I2 concentration in a potassium iodide silver plating solution increases with time in the lower pH range. Which decreases cathode current efficiency in silver deposition, making it necessary to control pH between 4.5 and 5.0. Silver deposits become less adhesive with increasing pH. We studied the effects of pH near electrode surfaces on silver deposit adhesion.
We found the following:
(1) The pH value near the cathode surface was much greater than that of bulk solution during electrodeposition without a buffer. The addition of KH2PO4 as a buffer markedly reduced the pH change near the electrode.
(2) Silver deposit adhesion to undercoated nickel surfaces was improved by adding KH2PO4.
