Atmospheric corrosion of copper at Heron Island

Atmospheric corrosion tests have been conducted at Heron Island, Queensland, a low SO2 marine environment. The corrosion rates for copper followed the linear bi-logarithmic law. X-ray diffraction identified atacamite (basic copper chloride) and cuprite (cuprous oxide) as the predominant corrosion products. Biogenic and anthropogenic sources of pollution did not have a measurable influence.

Atmospheric corrosion of quaternary bronzes (Cu-Sn-Zn-Pb): laboratory tests (accelerated ageing in wet & dry conditions)and field studies (the Bottego monument in Parma, Italy).

The interactions between outdoor bronzes and the environment, which lead to bronze corrosion, require a better understanding in order to design effective conservation strategies in the Cultural Heritage field. In the present work, investigations on real patinas of the outdoor monument to Vittorio Bottego (Parma, Italy) and laboratory studies on accelerated corrosion testing of inhibited (by silane-based films, with and without ceria nanoparticles) and non-inhibited quaternary bronzes are reported and discussed. In particular, a wet&dry ageing method was used both for testing the efficiency of the inhibitor and for patinating bronze coupons before applying the inhibitor. A wide range of spectroscopic techniques has been used, for characterizing the core metal (SEM+EDS, XRF, AAS), the corroded surfaces (SEM+EDS, portable XRF, micro-Raman, ATR-IR, Py-GC-MS) and the ageing solutions (AAS). The main conclusions were: 1. The investigations on the Bottego monument confirmed the differentiation of the corrosion products as a function of the exposure geometry, already observed in previous works, further highlighting the need to take into account the different surface features when selecting conservation procedures such as the application of inhibitors (i.e. the relative Sn enrichment in unsheltered areas requires inhibitors which effectively interact not only with Cu but also with Sn). 2. The ageing (pre-patination) cycle on coupons was able to reproduce the relative Sn enrichment that actually happens in real patinated surfaces, making the bronze specimens representative of the real support for bronze inhibitors. 3. The non-toxic silane-based inhibitors display a good protective efficiency towards pre-patinated surfaces, differently from other widely used inhibitors such as benzotriazole (BTA) and its derivatives. 4. The 3-mercapto-propyl-trimethoxy-silane (PropS-SH) additivated with CeO2 nanoparticles generally offered a better corrosion protection than PropS-SH.

Comparative atmospheric corrosion of primary and cold rolled copper in Australia

Atmospheric corrosion tests, according to ASTM G50, have been carried out in Queensland, Australia, at three different sites representing three different environmental conditions. A range of materials including primary copper (electrosheet) and electrolytic tough pitch (traditional cold rolled) copper have been exposed. Data is available for five exposure periods over a three year time span. X-Ray Diffraction has been used to determine the composition of the corrosion products. Corrosion rates have been determined for each material at each of the exposure sites and are compared with corrosion rates obtained from other long term atmospheric corrosion test programs. Primary copper sheet (electrosheet) behaves like traditionally produced cold rolled copper (C11000) sheet but with an increased corrosion rate. This difference between the rolled copper samples and the primary copper samples is probably due to a combination of factors related to the difference in crystallographic texture of the underlying copper, the morphology and texture of the cuprite layer, the surface roughness of the sheets, and the differences in mass. These factors combine together to provide an increased oxidation rate and TOW for the electrosheet material and which is significantly higher at the more tropical sites. For a sulfate environment (Urban) the initial corrosion product is cuprite with posnjakite and brochantite also occurring at longer exposures. Posnjakite is either washed away or converted to brochantite during further exposure. The amount of brochantite increases with exposure time and forms the blue-green patina layer. For a chloride environment (Marine) the initial corrosion product is cuprite with atacamite also occurring at longer exposures.

Atmospheric corrosion of copper and the colour, structure and composition of natural patinas on copper

This paper describes the results of atmospheric corrosion testing and of an examination of patina samples from Brisbane, Denmark, Sweden, France, USA and Austria. The aim was threefold: (1) to determine the structure of natural patinas and to relate their structure to their appearance in service and to the atmospheric corrosion of copper; (2) to understand why a brown rust coloured layer forms on the surface of some copper patinas; (3) to understand why some patinas are still black in colour despite being of significant age. During the atmospheric corrosion of copper, a two-layer patina forms on the copper surface. Cuprite is the initial corrosion product and cuprite is always the patina layer in contact with the copper. The growth laws describing patina formation indicate that the decreasing corrosion rate with increasing exposure time is due to the protective nature of the cuprite layer. The green patinas were typically characterised by an outer layer of brochantite, which forms as individual crystals on the surface of the cuprite layer, probably by a precipitation reaction from an aqueous surface layer on the cuprite layer. Natural patinas come in a variety of colours. The colour is controlled by the amount of the patina and its chemical composition. Thin patinas containing predominantly cuprite were black. If the patina was sufficiently thick, and the [Fe]/[Cu] ratio was low, then the patina was green, whereas if the [Fe]/[Cu] ratio was approximately 10 at%, then the patina is rust brown in colour. The iron was in solid solution in the brochantite, which might be designated as a (copper/iron) hydroxysulphate. In the brown patinas examined, the iron was distributed predominately in the outermost part of the patina. (c) 2005 Elsevier Ltd. All rights reserved.

Historic and modern alloys: atmospheric corrosion and development of accelerated ageing methodologies

The atmospheric corrosion of modern and historic alloys used in cultural heritage has been investigated by applying specific accelerated ageing methods. Three main research lines were carried out, involving different materials. In the first part, the atmospheric corrosion of a modern Cu-3Si-1Mn bronze was investigated through accelerated ageing tests simulating outdoor runoff conditions. The corrosion processes were evaluated through different analyses, and the results obtained were compared to those of a traditional quaternary bronze. The second line was carried out to characterise historic aluminium alloys used in aeronautics to develop and apply innovative protection strategies for their conservation. Historic wrecks were identified and characterised through micro and macroscale observations. Moreover, accelerated ageing tests were performed on both historic and modern alloys to compare their behaviour and select the best modern substrate to be used for the development of effective coatings. The third research line aimed to develop accelerate sampling and ageing methods to investigate the role of particulate matter (PM) in the atmospheric corrosion of bronzes and metals in general. The first approach consisted in the fine-tuning of an efficient accelerated method for ambient PM sampling on bronze specimens followed by their accelerated ageing, in order to establish a correlation between the PM and the substrate’s corrosion. After the accelerated ageing of the specimens, the corrosion was evaluated by surface characterisation and correlated to the PM features. The second approach consisted in the development of a synthetic PM formulation and of an artificial deposition method, which was performed by spraying mixtures containing the main PM inorganic fractions on a G-85 bronze with an airbrush. The deposition efficiency was assessed, and the effect of synthetic PM on the bronze corrosion was evaluated. The results were compared to those obtained by ambient PM deposition.

Indoors lead corrosion: Reassessing the role of formaldehyde

The present work is focused on the role of formaldehyde in indoors Pb corrosion, that is still a controversial issue. Pb coupons were exposed to the atmosphere produced by formaldehyde aqueous solutions (1% and 4% in volume) and corrosion was followed by Raman Microscopy. The compounds formed in both experiments were the same, but were not in agreement with previously reported results in the literature, that identified plumbonacrite, hidrocerussite and Pb oxide. The experiments here reported have clearly shown that formates are produced on Pb surfaces exposed to formaldehyde and that oxidants, such as H(2)O(2), are not necessary. Formaldehyde oxidation also occurs with powdered PbO in a controlled environment. The Raman spectra of the Pb formates are much more complex than the Pb(HCO(2))(2) spectrum and change when exposed to room conditions, by a slow reaction with CO(2), forming Pb carbonates (hidrocerussite and plumbonacrite mostly) and Pb(HCO(2))(2). Such spectral change may be responsible for the differences in terms of chemical composition of the corrosion layer when the data here reported is compared with the literature. Other factors that must be considered are the storage conditions (particularly relative humidity and CO(2) concentration) and time; the effect of metal composition cannot be discarded as it is well known that the presence of other metals can change significantly the Pb resistance to oxidation. (C) 2010 Elsevier B.V. All rights reserved.

Chemical characterization and anticorrosion properties of corrosion products formed on pure copper in synthetic rainwater of Rio de Janeiro and Sao Paulo

This work aims to characterize corrosion products formed on copper samples exposed to synthetic rainwater of Rio Janeiro and Sao Paulo. XRD and XPS were employed to determine their composition, while electrochemical techniques were used to evaluate their protective properties. XRD and XPS indicated the thickening of the corrosion layer with time. Electrochemical results showed that the protectiveness of the corrosion layer depends on the solution composition. Based on our findings a corrosion mechanism for copper in simulated rainwater is proposed where the role of NH(4)(+) ions in the cuprite layer partial regeneration is taken into account. (C) 2009 Elsevier Ltd. All rights reserved.

Study of a 9th century silver earrings set from Mikulčice: corrosion, conservation and maintenance

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Conservação e Restauro

Corrosion of steel reinforced concrete in the tropical coastal atmosphere of Havana City, Cuba

The influence of chloride deposition rate on concrete using an atmospheric corrosion approach is rarely studied in the literature. Seven exposure sites were selected in Havana City, Cuba, for exposure of reinforced concrete samples. Two significantly different atmospheric corrosivity levels with respect to corrosion of steel reinforced concrete were observed after two years of exposure depending on atmospheric chloride deposition and w/c ratio of the concrete. Changes in corrosion current are related to changes in chloride penetration and chloride atmospheric deposition. The influence of sulphur compound deposition could also be a parameter to consider in atmospheric corrosion of steel reinforced concrete.

Electrochemical impedance spectroscopy investigation of the electrochemical behaviour of copper coated with artificial patina layers and submitted to wet and dry cycles

Due to rain events historical monuments exposed to the atmosphere are frequently submitted to wet and dry cycles. During drying periods wetness is maintained in some confined regions and the corrosion product layer, generally denominated patinas, builds up and gets thicker. The aim of this study is to use electrochemical impedance spectroscopy (EIS) to investigate the electrochemical behaviour of pure copper coated with two artificial patina layers and submitted either to continuous or to intermittent immersion tests, this latter aiming to simulate wet and dry cycles. The experiments were performed in 0.1 mol dm(-3) NaCl solution and in artificial rainwater containing the most significant pollutants of the city of Sao Paulo. The results of the continuous immersion tests in the NaCl solution have shown that the coated samples behave like a porous electrode with finite pore length. On the other hand, in the intermittent tests a porous electrode response with semi-infinite pore length can be developed. The results were interpreted based on the model of de Levie and a critical comparison with previous interpretations reported in the literature for similar systems is presented. (C) 2011 Elsevier Ltd. All rights reserved.

The chemistry of copper patination

The chemistry of copper patination was investigated by two series of experiments. The chemistry of an aqueous copper-sulphate solution was studied at concentrations and pH values near those predicted in an electrolyte on copper exposed to the atmosphere. The electrochemical reactions in an electrolyte in contact with cuprite were investigated in a reaction vessel which used cuprite powder in artificial rainwater to study the electrochemistry of the atmospheric corrosion and patination of copper. Typical sulphate concentrations in rainwater are sufficient to precipitate posnjakite (Cu4SO4(OH)(6)2H(2)O)), a possible precursor to brochantite, within an hour of wetting a cuprite surface. Brochantite (Cu4SO4(OH)(6)), the most commonly found copper salt in natural patinas is responsible for their green appearance. Precipitation of brochantite from the electrolyte resulted from an increase in pH due to the cathodic reduction of oxygen and an increase in cupric ion concentrations by cuprite oxidation. (C) 1998 Elsevier Science Ltd. All rights reserved.

Assessment of Weathering Steel Bridge Performance in Iowa and Development of Inspection and Maintenance Techniques, RB17-012, 2013

Weathering steel is commonly used as a cost-effective alternative for bridge superstructures, as the costs and environmental impacts associated with the maintenance/replacement of paint coatings are theoretically eliminated. The performance of weathering steel depends on the proper formation of a surface patina, which consists of a dense layer of corrosion product used to protect the steel from further atmospheric corrosion. The development of the weathering steel patina may be hindered by environmental factors such as humid environments, wetting/drying cycles, sheltering, exposure to de-icing chlorides, and design details that permit water to pond on steel surfaces. Weathering steel bridges constructed over or adjacent to other roadways could be subjected to sufficient salt spray that would impede the development of an adequate patina. Addressing areas of corrosion on a weathering steel bridge superstructure where a protective patina has not formed is often costly and negates the anticipated cost savings for this type of steel superstructure. Early detection of weathering steel corrosion is important to extending the service life of the bridge structure; however, written inspection procedures are not available for inspectors to evaluate the performance or quality of the patina. This project focused on the evaluation of weathering steel bridge structures, including possible methods to assess the quality of the weathering steel patina and to properly maintain the quality of the patina. The objectives of this project are summarized as follows:  Identify weathering steel bridge structures that would be most vulnerable to chloride contamination, based on location, exposure, environment, and other factors.  Identify locations on an individual weathering steel bridge structure that would be most susceptible to chloride contamination, such as below joints, splash/spray zones, and areas of ponding water or debris.  Identify possible testing methods and/or inspection techniques for inspectors to evaluate the quality of the weathering steel patina at locations discussed above.  Identify possible methods to measure and evaluate the level of chloride contamination at the locations discussed above.  Evaluate the effectiveness of water washing on removing chlorides from the weathering steel patina.  Develop a general prioritization for the washing of bridge structures based on the structure’s location, environment, inspection observations, patina evaluation findings, and chloride test results.

Desempenho físico-químico de metais e estruturas de concreto de redes de distribuição de energia: estudo de caso na região de Manaus

The influence of natural aging furthered by atmospheric corrosion of parts of electric transformers and materials, as well as of concrete poles and cross arms containing corrosion inhibitors was evaluated in Manaus. Results for painted materials, it could showed that loss of specular gloss was more intensive in aliphatic polyurethane points than in acrylic polyurethane ones. No corrosion was observed for metal and concrete samples until 400 days of natural aging. Corrosion in steel reinforcement was noticed in some poles, arising from manufacturing faults, such as low cement content, water/cement ratio, thin concrete cover thickness, etc. The performance of corrosion inhibitors was assessed by many techniques after natural and accelerated aging in a 3.5% saline aqueous solution. The results show the need for better chemical component selection and its concentration in the concrete mixture.

Avaliação do efeito de gases poluentes na corrosão metálica: um experimento para o ensino da corrosão

In this work one proposes a didactic experience to simulate atmospheric corrosion of copper and nickel, due to sulfur dioxide presence. This is an opportunity to understand some basic aspects of atmospheric corrosion, by using fundamental concepts in chemistry, reactions of extraction and characterization of pollutants, as well as their participation in corrosion process. This subject opens a space for discussion about necessity of pollutant gases emissions control for preservation of materials and the environment.

Avaliação do efeito de gases poluentes na corrosão metálica: um experimento para o ensino da corrosão

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)