The detection of solutal convection during electrochemical measurement of the oxygen diffusivity in liquid tin

Abstract

Electrochemical titration was used as a means to determine the mass diffusivity of oxygen in liquid tin at various temperatures. Solutal convection was present depending on the conditions, and this was inferred from an enhancement in the effective diffusivity. The experiments were conducted in two different modes of operation, and in each case, we attempted to align the oxygen concentration gradient such that it was parallel to the gravitational field. In the first mode, the concentration gradient was such that the fluid was heavy at the bottom and lighter at the top, and in the second, the reverse was true. The second mode was potentially unstable and sometimes gave rise to substantial convection for large values of the oxygen concentration gradient. The measured effective diffusivities were then higher than the corresponding measurements in the first mode of operation. Activation energies in two different temperature ranges were obtained by using an Arrhenius relationship.