Portugaliae
Electrochimica Acta

The electrochemical corrosion behaviour of an electrodeposited Ni–28wt.%Al composite coating was characterized after 24 h and 72 h immersion periods in 3.5% NaCl solution, using electrochemical and surface probe techniques. Open circuit potential (OCP) and potentiodynamic polarization revealed that the Al particles modify the electrochemical corrosion behaviour of the Ni coating by shifting its EOCP more negatively and increasing its anodic dissolution current density, after 24 h immersion in 3.5% NaCl solution. Compared with the Ni coating, the composite can exhibit well–reduced anodic current density and slightly increased cathodic current with immersion up to 72 h. XPS characterization showed that a high rate of water adsorption and rapid formation of a continuous Ni(OH)2 initially occurs on the composite surface which, however, readily thickens during prolonged immersion time and promotes the corrosion product enrichment with Al2O3. This greatly decreased the rate of corrosion and susceptibility to pitting for the Ni–28wt.%Al composite after 72 h immersion in 3.5% NaCl solution.

Five different water soluble terpolymers, namely polyvinyl alcohol-g-poly(acrylamide-vinylsulfonate), polyvinyl alcohol-g-poly(acrylic acid-vinylsulfonate), polyvinyl alcohol-g-poly(acrylamide-vinyl benzene sulfonate), polyvinyl alcohol-g-poly(acrylic acid-vinyl benzene sulfonate) and polyvinyl alcohol-g-poly(vinylsulfonate-vinyl benzene sulfonate), have been designed, developed and tested for their efficacy to control N-80 steel corrosion in 10 % HCl, 3.5 % NaCl and simulated well water. The terpolymer characterization was carried out by FTIR. The inhibitors were tested by potentiodynamic and impedance techniques. The inhibitors were also tested in static and dynamic conditions at 55±5 °C, for 6 hours immersion period by weight loss method. Acrylamide terpolymers rendered the best inhibition efficiency in all the studied systems. The results provided a preliminary validation of the inhibitor such that they can be optimised and used for corrosion in oil and gas industries.

Anodic limiting currents were measured in an unstirred divided cell at an inclined small scale anode using a large scale cathode with angles of inclination from vertical axis as 45, 60 and 75°. Anode heights (II) vary from 1 cm to 6 cm and phosphoric acid concentration from 6 to 10 moles. Limiting currents for electropolishing of copper were between 5 and 58 mA.cm-2 depending on the operating conditions. A general correlation of data of all inclinations was obtained using the equation: I = 28.57(Ɵ 0.520.C -0.89.H -0.91) (1) with an average deviation of ±4%.

Cobalt impregnated zeolite-modified electrode was prepared by mixing cobalt–zeolite (Co–Z) and graphite powder with different percentages. Using the cyclic voltammetric technique, the electrochemical oxidation of hydrogen peroxide at such electrodes was investigated. Experiments on zeolite show that it is not electrochemically active towards hydrogen peroxide oxidation in NaOH solution. The presence of cobalt ions in the zeolite matrix, by soaking the electrode in an aqueous Co(NO3)2 solution, markedly enhances the electrocatalytic activity which was found to depend on the cobalt content. On the other hand, the presence of zeolite and/or Co metals in the catalyst is essential; however, the electro-catalytic activity depends on different percentages of Co–Z. Under the selected conditions, the anodic peak current was linearly dependent on the concentration of the hydrogen peroxide in the range 0.03–9 and 0.006-0.1 mM with CV and amperometric methods, respectively. The detection limits (S/N=3) were also estimated to be 17 and 2.5 µM.

Electrochemical reduction of boron from boron containing fluoroborate species present in KCl (81.54 mol%)-KF (18.45 mol%)-NaBF4 (1.67x10-4 mol cm-4) melt on a platinum electrode was studied by cyclic voltammetry and chronoamperometry. These studies were carried out over the temperature range 1073 - 1123 K. Boron-containing electroactive species is shown to reduce quasi-reversibly at low scan rates (ν < 0.1 Vs-1) and irreversibly at higher scan rates (> 0.1 V s-1) through a single-step three-electron process (B(III) + 3e → B). The transfer and diffusion coefficients of the electroactive species was measured for sodium fluoroborate in KCl-KF melt over the temperature range 1073-1123 K.