Effects of cathodic prevention on the chloride threshold for steel corrosion in concrete

This paper presents the results of long-term experimental tests aimed at studying the effects of cathodic prevention on the critical chloride threshold for the onset of pitting corrosion on steel bars in concrete. Cathodic prevention is applied when the structure is new and rebars are still passive being in contact with alkaline and chloride-free concrete. The results obtained showed that even very low values of current densities can increase the critical chloride threshold and, therefore, contribute to increase the service life of reinforced concrete structures in chloride-bearing environments.     

Alternating current anodizing of titanium in halogen acids combined with Anodic Spark Deposition: Morphological and structural variations

The identification of anodic processes able to generate high surface area TiO₂ layers is a key requirement, whenever applications focused on its photoactivity or the integration between titanium implants and human body are considered. To achieve this goal, this research proposes an innovative two-step anodizing procedure. The first step consists of supplying alternating current to titanium in halogen acid electrolyte which quickly modifies its morphology. HCl and HBr were found to roughen effectively the metal surface, thus increasing its surface area. The successive step, an Anodic Spark Deposition treatment, generates a thick, semicrystalline oxide, containing both anatase and rutile crystals.     

An investigation into the corrosion of Ag coins from the Greek colonies of Southern Italy. Part I: An in situ FT-IR and ERS investigation of the behaviour of Ag in contact with aqueous solutions containing 4-cyanopyridine

The electrochemical behaviour of polycrystalline Ag and Ag(1 1 1) electrodes in contact with neutral chloride and perchlorate solutions containing 4-cyanopyridine (4CP) was studied. The understanding of the interaction of organic adsorbates with precious metals and alloys in given environments can provide guidelines for the design of suitable corrosion inhibition systems meeting the peculiar requirements of archaeological standards. 4CP adsorbs onto Ag both in the presence and in the absence of chlorides and acts as a reversible film former, suitable for use with historical items. 4CP has been shown to alter markedly the anodic kinetics of Ag: active corrosion in chloride environment is changed to a pseudo-passivating behaviour and potential oscillations, typical for the formation of thick AgCl layers, are suppressed.In situ spectroelectrochemical FT-IR measurements were carried out using both p- and s-polarised radiation in order to clarify the potential-dependent behaviour of 4CP. FT-IR data were complemented by in situ electroreflectance experiments, which highlighted changes in the electronic structure of the Ag surface in the presence of 4CP. Cyclic voltammetry and differential capacitance measurements were employed to asses the electroactivity and adsorption ability of 4CP. The results obtained disclosed that 4CP is adsorbed intact in a neighbourhood of the corrosion potential in perchlorate and chloride solutions, it desorbs at high anodic potentials and it reacts cathodically.     

Contribution to the knowledge of the relationship between the electrochemical and corrosion behaviour and the structure of metallic materials subjected to cold plastic deformation

Within the framework of a systematic study of the effect of cold plastic deformation on the electrochemical behaviour (anodic and cathodic characteristics) and the corrosion behaviour (corrosion rates in the active region, evaluated by the method of Stem and Geary and by loss in weight) of metallic materials, the results relating to the case of austenitic stainless steels AISI 304, 304 L and 316, ARMCO iron and nickel deformed by tension and immersed in de-aerated sulphuric acid solution are presented and discussed with the aim of interpreting these aspects of their behaviour on the basis of the “structure” of the deformed materials.     

Anodic titanium oxide as immobilized photocatalyst in UV or visible light devices

Titanium anodizing can be a powerful technique to generate photoactive oxides, strongly adherent to the metallic substrate, and to modify their chemical composition by inducing doping effects. This work investigates the photocatalytic behavior of differently obtained anodic TiO(2) films under UV and visible light irradiation, so as to define the best treatment for wastewaters purifiers. Anodizing was performed in H(3)PO(4) and H(2)SO(4) mixtures or in fluoride containing electrolytes. Morphology, elemental composition and crystal structure of the anodic films were characterized by XDR, GDOES and SEM. When amorphous oxides were obtained, an annealing treatment was used to promote the formation of anatase crystals. Annealing was also performed in nitrogen atmosphere to induce nitrogen doping. The photocatalytic efficiency of anatase-enriched TiO(2) was investigated in rhodamine B photodegradation. Doping was induced not only by annealing but also directly by anodizing, and generated photoactivity in both the UV and Vis components of light.     

Interference colors of thin oxide layers on titanium

This work deals with the characterization of the color properties of different titanium oxide films, obtained by means of anodic oxidation. The color of these oxides varies with film thickness, since it is due to light interference phenomena taking place at the metal‐oxide‐air interfaces. Color measurements were carried out by using spectrophotometry techniques: the values obtained belong to the colorimetric space CIELAB, which is defined as standard colorimetric space. The results of these analyses were related to the oxide structure, analyzed with X‐ray diffraction techniques, which was determined to be either amorphous or semicrystalline. Also the oxide thickness was taken into account. This feature was derived both from ellipsometric data and from reflectance spectra: the two data are shown to be in good adherence. Both commercial purity titanium (grade 2 ASTM) and titanium alloy Ti‐6Al‐4V substrates were investigated. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 221–228, 2008     

Cathodic protection of new and old reinforced concrete structures

Current and potential distributions measured on concrete slabs and simulated by computer modelling are discussed in relation with the application of cathodic protection to new reinforced structures as a corrosion preventive method. The results show high penetration of cathodic protection over the depth of uncontaminated concrete, so that even a rebar relatively distant from the anode can be polarized, whereas the penetration is limited to the rebars near to the anode in chloride contaminated slabs with corroding rebars. The great throwing power and the wide range of protection potentials for uncorroding concrete structure enable safe application of the cathodic protection even to new prestressed structures.