Influence of Water Agent on High-Pressure/High-Temperature Transformation of Graphitic BC2N

Graphitic BC2N has been exposed to high pressure (7.7 GPa) and high temperature (800−2200 °C) in the presence of water as a fluid agent to explore the reactivity of the graphitic BC2N and crystallization behavior to cubic compounds in a B−C−N ternary system. The graphitic BC2N reacted with water above 1200 °C, which describes that the graphitic BC2N is similar to graphite in reactivity rather than hexagonal boron nitride (hBN). The dissolved BC2N was not recrystallized as a cubic B−C−N compound but was disproportionated into graphite and cubic boron nitride (cBN) in the temperature range of 1200−1800 °C. Then, the precipitated graphite was transformed into diamond above 2000 °C. The precipitation behavior of the cubic compounds in the BC2N−H2O system can be explained by the simple sum of the formation of cBN in hBN−H2O and that of diamond in graphite−H2O.