A new technique (tangent method) was proposed for the determination of the effective valence of impurity elements during solid-state electrotransport. It was shown that use of the tangent method could avoid several of the disadvantages of traditional methods. In order to evaluate the tangent method, Fe-C and Fe-N were chosen as model systems because their thermodynamic properties had been well-established. Experimental studies were carried using an initial uniform C content of 1300ppm[wt], a N content of 270ppm[wt], a temperature of 1273K, and a current density of between 3 and 5MA/m2. The measurements exhibited good reproducibility, and 3.7 and 3.1 were deduced to be the effective valences of C and N, respectively. These values were in good agreement with those which were obtained by using traditional methods. The values of the diffusion coefficients of C and N in -Fe, which were obtained by combining the tangent method with the traditional unsteady-state method, agreed well with published values.

K.Kuroda, Y.Horibe, T.Fujisawa, C.Yamauchi: Materials Transactions, 1995, 36[9], 1149-56