A mass transfer study of the diffusion controlled dissolution of cubical cavities under natural convection conditions

Abstract

The role of mass transfer in the rate of diffusion controlled dissolution of cubical cavities was studied using an electrochemical technique involving the measurement of the limiting current of the anodic dissolution of copper cavities in H 3PO 4. Cavity side length and H 3PO 4 concentration were varied to provide (Sc.Gr) range of 8.7 × 10 9 − 3.9 × 10 11. Under these conditions the mass transfer coefficients of cavity dissolution were correlated to other parameters by the equation Sh = 2.742 ( Sc.Gr) 0.22 The equation can be used in practice to predict the rate of diffusion controlled processes which might take place inside the cavity such as electropolishing and electrochemical machining. By comparing the experimental rate of mass transfer with the value calculated by adding the rates of mass transfer at different surfaces of the cavity a remarkable agreement was found denoting little convective interaction under the experimental conditions studied.