WO2011093488A1 - 球状窒化アルミニウム粉末の製造方法及び該方法により得られた球状窒化アルミニウム粉末 - Google Patents
球状窒化アルミニウム粉末の製造方法及び該方法により得られた球状窒化アルミニウム粉末 Download PDFInfo
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Definitions
- the present invention relates to a novel method for producing aluminum nitride powder having characteristics suitable as a filler for heat-dissipating sheets, heat-dissipating grease, adhesives, paints and the like, and spherical aluminum nitride powder obtained by the production method.
- a heat dissipation material in which silicone rubber or silicone grease is filled with a filler such as alumina or boron nitride is widely used in various electronic devices, for example, as a heat dissipation sheet or heat dissipation grease.
- a filler such as alumina or boron nitride
- Aluminum nitride is attracting attention as a filler for the heat dissipation material as described above because it has excellent electrical insulation and high thermal conductivity.
- the particles forming the powder are spherical and have a wide particle size of about several tens to several hundreds of ⁇ m. That is, in order to highly fill a filler or other medium with a filler without impairing moldability (fluidity), a powder containing spherical particles having a relatively large particle size and spherical particles having a relatively small particle size is used. This is because it is most desirable to form a packed structure in which small spherical particles are distributed between large spherical particles.
- an alumina reduction nitriding method is a method in which a mixture of alumina and carbon is heated in nitrogen to reduce alumina and further nitride to obtain aluminum nitride.
- the direct nitriding method is a method in which aluminum nitride is directly obtained from aluminum by reacting nitrogen with aluminum.
- the vapor phase method is a method in which aluminum nitride is obtained by heating after reacting alkylaluminum and ammonia.
- the obtained aluminum nitride powder has a particle shape close to a sphere, but the particle size is almost in the submicron order.
- the direct nitriding method aluminum nitride is obtained in the form of a lump, and this is adjusted to a predetermined particle size by pulverization and classification. Therefore, the particle size is relatively easy to control, but the particle shape is angular. It has a round shape and is far from spherical.
- aluminum nitride powders composed of particles having various shapes and particle diameters and methods for producing the powders have been proposed. However, both have advantages and disadvantages and still have the above-mentioned particle characteristics, and resin. An aluminum nitride powder that can be highly filled in a medium such as the above has not been obtained.
- Patent Document 1 discloses an aluminum nitride powder having a single particle diameter of 3 ⁇ m or more and having a rounded shape and a uniform single particle diameter. However, the particles of the aluminum nitride powder do not have a large particle size of 10 ⁇ m or more.
- Patent Documents 2 and 3 disclose a method of producing an alumina nitride powder by reducing and nitriding spherical alumina or hydrated alumina with nitrogen gas or ammonia gas in the presence of carbon. According to this method, an aluminum nitride powder having a particle shape close to a true sphere and a relatively large particle size can be obtained, and an aluminum nitride powder having a small particle size can also be obtained.
- the spherical aluminum nitride powder obtained by the methods described in these patent documents has a disadvantage that the particle strength is low because the aluminum powder easily becomes hollow and the particle size cannot be stably maintained.
- Patent Document 4 a molding aid is blended with AlN powder produced by a predetermined method, wet pulverized, and then granulated using a spray dryer, and BN is added to the obtained granule.
- spherical aluminum nitride powder is produced by mixing powders and firing and sintering the mixture at a high temperature in a nitrogen atmosphere.
- this method requires firing for sintering the obtained particles in addition to firing for nitriding of aluminum, and firing at a high temperature must be performed twice.
- pulverizing the aluminum nitride powder once manufactured is also required. Therefore, the production cost is excessive and industrial implementation is difficult.
- the aluminum nitride powder obtained by this method is obtained by sintering, the particles are easily bonded and deformed during sintering, and the crushing strength is improved by the growth of aluminum nitride crystal grains. It is easy to make large irregularities. Therefore, the obtained aluminum nitride powder has a problem that the specific surface area is small, the adhesiveness with the resin to be filled becomes low, and the strength of the obtained heat dissipation material becomes insufficient.
- Patent Document 5 aluminum nitride powder composed of irregularly shaped particles is spheroidized by aging (heat treatment) in a flux composed of a compound such as an alkaline earth element or a rare earth element, and then the flux is dissolved.
- a method for obtaining an isolated crystalline aluminum nitride powder is disclosed. In this method, an aluminum nitride powder having a shape and particle size suitable for high filling can be obtained.
- the aluminum nitride powder once manufactured must be further subjected to a special treatment. There is a problem. Further, the aluminum nitride powder obtained by this method has a drawback that the impurity content increases due to the use of a fluxing agent.
- an object of the present invention is to provide a method for efficiently producing a spherical aluminum nitride powder having an optimum size for filler application, high sphericity and high particle strength, and spherical aluminum nitride obtained by the production method. It is to provide a powder.
- the inventors of the present invention used a spherical granulated product obtained by granulating alumina powder or alumina hydrate powder once as a starting material, and reduced this. It has been found that by nitriding, an aluminum nitride powder comprising spherical particles having the intended properties can be produced with good productivity, and the present invention has been completed.
- a spherical granulated product of alumina powder or alumina hydrate powder is used as a starting material, and the spherical granulated product is supplied to a reductive nitriding step to perform reductive nitriding.
- a method for producing spherical aluminum nitride powder is provided.
- the production method of the present invention includes a heat treatment step of heat-treating the spherical granulated product to such an extent that the BET specific surface area is once maintained at least 2 m 2 / g before being supplied to the reduction nitriding step. Can do.
- the spherical granulated product is generally preferably obtained by spray-drying the powder, in which case the BET specific surface area is in the range of 30 to 500 m 2 / g, particularly 50 to 300 m 2 / g. Those are preferably used.
- reductive nitriding of the spherical granulated product or heat-treated product thereof is performed at a temperature of 1200 to 1800 ° C. in a nitrogen atmosphere in which a reducing agent is present.
- the average particle diameter (D 50 ) is in the range of 10 to 200 ⁇ m, and the BET specific surface area is composed of particles having an average sphericity of 0.8 or more and a crushing strength of 100 MPa or more. Can be obtained in the range of 0.5 to 20 m 2 / g.
- the spherical aluminum nitride powder preferably has a pore volume having a pore diameter of 2 ⁇ m or less in the range of 0.02 to 1.0 cm 3 / g.
- the above spherical aluminum nitride powder is suitably used as a filler for heat dissipation material.
- the granule is obtained by using agglomeration and adhesion of fine powder to solidify it into a rounded fine shape.
- the average particle diameter, the sphericity, the BET specific surface area, and the average crushing strength of the spherical aluminum nitride powder are values measured by the methods shown in Examples described later.
- a spherical granulated product of alumina or alumina hydrate having a specific specific surface area is used as a starting material, and this granulated product is reduced and nitrided and converted into aluminum nitride.
- Spherical aluminum nitride powder having a relatively large particle size that is optimal for filler applications and the like can be efficiently produced with a high conversion rate and a simple process.
- the sphericity of the particles is as high as 0.8 or more, the average particle diameter is in a relatively large range of 10 to 200 ⁇ m, and the BET specific surface area is 0.5 to 20 m 2 / g.
- the spherical aluminum nitride powder can be obtained. That is, this aluminum nitride powder has a shape close to a true sphere, and further includes particles having a wide average particle size ranging from particles having a relatively large particle size to particles having a small particle size. Yes. Therefore, the aluminum nitride powder can be highly filled into various media as a filler without impairing formability (fluidity).
- the particles of the aluminum nitride powder are solid as understood from the SEM photograph of FIG. 1 and the like, and the average crushing strength of the particles is as extremely high as 100 MPa or more. Therefore, in this aluminum nitride powder, particle collapse is effectively prevented, the above-described particle shape and particle size are stably maintained, and a decrease in packing property due to particle collapse is effectively avoided, and further, such as powdering There is no inconvenience. Furthermore, since no metal additive such as a fluxing agent is used, the purity of the aluminum nitride powder is extremely high.
- 6 is a SEM photograph showing the particle structure of the spherical aluminum nitride powder obtained in Example 5.
- 6 is a SEM photograph showing the particle structure of the spherical aluminum nitride powder obtained in Example 6.
- 4 is a SEM photograph showing the particle structure of spherical aluminum nitride powder obtained in Example 7.
- 4 is a SEM photograph showing the particle structure of spherical aluminum nitride powder obtained in Example 8.
- 4 is a SEM photograph showing the particle structure of the spherical aluminum nitride powder obtained in Comparative Example 1.
- 4 is a SEM photograph showing the particle structure of the spherical aluminum nitride powder obtained in Comparative Example 2.
- 4 is a SEM photograph showing the particle structure of the spherical aluminum nitride powder obtained in Comparative Example 3.
- spherical alumina or a granulated product of alumina hydrate is used as a starting material, and this granulated product (or a heat-treated product thereof) is supplied to a reduction nitriding step to perform nitriding reduction.
- the target spherical aluminum nitride powder is produced by appropriately performing post-treatment such as surface oxidation treatment.
- the spherical alumina or alumina hydrate granule used as a starting material is obtained by granulating alumina powder or alumina hydrate powder into a spherical shape.
- alumina may be used without particular limitation as long as it has a crystal structure such as ⁇ , ⁇ , ⁇ , ⁇ , and ⁇ .
- Alumina hydrate is converted to transition alumina such as ⁇ , ⁇ , ⁇ , ⁇ , and ⁇ -alumina by heat treatment. Examples of such alumina hydrate include boehmite, diaspore, water, and the like. An aluminum oxide etc. can be mentioned.
- Examples of the method for producing alumina and alumina hydrate as described above can be obtained by an alkoxide method, a Bayer method, an ammonium alum pyrolysis method, or an ammonium dosonite pyrolysis method.
- alumina and alumina hydrate having high purity and uniform particle size distribution can be obtained. Therefore, in the present invention, aluminum hydroxide obtained by purifying aluminum alkoxide obtained by the alkoxide method and hydrolyzing it, boehmite obtained by heat treatment of the aluminum hydroxide, transition alumina, ⁇ -alumina It is suitably used as a raw material.
- ⁇ -alumina, ⁇ -alumina, and boehmite are used as raw materials, there are advantages that the reductive nitridation reaction can be easily controlled and the nitridation easily proceeds.
- the starting material used in the present invention is a spherical granulated product of the above-mentioned alumina powder or alumina hydrate powder, it has a large specific surface area, and is formed between particles by reducing and nitriding this. Nitrogen gas penetrates into the granulated material through the gap, and reduction nitriding proceeds. As a result, it is possible to obtain a spherical aluminum nitride powder having a true spherical shape substantially equal to that of the granulated product and made of solid particles.
- the spherical granules for use as a starting material is set by adjusting the like granulation conditions, the range of the BET specific surface area of 30 ⁇ 500m 2 / g, particularly 50 ⁇ 300m 2 / g It is preferable.
- this spherical granulated product causes a decrease in specific surface area accompanying the sintering of particles in a temperature rising process in a reduction nitriding step performed at a high temperature, which will be described later, and the voids between the particles become narrow. Further, as will be described later, this spherical granulated product may be appropriately heat-treated prior to reductive nitriding in order to enhance the strength of the particles. A decrease occurs, and the voids between the particles become narrower.
- the BET specific surface area of the spherical granulated product is too small, voids between the particles are blocked in the temperature raising process in the reduction nitriding process or the heat treatment process appropriately performed, and the reduction to the inside of the spherical granulated product is performed. Nitriding is not sufficiently performed.
- the BET specific surface area of the spherical granulated product is preferably 500 m 2 / g or less, particularly preferably 300 m 2 / g or less.
- the sphericity of the spherical granulated product is preferably about the same as the sphericity of the target aluminum nitride powder particles.
- the short diameter (DS) is measured by an electron micrograph.
- the ratio (DS / DL) to the major axis (DL) is desirably 0.8 or more.
- the above-mentioned spherical granulated product can be obtained by various methods, but it is easy to control the particle size of the granulated product, economical efficiency, and can easily obtain a granulated product with high sphericity.
- a spray drying method is preferable. In this method, drying (granulation) is performed by spraying a liquid in which the fine powder of alumina or hydrated alumina described above is dispersed in a predetermined solvent (for example, alcohol or water).
- a predetermined solvent for example, alcohol or water
- a spray method a nozzle type, a disk type, etc. are typical, and any method can be adopted, but when a nozzle type spray dryer is used, the spray nozzle diameter should be controlled. There is an advantage that the particle diameter and BET specific surface area of the granulated product obtained can be controlled.
- the spray drying conditions are not limited at all, and may be appropriately selected depending on the size and type of the spray dryer used, the solid content concentration of the spray liquid, the viscosity, the flow rate, and the like.
- the spherical granulated product may include an alkaline earth metal compound, a rare earth element compound, a combination thereof, an alkaline earth metal for the purpose of low-temperature firing of a dispersant, a binder resin, a lubricant or aluminum nitride, if necessary. You may mix
- the spherical granulated product of the above-mentioned alumina powder or alumina hydrate powder can be directly supplied to the reductive nitriding step described later to carry out reductive nitriding, or the spherical granulated product is once heat treated. It can also be supplied to the reduction nitriding step after the heat treatment step. That is, in the reductive nitriding step, the spherical granulated material used as a raw material is kept at a high temperature of 1200 ° C. or higher, and thus shrinks by heating in the temperature rising process, resulting in the passage of particle size and the decrease in BET specific surface area.
- a spherical granulated product of ⁇ -alumina obtained by heat-treating a spherical granulated product of aluminum hydroxide or boehmite (the specific surface area being in the above-mentioned range) at about 600 ° C. for a certain time or 1100 ° C.
- the spherical granules of ⁇ -alumina obtained by heat treatment at the above temperature for a certain time can be supplied to the reduction nitriding step.
- the heat-treated product obtained by the heat treatment step should have a BET specific surface area of a certain degree or more (for example, 2 m 2 / g or more) as described below, and for this reason, the BET specific surface area is in an appropriate range. Even when such a heat treatment is performed, reductive nitridation is performed in a state having appropriate voids.
- the heat-treated spherical granule when supplied to the reduction nitriding step, the granulated product is reduced and nitrided in a dense state.
- the particle surface has very few irregularities and, therefore, its particle strength is high.
- the above heat treatment must be a heat treatment that keeps the BET specific surface area at least 2 m 2 / g or more. Specifically, it is necessary to set the heat treatment time in an appropriate range according to the heat treatment temperature and to keep the BET specific surface area within the above range.
- Reduction nitriding step In the present invention, the above-described spherical granulated product of alumina or hydrated alumina (or a heat-treated product thereof) is reduced in a reaction vessel formed of carbon or an aluminum nitride sintered body, for example, carbon or reducing agent.
- the target spherical aluminum nitride powder can be obtained by firing (reduction nitriding) at a predetermined temperature in a nitrogen atmosphere in which a reactive gas is present.
- the reducing gas used for the reductive nitriding can be used without limitation as long as it is a reducing gas.
- Specific examples include hydrogen, carbon monoxide, and ammonia.
- These reducing gases can be used as a mixture of two or more kinds, or can be used in combination with carbon described below.
- carbon black As the carbon used as the reducing agent, carbon black, graphite, and a carbon precursor that can be a carbon source at a high temperature can be used.
- carbon black such as furnace method and channel method and acetylene black can be used as the carbon black.
- the particle size of these carbon blacks is not particularly limited, but in general, those having a particle size of 0.01 to 20 ⁇ m are preferably used.
- the carbon precursor include synthetic resin condensates such as phenol resin, melamine resin, epoxy resin, and furanphenol resin, hydrocarbon compounds such as pitch and tar, and organic compounds such as cellulose, sucrose, polyvinylidene chloride, and polyphenylene.
- a compound that carbonizes in the solid phase or via the gas phase is preferable.
- a synthetic resin such as a phenol resin, cellulose, polyphenylene, and the like are preferable. These carbons are also preferably those having few impurities such as metals.
- the nitrogen atmosphere in the reaction vessel is supplied continuously or intermittently with an amount of nitrogen gas sufficient for the nitriding reaction of alumina or hydrated alumina spherical granules used as a raw material to proceed sufficiently. Formed by. Further, it is preferable that the reducing gas is supplied into the reaction vessel along with the nitrogen gas. Furthermore, the carbon (including the carbon precursor) used as the reducing agent can be present in the reaction vessel by various methods. For example, the spherical granulated material and the carbon are separately present in the reaction vessel. Alternatively, the spherical granulated product and carbon can be mixed and exist in the reaction vessel. In particular, it is preferable to use a mixture of spherical granules and carbon in that the aggregation of particles during reductive nitriding can be reliably prevented.
- the mixing ratio is generally in the range of 1 / 0.4 to 1 / 0.7 (weight ratio). Is preferred.
- the carbon and the spherical granulated product may be mixed by dry-mixing them under conditions such that the specific surface area of the spherical granulated product is maintained within a predetermined range by a blender, a mixer, a ball mill or the like.
- the reductive nitridation (calcination) performed in a nitrogen atmosphere in the presence of the reducing agent described above may be a condition known per se, specifically, a temperature of 1200 to 1800 ° C., preferably 1300 to 1700 ° C. It is carried out for about 20 hours, preferably about 2 to 10 hours.
- the firing temperature is lower than the above temperature range, the nitriding reaction does not proceed sufficiently, and the target aluminum nitride powder may not be obtained.
- the nitriding reaction proceeds sufficiently at a high temperature at which the firing temperature exceeds the above upper limit temperature, but oxynitride (AlON) with low thermal conductivity is often easily generated, and particle aggregation is likely to occur. There is a risk that it may be difficult to obtain an aluminum nitride powder having a target particle size.
- a surface oxidation treatment can be appropriately performed after the above baking (reduction nitriding).
- Such oxidation treatment for example, can remove carbon contained in aluminum nitride powder and improve the quality, but also improve its water resistance, for example, hold this powder in an environment containing moisture. Even in such a case, generation of ammonia odor can be effectively prevented.
- As a gas used for such an oxidation treatment any gas that can remove carbon such as air and oxygen can be used without any limitation. However, in consideration of economy and the oxygen content of the obtained aluminum nitride, air is preferable. is there.
- the treatment temperature is generally 500 to 900 ° C., preferably 600 to 750 ° C. in consideration of the decarbonization efficiency and excessive oxidation of the aluminum nitride surface.
- a spherical aluminum nitride powder having a high sphericity and a relatively large particle size can be obtained as described above.
- the sphericity is 0.8 or more, particularly 0.9 or more, and is composed of spherical particles that are very close to the sphere
- the sphericity is measured by an electron micrograph as described above, and is represented by the ratio (DS / DL) of the minor axis (DS) to the major axis (DL).
- the average particle diameter is represented by a particle diameter (D 50 ) that is 50% by volume integration by dispersing this powder in an appropriate solvent and using a laser diffraction scattering method.
- the most significant feature of the spherical aluminum nitride powder is that the particle strength is extremely high and the average crushing strength (JIS R 1639-5) is in the range of 100 MPa or more. That is, the particles forming the spherical aluminum nitride powder are solid, as shown in FIG. 2 showing the cross-sectional structure of the particles, no cavities are formed inside the particles, and have an extremely large average crushing strength. Show. Therefore, this spherical aluminum nitride powder does not cause particle collapse during handling, etc., and powder formation is effectively prevented, and the sphericity, average particle diameter, BET specific surface area of the particles as described above The particle characteristics such as are stably maintained without fluctuation.
- the spherical aluminum nitride powder of the present invention described above is solid and has a high crushing strength, but its specific surface area is very large as described above.
- a spherical aluminum nitride powder having such a large specific surface area while being made of particles having a high crushing strength has not been known at all.
- the spherical aluminum nitride powder of the present invention has fine pores inside the particles, and as can be understood from FIGS. 1 and 2, fine irregularities derived from the fine pores are formed on the particle surface. Therefore, it is considered to have a high crushing strength and a large specific surface area.
- the spherical aluminum nitride powder of the present invention has a pore structure giving a high specific surface area by measuring the pore distribution by a mercury intrusion method.
- the pore diameter is 0.1 to 2 ⁇ m and has a specific peak where the pore volume is maximized. It was confirmed that there are almost no pores having a diameter exceeding 2 ⁇ m in the particles.
- the volume of the pores having a pore diameter of 2 ⁇ m or less is in the range of 0.02 to 1.0 cm 3 / g, particularly 0.1 to 0.5 cm 3 / g.
- Such a pore distribution is not found in the spherical aluminum nitride powder obtained by the conventional method, as shown in a comparative example described later.
- the presence of the pores as described above brings about an effect of improving the adhesion of the aluminum nitride powder to a resin or the like.
- this aluminum nitride powder is used as a filler for filling a resin or grease or the like, since the resin or oil constituting the matrix (binder) enters into the pores, the anchor effect is exhibited, and these matrix and filler ( Adhesion with AlN powder) is improved and high thermal conductivity is imparted to these matrices.
- the matrix is a resin, it is possible to increase the strength of the molded body.
- the AlN powder of the present invention has a high conversion rate to aluminum nitride (hereinafter referred to as AlN conversion rate), for example, 50% or more, preferably compared to conventionally known aluminum nitride obtained by reducing and nitriding alumina.
- AlN conversion rate for example, 50% or more, preferably compared to conventionally known aluminum nitride obtained by reducing and nitriding alumina.
- the AlN conversion rate represents the conversion rate from alumina to aluminum nitride, and was obtained from the peak intensity ratio of aluminum nitride and alumina in the X-ray diffraction described later.
- the spherical aluminum nitride powder of the present invention is not particularly limited with respect to impurities such as cations, but since the aluminum nitride powder is produced without using a fluxing agent or the like, the cation content is extremely small, For example, it is 0.3% by weight or less, particularly 0.2% by weight or less.
- the spherical aluminum nitride powder of the present invention can be widely used as a filler for heat dissipation materials such as a heat dissipation sheet, a heat dissipation grease, a heat dissipation adhesive, a paint, and a heat conductive resin, in various applications utilizing the properties of aluminum nitride.
- the resin and grease used as the matrix of the heat dissipation material are thermosetting resins such as epoxy resins and phenol resins, thermoplastic resins such as polyethylene, polypropylene, polyamide, polycarbonate, polyimide, polyphenylene sulfide, silicone rubber, EPR, Examples thereof include rubbers such as SBR and silicone oil.
- a heat dissipation material it is preferable to add 150 to 1000 parts by weight per 100 parts by weight of resin or grease.
- such a heat dissipation material may be filled with one kind or several kinds of fillers such as alumina, boron nitride, zinc oxide, silicon carbide, and graphite.
- fillers for example, a surface treated with a silane coupling agent, phosphoric acid, phosphate, or the like may be used.
- the shape and particle size of the spherical aluminum nitride powder of the present invention and other fillers may be selected according to the characteristics and application of the heat dissipation material. Further, the mixing ratio of the spherical aluminum nitride powder and the other filler in the heat dissipation material can be adjusted as appropriate within the range of 1:99 to 99: 1.
- additives such as a plasticizer, a vulcanizing agent, a curing accelerator, and a release agent may be further added to the heat dissipation material.
- Cationic impurity content (metal element concentration) was determined by ICP emission analysis of the solution using ICP-1000 manufactured by Shimadzu Corporation after the aluminum nitride powder was alkali-melted and then neutralized with acid. Quantified.
- Average crushing strength The average crushing strength of the AlN powder was determined by a single particle compression test (JIS R 1639-5). Using a micro-compression tester (Shimadzu MTC-W), a single particle of 100 arbitrary particles was subjected to a compression test, the crushing strength was determined from the fracture test force and the particle size, and the arithmetic average was obtained.
- Pore size distribution of the AlN powder was determined by a mercury intrusion method using a pore distribution measuring device (manufactured by Micromeritics, Autopore IV9510).
- thermal conductivity of silicone rubber sheet A thermally conductive silicone rubber composition containing AlN powder is molded into a size of 10 cm ⁇ 6 cm and a thickness of 3 mm and heated in a hot air circulation oven at 150 ° C. for 1 hour. Then, the thermal conductivity of the AlN powder was measured using a thermal conductivity meter (QTM-500 manufactured by Kyoto Electronics Industry). In addition, in order to prevent electric leakage from the detection unit, the measurement was made through a polyvinylidene chloride film having a thickness of 10 ⁇ m.
- boehmite granules were prepared as granules of alumina hydrate powder as a starting material.
- the mixed powder was filled in a carbon container, subjected to reduction nitriding at 1600 ° C. for 3 hours under a nitrogen flow, and then subjected to an oxidation treatment at 680 ° C. for 8 hours under an air flow to obtain an AlN powder.
- the average particle diameter, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured by the above-described methods. The results are shown in Table 1.
- the SEM photograph of the obtained AlN powder is shown in FIG.
- a silicone rubber As a silicone rubber, uncomfortable silicone (Momentive Performance Materials Japan GTS TSE201) was prepared. 450 parts by weight of the AlN powder obtained above, 100 parts by weight of the silicone rubber and 0.5 parts by weight of the release agent were kneaded with a pressure kneader. Next, after the kneaded product is cooled, 0.5 part by weight of a crosslinking agent is further mixed using a roll, and then press-pressed at 180 ° C. for 15 minutes to obtain a sheet having a length of 10 cm, a width of 6 cm, and a thickness of 3 mm. Obtained. About the obtained sheet
- Example 2 An AlN powder was obtained in the same manner as in Example 1 except that the nitriding conditions were 1400 ° C. and 30 hours. About the obtained AlN powder, as in Example 1, the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended, In the same manner as in Example 1, the thermal conductivity, hardness, and tensile strength were measured. These results are shown in Table 1. Moreover, the SEM photograph of the obtained AlN powder is shown in FIG.
- Example 3 An AlN powder was obtained in the same manner as in Example 1 except that the nitriding conditions were 1650 ° C. and 15 hours. About the obtained AlN powder, as in Example 1, the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended, In the same manner as in Example 1, the thermal conductivity, hardness, and tensile strength were measured. These results are shown in Table 1. Moreover, the SEM photograph of the obtained AlN powder is shown in FIG.
- ⁇ -alumina granulated material was prepared as a granulated material of the starting alumina powder.
- An AlN powder was obtained in the same manner as in Example 1 except that the above ⁇ -alumina granulated material was used as a starting material.
- the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended,
- the thermal conductivity, hardness, and tensile strength were measured.
- boehmite granules were prepared as granules of alumina hydrate powder as a starting material.
- AlN powder was obtained in the same manner as in Example 1 except that the above boehmite granulate was used as a starting material and the nitriding conditions were changed to 1650 ° C. for 3 hours.
- the obtained AlN powder as in Example 1, the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended, In the same manner as in Example 1, the thermal conductivity, hardness, and tensile strength were measured. These results are shown in Table 1.
- the SEM photograph of the obtained AlN powder is shown in FIG.
- ⁇ -alumina granulated material was prepared as a granulated body of the starting alumina powder.
- An AlN powder was obtained in the same manner as in Example 1 except that the above ⁇ -alumina granulated material was used as a starting material and the nitriding conditions were changed to 1650 ° C. for 3 hours.
- the obtained AlN powder as in Example 1, the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended,
- the thermal conductivity, hardness, and tensile strength were measured.
- Example 7 The boehmite granule used in Example 1 was heat treated at 1200 ° C. for 5 hours under air flow to form ⁇ -alumina.
- the physical properties of this ⁇ -alumina granular material are as follows. ⁇ -alumina granular material (heat treated boehmite); Average particle diameter (D 50 ) by sieving method: 25 ⁇ m BET specific surface area: 10.7 m 2 / g Sphericality: 0.95
- Example 1 Using the above ⁇ -alumina granular material, reductive nitriding was performed in the same manner as in Example 1 to obtain an AlN powder. About the obtained AlN powder, as in Example 1, the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended, In the same manner as in Example 1, the thermal conductivity, hardness, and tensile strength were measured. These results are shown in Table 1. Moreover, the SEM photograph of the obtained AlN powder is shown in FIG.
- Example 8 The ⁇ -alumina granule used in Example 6 was further heat-treated at 1200 ° C. for 5 hours under air flow to form ⁇ -alumina.
- the physical properties of the ⁇ -alumina granular material ( ⁇ -alumina heat-treated product) are as follows. ⁇ -alumina granulated product; Average particle diameter (D 50 ) by sieving method: 19 ⁇ m BET specific surface area: 4.8 m 2 / g Sphericality: 0.95
- An AlN powder was obtained in the same manner as in Example 1 except that the above ⁇ -alumina granulated material was used. About the obtained AlN powder, as in Example 1, the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended, In the same manner as in Example 1, the thermal conductivity, hardness, and tensile strength were measured. These results are shown in Table 1. Moreover, the SEM photograph of the obtained AlN powder is shown in FIG.
- ⁇ -alumina powder having the following particle characteristics was prepared.
- ⁇ -alumina powder non-granulated product
- Average particle diameter (D 50 ) by laser diffraction scattering method 1.2 ⁇ m
- BET specific surface area 9.5 m 2 / g Sphericality: 0.65
- the above ⁇ -alumina powder 280 g and carbon black 140 g were mixed. Next, the mixed powder was filled in a carbon container, subjected to reduction nitriding at 1600 ° C. for 3 hours under a nitrogen flow, and then subjected to an oxidation treatment at 680 ° C. for 8 hours under an air flow to obtain an AlN powder. To 100 parts by weight of the obtained AlN powder, 5 parts by weight of yttria, 100 parts by weight of toluene solvent, 5 parts by weight of butyl methacrylate, and 2 parts by weight of hexaglycerin monooleate were added and mixed for 5 hours by a ball mill.
- a granulated product of spherical aluminum nitride powder having an average particle size of 22 ⁇ m was obtained by spray drying.
- the spray drying was performed under the following conditions. Spray drying conditions; Inlet temperature: 100 ° C Outlet temperature: 80 ° C Atomizer speed: 13000 rpm
- the obtained spherical AlN granulated product was filled in a boron nitride container and fired at 1750 ° C. for 5 hours with nitrogen circulation to obtain a spherical AlN powder.
- the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended, In the same manner as in Example 1, the thermal conductivity, hardness, and tensile strength were measured. These results are shown in Table 2.
- the SEM photograph of the obtained AlN powder is shown in FIG.
- spherical alumina having the following particle characteristics obtained by thermal spraying was prepared.
- Spherical alumina by spraying method non-granulated material
- Average particle diameter (D 50 ) by laser diffraction scattering method 16 ⁇ m
- BET specific surface area 0.17 m 2 / g Sphericality: 0.98
- An AlN powder was obtained in the same manner as in Example 1 except that the above spherical alumina was used. About the obtained AlN powder, as in Example 1, the average particle size, specific surface area, AlN conversion, sphericity, crushing strength, and pore size distribution were measured, and the silicone rubber sheet in which the AlN powder was blended, In the same manner as in Example 1, the thermal conductivity, hardness, and tensile strength were measured. These results are shown in Table 2. Moreover, the SEM photograph of the obtained AlN powder is shown in FIG.
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Abstract
Description
アルミナ還元窒化法は、アルミナとカーボンとの混合物を窒素中で加熱することにより、アルミナを還元し、さらに窒化させて窒化アルミニウムを得るという方法である。
直接窒化法は、アルミニウムに窒素を反応させることにより、アルミニウムから直接窒化アルミニウムを得るという方法である。
気相法は、アルキルアルミニウムとアンモニアを反応させた後、加熱することにより窒化アルミニウムを得るという方法である。
例えば、還元窒化法及び気相法では、得られる窒化アルミニウムの粉末は、粒子形状は球状に近いものの、その粒径はサブミクロンオーダーのものがほとんどである。
また、直接窒化法では、窒化アルミニウムは塊状で得られ、これを、粉砕・分級することにより所定の粒度に調製されるため、粒径の制御は比較的容易であるが、その粒子形状は角張った形をしており、球状からはかけ離れている。
更に、この方法によって得られる窒化アルミニウム粉末は、焼結によって得られるため、焼結の際に粒子同士が結合して変形し易く、また、窒化アルミニウムの結晶粒子の成長により圧壊強度は向上するものの、大きな凹凸ができ易い。そのため、得られる窒化アルミニウム粉末は、比表面積が小さく、そのために充填する樹脂との密着性が低くなり、得られる放熱材料の強度が不十分となるという問題を有する。
また、前記球状造粒物としては、一般に、前記粉末をスプレードライにより得られたものが好ましく、その場合、BET比表面積が30~500m2/g、特に50~300m2/gの範囲にあるものが好適に使用される。
更に、前記還元窒化工程において、還元剤が存在する窒素雰囲気において、1200~1800℃の温度で、前記球状造粒物またはその熱処理物の還元窒化が行われることが好適である。
また、本明細書において、球状窒化アルミニウム粉末の平均粒径、真球度、BET比表面積及び平均圧壊強度は、それぞれ、後述する実施例に示す方法によって測定した値である。
しかも、この窒化アルミニウム粉末の粒子は、図1等のSEM写真から理解されるように中実であり、この粒子の平均圧壊強度は100MPa以上と極めて高い。従って、この窒化アルミニウム粉末では粒子の崩壊が有効に防止され、上記の粒子形状や粒子の大きさが安定に保持され、粒子崩壊による充填性の低下が有効に回避され、更に、粉立ち等の不都合を生じることもない。
更に、フラックス剤等の金属添加剤を使用していないため、この窒化アルミニウム粉末の純度は極めて高い。
本発明の製造方法においては、出発原料として球状のアルミナ又はアルミナ水和物の造粒物を使用し、この造粒物(或いはその熱処理物)を、還元窒化工程に供給して窒化還元を行い、最後に、表面酸化処理等の後処理を適宜行うことにより、目的とする球状窒化アルミニウム粉末が製造される。
出発原料として用いる球状のアルミナ又はアルミナ水和物の造粒物(granule)は、アルミナ粉末又はアルミナ水和物粉末を球状に造粒することにより得られたものである。
かかる造粒物において、アルミナとしては、α、γ、θ、η、δ等の結晶構造を持つものであれば特に制限なく使用される。また、アルミナ水和物は、熱処理することによって、γ、θ、η、δなどの遷移アルミナ、さらにα-アルミナに変わるものであり、このようなアルミナ水和物としては、ベーマイト、ダイアスポア、水酸化アルミニウムなどを挙げることができる。
従って、本発明では、アルコキシド法によって得られたアルミニウムアルコキシドを精製し、これを加水分解して得られる水酸化アルミニウムや、該水酸化アルミニウムを熱処理して得られるベーマイト、遷移アルミナ、α-アルミナが原料として好適に使用される。特に、α-アルミナ、γ-アルミナ、ベーマイトを原料として用いた時には、還元窒化反応を制御し易く、また、窒化が進行し易いという利点がある。
更に、スプレードライの条件は、何ら制限されず、使用されるスプレードライ機の大きさや種類、噴霧液の固形分濃度、粘度、流量などによって適宜選択すれば良い。
本発明においては、上述したアルミナ粉末又はアルミナ水和物粉末の球状造粒物を、直接後述する還元窒化工程に供給して還元窒化を行うこともできるし、この球状造粒物を一旦熱処理する熱処理工程を経た後に還元窒化工程に供給することもできる。
即ち、還元窒化工程では、原料として用いる球状造粒物は1200℃以上の高温に保持されるため、その昇温過程での加熱により収縮し、粒径の経過やBET比表面積の低下を生じ、この後に還元窒化が行われることとなる。従って、この昇温過程で加えられる程度に熱処理されたものを、一旦、冷却した後に還元窒化工程に供給することも可能である。例えば、水酸化アルミニウムやベーマイトの球状造粒物(その比表面積は前述した範囲内である)を、約600℃で一定時間熱処理することにより得られたγ-アルミナの球状造粒物や1100℃以上の温度で一定時間熱処理することにより得られたα-アルミナの球状造粒物を、還元窒化工程に供給することもできる。
また、この熱処理が過酷であり、BET比表面積が極度に低下してしまうと、先にも述べた様に、造粒物の還元窒化における窒化の進行が遅くなり、窒化アルミニウムへの転化率が著しく低下してしまい、生産性の低下という不都合も招いてしまうからである。
本発明においては、上述したアルミナ又は水和アルミナの球状造粒物(或いはその熱処理物)を、カーボンや窒化アルミニウム焼結体等によって形成された反応容器内において、還元剤(例えば、カーボンや還元性ガス)が存在する窒素雰囲気下、所定の温度で焼成(還元窒化)することにより、目的とする球状窒化アルミニウム粉末を得ることができる。
これらの還元性ガスは、二種以上を混合して使用することもできるし、また、以下に述べるカーボンと併用することもできる。
前記カーボン前駆体としては、フェノール樹脂、メラミン樹脂、エポキシ樹脂、フランフェノール樹脂等の合成樹脂縮合物やピッチ、タール等の炭化水素化合物や、セルロース、ショ糖、ポリ塩化ビニリデン、ポリフェニレン等の有機化合物が挙げられるが、固相のままないしは気相を経由して炭素化する化合物が好ましい。特に、フェノール樹脂等の合成樹脂やセルロース、ポリフェニレンなどが好ましい。これらのカーボンも、金属等の不純物が少ないものが好ましい。
また、還元性ガスは、上記窒素ガスに同伴させて前記反応容器内に供給することが好ましい。
更に、還元剤として用いるカーボン(カーボン前駆体を含む)は、種々の方法で反応容器内に存在させることができ、例えば、反応容器内に原料の球状造粒物とカーボンとを分けて存在させることもできるし、球状造粒物とカーボンとを混合して反応容器内に存在させることもできる。特に、球状造粒物とカーボンとを混合して使用することは、還元窒化時における粒子の凝集を確実に防止することができるという点で好適である。
本発明においては、上記の焼成(還元窒化)後、適宜表面酸化処理を行うことができる。かかる酸化処理により、例えば、窒化アルミニウムの粉末中に含まれるカーボンを除去し、品質を向上させることができるばかりか、その耐水性を向上させ、例えば、水分を含む環境下にこの粉末を保持せしめた場合においても、アンモニア臭の発生等を有効に防止することができる。
このような酸化処理に用いるガスとしては、空気、酸素などの炭素を除去できるガスならば何等制限無く採用できるが、経済性や得られる窒化アルミニウムの酸素含有率を考慮して、空気が好適である。また、処理温度は一般的に500~900℃がよく、脱炭素の効率と窒化アルミニウム表面の過剰酸化を考慮して、600~750℃が好適である。
本発明においては、上記のようにして真球度が高く、比較的大きな粒子サイズの粒子からなる球状窒化アルミニウム粉末を得ることができる。
例えば、上述した方法によれば、図1の電子顕微鏡写真から理解されるように、真球度が0.8以上、特に、0.9以上と極めて真球に近い球形状粒子からなり、且つ、平均粒子径が10~200μm、特に20~50μmと比較的大きく、BET比表面積が0.5~20m2/g、特に0.8~17m2/gの範囲にある球状窒化アルミニウム粉末が得られ、成形性を損なわずに樹脂等のバインダに高充填するために適した粒子特性を有している。
従って、この球状窒化アルミニウム粉末は、取扱時等において粒子の崩壊を生じることがなく、粉立ち等が有効に防止され、また、上記のような粒子の真球度や平均粒径、BET比表面積等の粒子特性が変動することなく安定に保持される。例えば、前述した造粒を溶射法によって得られた、内部に空隙のない球状アルミナを出発原料として用いた場合、還元窒化時に内部に空洞ができてしまい、上記のような高い圧壊強度を示さない。
本発明の球状窒化アルミニウム粉末は、その粒子内部に微細な細孔を有しており、図1及び図2より理解されるように、微細な細孔に由来する微細な凹凸が粒子表面に形成されているため、高い圧壊強度と大きな比表面積とを有しているものと考えられる。
このような放熱材料には、本発明の球状窒化アルミニウム粉末以外に、アルミナ、窒化ホウ素、酸化亜鉛、炭化珪素、グラファイトなどのフィラーを一種、あるいは数種類充填しても良い。これらのフィラーは、例えばシランカップリング剤やリン酸又はリン酸塩などで表面処理したものを用いても良い。放熱材料の特性や用途に応じて、本発明の球状窒化アルミニウム粉末とそれ以外のフィラーの形状、粒径を選択すれば良い。また、放熱材料における球状窒化アルミニウム粉末とそれ以外のフィラーの混合比は、1:99~99:1の範囲で適宜調整できる。
さらに、放熱材料には、可塑剤、加硫剤、硬化促進剤、離形剤等の添加剤をさらに添加しても良い。
比表面積は、BET一点法にて測定を行った。
振とうふるい機(田中化学機械製)を用いて、90、75、63、53、45、38、32、22μm網目のふるい(JIS Z8801)をセットし、試料20g(アルミナ又はアルミナ水和物の造粒物)を入れて7分間振動した後、各ふるい上の試料重量を測定し、ふるい上のふるい上残存率が重量積算で50%となる粒径(D50)を求めた。
試料をホモジナイザーにて5%ピロリン酸ソーダ水溶液中に分散させ、レーザ回折粒度分布装置(日機装製MICROTRAC HRA)にて体積積算で50%となる平均粒径(D50)を測定した。
X線回折(CuKα、10~70°)にて、検量線法によって窒化アルミニウム(AlN)の主要ピーク((100)面に由来するピーク)と各アルミナ成分(α-アルミナ,θ-アルミナ,γ-アルミナ、δ-アルミナ等)の主要ピークのピーク強度を求め、このピーク強度から下記式(1)よりAlN転化率を算出した。
尚、その他の成分が含まれる場合は、その成分の主要ピークを選択し、式(1)の分母に加えた。
AlN転化率(%)=(Q/R)×100 ……(1)
式中、
Qは、AlNピーク強度であり、
Rは、AlNピーク強度と、アルミナ及びその他の成分のピーク強度と
の合計である。
α-アルミナ:(113)面に由来するピーク
γ-アルミナ:(400)面に由来するピーク
θ-アルミナ:(403)面に由来するピーク
δ-アルミナ:(046)面に由来するピーク
(5)真球度
電子顕微鏡の写真像から、任意の粒子100個を選んで、スケールを用いて粒子像の長径(DL)と短径(DS)とを測定し、その比(DS/DL)の平均値を真球度とした。
陽イオン不純物含有量(金属元素濃度)は、窒化アルミニウム粉末をアルカリ溶融後、酸で中和し、島津製作所製ICP-1000を使用して溶液のICP発光分析により定量した。
AlN粉末の平均圧壊強度は、単一粒子の圧縮試験(JIS R 1639-5)によって求めた。微小圧縮試験機(島津製作所製MTC-W)を用いて、任意の粒子100個の単独粒子の圧縮試験を行い、破壊試験力と粒径より圧壊強度を求め、算術平均した。
細孔分布測定装置(マイクロメリティックス社製、オートポアIV9510)を用い、水銀圧入法により、AlN粉末の細孔径分布を求めた。
AlN粉末が配合された熱伝導性シリコーンゴム組成物を、10cm×6cm、厚さ3mmの大きさに成形し150℃の熱風循環式オーブン中で1時間加熱して硬化し、熱伝導率計(京都電子工業製QTM-500)を用いてAlN粉末の熱伝導率を測定した。なお、検出部からの漏電防止のため、厚さ10μmのポリ塩化ビニリデンフイルムを介して測定した。
AlN粉末が配合された熱伝導性シリコーンゴム組成物を、150℃の熱風循環式オーブン中で1時間加熱して得た熱伝導性シリコーンゴムシートについて、JIS K6253によるデユロメータ硬さ試験機を用いて硬さを測定した。
前記熱伝導性シリコーンゴムシートについて、JIS K6301に準拠して引張試験を行い、破断時の引張強度を測定した。この引張強度が大きいほど、AlN粉末とマトリックスとの密着性が高い。
出発原料のアルミナ水和物粉末の造粒体として、下記のベーマイト造粒物を用意した。
ベーマイト造粒物;
ふるい法による平均粒径(D50):40μm
BET比表面積:135m2/g
真球度:0.98
得られたAlN粉末について、前述の方法にて、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定した。結果を表1に示す。また、得られたAlN粉末のSEM写真を図3に示す。
上記で得られたAlN粉末450重量部と、上記のシリコーンゴム100重量部及び離型剤0.5重量部とを加圧ニーダーにて混練した。次いで、混練物を冷却した後に、ロールを用いて、更に架橋剤0.5重量部を混合した後、180℃で15分間加圧プレスして、縦10cm、横6cm、厚さ3mmのシートを得た。
得られたシートについて、前述した方法で熱伝導率、硬さ及び引っ張り強度を測定した。結果を表1に示す。
窒化条件を1400℃、30時間とした以外は、実施例1と同様にしてAlN粉末を得た。
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表1に示す。
また、得られたAlN粉末のSEM写真を図4に示す。
窒化条件を1650℃、15時間とした以外は、実施例1と同様にしてAlN粉末を得た。
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表1に示す。
また、得られたAlN粉末のSEM写真を図5に示す。
出発原料のアルミナ粉末の造粒物として、下記のγ-アルミナ造粒物を用意した。
γ-アルミナ造粒物;
ふるい法による平均粒径(D50):38μm
BET比表面積:152m2/g
真球度:0.98
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表1に示す。
また、得られたAlN粉末のSEM写真を図6に示す。
出発原料のアルミナ水和物粉末の造粒体として、下記のベーマイト造粒物を用意した。
ベーマイト造粒物;
ふるい法による平均粒径(D50):20μm
BET比表面積:51m2/g
真球度:0.98
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表1に示す。
また、得られたAlN粉末のSEM写真を図7に示す。
出発原料のアルミナ粉末の造粒体として、下記のγ-アルミナ造粒物を用意した。
γ-アルミナ造粒物;
ふるい法による平均粒径(D50):19μm
BET比表面積:49m2/g
真球度:0.97
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表1に示す。
また、得られたAlN粉末のSEM写真を図8に示す。
実施例1で用いたベーマイト造粒物を、空気流通下1200℃で5時間熱処理してα-アルミナ化した。このα-アルミナ粒状物(ベーマイト熱処理物)の物性は以下のとおりである。
α-アルミナ粒状物(ベーマイト熱処理物);
ふるい法による平均粒径(D50):25μm
BET比表面積:10.7m2/g
真球度:0.95
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表1に示す。
また、得られたAlN粉末のSEM写真を図9に示す。
実施例6で用いたγ-アルミナ造粒物を、空気流通下1200℃で更に5時間熱処理してα-アルミナ化した。このα-アルミナ粒状物(γ―アルミナ熱処理物)の物性は以下のとおりである。
α-アルミナ造粒物;
ふるい法による平均粒径(D50):19μm
BET比表面積:4.8m2/g
真球度:0.95
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表1に示す。
また、得られたAlN粉末のSEM写真を図10に示す。
下記の粒子特性を有するα-アルミナ粉末を用意した。
α-アルミナ粉末(非造粒物);
レーザ回折散乱法による平均粒径(D50):1.2μm
BET比表面積:9.5m2/g
真球度:0.65
得られたAlN粉末100重量部に対し、イットリア5重量部、トルエン溶媒100重量部、メタクリル酸ブチル5重量部、ヘキサグリセリンモノオレート2重量部を加えてボールミルで5時間混合し、得られたスラリーをスプレードライにより平均粒径22μmの球状窒化アルミニウム粉末の造粒物を得た。尚、スプレードライは、下記条件で行った。
スプレードライ条件;
入口温度:100℃
出口温度:80℃
アトマイザー回転数:13000rpm
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表2に示す。
また、得られたAlN粉末のSEM写真を図11に示す。
スラリーのスプレードライ条件を下記のように変更した以外は、比較例1と同様にして球状AlN粉末を得た。
スプレードライ条件;
入口温度:100℃
出口温度:80℃
アトマイザー回転数:6000rpm
得られたAlN粉末の平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表2に示す。
また、得られたAlN粉末のSEM写真を図12に示す。
出発原料として、溶射法により得られた下記粒子特性を有する球状アルミナを用意した。
溶射法による球状アルミナ(非造粒物);
レーザ回折散乱法による平均粒径(D50):16μm
BET比表面積:0.17m2/g
真球度:0.98
得られたAlN粉末について、実施例1と同様、平均粒径、比表面積、AlN転化率、真球度、圧壊強度並びに細孔径分布を測定し、且つAlN粉末が配合されたシリコーンゴムシートについて、実施例1と同様に、熱伝導率、硬度及び引っ張り強度を測定した。これらの結果を表2に示す。
また、得られたAlN粉末のSEM写真を図13に示す。
Claims (7)
- アルミナ粉末又はアルミナ水和物粉末の球状造粒物を出発原料として使用し、該球状造粒物を、還元窒化工程に供給し、還元窒化を行うことを特徴とする球状窒化アルミニウム粉末の製造方法。
- 前記還元窒化工程に前記球状造粒物を供給する前に、該球状造粒物を、一旦、BET比表面積が少なくとも2m2/g以上に維持される程度に熱処理する熱処理工程を含む、請求項1に記載の製造方法。
- 前記球状造粒物が、前記アルミナ粉末又はアルミナ水和物粉末のスプレードライにより得られたものであり、30~500m2/gのBET比表面積を有している請求項1に記載の製造方法。
- 前記還元窒化工程において、還元剤が存在する窒素雰囲気において、1200~1800℃の温度で、前記球状造粒物またはその熱処理物の還元窒化が行われる請求項1記載の製造方法。
- 平均して0.8以上の真球度と100MPa以上の圧壊強度を有する粒子からなり、平均粒径(D50)が10~200μmの範囲にあり、BET比表面積が0.5~20m2/gの範囲にあることを特徴とする球状窒化アルミニウム粉末。
- 細孔直径が2μm以下の細孔の容積が、0.02~1.0cm3/gの範囲にある請求項5記載の球状窒化アルミニウム粉末。
- 請求項5に記載の球状窒化アルミニウム粉末よりなる放熱材料用フィラー。
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US9403680B2 (en) | 2013-02-04 | 2016-08-02 | Tokuyama Corporation | Method for producing sintered aluminum nitride granules |
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JP2016124908A (ja) * | 2014-12-26 | 2016-07-11 | 株式会社トクヤマ | 樹脂成形体 |
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KR20120120268A (ko) | 2012-11-01 |
JP5686748B2 (ja) | 2015-03-18 |
CN102686511A (zh) | 2012-09-19 |
US20120258310A1 (en) | 2012-10-11 |
CN102686511B (zh) | 2014-11-19 |
TW201132579A (en) | 2011-10-01 |
EP2530049A1 (en) | 2012-12-05 |
JPWO2011093488A1 (ja) | 2013-06-06 |
TWI573758B (zh) | 2017-03-11 |
US9199848B2 (en) | 2015-12-01 |
EP2530049A4 (en) | 2014-06-04 |
KR101545776B1 (ko) | 2015-08-19 |
EP2530049B1 (en) | 2016-07-20 |
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