Elsayed A. Ashour

Effect of sulfide ions on the corrosion behaviour of Al–brass and Cu10Ni alloys in salt water

The stress corrosion cracking (SCC) behavior of Al-brass and Cu10Ni alloys was investigated in 3.5% NaCl solution in absence and in presence of different concentrations of Na2S under open-circuit potentials using the constant slow strain rate technique. The results indicated that the Cu10Ni alloy is more susceptible to stress corrosion cracking than as-received Al-brass at strain rate of 3.5 × 10−6 s−1 in 3.5% NaCl in presence of high concentration of sulfide ions (1000 ppm). The sulfide ions (up to 500 ppm) has no effect on the stress corrosion cracking of the annealed Al-brass in 3.5% NaCl at two strain rates of 7.4 × 10−6 and 3.5 × 10−6 s−1. The results support film rupture for Al-brass and sulfide stress corrosion cracking assisted with pitting corrosion for Cu10Ni at slip steps as the operating mechanisms.

Electrochemical behaviour of a copper-aluminium alloy in concentrated alkaline solutions

The electrochemical behaviour of a low-aluminium copper alloy (Alfa aluminium-bronze) in concentrated (1–8 N) NaOH is characteristically passive over broad potential regions, exhibiting passive currents that increase with alkali concentration. This passive behaviour is attributed to a duplex film, with an inner compact part composed of Cu2O and Al2O3·xH2O and an outer porous part composed of Cu(OH)2 and Al2O3·xH2O. The film undergoes dissolution at the film-electrolyte interface while it is continuously forming at the alloy-film interface. The film thickness is shown to increase with potential such that the potential gradient in the film is constant. The alloy undergoes selective dissolution with the de-aluminification factor depending on the potential and alkali concentration. X-ray diffraction analysis of the polarized alloy surface revealed the presence of Cu(OH)2 and the selective dissolution of the grains oriented in the 111 direction with enrichment in the grains oriented in the 220 direction.

Corrosion of α‐Al Bronze in Saline Water

The corrosion behavior of {alpha}-Al-bronze (Cu-7% Al) was studied in 3.4% NaCl solution for extended periods of time using X-ray diffraction, X-ray photoelectron spectroscopy, optical and scanning electron microscopy, and electrochemical polarization measurements. Corrosive attack occurs very early leading to general corrosion and pit nucleation, coalescence, growth and eventual merging of neighboring pits together to give multiple trough-like cavities. The corrosion products which form under free corrosion conditions appear as a duplex film with an inner adherent layer of Al{sub 2}O{sub 3} and an outer layer of Cu{sub 2}O, Cu{sub 2}(OH){sub 3}Cl, and Cu(OH)Cl. The x-ray measurements revealed several significant findings: (1) the Cu(111) plane corrodes preferentially, (2) Cu{sub 2}O forms very early under open-circuit conditions and grows progressively with time. Conversely Cu(OH)Cl was detected microscopically on the corroded surface after 9 days and by X-ray diffraction after much longer times, (3) CuCl forms only at anodic potentials, considerably higher than the free corrosion potential. Indeed, it was not detected under free corrosion conditions, and (4) the composition of the corrosion products which were retained on the alloy surface is quite different from those which spalled off the corroding surface.

Effect of benzotriazole on the corrosion of alpha brass in sulfide polluted salt water

Benzotriazole (BTAH) is shown to decrease the extent of localized corrosion of alpha brass in salt water contaminated by sulfide ions. The results are interpreted in terms of competitive adsorption of BTAH and sulfide ions on the brass surface and in view of the catalytic effects of dissolved sulfide as well as sulfide scale on the rates of the partial reactions. As the concentration of BTAH increases, the degree of coverage of the surface with sulfide decreases and, hence, also the rates of the partial reactions and the overall corrosion reaction.

Recent advances in the use of metal oxide-based photocathodes for solar fuel production

Harvesting solar energy for the production of clean fuel by a photoelectrochemical system is a very attractive, yet a challenging task. This review focuses on the recent efforts done to tailor metal oxide-based photocathode materials for the solar-driven hydrogen production. The materials are classified into three categories: simple oxides, complex oxides, and photocathodes used in p-n self-biased heterojunction cells. Generally, three strategies have been recommended to tailor p-type metal oxide semiconductors to meet the requirements for efficient solar-driven water splitting, namely (1) coating the p-type metal oxide either with a protective layer or a dye, (2) using co-catalyst, and (3) merging the p-type material with an n-type photoanode with the proper optical and electrical properties. In the light of those strategies, the optical, structural, and photoelectrochemical characteristics of such assemblies are discussed.

Inhibitive effects of benzotriazole on the stress corrosion cracking of α-brass in nitrite solution

Abstract The addition of benzotriazole (BTA) to 0.1 M sodium nitrite solution produces an inhibitive effect on the stress corrosion cracking (SCC) of α-brass under applied anodic potential. The maximum stress and the time to failure increased with the BTA concentration. The mode of cracking changed from transgranular, in nitrite solution alone or in the presence of low concentrations of BTA, to ductile failure at higher concentrations of BTA. Some electrochemical measurements were obtained to complement the SCC measurements. The results are interpreted in the light of the inhibiting effects of BTA on dezincification, and hence the subsequent SCC of the brass.

Inhibiting effects of benzotriazole on the corrosion of α-Al-bronze in saline water

The inhibiting effect of benzotriazole (BTA) on the corrosion of α-Al-bronze (Cu-7% Al) in 3.4% NaCl was studied. BTA showed good inhibition effects from short up to extended periods of time (about six weeks). The morphologies of the alloy surface were monitored after various periods of corrosion in the absence and presence of BTA, using SEM. The corrosion products were identified by X-ray diffraction. Corrosive attack occurs very early in the absence of BTA, leading to general and pitting corrosion. BTA was found to have a stronger inhibiting effect on the anodic dissolution of copper than on the cathodic reduction of oxygen. The current-potential relation is divided into two regions: region I within which BTA has a strong effect on the charge transfer kinetics, and a limiting current region where BTA has no significant inhibiting effect. It is also shown that the interaction of BTA with a Cu20-covered alloy surface is faster than on reduced alloy surfaces, although the protection efficiency on the latter is slightly better than on the former.

Effects of Sulfide Ions on the Integrity of the Protective Film of Benzotriazole on Alpha Brass in Salt Water

The addition of sulfide ions to a solution of 0.58 M NaCl containing benzotriazole (BTAH) results in a decrease of the inhibiting efficiency of BTAH and a momentary increase of the dissolution rate of alpha brass at potentials above the corrosion potential. The effect depends on the sulfide ion concentration and the potential selected for the tests. The results are explained by decomposition of the protective Cu(I)BTA film, caused by the extraction of Cu(I) ions from the film and formation of Cu{sub 2}S: nS{sup 2{minus}} + 2[Cu(I)BTA]{sub n} {yields} nCu{sub 2}S + 2nBTA{sup {minus}}. The breakdown of the film allows metal dissolution from the bare surface and further promotes the effects of sulfide ions.

Adsorption–Desorption Kinetics of Benzotriazole on Cathodically Polarized Copper

We describe a facile and simple electrochemical method to study the durability and adsorption–desorption kinetics of benzotriazole BTAH on cathodically polarized copper. The adsorption and the protective film formation are time-dependent processes. In solutions containing a very low concentration of BTAH 10−4 M , the results suggested that protection is attributed to a reversible physisorption process. The rate and extent of adsorption increased as a function of BTAH concentration in the electrolyte. The adsorbed BTAH desorbed entirely from the copper surface upon the removal of BTAH from the electrolyte. However, at higher BTAH concentrations 10−3 M , the process involves the formation of a film that remained stable and acted as a protective substrate even after the removal of BTAH from the electrolyte, i.e., the irreversible process.

Electrochemical characterization and stress corrosion cracking behavior of α-brass in molybdate-containing electrolytes

One of the major challenges in material design is the achievement of reasonable operational efficiency through understanding the factors affecting the material’s performance particularly strength and service lifetime characteristics. In this work, the electrochemical behavior of 72Cu–28Zn α-brass alloy in Na2MoO4-containing electrolytes was investigated using potentiodynamic polarization and electrochemical frequency modulation techniques complemented with scanning electron microscopy. Also, stress corrosion cracking behavior of the alloy under both open-circuit potential and anodic applied potentials, using the slow strain rate technique, was evaluated. The results drawn from the different techniques are comparable.