*2.3. Gravimetric Measurement*

Gravimetric measurements were carried out by immersing the samples for 24 h in pure water saturated with carbon dioxide at 25 ◦C. The solution was thermostated in a water bath. After the immersion time had elapsed, the specimens were removed and ultrasonically washed in ethanol, dried, and reweighed. The weight loss was determined using an analytical balance with the accuracy of ±0.1 mg. In each case, the experiment was conducted three times. The corrosion rate (*CR*) in mm·y−<sup>1</sup> was obtained from the following equation [6]:

$$CR\ (\text{mm y}^{-1}) = \frac{87.6\ \Delta m}{d\ A\ \text{t}}\tag{1}$$

where Δ*m* is the weight loss, *A* is the surface of the sample (cm2), *d* is the density (7.87 g cm<sup>−</sup>3), and *t* is the immersion time (h).

#### *2.4. Electrochemical Measurement*

The electrochemical measurements were carried out with a Gamry 600 potentiostat (Gamry Instruments, Warminster, PA, USA). The electrochemical cell consisted of a working electrode, a saturated calomel reference electrode (SCE) and a platinum counter electrode. The experiments were performed at 25 ◦C in pure water saturated with carbon dioxide. The electrolyte conductivity was 190 μS cm−<sup>1</sup> and the pH was 4.12. The tests were carried out using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP). The EIS measurements were performed at an amplitude of 40 mV in the frequency range from 1 kHz to 10 mHz. Both measurements were carried out at intervals of 3, 6, 12, 18, and 24 h. The PDP measurements were performed by sweeping the potential from −1.0 to −0.4 V vs. SCE with a scan rate of 1 mV s−<sup>1</sup> after holding the specimen at open circuit potential for 24 h in the tested solutions. The corrosion rate (*CR*) was calculated according to the ASTM G102 [20] using the following equation:

$$\text{CR (mm y}^{-1}) = \frac{3.27 \times 10^{-3} \text{ } i\_{\text{corr}} \, E\_W}{d} \tag{2}$$

where *i*corr is the corrosion current density, *E*w is the equivalent weight of the metal, and *d* is the density of the metal. 3.27 × <sup>10</sup>−<sup>3</sup> is the conversion factor.
