a planetary ball mill mixer, etc., a ribbon mixer, a double shaft paddle mixer, a conical screw mixer, etc. Wet and dry stirring and the like. When mixing alumina and carbon, a sintering aid such as yttria, yttrium aluminate, or calcium aluminate may be added as necessary. By adding a sintering aid in advance, it is possible to obtain a sintered body by directly forming and firing the obtained aluminum nitride without adding a sintering aid.

In the present invention, the granulation method is adopted without any limitation such as compression granulation, extrusion granulation, tumbling granulation and spray granulation, and can be carried out by adopting known operating conditions without any limitation. The rolling granulation method is preferred in view of the fact that the density and strength of the obtained granules can be surely adjusted to the ranges described below, and further, in consideration of the size, particle size distribution, operability, and economy.

The binder solution used as needed at the time of preparing the granules is preferably a binder that does not remain as impurities in the obtained aluminum nitride. For example, polyvinyl alcohol, alginate,
Sugar, cellulose ether, dextrin, starch,
Organic binders such as molasses, polyvinylpyrrolidone, and phenolic resin, and inorganic binders such as sodium aluminate.

The above-mentioned binder solution is used for the solvent 10
0 to 15 parts by weight, preferably 0.1 to 15 parts by weight, based on 0 parts by weight.
It is preferable to mix 5 parts by weight.

For example, the mixing ratio of the mixed powder of alumina and carbon black and the binder solution in tumbling granulation is as follows:
With respect to 100 parts by weight of the mixed powder, the weight fraction of carbon black in the mixed powder and the DBP of the carbon black were determined.
0.8 to 2 parts by weight of the value of each product of the oiling amount and the specific gravity of the solvent of the binder solution, preferably 0.9 to 2.0 times the value
It is preferable to mix in a range of 1.5 times by weight. The granulation conditions in the tumbling granulation can be carried out by employing known operating conditions without any limitation. As a type of the granulator, a plate-type rolling granulator, a drum-type rolling granulator, or the like can be used as appropriate. The granulation is preferably performed so that the average particle diameter of the obtained granules is 2 to 30 mm. The supply of the mixed powder of alumina and carbon black to such a granulator and the supply of the binder solution may be performed by any method.For example, each component described above may be separately supplied to a dish of a granulator or a drum. good. Usually, a mixed powder of alumina and carbon black, and a binder solution obtained by dissolving a binder in advance in the above-described mixing range, a premixed material such as a mixer, or a dish of a granulator, or
Put it in the drum. After the introduction, the plate or drum of the granulator is rotated to generate nuclei. After the nucleation, it is preferable to carry out the method by supplying a mixed powder of alumina and carbon black and a binder solution to a dish or a drum of a granulator so as to be within the above-mentioned mixing range.

In the present invention, the granules obtained by the above-mentioned method are subjected to a reduction and nitriding reaction after drying and removing the solvent used as required. Such drying methods include stationary, fluidized bed batch drying, tunnel, kiln,
Any method may be used as long as the granules are not broken, such as fluidized bed continuous drying. The drying conditions include a temperature and a time at which the solvent can be removed and the binder is not adversely affected, without any particular limitation. Generally, room temperature to 300
It is desirable to dry at 50 ° C., preferably at 50 to 200 ° C., for a time that can remove substantially all of the solvent by drying.

In the present invention, one of the important requirements is that the density of the dried granules exceeds 0.9 g / cm ³ ,
2.0 g / cm ³ or less. When the density of the granulated material is 0.9 g / cm ³ or less, the granulated material generally has low strength, and when left in a crucible, the granulated material collapses due to the load of the granulated material. And clogs the gaps between the granules and prevents the contact between the reaction gas and the granules, thereby reducing the reaction efficiency. Further, at the low density, by selecting a binder or the like, it is possible to obtain a granulated body satisfying the strength,
When a green body is formed from aluminum nitride powder obtained by subjecting this to a reduction nitridation reaction, the molding density also decreases, and the shrinkage during sintering also increases.

On the other hand, when the density of the granulated material exceeds 2.0 g / cm ³ , the green density is reduced from the aluminum nitride powder obtained by reduction nitridation of the granulated material, and the green density is reduced. The shrinkage rate at the time of knotting increases. If the shrinkage at the time of sintering is large, the dimensional accuracy of the sintered body is deteriorated, which causes a defect. Density of the granule, more preferably ^{1.0g / cm 3 ~1.6g / cm 3} .

In the present invention, another important requirement is that the strength per granule is 10 g or more and less than 2000 g. That is, since the granules having a strength of less than 10 g have a small strength, when the granules are allowed to stand still in a crucible, the granules are broken by the load of the granules, and the broken granules are formed of the granules and the granules. It is not preferable because the gap is clogged, the contact between the reaction gas and the granulated body is hindered, and the reaction efficiency is reduced. Further, in the case of a granulated body having a strength of 2,000 g or more, the compacting density when the green body is compacted from the aluminum nitride powder obtained by subjecting the granulated product to a reduction nitriding reaction is reduced, and the shrinkage rate when sintering the compact is reduced. growing. If the shrinkage ratio during sintering is large, the dimensional accuracy of the sintered body is deteriorated, which causes defects.

More preferably, 50 g or more and 1800 g
Is less than. Further, even if the strength of one granule is 10 g or more, a granule having a density of less than 0.9 g / cm ³ is formed by strong bonding between particles constituting the granule. Because it is making granules, it has many voids inside. Therefore, in the nitride powder obtained therefrom, the compaction density is low, and the shrinkage during sintering is high.
If the shrinkage ratio during sintering is large, the dimensional accuracy of the sintered body is deteriorated, which causes defects.

In the present invention, it is important that the density in the dry state and the breaking strength, which show the characteristics of the above-mentioned granules, satisfy both of these conditions in order to achieve the object of the present invention. Further, these conditions are not necessarily correlated, and there are some granules whose density is within the range of the present invention but also have low breaking strength. Some have high strength. Even in such one condition, in the case of a granulated product which is out of the range of the present invention,
As described above, the aluminum nitride powder intended for the present invention cannot be obtained.

The average particle size of the granules used in the present invention is determined in consideration of the resistance when the reaction gas flows through the gap between the granules and the diffusion speed of the reaction gas inside the granules. And 2
It is more preferable that the ratio of the maximum diameter / minimum diameter of the granules to be used is less than 5. More preferably, the average particle size of the granules to be used is from 4 mm to
20 mm, and the ratio of the maximum diameter / minimum diameter of the granules is less than 3.

The structure of the crucible used in the present invention can be adopted without any limitation as long as the above-mentioned granulated material can be left in the crucible and brought into contact with the reaction gas. Preferably, a crucible having a structure in which a reaction gas is introduced into a reaction gas introduction part and a gas discharge part after the reaction is provided in the other part, thereby allowing a reaction gas to flow through a gap between the granulated body and the granulated body. It is. For example, the structure of this crucible is
The crucible is provided with a reaction gas inlet at the top and one or more gas discharge holes with a diameter smaller than the granulated material at the bottom. The size of the hole at the bottom of the crucible is The shape may be any of a circle, an ellipse, and a polygon as long as the raw material granules do not pass through. The opening ratio may be any ratio as long as it can withstand its own weight and the weight of the granules that are left standing, and is preferably 20 to 50% with respect to the bottom surface. The crucible is made of graphite, alumina, boron nitride, silicon nitride, silicon carbide, aluminum nitride or the like without any limitation, but graphite is preferred. The external shape of the crucible is prismatic or cylindrical. The crucibles are preferably used in a single-stage or in a multi-stage manner.

In the present invention, the filling height of the granules is preferably 300 mm or less in view of radiation from a crucible which is a source of heat required for the reaction, heat transfer, and operability during handling.

As the reaction gas in the present invention, any gas containing a nitrogen source such as nitrogen or ammonia can be used without any limitation, but nitrogen gas is preferable. The supply amount of the reaction gas may be maintained at a nitrogen concentration at which the reductive nitridation reaction is sufficiently performed, and is preferably maintained such that the concentration of carbon monoxide in the produced gas is less than 25%. The firing furnace to be used is a batch furnace, a tunnel type pusher furnace, a vertical furnace capable of moving the crucible in the furnace up and down, etc., as long as the granulated material can be left in the crucible and brought into contact with the reaction gas. There are no restrictions. In the reduction nitridation reaction, the granulated body is allowed to stand in a crucible,
It is preferable to stack the crucibles in an arbitrary number of stages and put the stacked reaction vessels in a tunnel type pusher furnace to perform firing.

In the present invention, the temperature of the reductive nitridation reaction is
The temperature is preferably from 1400 to 1800 ° C., and the temperature is kept at or above this temperature until the reductive nitriding reaction is completed. Conditions for raising the temperature until the reductive nitridation reaction is performed and conditions for lowering the temperature after the reaction are arbitrary.
If the granulated material after reduction nitridation has excess carbon, it must be decarbonized. The oxidizing atmosphere for decarbonizing is not limited as long as it is an atmosphere that can remove carbon, such as air and oxygen. It can be adopted without any problem, and its operating temperature is 500 ℃ ~
800 ° C. Air is preferred in view of economy and the oxygen content of the resulting aluminum nitride. The decarbonization temperature is preferably from 600 ° C. to 750 ° C. in consideration of the efficiency of decarbonization and excessive oxidation of the aluminum nitride surface.

In the present invention, the aluminum nitride powder obtained by the reductive nitridation reaction is generally obtained as a lump having the shape of a granulated body. Since the lump has extremely low strength, it is pulverized into a powder state at the time of handling.If a sintering aid is added when carbon and alumina are mixed, press molding and sintering may be performed as it is to obtain a sintered body. . If necessary, the mass can be forcibly pulverized into aluminum nitride powder.

As a method for sintering the aluminum nitride obtained by the method of the present invention, a known method is employed without any particular limitation.
For example, when aluminum nitride is obtained as a powder as described above, generally, 1) a slurry is prepared by mixing a predetermined amount of aluminum nitride powder, a sintering aid, a binder, and a solvent with a ball mill or the like. The slurry is formed into granules by spray drying or the like, and the granules are formed into a compact by press molding or the like. A method of removing a binder and the like in the molded body by degreasing and firing the molded body after degreasing to obtain a sintered body.

2) The slurry composed of the aluminum nitride powder, the sintering aid, the binder, and the solvent prepared as described above is formed into a sheet-shaped formed body (green sheet) by a doctor blade method or the like, and degreased and fired. To obtain a sintered body.

Is preferred.

[0038]

According to the method of the present invention, the reduction nitriding reaction is carried out by a standing reaction without a crucible.
Values as low as less than can be employed. In addition, by adjusting the density to a certain range, the cohesive force of the particles in the granulated body can be suppressed to be weak. When aluminum nitride is produced from such a granulated product by a nitridation-reduction reaction, a three-dimensional structure formed by agglomeration of primary particles of the obtained aluminum nitride or sintering at a contact portion between the primary particles becomes weak. As a result, with a small external force, the three-dimensional structure of the aluminum nitride is broken, and the primary particles of the aluminum nitride can be made dense.

Accordingly, the density of the aluminum nitride compact obtained by using the aluminum nitride powder increases, and as a result, the shrinkage ratio during sintering decreases, and the dimensional accuracy of the sintered compact improves. Presumed.

[0040]

According to the present invention, the three-dimensional structure of the obtained aluminum nitride is weakened by adjusting the strength and density of the granulated material of the raw material to be subjected to the nitriding reaction to a specific range. It is possible to increase the molding density at the time of sintering, as a result, the shrinkage during sintering is reduced,
This has the effect of improving the dimensional accuracy of the sintered body.

[0041]

The present invention will now be described with reference to the following examples.
It is not limited to these examples.

The conditions for the reduction and nitridation reaction were as follows: the temperature was raised at 10 ° C./min and kept at 1600 ° C. The holding at 1600 ° C. was performed until carbon monoxide generated during the reductive nitridation reaction became less than 1000 ppm in the gas discharged out of the reaction system.

For decarbonization, the powder after reduction nitriding was placed in a flat plate and kept at 650 ° C. for 8 hours in air.

In the measurement of the density and strength of the granules in the present invention, granules dried in air at 150 ° C. for 12 hours or more were used. The density was obtained by calculation from the shape and size of the granules and the weight. The strength of the granulated body was measured with a Kiya hardness meter.

The reaction time was 1600 ° C./min.
Under the condition of holding at ℃, the gas after the reduction and nitridation discharged out of the system was analyzed by gas chromatography, and the reaction was started when the concentration of carbon monoxide in the gas became 1000 ppm or more. The time from the start of the reaction to the end of the reaction was defined as the end of the reaction.

The molding density of the aluminum nitride powder was as follows: 3 g of the powder was placed in a mold having an inner diameter of 20 mm, and 200 kg / cm
^It was uniaxially molded in ² and calculated from the shape dimensions and weight of the obtained molded body.

The shrinkage ratio of aluminum nitride was calculated from the above-mentioned molding density and theoretical density of the sintered body as follows.

Shrinkage = (1−Molding density / Sintered body theoretical density) Whether or not the reductive nitridation reaction was completed was confirmed by X-ray diffraction.

Example 1 α-alumina having an average particle size of 2.5 μm and an average particle size of 0.
02 μm carbon black (furnace black) was mixed in a dry ball mill at a weight ratio of 2: 1 to obtain a granulated raw material. On the other hand, HLB is 14.5 with respect to 97 parts by weight of water, and a surfactant of polyoxyethylene alkyl ether “Actinol F-12” (trade name; Matsumoto Yushi Co., Ltd.)
1) and 2 parts by weight of polyvinyl alcohol having a polymerization degree of 500 were dissolved to obtain a binder. Using these raw materials and the binder, a granulated body was produced by a drum type rolling continuous granulator. The average value of the obtained granule diameters was 7.
6 mm. The obtained granules were dried at 150 ° C. for 12 hours to obtain raw material granules. The density of the raw material granules is 1.1
g / cm ³ , and the strength was 880 g.

6.66 kg of the raw material granules were placed in a graphite setter.
The thickness of the packed layer at that time was 42 mm. Graphite setters filled with granules are stacked in three stages,
It was baked at 1600 ° C. The graphite setter used was a dish-shaped setter whose upper part was opened, and the inner dimension was (W) 510.
mm × (L) 520mm × (H) 120mm
m. In addition, 4mm x 3
A large number of 0 mm holes were regularly formed, and the aperture ratio at that time was 35% with respect to the area of the bottom surface of the graphite setter. During the firing, the nitrogen gas flow path is such that nitrogen gas introduced from the upper open part of the upper graphite setter flows through the gap between the granules and the graphite in the middle through the hole at the bottom of the reaction vessel. It is introduced into the setter and follows the same route to be discharged out of the system through the hole in the bottom of the lower graphite setter. The flow rate of the introduced nitrogen gas is 23 Nm ³ / hr. Reaction time is 4
20 minutes.

The obtained aluminum nitride was pulverized into powder to have a molding density of 1.51 g / cm ³ .
The shrinkage was 53%. Further, analysis by X-ray diffraction revealed a single phase of aluminum nitride. Table 1 shows the working conditions and results.

Example 2 In Example 1, the granules produced in Example 1 were put into a cylindrical drum at an apparent filling rate of 60%, and the cylindrical drum was rotated at 40% of the critical rotation speed for 3 hours. The same operation was carried out except that a granulated body having a higher density of the granulated medium therein was used. The density of the raw material granules in this example is 1.3 g / c.
m ³ , strength was 1150 g, average diameter was 7.2 mm, and packed layer thickness was 38 mm. The reaction time was 220 minutes.

The obtained aluminum nitride was pulverized into powder to have a molding density of 1.50 g / cm ³ and a shrinkage of 54%. Further, analysis by X-ray diffraction revealed a single phase of aluminum nitride. Table 1 shows the implementation conditions,
The results are shown.

Example 3 In Example 1, the composition of the binder solution was changed to water 98.8.
The same operation was performed except that the surfactant was 1 part by weight and the polyvinyl alcohol was 0.2 part by weight based on parts by weight. The density of the raw material granules in this example is 1.1 g / c.
m ³ , strength was 440 g, average diameter was 7.8 mm, and packed layer thickness was 41 mm. The reaction time was 210 minutes.

The obtained aluminum nitride was pulverized into powder to obtain a powder having a molding density of 1.53 g / cm ³ and a shrinkage of 53%. Further, analysis by X-ray diffraction revealed a single phase of aluminum nitride. Table 1 shows the implementation conditions,
The results are shown.

Example 4 The procedure of Example 1 was repeated except that the composition of the binder solution was changed to 1 part by weight of a surfactant and 3 parts by weight of polyvinyl alcohol with respect to 96 parts by weight of water. The density of the raw material granules in this example was 1.2 g / cm ³ , the strength was 1320 g, the average diameter was 7.4 mm, and the thickness of the packed bed was 39 mm. The reaction time was 220 minutes.

The obtained aluminum nitride was pulverized into powder to have a molding density of 1.49 g / cm ³ and a shrinkage of 54%. Further, analysis by X-ray diffraction revealed a single phase of aluminum nitride. Table 1 shows the implementation conditions,
The results are shown.

Example 5 In Example 3, the granules produced in Example 3 were put into a cylindrical drum at an apparent filling rate of 60%, and the cylindrical drum was rotated at 40% of the critical rotation speed for 3 hours. The same operation was carried out except that a granulated body having a higher density of the granulated medium therein was used. The density of the raw material granules in this example is 1.3 g / c.
m ³ , strength was 970 g, average diameter was 7.2 mm, and packed layer thickness was 38 mm. The reaction time was 220 minutes.

The obtained aluminum nitride was pulverized into powder to have a molding density of 1.51 g / cm ³ and a shrinkage of 54%. Further, analysis by X-ray diffraction revealed a single phase of aluminum nitride. Table 1 shows the implementation conditions,
The results are shown.

Example 6 In Example 4, the granules produced in Example 4 were charged into a cylindrical drum at an apparent filling rate of 60%, and the cylindrical drum was rotated at 40% of the critical rotation speed for 3 hours. The same operation was carried out except that a granulated body having a higher density of the granulated medium therein was used. The density of the raw material granules in this example is 1.4 g / c.
m ³ , strength is 1570 g, average diameter is 7.1 mm,
The packed layer thickness was 38 mm. The reaction time was 230 minutes.

The obtained aluminum nitride was pulverized into powder to obtain a molding density of 1.47 g / cm ³ and a shrinkage of 55%. Further, analysis by X-ray diffraction revealed a single phase of aluminum nitride. Table 1 shows the implementation conditions,
The results are shown.

Comparative Example 1 α-alumina having an average particle size of 2.5 μm and an average particle size of 0.
02 μm carbon black (furnace black) was mixed in a dry ball mill at a weight ratio of 2: 1 to obtain a raw material powder. The light powder bulk density of the raw material powder was 0.5 g / cm ³ and the graphite setter was filled with 2.86 kg, and the packed layer thickness at that time was 27 mm. Similarly, seven stages of graphite setters filled with raw material powder were stacked. The used graphite setter has an inner dimension (W) 510 mm x (L) with the upper part opened.
It is a dish-shaped setter of 520 mm × (H) 50 mm and plate thickness 10 mm, and (W) 510 mm × (L) 80 m in the center.
The bottom of the graphite setter of m (including plate thickness) × (H) 40 mm is opened, and a gas discharge chamber is provided which is separated from a room for filling the raw material powder. When the graphite setters are stacked, the gas discharge chambers coincide and become chimney-shaped. 510mm × 5
There is a notch at the top of both 0 mm side walls for introducing 490 mm × 20 mm nitrogen gas. The flow path of the nitrogen gas at the time of firing passes through the surface of the raw material powder filled with the nitrogen gas entered from one of the cuts, and is discharged from the gas outlet to the outside of the system.

The obtained aluminum nitride was pulverized into a powder to obtain a powder having a molding density of 1.56 g / cm ³ and a shrinkage of 52%. Analysis by X-ray diffraction showed that the powder was an aluminum nitride single phase. The reaction time required a long time of 650 minutes. Table 1 shows the working conditions and results.

Comparative Example 2 40 parts by weight of a binder having the same composition as in Example 1 was added to 100 parts by weight of the mixed raw material of α-alumina and carbon black in Example 1, and the mixture was kneaded with a kneader. Uniaxial pressing (pressing pressure: 500 kg / cm
² ) The obtained granules were dried under the same conditions as in Example 1 to obtain raw material granules. This raw material granule has a cylindrical shape of φ10 × 10 mm and a density of 2.3 g /
cm ³ and strength was 1640 g. The other conditions were operated in the same manner as in Example 1 to obtain an aluminum nitride powder.
The reaction time was 250 minutes.

When the obtained aluminum nitride was analyzed by X-ray diffraction, it was found to be a single phase of aluminum nitride. Also,
This was pulverized into powder to obtain a molding density of 1.35 g.
/ Cm ³ and the shrinkage ratio was as large as 59%. Table 1
Shows the implementation conditions and results.

Comparative Example 3 10 parts by weight of polyvinyl alcohol having a polymerization degree of 500 was dissolved in 100 parts by weight of the mixed raw material of α-alumina and carbon black in Example 1, and a binder was used. Other than the above, kneaded in a kneader in the same manner as in Comparative Example 2,
The resulting mixture is pressed uniaxially (press pressure: 300 kg /
cm ² ), and the obtained granules were dried under the same conditions as in Example 1 to obtain raw material granules. This raw material granule has a cylindrical shape of φ10 × 10 mm and a density of 1.7.
g / cm ³ , and the strength was 3730 g. The other conditions were operated in the same manner as in Example 1 to obtain an aluminum nitride powder. The reaction time was 230 minutes.

When the obtained aluminum nitride was analyzed by X-ray diffraction, it was found to be a single phase of aluminum nitride. Also,
This was pulverized into powder to obtain a molding density of 1.33 g.
/ Cm ³ and the shrinkage ratio was as large as 59%. Table 1
Shows the implementation conditions and results.

Comparative Example 4 10 parts by weight of polyvinyl alcohol having a polymerization degree of 500 was dissolved in 100 parts by weight of the mixed raw material of α-alumina and carbon black in Example 1, and a binder was used. Other than the above, kneaded in a kneader in the same manner as in Comparative Example 2,
The obtained mixture is pressed uniaxially (press pressure: 500 kg /
cm ² ), and the obtained granules were dried under the same conditions as in Example 1 to obtain raw material granules. This raw material granule was a column of φ10 × 10 mm and had a density of 2.9.
g / cm ³ , and the strength was 6,820 g. Other conditions were operated similarly to Example 1, and aluminum nitride was obtained.
The reaction time was 270 minutes.

When the obtained aluminum nitride was analyzed by X-ray diffraction, it was found to be a single phase of aluminum nitride. Also,
This was pulverized into powder to obtain a molding density of 1.28 g.
/ Cm ³ and the shrinkage ratio was as large as 61%. Table 1
Shows the implementation conditions and results.

Comparative Example 5 A binder was prepared by dissolving 7 parts by weight of cellulose with respect to 100 parts by weight of the mixed raw material of α-alumina and carbon black in Example 1 and kneaded with a kneader. It was thermally decomposed at 600 ° C. for 5 hours in an atmosphere. The mixture obtained by pyrolysis is pressed uniaxially (press pressure: 5k
g / cm ² ), and the obtained granules were dried under the same conditions as in Example 1 to obtain raw material granules. This raw material granule was a columnar shape of φ10 × 10 mm, the density was 0.7 g / cm ³ , and the strength was 70 g. The other conditions were operated in the same manner as in Example 1 to obtain an aluminum nitride powder. The reaction time was 210 minutes.

When the obtained aluminum nitride was analyzed by X-ray diffraction, it was found to be a single phase of aluminum nitride. Also,
This was pulverized into powder to obtain a molding density of 1.32 g.
/ Cm ^3, and the shrinkage was as large as 60%. Table 1
Shows the implementation conditions and results.

[0072]

[Table 1]

Claims (2)

[Claims] 1. A dry powder having a density of more than 0.9 and not more than 2.0 g / cm ³ from a mixed powder comprising alumina or an alumina precursor and carbon or a carbon source, and destruction per piece. Strength is 10g or more and 2000g
A method for producing aluminum nitride, comprising: granulating a granulated material having a particle size of less than 1, granulating the granulated material, leaving the granulated material in a crucible, and performing a reduction nitriding reaction in a reaction gas atmosphere. 2. The method for producing aluminum nitride powder according to claim 1, wherein the diameter of the granulated body is 2 to 30 mm.