Fabrication and formation mechanism of high aspect ratio boron nitride nanosheets prepared by ammonium borane

Due to the small size of commercial BN crystal and the unique interlayer interaction of BN , the traditional exfoliate method makes it difficult to fabricate BN nanosheets (BNNSs ) with high aspect ratio (>5000 ). High aspect ratio BNNSs were obtained by sintering ammonium borane and centrifugal separation of the sintering products. The synthesis mechanism and structure of BN nanosheets were characterized by FTIR , TG , TEM and XRD. The results show that the cross -linking and dehydrogenation of ammonium borane begin when the temperature is over 80 degrees C. Hydrogen releasing results in the formation of foam structure during the cross link process of ammonium borune ,and finally the inorganic process was completed at 1000 degrees C to obtain the BN foam containing BNNSs. The as -prepared BNNSs are hexagonal crystal structure , with a thickness of about 1.5 nm and an average width of 30 mu m. The width -thickness ratio reaches 20000. The high aspect ratio BNNSs were introduced to polyvinyl alcohol (PVA ) to prepare the BNNS/PVA composite film. The composite film shows significant improvement in thermal conductivity and mechanical properties , fully explains the application advantages of high aspect ratio BNNSs in the field of BN based composites.