Jorge A. Calderón

The oxidative stability of biodiesel and its impact on the deterioration of metallic and polymeric materials: a review

The purpose of this paper is to analyze the main issues concerned with the oxidative and storage stabilities of biodiesel and how they affect different metallic and polymeric materials present in automotive parts and in biodiesel storage structures. In addition, this work presents a review of the techniques used for measuring the oxidative stability and for evaluating the degradation of metallic and polymeric materials. When biodiesel is oxidized, a series of changes in its properties occurs. These changes not only affect biodiesel quality, but also the properties of the materials that are in contact with it. Upon oxidation, biodiesel properties like the acid value, peroxide value and viscosity increase, while the iodine value and the content of methyl esters decrease. The changes in the chemical and physical properties of biodiesel can affect the integrity and stability of the material. The situation reviewed in this paper, which talks about the stability of materials, could limit the extensive use of biodiesel. Such measures have been proposed in several countries, and it is a topic of great importance for biodiesel technology.

Influence of Surface Treatment on Magnetic Properties of Fe3O4 Nanoparticles Synthesized by Electrochemical Method

The changes of magnetic properties in magnetite nanoparticles during two different stabilization processes were investigated. Magnetic nanoparticles (MNPs) were obtained by electrochemical synthesis from two kinds of salts: (CH3)4NCl and NaCl. After that, two methods-steric and electrostatic-were used to stabilize MNPs with oleic acid (OA) and sodium hydroxide (NaOH), respectively. As a consequence, aqueous and organic dispersions were obtained after surface modification. The coated nanoparticles were characterized by TEM, zeta potential, thermogravimetry analysis (TGA), cyclic voltammetry (CV), magnetization measurements, and infrared and Mössbauer spectroscopy. The results showed that the particles were between 8 and 13 nm in size. In addition, the MNPs were coated with negative charge layers from NaOH by physisorption and coated with carboxylate groups from OA by the chemisorption process, and hence, they exhibited different reactivity and behavior depending on the nature of the electrolyte used in the electrochemical synthesis. Furthermore, the uncoated and coated MNPs had a narrow size distribution. Additionally, the saturation magnetization values showed dependence on the magnetite synthesis conditions and surface modifiers.

Electrochemistry of copper in ionic liquids with different coordinating properties

The electrochemical behavior of Cu was evaluated in two different ionic liquids (ILs) that had the same piperidinium-based cations but different anions with different coordinating properties: bis(trifluoromethanesulfonylimide) ([Tf2N]) (strong coordinating property) and tetracyanoborate ([B(CN)4]) (weak coordinating property). Cyclic voltammetry and electrochemical impedance spectroscopy showed that the electrochemical behavior of Cu depends strongly on these coordinating properties. In the strongly coordinating IL, Cu exhibits no passivation, but a passivating film is formed on the metal surface in the weakly coordinating IL. Scanning electron microscopy indicated that Cu suffered from pitting corrosion in the presence of the strongly coordinating IL. Raman spectroscopy elucidated the formation of a thin film of Cu2O in both ILs, due to the trace presence of H2O (below 70 ppm). In the [Tf2N]-based IL, a Cu salt forms with the IL as the potential increases, but it is not enough to passivate the metal due to the solubility of the salt in the IL. In the [B(CN)4]-based IL, even at lower potentials, a Cu[B(CN)4] layer is formed that passivates the metal.

Corrosion mitigation of buried structures by soils modification

Carbon steel samples were buried in loamy soil modified with lime, fly-ash and Portland cement in ratio of 5 and 10% during 60 days. Corrosion attack was assessed by electrochemical impedance spectroscopy. Loamy soil without modification was taken as reference. The corrosion products in rust were characterized by Raman spectroscopy. It was found that soil with fly-ash and Portland cement can develop corrosion protection to bare steel due to the changing of formed rust on steel samples. Lepidocrocite and Goethite were found as major constituents in formed rust on buried steel in soil modified with fly-ash and cement, while Magnetite was found in formed rust on buried steel in soil without addition of cementitious materials and modified with lime. According to the electrochemical results, the soil with 5% of fly-ash exhibited the anticorrosive best performance.

THE CORROSION PROCESS OF P-110 STEEL IN STIMULATION FLUIDS USED IN THE OIL INDUSTRY

were measured at 25 and 80°C, respectively. The hydrodynamic regime plays an important role in the corrosion of steel only in the disodium solution, where corrosion rates were increased at higher rotation speeds of the electrode. The cathodic depolarization effect is more important in the EDTA-Na2 than in the EDTA-Na4 solution, making it more corrosive.

New combination between chitosan, single walled carbon nanotubes and neodymium(III) oxide found to be useful in the electrochemical determination of rutin in the presence of morin and quercetin

A glassy carbon electrode surface was modified with a new combination of chitosan, single walled carbon nanotubes (SWCNT) and neodymium(III) oxide (NdOX) and was found to be effective in the detection of rutin (RU), a natural antioxidant. The modified electrode displayed high activity toward the oxidation of RU compared to other flavonoids, such as quercetin (Q) and morin (MO). The oxidation peaks of RU, MO and Q were exhibited at +0.53, +0.42 and +0.39 V, respectively. Moreover, anodic peak currents were 37.27, 10.39 and 2.27 μA, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the electrode surface, and square wave voltammetry (SWV) was used to quantify RU. The detection limit (3σ/b) was 0.092 μmol L−1, and the RSD was 2.5%. A new sensor was used in the quantification of RU in roasted beans infusion of Coffea arabiga L. and extract of Zamia furfuracea L.f. ex Aiton with satisfactory results.

Evaluation of the corrosion behavior of the al-356 alloy in NaCl solutions

Cellular metals are a new class of materials with promising applications and a unique combination of physical, chemical and mechanical properties. The Al-356 alloy is used to manufacture metal foams from NaCl preforms. Despite the usefulness of these materials, their performance may be affected by corrosion due to residual salt. This paper reports the study of the behavior of the Al-356 alloy in chloride solutions by electrochemical techniques in rotating disk electrode. The cathodic reaction of oxygen reduction is the crucial stage of process dissolution of the material, which shows that is the oxygen transport which limits the corrosion process.

Electrochemical Behavior of Copper in Drinking Water: Evaluation of Dissolution Process at Low Anodic Overpotential

O comportamento eletroquimico do cobre em agua potavel foi estudado por polarizacao potenciodinâmica e espectroscopia de impedância eletroquimica em ate quatro dias depois de imersao em condicoes hidrodinâmicas diferentes. Os resultados de impedância foram interpretados usando modelos de circuito equivalente, os quais mostraram um aumento da espessura do filme com o tempo, que impede a difusao de especies de cobre atraves da camada de oxido de cobre formada. Essa camada de oxido e maior em condicao de estagnacao. A baixos sobrepotenciais anodicos, os diagramas de impedância apresentam pelo menos quatro constantes de tempo que poderiam ser explicadas pela existencia de diferentes pocessos faradaicos, a adsorcao/dessorcao de especies intermediarias, processos de difusao e a formacao de uma camada de oxido na superficie de cobre. Na regiao anodica, a resistencia total a corrosao diminui, possivelmente devido a dissolucao das especies de cobre e ao aumento da difusao atraves da camada de oxido, principalmente sob condicoes hidrodinâmicas.

POSSIBILITIES OF CORROSION ASSESSMENT OF METALS IN BIODIESEL USING EIS

-2 ) to be associated with a metal double layer capacitance, the values of these capacitances increased with the increment of the exposition time. It is pos- sible that for longer times of exposition, the electrochemical parameter related with the lowest capacitive loop of the impedance can be associated to the metal corrosion phenomena. ABSTRACT

Electrodeposition of Polypyrrole Films: Influence of Fe3O4 Nanoparticles and Platinum Co-Deposition

Inorganic particles/conductive polymers composites in bulk or films have been subject of intense study during the last decade. This type of materials offer the potential to being used in batteries, electro-chemical display devices, molecular electronics, electromagnetic shields, opto-electronic applications, microwave-absorbing materials, and even for corrosion protection (Garcia et al., 2002; McNally et al., 2005). Conducting polymers have some specific problems that make difficult its use in the above applications. Instability under oxygen and UV exposure, easily doping and over-oxidation are the most common among others. A novel strategy have been reported to improve its properties and extend the application range of these materials, this is the incorporation of inorganic particles of metallic oxides such as MnO2, V2O5, TiO2, Fe2O3, Fe3O4 and WO3 or metallic particles of Zn, Cu, Au, Pt into the conductive polymer (Demets et al., 2000; Ferreira et al., 2001; Kawai et al., 1990; Kuwabata et al., 2000; Lenz et al., 2003; Montoya et al., 2010; Vishnuvardhan et al., 2006). For example we have recently demonstrated that the incorporation of magnetite into polypyrrole (PPy) decreases the electric resistance of the polymeric film and not only stabilize the polaronic form of the polypyrrole, but also preserve the polymer from further oxidation (Montoya et al., 2010). Polypyrrole (PPy) exhibits interesting properties such as high conductivity, relatively good environmental stability, and wide technological applications. PPy can be obtained either by chemical and electrochemical polymerization. The electropolymerization is considered a controlled synthesis method that provides better control of thickness and morphology of films (by controlling parameters as current, voltage, and time), efficient (high materialtransfer efficiency with nearly 100% material utilization and recovery), and environmentally safe (usually a water-based process). The aim of this chapter is to show in detail, two particular cases concerning the development of PPy/inorganic particles composite coatings deposited on stainless steel. First of all, a brief introduction is presented discussing the electrochemical polymerization methods. Then, as a first case, the effect of magnetite (Fe3O4) nanoparticles on the polymer matrix is presented. The second case is the co-deposition of platinum/PPy. Both studies show the effect of the addition of the inorganic phase on the