Abstract
Ascorbic (Asc) acid as an environmentally friendly additive for nickel electrodeposition from Watts bath has been inspected. X-ray diffraction (XRD) and scanning electron microscopy (SEM) examinations were employed to assess the structure and morphology of the prepared Ni coatings. The influence of Asc acid on the current efficacy, polarization behavior, current-time transients, anodic linear stripping voltammetry, and macro-throwing power are the main points addressed in this research. Asc acid addition to the bath resulted in significant improvements in some important characteristics of the prepared Ni coatings, such as microhardness, throwing power, and corrosion resistance. The great shift of the polarization curves towards the less noble direction upon the addition of Asc acid demonstrated the inhibition of Ni deposition, which might be assigned to Asc acid adsorption on the cathode’s active sites thus, delaying the rate of Ni2+ deposition. The data matched well with the Langmuir adsorption isotherm. The chronoamperometry study revealed that the formation of nickel nuclei is controlled by diffusion via a nucleation and growth mechanism. The inclusion of Asc acid into the Watts bath not only modified the texture of the formed Ni coatings, as demonstrated from XRD analysis but also produced more fine grains as shown by SEM observation. Such desirable characteristics made the prepared Ni coatings able to effectively resist both the uniform and pitting corrosion processes in NaCl solutions, as evidenced from Tafel extrapolation, linear polarization resistance (LPR), and potentiodynamic anodic polarization measurements. Computational studies based on the density functional theory (DFT) and Monte Carlo simulation revealed the formation of several nickel complexes in the bath based on the three known forms of ascorbic acid under acidic conditions. All these in situ generated compounds having a high tendency for adsorption on the copper surface are believed to participate in the delay of the rate of electroplating.