Claudia Marcela Méndez

Corrosion of Al–Mg Alloys in Ethanol

Technological changes driven to solve the energy problems existing in the world today, offer a key opportunity for sciences related to the selection of materials. Specifically for production industries and handling biofuel, it is crucial the effectiveness of materials against corrosion, so in recent years the increase is denoted in corrosion studies of metallic alloys applied in these industries. The aim of this work is to study the corrosion behavior of aluminum-magnesium alloys, using potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) tests in ethanol (99.5% v/v) at room temperature, evaluating the effects of microstructure and percentage of magnesium addition. Furthermore, the mechanisms involved in corrosion are proposed, compared to the different theories suggested by other authors.

Análisis de la resistencia a la corrosión en lluvia ácida simulada de lasaleaciones Zn-Sn

El zinc y el estano, junto con las aleaciones Zn-Sn, son empleados en la industria como recubrimientos del acero frente a la corrosion. Uno de sus usos mas frecuentes es el galvanizado para exteriores, el cual es afectado por la corrosion debido a la lluvia acida. El objetivo del trabajo es evaluar el comportamiento electroquimico que presentan las aleaciones Zn-Sn, con respecto a los metales puros, en una solucion acuosa de lluvia acida simulada compuesta por 31,85 mg/L H2SO4, 15,75 mg/L HNO3, 21,25 mg/L NaNO3, 46,20 mg/L (NH4)2SO4, 31,95 mg/L Na2SO4, 84,85 mg/L NaCl, con un pH entre 3,5 y 4,0, a temperatura ambiente (25oC). Para ello, se emplearon probetas de aleaciones con diferentes porcentajes en peso de estano (6, 10 y 50), y de los metales puros, solidificadas horizontalmente. Se tomaron muestras de cada estructura de grano revelada y se las desbastaron con papeles de SiC, de granulometria entre #60 y #1200. Posteriormente, se realizaron medidas de polarizacion potenciodinamica en una celda electroquimica convencional de tres electrodos y ensayos de inmersion. Cada probeta se examino mediante microscopia optica, antes y despues de realizar los ensayos. De las curvas potenciodinamicas se observo para los cortes transversales, que a medida que aumenta el contenido de estano en la aleacion, los potenciales tienden a valores mas nobles. A partir de los ensayos de inmersion se denoto que la estructura columnar de zinc y las aleaciones presentan una mayor perdida de masa que las demas estructuras. Ademas, el zinc y las aleaciones presentaron la velocidad maxima de corrosion al primer dia de inmersion, para todas las estructuras de grano. En las micrografias se evidencio que el zinc presento corrosion generalizada.

Corrosion Resistance of Al-Cu Alloys in Function of the Microstructure

Aluminum and its alloys are characterized by low density, high electrical and thermal conductivity, and good resistance to corrosion in certain media such as air. The mechanical strength alloy is achieved. The objective of the present research consist on studying the type of structure (columnar, equiaxed or with columnar to equiaxed transition, CET) using parameters of the solidification process and electrochemical parameters in Al, Cu and Al-Cu alloys with different concentrations. In order to obtain columnar, equiaxed and CET structures, the alloys were directionally solidified upwards in an experimental set up with a set of thermocouples in the samples which permit to determine the time dependent profiles during the process. The electrochemical studies of the samples were realized by using an electrochemical impedance spectroscopy (EIS) technique and potentio-dynamic polarization curves immersed in 3% NaCl solution at room temperature. In general, we observed that the susceptibility to corrosion of the different structures depends on the size of the secondary dendritic spacing and the proportion of Al2Cu phase and Al-rich phase.

Corrosion Resistance of Zn-Sn Alloys Horizontally Directionally Solidified

The aim of this study is to evaluate the effects of the microstructural arrangement of Zn-Sn alloys horizontally directionally solidified on its resultant corrosion behavior. In this context, a water-cooled horizontal unidirectional solidification system was used to obtain alloy samples. Electrochemical impedance spectroscopy and potentiodynamic polarization curves were used to analyze the corrosion resistance in a 3% NaCl solution at 25 °C. Microscopic observation of the samples denote a higher susceptibility to pitting corrosion by the Sn, with lots of deep and localized pitting in the order of 10 microns. On the other hand, samples of Zn-Sn alloys and pure Zn showed a more generalized corrosion, with largest number of pinholes and with a depth of 4–5 microns approximately. Also, it was found that the presence of Sn in the analyzed samples affects the corrosion potential, becoming the alloys nobler respect to pure Zn.

Electrochemical Characterization of Al–Li–Cu–Mg Alloys

The aluminum-lithium (Al–Li) alloys were developed with the objective of obtaining, mainly, low weight products in structural elements of planes that was later joined by the aerospace industry. They has been developed, among others, by the aeronautical industry due to its special characteristics. In the present research, aluminum-lithium-copper-magnesium alloys were solidified under different conditions of cooling rates. The microstructures were observed and measured. To determine the susceptibility to corrosion, working electrodes were prepared in different positions along the specimens and cyclic potentiodynamic polarization measurements were conducted, using NaCl 0.5 M solution at room temperature.

Corrosion of Nonferrous Metals and Their Alloys

Corrosion is the result of the interaction of a material (metal) with its environment. %e corrosion process depends on the properties of both metal (and alloy) and surrounding environment. Usually, the more important factors causing corrosion are concentration of aggressive species (e.g., chloride), acidity (pH), fluid velocity, temperature, and potential (oxidizing power). Steel and other ferrous alloys are consumed in exceedingly large quantities because they have such a wide range of mechanical properties, may be fabricated with relative ease, and are economical to produce. However, steels have some distinct limitations, chiefly a relatively high density, a comparatively low electrical conductivity, and an inherent susceptibility to corrosion in some common environments. %us, for many applications, it is advantageous or even necessary to use other alloys that have more suitable property combinations. Alloy systems are classified either according to the base metal or according to some specific characteristic that a group of alloys shares. Authors were invited to submit original research articles and reviews for this special issue that included all aspects of the corrosion process of the following metal and alloy systems: aluminum, copper, magnesium, and titanium alloys; the refractory metals; the superalloys; the noble metals; and miscellaneous alloys, including those that have nickel, lead, tin, zirconium, and zinc as base metals. %e papers published in this special issue are as follows:

Green Extract of Mate Tea as Corrosion Inhibitor of Copper and Aluminum

Many of the corrosion inhibitors in current use are expensive and toxic so the current trend is to study compounds that are environmentally friendly and efficient. Inhibitors are easy to use and they have the additional advantage that can be applied in situ and without causing significant disruption in the process. In the present work we investigate the influence of the aqueous extract of yerba mate as corrosion inhibitor of copper and aluminum in 0.5 M NaCl and 1 M HCl solutions, using different electrochemical techniques. The following inhibition efficiencies: 56% for copper in 0.5 M NaCl with 25% concentration of extract, 17% for copper in 1 M HCl with 5% concentration of extract, and 99% for aluminum in 0.5 M NaCl for 1% concentration of extract were obtained by potentiodynamic polarization.

Corrosion Resistance of Different Aluminum Alloys in Ethanol

The aim of this work is to study the corrosion behavior of Aluminum alloys with silicon and magnesium, by potentiodynamic polarization tests and Electrochemical Impedance Spectroscopy in bioethanol solution (92o – 96o), room temperature and pH 6.5, evaluating the effects of the addition of CH3COOK and ClO4Li as supported electrolytes. The results show that adding ClO4Li to the alcoholic solution induces pitting corrosion, possibly reducing ClO4- to Cl-. Whereas that, CH3COOK causes inhibition of the corrosion, and increasing of passivation of the metal, a phenomenon which is attributable to the generation of corrosion products.

Passive Films Formed on Stainless Steels in Phosphate Buffer Solution

The behaviour of passive films formed on directionally solidified stainless steels, 18Cr10N2Mo0.08C, 18Cr14N8Mo0.03C and 18Cr10Ni8Mo0.08C, in different areas that were formed during solidification (columnar, columnar-to-equiaxed transition (CET) and equiaxed) was studied using electrochemical testing in Na2HPO4 with / without NaCl. The behavior of stainless steel in the presence of phosphate chlorides is the best compared to non-chloride phosphate.

Electrochemical Properties of Al-Cu Alloys in NaCl Solutions

In this paper the structure of aluminum based alloys and their corrosion behavior by using different electrochemical techniques as characterization methods are considered. Currently, it becomes imperative to know the role of the Al2Cu against the susceptibility to corrosion of these alloys. The present work aims to studying the electrochemical behavior of aluminum base alloys with the following compositions: Al-1wt.%Cu, Al-4.5wt.%Cu and Al-15wt.%Cu (with different grain structures), in 1M NaCl solutions, at room temperature. Cyclic potentiodynamic polarization tests were performed and were found that the alloys with more than 1wt.%Cu in the matrix have an unstable behavior and without tendency to reach passivity. The equivalent circuits derived from electrochemical impedance spectroscopy technique (EIS) generally showed two capacitive contributions. The susceptibility to corrosion becomes a complex function, not only of copper concentration and structure, but also with interdendritic spacings and distribution of phases in the alloys.