Hydrothermal hot-pressing induced phase transition in hexagonal boron nitride

The phase transition of hBN nanocrystals induced by hydrothermal hot-pressing process has been investigated by XRD, FTIR, TEM and HRTEM. it was found that a phase transition of hBN -> tBN -> aBN occurred with increasing hot-pressing temperature, i.e., hBN transformed into tBN at above 270 degrees C, and followed by another transformation from tBN to aBN at 310 degrees C. In addition, FTIR spectra and HRTEM images indicate that a small amount of CBN formed directly from the amorphous BN matrix at 75 MPa and 310 degrees C. This phenomenon is similar to what happened in conventional high temperature and high pressure method, which is believed to promote the phase transition from hBN to cBN. (C) 2009 Elsevier Masson SAS. All rights reserved.