Pitting corrosion studies on Al and Al–Zn alloys in SCN− solutions

Electrochemical Investigations on the Corrosion Behavior of 904L Stainless Steel in LiBr Solutions

The pitting corrosion susceptibility of 904L stainless steel in aerated LiBr solutions was investigated. The influence of various experimental variables, including electrolyte concentrations, pH, scan rate, temperatures, and constant potential has been studied using electrochemical measurements, such as cyclic potentiodynamic polarization, potentiostatic techniques, and electrochemical impedance spectroscopy (EIS). The surface morphology of 904L stainless steel was examined by scanning electron microscope (SEM). The rate of uniform corrosion and susceptibility toward pitting corrosion increases with an increase in LiBr concentrations and temperature. Increasing the pH of the solution decreases the rate of both uniform and pitting corrosion. An increase in the scan rate enhances the uniform corrosion, but suppresses the pitting corrosion. EIS diagrams displayed a depressed semicircles with the center under the real axis. Bode plots support the result that the uniform corrosion resistance of the alloy in LiBr solutions decreases with increasing Br− anion concentration. The observations suggest that this one time constant may actually be the overlap of two-time constants.

Electrodissolution-Coupled Hafnium Alkoxide Synthesis with High Environmental and Economic Benefits

The conventional thermal method of preparing hafnium alkoxides [Hf(OR)₄ , R=alkyl] - excellent precursors for gate-dielectric HfO₂ on semiconductors - is severely hindered by its unsatisfactory environmental and economic burdens. Herein, we propose a promising electrodissolution-coupled Hf(OR)₄ synthesis (EHS) system for green and efficient electrosynthesis of Hf(OR)₄ . The operational principle of the electrically driven system consists of two simultaneous heterogeneous reactions of Hf dissolution and alcohol dehydrogenation, plus a spontaneous solution-based combination reaction. In applying ethanol as solvent and Hf metal as electrodissolution medium, we achieved waste-free production of high-purity hafnium ethoxide [Hf(OEt)₄ ] with an equivalent "a concomitant" reduction in CO₂ emission of 187.33 g CO₂ per kg Hf(OEt)₄ and a high net profit of 30 477 USD per kg Hf(OEt)₄ . This system is very competitive with the thermal process, which unavoidably releases substantial waste and CO₂ for a net profit of 27 700 USD per kg Hf(OEt)₄ . We anticipate that the environmental and economic benefits of the EHS process could pave the way for its practical application.

Corrosion behavior of pure titanium anodes in saline medium and their performance for humic acid removal by electrocoagulation

The corrosion behavior of Ti electrodes and the dependence of their anodic dissolution with the experimental conditions, namely pH, current density (j) and supporting electrolyte nature, have been investigated. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests have been performed. It has been found that pH has a relevant effect on the electrochemical dissolution of Ti. In chloride medium, metal dissolution was partially caused by pitting corrosion and the corrosion potential was shifted to more cathodic values. Conversely, in phosphate medium, corrosion was inhibited by the formation of a compact passive layer of titanium hydroxide/phosphate. Further, the mechanisms of sacrificial Ti anode dissolution during the electrocoagulation process are discussed. The influence of the supporting electrolyte, pH and j on the effectiveness of the electrocoagulation process for humic acid (HA) removal was assessed. Under optimized conditions, total decolorization was achieved in 60 min, eventually attaining 94% total organic carbon (TOC) removal.

A Molecular Approach for Mitigation of Aluminum Pitting based on Films of Zinc(II) and Gallium(III) Metallosurfactants

The use of metallosurfactants to prevent pitting corrosion of aluminum surfaces is discussed based on the behavior of the metallosurfactants [Zn^II (L^N2O2 )H₂ O] (1) and [Ga^III (L^N2O3 )] (2). These species were deposited as multilayer Langmuir-Blodgett films and characterized by IR reflection absorption spectroscopy and UV/Vis spectroscopy. Scanning electron microscopy images, potentiodynamic polarization experiments, and electrochemical impedance spectroscopy were used to assess corrosion mitigation. Both metallosurfactants demonstrate superior anticorrosion activity due to the presence of redox-inactive 3d¹⁰ metal ions that enhance the structural resistance of the ordered molecular films and limit chloride mobility and electron transfer.

The Influence of Microstructure on the Passive Layer Chemistry and Corrosion Resistance for Some Titanium-Based Alloys

The effect of microstructure and chemistry on the kinetics of passive layer growth and passivity breakdown of some Ti-based alloys, namely Ti-6Al-4V, Ti-6Al-7Nb and TC21 alloys, was studied. The rate of pitting corrosion was evaluated using cyclic polarization measurements. Chronoamperometry was applied to assess the passive layer growth kinetics and breakdown. Microstructure influence on the uniform corrosion rate of these alloys was also investigated employing dynamic electrochemical impedance spectroscopy (DEIS). Corrosion studies were performed in 0.9% NaCl solution at 37 °C, and the obtained results were compared with ultrapure Ti (99.99%). The different phases of the microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Chemical composition and chemistry of the corroded surfaces were studied using X-ray photoelectron spectroscopy (XPS) analysis. For all studied alloys, the microstructure consisted of α matrix, which was strengthened by β phase. The highest and the lowest values of the β phase's volume fraction were recorded for TC21 and Ti-Al-Nb alloys, respectively. The susceptibility of the investigated alloys toward pitting corrosion was enhanced following the sequence: Ti-6Al-7Nb < Ti-6Al-4V << TC21. Ti-6Al-7Nb alloy recorded the lowest pitting corrosion resistance (Rpit) among studied alloys, approaching that of pure Ti. The obvious changes in the microstructure of these alloys, together with XPS findings, were adopted to interpret the pronounced variation in the corrosion behavior of these materials.

Dynamic corrosion behavior of superhydrophobic surfaces

For superhydrophobic surfaces immersed in water, a thin layer of air could be entrapped in the solid/liquid interface. This air may hinder the diffusion of dissolved corrosive species (such as Cl⁻ ions in water) to the metallic substrate and, consequently, protect the metal from corrosion. However, in the dynamic water, the relative motion between the solid and the liquid would labilize the entrapped air and, consequently, decrease the corrosion resistance. In this work, to clarify the role of water flow velocity in such corrosion behavior, a superhydrophobic surface on aluminum substrates coded as Al–HCl–H₂O–BT–SA was prepared by sequential treatment with HCl, boiling water, bis-(γ-triethoxysilylpropyl)-tetrasulfide (KH-Si69, BT) and stearic acid (SA). The contrast samples coded as Al–HCl–BT–SA, Al–HCl–H₂O–SA, and Al–HCl–SA were also prepared similarly by omitting the treatment in boiling-water, the BT passivation, and the treatment in boiling-water/passivation by BT, respectively. These samples were then immersed into an aqueous solution of NaCl with different flow velocity (0, 0.5, 1.0, 1.5, and 2.0 m s⁻¹), and its dynamic corrosion behavior was investigated. The results showed that, as the flow velocity increased, the corrosion resistance of the Al–HCl–H₂O–BT–SA sample indeed deteriorated. However, compared with the contrast samples of Al–HCl–BT–SA, Al–HCl–H₂O–SA, and Al–HCl–SA, the deterioration in corrosion resistance for the Al–HCl–H₂O–BT–SA sample was much lower, implying that the dynamic corrosion resistance of the superhydrophobic surfaces was closely related with the micro-structures and the organic passivated layers. The present study therefore provided a fundamental understanding for the applications of superhydrophobic samples to prevent the corrosion, especially, for various vessels in dynamic water.

For superhydrophobic surfaces immersed in water, a thin layer of air could be entrapped in the solid/liquid interface.

Catalytic impact of alloyed Al on the corrosion behavior of Co50Ni23Ga26Al1.0 magnetic shape memory alloy and catalysis applications for efficient electrochemical H2 generation

The electrochemical and corrosion behaviour of Co₅₀Ni₂₃Ga_27−xAl_x (x = 0 and 1.0 wt%) magnetic shape memory alloys (MSMAs) was studied in 0.5 M NaCl solutions using various electrochemical techniques.

Performances of an Al–0.15 Bi–0.15 Pb–0.035 Ga alloy as an anode for Al–air batteries in neutral and alkaline electrolytes

Aluminum is a very good candidate anode for metal–air batteries due to its negative electrode potential, high theoretical electrochemical equivalent value, abundant reserves and environmental friendliness.

Effect of Ag Addition on the Electrochemical Performance of Cu10Al in Artificial Saliva

In this work we proposed to evaluate the corrosion resistance of four different alloys by electrochemical techniques, a binary alloy Cu10Al, and three ternary alloys Cu10Al-xAg (x = 5, 10, and 15 wt.%) to be used like biomaterials in dental application. Biomaterials proposed were tested in artificial saliva at 37°C for 48 h. In addition, pure metals Cu, Al, Ag, and Ti as reference materials were evaluated. In general the short time tests indicated that the Ag addition increases the corrosion resistance and reduces the extent of localized attack of the binary alloy. Moreover, tests for 48 hours showed that the Ag addition increases the stability of the passive layer, thereby reducing the corrosion rate of the binary alloy. SEM analysis showed that Cu10Al alloy was preferably corroded by grain boundaries, and the Ag addition modified the form of attack of the binary alloy. Cu-rich phases reacted with SCN⁻ anions forming a film of CuSCN, and the Ag-rich phase is prone to react with SCN⁻ anions forming AgSCN. Thus, binary and ternary alloys are susceptible to tarnish in the presence of thiocyanate ions.

Enhanced electrochemical performance of Al–0.9Mg–1Zn–0.1Mn–0.05Bi–0.02In fabricated from commercially pure aluminum for use as the anode of alkaline batteries

The electrochemical performance of Al–0.9Mg–1Zn–0.1Mn–0.05Bi–0.02In (wt%) from commercially pure aluminum has been determined using open circuit potential–time measurement, galvanostatic discharge, potentiodynamic polarization and electrochemical impedance spectroscopy.

Performance of Al–1Mg–1Zn–0.1Bi–0.02In as anode for the Al–AgO battery

In this study, an Al–AgO battery based on Al and Al–1Mg–1Zn–0.1Bi–0.02In (wt%) was prepared and the battery performance was investigated by a constant current discharge test in 4 M NaOH and 7 M KOH solutions.

Effect of bromide ions on the corrosion behavior of hafnium in anhydrous ethanol

The electrochemical behaviors of hafnium (Hf) in Et₄NBr ethanol solutions were investigated using cyclic voltammetry, potentiodynamic polarization, chronoamperometry, impedance and SEM techniques.

Activation of aluminum as an effective reducing agent by pitting corrosion for wet-chemical synthesis

Metallic aluminum (Al) is of interest as a reducing agent because of its low standard reduction potential. However, its surface is invariably covered with a dense aluminum oxide film, which prevents its effective use as a reducing agent in wet-chemical synthesis. Pitting corrosion, known as an undesired reaction destroying Al and is enhanced by anions such as F⁻, Cl⁻, and Br⁻ in aqueous solutions, is applied here for the first time to activate Al as a reducing agent for wet-chemical synthesis of a diverse array of metals and alloys. Specifically, we demonstrate the synthesis of highly dispersed palladium nanoparticles on carbon black with stabilizers and the intermetallic Cu₂Sb/C, which are promising candidates, respectively, for fuel cell catalysts and lithium-ion battery anodes. Atomic hydrogen, an intermediate during the pitting corrosion of Al in protonic solvents (e.g., water and ethylene glycol), is validated as the actual reducing agent.

Uniform and Pitting Corrosion Processes of Al, Al-6061, Al-Zn and Al-Cu Alloys Exposed to SCN- Solutions and the Effect of Some Inorganic Anions

The effect of the alloying elements and some inorganic inhibitors (WO4 2-, MoO4 2-, SiO3 2- and CrO4 2- anions) on the uniform and pitting corrosion characteristics of Al-6061, Al-4.5% Cu, Al-7.5% Cu, Al-6% Zn and Al-12% Zn alloys were studied in 0.04M KSCN solution. Susceptibility of the tested alloys towards pitting corrosion was investigated using transient (potentiostatic and galvanostatic) measurements. An independent method of chemical analysis, namely ICP-AES (inductively coupled plasma atomic emission spectroscopy) was also used to study the effect of the alloying elements and the tested inorganic anions on the uniform corrosion of these materials. Results obtained were compared with pure Al. ICP measurements revealed that the alloyed Cu and alloyed Zn enhance uniform corrosion of the Al samples, while WO4 2-, MoO4 2-, SiO3 2- and CrO4 2- anions suppressed it. Transient measurements showed that nucleation of pit takes place after an incubation time (t i). The rate of pit initiation and growth (t i -1 ) increased with increase in SCN- concentration, applied anodic current, applied anodic potential and solution temperature. This rate of pit initiation and growth decreased in presence of inorganic inhibitors to an extent depending on the concentration and type of the introduced inhibitor. Alloyed Zn was found to accelerate pitting attack, while alloyed Cu suppressed it. Among the tested Al alloys, Al-6061 presented the highest resistance towards uniform and pitting corrosion processes. SiO3 2- and CrO4 2- were the most efficient anions in inhibiting uniform and pitting corrosion processes of Al in these solutions.