MECHANISM OF ELECTRODEPOSITION OF COPPER FROM CUPRIC PYROPHOSPHATE SOLUTIONS

1977 
Abstract Cathodic polarization curves were measured for copper in cupric pyrophosphate solutions of different concentrations and temperatures. A rotating disc electrode was used to eliminate concentration polarization. For all solutions, two potential regions are distinguishable in the polarization curve; one is less negative than a critical potential Eb around −0.75 V vs sce (Region I) and the other more negative than Eb (Region II). A weak adsorption of pyrophosphate ions and hence some inhibition of the electrodeposition of copper is expected for Region I but there is no adsorption in Region II. The exchange current density io for the copper deposition was obtained by extrapolating the Tafel relation observed in Region II to the rest potential corresponding to the equilibrium potential. The following reaction mechanisms are proposed to explain the dependence of io on the concentration of Cu(P2O7)6−2 and P2O4−7 ions. Apparent activation energies are estimated to be about 11 kcal/mol in both cases.
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