Synthesis And Growth Mechanism Of Low Dimensional B-C-N Nanomaterials

The boron carbon nitride?B-C-N?ternary nanomaterials with exceptional properties such as wide band gap,excellent thermal conductivity,high bulk modulus,extreme hardness and transparency in the optical and UV range that find application in most fields ranging from micro-electronics,bio-sensors,and cutting tools to materials for space age technology.A number of approaches,including arc-discharge,pyrolysis,and chemical vapor deposition?CVD?have been used to grow B-C-N nanomaterials.However,the B-C-N nanomaterials prepared by these methods either suffer from low yield and/or low purity,which would greatly limit the application of B-C-N nanomaterials.Moreover,controlling the morphology of nano-and micromaterials is of tremendous importance for applications in electrics,photonics,and sensing,but the controllable growth of these nano-and microstructures with different morphology via a simple and effective synthesis process remained a challenge until recently.Here we report that synthesize B-C-N nanosheet-assembled microwires at large scale and high purity at elevated temperatures in flowing ammonia,using FeCl3 as catalysts,amorphous B powder,absolute ethyl alcohol and ammonia as B,C and N sources,respectively.The diameter of the microwires is about 1?m,while the nanosheets have an average thickness of less than 20nm.We have investigated the influences of different process conditions on the phase,composition,and bonding properties of the B-C-N.The results indicated that the gaseous B-containing source,catalyst alloy droplets,and the flow rates of absolute ethyl alcohol are the key role,which impact the growth of nanotubes and microwires mostly.The diameters of B-C-N microwires increase with temperature and the formation of B-C bond and C-N bond are difficult at low temperature.Less content of catalyst can induce the decreasing amount of B-containing gas and molten alloy droplets,which lead to a lower yield of microtwires.The production can be reduced because of incomplete reaction caused by shorter reaction time.While carbon forms can be produced by prolonging reaction time.The diameters of microwires are quite uniform at lower flow rates of absolute ethyl alcohol.But as this rate is increased,the morphology of the as-prepared products gradually changes from microwires to micromikes.The demands of property investigation and applications are required for an effective route to mass production of B-C-NNTs with high purity.We report that synthesize various morphologies of B-C-N nano-and microstructure materials via solid-state reaction method using FeCl₂ as catalysts,amorphous B powder,absolute ethyl alcohol and ammonia as B,C and N sources,respectively.The diameter of the nanotube is about 90nm.Meanwhile,significant changes to the morphology were observed,including nanowires,microwires,micromikes and microfunnels,by simply regulating the growth conditions.These results provide a facile route for the selective preparation of B-C-N nano-and micromaterials.The possible growth mechanism of the B-C-N nano-and microstructures was also investigated after comprehensively analyzing all the data.A combination growth mechanism of vapor-liquid-solid and solid-liquid-solid model is proposed for the formation of B-C-N nanotubes,while a combination growth mechanism of vapor-liquid-solid and vapor-solid model is proposed for the formation of B-C-N nanosheet-assembled B-C-N microwire.