Bulk quantities of hexagonal boron nitride (h-BN) nanosheets have been synthesized via a simple template- and catalyst-free chemical vapor deposition process at 1100−1300 °C. Adjusting the synthesis and chemical reaction parameters, the thickness of the BN nanosheets can be tuned in a range of 25−50 nm. Fourier transform infrared spectra and electron energy loss spectra reveal the typical nature of sp2-hybridization for the BN nanosheets. It shows an onset oxidation temperature of 850 °C for BN nanosheets compared with only about 400 °C for that of carbon nanotubes under the same conditions. It reveals a strong and narrow cathodoluminescence emission in the ultraviolet range from the h-BN nanosheets, displaying strong ultraviolet lasing behavior. The fact that this luminescence response would be rather insensitive to size makes the BN nanosheets ideal candidates for lasing optical devices in the UV regime. The h-BN nanosheets are also better candidates for composite materials in high-temperature and hazardous environments.
The inferior rate performance, cyclability, and low-temperature performance plague the wide application of natural graphite (NG). In this work, NG was modified with polyvinylidene fluoride (PVDF) by a simple hydrothermal route at 180 °C and subsequent sintering at 300 °C. The two-step treatment not only boosted the graphitization degree of NG but also strengthened the binding of PVDF with NG to yield uniform PVDF coating and F-doping adjacent to the NG surface. The modification contributes to enhancing the structural stability of NG, electron transfer, and Li-ion diffusion, facilitating the formation of a uniform and dense solid electrolyte interface film, reducing impedance, and alleviating polarization, thus endowing the PVDF-modified NG with elevated electrochemical performance, especially the marked enhancement in rate performance, cyclability, and low-temperature performance. This work opens up a simple avenue to promote the performance of NG, and the technique could be scaled up to industrially produce NG with high performance in a wide temperature range.
Abstract Meshy boron nitride (BN) was synthesized by the reaction of NaBH 4 and CS(NH 2 ) 2 at 550 °C for 10 h. X‐ray diffraction indicates the formation of hexagonal boron nitride (h‐BN) with lattice constants a = 2.501 and c = 6.724 Å. Observations by TEM show that the BN obtained has a meshy structure with a quantity of pores distributing on each mesh. The nitrogen adsorption–desorption test gives a high surface area of 220 m 2 g –1 for the meshy BN. The cathode‐luminescence spectrum exhibits a strong peak at 354 nm in the ultraviolet range. Thermogravimetric analysis proves that the meshy BN has good thermal stability and oxidation resistance up to 800 °C. The formation of meshy BN is due to the promotion of sulfur‐containing compounds for the cross‐linking of borazine and subsequent pyrolysis.
Polymers and their composites,which have an important application value in engineering,are a kind of important wear-resistant material.According to the use,their friction types typically have sliding wear,cavitation wear and erosion wear.In this paper,the friction type and corresponding wear mechanism were introduced.
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