Carbon segregation on a tungsten surface

New measurements are performed and a comprehensive analysis of experimental data is made on the dependence of equilibrium carbon coverage θ on a tungsten surface on its temperature and the degree of carbon loading. It is shown that if the volume is free of carbon, the variation of θ for T≥1400 K can be approximately described by the balance between the carbon flows through the boundary with the activation energy for transition into the bulk E₁=4.6 eV and the segregation energy ΔE=1.7 eV. For tungsten loaded preliminarily with carbon to a content of ≈10^?2 at. %, the θ(T) relation cannot be described in terms of the equilibrium conditions with constant E₁ and ΔE, because these quantities depend on the degree of carbon loading; E₁ grows from 4.6 to 6.8 eV and ΔE grows from 1.7 to 2.3 eV with an increase in carbon content from 0 to 10^?2 at. %. These variations are attributed to the bonds becoming stronger in carbon-loaded tungsten with increasing carbon content.