Electromigration of carbon in α-iron

Abstract

Electromigration of carbon in α-iron has been investigated by the steady-state method to determine the effective charge number Z* of carbon as functions of the electric current density and the temperature in the ranges 97–867 A/cm2 and 550–850 °C, respectively. It has been found that the drift velocity of carbon is proportional to the electric current density, that is, Z* is independent of the electric current density, and Z* decreases from +12.2 to +3.6 with increasing temperature from 550 to 850 °C, showing larger temperature dependence in the ferromagnetic α-iron. This is explained in terms of the spin-disorder scattering model. Z* estimated from the electrical resistivity data depends on temperature in a way similar to that determined from the electromigration. From the dependence of Z* on the resistivity increment in α-iron due to solution of carbon, the true charge number of carbon has been determined to be about zero. Thus, it is concluded that the carbon ion is subjected not to the electrostatic force but to the drag force from the current carriers during electromigration.