C.M. Abreu

Electrochemical behaviour of zinc-rich epoxy paints in 3% NaCl solution

Electrochemical impedance spectroscopy (EIS) in the 100kHz–1mHz frequency range was employed as the main electrochemical technique to study the corrosion protection behaviour of a zinc-rich epoxy paint in 3% NaCl solution. The EIS results obtained at the open-circuit corrosion potential have been interpreted using a model involving the impedance of particle to particle contact to account for the increasing resistance between zinc particles with immersion period, in addition to the impedance due to the zinc surface oxide layer and the electrical resistivity of the binder. Galvanic current and dc potential measurements allowed us to conclude that the cathodic protection effect of the paint takes some time to be achieved. The loss of cathodic protection is due to a double effect: the decrease of the ZnFe area ratio due to Zn corrosion and the loss of electric contact between Zn to Zn particles. Even when the cathodic protection effect by Zn dust became weak, the substrate steel is still protected against corrosion due to the barrier nature of the ZRP film reinforced by Zn corrosion products.

Galvanic coupling between carbon steel and austenitic stainless steel in alkaline media

The galvanic currents between carbon steel and two types of stainless steels have been studied in solutions of pH close to that of concrete. The situations analysed were passivity and active corrosion induced by chlorides. In all cases the galvanic effects recorded were of minor importance indicating that no significant risk of galvanic corrosion exists when carbon steel and stainless steel are electrically coupled in reinforced concrete structures. Oxygen reduction current is lower for stainless steel than for passive carbon steel. The results have been interpreted by means of EIS in terms of the resistivity of the passive layer formed on steels.

A New Approach to the Determination of the Cathodic Protection Period in Zinc-Rich Paints

Abstract The present study examined the behavior of zinc-rich paints (ZRP) based on an epoxy binder in 3% sodium chloride (NaCl) solution. The study focused on the effect of some design parameters ...

Characterisation of the electrochemical behaviour of cerium implanted stainless steels

Passive layers formed on a Ce implanted stainless steel in alkaline media are studied to clarify its beneficial effect on stainless steel corrosion resistance. An important decrease in iron and chromium activity peaks is detected by electrochemical techniques. X-ray photoelectron spectroscopy (XPS) analysis shows passive film thickness decreasing together with changes in chemical composition. Cerium implantation modifies the conductivity properties of the passive film, as it is inferred from EIS measurements.

Modifications of the stainless steels passive film induced by cerium implantation

In this work X-ray photoelectron spectroscopy studies and cyclic voltammetry are combined to elucidate the effect of Ce implantation on the formation and evolution of passive layers generated on AISI 430 and AISI 304L steels in alkaline medium. The passive films develop in implanted steels result thinner and less defective than in unimplanted. This result is interpreted in terms of a cerium-induced inhibition of the passive film re-oxidation (formation of iron and chromium oxides). The main difference between the behaviour of the two types of steel (ferritic and austenitic) seems to be related to the enrichment in nickel promoted by cerium in the outermost layer of AISI 304L.

Microstructure of the Passive Layer Formed on Different Austenitic Stainless Steels Implanted with Molybdenum

Two austenitic stainless steels have been implanted at 150 keV with Mo at a fluence of 3.5x1015 ions/cm2. The effects of ion implantation in the chemical composition of the passive films was evaluated by x-ray photoelectron spectroscopy (XPS) and glancing angle x-ray diffraction (GAXRD) was used to determine the induced structural modifications. The results of the pitting corrosion studies carried out in neutral chloride medium as well as the morphology of the localized attack are discussed.

An Insight on the Influence of Ion Implantation on the Pitting Corrosion Resistance of AISI 430 Stainless Steel

Research on the effect of ion implantation on the corrosion behaviour of metals has been carried out for years, but some difficulties arise in the comparison of the obtained results due to variations in experimental conditions (alloys, surface preparation, doses, experimental techniques...). This work tries to overcome those differences, presenting the effect of several elements (Ce+, N+, Cr+ and Cr+ N+) implanted in similar conditions on the pitting corrosion resistance of AISI 430 stainless steel. Potentiodynamic measurements in 1M NaCl demonstrate the beneficial effect of all the implanted elements, showing that Ce+ is the less efficient ion, while Cr+ N+ co-implantation gives the best results in terms of localized attack resistance. Pitting morphology is explained in terms of the XPS and GIXRD data that allow chemical and structural characterization of the implanted layer. Those results help to enlighten the protection mechanisms involved in the considered implantations.

The effect of the Cerium ion implantation in the passive films properties of a duplex stainless steel

Abstract The effect of Ce+ implantation on the electrochemical behaviour of SAF 2205 DSS is studied in alkaline medium. XPS studies have detected the implanted cerium as Ce3+ throughout the oxide films. The peak current of the magnetite formation peak is directly related to the passive film thickness. Nevertheless, the Cr3+ oxidation process is not affected by cerium implantation, which suggests cerium incorporation in the iron spinel.

Analysis of the Passive Layer Developed on Two Stainless Steels Co-Implanted with Chromium and Nitrogen

Surface analysis techniques (XPS and grazing incidence X-ray diffraction GIXRD) and electrochemical techniques have been combined to elucidate the effect resulting from Cr+ and N+ co-implantation in the formation and evolution of passive layers generated on two different stainless steels (AISI 430 and AISI 304L) in alkaline medium. The results show that the nitrides formed on AISI 430, identified as (Cr,Fe)2N1-x, are less resistant to dissolution while the nitride phase formed in AISI 304L, NCr with nanocrystalline structure, allows the compact growth of the oxide film.

An insight on the role of Nickel in the passive films generated on different stainless steels

The conductivity of air-formed films on Fe-Cr-Ni alloys is studied in alkaline solution using Impedance Spectroscopy. Increasing Ni content in the alloy decreases conductivity and produces thinner films. Air-formed films are not homogeneous from the electrical point of view and two well differentiated conducting paths appear in parallel to dielectric islands.