Study On Controllable Synthesis And Phase Transformation Of Boron Nitride Nanoparticles

A multi-steps reaction method, which was used in the controllable synthesis of BN nanoparticles, was developed in this thesis. The key factors, including the temperature, pressure, reaction steps and additives, have been systematically investigated. Furthermore, the phase transformation of BN nanoparticles was investigated by using the BN nanoparticles as the starting materials.Boron nitride nanoparticles were synthesized at 265℃and 1OMPa by using the multi-steps reaction route via the reaction between BCI3 and NaN3 in benzene. The experimental results indicate that, the crystalline perfection of the products improved significantly with the increase of reaction steps. At the same time, a phase transformation from tBN/hBN to cBN may have happened. At 250℃, the crystalline perfection of BN nanoparticles is fairly poor due to the low reactivity of the reactants. When the temperature increased, the crystalline perfection and the content of cBN of the samples increased. Besides, increasing the reaction steps is also beneficial for the increase of cBN content. Moreover, the side-reactions participated by the solvent were greatly suppressed by the multi-steps reaction route. On the other hand, properly increasing the pressure is helpful for both improving the crystalline perfection and increasing the cBN content of BN samples. By analyzing the experimental results, we preliminarily explored the reaction process and mechanism of multi-steps reaction method.Furthermore, N(CH3)3 was used as the supplementary nitrogen source and NaN3 was replaeced by Li3N, and their effect on the phases and crystalline perfection of BN nanoparticles was investigated. The results suggest that both the cBN content and the crystalline perfection of the samples were improved when the ratio between the amount of nitrogen source provided by N(CH3)3 and NaN3 and the boron source provided by BCI3 was slightly larger than stoichiometric proportion. Besides, the crystalline perfection of BN nanoparticles can also be improved by replacing NaN3 with Li3N. Accompanying the increase of reaction steps, a phase transformation from tBN/hBN to cBN happened, which resulted the increase of cBN content in the samples.Although the newly developed multi-steps reaction route is by no means perfect, it can be expected that this route might provide a facile and convenient method for synthesizing nitride nanoparticles and growing bulk crystal under mild conditions in the future.