SEGREGATION OF CARBON IN IRON AND MOLYBDENUM

The segregation of nitrogen, phosphorus, sulphur and carbon in iron ca uses the formation of Fe-X-X bonds on the surface. The system metal (F e(111),Mo(100))-carbon has been studied using the AES method. The bond s Fe-C observed for lower surface coverages were transformed to Fe-C-C bonds for higher coverages and the interaction between iron atoms aci d carbon atoms decreased. In the case of molybdenum the two different adsorption states were observed without a formation of C-C bonding. Th e enthalpy of segregation for both adsorption states for iron and moly bdenum has been determined using the Langmuir-McLean equation. The ent halpy of carbon segregation at the first adsorption state (lower carbo n coverages) was -140 and -68 kJ/mol for Fe(111) and Mo(100) surfaces, respectively, and for the second adsorption state -60 and -47 kJ/mol, respectively. The further increase of the carbon surface concentratio n caused the formation of 3D graphite on the Fe(111) surface and of ca rbide-like compounds on the Mo(100) surface.