To obtain BN powder with a high crystallinity that has excellent shape retention and handling properties with high N2 gas permeability via bulk B2O3, as an intermediate, that can suitably cope with blocking of the production process by dehydrating a mixture containing an orthoboric acid powder and a carbonaceous powder having an average particle size, respectively and heating the mixture.
A mixture of an orthoboric acid powder with an average particle size of ≥100μm, preferably ≥500μm, particularly 700-1,000μm and a carbonaceous powder (for example, acetylene black), in a preferred embodiment, the average diameter of the powders other than orthoboric acid is less than 1/5 that of the orthoboric acid particle, is dehydrated, preferably at 300-450°C to prepare bulk boron oxide, preferably with a density of 0.4-0.7g/cm3, particularly of 0.5-0.6g/cm3, then fired in a nitrogen atmosphere, preferably over 1,600°C.
TAKEI HIROAKI
KONYA YOSHIHARU
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