Effect of water-soluble chitosan on the electrochemical corrosion behaviour of mild steel

This article outlines the role of chitosan as a potent inhibitor on mild steel in 3.65% NaCl. The protective ability of chitosan was evaluated by potentiodynamic polarization (PP) mea- surements in 36.5% sodium chloride medium. The outcome of the experiment shows that mild steel in sodium chloride solution containing chitosan nanoparticles exhibit better cor- rosion protection than mild steel in NaCl solution alone because the anodic and cathodic site of the steel were blocked by chitosan nanoparticles, thereby minimising the incursion of the salt solution by forming a thin film on the mild steel surface. The inhibitive effi- ciency of chitosan nanoparticles was also studied using weight loss. The weight loss by mild steel in NaCl solution was found to be higher than those immersed in NaCl-chitosan nanoparticulate solutions. The loss in weight reduces as the concentration of chitosan nanoparticles increases, indicating the fortifying ability of chitosan nanoparticles. Results obtained show that chitosan could offer inhibition efficiency above 90%. The mixed inhibi- tion characteristic of chitosan was demonstrated by the Tafel curve. The Langmuir isotherm possesses an R 2 value of 0.9957 indicating the effectiveness of chitosan as an inhibito

Controlling the corrosion and cathodic activation of magnesium via microalloying additions of Ge

The evolution of corrosion morphology and kinetics for magnesium (Mg) have been demonstrated to be influenced by cathodic activation, which implies that the rate of the cathodic partial reaction is enhanced as a result of anodic dissolution. This phenomenon was recently demonstrated to be moderated by the use of arsenic (As) alloying as a poison for the cathodic reaction, leading to significantly improved corrosion resistance. The pursuit of alternatives to toxic As is important as a means to imparting a technologically safe and effective corrosion control method for Mg (and its alloys). In this work, Mg was microalloyed with germanium (Ge), with the aim of improving corrosion resistance by retarding cathodic activation. Based on a combined analysis herein, we report that Ge is potent in supressing the cathodic hydrogen evolution reaction (reduction of water) upon Mg, improving corrosion resistance. With the addition of Ge, cathodic activation of Mg subject to cyclic polarisation was also hindered, with beneficial implications for future Mg electrodes

Reducing the corrosion rate of magnesium via microalloying additions of group 14 and 15 elements

A characteristic of magnesium (Mg) dissolution is that dissolution is accompanied by a concomitant increase in the hydrogen evolution reaction (HER), a phenomenon known as cathodic activation. When magnesium undergoes free corrosion or forced dissolution in response to anodic polarisation, cathodic activation is manifest, which allows magnesium dissolution to readily proceed. However, recent work revealed that alloying magnesium with micro additions of arsenic, As (a group 15 element) was capable of retarding cathodic activation, resulting in a significant reduction in the corrosion rate of Mg-As alloys. As such, in the pursuit of elements with similar chemical and electrochemical properties to arsenic, but with less toxicity, a number of group 14 and 15 elements were alloyed with magnesium and reported herein. Based on the binary alloying additions studied herein, it was revealed that Bi, Ge, Pb, Sb and Sn, demonstrated suppression of cathodic activation of Mg following anodic polarisation (about one order of magnitude lower based on the cyclic galvanostatic-potentiostatic testing), in addition to lower free corrosion rates (about one order of magnitude based on the mass loss and hydrogen evolution testing). Employing a number of corrosion rate assessments, including online atomic emission spectroelectrochemistry, it was shown that reduction in Mg corrosion rates – historically considered difficult to achieve – can be robustly demonstrated. The present work has implications for the development of more corrosion resistant Mg alloys, Mg anodes for cathodic protection, or for the use of Mg as a primary battery electrode

Simultaneously improving the corrosion resistance and strength of magnesium via low levels of Zn and Ge additions

Satisfactory corrosion resistance remains an issue in the widespread implementation of magnesium (Mg). The use of alloying to improve mechanical properties of Mg generally accelerates corrosion due to microstructural heterogeneity. However, recent works have revealed that additions of elements serving as ‘cathodic poisons’ such as arsenic (As) and germanium (Ge) can reduce cathodic reaction rates and suppress cathodic activation - imparting corrosion resistance. The effect of Ge was translated into a ternary (and mechanically relevant) Mg-alloy system for the first time, revealing an alloy system with a balance of properties, and low rate of corrosion relative to Mg-alloys to date

The effect of iron re-deposition on the corrosion of impurity-containing magnesium

This article provides a contribution towards the mechanistic understanding of surface phenomena observed during the corrosion of Mg-based substrates particularly in the low anodic polarization range. The concept considers the recent literature explaining cathodic hydrogen evolution from noble acting areas even during global anodic polarization. Heavy metal impurities in the ppm range or intermetallics are always present even in highly pure magnesium. Their potential effect was investigated here in more detail. The experimental results contribute to understanding the role of iron impurities in dark area formation and suggest a way for linking the observed phenomena to the recent literature. The shown enhanced cathodic activity of dark areas especially at the corrosion front and the superfluous hydrogen are linked to an iron re-deposition mechanism due to iron reduction. The proposed mechanism is based on the results obtained from innovative characterisation techniques using magnetic fields, diffraction experiments and transmission electron microscopy, which show the formation of iron rich zones, especially at the corrosion front offering "in statu nascendi" metallic Fe films acting as active cathodes for hydrogen reduction

Corrosion Protection Effect of Chitosan on the Performance Characteristics of A6063 Alloy

This article outlines the behaviour of water-soluble chitosan as an effective inhibitor on aluminium alloy in 3.65% NaCl at room temperature. The inhibitive ability of water-soluble chitosan was examined using electrochemical potentiodynamic polarization techniques, mass loss measurements and computational studies. The outcome of the experiment reveals that chitosan inhibited aluminium alloy in sodium chloride solution exhibits better corrosion protection than the uninhibited because chitosan nanoparticles minimize the ingression of chloride ion into the active sites of aluminium alloy by forming thin film on its surface. The losses in mass by the inhibited aluminium alloy were found to reduce as the concentration of chitosan increases. Results obtained showed that chitosan could offer inhibition efficiency above 70%. Polarization curve demonstrated that chitosan in 3.65% NaCl at room temperature acted as a mixed-type inhibitor. Adsorption of chitosan nanoparticles on the aluminium alloy was found to follow Langmuir adsorption isotherm with correlation regression coefficient (R2 ) value of 0.9961

Electrochemical dissolution characteristics of Zn, Mg, Al and ZnMg(Al) alloys

Thema der Dissertation ist die Untersuchung des elektrochemischen Auflösungsverhaltens von Zink, Magnesium, Aluminium und von zinkreichen Gusslegierungen. Um detallierte Einblicke in den Mechanismus der Korrosion dieser Materialien zu erhalten, wurde eine mikroelektrochemische Durchflusszelle mit verschiedenen Online-Analysemethoden gekoppelt. Hierfür wurde zur Quantifizierung der Metallauflösung ein UV-VIS-Spektrometer bzw. ein induktiv gekoppeltes Plasma-Massenspektrometer verwendet. Zur Analyse der Wasserstoffentwicklung auf Magnesium und Aluminium wurde die Durchflusszelle mit einem MIMS (Membrane Inlet-Massenspektrometer) gekoppelt. Ein Vergleich von elektrochemischen Daten und simultan ermittelter Metallauflösung bzw. Gasentwicklung zeigt den Einfluss der oberflächennahen Reaktionsbedingungen auf die Korrosion der untersuchten Materialien und liefert neue mechanistische Erkenntnisse zur Auflösung von Metallen und zinkreichen Legierungen

Investigating the real time dissolution of Mg using online analysis by ICP-MS

Dissolution of magnesium was studied using an electrochemical flow cell combined with online analytics. The method has high sensitivity and congruency between electrochemical polarization experiments and magnesium concentrations detected downstream via inductively coupled plasma - mass spectroscopy (ICP-MS). The method used allowed quantification of magnesium dissolution during anodic and cathodic polarization and also without external currents, i.e. determination of dissolution rate at open circuit, which is not accessible by electrochemical techniques. The relationship between the applied current, and dissolved magnesium measured is presented and discussed in the broader context of past and recent works studying magnesium corrosion. The development of a surface film during anodic dissolution is described on the basis of an inventory of currents measured and applied. (C) 2014 The Electrochemical Society. All rights reserved