Pressure and temperature region of diamond formation in systems graphite and Fe containing alloy

The pressure and temperature region of diamond formation was determined using Fe50wt.%-Co50wt.% and Fe66wt.%-Ni34wt.% (invar) alloys as solvents of carbon. Pressure and temperature values were estimated based on the minimum pressure and temperature conditions of diamond formation in the pure Ni-carbon system (5.4 GPa and 1384 degrees C). In the Fe-Co-C system, it was found that the nucleation density of diamond was very small between 1190 degrees C and 1310 degrees C, but the density and particle size increased markedly at 1310 degrees C in the pressure range 5.6-6.0 GPa. Although a minimum temperature of diamond formation was detected at 1190 degrees C at 6 GPa in the Fe-Co-C system, the region of no diamond formation was observed at a lower pressure, with the nucleation barrier being near the minimum pressure and temperature condition. The region of diamond formation in the system Fe-Ni-C was bounded by the equilibrium line and the estimated eutectic line of the system. The minimum temperature of diamond formation was detected at about 1280 degrees C at 5.2 GPa. The P-T regions of diamond formation for both the Fe-Co-C and Fe-Ni-C systems are discussed based on the stability of carbide in the solvents.