A MASS-TRANSFER STUDY OF THE DIFFUSION-CONTROLLED DISSOLUTION OF CUBICAL CAVITIES UNDER NATURAL-CONVECTION CONDITIONS

The role of mass transfer in the rate of diffusion controlled dissolut ion of cubical cavities was studied using an electrochemical technique involving the measurement of the limiting current of the anodic disso lution of copper cavities in H3PO4. Cavity side length and H3PO4 conce ntration were varied to provide (Sc.Gr) range of 8.7 x 10(9) - 3.9 x 1 0(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 th e 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 calcu lated by adding the rates of mass transfer at different surfaces of th e cavity a remarkable agreement was found denoting little convective i nteraction under the experimental conditions studied.