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Since its introduction in 1933, the concept of patinas as a corrosion-controlling mechanism has been playing an important role in many structural applications. The analysis of the initial stages of the corrosive attack showed that this phenomenon, which was considered uniform at first, is actually a moderate one, non-metallic inclusions in structural steels being the preferred points of attack. Long-lasting tests were carried out in Argentina, at the urban site of Villa Martelli's outdoor test station. Specimens were obtained from a hot-rolled structural steel sample of 3.5 mm thickness, 45 mm wide and 300 mm long. The outdoor tests were carried out over 35 years. The results obtained by optical microscopy, electron scanning, and electron probe microanalysis showed that the addition of micro-alloying elements modifies steel behaviour. This modification means an increase in steel resistance to atmospheric corrosion.

Since its introduction in 1933, the concept of patinas as a corrosion controlling mechanism has been playing an important role in many structural applications. The analysis of the initial stages of the corrosive attack showed that this phenomenon, which was considered uniform at first, is actually a moderate one being the non-metallic inclusions in structural steels, the preferred points of attack.Long-lasting tests were carried out in the urban site of Villa MartelliArgentina outdoor tests station. Specimens were obtained from a hot-rolled structural steel sample of 3.5 mm thickness, 45 mm wide and 300 mm long. The outdoor tests were carried out over 35 years. The results were obtained by optical microscopy, electron scanning, and electron probe microanalysis showing that the addition of microalloyed elements modifies steel behaviour. This modification means a steel increase resistance towards atmospheric corrosion.

When submerging a pure metal or an alloy in an aqueous solution, a migration of metallic ions between the solid phase and the aqueous phase starts immediately. In fact, it is a constant exchange of metallic ions in which the prevailing speed will be the one leading to a decrease of the free energy (W) of the system.The passing of the metallic ions to the solution will create a potential difference in the metal-solution interface, which will hinder the passage of new ions. A potential difference will be reached, in which the free energy variation will be null, and a thermodynamic equilibrium will exist.If the metal is submerged into a solution that has its own ions, the electrochemical potential will be different in each metal. Noble metals are those like gold (Au), and Platinum (Pt), whose ions are deposited on the metallic solid phase thus increasing their potential with respect to the solution. The metal will be traditionally more positive than the solution.Those metals like Iron (Fe) and Zinc (Zn) will have a tendency to pass to a solution, no matter their ionic concentration, getting the metallic solid phase lower potentials than the solution, or negative potentials in contrast with noble metals.The direct measurement of the potential difference between the metal and the solution is experimentally impossible. However, a cell with two electrodes can be formed to measure the potential difference between the two. One of the electrodes will be the pure metal or alloy, whose potential we are interested in finding out, and the other will be an electrode with an easy-to-reproduce potential to take it as a pattern. The electrode taken as a reference is the one called hydrogen (H) electrode, which is a platinised platinum electrode submerged in an acid solution (pH = 0) with a hydrogen activity equal to 1.0 M, over which hydrogen bubbles at a specified atmospheric pressure. Traditionally, zero potential is assigned to every temperature.