Sayed S. Abd El-Rehim

Experimental and Theoretical Investigations of Adsorption andInhibitive Properties of Tween 80 on Corrosion of Aluminum Alloy(A5754) in Alkaline Media

Abstract The inhibition behavior of Polyoxyethylene (20) sorbitan monooleate (Tween 80) as a non-toxic corrosion inhibitor for aluminum alloy (A5754) was investigated in 0.5 M NaOH solution by means of polarization measurement and quantum chemistry method. A significant inhibition in the corrosion rate of A5754 in NaOH solution was observed in the presence of Tween 80. As a result of adsorption of the inhibitor on the metal surface, the inhibition of this compound increases with its concentration but decreases with temperature. Polarization curves showed that Tween 80 acted as mixed inhibitor. The adsorption of Tween 80 obeys the Langmuir adsorption isotherm. Comprehensive adsorption (physisorption and chemisorption) of the inhibitor molecules on the A5754 surface was suggested based on the thermodynamic adsorption parameters. Correlation between quantum chemical calculations and inhibition efficiency of the investigated compounds was discussed using DFT method.

Aluminum Titania Nanoparticle Composites as Nonprecious Catalysts for Efficient Electrochemical Generation of H2

In this paper, we demonstrated, for the first time, aluminum titania nanoparticle (Al-TiO2 NP) composites with variable amounts of TiO2 NPs as nonprecious active catalysts for the electrochemical generation of H2. These materials were synthesized by mixing desired amounts of hydrogen titanate nanotubes (TNTs), fabricated here by a cost-effective approach at moderate hydrothermal conditions, with aluminum powder (purity 99.7%; size 35 μm). The mixture was compacted under an applied uniaxial stress of 300 MPa followed by sintering at 500 °C for 1 h. After sintering had been completed, all TNTs were found to convert to TiO2 NPs (average particle size 15 nm). Finally, Al-xTiO2 NP nanocomposites (x = 1, 3, 5, and 10) were obtained and characterized by scanning electron microscopy/energy-dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscopy. The hydrogen evolution reaction (HER) activity of these materials was studied in 0.5 M H2SO4 at 298 K using polarization and impedance measurements. The nanocomposite of chemical composition Al-5% TiO2 NPs showed the best catalytic performance for the HER, with an onset potential (EHER), a Tafel slope (βc), and an exchange current density (j0) of -100 mV (RHE), 59.8 mV decade(-1), and 0.14 mA cm(-2), respectively. This HER activity is not far from that of the commercial platinum/carbon catalyst (EHER = 0.0 mV, βc = 31 mV dec(-1), and j0 = 0.78 mA cm(-2)). The best catalyst also exhibited good stability after 10000 repetitive cycles with negligible loss in current.

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 Co50Ni23Ga27−xAlx (x = 0 and 1.0 wt%) magnetic shape memory alloys (MSMAs) was studied in 0.5 M NaCl solutions using various electrochemical techniques. Results showed remarkable activation of the tested MSMA toward pitting corrosion upon alloying it with Al. XPS examination confirmed the activation influence of alloyed Al. It proved that the presence of Al in the alloys matrix weakens its passivity, as manifested by a lower amount of gallium oxides and Cl− adsorption in the aluminium containing MSMA sample. Alloyed Al also activated significantly the tested MSMA for the hydrogen evolution reaction (HER), as indicated by cathodic polarization, electrochemical impedance spectroscopy (EIS), and faradaic efficiency (FE) measurements. Such measurements were performed in 0.1 M KOH solutions and showed that the Co50Ni23Ga26Al1.0 alloy is much more active for the HER than Co, Ni, Co50Ni50, and Co50Ni23Ga27 electrodes. The catalytic impact of pitting corrosion, proved to be catalyzed by Al, on the HER activity of the CoNiGaAl alloy was also studied. The pitted Co50Ni23Ga26Al1.0 MSMA, the best catalyst here, exhibited high HER catalytic performance with an exchange current density (jo) of 0.2 mA cm−2 and FE 96%, and thus approached Pt/C (jo = 0.6 mA cm−2 and FE ∼ 100%). Our best catalyst also showed good stability and durability after 3000 cycles of cathodic polarization between the corrosion potential (Ecorr) and −1.0 V vs. RHE, and 24 h of electrolysis at a high cathodic current density of 100 mA cm−2. Microstructure changes made by Al, together with findings obtained from SEM/EDX mapping and XPS studies, were used to interpret its activation influence towards the HER.

Influence of Nonoxynol-9 on the Corrosion Inhibition of Carbon Steel in 1.0 M Hydrochloric Acid Solution

Abstract The inhibitory performance of nonoxynol-9 (N9) as a corrosion inhibitor for carbon steel was evaluated in 1.0 M HCl solution at different temperatures. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and quantum chemical calculation methods were used in this study. The results indicated that the corrosion rate decreased with increasing concentration of N9 up 150 ppm and decreased with the increase in temperature of the medium. The comparison between the results obtained by polarization and EIS methods showed a good agreement. The corrosion inhibition effect of N9 could be related to the adsorption of N9 molecules on the metal surface. Polarization curves indicated that N9 behaves as a mixed type inhibitor. EIS exhibited one capacitive loop which indicates that the corrosion reaction is controlled by charge transfer process. The inhibition mechanism of N9 involves physical interaction between the inhibitor and metal surface. The adsorption of N9 on carbon steel affords physisorption process and obeyed the Langmuir adsorption isotherm.

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

Abstract The effect of the alloying elements and some inorganic inhibitors (WO42-, MoO42-, SiO32- and CrO42- 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 WO42-, MoO42-, SiO32- and CrO42- anions suppressed it. Transient measurements showed that nucleation of pit takes place after an incubation time (ti). The rate of pit initiation and growth (ti-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. SiO32- and CrO42- were the most efficient anions in inhibiting uniform and pitting corrosion processes of Al in these solutions.