Boundary layer visualization and mass transfer studies on a rotating electroplating mandrel: Exploratory experimentation and technique development

An electrochemical technique for visualization of the laminar diffusion (concentration) boundary layer on a rotating mandrel is described. This technique utilizes the change in pH near the surface associated with formation of an alkaline solution formed by electrolysis of dilute sodium chloride solution at the rotating cathode. The alkaline boundary layer is made visible by phenolphthalein indicator. Development of a technique suitable for determining mass transfer rates on a rotating mandrel of arbitrary axisymmetric contour is also described. This technique utilizes dissolution of a thin coating of benzoic acid in water and has applicability to modeling of an electroplating process.