Anodic behavior of zinc in aqueous borate electrolytes

Abstract The behavior of zinc in aqueous borate electrolytes at anodic polarization in galvanostatic regime was investigated. Induction periods and voltage breakdown phenomena were observed in the respective kinetic curves. The dependence of the duration of these induction periods on the polarization conditions (j = 5 ÷ 60 mA cm−2; H3BO3 content  =  0.1 ÷ 3 wt %; pH 5.8 ÷ 8.2; t = 10 ÷ 30 °C) was studied. The registered breakdown voltages obey the law of Burger and Wu, and exceeded 200 V. Clear periodical oscillations of the forming voltage were registered at high current densities. The obtained films were submitted to X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR). The data obtained by these observations have revealed that these layers are composed of amorphous 2ZnO.3BO3.7H2O. Furthermore, on the basis of the scanning electron microscopy (SEM) observations a conceptual model was developed for qualitative explanation of the film growth mechanism. The appearance of high amplitude oscillations was explained by complete disjoining of the layer due to accumulation of mechanical stress. These conclusions were confirmed by obtained atomic force microscopy (AFM) images and (ICP-OES) measurements of the electrolytes after the respective polarizations.