Steel cathodic protection afforded by zinc, aluminium and zinc/aluminium alloy coatings in the atmosphere

Zinc has traditionally been the metallic material most widely used to protect steel against atmospheric corrosion due to its ability to afford cathodic protection to steel in all types of natural atmospheres. In recent decades, aluminium and zinc/aluminium alloy coatings have been used instead of zinc in certain atmospheric applications. Although these coatings present some advantages over zinc, they are not able to cathodically protect steel substrates in all types of natural atmospheres. The present paper assesses the cathodic protection afforded by Al (flame spraying), Al/13 Si (hot dipping), 55Al/Zn (hot dipping), Zn/15Al (flame spraying), Zn/5Al (hot dipping), Zn (hot dipping), Zn (discontinuous hot dipping) and Zn (electroplating). Aluminium and aluminium-rich alloy coatings (55%Al/Zn) provide cathodic protection to the steel substrate only in atmospheres that are highly contaminated with chloride ions (>100 mg Cl- m-2 day-1) where these coatings become active. © 2004 Elsevier B.V. All rights reserved.Peer Reviewe

Efecto de la humedad relativa y los contaminantes atmosféricos NO2 y/o SO2 en la corrosión del cobre

10 pages, 8 figures.[EN] A study has been made of the individual and combined roles of NO2 and SO2 atmospheric contaminants on corrosion and patina formation on copper in humid atmospheres. In most cases the combined effect of the two contaminants has been greater than the sum of their individual effects, although exception have been found with the mixture of800|ig/m^NO2 + 800 jig/m SOj- XPS analysis has revealed important composition changes in the outermost layer of films formed on copper, depending on the nature of the atmospheric contaminant and humidity level. The presence of sulphates and sulphites has been clearly observed in exposure to atmospheres contaminated with SO2 at 50, 70 and 90 % RH. Nitrates and nitrites have been detected in exposure to NO2 at 50 and 70 %RH, but not at 90 % RH. A hydrogenated nitrogen compound has been detected with the mixture of NO2 and SO2 at 90 % RH .In this atmosphere, a certain inhibiting effect has been seen.[ES] Se ha estudiado el papel de los contaminantes atmosféricos NO2 y SOj y de una mezcla de ambos, en la corrosión y formación de pátina sobre el cobre expuesto en atmósferas húmedas. Por lo general, el efecto combinado de los dos contaminantes es mayor que la suma de los efectos individuales, aunque se han encontrado excepciones con la mezcla de 800 |lg/m^ NO2 + 800 |lg/m SO2. El análisis por XPS ha revelado cambios importantes en la composición de las películas superficiales más externas formadas sobre el cobre, según la naturaleza del contaminante y nivel de humedad. En la exposición al SO2 se ha revelado la formación de sulfatos y sulfitos a todas las humedades ensayadas (50, 70 y 90 % HR). En la exposición al NO2 se han detectado nitratos y nitritos, pero sólo cuando la humedad atmosférica era del 50 y 70 % RH, y no al 90 % RH. Curiosamente, en la exposición a la mezcla de NO2 y SO2 al 90 % HR se ha detectado la presencia de un compuesto hidrogenado de nitrógeno. En esta atmósfera se ha observado un ligero efecto inhibidor.Peer reviewe

Effect of marine aerosol on atmospheric corrosion

Saline particles in marine atmospheres accelerate metallic corrosion processes. However, quantitative information about the effect of salinity on atmospheric corrosion is very scarce. The relationship between salinity and steel corrosion is discussed, along with the relationship between salinity/steel corrosion and distance from the coast. The study was based on data compiled from the literature referring to research carried out in different parts of the world during the last 40 years.Peer Reviewe

Salinity in marine atmospheric corrosion: Its dependence on the wind regime existing in the site

Salinity in marine atmospheres accelerates metallic corrosion and varies within very broad limits, ranging from extremely high values close to surf to low values near calm waters. The concentration of marine aerosol in the atmosphere depends upon several factors such as altitude, distance from the sea, land orography, land topography, direction and velocity of prevailing winds, etc. This paper has focused on the influence of winds on the salinity values recorded at a testing site located on the coast of Tarragona (Spain). The results obtained in this study suggest that there are certain marine wind directions (referred to here as 'saline winds') which especially contribute to the entrainment of marine aerosol from the sea towards the land. There seems to be a critical velocity (close to 3 m s-1) for saline winds, above which coastal atmospheric salinity notably increases.Peer Reviewe

X-ray photoelectron spectroscopy study of the effect of nitrogen dioxide and sulfur dioxide on the atmospheric corrosion of copper at low relative humidity values

A study has been made of the individual and combined roles of nitrogen dioxide (NO2) and sulfur dioxide (SO2) atmospheric pollutants on corrosion and patina formation on copper in atmospheres with comparatively low water contents (70% and 50% relative humidity [RH]) for exposure times of up to 28 days. X-ray photoelectron spectroscopy (XPS) analysis has revealed some important compositional changes in the outermost atomic layers of films formed on copper, depending on the nature of the atmospheric pollutant, the humidity level, and the exposure time. After 7 days of exposure to NO2, a significant nitrogen content is detected (mainly as nitrates). In contrast, in exposure to SO2, copper oxides are present on the patina surface even after 21 days of exposure. In exposures to the mixture of NO2 + SO2, a nitrate layer grows on a copper sulfate film. As with NO2 alone, the appearance of nitrates leads to an appreciable increase in mass gain values. © 2005, NACE International.Peer Reviewe

Interaction of copper and NO2: Effect of joint presence of SO2, relative humidity and temperature

This paper reports laboratory tests involving the dry deposition on copper surfaces of NO2, alone and in combination with SO2, at different concentrations (200 and 800 μg m-3), temperatures (15, 25 and 35 °C) and relative humidities (50%, 70% and 90%). Gravimetric results and characterisation of the corrosion products by optical microscopy, scanning electron microscopy (SEM/EDX), grazing incidence X-ray diffraction (GIXD) and X-ray photoelectron spectroscopy (XPS) show that the corrosive effect of NO2 acting alone depends greatly on the RH. At 90% RH copper behaves in the same way as in unpolluted atmospheres, while at lower RH localised attack is detected. Analysis reveals the presence of basic copper nitrate (gerhardtite, Cu2(OH)3NO3). However, in SO2-polluted atmospheres no differential behaviour with RH or temperature is observed. In these atmospheres copper corrosion is similar to that obtained in unpolluted or in NO2-polluted atmospheres at high RH, although GIXD detects basic copper sulphate (posnjakite, Cu4(OH)6SO4·2H2O). In the case of mixed atmospheres (SO2+NO2) a significant accelerating effect is observed when [NO2]>[SO2]. Otherwise an inhibitive effect is detected. At high RH in the presence of SO2, NO2 favours SO2 oxidation and finally sulphuric acid formation, which attacks the cuprite layer. S-containing compounds, especially basic copper sulphate, are easily detected by GIXD and XPS in the outermost corrosion product layer. However, at low RH, NO2 reacts preferentially with adsorbed water to produce nitrous and nitric acids that attack the cuprite layer. In this case, an outer corrosion product layer containing copper nitrite (soluble) and basic copper nitrate is formed over an intermediate layer that contains significant amounts of basic copper sulphate from the previous interaction of sulphuric acid and cuprite. © 2007 Elsevier Ltd. All rights reserved.Peer Reviewe

Marine atmospheric corrosion of reference metals in tropical climates of Latin-America

This article presents the results obtained at 16 tropical test sites participating in the >Ibero-American Map of Atmospheric Corrosiveness> (MICAT), a project on atmospheric corrosion carried out during the period 1988-1994 at some 70 test sites distributed across 12 countries of the Latin-American region, Spain and Portugal. The tropical climate and its different climatic variants are characterized by high average air temperatures, with considerable daily thermal fluctuations, high average relative humidity, and generally high precipitation volumes. The work is structured in three main blocks: apparently unpolluted atmospheres (i), and marine atmospheres, differentiating between pure marine atmospheres (ii) and those in which both chloride (Cl) and sulfur dioxide (SO2) pollutants coexist (iii). In each block an attempt was made to determine the role of the tropical climate in the magnitude of corrosion attack shown by four typical reference metals (mild steel, zinc, copper and aluminum) exposed for one-year periods in tropical atmospheric exposure conditions.Peer Reviewe

El siglo XIX: Bolivia y América latina

Este libro es resultado del Primer Encuentro Internacional de Historia sobre "El Siglo XIX en Bolivia y América Latina", organizado por la Coordinadora de Historia y el Instituto Francés de Estudios Andinos (IFEA) el año 1994 en la ciudad de Sucre en homenaje postumo a Gunnar Mendoza. Dedicado al siglo XIX, por ser un período poco abordado en general por la historiografía de los últimos años, tuvo el propósito de analizar, con mayor profundidad y rigor, tanto las continuidades coloniales como las rupturas que lo caracterizaron. En la medida en que participaron bolivianos y bolivianistas de Europa y Estados Unidos, así como investigadores latinoamericanos de Argentina, Perú, Chile, Ecuador y Colombia, esperamos que este volumen que hoy presentamos constituya un aporte y una referencia para el análisis de esta época fundacional de los estados-naciones de América Latina