Corrosion

Int. J. Electrochem. Sci., 4 (2009) 144 - 155 International Journal of

ELECTROCHEMICAL SCIENCE
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Fractal Analysis of the Corrosion Inhibition of Carbon Steel in a Bromide Solution by Lithium Chromate
E. Sarmiento, J. G. González-Rodriguez*, J. Uruchurtu, O.Sarmiento, M. Menchaca Universidad Autonoma del Estado de Morelos-CIICAp Av. Universidad 1001,Col. Chamilpa,62209Cuernavaca, Mor., Mexico * E-mail: juch25@uaem.mx Received: 26 September 2008 / Accepted: 11 November 2008 / Published: 20 December 2008

Electrochemical noise results obtained for mild steel corrosion conditions under a lithium bromideethylene glycol solution and in the presence of different concentrations of lithium chromates (Li2CrO4) as corrosion inhibitor are shown. The evaluation wasperformed from the fractal dimension of the electrochemical noise-time series obtained using the so called the Rescale Range Analysis (R/S) proposed by Hurst. The steel under different inhibitor concentrations were exposed to a lithium bromide environment and electrochemical potential/current noise measurements were performed. Afterwards, the fractal dimensions were calculated from the time seriesobtained for the different condition signals. This dimension is obtained from the empirical law R/S = (τ/2)H where R represents the difference between the maximum and minimum values of the variable, S the standard deviation of the time series, τ is the period of time measured and H the Hurst exponent between 0 < H < 1. The calculation of the Hurst exponent and fractal dimension of the time seriescomes from the slope of the R/S plot. For comparison electrochemical impedance spectroscopy was also performed. The fractal analysis of electrochemical noise helps to evaluate the inhibitor protection performance under the corrosion conditions tested.

Keywords: Steel, inhibition, bromide solution, Fractals, Hurst.

1. INTRODUCTION The cheapest and first structural material candidate one can haveis carbon steel that has been used since ancient times. However, it is not precisely the most corrosion resistant for many industrial environments especially in the presence of chlorides [1-3]. For this reason, the expected high corrosion effects of the LiBr aqueous solutions, solutions used in absorption heat transformers [4] which are some of the most promissory elements to make an improvementof the industrial waste heat. Lithium bromide (LiBr) heavy brines are one of the most widely used absorbents, however, extremely

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corrosive [5-8]. An alternative system that reduces some of the disadvantages of the mixture water/LiBr is to add ethylene glycol to this system [5] because some thermo-physical properties of the LiBr/water mixture,such as thermal conductivity, viscosity, maximum concentration etc…, are improved [5]. Alternatively, corrosion, inhibitors can be used for corrosion control in closed systems and as an alternative of efficiency-cost for materials use. The affectivity of some corrosion inhibitors depends upon the type of material, its properties and the corrosive environment. Molybdate (MoO42-) is a very effectivepassivating inhibitor at relatively high levels. Molybdates are inorganic, passivating inhibitors which have been used satisfactorily in many corrosive environments. For instance, they have been used to prevent mild steel [9] and cold rolling steel [10] corrosion in simulated cooling water, in the zinc corrosion inhibition in acidic solutions [11], used to seal phosphate coatings on hot-dipgalvanized steel [12] or on the bacterial corrosion or iron [13]. In a similar way, they have been used on the corrosion inhibition of galvanized steel and aluminum[14] and zinc [19] in NaCl solutions, for the zinc corrosion inhibition in acidic solutions [15], on the pit initiation of pure aluminum in HCl solutions [16] or even used in sol-gel coatings for mild steel [17]. Electrochemical impedance...