Esteban García Ochoa

Coating is one of the most common and effective ways to protect metallic elements from corrosion. The evaluation of a coating’s performance is related to its quality and durability. Neutral salt spray (NSS) is a common accelerated test used for coatings. Commercial polyester/melamine coil coatings applied on aluminum specimens were exposed to NSS and recorded at 0, 200,400, 600 and 1000 h of exposure. Coating performance changed with time of exposure. The main degradation process is due to the hydrolysis of the coating. A decrease in corrosion rate was observed due to the sealing of the coating, probably due to the deposition of corrosion products, salts, or a mixture of both. EN (electrochemical noise) was a more sensitive technique comapred to EIS (electrochemical impedance spectroscopy). The first changes in the coating were detected after 400 h of exposure by EIS and after 200 h by EN. EIS and EN showed equivalent results in studying the corrosion evolution of coated aluminum. Non-linear analysis using recursive plots (RP) showed the chaotic dynamics occurring with time and the interaction of micro electrochemical cells that formed on the metallic surface; it offered information similar tothe traditional EIS technique and adds complementary data to understand the corrosion phenomenon.

Cast iron has stood for centuries of invention. It is a very versatile and durable material. Coating systems are a low-maintenance protection method. The purpose of this research is to increase the Paraloid coating’s resistance when applied to iron in high humidity atmospheres, with the addition of caffeine (1,3,7-dimethylxanthine) and nicotine (S)-3-(1-methylpyrrolidin-2-yl) pyridine as corrosion inhibitors; the resistance of protection versus exposure time will be evaluated by using electrochemical noise. A statistical analysis of the electrochemical noise signals was carried out. Recurrence plots were used as a powerful tool in the analysis to complement the data obtained and they predicted the evaluation of coatings behaviors performance versus time. The outcomes show that the addition of inhibitors increases and improves the performance as a temporary protection of Paraloid and that protection in high relative humidity was improved. Recurrence plots and parameter quantification show the variances in the surface corrosion dynamics.

The corrosion initiation process dynamics of reinforcement steel coated with mortar is studied using a non-linear signal analysis technique named “recurrence plot”. Electrochemical noise current-time series with an open circuit are analyzed to determine the magnitude of the interaction of corrosion microcells in presence and in absence of a corrosion inhibitor. The corrosion dynamic shows a complex nature. The interaction among corrosion micro-cells changes depends on a localization index (LI). A higher L_I implies a more discrete distribution of corrosion micro-cells along with a significant interaction, and a corrosion system auto-organization.