JP3053881B2 - Method for producing aluminum nitride powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing aluminum nitride powder. More specifically, the present invention relates to a method for producing a high-purity aluminum nitride powder suitable as a raw material of an aluminum nitride sintered body.

[0002]

2. Description of the Related Art Among the conventionally known methods for producing aluminum nitride powder, as a method for easily mass-producing high-purity products, a raw material mixture obtained by mixing aluminum powder and carbon powder is used. 1 in a nitrogen atmosphere
A reduction nitriding method of heating to 500 to 2000 ° C. is often used.

[0003] As described above, in the reduction nitriding method, since a solid mixture of alumina powder and carbon powder is obtained, it is usually difficult to obtain a uniform raw material mixture, and the unreacted rate of carbon powder is high.

Therefore, by changing the raw materials or improving the mixing method to prepare a raw material mixture in which the two powder components are more uniformly dispersed, the object is to reduce the unreacted rate of the carbon powder. The following method is known as a method for producing aluminum nitride powder.

1) After dispersing aluminum alkoxide and carbon powder in an organic solvent, water is added to hydrolyze the aluminum alkoxide to produce aluminum hydroxide or alumina. Then, the mixture of aluminum hydroxide or alumina and carbon is heated under reduced pressure to remove water, alcohol and organic solvent to obtain a mixed powder. A method of heating the obtained mixed powder in a nitrogen atmosphere (JP-A-61-183108).

2) Furfuryl alcohol is added to a solution in which aluminum hydroxide particles are dispersed, and then the furfuryl alcohol is polymerized. The obtained mixture of aluminum hydroxide and the polymer is heated in a nitrogen atmosphere. Method (EP3
11, 345).

[0007]

However, in the method for producing aluminum nitride powder described in the above 1) or 2), the heating temperature is set to 140 as in the conventional reduction nitriding method.
Since the temperature was as high as 0 to 1650 ° C., grain growth of aluminum nitride occurred during heating, and only an aluminum nitride powder having a large particle size and a large variation in the particle size was obtained.

[0008] The bulk density of the sintered body obtained by sintering the aluminum nitride powder having both large particle size and large variation in particle size is low. That is, the aluminum nitride powder produced by the conventional production method is not yet satisfactory as a raw material for a sintered body, which is a main application.

Further, it is desired to lower the heating temperature when obtaining the aluminum nitride powder for reasons such as energy saving and operability. Therefore, the above heating temperature 140
It is desired to lower 0 to 1650 ° C.

[0010]

The present inventors have made intensive studies to solve the above problems, and as a result, as a polymerizable compound having a nitrogen atom and a carbon atom for reductive nitriding, and a specific aluminum source. By using an aluminum compound as a raw material and heat-treating the aluminum hydroxide dispersion polymer obtained from both, the nitrogen atoms in the polymerizable compound described above efficiently contribute to the production of aluminum nitride powder without volatilization, It has been found that the heating temperature of the aluminum hydroxide-dispersed polymer can be lowered, and that the obtained aluminum nitride powder is fine, monodisperse, and can be easily sintered, thereby completing the present invention. Reached.

The present invention relates to an aluminum compound represented by the general formula (I) AlR ₃ (I) (wherein R represents a halogen atom or an alkoxy group) and a polymerizable compound having a nitrogen atom and a carbon atom. Aluminum hydroxide is precipitated in the contained mixture, and then the polymerizable compound is polymerized to form an aluminum hydroxide dispersion polymer.The aluminum hydroxide dispersion polymer is then placed in a non-oxidizing atmosphere. A method for producing aluminum nitride powder, comprising heating to 700 ° C. or higher.

In the present invention, aluminum hydroxide is precipitated in a mixed solution containing the aluminum compound represented by the general formula (I) and a polymerizable compound having a nitrogen atom and a carbon atom.

As the aluminum compound used in the present invention, known aluminum compounds can be used without limitation as long as they are represented by the above general formula (I). For example, aluminum halides such as aluminum trichloride and aluminum tribromide or hydrates thereof, and aluminum alkoxides such as aluminum ethoxide, aluminum isopropoxide and aluminum butoxide are used alone or in combination.

The polymerizable compound having a nitrogen atom and a carbon atom (hereinafter, also simply referred to as a polymerizable compound) used in the present invention has a reductive nitridation effect on precipitated aluminum hydroxide, and has a nitrogen atom and a carbon atom. And a known compound having polymerizability can be used without limitation. For example, acrylonitrile, acrylamide,
Vinylpyridine, vinylidene cyanide, trifluoronitrosomethane, hexamethylenediamine, aminocaproic acid, aminoenanthic acid, aminoundecanoic acid, diaminobenzidine, dimethylpiperazine, phenylenediamine, isophthalic hydrazide, hexamethylenediisocyanate, tolylene diisocyanate , Phenylenediisocyanate, melamine, urea, aziridine, azetidine, ethyleneimine, succinimide, or oligomers and mixtures thereof are used alone or in combination. Among them, preferred are melamine, methylol melamine, urea, methylol urea, and condensation oligomers thereof.

The above mixed solution preferably contains water or an organic solvent in addition to the above-mentioned aluminum compound and polymerizable compound. As the organic solvent, a known organic solvent can be used without limitation. Examples include alcohols such as ethanol, propanol and butanol, ethers such as diethyl ether, dipropyl ether and dibutyl ether, and halogenated hydrocarbons such as carbon tetrachloride.

Although the state of the above-mentioned mixed solution is not particularly determined, it is usually in the form of a solution or a suspension.

The content of the polymerizable compound in the above mixture is not particularly limited, but the ratio of the number of nitrogen atoms in the polymerizable compound to the number of aluminum atoms in the aluminum compound (N / Al) is 0.1 to 100. Determining the content of the polymerizable compound as described above, nitrogen in the polymerizable compound sufficiently contributes to the production of aluminum nitride powder,
This is preferable because the heating temperature of the aluminum hydroxide-dispersed polymer described below can be lowered and the amount of residual carbon in the product aluminum nitride powder can be reduced.

In determining the content of the polymerizable compound, the atomic ratio of carbon atoms in the polymerizable compound to aluminum atoms in the aluminum compound (C / A
When l) is determined to be 1.5 to 25, the reduction and nitridation reaction of the precipitated aluminum hydroxide is completed, the unreacted aluminum oxide can be prevented from remaining, and the residual carbon amount is small. This is preferable because decarbonization treatment may be unnecessary.

The aluminum compound and the polymerizable compound in the above-mentioned mixed solution are uniformly mixed before the aluminum hydroxide is precipitated. Is more preferably present because aluminum nitride powder can be generated more efficiently.

The method of mixing the above aluminum compound and the polymerizable compound is not particularly limited. For example, a method of adding a polymerizable compound to a liquid containing an aluminum compound, a method of adding an aluminum compound to a liquid containing a polymerizable compound, mixing the aluminum compound and the polymerizable compound in advance, and then optionally And a method of adding water or an organic solvent to the mixture.

In the present invention, a method for precipitating aluminum hydroxide, which is usually in the form of colloid, in a mixed solution can be employed without limitation to a known method. For example, when the aluminum compound is the above-mentioned aluminum alkoxide, the aluminum alkoxide in the mixed solution is 2
There is a method in which water of about 50 times mol is added to the mixed solution and the aluminum alkoxide is hydrolyzed to precipitate aluminum hydroxide. When the aluminum compound is the above-mentioned aluminum halide or a hydrate thereof, there is a method of precipitating aluminum hydroxide by adding an alkaline aqueous solution such as aqueous ammonia to the mixed solution. In this method, it is preferable that the pH of the mixed solution is 5 to 9 in order to prevent generation of aluminum ions or aluminate ions and to facilitate precipitation of aluminum hydroxide. More preferably, the pH of the mixture is 6-8.

After the above-mentioned precipitation of aluminum hydroxide, the polymerizable compound is polymerized to form an aluminum hydroxide dispersion polymer. As a method for polymerizing this polymerizable compound, a known polymerization method can be employed without limitation. For example, polymerization methods such as polymerization using an initiator, thermal polymerization, photopolymerization, radiation polymerization, and plasma polymerization can be used. Preferably, thermal polymerization is used.

In the polymerization of the above-mentioned polymerizable compound, a compound capable of polycondensation, polyaddition or addition condensation with the polymerizable compound may be added to carry out polycondensation, polyaddition or addition condensation. Examples thereof include polycondensation or polyaddition by adding a dicarboxylic acid such as adipic acid and sebacic acid, polycondensation by adding adipic acid dichloride, isophthalic chloride, and addition condensation by adding formaldehyde and the like. Of these, formaldehyde is preferred. When melamine is used as the polymerizable compound with this formaldehyde, the formaldehyde is usually added in an amount of 1 to 6 times the mol of the melamine, and the mixture is heated to 50 to 100 ° C. with stirring to form the melamine. Addition condensation of formaldehyde.

By the polymerization of the polymerizable compound described above, an aluminum hydroxide-dispersed polymer in which aluminum hydroxide is dispersed and which has a nitrogen atom and a carbon atom is obtained.

The aluminum hydroxide dispersion polymer is heated to 700 ° C. or higher in a non-oxidizing atmosphere to obtain an aluminum nitride powder.

When the aluminum hydroxide-dispersed polymer is heated to the above-mentioned specific temperature, the aluminum hydroxide-dispersed polymer is previously separated by a known method such as solvent distillation, filtration, centrifugation and the like. It is preferable to dry the aluminum oxide dispersion polymer at a temperature of room temperature to 500 ° C.

The components constituting the non-oxidizing atmosphere during the heat treatment of the aluminum hydroxide dispersion polymer include, for example, argon, nitrogen, hydrogen, ammonia, helium and the like. Among them, nitrogen and ammonia are preferable because not only nitridation by nitrogen in the polymerizable compound but also nitridation by nitrogen in the atmosphere occur.

On the other hand, when the aluminum hydroxide dispersion polymer is heated in an oxidizing atmosphere, aluminum nitride is not produced because aluminum oxide is more stable than aluminum nitride.

The heating temperature of the aluminum hydroxide dispersion polymer in the present invention is 700 ° C. or higher as described above. Preferably 900-1700 ° C, most preferably 1
000 to 1500 ° C. If the heating temperature is lower than 700 ° C., it takes a long time to complete the reaction, so that it is not practical. The heating time is not particularly limited, but is preferably 10 minutes to 6 hours, and more preferably 30 minutes to 4 hours.

If necessary, the aluminum nitride powder obtained by the production method of the present invention may be heated to 300 to 700 ° C. in an oxidizing atmosphere such as air or oxygen to remove excess carbon.

The aluminum nitride powder obtained by the production method of the present invention has a particle size in the range of 0.01 to 1 μm and is an aluminum nitride powder having good dispersibility.

[0032]

[Action]

According to the present invention, a polymerizable compound having a nitrogen atom and a carbon atom and an aluminum compound represented by a specific general formula are solid-liquid or liquid-liquid mixed, and then aluminum hydroxide is precipitated. Next, by polymerizing the polymerizable compound, an aluminum hydroxide dispersed polymer in which fine aluminum hydroxide is uniformly mixed in the polymer of the polymerizable compound is obtained. When the aluminum hydroxide dispersion polymer having the above characteristics is heated, an aluminum nitride powder can be produced at a lower heating temperature as compared with the conventional reduction nitriding method. In addition, since aluminum hydroxide is uniformly dispersed in the aluminum hydroxide-dispersed polymer, it is possible to easily mass-produce fine aluminum nitride powder having excellent dispersibility.

The aluminum nitride powder produced by the production method of the present invention is easily sinterable, and can obtain not only a low sintering temperature but also a dense aluminum nitride sintered body. Further, the aluminum nitride powder produced by the production method of the present invention has good dispersibility in a resin, and thus is suitable as a raw material of a composite resin material having excellent heat conductivity.

[0034]

EXAMPLES Examples 1-4 In a three-necked flask equipped with a stirrer, dropping funnel and reflux condenser, 150 g of aluminum isopropoxide and 112 g of melamine were weighed, and 1400 ml of isopropyl alcohol was added. This was refluxed with stirring for 1 hour to obtain an isopropyl alcohol solution of aluminum isopropoxide in which melamine was dispersed.

To this isopropyl alcohol solution, add water 1
40 ml was dropped from the dropping funnel. By this water dripping,
Aluminum isopropoxide was hydrolyzed to precipitate aluminum hydroxide. Continue with 37% formalin 1
By adding 45 g dropwise and heating at 70 ° C. for 4 hours, melamine and methylol melamine were added and condensed to obtain a white, paste-like melamine resin in which aluminum hydroxide was dispersed.

After the melamine resin in which the aluminum hydroxide is dispersed is taken out by distilling off the solvent, the melamine resin is dissolved in air.
The melamine resin in which the dried aluminum hydroxide was dispersed was heated to 0 ° C., and then heated in a graphite boat to a heating temperature at a rate of 5 ° C./min in a nitrogen stream in a graphite boat. For 4 hours to obtain an aluminum nitride powder. The heating temperature was 900 ° C, 1100 ° C, 13 ° C.
00 ° C and 1500 ° C.

With respect to the aluminum nitride powder obtained by the above-mentioned operation, identification of a formed phase by powder X-ray diffraction method, measurement of particle diameter by scanning electron microscope photograph, measurement of specific surface area by BET method, carbon measurement by thermogravimetric analysis The content was measured. Table 1 shows the results.

The aluminum nitride powder obtained at a heating temperature of 1500 ° C. (Example 4) was further heated at 650 ° C. in air.
For 2 hours to remove unreacted carbon. The aluminum nitride powder 100 from which the unreacted carbon has been removed
A sintered material obtained by adding 5 parts by weight of calcium oxide as a sintering aid to 100 parts by weight was molded into a 100 mmφ × 5 mm disk by isostatic pressing at 200 MPa. This disk-shaped molded product was heated to a sintering temperature of 1650 ° C. at a rate of 5 ° C./min under a nitrogen stream, and the sintering temperature was raised to 3
After holding for a time, a sintered body of aluminum nitride was obtained. The bulk density of the obtained sintered body was measured by the Archimedes method. Table 3 shows the results.

Example 5 In a three-necked flask equipped with a stirrer, a dropping funnel and a reflux condenser, 150 g of aluminum isopropoxide and 450 g of melamine were weighed, and 1400 ml of isopropyl alcohol was added. This was refluxed with stirring for 1 hour to obtain an isopropyl alcohol solution of aluminum isopropoxide in which melamine was dispersed.

To this isopropyl alcohol solution, add water 1
40 ml was dropped from the dropping funnel. By this water dripping,
Aluminum isopropoxide was hydrolyzed to precipitate aluminum hydroxide. Continue with 37% formalin 5
By dropping 80 g and heating at 70 ° C. for 4 hours, melamine and methylol melamine were added and condensed to obtain a white, paste-like melamine resin in which aluminum hydroxide was dispersed.

After the melamine resin in which the aluminum hydroxide is dispersed is taken out by distilling off the solvent, the melamine resin is dissolved in air.
The melamine resin in which the dried aluminum hydroxide was dispersed was heated to 0 ° C., and the dried melamine resin was heated to 1500 ° C. in a graphite boat at a rate of 5 ° C./min under an argon stream, and the heating temperature was lowered. Holding for 4 hours, an aluminum nitride powder was obtained.

With respect to the aluminum nitride powder obtained by the above-mentioned operation, identification of a generated phase by powder X-ray diffraction method, measurement of particle diameter by scanning electron microscope photograph, measurement of specific surface area by BET method, and carbonization by thermogravimetric analysis The content was measured. Table 1 shows the results.

Example 6 176 g of AlCl ₃ .6H ₂ O and 112 g of melamine were weighed into a _three -necked flask equipped with a stirrer, a dropping funnel and a reflux condenser, and 330 g of water was dropped from the dropping funnel and stirred. It was dissolved AlCl ₃ · 6H ₂ O Te. Furthermore,
145 g of 37% formalin was dropped from the dropping funnel, and the mixture was heated and refluxed with stirring for 30 minutes. The dropwise formalin melamine dissolved by methylolated, an aqueous solution of methylol melamine and AlCl ₃ · 6H ₂ O was obtained. An aqueous solution of the methylol melamine and AlCl ₃ · 6H ₂ O, by the pH of the aqueous solution and 7 by adding 0.1N- ammonia water 20 ml, to precipitate the colloidal aluminum hydroxide. By heating the solution in which the colloidal aluminum hydroxide was precipitated at 70 ° C. for 4 hours, methylolmelamine was condensed to obtain a white, paste-like melamine resin in which aluminum hydroxide was dispersed.

After the melamine resin in which the aluminum hydroxide is dispersed is taken out by distilling off the solvent, the melamine resin is dissolved in air.
The melamine resin in which the dried aluminum hydroxide was dispersed was heated to 0 ° C. and then heated to 1500 ° C. in a graphite boat at a rate of 5 ° C./min under a nitrogen stream in a graphite boat. Holding for 4 hours, an aluminum nitride powder was obtained.

With respect to the aluminum nitride powder obtained by the above-mentioned operation, identification of a generated phase by powder X-ray diffraction method, measurement of particle diameter by scanning electron micrograph, measurement of specific surface area by BET method, and carbonization by thermogravimetric analysis The content was measured. Table 1 shows the results.

Comparative Example 1 A three-necked flask equipped with a stirrer, a dropping funnel and a reflux condenser was charged with 44 g of aluminum hydroxide and melamine 112.
g, and weigh 1400 ml of isopropyl alcohol.
added. This was refluxed with stirring for 1 hour to obtain an isopropyl alcohol solution containing aluminum hydroxide and melamine. 145 g of 37% formalin was added dropwise to this isopropyl alcohol solution,
By heating at 70 ° C. for 4 hours, methylol melamine was polymerized to obtain a melamine resin containing aluminum hydroxide.

After removing the melamine resin containing the aluminum hydroxide by distillation of the solvent,
After drying by heating to 50 ° C., the melamine resin containing the dried aluminum hydroxide is placed in a graphite boat under a stream of argon at a rate of 5 ° C./min.
The mixture was heated to 0 ° C., and the heating temperature was maintained for 4 hours to obtain an aluminum nitride powder.

With respect to the aluminum nitride powder obtained by the above-mentioned operation, the generated phase was identified by the powder X-ray diffraction method. Table 2 shows the results.

Comparative Example 2 A three-necked flask equipped with a stirrer, a dropping funnel and a reflux condenser was charged with 44 g of aluminum hydroxide and melamine 112.
g, and weigh 1400 ml of isopropyl alcohol.
added. This was refluxed with stirring for 1 hour to obtain an isopropyl alcohol solution containing aluminum hydroxide and melamine. 145 g of 37% formalin was added dropwise to this isopropyl alcohol solution,
By heating at 70 ° C. for 4 hours, methylol melamine was polymerized to obtain a melamine resin containing aluminum hydroxide.

After the melamine resin containing aluminum hydroxide is taken out by distilling off the solvent, the melamine resin
After drying by heating to 50 ° C., the melamine resin containing the dried aluminum hydroxide was placed in a graphite boat under a stream of argon at a rate of 5 ° C./min at a rate of 160 ° C./min.
The mixture was heated to 0 ° C., and the heating temperature was maintained for 4 hours to obtain an aluminum nitride powder.

With respect to the aluminum nitride powder obtained by the above-mentioned operation, identification of a formed phase by powder X-ray diffraction method, measurement of particle diameter by scanning electron microscope photograph, measurement of specific surface area by BET method, and carbonization by thermogravimetric analysis The content was measured. Table 2 shows the results.

Comparative Example 3 To 100 parts by weight of a commercially available aluminum nitride powder synthesized by reduction nitriding of alumina, 5 parts by weight of calcium oxide was added as a sintering aid, and a pressure of 10 mmφ × 5 mm was obtained by isostatic pressing at 200 MPa. It was shaped into a disk. The disk-shaped molded product was heated to a sintering temperature of 1650 ° C. at a rate of 5 ° C./min in a nitrogen stream, and the sintering temperature was maintained for 3 hours to obtain a sintered body of aluminum nitride. . The bulk density of the obtained sintered body was measured by the Archimedes method. Table 3 shows the results.

[0053]

[Table 1]

[Table 2]

[Table 3]

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-30307 (JP, A) JP-A-1-239006 (JP, A) JP-A-2-293308 (JP, A) JP-A-1- 298012 (JP, A) JP-A-3-126606 (JP, A) JP-A-3-6224 (JP, A) JP-A-3-93669 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 21/072

Claims (1)

(57) [Claims] An aluminum compound represented by the general formula (I) AlR ₃ (I) (wherein R represents a halogen atom or an alkoxy group), and a polymerizable compound having a nitrogen atom and a carbon atom are included. Aluminum hydroxide was precipitated in the mixed solution, and then the polymerizable compound was polymerized to form an aluminum hydroxide dispersion polymer. Then, the aluminum hydroxide dispersion polymer was heated at 700 ° C. in a non-oxidizing atmosphere. A method for producing an aluminum nitride powder, comprising heating as described above.