Electrochemical behaviour of copper in neutral aerated chloride solution. I. Steady-state investigation

The electrochemical behaviour of a Cu rotating disc electrode in neutral aerated NaCl solution was investigated in the cathodic and anodic ranges and at the corrosion potential. In the cathodic range, where the reduction of oxygen takes place, reduction peaks allow the identification and quantitative evaluation of insoluble corrosion products (CuCl and Cu₂O). In the anodic range Cu is dissolved, most likely as CuCl ₂ ^– . A new mechanism for the anodic dissolution is proposed after comparing our data with previously published mechanisms. Corrosion currents were found to decrease with time and to be a function of the rotation rate of the electrode. Both the mixed kinetics of the anodic partial reaction and diffusion through a porous layer seem to be relevant in controllingl _corr.     

An electrochemical and Raman spectroscopic investigation of synergetic effects in the corrosion inhibition of copper

The synergetic inhibition of copper corrosion by benzotriazole (BTA) and benzylamine (BZA) in chloride and cyanide media is assessed by voltammetric and ac impedance measurements. BZA enhances the performance of the strong inhibitor BTA by accelerating the growth of a protective surface layer; used alone, BZA is ineffective as an inhibitor. The competitive adsorption of aggressive anions and inhibitors is studied by surface enhanced Raman scattering (SERS). The dramatic increase in corrosion caused by low concentrations of cyanide ions is shown to be due to the displacement of BTA from the copper electrode surface; comparisons are made with the behaviour of mercaptobenzoxazole (MBO).     

Electrochemical investigations on composite iron electrodes

In spite of the many studies performed since the beginning of the last century, the Fe electrode, used as negative of both Ni/Fe and Fe/Air batteries, still poses several problems. For instance, according to the current literature, the following points are still not clear: (i) whether and how the depth of discharge affects electrode performance; (ii) what pathway the discharge follows, generally assumed as it is to involve consecutive Fe → Fe^II and Fe^II → Fe^III oxidation; (iii) why, at room temperature, only a minor fraction of the large theoretical capacity can be exploited. The present paper shows that deep discharges do increase Fe electrode performance, since they induce a transitory inhibition of hydrogen evolution. Likewise, Fe/Metal oxide composite electrodes have shown that the formation of Fe^III in discharge can take place directly from Fe, when the discharging rate applied is no longer compatible with the increase in electrode resistance due to oxidation products. Fe/Intermetallic compound composite electrodes have been studied as possible routes for increasing the efficiency of Fe capacity: useful indications have been gained as regards the compatibility of Fe with an IMC for charge storage.     

Anodic synthesis of sulfur-bridged polyaniline coatings onto Fe sheets

Sulfur-bridged polyaniline coatings are obtained onto Fe anodes by electrolyzing a basic solution of one aniline and ammonium sulfide. Their sulfur content ranges from 7% to 17%, depending on the substituents on aniline. Variously substituted anilines may be polymerized in this way and coating pollution by azobenzene formed in a side reaction is almost completely avoided. Sulfur probably enters the polymer chains through a free radical mechanism. HS^? intermediates being formed by both homogeneous and anodic oxidation of HS^? anions. Coatings from N-allylaniline, being thermally curable, show satisfactory physical properties.     

Polymeric coatings on steel produced by the electroinitiated polymerization of acrylic monomers

The results of the electropolymerization in situ of certain acrylic and methacrylic esters to produce coherent, continuous coatings on steel sheet cathodes using tetra-n-butyl ammonium perchlorate as supporting electrolyte in either DMF or DMSO under galvanostatic conditions are described. The effect of monomer concentration, applied current and electrolysis time have been considered. It has been found that the coating formation is favoured when the solubility parameter of the growing polymer is sufficiently different to that of the media. Under these conditions insulating deposits form on the electrode, resulting in strong increases of the electric resistance of the system. The parallel increase of voltage recorded under galvanostatic conditions was used to explain the formation of the films in terms of ‘throwing power’ and coherence. The best coating results for adhesion and hardness were obtained by copolymerizing in situ suitable mixtures of methacrylonitrile and isobutyl methacrylate.     

The effect of triton on the electropolymerization of phenol; an investigation of the adhesion of coatings using surface enhanced Raman scattering (SERS)

The physical properties and adhesion of protective amine-modified polyoxyphenylene coatings, electroformed in situ onto metal substrates, have been found to be greatly improved by the addition of small quantities of the surfactant Triton to the electrolyte. The role of Triton is investigated using ir and Raman spectroscopic techniques. Triton is found to be present both at the metal substrate surface and dispersed throughout the polymer, becoming chemically bonded to the polymer after curing in air.     

The influence of amines on the anodic coupling of phenols to polyoxyphenylene films

The formation of protective polyoxyphenylene coatings onto Fe, Zn and Cu sheets by anodic oxidation of phenol/amine systems has been investigated. It was found that thick homogeneous coatings are obtained only when a suitable amine is present in the electrolysis solution. The amine not only stops the anodic formation of passivating metal oxides which inhibit polymer growth, but also enters into the structure of the coatings. The polymer chains obtained from phenols are, in fact, highly modified by amine molecules grafted onto the phenoxy units.In collaboration with Centro Ricerche FIAT Spa, 10043 Orbassano, Italy.     

Phenol electropolymerization: a straight route from monomers to polymer coatings

Recent results on phenol electropolymerization aimed at the simultaneous production and deposition of protective coatings are described. Discussion is especially focused on the electrochemical growth mechanism of the non-conducting polymer films (previously unpublished chronoamperometric and chronopotentiometric results are provided and compared with a simple model), incorporation of corrosion inhibitors, the selected inhibitor being 2-benzothiazolylthiosuccinic acid, coating of phosphated mild steel and phosphated galvanized steel via the cathodic deposition of minor Zn amounts in the phosphate layer pores and protective performance of the coated samples, studied by a.c. impedance. It is shown that significant advances have been achieved since 1987, when a comprehensive review was published, in both the fundamental understanding of the process and the protective capabilities of the coatings.     

Physical properties of 2-hydroxyethyl methacrylate-grafted silk fibers

This paper deals with the physical properties of silk fibers grafted with 2-hydroxyethyl methacrylate (HEMA). Both tensile strength and elongation measured in the dry and wet states gradually decreased with increasing weight gain. The initial modulus of the grafted silk fibers in the dry state sharply increased in the weight gain range of 0–16%, then decreased to a lower value than the reference untreated sample. The refractive indices parallel and perpendicular to the fiber axis decreased, though the former showed a steeper slope. Accordingly, birefringence and isotropic refractive index also decreased, suggesting a lower degree of crystallinity and molecular orientation of grafted silk fibers. DSC, TMA, and TGA curves of the HEMA-grafted silk fibers indicated an increased higher thermal stability of silk fibers due to the HEMA grafting. The dynamic mechanical measurements showed that the thermally induced molecular movement of both amorphous and crystalline domains of silk fibers was enhanced by HEMA grafting. X-ray diffraction curves, however, implied that the crystalline structure of the silk fibroin remained unchanged regardless of HEMA polymerization. The introduction of HEMA polymer in silk fibers was evidenced by the infrared spectra, exhibiting the absorption bands characteristic of either the grafted HEMA polymer and the fibroin molecules with ordered β structure. © 1993 John Wiley & Sons, Inc.     

Changes in the fine structure of silk fibroin fibers following gamma irradiation

The physicochemical changes of silk fibers irradiated with γ-rays was studied in relation to the amount of absorbed does in the range 0–21 Mrad. The yellowing index (b/L) suddenly increased at low dose for both raw and degummed silk fibers. An equilibrium value was attained from 10 Mrad upward. The tensile properties were significantly affected by exposure to γ-rays. Both strength and elongation at break decreased at almost the same rate and extent, attaining a final value that was one-half of the untreated control. The birefringence and isotropic refractive index of exposed silk fibers decreased, the effect being larger in the low dose range, suggesting a decrease of crystallinity and molecular orientation. X-ray diffraction curves, however, demonstrated that the crystalline structure remained unchanged even after exposure of the highest γ-ray dose. The thermal behavior evaluated by DSC and TMA measurements showed that the γ-irradiation induced a slight decrease of thermal stability in irradiated silk fibers, this effect being detectable only at 21 Mrad of the absorbed dose. The dynamic viscoelastic behavior suggested that the thermal movement of the fibroin molecules in the amorphous and crystalline regions increased with increasing absorbed dose, attributing to the physicochemical modifications induced by the ionizing radiations. © 1994 John Wiley & Sons, Inc.