Evaluation of the sacrificial behavior

The effect of applied current, testing time and microstructure on the electrochemical properties of magnesium-based sacrificial anode in potable water was evaluated by Andrei et al. (2003). The Al-Zn Mg alloy AZ63 alloy was utilized as the Mg sacrificial anode for use in potable water considered as a high-resistivity electrolyte. The anodes were tested in order to evaluate the main anode properties such as efficiency, current capacity and charge 

The corrosion process of a sacrificial Mg alloy is evaluated in the laboratory in either 3% NaCl solution or a solution containing 5g CaS04. 2H2O and 0.1 g Mg (0H)2/L), as recommended after the ASTM G97 standard. Beside the ASTM procedure, there is also the Mexican test method (NMX-K-109-1977, Magnesium anodes used in cathodic protection ) that considers a test environment made of artificial seawater. Both standards consider galvanostatic tests, in which a known direct current is passed through test cells connected in series in order to determine efficiency of sacrificial anode materials (Guadarrama-Mu-oz et al., 2006). 

Polarization curves were carried out, in each testing solution, after 6h of exposme time. This period of time showed near steady-state conditions of the Eqc (A 10 mV for 60 min) are reached. All polarization curves were recorded potentiodynamically with a sweep rate of 10 mV/min. A potential range of + 300mV, referred to as was selected. 

The 3% NaCl solution is more aggressive to the Mg alloy specimens than the ASTM solution. It can be stated also that, during all the exposure time, M3 alloy shows the more noble values of E, -, Ml specimen shows the more active values of E c, while M2 gives values of Eqc between those of Ml and M3 values. The measured data indicate that the Ml sample is the only one that fulfills the value of open circuit potential as stated in the 

The Nyquist representation of the impedance shows two clear semicircles that can be associated to two time constants (Fig. 2.17), therefore to two 

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