Classification of boron nitride materials and application

Boron nitride, chemical formula BN, a non-oxide material, is the isoelectronic body of carbon (C2), its crystal structure is similar to graphite, is currently one of the more studied and applied nitride ceramic materials.  According to the crystal structure type, BN mainly includes hexagonal boron nitride (H-BN), cubic boron nitride (C-BN), rhombic boron nitride (R-BN), wurtzite boron nitride (W-BN).  

Classification of boron nitride nanomaterials  

1. Isotropic BN nanomaterials refer to solid and hollow nanospheres with central point symmetry and similar nanostructures.  As early as 1990, there was a patent claiming that using BCl3 and ammonia as raw materials, using CVD method to prepare spherical BN particles at low temperature.  BN hollow nanospheres were prepared by solvothermal method using Zn and KBH4/NH4BF4 as raw materials.  

2. Anisotropic BN nanomaterials

(1) Boron nitride nanotubes: the structure of boron nitride nanotubes is similar to that of carbon nanotubes. B atoms and N atoms replace C atoms in the graphite layer alternately to form nanotube-like structures, which can be divided into single-walled tubes and multi-walled tubes.  Boron nitride nanotubes come in three structural types: armchair, serrated and chiral.  The commonly used preparation methods mainly include arc discharge, laser burning, ball milling, plasma injection, carbon nanotubes replacement, chemical vapor deposition and so on.  

(2) Boron nitride nanowires (BNNW) are generally generated in the process of preparing boron nitride nanotubes.  Boron nitride nanowire was synthesized from ammonia and boron oxide, but the quality and ammonification process of precursor nanowire were difficult to control.  Although boron nitride nanowires have better oxidation resistance and dielectric properties than carbon fiber, compared with carbon fiber, research on boron nitride nanowires is much less.  Currently, research is also underway on a polymer precursor that can be used to synthesize boron nitride nanowires. The precursor is a borazane.  

(3) Boron nitride nanosheets: the structure of two-dimensional hexagonal boron nitride nanosheets is similar to that of graphite, which can be regarded as the replacement of C atoms in graphite by B and N atoms successively.  In multilayer BORON nitride sheets, there is an interaction force between each BN layer due to the polarization between B-N bonds.  Therefore, monolayer boron nitride nanosheets are difficult to obtain, while multilayer boron nitride nanosheets are beneficial to the stability of the whole structure.  

Application of boron nitride nanomaterials  

1. Boron nitride coating: at high temperature has obvious chemical inertia, so that boron nitride coating can be used to protect aluminum, magnesium, zinc alloy and other materials from high temperature oxidation.  

2. BN's high thermal conductivity: BN's high thermal conductivity has always been the enthusiasm of scientific research workers, mainly using the high thermal conductivity of nano H-BN and C-BN to prepare composite materials to accelerate the heat dissipation and thermal conductivity effect.  At the same time, it can solve the problem that the high resistivity materials need to avoid short circuit when the thermal conductivity materials are in contact with the electrical components in operation.  

3. Water purification: effective removal of oil, organic solvents and dyes from water is a global water conservation issue.  

4. Hydrogen storage materials: hydrogen is the cleanest energy at present and has bright development prospects for solving the problem of air pollution.  Using melamine and boric acid as precursors, porous BN nanoribbons were prepared at 900-1100℃ with a specific surface area of 1488m2/g.  

As an advanced nanomaterial and ceramic material, boron nitride nanomaterial has been favored by various fields for its excellent physical and chemical properties, and will play a more important role in photoelectric, environmental protection and daily chemical fields.