**2.3 Electrochemical (corrosion) characterization**

The electrochemical behaviour of the samples (plates 10 x 10 x 0.05mm) was studied in a standard three-electrode thermostated cell (100 ml volume). The model corrosion medium was 0.1 N H2SO4 ("p.a." Merck) after deaeration with additionally purified argon at 25C*.* A counter electrode, representing a platinum plate (10x10x0.6mm), and a mercury/mercurous sulfate reference electrode (MSE), (EHg/Hg2SO4= +0.642V versus SHE) were used. All potentials in the text are related to MSE. The anodic and cathodic polarization curves were obtained using a 273 EG&G potentiostat/galvanostat and computer-aided processing of the results according to an "Echem" programme, with a potential sweeping rate of 10 mV/s within a potential range from –1.500 to +1.500V*.* The recording of the potentiodynamic curves was carried out starting from the stationary corrosion potential (Est), measured in the absence of external current (at open circuit) in the anode and cathode directions. We used a separate electrode for each recorded curve. The stationary corrosion potential of the samples under investigation was determined by direct measurement of the function "Est–time" at open circuit (with respect to the same reference electrode) after immersing the samples in 0.1 N H2SO4 in the absence and in the presence of Ce4+. The Est was established after a sufficiently long time interval - from few minutes to several decades of minutes until the moment, when the corrosion potential change did not exceed 1-3mV for 5 min.
