Ayssar Nahlé

The electrochemical etching of tungsten STM tips

The achievement of high resolution in scanning tunnelling microscopy (STM) relies on the use of sharp, high-aspect ratio tips which are usually produced from electrochemical etching of metals such as tungsten or platinum/platinum–iridium alloys under dc or ac conditions. A few general reviews on tip fabrication methods have appeared in the literature 1, 2, 3, 4 and 5, but many STM publications omit crucial details on the tip preparation method for their studies. Where they are reported, very little attention is given to optimizing the methods used to produce tips of high aspect ratio and small radii of curvature. Recently, much effort has focused on the use of two-step fabrication techniques; the first step to produce a fine point using electrochemical etching, followed by a second process, usually ion-milling, to obtain the sharp tip apex [6]. For many applications, including those where atomic resolution is not required, two-step fabrication methods are often unnecessary and electrochemical etching alone will produce sufficiently sharp tips. This short communication reports the findings of a systematic study to address the relative importance of various factors affecting one-step electrochemical etching of tungsten wire to produce sharp tips under steady-state dc conditions. The aim was to define conditions where the etching rate was high while achieving acceptably sharp tips.

Mass transport to reticulated vitreous carbon rotating cylinder electrodes

Mass transport to rotating cylinder electrodes (radius 0.5 cm and height 1.2 cm) fabricated from reticulated vitreous carbon (RVCRCE) was investigated using linear sweep voltammetry in a 0.5 m Na2SO4 + 1 mm CUSO4 electrolyte at pH 2. At a fixed cupric ion concentration the limiting current was found to be dependent upon velocity to the power 0.55 to 0.71 depending upon the porosity grade of the carbon foam. The product of mass transport coefficient and specific electrode area, km Ae, was found to be approximately 0.51 s−1 at 157 rad s−1 (corresponding to 1500 rpm) for the 100 ppi material. The experimental data are compared to the predicted performance of a hydrodynamically smooth rotating disc electrode (RDE) and rotating cylinder electrode (RCS).

UAE Neem Extract as a Corrosion Inhibitor for Carbon Steel in HCl Solution

The effect of aqueous extract of UAE Neem (Azadirachta Indica) on the corrosion inhibition of carbon steel in 1.0 M HCl solution was investigated electrochemically, and by weight-loss experiments at temperatures ranging from 303 to 343 K. The percentage inhibition increased with the increase of the concentration of the inhibitor. At a concentration of 2.0 g/L, the percentage inhibition reached about 87% at room temperature and 80% at 303 K. The percentage inhibition decreased with the increase of temperature. The thermodynamic parameters for the adsorption of this inhibitor on the metal surface were calculated using the Temkin adsorption isotherm. The aqueous Neem leaves extract was found to be an excellent potential corrosion inhibitor because of the high content of tannin content as well as the presence of a series of complex triterpene glycosides.

A Rapid Electrochemical Test for Porosity in Electroless Nickel Coatings on Carbon Steel Substrates

SummaryA rapid electrochemical test for the determination of porosity in electroless nickel coatings on carbon steel is described. The technique is based on the charge under the anodic peaks during the reverse cathodic scan of the cyclic voltammograms for various immersion times (ranging from 0 to 2 hours) of nickel-coated steel samples (0 to 24 μm thickness) in a solution consisting of 150 mL of 0.1 M H2SO4 and 10 mL of 0.1 M K4Fe(CN)6 at 298 K. It was found that approximately 44% of the steel area remained uncovered with nickel after 2 minutes deposition time (0.4 μn thick). This percentage of uncovered area with nickel decreased to approximately 3 % when the steel samples had been immersed for 14 minutes (2.8 μm thick); essentially complete coverage occurred after an immersion time greater than 30 minutes (6 μm thick).

Inhibition of carbon steel corrosion by 4‐vinylbenzyl triphenyl phosphonium chloride in HCl solution

Purpose – The purpose of this paper is to study electrochemically and by weight loss experiments the effect of 4‐vinylbenzyl triphenyl phosphonium chloride on the corrosion inhibition of mild steel in 1.0 M HCl solution, which will serve researchers in the field of corrosion.Design/methodology/approach – Electrochemical and weight loss measurements were carried out on carbon steel specimens in 1.0 M HCl and in 1.0 M HCl containing various concentrations (1.0 × 10−7 to 1.0 × 10−4 M) of the laboratory synthesized 4‐vinylbenzyl triphenyl phosphonium chloride at temperatures ranging from 303 to 343 K.Findings – 4‐vinylbenzyl triphenyl phosphonium chloride was found to be a highly efficient inhibitor for carbon steel in 1.0 M HCl solution, reaching about 99 per cent at the concentration of 1 × 10−4 M at room temperature and about 96 per cent at 303 K, a concentration and temperature considered to be very moderate. The percentage of inhibition in the presence of this inhibitor was decreased with temperature whi...

X-ray design constraints for in situ electrochemical cells: importance of window material, electrolyte and X-ray wavelength

The need to calculate X-ray absorption losses through window materials and electrolytes in electrochemical cells used for in situ X-ray studies is highlighted. Calculations of the loss of beam intensity through Mylar windows of various thicknesses and at different wavelengths are carried out. Other window materials, such as polyethylene, polyimide (Kapton), polymethylmethacrylate (Perspex), polycarbonate (Lexan) and polyamide (Kevlar), are considered. Linear absorption coefficients and loss of intensity through different thicknesses of these materials at the Cu Kα wavelength are considered. Calculations of loss of intensity for a typical experimental case involving a Mylar cell window and a 1.029 M H2SO4 electrolyte are presented.

Scanning probe microscopy studies of Ebonex(R) electrodes

The porosity of Ebonex® electrodes is known to have a marked affect on their electrochemical properties. Atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) have been used to investigate the topography of porous and fully-hardened (nonporous) Ebonex® at high resolution. AFM has also been used to study the early stages of copper electrodeposition on porous Ebonex® electrodes. Initial copper nucleation and growth were found to occur preferentially at surface pores.

Corrosion inhibition of mild steel by P,P′‐Bis (triphenylphosphonio) methyl benzophenone dibromide in HCl solution

Purpose – The purpose of this paper is to study electrochemically and by weight loss experiments the effect of P,P′‐Bis (triphenylphosphonio) methyl benzophenone dibromide (TPPMB) on the corrosion inhibition of mild steel in 1.0M HCl solution, which will serve researchers in the field of corrosion.Design/methodology/approach – Weight loss measurements were carried out on mild steel specimens in 1.0M HCl and in 1.0M HCl containing various concentrations (2×10−8M and 2×10−5M) of the laboratory synthesized TPPMB at temperatures ranging from 303 to 343 K.Findings – TPPMB was found to be a highly efficient inhibitor for mild steel in 1.0M HCl solution, reaching about 98% at the concentration of 2×10−5M at 303 K, a concentration and temperature considered to be very moderate. The percentage of inhibition in the presence of this inhibitor was decreased with temperature which indicates that physical adsorption was the predominant inhibition mechanism because the quantity of adsorbed inhibitor decreases with incre...

Essential oil of “Foeniculum vulgare”: antioxidant and corrosion inhibitor on mild steel immersed in hydrochloric medium

Purpose The inhibition effect of Foeniculum vulgare seeds’ (FVS) extract on the corrosion of mild steel in acidic medium was studied using weight loss, electrochemical impedance spectroscopy and Tafel polarization, as well as the surface morphology of the mild steel. Design/methodology/approach Weight loss measurements, potentiodynamic tests, electrochemical impedance spectroscopy studies and gas chromatography/mass spectrometry and scanning electron microscopy analysis of FVS extract were performed. Findings FVS extract acts as a good inhibitor for the corrosion of mild steel in 1.0 M HCl. The inhibition efficiency increases with the increase in inhibitor concentration but decreases with the increase of temperature. Practical implications FVS extract was observed to play an important role in the corrosion inhibition of mild steel in acidic solution. Originality/value This paper is intended to be added to the family of green inhibitors which are highly efficient inhibitors and can be used in the area of corrosion prevention and control.

Synchrotron X-Ray studies of potentiostatically formed phosphate layers on steel

The phosphating of steel in an aqueous zinc-phosphating bath has been studied. Phase formation was controlled poentiostatically and phase identification was performed by X-ray diffraction, using synchrotron radiation, which enabled the time development of phosphate coatings to be studied. Two phases are formed during the phosphating process: hopeite and phosphophyllite, the diffraction patterns of which resemble those obtained from mineral standards. At potentials more negative than 0.6 V vs SCE a pure hopeite phase is formed