Hexagonal boron nitride powder and method for producing the same, and composition and heat dissipation material using the same

1. A hexagonal boron nitride powder comprising an aggregate of primary particles of hexagonal boron nitride,

comprising boron as an impurity element at a content of 1.00 to 30.00% by mass and oxygen as an impurity element at a content of 0 to 1.00% by mass, and

having a peak in a particle diameter range of 10.0 μm or more and less than 100.0 μm and a 50% volume cumulative particle diameter D 50 (d1) of 30.0 to 200.0 μm in a particle size distribution curve representing volume-based frequency distribution,

wherein the hexagonal nitride powder has a structure such that, when the hexagonal boron nitride powder is ultrasonically treated under the following condition 1 for 1 minute, a ratio of a height (a1) of the peak before the ultrasonic treatment to a height (a2) of the peak after treatment, a2/a1, being 0.80 to 1.00 and a ratio of a 50% volume cumulative particle diameter D 50 (d1) before ultrasonic treatment to a 50% volume cumulative particle diameter D 50 (d2) after the ultrasonic treatment, d2/d1, being 0.80 to 1.00,

[condition 1] a powder sample dispersion obtained by mixing 0.06 g of the hexagonal boron nitride powder, 0.005 g of a detergent (“Mama Lemon (registered trademark)”, manufactured by Lion Corporation) and 50 g of water (20° C.) is placed in a 50 mL glass beaker having a barrel inner diameter of 40 mm and a height of 60 mm, and an end of a tip of a vibrator of an ultrasonic generator is set at a height of 1 cm from a bottom surface of a central portion of the beaker, and ultrasonic treatment is performed at an output of 150 W and an oscillation frequency of 19.5 kHz, and

wherein the boron as an impurity element is a boron atom not bound to a nitrogen atom and which does not form a hexagonal boron nitride molecule.

2. The hexagonal boron nitride powder according to claim 1 , having a BET specific surface area of 0.1 m 2 /g or more and less than 5.0 m 2 /g, and the primary particles each having a smooth surface.

3. The hexagonal boron nitride powder according to claim 1 , having a crystallite diameter derived from a (002) plane of hexagonal boron nitride, as determined by powder X-ray diffraction measurement, of 250 Å or more and less than 375 Å.

4. The hexagonal boron nitride powder according to claim 1 , having a BET specific surface area of 0.1 m 2 /g or more and less than 5.0 m 2 /g.

5. The hexagonal boron nitride powder according to claim 1 , wherein the content of the boron as the impurity element is 5.00 to 28.00% by mass.

6. The hexagonal boron nitride powder according to claim 1 , wherein the content of the boron as the impurity element is 10.00 to 25.00% by mass.

7. A composition comprising a base material comprising one or two or more selected from the group consisting of a resin and a rubber, and the hexagonal boron nitride powder according to claim 1 .

8. A heat dissipation material comprising the composition according to claim 7 .

9. The heat dissipation material according to claim 8 , being a heat dissipation sheet.

10. The heat dissipation material according to claim 9 , wherein a ratio of a diffraction peak intensity (I(002)) of a (002) plane to a diffraction peak intensity (I(100)) of a (100) plane, I(002)/I(100), of primary particles of hexagonal boron nitride, as determined in a direction perpendicular to a thickness direction of the heat dissipation sheet by X-ray diffraction measurement, is 7.0 to 15.

11. A method for producing the hexagonal boron nitride powder according to claim 1 , comprising:

step 1 of preparing a mixed powder comprising a boron powder and one or two or more boron compounds selected from the group consisting of a boron oxoacid and boron oxide,

step 2 of calcining the mixed powder under a noble gas atmosphere at 1200° C. or more and less than 1800° C. to obtain a calcined powder,

step 3 of granulating the calcined powder to obtain a granulated powder having a particle diameter of 10 to 200 μm,

step 4 of melting the granulated powder under a noble gas atmosphere at 1800 to 2300° C. to obtain a molten powder, and

step 5 of firing the molten powder under a nitrogen gas atmosphere at 2000 to 2300° C. to obtain a hexagonal boron nitride powder.

12. The method for producing the hexagonal boron nitride powder according to claim 11 , wherein the calcined powder obtained in the step 2 comprises boron suboxide.

13. The method for producing the hexagonal boron nitride powder according to claim 11 , wherein in the step 3, at least any of boron oxide and hexagonal boron nitride is added to the calcined powder for granulation.