Hamdy H. Hassan

Corrosion inhibition of aluminum by 1,1(lauryl amido)propyl ammonium chloride in HCl solution

Abstract The corrosion inhibition characteristics of 1,1(lauryl amido)propyl ammonium chloride, as a cationic surfactant (CS), on aluminum in HCl solution have been studied in the temperature range 10–60°C by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques. Results obtained show that the inhibition occurs through adsorption of the surfactant on the metal surface without modifying the mechanism of corrosion process. The surfactant acts predominately as anodic inhibitor. The inhibition efficiency increases with an increase in the surfactant concentration, but decreases with an increase in temperature. Maximum inhibition is observed around its critical micelle concentration (CMC). Frumkin isotherm fits well the experimental data. Thermodynamic functions for both dissolution and adsorption processes were determined. Results obtained from the three methods are in good agreement.

ELECTROPLATING OF ZINC-NICKEL BINARY ALLOYS FROM ACETATE BATHS

Zinc-nickel binary alloys have been successfully electrodeposited onto steel sheets from baths containing zinc acetate, nickel acetate and acetic acid (pH 4.4–4.6). The potentiodynamic cathodic polarization, cathodic current efficiency, morphology and composition of the deposits were determined for a variety of bath composition, temperature, current density and superimposed ac on dc. The baths are characterized by high cathodic current efficiency for co-deposition. The co-deposition shows an anomalous behaviour with zinc being the preferentially deposited metal. X-ray tests revealed the presence of a single γ-phase (rich-zinc alloys) with body centered cubic structure.

Anodic behaviour of tin in maleic acid solution and the effect of some inorganic inhibitors

The anodic behaviour of a tin electrode in maleic acid solutions was investigated by potentiodynamic and chronopotentiometric methods. Measurements were conducted under different experimental conditions. The results demonstrated that the polarization curves exhibit active/passive transition. In active regions, tin dissolves as Sn2+ which is subsequently oxidized to Sn4+ and the dissolution process is controlled partly by diffusion of the solution species. The passivity is due to the presence of thin film of SnO2 on the anode surface formed by dehydration of precipitated Sn(OH)4. The active dissolution of tin increases with increasing acid concentration, temperature and scan rate. The potential transients showed that the passivation time decreases with increasing applied current density. The effect of adding increasing concentrations of CrO42−, MoO42− and NO2− ions on the anodic behaviour of tin in maleic acid was studied. These ions inhibit the active dissolution of tin and promote the attainment of passivity. The extent of these changes depends upon the type and concentration of the inhibitor.

Electrochemical Behaviour of a Silver Electrode in NaOH Solutions

Summary. Studies of the electrochemistry of metals and alloys are very important fields of scientific and industrial work. The present investigation includes detailed studies on the corrosion and electrochemical behaviour of Ag in aqueous NaOH solutions under various conditions using cyclic voltammetry, chronoamperometry, and potentiostatic techniques. It was found that the anodic polarization curve of Ag in NaOH solutions is characterized by the occurrence of five anodic peaks (A1–A5). A1 is due to the electroformation of soluble [Ag(OH)2]− complex species, A2 to the electroformation of Ag2O, A3 to nucleation and three dimensional growth of the Ag2O layer, A4 to the formation of AgO, and A5 presumably to the formation of Ag2O3. X-ray diffraction patterns confirmed the existence of passive Ag2O and AgO layers on the electrode surface potentiodynamically polarized up to oxygen evolution.The cathodic part of the cyclic voltammograms is characterized by the occurrence of an activated anodic peak (A6) corresponding to the electrooxidation of Ag to Ag2O and three cathodic peaks (C1, C2, C2′) corresponding to the electroreduction of AgO to Ag2O and Ag2O to Ag, respectively.Zusammenfassung. Die Elektrochemie von Metallen und Legierungen stellt ein wichtiges Arbeitsgebiet in Forschung und Industrie dar. Die hier vorgestellte Untersuchung beinhaltet detaillierte Studien zur Korrosion und zum elektrochemischen Verhalten von Silber in wäßrigen Natriumhydroxidlösungen mittels cyclischer Voltammetrie, Chronoamperometrie und potentiostatischer Techniken. Die anodische Polarisationskurve von Ag in NaOH wird durch das Auftreten von fünf anodischen Peaks (A1–A5) charakterisiert. A1 resultiert aus der elektrochemischen Bildung von löslichen komplexen Species des Typs [Ag(OH)2]−, A2 aus jener von Ag2O, A3 geht auf Keimbildung und dreidimensionales Wachstum der Ag2O-Schicht zurück, A4 auf die Bildung von AgO, und A5 wird vermutlich durch die Bildung von Ag2O3 verursacht. Röntgendiffraktionsmuster bestätigen die Existenz passiver Ag2O- und AgO-Schichten an der Elektrodenoberfläche bei potentiodynamischer Polarisation bis zur Wasserstoffentwicklung.Der kathodische Teil der cyclischen Voltammogramme wird durch einen aktivierten anodischen Peak (A6, entsprechend der Elektrooxidation von Ag zu Ag2O) und drei kathodische Peaks (C1, C2, C2′, entsprechend der Elektroreduktion von AgO zu Ag2O und von Ag2O zu Ag) charakterisiert.

Corrosion behaviour of zinc in sodium perchlorate solutions

Abstract I investigate the corrosion behaviour of zinc in aerated neutral perchlorate solutions. Three different techniques, namely, potentiodynamic polarisation, potentiostatic current time transient, and electrochemical impedance spectroscopy (EIS), are used. The potentiodynamic anodic polarisation cyclic voltammetry curves exhibit an active/passive transition followed by pitting corrosion, confirmed by SEM, due to the diffusion-controlled formation of a ZnO film by the dissolution–precipitation mechanism. The cyclic voltammograms show an anodic peak AI and two cathodic peaks CI and CII. The peaks AI and CII are correlated to the formation and reduction of ZnO film, respectively, and CI is attributed to the reduction of the pitting corrosion products. The potentiostatic current time transients at different electrolyte concentrations and applied potentials involve three stages: the first involving ZnO layer growth, and the second and third involving pit nucleation and growth, respectively. The nucleation rate (ti−1) increases with increasing electrolyte concentration and anodic applied potential. EIS shows an increase in the charge transfer resistance with applied potential near the anodic peak AI as a result of passive film formation. At higher anodic potentials, the charge transfer resistance decreases as the applied potential approaches the breakdown potential Eb. A nearly ideal Warburg tail of a dihedral angle of 45° is obtained, suggesting that the corrosion of Zn in NaClO4 solution is controlled by diffusion in the passive range.

Role of ClO4− in breakdown of tin passivity in NaOH solutions

Abstract The anodic behaviour of a tin electrode in NaOH solutions containing different concentrations of NaClO4 was studied by employing potentiodynamic, potential transient under constant current density methods and complemented with scanning electron microscopy (SEM). In perchlorate-free NaOH solutions, the E/i response exhibits active/passive transition. The active region involves two anodic peaks corresponding to the formation of Sn(II) and Sn(IV) species respectively. The permanent passive layer is duplex and consists of SnO and SnO2. Additions of NaClO4 to the alkali solution, accelerates the active dissolution of tin and tends to breakdown the duplex passive layer at a certain breakdown potential. SEM examination confirms the occurrence of film breakdown. The breakdown potential decreases with an increase in ClO4− concentration, but increases with increasing both OH− concentration and scan rate. The potential–time transients display that the incubation time for pit initiation decreases with increasing both ClO4− concentration and anodic current density.

The influence of some sulphur-containing anions on the anodic behaviour of zinc in an alkaline medium

Abstract The anodic behaviour of Zn in 0.1 M NaOH containing various concentrations of Na2SO4, Na2SO3, Na2S, Na2S2O3 or NH4SCN was studied by means of the potentiodynamic technique, complemented by X-ray diffraction analysis and scanning electron microscopy. In the absence of sulphur-containing anions in solution, the cyclic voltammogram displays two anodic peaks in the forward scan prior to reaching the oxygen evolution potential. The first anodic peak A1 is related to the electroformation of Zn(OH)2, while the more positive peak A2 is assigned to the formation of ZnO2. The reverse scan exhibits a reactivated anodic peak A3 and one cathodic peak C1 prior to reaching the hydrogen evolution potential. The presence of either SO2−4 or SO2−3 stimulates the active dissolution of Zn while the presence of S2− (and/or SH−), S2O2−3 or SCN− inhibits it, presumably as a result of electroformation of sulphur-containing solid phases preceding the formation of Zn(OH)2. Also, the presence of one of the cited anions studied in the alkali solution produces pitting of Zn at a certain specific pitting potential. The existence of pitting is confirmed by scanning electron microscopy. The aggressiveness of the sulphur species decreases in the order SCN− > SO2−4 > SO2−3 > S2O2−3 > S2−. The pitting potential decreases with increasing concentration of the sulphur species.

Perchlorate Pitting Corrosion of a Passivated Silver Electrode

Summary. The passivation and pitting breakdown of a silver electrode in sodium hydroxide solutions containing sodium perchlorate was studied using potentiodynamic and potentiostatic techniques. In perchlorate-free alkali solution, the voltammogram exhibits three anodic peaks prior to oxygen evolution. The first two peaks correspond to the oxidation of Ag and formation of a passive film of Ag2O on the electrode surface, the third to the conversion of Ag2O to AgO. In the presence of ClO4−, the voltammogram depends considerably on perchlorate concentration. ClO4− increases the height of the three anodic peaks, and at potentials above a limiting value breakdown of the anodic passivity and initiation of pitting corrosion occurs. The pitting potential decreases linearly with ClO4− concentration but increases with scan rate. The potentiostatic current/time transients show that pitting corrosion can be described in terms of an instantaneous three dimensional growth under diffusion control.Zusammenfassung. Passivierung und Lochfraßkorrosion einer Silberelektrode in Natriumperchlorat enthaltenden Natriumhydroxidlösungen wurden mit potentiodynamischen und potentiostatischen Methoden untersucht. In perchloratfreier alkalischer Lösung zeigt das Voltammogramm vor Beginn der Sauerstoffentwicklung drei anodische Peaks. Die ersten beiden entsprechen der Oxidation von Ag und der Bildung einer passivierenden Ag2O-Schicht auf der Elektrodenoberfläche, der dritte einer Umwandlung von Ag2O in AgO. In Gegenwart von ClO4− wurde eine ausgeprägte Abhängigkeit der Voltammogramme von der Perchloratkonzentration festgestellt. Durch die Anwesenheit von ClO4− wird die Intensität der drei anodischen Peaks erhöht, und ab einem gewissen Potential bricht die Passivierung unter Eintreten von Lochfraßkorrosion zusammen. Das Lochfraßpotential nimmt linear mit der Konzentration von ClO4− ab und steigt mit der Scangeschwindigkeit. Die potentiostatischen Strom/Zeit-Diagramme zeigen, daß die Lochfraßkorrosion als diffusionskontrolliertes dreidimensionales Wachstum charakterisiert werden kann.

Surface functionality and electrochemical investigations of a graphitic electrode as a candidate for alkaline energy conversion and storage devices.

Graphite is a typical electrocatalyst support in alkaline energy conversion and storage devices such as fuel cells, supercapacitores and lithium ion batteries. The electrochemical behaviour of a graphite electrode in 0.5 M NaOH was studied to elucidate its surface structure/electrochemical activity relationship. Graphite voltammograms are characterized by an anodic shoulder AI and a cathodic peak CI in addition to the oxygen reduction reaction plateaus, PI and PII. AI and CI were attributed to oxidation and reduction of some graphite surface function groups, respectively. Rotating ring disk electrode (RRDE) study revealed two different oxygen types assigned as inner and outer oxygen. The inner oxygen was reduced via the more efficient 4-electron pathway. The outer oxygen reduction proceeded with a lower efficient 2-electron pathway. The calculated percentages of the 4-electron pathway were ranged from 70% to 90%. A full mechanism for the graphite surface function groups changes over the studied potential window was suggested through the combination between the voltammetric, FT-IR and Raman results.

Tailoring the Oxygen Reduction Activity of Hemoglobin through Immobilization within Microporous Organic Polymer–Graphene Composite

A facile one-pot, bottom-up approach to construct composite materials of graphene and a pyrimidine-based porous-organic polymer (PyPOP), as host for immobilizing human hemoglobin (Hb) biofunctional molecules, is reported. The graphene was selected because of its excellent electrical conductivity, while the PyPOP was utilized because of its pronounced permanent microporosity and chemical functionality. This approach enabled enclathration of the hemoglobin within the microporous composite through a ship-in-a-bottle process, where the composite of the PyPOP@G was constructed from its molecular precursors, under mild reaction conditions. The composite-enclathrated Fe-protoporphyrin-IX demonstrated electrocatalytic activity toward oxygen reduction, as a functional metallocomplex, yet with a distinct microenvironment provided by the globin protein. This approach delineates a pathway for platform microporous functional solids, where fine-tuning of functionality is facilitated by judicious choice of the active host molecules or complexes, targeting specific application.