CUBIC-BN - A NEW PREPARATION PROCESS AT M EDIUM PRESSURE AND TEMPERATURE VALUES

Cubic-BN (c-BN) is characterized by exceptional physico-chimical prope rties comparable to that of the diamond. The conventional proceses for preparing such a material involve high pressures (P greater than or e qual to 5 GPa) and high temperatures (T > 1,200 degrees C) through a f lux-assisted conversion of the hexagonal form to the cubic one. On the basis of new thermodynamical calculations claiming the stability of c -BN in normal pressure conditions, we have set up a new preparation ro ute reducing the kinetical effects and based on the use of a nitriding solvent (as NH2NH2) in supercritical conditions. Such a process lends to the preparation and the crystal-growth of c-BN in reduced pressure and temperature conditions (1.5 < P < 2.5 GPa; 500 < T < 700 degrees C).