Process for preparing an amorphous ultrahard material on the basis of boron nitride

A process for preparing an amorphous ultrahard material based on boron nitride and able to scratch diamond from a starting material containing crystalline hexagonal or crystalline turbostratic boron nitride, said starting material having a structure with crystal lattice layers, wherein the starting material is compressed at pressure of at least 70 Kbar and heated to temperatures of at least 1650.degree. C. until a boron nitride melt is obtained, the boron nitride melt formed is quenched by shutting off a heat supply, and the quenched boron nitride melt is then relieved of the pressure, and wherein the hexagonal or turbostratic boron nitride of the starting material is treated in the presence of a crystallisation inhibitor, said crystallisation inhibitor being an oxygen donor which is a chemical substance releasing oxygen and which is a strong oxidant that reacts with the boron nitride of the starting material at pressures of at least 70 Kbar and at temperatures of at least 1650.degree. C. and whose reaction products are incorporated into crystal lattice layers of the boron nitride;

• said oxygen donor being a peroxide or a compound containing alkali metal and/or alkaline earth metal.