The corrosion-trend monitoring with the impedance technique

Abstract

The physical meaning of monitoring corrosion rates and states of the metal‐solution interphase using sinusoidal current at various frequencies is discussed. Three methods concerning low‐frequency measurements, area method associated to Nyquist's diagrams and the capacitance of the double layer are examined. The basic concepts underlying the use of these techniques are given and, in the case of low‐frequency signals, some considerations on the mathematical theory based on the Kramers‐Kronig relations between real and imaginary parts of Z(ω) are developed. The examples treated refer to laboratory and pilot‐plant tests and illustrate the usefulness of monitoring electrochemical processes taking place in a very large class of systems. In the case of low‐frequency measurements satisfactory results were obtained, for instance, for iron in 1, 2 and 3 N H2SO4solutions at 25°C and for aluminium brass in a 5 % wt HCl solution at 70°C. The capacitance method was employed to examine the behaviour of iron in 5 % wt HCl solutions containing a corrosion inhibitor at various concentrations at temperatures ranging from 35 to 90°C. Experimental results show that the impedance technique is a valid tool to investigate the behaviour of electrochemical systems without any restraint on the shape of their voltage‐current characteristic. Lastly, some considerations concern specific software developed to perform electrochemical measurements with commercial computerized systems and to process experimental data in real time.

Analyzing results of impedance spectroscopy using novel evolutionary programming techniques

“…Such systems can be found in various areas of science and engineering, for example in solid-state electrochemistry [2,3], device manufacturing [4], fuel cells [5], applied electrochemistry [1,6,7] and corrosion phenomena [8][9][10]. While Impedance Spectroscopy (IS) is a very sensitive technique, the data provided by the experiment are hard to deal with.…”