Studies on Thermal Diffusion of Molten Alloys (6th Report). Estimation of Fundamental Constants of Pb-Sn and Cd-Sn Alloys

Abstract

The fundamental quantities in Soret effect for molten alloys can be determined from the thermal diffusion data as follows. As the equation of the first order reaction rate d(Δn)⁄dt=k(Δn_s−Δn) where the rate constant k is equated to π²D⁄a² is satisfied well at the primary stage of separation in the case of Pb or Cd dilute solutions, the ordinary diffusion constants and at the same time, from their temperature dependence, the activation energies can be obtained experimentally from k measurements. Their magnitudes lie respectively between 2.4×10⁻⁵∼5.1×10⁻⁵ cm²/sec and 4.4∼5.6 kcal/mol for Pb-Sn and 2.5×10⁻⁵∼5.2×10⁻⁵ cm²/sec and 4.7∼6.0 kcal/mol for Cd-Sn. It is proved that, considering the nature of measurements, the above values are reasonably close to those by other methods. The thermal diffusion constants are obtained by multiplying the Soret coefficients by the ordinary diffusion constants.As the latter are estimated to be 5.8×10⁻⁴∼2.2×10⁻³ deg⁻¹ for Pb-Sn and 5.6×10⁻⁴∼1.9×10⁻³ deg⁻¹ for Cd-Sn from the experimental determination, the former amount to 2.4×10⁻⁸∼8.6×10⁻⁸ cm²/sec·deg. for Pb-Sn and 2.5×10⁻⁸∼8.8×10⁻⁸ cm²/sec·deg. for Cd-Sn respectively.