The role of viscosity in thin- layer electrodeposition

S. DENGRA, G. A. GONZÁLEZ, G. MARSHALL, F. V. MOLINA, M. ROSSO

Santa Fe, Argentina

Congreso; XICongreso Argentino de Fisicoquímica y Química Inorgánica y I Congreso Fisicoquímica del Mercosur; 1999

Asociación Argentina de Investigación Fisicoquímica

Recent work demonstrates the relevance of convection during the growth of patterns in thin layer electrochemical deposition. Convection is driven mainly by coulombic due to local charges and by buoyancy forces due to concentration gradients that lead to density gradients. The viscosity of the electrolyte plays an important role in fluid convection. Here we study experimentally and by theoretical modelling the effects of variations in viscosity on growth morphology and ion transport when gravitoconvection prevails. Simultaneous use of optical absorption or schlieren techniques and the use of pH indicators allow to follow the development of the cathodic and anodic concentration fronts, the convective fronts and the pH front, under the conditions in which gravitoconvection prevails. It was confirmed the presence of a first morphology transition occurring when a migratory pH front emanating from the anode encounters the deposit front, called the Hecker effect, and of a second morphology transition. The latter was originally attributed to the encounter of the anodic convective front with the deposit front, but we have found that, depending on the experimental conditions, the anodic front may play no role in this second transition. This leads us to suggest the existence of a “hidden”  migratory front. Simulations based on a theoretical model using dimensionless quantities show close agreement with the experimental results.