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.     

Seasonal variations in corrosion rate and runoff rate of copper roofs in an urban and a rural atmospheric environment

This paper summarizes the results from an extensive field exposure program implemented to study possible seasonal dependencies of copper corrosion rates and runoff rates. Two-year exposures in one urban and one rural environment were performed at four different starting seasons. An extensive multi-analytical approach was undertaken of all exposed samples.Seasonal differences in corrosion product formation was observed during the first month of exposure and attributed mainly to differences in relative humidity conditions. Seasonal differences in corrosion rate at the rural site could be discerned throughout the whole two-year exposure, again, mainly attributed to differences in relative humidity. No seasonal effect could be observed at the urban site indicating that other parameters influenced the corrosion kinetics at this site. While corrosion rates exhibit a continuous decrease with exposure time, the yearly runoff rates are independent of time. Depending on starting months the yearly copper runoff rates ranged from 1.1 to 1.7 g m⁻² y⁻¹ for the urban site, and from 0.6 to 1.0 g m⁻² y⁻¹ for the rural site. These seasonal variations were primarily attributed to differences in precipitation quantity and environmental characteristics. Runoff rates are significantly lower than corrosion rates as long as the adhering copper patina is growing with exposure time.A full risk assessment requires not only information on the total amount of copper in the runoff, but also on its chemical speciation. Under present conditions, 70–90% of all copper in runoff water collected immediately after leaving the surface is present as the most bioavailable form, the hydrated cupric ion, Cu(H₂O)₆²⁺.     

The atmospheric corrosion of quaternary bronzes: The leaching action of acid rain

The effect of leaching rain on the corrosion behaviour of bronze UNSC83600 was investigated as to the influence of alloying elements (Cu, Sn, Zn, Pb) through dropping tests simulating a severe runoff condition with a solution reproducing natural acid rain. Corrosion was followed with time monitoring both samples and leaching solutions (up to 30 days) by SEM, EDS, Raman spectroscopy, XRD, AAS. The bronze patina behaves as a porous layer enriched in stable tin compounds allowing uniform dissolution of Cu, Zn and partly of Pb. Laboratory results are in good agreement with field studies of outdoor bronzes in unsheltered condition.     

A field study on the first flush effect of copper roof runoff

The runoff of four copper roof surfaces with different aspects were monitored in a field study in order to identify the existence of the first flush effect and to determine the influences. It was found that almost 40% of all sampled precipitation events exhibited a moderate first flush effect regarding the distribution of copper mass in the roof runoff. There was a significant impact of the roof aspect on the presence and on the magnitude of the first flush. No correlation was found between the first flush effect and weather parameters, such as rain height, rain intensity, and antecedent dry weather period.     

Effect of direct current electric field on atmospheric corrosion behavior of copper under thin electrolyte layer

A thin layer electrochemical cell was successfully developed to study the atmospheric corrosion behavior of copper film in printed circuit board (PCB-Cu) under thin electrolyte layer (TEL) and direct current electric field (DCEF) by electrochemical impedance and electrochemical noise analysis. The electrochemical measurements and SEM morphologies after corrosion test indicate that DCEF decreases the corrosion of PCB-Cu under TEL. The corrosion rate and probability of pitting corrosion of PCB-Cu under DCEF decrease due to the electric migration of aggressive Cl⁻ ion out of working electrode surface.     

Mechanistic studies of corrosion product flaking on copper and copper-based alloys in marine environments

The mechanism of corrosion product flaking on bare copper sheet and three copper-based alloys in chloride rich environments has been explored through field and laboratory exposures. The tendency for flaking is much more pronounced on Cu and Cu–4 wt%Sn than on Cu–15 wt%Zn and Cu–5 wt%Al–5 wt%Zn. This difference is explained by the initial formation of zinc and zinc–aluminum hydroxycarbonates on Cu15Zn and Cu5Al5Zn, which delays the formation of CuCl, a precursor of Cu₂(OH)₃Cl. As a result, the observed volume expansion during transformation of CuCl to Cu₂(OH)₃Cl, and concomitant corrosion product flaking, is less severe on Cu15Zn and Cu5Al5Zn than on Cu and Cu4Sn.     

The atmospheric corrosion of quaternary bronzes: The action of stagnant rain water

The corrosion behaviour of a quaternary bronze UNS C83600 exposed to stagnant acid rain was examined through wet-dry tests. During the tests, parallel monitoring was performed to determine the evolution of both the bronze surface and the weathering solution composition. The results show that the kinetics of bronze oxidation is governed by diffusion through a two-layer patina: an inner Sn-rich layer and an external Cu and Pb-rich layer. The corrosion rate of the alloy decreases with time, but the dissolution of individual metals (Cu, Zn and Pb) in the environment increases with different trends, showing progressive patina destabilisation.     

Multianalytical in-situ investigations of the early stages of corrosion of copper, zinc and binary copper/zinc alloys

A new experimental infrared reflection absorption spectroscopy (IRRAS) set-up for in-situ investigation of corrosion phenomena occurring in the metal–atmosphere interface was developed. It was applied in combination with in-situ tapping-mode atomic force microscopy (TM-AFM) and phase detection imaging (PDI) to study the early stages of corrosion of pure copper and pure zinc as well as to determine the influence of increasing zinc contents in brass. Additionally, ex-situ secondary ion mass spectrometry (SIMS) investigations were carried out on the samples after exposure.The investigations were accomplished in synthetic air with 80% relative humidity (RH) and synthetic air with 80% RH and 250 ppb SO₂. The experiments showed that an increase of the zinc content in the brass alloy yields to an increase of the dimension of the corrosion features formed on the metal surface during weathering. Large features on top of smaller features were observed with TM-AFM on the surfaces exposed to SO₂-containing humidified air, which could be identified by IRRAS as metal sulphur compounds. Furthermore, an increased amount of physisorbed water on the metal surfaces was determined with IRRAS in dependence of the increasing zinc content in the brass samples.     

Differences between corrosion products formed on copper exposed in Tokyo in summer and winter

We analyzed the copper corrosion products that formed during a month in summer and a month in winter at three sites in Tokyo using several analytical techniques. The X-ray diffraction patterns revealed that cuprite Cu₂O and posnjakite Cu₄SO₄(OH)₆·H₂O formed on copper exposed in summer. By contrast, only cuprite was found in winter exposed copper. The X-ray fluorescence results indicated that the amounts of sulfur and chlorine on the copper plates exposed in summer were much greater than those in winter. This could be explained by the change in particulate sulfate and sea salt concentrations. Depth profiling analysis by Auger electron spectroscopy revealed that the oxide layer formed in summer was thicker than that in winter. This difference in oxide layer thickness could have been due to the differences in temperature, relative humidity, and the amount of sulfur and chlorine on the copper plate.     

Atmospheric corrosion of field-exposed magnesium alloy AZ91D

The magnesium alloy AZ91D was exposed in three different types of atmospheric environment, viz. urban, rural and marine exposure sites. Corrosion rates, corrosion products formed, and the influence of the microstructure on the corrosion behaviour of the alloy were investigated. The corrosion rate of AZ91D exposed in the marine environment was 4.2 μm/year, and in the rural and urban environments 2.2 and 1.8 μm/year, respectively. The main corrosion product found was magnesium carbonate hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O), which was formed at all three exposure sites. The corrosion attack started in the -phase in larger grains at the boundary between the -phase and the eutectic -/β-phase. Microgalvanic elements were formed with the eutectic -/β-Mg phase as cathodic site and the -Mg grains as anodes. The Al–Mn particles played a minor roll in the initiation process, even though these particles are the most noble in the microstructure and thus the driving force for a corrosion attack around these particles could be expected to be high. A close resemblance was observed between the corrosion mechanisms operating under the field-exposure conditions described here and the mechanisms operating under the previously reported laboratory conditions.     

Organic films for protection of copper and bronze against acid rain corrosion

In this paper, the anticorrosive effects of surface films formed on copper and bronzes by different organic inhibitors (mainly benzotriazole derivatives) are evaluated. Several alloys, nominally similar in composition to ancient artistic bronzes, were studied in comparison with copper. The protective efficiency of the organic coatings was tested by electrochemical ac and dc measurements performed both in acid and neutral rain. The experimental data show that benzotriazole derivatives with a long aliphatic chain form thin and very protective films on copper. The presence of the alloying elements (e.g. Sn, Zn, Pb) and multiphasic structures decrease the organic film performances. Nevertheless, among the compounds used, the most efficient, 5-octyl-1,2,3-benzotriazole (C8), seems to be a promising coating in the bronze conservation field.     

Behaviour of copper during alkaline corrosion of Al–Cu alloys

Enrichment of copper beneath amorphous anodic films on relatively dilute, solid-solution Al–Cu alloys is necessary before copper can be oxidized and incorporated into the oxide layer. A similar enrichment arises during electropolishing, which also develops an amorphous oxide. In these cases, external polarization is applied, usually generating a relatively high oxidation rate. In contrast, enrichment behaviour at the corrosion potential has received less attention. The present study examines the corrosion of Al–Cu alloys, containing up to 6.7 at.% Cu, in 0.1 M sodium hydroxide solution at 293 K. Copper is again found to enrich in the alloy, similarly to behaviour with anodic polarization. However, following enrichment, discrete copper-rich particles appear to be generated in the corrosion product. These are suggested to be nanoparticles of copper, since the corrosion potentials of the alloys are low relative to that required for oxidation of copper. The corrosion rate increases with increase of both time and copper content of the alloy, probably associated with a greater cathodic activity due to an increasing number of nanoparticles. The corrosion proceeds with loss of aluminium species to the sodium hydroxide solution, but with retention of copper in the layer of hydrated alumina corrosion product.     

Application of automated electrical resistance sensors for measurement of corrosion rate of copper,bronze and iron in model indoor atmospheres containing short-chain volatile carboxylic acids

The corrosion rate of copper and bronze Cu-8 wt.%Sn increased rapidly when the concentration of formic or acetic acid in air reached about 300 ppb at 80% relative humidity (RH) and a temperature of 20 °C. It decreased slowly during the several days after pollutant removal due to the slow rate of pollutant desorption from the metal surfaces. Corrosion of these metals was barely affected by the acids at RH up to 60%. For iron, the critical concentration of formic acid in air which led to surface activation at 80% RH was between 1000 and 1590 ppb.     

Inhibition of copper corrosion by 1,2,3-benzotriazole: A review

Benzotriazole (BTAH) has been known for more than sixty years to be a very effective inhibitor of corrosion for copper and its alloys. In spite of numerous studies devoted to the investigation of BTAH action, the mechanism of its action is still not completely understood. The aim of this review is to summarize important work in the field of BTAH as a copper corrosion inhibitor, from the early discoveries to the present time. Special attention is given to the BTAH surface structure. The disagreement between findings and mechanisms is discussed.     

Application of GC-MS metabolic profiling to ‘blue-green water’ from microbial influenced corrosion in copper pipes

This paper presents a novel application of fluorescence spectroscopy and gas chromatography-mass spectrometry (GC-MS) to water samples exposed to copper piping which had undergone some degree of microbial influenced corrosion. Using 3D fluorescence spectroscopy we were able to observe the ‘protein-like’ fluorophore associated with presence of bacteria, and cross reference this with derivatized fatty acid metabolites determined via GC-MS analyses of the same sample. This methodology can be used as a simple screening tool to establish the presence or otherwise of microbial processes in waters, and correlation of specific metabolite profiles with different microbes will further enhance the utility of this tool.     

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.     

Aluminium electroplated from ionic liquids as protective coating against steel corrosion

The protective action of thin layers of aluminium electroplated on a carbon steel (UNI Fe360B) has been studied. The coatings were obtained via electroreduction, at room temperature, from an ionic liquid constituted by 1-butyl-3-methyl-imidazolium heptachloroaluminate. Coatings of different thickness, ranging from 10 to 40 μm, were obtained. Their morphology and chemical composition were investigated using SEM microscopy coupled with EDX microanalysis and X-ray diffraction. Electrochemical tests (potentiodynamic polarization curves, open-circuit potential and electrochemical impedance spectroscopy) were performed in order to characterise the corrosion resistance of the coating in 3.5% NaCl aqueous solution. Visual investigation of the samples during long term of exposition to neutral salt spray gave an evaluation of their free corrosion properties. It was found that the aluminium layers deposited from ionic liquids significantly protect the substrate from the general corrosion and this action increases with the coating thickness.     

On the corrosion resistance of porous electroplated zinc coatings in different corrosive media

The corrosion resistance of an electroplated (EP) Zn coating whose surface was chemically etched to produce surface defects (pores) is investigated in this work. Impedance and DC polarisation measurements were employed to study the behaviour of such coating in various corrosive media (NaCl, NaOH and rain water). Four different faradaic relaxation processes were clearly revealed in different NaCl concentrations (from 0.1 to 1 M). In the most concentrated solutions at least three relaxation processes at low frequencies (LF) appeared and were related to zinc deposition and dissolution. At lower concentrations and depending on the pH, only one process was observed. The charge transfer resistance (R_ct) and the corrosion current (I_corr) were practically stable in the pH range 5-10. In deaerated NaCl 0.1 M, the EIS diagrams showed two time constants at very close frequencies. From the EIS diagrams the porous nature of the coating was highlighted and showed that the dissolution mechanisms occurred at the base of the pores.     

Accelerated corrosion of MoO3-deposited copper

The accelerated oxidation kinetics of MoO₃-deposited copper were studied in the temperature range of 480–700 °C in air. The accelerated oxidation followed the parabolic-rate law, indicating that the process was diffusion-controlled. Oxygen diffusion along liquid channels in the oxide scale was inferred to be the rate-limiting step in the overall mechanism. The rate constant increased from 9.2 × 10⁻⁶ to 3.8 × 10⁻⁵ kg² m⁻⁴ s⁻¹ with increasing the deposit mass from 0.3 to 0.9 kg m⁻² at 700 °C.     

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.