The study of aluminium corrosion in acidic solution with nontoxic inhibitors

The inhibitory activity of some substituted N-arylpyrroles on aluminium corrosion in hydrochloric acid was studied in relation to inhibitor concentration, using potentiodynamic and impedance spectroscopy techniques. All investigated compounds were found to act as cathodic-type inhibitors and inhibition was ascribed to the adsorption of inhibitor onto the electrode surface. The inhibiting efficiency of the additives depended on the inductive power of the groups attached to the benzene and/or pyrrole ring. The carbaldehyde group showed better inhibiting power due to additional condensation on the electrode surface. The impedance results analysed in terms of the polarization resistance showed that the EIS technique can be successfully applied in the determination of corrosion resistance in systems where the corrosion kinetics are not simple.     

Corrosion protection performance of novel hybrid polyaniline/sol–gel coatings on an aluminium 2024 alloy in neutral, alkaline and acidic solutions

In this study the corrosion performance of a novel coating, consisting of a combination of silica sol–gel and conductive polymer, in 3.5% NaCl at different pH levels is presented. Electrochemical Impedance Spectroscopy showed the impedance of the coating remained stable for up to 24 months in neutral 3.5% NaCl solution. No corrosion or delamination was observed after 500 h in salt spray tests and Scanning Vibrating Electrode Technique tests showed the coating exhibited a “self healing” property. The surface morphology was characterised by Scanning Electron Microscopy and the mechanical properties, notably adhesion, were studied using pull off and cross cut techniques.     

Corrosion and corrosion inhibition of alumina particulate/aluminium alloys metal matrix composites in neutral chloride solutions

A study of the corrosion behaviour and corrosion inhibition of AA 6061 and AA 2014 metal matrix composites (MMCs) reinforced with alumina particles, during exposures to 0.1m NaCl solution is reported. Many tungsten and molybdenum-containing inorganic salts were tested as corrosion inhibitors, but only ammonium tetrathiotungstate afforded good inhibiting properties, particularly towards the AA 2014-based MMC. The corrosion behaviour of the composites in uninhibited or inhibited solutions was compared by different techniques to that exhibited by the corresponding matrices. The techniques adopted included weight loss measurements, electron probe microanalysis (EPMA), scanning electron microscopy (SEM), linear polarization resistance measurements, polarization curve recordings and current noise analysis. The analysis of the current fluctuations showed that different patterns of the time records were obtained during pit initiation, stable pitting and general corrosion. The power spectrum density plots exhibited f– trends, with values around 20dBdecade–1 when corrosion was mainly localized in pits, while values tending to zero were measured when general corrosion became dominant.     

Growth of zinc dendrites in acidic zinc chloride solutions

The heights and widths of zinc dendrites were measured in pure zinc chloride solutions in the concentration and pH range prevailing in zinc-halogen load leveling batteries.At constant overpotential the height increases linearly with time, indicating a constant growth rate. The higher the concentration and the overpotential, the faster is the growth. The critical overpotential for initiation of dendrite growth is 14 mV independent on the concentration. The growth rate increases when the pH decreases. The influence of hydrogen gas evolved at low pH on the growth rate is discussed. Propagation rate is discussed in terms of an extended Barton-Bockris model. When the height of the dendrite is smaller than the diffusion layer thickness, mass transport to the tip is linear and the dendrite propagates in an exponential manner. When the height is larger than the diffusion layer, mass transport to the tip is spherical and the propagation is linear with time. At constant overpotential the widht is a linear function of the square root of the height, indicating that the dendrite has a shape which is preserved during the growth and the tip radius is maintained constant as predicted by the theory.     

Indole and 5-chloroindole as inhibitors of anodic dissolution and cathodic deposition of copper in acidic chloride solutions

The effect of indole, IN, and 5-chloroindole, Cl-IN, on the anodic dissolution of copper in acidic sodium chloride solutions was studied using voltammetry on a rotating disc electrode (RDE). Both compounds used at 10^–3 M concentration act as strong inhibitors on the copper dissolution, but indole exhibits better inhibiting properties. The inhibitory action substantially increases with decreasing solution pH. The influence of these organic additives on the electrodeposition of copper on platinum was also investigated using RDE and electrochemical quartz crystal microbalance (EQCM) techniques. The EQCM measurements show that a sparingly soluble layer of the inhibitor is responsible for the protective effects observed in chloride solutions.     

Electrochemical study of aluminium ion reduction in acidic AlCl3-n-butyl-pyridinium chloride melts

Electrochemical reduction of AlCl₃ dissolved in acidic AlCl₃-n-butyl-pyridinium chloride melt was studied by linear sweep voltammetry and chronopotentiometry at tungsten and platinum electrodes, in the Al₂Cl ₇ ^? concentration range 0.3 to 0.5 M between 30 and 60°C. Al₂Cl ₇ ^? bulk reduction was preceded by a nucleation (tungsten) or alloy formation phenomenon (platinum). The overall results agree rather well with the mechanism: $$\begin{gathered} 2AlCl_4^ - \rightleftarrows Al_2 Cl_7^ - + Cl^ - \hfill \\ 4Al_2 Cl_7^ - + 3e \rightleftarrows Al + 7AlCl_4^ - \hfill \\ \end{gathered} $$ The electrochemical reaction appeared quasi-reversible. Calculated values of the product of the transfer coefficient by the number of the electron exchanged in the rate determining step were in the range 0.45 to 0.7. Diffusion coefficients for Al₂Cl ₇ ^? were calculated.     

The application of electrochemical impedance techniques to aluminium corrosion in acidic chloride solution

Electrochemical impedance techniques are applied to the study of aluminium corrosion in hydrochloric acid solution in the passive region. Impedance spectra are obtained in stationary solution and in solution moving due to electrode rotation. The form of the spectra shows the importance of multistep dissolution, ionic migration through the oxide layer, relaxation effects and the influence of chloride ion.     

Electrochemical behaviour of aluminium in the presence of EDTA-containing chloride solutions

The electrochemical behaviour of pure aluminium in an EDTA-containing chloride solution was investigated using potentiodynamic and potentiostatic electrochemical techniques and electrochemical impedance spectroscopy. A pronounced EDTA-induced anodic dissolution was observed in alkaline solutions, but the presence of EDTA in solution had little activating effect on the passivation properties at pH values close to 4.0. This was attributed to the relative stability of the Al(EDTA)^– complex formed at the different pH values. This EDTA-induced activation had no deleterious effect on pitting attack, in fact, higher breakdown potentials were observed in the presence of EDTA. This was attributed to the buffering action of EDTA, which inhibited the attainment of a critical pit solution composition. But, in the presence of molybdate, EDTA had no observable effect on pitting attack. The impedance spectra recorded in the presence of EDTA showed evidence for the adsorption of EDTA species during the dissolution process, which in turn, form a large capacitive network, with capacitance values of the order of 3 mF cm^–2 in the low frequency region.     

Corrosion inhibition of aluminium in acid solutions by some imidazoline derivatives

2-Pentadecyl-1,3-imidazoline (PDI), 2-Undecyl-1,3-imidazoline (UDI), 2-Heptadecyl-1,3-imidazoline (HDI), 2-Nonyl-1,3-imidazoline (NI) were synthesized and characterized by FT-IR and NMR Studies. The corrosion inhibition properties of these compounds on aluminium in 1 M HCl and 0.5 M H₂SO₄ were investigated by weight loss, potentiodynamic polarization, electrochemical impedance and scanning electron microscopic techniques. The weight loss study showed that the inhibition efficiency increases with increase in the concentration of the inhibitor and was found to be inversely related to time and temperature while it shows no significant change with increase in acid concentration. The effectiveness of these inhibitors were in the order of UDI > NI > PDI > HDI .The values of activation energy, free energy of adsorption, heat of adsorption, enthalpy of activation and entropy of activation were also calculated to elaborate the mechanism of corrosion inhibition. The adsorption of these compounds on aluminium surface follows the Langmuir adsorption isotherm. The potentiodynamic polarization data show that the compounds studied are mixed type inhibitors. Electrochemical impedance was used to investigate the mechanism of corrosion inhibition. The surface characteristics of inhibited and uninhibited metal samples were investigated by scanning electron microscopy (SEM).     

Pit formation in relation to the etching of aluminium in chloride solutions

The pitting potential,E _p , has been determined by steady-state and linear potential sweep methods.E _p is is shown to be a logarithmic function of the chloride concentration; the form of the function yields information about the equilibria between electrode and electrolyte species atE _p . Values of the enthalpy of activation for the pitting process have been determined by measuring the rate of pit propagation at constant driving potential at a series of temperatures. An ‘ad hoc’ interpretation of the data has been avoided and an attempt made to present the results using a more theoretical approach.     

Pyridine and its derivatives as inhibitors of aluminium corrosion in chloride solution

Pyridine and its selected derivatives (symmetric collidine and 2,5-dibrompyridine) have been studied as corrosion inhibitors for high purity aluminium in a 2m NaCl solution at 25°C and 35°C using d.c. polarization techniques. The investigations were carried out with a wide range of concentrations of the compounds examined (from 0.5×10–5m to 1×10–3m). The results show that the derivatives are adsorbed on aluminium according to the Freundlich isotherm. The values of the standard free energy of adsorption suggest that the adsorptive properties of the compounds under consideration approach the physical type. The polarization curves show that the compounds act as cathodic-type inhibitors.     

Polyethylene glycol and polyvinyl alcohol as corrosion inhibitors for aluminium in acidic medium

The corrosion inhibition of aluminum in H₂SO₄ in the presence of polyethylene glycol (PEG) and polyvinyl alcohol (PVA) as inhibitors at 30–60 °C was studied using gravimetric, gasometric, and thermometric techniques. The inhibition efficiency (%I) increased with increase in concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PEG and PVA were found to obey Temkin adsorption isotherm at all concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. PEG was found to be a better inhibitor than PVA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Corrosion of zirconia ceramics in acidic solutions at high pressures and temperatures

Changes in microstructure and phase composition of ceria stabilized tetragonal zirconia polycrystals (Ce-TZP), magnesia and yttria partially stabilized zirconia [(Mg,Y)-PSZ] and magnesia partially stabilized zirconia (Mg-PSZ) were studied in diluted aqueous HCl, H₂SO₄ or H₃PO₄ solutions at a temperature of 390° C and a pressure of 27 MPa. Ce-TZP is corrosion resistant under these conditions in HCl, while Mg-PSZ is attacked severely and (Mg,Y)-PSZ undergoes a surface tetragonal to monoclinic phase transformation. All investigated zirconia ceramics suffer severe weight losses and transformation to the monoclinic phase on the surface in H₂SO₄. Only a small weight gain and a slight increase of m-phase on the surface of the ceramics is found in H₃PO₄.     

The reduction of ferric chloride by aluminium in aluminium chloride melts

The rate of reduction of FeCl₃ to FeCl₂ by metallic aluminium in AIcl₃ melts has been studied at 212, 227 and 242 °C. Within the range of conditions investigated, the rate of reduction was proportional to the ferric ion concentration in the melt and to the surface area of the aluminium. After an initial coverage of the aluminium by a protective film of iron the reduction proceeded effectively only to the ferrous state.     

铝及铝合金在硝酸溶液中的腐蚀及缓蚀剂

简要介绍了铝及铝合金在各种浓度的硝酸溶液中,在不同温度条件下的腐蚀特性及某些有机及无机缓蚀剂的缓蚀效率．     

Corrosion properties of electrodeposited cobalt in sulfate solutions containing chloride ions

The corrosion properties of electrodeposited pure cobalt were investigated in deaerated 0.5 M Na₂SO₄ solutions at pH 5, 7, 10 and 13 by using polarization techniques. The effect of chloride concentration (0.01 and 0.1 M NaCl) was also studied. The results showed that increasing pH shifted the anodic polarization curves to more negative potentials. At pH 5 and 7, cobalt exhibited active dissolution without any distinctive transition to passivation. However, at pH 10, the metal surface was partially passivated and anodic current increased sharply at approximately −0.2 V_SCE and the corroded surface revealed several well-defined pits. On the other hand, at pH 13, a clear passivation region was observed within the potential range of −0.5 to 0.6 V_SCE. With increasing chloride concentrations of 0, 0.01, and 0.1 M at pH 10, both the anodic current and the number of pits on the cobalt surface were gradually increased. X-ray photoelectron spectroscopic investigations showed that the cobalt surface was covered mostly with cobalt hydroxide after anodic polarization at pH 10 in 0.1 M NaCl.     

Tungstate induced corrosion of some aluminium alloys in acidic chloride solution — An approach for controlling it with morpholine

The corrosion behaviour of some aluminium alloys (1060, 1100 and 3003) in acidic chloride solution (pH=1) have been studied in the presence of various concentrations of tungstate ions. The alloy most vulnerable to the effects of tungstate ions is 1100 followed by 1060 and 3003 alloys. After six hours of immersion the alloys exhibit 6 to 8 times higher corrosion rates compared to that in the blank solution containing only chloride ions. The experiments suggest that the tungstate ion stimulates the corrosion of aluminium by acting as a cathodic depolarizer. Morpholine effectively arrests the dissolution of the alloys in the blank electrolyte as well as in the presence of tungstate ions. Morpholine polarizes local cathodic sites to act as an inhibitor. Tungstate ions are not adsorbed on the surface in the presence of morpholine and a synergistic effect is obtained at higher concentrations of morpholine. A Langmuir adsorption isotherm has been used to explain the data.     

Corrosion control of Cu-Ni alloys in neutral chloride solutions by amino acids

The corrosion inhibition of Cu-Ni alloys was investigated in aqueous chloride solutions using amino acids as environmentally safe materials. The corrosion rate was calculated in absence and presence of the corrosion inhibitor using polarization and impedance techniques. The inhibition efficiency of the different amino acids was also calculated.The experimental results have shown that a simple amino acid like glycine can be used as efficient corrosion inhibitor for the Cu-Ni alloys in neutral chloride solutions. An inhibition efficiency of about 85% could be achieved at very low concentrations of the amino acid (0.1 mM). For low Ni content alloy (Cu-5Ni), 2.0 mM cysteine shows a remarkable high (∼96%) corrosion inhibition efficiency. The experimental impedance data were fitted to theoretical data according to a proposed equivalent circuit model for the electrode/electrolyte interface, and the mechanism of the corrosion inhibition process was suggested. Different adsorption isotherms were tested and the corrosion inhibition process was found to depend on the adsorption of the amino acid molecules and/or the deposition of corrosion products on the alloy surface. The adsorption free energy of cysteine on Cu-5Ni (−37.81 kJ mol⁻¹) reveals a strong physical adsorption of the inhibitor on the alloy surface.