Conversion Behavior of Various Hexagonal Boron Nitrides to Cubic Boron Nitride

Cubic boron nitride (cBN) is synthesized from seven kinds of the hexagonal boronnitride (hBN) under a pressure of 4.6 GPa and a temperature of 1 600 ℃ with catalyst by using a cubic anvil press. The contrast to the standard curve is made in the present work, and the conversion yields of different kinds of hBN to cBN are measured by powder X-ray diffraction. The relative degree of three-dimensional order of various hBN raw materials is determined. Graphitization index (G.I value), crystalline grain size, and unit cell constants are calculated on data of XRD, and their effects on the conversion yields of hBN to cBN investigated. The hBN with better crystallinity and smaller crystalline grain size shows higher conversion rate to cBN. On the phase transformation from hBN to cBN, we suggest a direct conversion with two-dimensional nucleation as a possible mechanism. The theoretical description based on the homogeneous nucleation mechanism yields reasonable results according to experimental data.