The influence of hBN crystallinity and additive Lithium hydride on cBN synthesis in Li3N–hBN system

In this paper, the influence of hBN crystallinity and additive Lithium hydride (LiH) on cBN synthesis with Lithium nitride (Li3N) as catalyst was investigated under the pressure of 4.5–5 GPa and the temperature of 1500–1700 °C. hBN with different crystallinities was obtained by the same hBN. Some were explored to high pressure and high temperature, and others were subjected to heat treatment with alkali. X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectronic spectroscopy (XPS) were used to characterize the property of the starting materials. The synthesized samples were observed by optical microscopy (OM). The results indicated that besides the crystallinity of hBN, which is a general parameter for controlling the structural quality of hBN powders, some other factors such as the content of B+ at the surface of hBN and additive LiH all strongly influence the synthesis of cBN.