M. Delucchi

Nickel-cobalt oxide-coated electrodes : influence of the preparation technique on oxygen evolution reaction (OER) in an alkaline solution

Abstract The oxygen evolution reaction (OER) was investigated at 60°C in 15 wt% NaOH solution on NiCo 2 O 4 electrodes. Nickel–cobalt oxides were obtained by different preparation techniques and they were applied to chemically pickled nickel plates. Fresh and artificially aged electrodes were subjected to electrochemical tests. The ageing was performed for 21 days. The correlation between the coating preparations and their electrochemical performances was investigated by analysis of the electrochemical data. The efficiency of the NiCo 2 O 4 electrodes changed significantly with the changing of the preparation method. Two Tafel slopes for the OER were observed in most cases. This behaviour was interpreted on the basis of a change in the valence state of the oxide. The kinetic parameters obtained on NiCo 2 O 4 electrodes were compared and discussed according to the preparation methods.

Electrochemical and corrosion behaviour of cold rolled AISI 301 in 1 M H2SO4

Abstract Stainless steels (SS) are widely used in several fields. In recent years, the good corrosion resistance as well as the remarkable mechanical properties of SS have made it an even more utilised material. Such extensive utilisation produces new concern about its ability to maintain good properties after many working processes. In this paper an AISI 301 SS with different degrees of cold deformation has been considered. The cold working of these materials produces some important changes in the microstructure (i.e. grain size, crystallographic texture) and involves phase transformations (γ→α′). Electrochemical measurements have been used to investigate the corrosion behaviour of the alloy in sulphuric acid in the presence of chlorides. In the anodic behaviour of the cold rolled with respect to the annealed SS, a moderate variation of the passivity region but a remarkable increase of the current density was observed. Morphological analyses have been performed to relate the electrochemical results to the alloy structure. The relationship between metallurgical properties and corrosion behaviour has been discussed.

Study of chromate-free pretreatments and primers for the protection of galvanised steel sheets

Environmental problems in the coil-coating industry have caused a trend towards non-polluting pretreatment/primer combinations. In this work some environmentally-friendly systems have been studied. Impedance spectroscopy on deformed (T-bent) and damaged samples has been used as a tool to obtain a selective evaluation of the best systems. Nitro-cobalt chemical conversion, with fluo-zirconate passivation coated by an epoxy-polyurethane primer having ionic exchange active pigments, gave the best solution for the systems studied.

Crack-bridging ability and liquid water permeability of protective coatings for concrete

A surface coating for concrete can be exposed to a wide range of environments, movements and stresses depending on which application the structure is used for. Therefore the coatings have different requirements to satisfactorily protect concrete constructions in different service environments. Water permeability is an important factor to be considered in evaluating the performance of a coating since water penetration generally leads to the degradation of the substrate (concrete) and/or to the electrochemical reaction of steel when it is present (reinforced concrete). The crack-bridging ability of coatings is another important characteristic that has to be evaluated to assess if a coating can protect a concrete structure which surely will crack. This study investigates the relative importance of the parameters water permeability rate and viscoelasticity of coatings for different applications.

Electrochemical and physico-chemical characterization of fluorinated organic coatings for steel and concrete protection: influence of the pigment volume concentration

In this paper the electrochemical and physico-chemical characterization of fluorinated coatings was carried out. Their water permeability and its dependence on the pigment volume concentration (PVC) was quantitatively investigated through electrochemical impedance measurements and a linear relationship between the maximum amount of permeated water and the PVC was found. The impedance data analysis, performed through equivalent circuit modelling, on results obtained on undamaged and artificially damaged coatings was used to evaluate the protective performance and the retention of the coating adhesion once exposed to aggressive environments. It demonstrated that these properties are not remarkably affected by the PVC variation, even if the lower the PVC, the higher the performance of the coatings. The influence of the pigment concentration on some physico-chemical properties (water vapour diffusion coefficient, tensile strength, tensile strain and gloss) was also evaluated for the optimization of the coating formulation.

Investigation on physico-chemical and electrochemical properties of fluoropolyether coatings

A series of model coatings made of perfluoropolyether (PFPE) and different isocyanurate blocks were prepared and investigated through differential scanning calorimetry (DSC), dynamic-mechanical analysis (DMA) and electrochemical impedance spectroscopy (EIS) measurements. Phase transitions, dielectric constants and water permeability were also evaluated. The result was that the molecular weight of PFPE segment as well as the chemical nature of isocyanurate block influence the properties of the final urethane coatings. In general, polyphasic polyurethane networks are formed, but in some cases more homogeneous structures are promoted by the use of low molecular weight PFPE segments. Lower water permeabilities are obtained by the higher Tg and harder IPDI containing coatings. Very efficient barrier behaviour even at long exposure are shown by coatings made with lower molecular weight PFPE macromers.

Study of the crack-bridging ability of organic coatings for concrete: analysis of the mechanical behaviour of unsupported and supported films

Abstract The interest in using organic coatings to protect concrete structures has increased rapidly in recent years. One of the main parameters requested of these films for protecting structures is that they maintain their integrity even if the underlying concrete cracks. In this paper, a technique to evaluate the crack-bridging ability (CBA) of the coatings is addressed. In addition, the CBA of different organic coatings is analysed on the basis of the mechanical behaviour of the unsupported films during stress–strain measurements. Experimental results suggest a power law relationship between CBA and the tensile strength of the coating.