Mass Transport Phenomena in the Molten Sulfur-Sodium Polysulfide System

The exchange rate for mass transfer of sulfur across the sulfur-sulfur saturated sodium pentasulfide interface was investigated by S-35 tracer studies and found to be 0.19 ± 0.04g S/cm/hr at 300°C. The self-diffusion coefficients of sulfur in NaS and NaS as determined by the capillary method using S-35 labeling were 2.3 ± 1.1 × 10 and 1.5 ± 0.4 × 10 cm sec, respectively, at 300°C. The diffusion coefficient of the electroactive species in NaS was determined by chronopotentiometry at a rotating disk electrode. Its value is 7 × 10~7 cm sec at 300°C. Approximate values of the activation energy of diffusion and nC in NaS are given. A first attempt is made, in terms of a mechanistic model of the mass-transfer processes, to explain the different data obtained for D from tracer and electrochemical experiments, respectively. © 1980, The Electrochemical Society, Inc. All rights reserved.