Corrosion behavior of iron-based alloys in the LiBr + ethylene glycol + H 2 O mixture E. Samiento-Bustos a , J.G. González-Rodriguez a,b, * , J. Uruchurtu a , V.M. Salinas-Bravo c a Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, CP 62210, Cuernavaca, Morelos, Mexico b CIMAV-Miguel de Cervantes 120, Chihuahua, Chih., Mexico c Instituto de Investigaciones Eléctricas, Gerencia de Materiales y Proceso Químicos, Av. Reforma 113, Col. Palmira, CP 62490, Cuernavaca, Morelos, Mexico article info Article history: Received 22 October 2008 Accepted 10 February 2009 Available online 20 February 2009 Keywords: A. Steels C. Pitting corrosion B. Electrochemical noise Impedance spectroscopy abstract The corrosion resistance of 1018 carbon steel, 304 and 316 type stainless steels in the LiBr (55 wt.%) + ethylene glycol + H 2 O mixture at 25, 50 and 80 °C has been studied using electrochemical techniques which included potentiodynamic polarization curves, electrochemical noise and electrochem- ical impedance spectroscopy techniques. Results showed that, at all tested temperature, the three steels exhibited an active–passive behavior. Carbon steel showed the highest corrosion rate, since both the pas- sive and corrosion current density values were between two and four orders of magnitude higher than those found for both stainless steels. Similarly, the most active pitting potential values was for 1018 car- bon steel. For 1018 carbon steel, the corrosion process was under a mixed diffusion and charge transfer at 25 °C, whereas at 50 and 80 °C a pure diffusion controlled process could be observed. For 316 type stain- less steel, at 25 and 50 °C a species adsorption controlled process was observed, whereas at 80 °C a dif- fusion controlled mechanism was present. Additionally, at 25 °C, the three steels were more susceptible to uniform type of corrosion, whereas at 50 and 80 °C they were very susceptible to localized type of corrosion. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Ethylene glycol is widely used as coolant in automotive heat exchangers, mixed with water, in a pH range between 7 and 8, due to its great heat absorption capacity [1–4]. However, lithium bromide (LiBr) heavy brines are one of the most widely used absor- bents [5–8] in absorption heat transformers because LiBr possesses favorable thermo physical properties. However, LiBr can cause seri- ous corrosion problems on metallic components of cooling systems and heat exchangers at absorption plants such as carbon steel, stainless steel, copper alloys and titanium [9]. An alternative way to reduce some of these disadvantages of the water/LiBr mixture is to add ethylene glycol to the system [8] because some thermo physical properties of the LiBr/water mixture, such as thermal con- ductivity, viscosity, maximum concentration etc. are improved [10,11]. The cheapest and first structural material candidate one can have is carbon steel [12], however, it is not precisely the most corrosion resistant for many environments [13,14]. For this reason, there exist a few works on the corrosion performance of carbon steel, but there are too many about the performance of stainless steels in LiBr–water mixtures [5–7,15–18]. An alternative way to reduce corrosion rate is by using inorganic inhibitors such as chro- mates, nitrates, molybdates, etc. just like the reported recently by Sarmiento-Bustos et al. [19]. Thus, the aim of the present work is to evaluate the corrosion performance of typical iron-based alloys commonly used in heat absorption systems such as 1018 carbon steel and 304 and 316 type stainless steels in the new proposed LiBr + ethylene glycol + H 2 O heat absorber mixture, and try to give some insights on the involved corrosion mechanisms. 2. Experimental procedure Materials tested included 1018 carbon steel, 304 and 316 type stainless steels, with chemical composition as given in Table 1, and encapsulated in a commercial polymeric resin. Cylindrical probes with 5.9 mm in diameter and an exposed area of 0.2728 cm 2 to the solution were used. All of them were abraded with papers 600 grade emery paper, and finally rinsed with dis- tilled water and ethanol (C 2 H 5 OH). Solution used was a normally aerated LiBr + ethyleneglycol + H 2 O mixture at room temperature, in a concentration of 614 and 217 g/l for LiBr and ethylene glycol, respectively. This concentration was chosen because, according to literature [10,11], the best thermo physical properties of the fluid are obtained at this concentration and re-crystallization of the lith- ium bromide is avoided. Polarization curves were obtained by polar- izing the specimens from 1000 to 1000 mV respect to the free corrosion potential value, E corr , at a scanning rate of 60 mV/min. 0010-938X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2009.02.008 * Corresponding author. Address: Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, CP 62210, Cuernavaca, Morelos, Mexico. Tel./fax: +52 777 3 29 70 84. E-mail address: ggonzalez@uaem.mx (J.G. González-Rodriguez). Corrosion Science 51 (2009) 1107–1114 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci