E. Almeida

Atmospheric corrosion of copper in Ibero-America

Abstract Within the framework of the American Map of Atmospheric Corrosiveness (MICAT) project, 4 years of field research on atmospheric corrosion carried out in 14 countries of Ibero-America, this paper reports atmospheric copper corrosion in 21 unpolluted rural atmospheres and 45 marine atmospheres covering a broad interval of climatic conditions. High temperatures and relative humidities seem to promote greater copper corrosion in rural atmospheres; attack rates are found in the range of 0.1 μm/y to 2 μm/y, and corrosion product layers, generally comprising only cuprite (Cu2O), are discontinuous and have open structures with patinas acquiring increasingly darker colors (from salmon pink to dull brown) with exposure time. From the results obtained at marine sites, a critical deposition rate threshold is inferred for atmospheric salinity (20 mgCl−/m2 per day), after which the atmospheric corrosion of this material is intensified.

Atmospheric corrosion of zinc. Part 2 : Marine atmospheres

Abstract This paper summarises the results obtained in the MICAT (Mapa Ibero-Americano de Corrosão Atmosférica (Latin American Map of Atmospheric Corrosion)) atmospheric corrosion project (an Iberoamerican project on atmospheric corrosion, involving 14 countries and 75 atmospheric test sites) for zinc specimens exposed in the Latin American region for 1–4 years at 23 pure marine and 19 mixed marine (i.e. SO2 polluted) sites. The atmospheres at these sites were characterised climatologically and in terms of their pollution levels so that their corrosivity could be expressed in accordance with ISO standards. Morphological and chemical characterisation of the zinc corrosion product layers (ZCPLs) was performed using scanning electron microscopy coupled with energy dispersive spectrometry (SEM–EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and soluble salt evaluation techniques. The results obtained show that the corrosion rate of zinc is a function of both the chloride pollution level and the time of wetness. Some synergetic effects of Cl- and SO2 were demonstrated, although some special types of behaviour were also observed.

The influence of the interfacial conditions on rust conversion by phosphoric acid

Abstract The results from an experimental study on rust conversion by phosphoric acid are presented. Steel surfaces were pre-rusted for variable periods in a natural atmosphere, subsequently brushed and pretreated with phosphoric acid solutions at different concentrations. It was found that the conversion of rust depends strongly on the time of exposure and on the acid concentration used in the pretreatment. Analysis of the surfaces with optical and scanning electron microscopy (SEM) equipped with EDS, X-ray diffraction (XRD), FTIR, Mossbauer spectroscopy and other methods were used in this work.

Atmospheric corrosion of zinc. Part 1 : Rural and urban atmospheres

Abstract This paper summarises the results obtianed in the MICAT (Mapa Ibero-Americano de Corrosão Atmosférica (Latin American Map of Atmospheric Corrosion)) atmospheric corrosion project (an Iberoamerican project on atmospheric corrosion, involving 14 countries and 75 atmospheric test sites) for zinc specimens exposed for 1–4 years in 21 rural and urban atmospheres of the Latin American region. During the study, all of these atmospheres were characterised according to international standards. Complementary morphological and chemical studies were carried out using scanning electron microscopy coupled with energy dispersive spectrometry (SEM–EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to correlate atmospheric characteristics and the properties of zinc corrosion product layers (ZCPLs). Soluble salts retained in these ZCPLs were also determined. The study has provided clear evidence about the wide range of zinc corrosion rates occurring in rural atmospheres and suggests an interpretation of this behaviour.

Use of electrochemical impedance spectroscopy for studying corrosion at overlapped joints

The potential of electrochemical impedance spectroscopy (EIS) as implemented with specially designed sensors for characterising the response to corrosion of overlapped metal joints is demonstrated. The EIS technique provides quantitative information on the effect of overlap in pre-painted metal sheets on the deterioration of the organic coating before any visual symptom becomes apparent. Examples of the estimation of the effects of underfilm contamination, nature of the substrate, and exposure conditions on the electrochemical parameters that govern corrosion in these situations (in relation to both the coating and the reactions that take place at the metal/coating interface) are provided.

Lap-joint corrosion of automotive coated materials in chloride media. Part 2 – Galvannealed steel

The main aim of this work is to study the lap-joint corrosion of present-day zinc-coated automotive painting substrates, namely electrogalvanized steel, galvanneal, and electrogalvanized/galvanneal assemblies. The first part of the work (E. Almeida, M. Morcillo, Surf. Coat. Technol., in press) was dedicated to specific aspects concerning electrogalvanized steel. In this second part, galvannealed steel is studied using special specimens with spot-welded lap-joints, before and after salt-spray exposure. The corrosion mechanisms proposed as a consequence of this study have been based on results obtained by visual observation, scanning electron microscopy (SEM) associated with X-ray energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Auger spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The experimental results obtained showed that the use of galvannealing did not alter the main mechanisms or chemical reactions involved in lap-joint corrosion already observed for electrogalvanized steel. However, in the case of galvanneal, the corrosion propagation step seems to be significantly moderate.

Atmospheric corrosion of mild steel. Part II – Marine atmospheres

This paper summarizes the results obtained in the MICAT project for mild steel specimens exposed for 1 to 4 years in 47 marine atmospheres in the Ibero-American region. All these atmospheres were characterized for climatology, pollution and corrosion rates according to ISO standards. Complementary morphological and chemical characterization of the steel corrosion product layers (SCPLs) formed in these atmospheres was carried out. The overall analysis of results contributes to understanding, in a systematic way, how atmospheric corrosivity categories can be correlated with corrosion mechanisms. Special aspects of the atmospheres, from pure to mixed marine, were considered. Atmospharische Korrosion von unlegiertem Stahl. Teil II – Meeres- und Kustenatmosphare Die Arbeit fasst die Ergebnisse zusammen, die in dem MICAT Projekt fur unlegierte Stahlproben, die 1 bis 4 Jahre in 47 Meeres- bzw. Kustenatmospharen in der Ibero-Amerikanischen Region ausgelagert waren, erhalten wurden. Alle diese Atmospharen wurden entsprechend den ISO Normen im Hinblick auf klimatische Verhaltnisse, Luftverunreinigung und Korrosionsgeschwindigkeiten charakterisiert. Zusatzlich erfolgte eine chemische und morphologische Charakterisierung der sich in diesen Atmospharen gebildeten Stahlkorrosionsproduktschichten. Die allgemeine Analyse der Ergebnisse tragt in einer systematischen Art und Weise zum Verstandnis bei, wie die atmospharischen Korrosionskategorien mit dem Korrosionsmechanismus korreliert werden konnen. Spezielle Aspekte der Atmospharen, von reinen zu gemischten Atmospharen, wurden berucksichtigt.

Atmospheric corrosion of mild steel. Part I – Rural and urban atmospheres

This paper summarizes the results obtained in the MICAT project for mild steel specimens exposed for 1 to 4 years in 22 rural and urban atmospheres in the Ibero-American region. Test site characterization and chemical and morphological determination of the steel corrosion product layers (SCPLs) contributed to understanding the corrosion phenomena involved. It was observed how some climatological factors could affect steel corrosion rates and SCPL properties. Although the studied atmospheres were classified into different ISO groups, steel corrosion rates did not differ significantly between them. The only common characteristic of these atmospheres was an increase in SCPLs protectiveness with exposure time. Atmospharische Korrosion von unlegiertem Stahl. Teil I – Land- und Stadtatmosphare Die Arbeit fasst die Ergebnisse zusammen, die in dem MICAT Projekt fur unlegierte Stahlproben, die 1 bis 4 Jahre in 22 landlichen und stadtischen Atmospharen in der Ibero-Amerikanischen Region ausgelagert waren, erhalten wurden. Die Charakterisierung der Versuchsstandorte und die chemische und morphologische Bestimmung der Stahlkorrosionsproduktschichten tragen zum Verstandnis der beteiligten Korrosionsphanomene bei. Es wurde beobachtet, wie einige klimatologische Faktoren die Korrosionsgeschwindigkeiten und die Eigenschaften der Korrosionsproduktschicht beeinflussen konnen. Obwohl die untersuchten Atmospharen in verschiedene ISO Gruppen klassifiziert waren, unterschieden sich die Stahlkorrosionsgeschwindigkeiten nicht nennenswert voneinander. Das einzige gemeinsame Merkmal dieser Atmospharen war eine Zunahme der Schutzeigenschaften der Korrosionsproduktschichten mit der Auslagerungszeit.

Lap-joint corrosion of automotive coated materials in chloride media. Part 1 — Electrogalvanized steel

Lap-joint corrosion has been studied by several authors. However, the mechanisms involved in this type of corrosion, in the specific case of new painting substrates for the automotive industry, are not at all clear. The main purpose of this work is to study lap-joint corrosion in modern automotive painting substrates, namely electrogalvanized steel, galvanneal and electrogalvanized/galvanneal assemblies. In this first part of the work, electrogalvanized steel is studied using special specimens with spot-welded lap-joints, before and after salt-spray exposure. Special lap-joint spacements and positions were involved. The corrosion mechanisms proposed were based on the results obtained by visual observations, scanning electron microscopy (SEM) associated with X-ray energy dispersive spectrometry (EDS), X-ray diffraction (XRD), Auger spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS).

Discrimination by EIS of degradation mechanisms in lap joints of coated metal sheet

The information derived from inspedance diagrams obtained by using electrochemical sensors specifically designed for lap joints testing of coated metallic sheets is analyzed. The electrochemical sensors were made by means of steel or zinc sheets, uncontaminated or contaminated with variable amounts of sodium chloride, and overcoated with organic coatings. Such sensors show the effect of the nature of the metallic substrate, the underfilm saline contamination, and the relative humidity of the environment outside the lap joint.The results show that the information obtained from electrochemical impedance spectroscopy (EIS) on the behavior within the lap joints can be assessed by the criteria traditionally used for plain painted metal surfaces.By modeling the data, it is possible to discriminate between effects due to the organic coating and to the corrosion reaction at the metal-coating interface.