The age of synthetic diamonds began with the construction of the equilibrium phase diagrams of carbon. In 1939, O. I. Leipunskii [1] proposed a method for the thermodynamic calculation of the pressure dependence of the temperature of graphite-diamond equilibrium (G ~ D). Later investigations (calculations [2][3][4] and experiments in the temperature range 1500-2700 K [5]) largely substantiated and somewhat refined the data in [1]. The conditions of melting of carbon were determined, and it was proposed that metallic carbon exists at pressures above 60 GPa. The current form of the P-T phase diagram is shown in Fig. I. The thermodynamically stable form of carbon at atmospheric pressure is graphite. However, diamond can exist for a nearly unlimited time at room temperature or lower. Its graphitization begins at 1300-2100 K. Nor does graphite change into diamond with an increase in pressure to the values characteristic of the region of thermodynamic stability of diamond. A pressure considerably greater than the equilibrium pressure is needed for the G --* D transformation. Also, the lower the temperature, the greater the amount by which the equilibrium pressure must be exceeded in order to realize this transformation [7].The work of O. I. Leipunskii foreshadowed all presently known methods of producing diamond: the direct G --, D transformation in the solid state (conditions far from equilibrium, deep within the region of stability of diamond, at very high temperatures and pressures); recrystallization through the liquid or gas phase in the region of stability of diamond, but near the boundaries of the P-and T-equilibrium states; epitaxial growth on a diamond substrate in the region of thermodynamic stability of graphite. Industry employs recrystallization through a liquid --an equilibrium metallic melt that is thermodynamically stable. Recrystallization through a metastable melt is also possible, but this process is nearly uncontrollable, forms only small diamonds, and forms these diamonds only in a mixture with carbides that are simultaneously crystallized from the metastable melt [8]. The yield of diamond relative to the initial quantity of graphite is very low.The direct G --, D transformation requires a pressure on the order of 12 GPa and a temperature of about 3000 K. Diamond can be produced at considerably lower temperatures in the presence of certain metals, mainly metals belonging to the iron and platinum groups. Figure 2 shows the P-T region in which diamond is formed in the presence of different metals. The D ~ G equilibrium line is shown for comparison. Figure 3 shows the melting points of the metals, equilibrium carbon-bearing eutectics or peritectics in alloys of these metals with carbon, and metastable eutectics formed by contact of the same metals with carbon. The figure also shows the lowest temperatures at which diamond forms from graphite in the presence of the given metals.Such diamond-synthesis parameters as pressure and temperature can be determined only within the region in which a stable liqu...