▎ 摘　　要

Results obtained during the determination of the solubility limit of carbon in metal based on the detection of the time instant of the nucleation of the new phase, graphene, have been considered. Graphene is easily detected by the surface-sensitive methods of thermionic emission and electron Auger spectroscopy. It has been shown that the nucleation of the first graphene islands and the formation of the graphene monolayer covering the whole surface and even the multilayer graphite film on it can be used as the time instant of the phase transition depending on the sensitivity of the method. The solubility limits differ by many times depending on the determination method. This indicates the physical ambiguity of this physical characteristic of the double systems analogous in physical meaning to the pressure of the saturated vapor for the phase transitions in the one-component systems.