New Method for the Measurement of Effective Valence in Solid State Electrotransport and the Application to the Fe-C and Fe-N Systems

A new method (Tangent method) was developed for the determination of the effective valence of interstitial impurity elements that is one of the most important factors for the evaluation of the effectiveness of the solid state electrotransport (SSE). The Tangent method can overcome all the weak points in the traditional methods. For the confirmation of the Tangent method, the Fe-C and Fe-N systems were picked up as model systems, because the thermodynamic properties of these systems had been well established and there had been many reports on the SSE process of these systems. And experimental studies have been conducted under the following conditions: initial uniform carbon content=1300 mass ppm, nitrogen one=270 mass ppm, temperature=1273 K and current density=3∼5×106 Am−2.The measurements shows good reproducibility and the following results were obtained:(i) +3.7 and +3.1 were obtained as the effective valences of carbon and nitrogen, respectively.(ii) These values are in good agreement with the ones measured by traditional methods.(iii) The values of diffusion coefficient of carbon and nitrogen in γ-iron, which were obtained in the combination of the Tangent method and the traditional unsteady state method, agree well with the values in the literature.