Long-term atmospheric corrosion of mild steel

A great deal of information is available on the atmospheric corrosion of mild steel in the short, mid and even long term, but studies of the structure and morphology of corrosion layers are less abundant and generally deal with those formed in just a few years. The present study assesses the structure and morphology of corrosion product layers formed on mild steel after 13 years of exposure in five Spanish atmospheres of different types: rural, urban, industrial and marine (mild and severe). The corrosion layers have been characterised by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). Long-term corrosion is seen to be more severe in the industrial and marine atmospheres, and less so in the rural and urban atmospheres. In all cases the corrosion rate is seen to decrease with exposure time, stabilising after the first 4–6 years of exposure. The most relevant aspects to be noted are (a) the great compaction of the rust layers formed in the rural and urban atmospheres, (b) the formation of hematite and ferrihydrite phases (not commonly found) in the industrial and marine atmospheres, respectively and (c) identification of the typical morphological structures of lepidocrocite (sandy crystals and flowery plates), goethite (cotton balls structures) and akaganeite (cotton balls structures and cigar-shaped crystals).     

Outdoor atmospheric corrosion of copper in Saudi Arabia

Abstract

Copper specimens have been exposed to the action of marine, marine industrial, urban and rural atmospheres of Saudi Arabia. Environmental factors such as average temperature, average relative humidity and deposition rates of atmospheric pollutants (i.e. Cl^- and SO₂) was investigated. By applying the standard ISO 9223, the aggressiveness of the atmospheres corresponding to the different test stations has been determined. Calculations of corrosion rates were made via loss of weight after one, two and three years of exposure and characterisation of the corrosion products formed on samples have been analysed using X-ray diffraction. Three main sequences have been identified on outdoor copper, representing different reaction routes in chloride dominated environments. Many kinds of patina were found on copper specimens such as cuprite (Cu₂ O), atacamite (Cu₂ Cl(OH)₃), paratacamite (Cu₂ (OH)₃Cl), copper amine nitrite hydroxide, gerhardite, copper hydroxide nitrate and copper amine nitrate.     

Effect of unusually elevated SO2 atmospheric content on the corrosion of high power electrical conductors - Part 3. Pure copper

This research work belongs to a series of studies simultaneously performed with two previous publications in this journal as Part I. Al and 6201 Al alloy and Part 2. Pure copper. The aim of the project was to have a comparative picture of the joint effect of marine and industrial atmospheric pollutants on the corrosion resistance of wire metals employed for high power electric transmission. This one is also based on the pure Cu behaviour, but limited to six marine-industrial atmospheres with extremely high SO₂ contents. The interest in this study was triggered by unusual results considered appropriate to investigate. Weight loss after 4 and 11 months exposure was determined and morphology of the attack was analysed through SEM-ESEM-EDX. Polarisation of samples after exposure to all the test sites as compared to bare Cu clarified the effect of unusually high SO₂ pollutant contents in these atmospheres on the high protectiveness of the corrosion products formed.     

Long-term atmospheric corrosion of zinc

A great deal of information is available on the short- and mid-term atmospheric corrosion of zinc: corrosion rate data as a function of atmosphere type, corrosion mechanisms, effect of environmental variables, effect of surface orientation, damage functions, etc. However, very little information has been published on the atmospheric corrosion of zinc over long time periods (10-20 years), despite its great usefulness. On the other hand, many studies have analyzed the nature of corrosion products formed on zinc in a wide range of atmospheric environments, using different experimental techniques, but few have focused on the morphology of corrosion product layers. This paper reports the characteristics—mainly composition and morphology—of corrosion products formed on zinc panels after long-term exposure (13-16 years) in various types of atmospheres in Spain: rural, urban, industrial, mild marine and severe marine.     

Studies of long-term weathering of aluminium in the atmosphere

Much information is available on the short- and mid-term atmospheric corrosion of aluminium, in the form of corrosion data (mass loss and pit penetration) as a function of atmosphere type, corrosion mechanisms, environmental variables, surface orientation, etc. However, information on the atmospheric corrosion of aluminium over longer tune periods (10-20 years) is scarce, despite its great usefulness. Furthermore, few studies have focused on the morphology of corrosion product layers. This paper reports corrosion data and morphology of corrosion products formed on aluminium panels after long-term exposure (13-16 years) in various types of atmospheres in Spain: rural, urban, industrial and marine.     

Effect of atmospheric pollutants on the corrosion of high power electrical conductors - Part 2. Pure copper

The research work performed during this study was simultaneously followed with another one published in this journal as Part I. A1 and 6201 A1 alloy. Its aim was to reveal a comparative picture of the joint effect of marine and industrial atmospheric pollutants on the corrosion resistance of wire metals employed for electric transmission conductors. Weight loss after 4, 11, 16 and 24 months exposure was determined and morphology of the attack analysed through SEM-ESEM-EDX. Cu corrosion products showed higher protectiveness than those of Al in marine sites for the lowest [Cl⁻] and in marine-industrial atmospheres even for the highest SO₂ contents. Respect to marine sites where [Cl⁻] was higher than [SO₂] Cu was more susceptible than A1.     

Atmospheric corrosion of nickel in various outdoor environments

As part of a field exposure program in the north-west of France on atmospheric corrosion of metal and alloys, this study presents the results of the behaviour of nickel panels exposed in industrial, urban and rural atmospheres. Mass measurements were investigated during the exposure and adherent corrosion layers were followed by means of several methods of analysis: Fourier transform infrared reflection-absorption spectroscopy, X-ray diffraction and scanning electron microscopy with X-ray microanalysis. In order to determine all the chemical species formed in the corrosion layers, corrosion products released from the surface by rainfall were also studied by collecting the streaming water from the nickel surfaces. Anionic and cationic quantities in the streaming water were determined respectively with ionic chromatography and polarography. The nickel attack appears as a pitting corrosion process accompanied by the formation of soluble corrosion products in dry exposure periods, these being regularly dissolved by rainfall events. Pits are associated with the formation of nickel salts, mainly sulphates and chlorides with small amounts of nitrate, and surrounded by carbonate species. The corrosion rate increases from rural to industrial areas.     

Corrosion-induced copper runoff from naturally and pre-patinated copper in a marine environment

Corrosion-induced copper runoff has been monitored for copper sheet, naturally patinated copper and pre-patinated copper, with and without surface treatments, in a marine environment during one year. The study comprises solution measurements on total copper runoff rates, sulphates and chlorides released from the patina, and parallel surface analytical studies on patina formation, combined with electrochemical impedance measurements on changes in barrier properties during exposure. Bioassay tests and model predictions were applied to elucidate copper bioavailability at the immediate release situation. The runoff rate of copper was significantly lower compared to the corrosion rate throughout the exposure period. At comparable rain quantities, copper runoff rates were significantly lower at the marine site compared to similar data obtained in an urban environment. The bioavailable concentration of released copper was significantly lower compared to the total copper concentration.     

Evolution of patinas on copper exposed in a suburban area

Copper plates were exposed under sheltered outdoor conditions for up to one year, starting in September 2001 in Musashino City, Tokyo, a suburban area. Following various periods of exposure, the patinas on the plates were characterized to investigate their evolution by using X-ray fluorescence analysis, X-ray diffraction, field emission scanning electron microscopy, and glow discharge optical emission spectroscopy. The difference in the roles of sulfur and chlorine in the early stages of copper patination were identified by analyzing the depth profiles of these two elements. Sulfur was found on top of the patina as cupric sulfates such as posnjakite (Cu₄SO₄(OH)₆ · H₂O) or brochantite (Cu₄SO₄(OH)₆). Brochantite appeared only after 12 months of exposure. In contrast, chlorine was found on the surface after only one month of exposure. It gradually penetrated the patina as the exposure period lengthened, forming copper chloride complexes. Chloride ions accumulated at the patina/copper interface, forming nantokite (CuCl), which promoted corrosion.     

Corrosion of copper and silver plates by volcanic gases

Corrosion products that had been formed on copper and silver plates exposed in Miyake Island, where suffered a volcanic eruption in 2000, were analyzed by X-ray techniques to get better understanding of copper and silver corrosion in harsh environment. The exposure experiment was carried out from September 2004 to April 2005. Many kinds of patina were found on copper such as cuprite (Cu₂O), posnjakite (Cu₄SO₄(OH)₆ · H₂O), brochantite (Cu₄SO₄(OH)₆), antlerite (Cu₃SO₄(OH)₄), and geerite (Cu₈S₅). For silver, silver chloride (AgCl) and silver sulfide (Ag₂S) were formed. Although the volcanic activity had greatly subsided, the atmospheric corrosion of copper and silver plates exposed on Miyake Island was mainly affected by volcanic gases, wet-dry cycles in the environment, and sea-salt aerosols.     

A study of copper runoff in an urban atmosphere

Initiated by the concern in several countries regarding the release of copper from, e.g., roofs, facings and other outdoor constructions, the present study aims to compare runoff rates with corrosion rates during exposure of copper in an urban atmosphere. The copper runoff rate turns out to be relatively stable during the 2 year period studied, with an average rate per year of around 135 μg Cu cm⁻². This stable runoff rate is associated with the formation and dissolution properties of cuprite (Cu₂O), which is the dominating copper patina phase throughout the 2 year period. The copper corrosion rate, on the other hand, is highly time-dependent. It exhibits an initially high value and decreases with exposure time. As a consequence, the ratio between copper runoff and copper mass loss is very low in the beginning, around 7% after 1 month, and increases with time to reach around 22% after 2 years. With prolonged exposure this ratio eventually reaches 100%, corresponding to a copper patina thickness that does not change any further with time.     

Corrosion of copper in seawater and its aerosols in a tropical island

A complete characterization of copper corrosion behavior has been carried out under permanent immersion, water line, splash zone and at the atmosphere (near and far from the sea) at the tropical Cuban archipelago. No significant differences have been determined for corrosion of copper under complete immersion for test sites representative of Cuban archipelago. The maximum corrosion rate was observed on the line of water, related to the partial removing of the corrosion products layer due to water movement (waves) and a higher availability of oxygen. Patina composition was characterized using XRD, IR, EDS and SEM techniques. Paratacamite (Cu₂(OH)₃Cl) was the main component of the patina formed under complete immersion, on the line of water and in the splash zone. In poorly polluted atmospheric marine environments also atacamite (another structural modification of Cu₂(OH)₃Cl) was found. When environmental SO₂ reaches a competitive level with the chloride aerosol the patina formed is a complex mixture of basic cupric chlorides (paratacamite and atacamite) and basic cupric sulfates, antlerite (Cu₃(SO₄)(OH)₄) and brochantite (Cu₄(SO₄)(OH)₆). Brochantite and basic cupric chlorides are detected at inland rural sites. The patina morphology reveals details about the local environment in which it is formed and shed light on its more or less protective role for the metal. The relatively large corrosion rate under complete immersion and on the line of water is related to the formation of a patina with poor adherence to the metal surface and to a porous layer of cuprite formed by relatively large octahedral crystals.     

Changes in corrosion rates in atmospheres with changing corrosivity

Abstract

This paper presents a study on the atmospheric corrosion of carbon steels, zinc, copper and aluminium in the industrial atmosphere. Trends representative for Central Europe are evaluated on the results for the Czech test site Kopisty. The climatic data and levels of pollutants, namely SO₂, have been measured, collected and analysed over 25 years. The corrosion rate of structural metals is significantly affected by SO₂ and the metals quickly react to the decrease of SO₂. The corrosion of both newly exposed metals and surfaces formerly exposed to polluted environments slowed when SO₂ pollution in the atmosphere was reduced. The study does not reflect the effects in atmospheric corrosion systems with dominating chloride influences (marine and marine–industrial atmospheres). The chemical composition and morphology of the corrosion product layers of zinc, copper and aluminium are presented and compared. The comparison of the corrosion rates and corrosion product compositions of zinc after 1, 20 and 100 years of exposure is presented.     

Ex-situ and in-situ X-ray diffractions of corrosion products freshly formed on the surface of an iron-silicon alloy

Ex-situ X-ray diffraction measurements of a small amount of samples extracted from wet corrosion products freshly formed on a pure iron and iron-2 mass% silicon surfaces have been conducted using synchrotron radiation for clarifying the formation process of corrosion products. The results showed that γ-FeOOH was formed on the outer side of wet corrosion products formed on the surface of the pure iron by sodium chloride solution, while γ-FeOOH, α-FeOOH, Fe₃O₄, and green rusts were formed on the inner side. On the other hand, in comparison to the case of the pure iron, a significant formation of β-FeOOH was observed in the iron-silicon alloy. Influences of silicon alloying on corrosion products formed by aqueous solution containing sulfate ions were also observed. Furthermore, in-situ diffraction measurements by a conventional X-ray source were conducted for analyzing corrosion products formed on the pure iron and iron-silicon alloy surfaces by cyclic exposure to wet and dry atmospheres. The results obtained by the in-situ diffraction and ex-situ diffraction measurements on the corrosion products were consistent.     

Atmospheric corrosion of hot and cold rolled carbon steel under field exposure in Saudi Arabia

Carbon steel (hot and cold rolled) specimens have been exposed to the action of different atmospheres at 20 test sites distributed in Saudi Arabia and was investigated in terms of environmental factors such as average temperature, average relative humidity and deposition rates of atmospheric pollutants (Cl⁻ and SO₂). Applying the standard ISO 9223 norm aggressiveness of the atmospheres corresponding to 0the different test sites has been determined. Calculations of corrosion rates were made via loss of weight and characterization of the corrosion products formed on samples has been carried out by means of X-ray diffraction (XRD). The major constituent of the rust formed in marine and marine-industrial environment is goethite (α-FeOOH). These samples also show the presence of a large proportion of lepidocrocite (γ-FeOOH) and small amounts of ferrihydrite and maghemite (γ-Fe₂O₃). In the case of urban and rural samples goethite is the major constituent of corrosion layers. The rust formed under the urban environment also contains large amounts of ferrihydrite and in a lesser proportion, of goethite and maghemite.     

Copper patinas formed in the atmosphere—III. A semi-quantitative assessment of rates and constraints in the greater New York metropolitan area

Because of the ability of copper to interact with a variety of atmospheric species and to retain the signatures of those interactions in a stable patina layer, copper is a particularly appropriate material for a study of the rates of corrosion processes. The rate of formation of copper patinas in a specific geographical location is dependent upon the atmospheric concentrations of corrosive species, their degree of interaction with the copper surface, and the mechanisms and rates of the processes that govern interaction. A semi-quantitative model of patina growth is developed for samples exposed for up to several decades to the atmosphere in the greater New York City metropolitan area. In contrast to previous studies of patina chemistry, which have dealt with equilibrium conditions, the present work treats the problem from a kinetic standpoint. Under modern atmospheric circumstances, it is shown that neither the supply of atmospheric water, the supply of incorporated corrosive species from the atmosphere, nor the rate of oxidation chemistry are limiting factors in patina growth. Rather, the growth is controlled by the rate of cementation of patina components at early stages of the growth process and by the supply of diffusing copper ions at later stages. To assess patina formation on a historical basis, estimates are made of atmospheric and precipitation chemistry in the greater New York City metropolitan area over the past century. The rapid formation of modern patinas, compared with those formed a few decades ago, is shown to be a consequence of increased atmospheric levels of strong inorganic acids, particularly H₂SO₄, perhaps in combination with increased concentrations of atmospheric oxidizing species and organic compounds.     

Pitting of zinc: Observations on atmospheric corrosion in tropical countries

A five-nation study has investigated the mechanisms and rates of the atmospheric corrosion of zinc and steel in tropical regions in Australia, Thailand, Indonesia, Vietnam and The Philippines. For the study, 18 exposure sites encompassing severe marine, marine, severe industrial, industrial, marine/industrial, urban and highland environments were established across the countries. At each location, zinc and steel plates were exposed for periods of three months and one year, and measurements were taken of a wide range of surface-response and climatic parameters, including gaseous SO_x and NO_x, airborne salinity, relative humidity (RH) and temperature, rainwater composition, surface temperature and time of wetness (TOW). Exposed plates were used to determine mass loss, the nature of corrosion products (using FTIR and SEM-EDS) and the morphologies of corrosion layers (via SEM-EDS). Regression analysis indicated that the prime factors controlling zinc corrosion rate were climate (temperature and rainfall) and surface-response (TOW), and surprisingly not pollutant levels, despite significant variation in SO_x levels across the sites. SEM studies indicated the presence of pitting below the oxide layers on zinc, particularly those plates exposed at marine and other sites with relatively low SO_x levels. In contrast, no pitting was observed (or pits had very low aspect ratios) in the specimens exposed at sites with high SO_x levels. The possible processes leading to the observed damage patterns are discussed.     

Corrosion product formation during NaCl induced atmospheric corrosion of magnesium alloy AZ91D

Magnesium alloy AZ91D was exposed in humid air at 95% relative humidity (RH) with a deposition of 70 μg/cm⁻² NaCl. The corrosion products formed and the surface electrolyte were analysed after different exposure times using ex situ and in situ FTIR spectroscopy, X-ray diffraction and Ion Chromatography. The results show that magnesium carbonates are the main solid corrosion products formed under these conditions. The corrosion products identified were the magnesium carbonates hydromagnesite (Mg₅ (CO₃)₄ (OH)₂4H₂O) and nesquehonite (MgCO₃ 3H₂O). The corrosion attack starts with the formation of magnesite at locations with higher NaCl contents. At 95% RH, a sequence of reactions was observed with the initial formation of magnesite, which transformed into nesquehonite after 2-3 days. Long exposures result in the formation of pits containing brucite (Mg(OH₂)) covered with hydromagnesite crusts. The hydromagnesite crusts restrict the transport of CO₂ and O₂ to the magnesium surface and thereby favour the formation of brucite. Analysis of the surface electrolyte showed that the NaCl applied on the surface at the beginning was essentially preserved during the initial corrosion process. Since the applied salt was not bound in sparingly soluble corrosion products a layer of NaCl electrolyte was present on the surface during the whole exposure. Thus, Na⁺ and Cl⁻ ions can participate in the corrosion process during the whole time and the availability of these species will not restrict the atmospheric corrosion of AZ91D under these conditions. It is suggested that the corrosion behaviour of AZ91D is rather controlled by factors related to the microstructure of the alloy and formation of solid carbonate containing corrosion products blocking active corrosion sites on the surface.     

The atmospheric corrosion of copper at two sites in Portugal: a comparative study

This paper presents a comparative study on the atmospheric corrosion of copper, at two sites, in Portugal, with exposures started in two different seasons (summer and winter). Particular attention is devoted to the initial stages of the corrosion process.The levels of pollutants, namely of SO₂ and chlorides, in both atmospheres, have been measured, over the periods from August 1999 to July 2000 and from November 2000 until July 2001. Climatic data for both sites and both periods has been collected and analysed.Kinetics of the corrosion process (weight losses) have shown to be described by: Δm=kt^0.6 and Δm=kt^0.4, with k equal to 3.4 (g m⁻² month^−0.6) and 17 (g m⁻² month^−0.4), for the one year exposures, started in summer, at the urban and maritime atmospheres, respectively. Exposures started in winter, at the urban atmosphere, have lead to kinetics described by Δm=kt^0.7 with k=5.0 (g m⁻² month^−0.7).The chemical composition and the morphology of the copper patinas, corresponding to exposures of 2 and 12 months, at the two sites, are compared as well as the morphology of the corroded surfaces.     

Effect of atmospheric pollutants on the corrosion of high power electrical conductors: Part 1. Aluminium and AA6201 alloy

The aim of this study was to evaluate the joint effect of marine and industrial pollutants on the atmospheric corrosion of aluminium and its AA6201 alloy. Weight loss was determined after 4, 11, 16 and 24 months exposure being morphology and attack intensity analysed through SEM-EDX. Both materials showed the most intense attack for the highest SO₂ contents. Good correlation among weight loss, attack depth and tensile strength to rupture with time and with pollutant contents was determined for both materials in most sites. The cause for low aggressiveness of the heaviest Cl⁻ polluted atmosphere on aluminium was electrochemically demonstrated.