In this work a systematic study on the kinetics of Ni electrodeposition in acid sulfate media over a wide pH range was carried out. Two distinct electrodeposition behaviors were experimentally detected as a function of pH. Accordingly, it is suggested that Ni electrodeposition takes place through different intermediates: In the lower pH range, Ni(normalI)ads species predominates at the electrode surface, and its formation is deactivated with increasing pH, whereas in less acid solutions, Ni electrodeposition occurs via two species, [Ni(OH)]ads and [Ni(OH)]ads+ . The chemical nature of Ni(normalI)ads , [Ni(OH)]ads and [Ni(OH)]ads+ species is discussed on the basis of the interfacial pH behavior.

Dental implant systems are composed of an implant, prosthetic components, and a crown. Since the implants are made of commercially pure Ti (cp Ti) and prosthetic components are often made of Ti and CoCrMo alloys, a galvanic couple between these two devices may lead to galvanic corrosion, ions release, and even loss of the implant. This study aimed to investigate the corrosion resistance and measure the galvanic potential between cp Ti alloys (annealed microstructured cp Ti G4 and cold-worked nanostructured cp Ti G4) and a CoCrMo alloy. The corrosion resistance has been characterized by measuring the open circuit potential, the potentiodynamic polarization, the potentiostatic polarization, and the zero-resistance current. The cp Ti has been tested before and after a surface acid treatment. The samples’ surfaces have been examined by scanning electron microscopy, and their surface roughness has been measured by a 3D optical profilometer. The polarization results showed that the CoCrMo alloy showed lower corrosion resistance than cp Ti. The surface acid treatment improves dental implant corrosion resistance. The galvanic analysis showed that the cp Ti without surface treatment behaved as an anode and after the acid treatment has a cathodic behavior in relation to the CrCoMo alloy. The highest value of galvanic current was cp TiG4 acid etched in contact with CoCrMo, in pH 2 solution. The galvanic couple with the lowest current has been the nanostructured cp Ti in contact with CoCrMo alloy.

The electrochemical mechanism of Ni electrodeposition in an acid sulfate medium with pH ranging from 1 to 6 is evaluated. For pH≤3 , a reaction model already available in the literature accounts satisfactorily for the experimental results shown in Part I of the present paper. However, this model cannot explain the results obtained in the pH interval of 4–6. A complementary model is then proposed, considering the formation of two species: (i) [Ni(OH)]ads+ , the relaxation of which is associated with a capacitive loop at medium frequencies, and (ii) [Ni(OH)]ads , the relaxation of which gives rise to an inductive loop at low frequencies. The validation of this model has been accomplished by the comparison with the experimental polarization curves and impedance measurements. A good agreement is found between the simulated and experimental results. By using the previous model proposed by Epelboin et al. [ J. Electroanal. Chem. , 119 , 61 (1981)] for pH≤3 together with the present complementary model, Ni electrodeposition can now be explained in the whole pH range of 1–6.

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