Héctor Cruz Mejía

The corrosion behavior of copper and copper-functionalized boron nitride nanocomposites (Cu-BNNS) was studied in a 3.5 wt.% NaCl solution. Polarization curves and cyclic voltammetry experiments were used to differentiate the various stages of corrosion behavior. Additionally, electrochemical impedance spectroscopy (EIS) was used to understand the different steps in the degradation mechanism. The EIS results were analyzed using adsorption models at open circuit potential and at a bias potential of 250 mV, and different reaction kinetics parameters were quantified. During the first hour of immersion, the formation of CuCl increased on the Cu-BNNS, where the reaction constant for the formation of adsorbed CuCl was lower in the impedance model. However, on the Cu electrode, CuCl was not formed during the first hour, and the reaction constant was higher. The proposed model is consistent with the experimental observations from cyclic voltammetry, polarization, and scanning electron microscopy.

Aluminum-based alloys have been considered candidate materials for cathodic protection anodes. However, the Al-based alloys can form a layer of alumina, which is a drawback in a sacrificial anode. The anodes must exhibit uniform corrosion to achieve better performance. Aluminum can be alloyed with Zn to improve their performance. In this sense, in the present research, the electrochemical corrosion performance of Al-xZn alloys (x = 1.5, 3.5, and 5 at.% Zn) exposed to 3.5 wt.% NaCl for 24 h was evaluated. Polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) were used to identify the electrochemical behavior. The microstructure of the samples before the corrosion assessment was characterized by means of X-ray diffraction analyses (XRD) and scanning electron microscopy (SEM). In addition, microstructures of the corroded surfaces were characterized using X-ray mappings via SEM. Polarization curves indicated that Zn additions changed the pseudo-passivation behavior from what pure Al exhibited in a uniform dissolution regime. Furthermore, the addition of Zn shifted the corrosion potential to the active side and increased the corrosion rate. This behavior was consistent with the proportional decrease in polarization resistance (R_p) and charge transfer resistance (R_ct) in the EIS. The analysis of EIS was done using a mathematical model related to an adsorption electrochemical mechanism. The adsorption of chloride at the Al-Zn alloy surface formed aluminum chloride intermediates, which controlled the rate of the process. The rate constants of the reactions of a proposed chemical mechanism were evaluated.