Boron nitride powder, method for producing same, and heat-dissipating member produced using same
To provide a boron nitride powder having excellent heat conductivity and high particle strength. Provided is a boron nitride powder which comprises bulky boron nitride formed such that scaly primary particles of hexagonal boron nitride are aggregated to form bulky particles, and which has the following characteristics (A) to (C): (A) a particle strength of the bulky particles at a cumulative breakdown rate of 63.2% is 5.0 MPa or more; (B) an average particle size of the boron nitride powder is 2 μm or more and 20 μm or less; and (C) an orientation index of the boron nitride powder as determined from X-ray diffraction is 20 or less.
1. A boron nitride powder which comprises bulky boron nitride formed such that scaly primary particles of hexagonal boron nitride are aggregated to form bulky particles, and which has the following characteristics (A) to (C):
(A) a particle strength of the bulky particles at a cumulative breakdown rate of 63.2% is 5.0 MPa or more;
(B) an average particle size of the boron nitride powder is 2 μm or more and 20 μm or less; and
(C) an orientation index of the boron nitride powder as determined from X-ray diffraction is 20 or less.
2. A heat-dissipating member comprising the boron nitride powder according to claim 1 and having a film thickness of 100 μm or less.
3. A method for producing the boron nitride powder according to claim 1 , the method comprising:
a pressure nitriding baking step of baking boron carbide having a carbon content of 18% or more and 21% or less and an average particle size of 5 μm or more and 15 μm or less in a pressurized nitrogen atmosphere at 1800° C. or more and 0.6 MPa or more;
a decarbonizing crystallization step of mixing a baked product obtained by the pressure nitriding baking step is mixed with a boron source, and heating the resulting mixture to a temperature capable of initiating decarbonization, then heating the mixture to a retention temperature of 1800° C. or more at a temperature rising rate of 5° C./min or less, and retaining the mixture in nitrogen atmosphere at the retention temperature to obtain bulky boron nitride;
a pulverizing step of pulverizing the bulky boron nitride obtained by the decarbonizing crystallization step to obtain the boron nitride powder having an average particle size of 2 μm or more and 20 μm or less.
4. A method for producing the boron nitride powder according to claim 1 , the method comprising:
a vapor phase reaction step of subjecting alkoxide borate gas and ammonia gas to vapor phase reaction at 750° C. or more;
a crystallization step of heating an intermediate obtained by the vapor phase reaction step until a baking temperature of 1500° C. or more is reached under conditions of an atmosphere containing 20 vol % or less of ammonia up to 1000° C. and an atmosphere containing 50 vol % or more of ammonia at 1000° C. or more, and baking the intermediate at the baking temperature to obtain bulky boron nitride;
a pulverizing step of pulverizing the bulky boron nitride obtained by the crystallization step to obtain the boron nitride powder having an average particle size of 2 μm or more and 20 μm or less.