A hexagonal boron nitride powder having an average longer diameter (L) of primary particles in the hexagonal boron nitride powder of more than 10.0 μm and 30.0 μm or less, an average thickness (D) of the primary particles in the hexagonal boron nitride powder of 1.0 μm or more, a ratio of the average longer diameter (L) to the average thickness (D), [L/D], of 3.0 or more and 5.0 or less, and a content of primary particles having a ratio of a longer diameter (1) to a thickness (d), [l/d], of 3.0 or more and 5.0 or less of 25% or more, a method for producing the hexagonal boron nitride powder, and a resin composition and a resin sheet each containing the hexagonal boron nitride powder.

Ultra-lightweight aerogels and methods for fabricating such aerogels from ammonia borane and a support structure, where the support structure is either two-dimensional nanostructures, or hydrocarbon polymer colloids. The components are mixed, then annealed. The properties of the disclosed aerogels can be tuned by controlling the ratio between the support structure and the ammonia borane, or by infiltrating the aerogels with additives.

Provided is a method for producing, with a small amount of lithium, a hexagonal boron nitride powder containing thick hexagonal boron nitride particles. A method for producing a hexagonal boron nitride powder, including the steps of: preparing a mixed powder which contains an organic compound containing nitrogen atoms, a boron source which contains boron atoms whose molar ratio with respect to the nitrogen atoms is adjusted to be 0.26 or more and 0.67 or less, and an alkali metal in which lithium atoms are adjusted to be in a range of 30 mol % or more and less than 100 mol %, the alkali metal being present such that a molar ratio of the boron atoms with respect to alkali metal atoms contained in the alkali metal is 0.75 or more and 3.35 or less; and heating the mixed powder at a maximum temperature of 1200° C. or higher and 1500° C. or lower.

This disclosure relates to porous boron nitride and a method for preparing the same. The porous boron nitride of the present invention may be obtained by mixing a boron source with a nitrogen source, heating the mixture to form a compound, and then, extracting elements other than boron and nitrogen. The porous boron nitride of the present invention comprises both micropores and mesopoers, and it has a large specific surface area, and thus, may be usefully used in various fields.

It is an object to achieve a resin sheet having high thermal conductance and high dielectric strength. Hexagonal boron nitride powder in accordance with an aspect of the present invention includes hexagonal boron nitride agglomerate particles each including agglomerated hexagonal boron nitride primary particles, and has a specific surface area of not less than 0.5 m.sup.2/g and not more than 5.0 m.sup.2/g. The hexagonal boron nitride primary particles each have a long diameter of not less than 0.6 μm and not more than 4.0 μm and an aspect ratio of not less than 1.5 and not more than 5.0.

The boron nitride nanomaterial of the present invention is a boron nitride nanomaterial comprising a boron nitride nanotube and a boron nitride nanosheet, and having a peak top of a Raman spectrum located at 1369 cm.sup.−1 or more.

A flexible boron nitride nanoribbon aerogel has an interconnected three-dimensional porous network structure which is formed by mutually twining and contacting boron nitride nanoribbons and consists of macropores having a pore diameter of more than 50 nm, mesopores having a pore diameter of 2-50 nm and micropores having a pore diameter of less than 2 nm. The preparation method of the flexible boron nitride nanoribbon aerogel includes the following steps: performing high-temperature dissolution on boric acid and a nitrogen-containing precursor to form a transparent precursor solution, preparing the transparent precursor solution into precursor hydrogel, subsequently drying and performing high-temperature pyrolysis to obtain the flexible boron nitride nanoribbon aerogel. The boron nitride nanoribbon aerogel has excellent flexibility and resilience and can withstand different forms of loads from the outside within a wide temperature range.

One aspect of the present invention is a boron nitride powder composed of aggregates of primary particles of boron nitride, wherein the boron nitride powder has an average diameter of 40 μm or more and an average sphericity of less than 0.70.

A method of producing hexagonal boron nitride by chemical vapour deposition on a substrate, the method comprising: (a) a step of heating the substrate at a first temperature for a first time; (b) a step of exposing the substrate to a precursor containing boron and a precursor containing nitrogen at a first partial pressure of the precursor(s) at a second temperature for a second time, wherein either a single precursor is used as the precursor containing boron and as the precursor containing nitrogen or different precursors are used as the precursor containing boron and the precursor containing nitrogen; (c) a step of heating the substrate at a third temperature for a third time without the precursor; and (d) a step of exposing the substrate to the precursors at a fourth temperature at a second partial pressure of the precursor(s) for a fourth time.

BN nanosheets are prepared by a method comprising heating to a temperature of at least 500 C., a mixture comprising: (1) an alkali borohydride, and (2) an ammonium salt. NaN.sub.3 may be included to increase the yield. No catalyst is required, and the product produced contains less than 0.1 atomic percent metal impurities.