Determination of diffusion coefficients of Zn, Co and Ni in aluminium by a resistometric method

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Abstract
The impurity diffusion parameters of Zn, Co and Ni have been determined in aluminium by measurements of electrical resistance. It is shown experimentally that in the case of Co and Ni, surface layers with constant concentrations were formed during the isothermal diffusion treatments and so the resistance measurements made possible the determination of the temperature dependence of the saturation concentrations too. It is also shown that the determination of the diffusion activation energy is possible from resistance measurements when the initial and boundary conditions are not exactly known (but when they do not vary with temperature). The measurements gave for the pre-exponential factors (D 0) and the energies of activation (Q) : D 0 Zn = (0.20 ± 0.08) cm2/s, QZn = (1.25 ± 0.02) eV; D 0co = (141 ± 137)cm2/s, Q Co = (1.75 ± 0.07) eV; D 0 Ni = (4.4 ± 3.l) cm2/s, Q N1 = (1.51 ± 0.06) eV, respectively. The diffusion parameters of Zn and Co are in good agreement with previous results in the literature : no data on the impurity diffusion coefficients of Ni in aluminium have as yet been published. In the interpretation of experimental results it has been concluded that the energy differences calculated from the Le Claire model (Le Claire 1962) disagree with δQ exp =Q i–Q self, even in those cases when the phase-shift method, used in the calculation of the excess potential around the impurities, gave better resistivity values than those obtained from the resonant scattering condition. The method of Neumann and Hirschwald (1973) also gives much smaller δQ values than those determined experimentally. A possible interpretation of the discrepancies between the experimental and theoretical results is suggested by supposing that not only inpurity-vacancy pairs but higher-order complexes, i.e. two-impurity-vacancy triplets are also formed and play an important role in the diffusion of transition metal impurities.