Preparation And Application Of Boron Nitride Nano Materials

Hexagonal boron nitride?h-BN?have great potential applications in aerospace radiation shielding materials,thermal interface materials,deep ultraviolet emission materials and many other fields due to their excellent performances in oxidation resistence,radiation shield,heat conduction and so on.However,it is still a major challenge on the controllable and large scale preparation of boron nitride nanotubes?BNNTs?and nanosheets?BNNSs?in high quality.In this paper,BNNTs and BNNSs are prepared by CVD method using borate as precursor.And the thermal conductivity of polyvinyl alcohol?PVA?composites are studied with homemade BNNSs.A novel method to synthesize BNNSs using magnesium boratea as precursor,under an ammonia atmosphere,has been studied.The thickness and size of the products increase with the rises of temperature,the extension of the reaction time before the complete reaction of precursor and the amount of boron in the precursor.At the same time,increasing the temperature can shorten the complete reaction time of the precursor.And the as-grown products reveal the MgO@BNNSs core-shell structures.It's worth noting that this method gives rise to gram-level yield with efficiency up to 76%in terms of the boron productivity.BNNTs are prepared by using MgB₄O₇ as precursor with LiNO₃,Fe?NO₃?₃.9H₂O,Fe/Mo vermiculite as catalyst via CVD method.The ball-milled precursor can be more efficiently and uniformly to load with the catalyst.And We have studied the effect of process parameters on the morphology of the product when using Fe?NO₃?₃.9H₂O as catalyst.It's found that high-quality BNNTs can be prepared at 1300oC with 200 sccm NH₃ when the mass ratio of precursor to Fe?NO₃?₃.9H₂O catalyst was 1:0.08.While using Fe/Mo vermiculite as the catalyst,the yield of BNNTs increases obviously.Because Fe/Mo alloying catalysts have higher activity relative to Fe catalysts.It's found that LiNO₃ can help to reduce the diameter of BNNTs.BNNSs are used as nanofillers to fabricate a series of PVA nanocomposites and their thermal properties are studied.Compared with pure PVA,filling a certain amount of BNNSs can significantly improve the thermal conductivity and thermal stability of PVA.Increasing BNNSs content in BNNSs/PVA nanocomposites can improve the number of thermal conduction channels per unit area,and the thermal diffusivity of BNNSs/PVA increases.