Investigation of the chemical reactivity and stability of c-BNP

Bulk material of cubic boron nitride (c-BN) is commercially achieved via high pressure-high temperature (HPHT) synthesis from h-BN with various catalysts (flux precursors). Since recent investigations indicated c-BN to be the stable modification at standard conditions there is considerable interest to realise a c-BN synthesis at normal or low pressure. Thus growth conditions allowing high mobility for boron and nitrogen atoms have to be found. The interaction of c-BN with various flux precursors used under HPHT conditions was investigated up to 1300 degrees C at ambient pressure. The reagents were chosen with regard to their ability to stabilize intermediate reaction products. Metals, nitrides and fluorides were applied for the chemical attack. The morphological changes and degradation of the c-BN crystals were examined by scanning electron microscopy (SEM), X-ray diffraction and infrared spectroscopy. SEM studies indicate that the degradation of c-BN depends strongly on the nature of the flux precursors. Those leading to an intermediate phase during the reaction exhibit distinct etching figures on (111)-planes of c-BN, while reagents leading to the formation of several products cause an inhomogeneous decay. Since the degradation of c-BN resembles the reversed growth, the reaction mechanism of the interaction of c-BN with reactive melts allows to establish a growth and degradation model of the cubic phase. The results shall help finding new routes to grow c-BN in a low pressure-melt or chemical vapour deposition process. (C) 1999 Elsevier Science S.A. All rights reserved.