Transformation of Cubic Boron Nitride to a Graphitic Form of Hexagonal Boron Nitride

R. H. WENTORF1 has reported that a fragment of borazon (synthetic cubic boron nitride) was twice heated to over 2000°C. in vacuo without change. Dr. Wentorf was kind enough to supply us with some small specimens, both black and yellow. Some of these, which gave random-rotation X-ray photographs showing them to be twins (only two nearly single crystals were found), we heated in graphite specimen holders in a high-frequency vacuum furnace (10−5 cm. mercury) in a series of experiments to compare their behaviour with that of diamonds of various kinds. Table 1 shows the effects given by subsequent X-ray powder photographs.