Corrosion behavior of aluminum exposed to a biodiesel L. Díaz-Ballote a, * , J.F. López-Sansores b , L. Maldonado-López a , L.F. Garfias-Mesias c a Departamento de Física Aplicada, CINVESTAV-IPN, Mérida Yucatán, 97310, Mexico b Facultad de Química, UADY, Mérida Yucatán, 97310, Mexico c Corrosion and Materials Technology Laboratory, DNV/CCT, Dublin, Ohio, 43017, USA article info Article history: Received 19 September 2008 Received in revised form 12 October 2008 Accepted 15 October 2008 Available online 1 November 2008 Keywords: Biodiesel Corrosion Aluminum KOH abstract Aluminum was exposed to biodiesel with different levels of contaminants and impurities, and its corro- sion behavior was evaluated by conventional electrochemical techniques. It was found that the corrosion behavior of aluminum in biodiesel contaminated with alkalis is similar to the corrosion behavior of alu- minum in aqueous solutions. In addition, it was demonstrated that corrosion of aluminum can be used as a quantitative indication of the biodiesel purity. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Biodiesel (diesel derived from renewable biological sources such as vegetable oil or animal fat by a transesterification process) is currently in regular use as an alternative fuel over conventional oil derived diesel (petrodiesel) [1–5]. A common transesterification process is catalyzed by a strong base like KOH or NaOH [6–9]. After a successful transesterification process, the reaction solution is poured into a separatory funnel. Glycerol and biodiesel are typi- cally separated by gravity. Glycerol is removed, and biodiesel is ready for further purification. Typical contaminants such as resid- ual glycerol, catalysts, free fatty acids, water, and other contami- nants present in the biodiesel are washed in order to improve the biodiesel quality to meet the ASTM standard D6751-02. Aluminum and its alloys have a low atomic weight and high strength to density ratio. These properties make them very useful for construction of parts in the automotive industry [10], such as engine blocks or pistons [11–13]. Although the corrosion behavior of aluminum and its alloys has been extensively studied in aqueous solutions containing different aggressive species and pH values, no attention has been paid to the corrosion behavior of aluminum ex- posed to biodiesels. Aluminum is prone to corrosion due to its neg- ative standard potential of 1.66 V vs. NHE [14]. In addition, the corrosion resistance of aluminum has a strong dependency on pH. At extreme pH values, the corrosion resistance of aluminum decreases dramatically, particularly in alkaline solutions, which dissolve the protective oxide layer. For the automotive industry, the main concern is increased levels of residual catalyst alkalis after the synthesis of biodiesel, which could promote high corro- sion rates of key automotive parts. Therefore, it is important to undertake a systematic study of the corrosion behavior of alumi- num exposed to biodiesels. Since washing the biodiesel removes contaminants, each step of this process becomes suitable to mimic biodiesels with various levels of contaminants. The main aim of the present work was to investigate the corro- sion behavior of aluminum exposed to various biodiesels at differ- ent stages of the washing process. Aluminum corrosion behavior is obtained by electrochemical techniques such as open circuit po- tential, linear polarization and electrochemical impedance spectroscopy. 2. Experimental procedure 2.1. Materials The biodiesel used in the present work was prepared from com- mercially available canola oil acquired from a local supermarket. Anhydrous ethanol (EtOH) and potassium hydroxide (KOH) analyt- ical grade were also used in the process. Samples consisting of 99.999% pure aluminum (Goodfellow Materials Ltd., Cambridge, UK) were used as working electrodes. 2.2. Synthesis of biodiesel The transesterification reaction was carried out following the method described by Tickell [15]. The reaction was allowed to 1388-2481/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2008.10.027 * Corresponding author. Tel.: +52 999 942 9437; fax: +52 981 2917. E-mail address: luisdiaz@mda.cinvestav.mx (L. Díaz-Ballote). Electrochemistry Communications 11 (2009) 41–44 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom