A corrosion study has been made using the electrochemical current and potential noise technique, polarization curves and conventional weight loss method to determine the corrosion resistance of a carbon steel exposed to LiBr-H2O (50% wt.) corrosive solution at 25, 50, 60, 70 and 80°C. From the noise measurements, the resistance noise (Rn) was determined, and then the Stern-Geary equation and Faraday?s Law were used to determine the mass loss. The results indicated that the corrosion rates increased with temperature. SEM observations of the corroded samples indicated that the carbon steel suffered localized corrosion; these results were according to the pitting index obtained from the current time series data. To support the corrosion mechanism, EDS analysis of the corrosion products were also made. Through the polarization curves, the Tafel slopes were obtained together with some qualitative corrosion characteristics of the carbon steel.
Until now, it has been published several works about the corrosion of stainless steel caused by lithium bromide solutions [1-5], which have been frequently studied using the potentiodynamic polarization curves (PPC) under limited temperature conditions. The utilization of the potentiodynamic polarization curves applying high potentials is important due to that a basic knowledge about the corrosion mechanism and a general behavior of the material can be obtained. Through the PPC technique, it is also possible to determine the corrosion potential, the current density, passivation and re-passivation regions, limit currents, etc., but it is not possible to obtain the corrosion kinetics, nevertheless, the polarization curves provide an useful information to compare the corrosion resistance of different materials under the same experimental conditions. The electrochemical technique such as current and potential noise, besides providing the corrosion mechanism, provides the tools to determine the corrosion rate in time without perturbing the material. Recent works have been published where the electrochemical noise technique have been applied to determine the corrosion rates and type of corrosion of some stainless steel materials [6-9]. Noise is a term describing the variation of a variable signal in time [10]. In the case of corrosion phenomenon, the process is random in time, and it is the result of transients which behavior presents a suddenly decrease of potential and/or an increase of current respect to an average value, companied of an exponential recovery of potential and/or a decrease of current; such behavior is interpreted as a breakdown of an oxide film (passivaton film) or localizedcorrosion events [10]. The noise signals in current and potential have certain characteristics, which can represent the type of corrosion suffered by a material. The electrochemical technique can also be applied for determining the corrosion rate throughout the noise resistance Rn obtained by means of the relationship between the standard deviation of potential and the standard deviation of current [11]. The objective of the present work was to obtain the corrosion rates and determine the type of corrosion (general-pitting) of carbon steel exposed to 50 wt. % aqueous lithium bromide solution at 25, 50, 60, 70 and 80°C, using the electrochemical noise technique and polarization curves.
