1. Synthesis of ultra-hard materials

In this section, we focus on the synthesis of diamond and cubic boron nitride. To illustrate the point, a simplified phase diagram of carbon is shown in figure , with the different areas of existence and synthesis.

Two main routes are followed in the preparation of synthetic diamond.

• The original General Electric method was developed by H. Tracy Hall in the 1950s. Using conditions of high pressure – high temperature (HP-HT), it is still widely used, given its relatively low cost on an industrial scale. It requires the use of large presses weighing several hundred tonnes to produce pressures of the order of 10 GPa (1 gigapascal = 10 ⁹ Pa = 10 kbar = 10,000 times atmospheric pressure) at T ≍ 3,000 K, i.e. nature's conditions in its production of natural...