Passivity breakdown on copper: Influence of borate anion
By Zhou, Yuting; Xu, Aoni; Mao, Feixiong; Yu, Jingkun; Kong, Decheng; Dong, Chaofang; Macdonald, Digby D.
Published in Electrochimica Acta
2019
Abstract
Passivity breakdown on pure copper in borate buffer solution containing chloride has been studied and the results have been analyzed using the Point Defect Model (PDM). Boric acid acts as an inhibitor of passivity breakdown for copper in chloride-containing solution. It is postulated that the deprotonated boric acid and/or polyborate species can be absorbed into surface oxygen vacancies of the barrier layer in competition with chloride ion, as indicated from ab initio modelling. The principal inhibitive species in the boric acid/NaOH system have been studied by thermodynamic equilibrium calculation and surface enhanced Raman Spectroscopy (SERS). The critical areal vacancy concentration of condensed cation vacancies at the metal/barrier layer (Cu2O) interface that leads to the breakdown of the passive film is estimated to be ≤ 1.06 × 1014 cm−2 experimentally. The distributions of the critical breakdown potential, as measured experimentally in chloride-containing solutions having different concentrations of borate, are near normal and the cumulative probability distributions are consistent with those calculated from the PDM.