Changrui Zhang

Ultralight boron nitride aerogels via template-assisted chemical vapor deposition

Boron nitride (BN) aerogels are porous materials with a continuous three-dimensional network structure. They are attracting increasing attention for a wide range of applications. Here, we report the template-assisted synthesis of BN aerogels by catalyst-free, low-pressure chemical vapor deposition on graphene-carbon nanotube composite aerogels using borazine as the B and N sources with a relatively low temperature of 900 °C. The three-dimensional structure of the BN aerogels was achieved through the structural design of carbon aerogel templates. The BN aerogels have an ultrahigh specific surface area, ultralow density, excellent oil absorbing ability, and high temperature oxidation resistance. The specific surface area of BN aerogels can reach up to 1051 m2 g−1, 2-3 times larger than the reported BN aerogels. The mass density can be as low as 0.6 mg cm−3, much lower than that of air. The BN aerogels exhibit high hydrophobic properties and can absorb up to 160 times their weight in oil. This is much higher than porous BN nanosheets reported previously. The BN aerogels can be restored for reuse after oil absorption simply by burning them in air. This is because of their high temperature oxidation resistance and suggests broad utility as water treatment tools.

Van der Waals epitaxy and characterization of hexagonal boron nitride nanosheets on graphene

Graphene is highly sensitive to environmental influences, and thus, it is worthwhile to deposit protective layers on graphene without impairing its excellent properties. Hexagonal boron nitride (h-BN), a well-known dielectric material, may afford the necessary protection. In this research, we demonstrated the van der Waals epitaxy of h-BN nanosheets on mechanically exfoliated graphene by chemical vapor deposition, using borazine as the precursor to h-BN. The h-BN nanosheets had a triangular morphology on a narrow graphene belt but a polygonal morphology on a larger graphene film. The h-BN nanosheets on graphene were highly crystalline, except for various in-plane lattice orientations. Interestingly, the h-BN nanosheets preferred to grow on graphene than on SiO2/Si under the chosen experimental conditions, and this selective growth spoke of potential promise for application to the preparation of graphene/h-BN superlattice structures fabricated on SiO2/Si.

Low-Cost Preparation of Boron Nitride Ceramic Powders

The amorphous boron nitride ceramic powders were prepared at 750–950 °C by the low-cost urea route, and the effects of preparation temperatures, molar ratios of the raw materials and oxidation treatment on the composition, structure and surface morphology of the products were investigated through FTIR, XRD and SEM. The results show that the products ceramize and crystallize gradually with the increase of the temperature. When the molar ratio and reaction temperature are 3:2 and 850 °C, respectively, the products have high purity, compact structure and nice shape. The oxidation treatment at 450 °C will not impair the composition and structure of boron nitride but effectively remove the impurities.

Fabrication and properties of SiNO continuous fiber reinforced BN wave-transparent composites

SiNO continuous fiber reinforced boron nitride (BN) wave-transparent composites (SiNOf/BN) have been fabricated by a precursor infiltration pyrolysis (PIP) method using borazine as the precursor. The densification behavior, microstructures, mechanical properties, and dielectric properties of the composites have been investigated. After four PIP cycles, the density of the composites had increased from 1.1 g·cm−3 to 1.81 g·cm−3. A flexural strength of 128.9 MPa and an elastic modulus of 23.5 GPa were achieved. The obtained composites have relatively high density and the fracture faces show distinct fiber pull-out and interface de-bonding features. The dielectric properties of the SiNOf/BN composites, including the dielectric constant of 3.61 and the dielectric loss angle tangent of 5.7×10−3, are excellent for application as wave-transparent materials.