Copper Patina Research Articles

Effects of wax-based anti-graffiti on copper patina composition and dissolution during four years of outdoor urban exposure

The protection against graffiti has become a serious problem in most cities. Unfortunately such form of vandalism does not save the cultural heritage. The use of anti-graffiti coatings is a common treatment that can also temporary protect the surface from degradation due to interactions with the environment. Aspects that have not yet been sufficiently investigated from a metal artefact perspective are whether the presence of the anti-graffiti coating will influence the patina composition and reduce the degree of patina dissolution. Long-term (four years) effects of wax-based anti-graffiti coatings on bare copper sheet and pre-patinated copper exposed to urban atmospheric conditions are presented and discussed in terms of changes in patina dissolution rates, barrier properties and composition. The investigation is based on a multi-analytical approach combining chemical analysis, analytical and electrochemical tools (stereomicroscopy, FTIR, XRD, SEM/EDS, AAS, EIS, colorimetric measurements). Results are believed to provide important information related to the long-term applicability of such coatings to preserve the Cultural Heritage.

Dynamic secondary ion mass spectrometry and X-ray photoelectron spectroscopy on artistic bronze and copper artificial patinas

To prevent the natural processes of decay and to develop and improve the treatments of conservation and restoration of artistic bronzes meaning statues and sculptures, it is important understanding the patination processes and the knowledge of artificially corroded surfaces. Chemical and physical characterization of artificial patinas obtained on artistic bronzes and coppers by using the 19th century Western traditional patination techniques and recipes by means of SEM–EDS, light microscopy and ATR/FT-IR has been done in previous studies [I.Z. Balta, L. Robbiola, Characterization of artificial black patinas on artistic cast bronze and pure copper by using SEM–EDS and light microscopy, in: Proceedings of the 13th European Microscopy Congress, 22–27 August 2004, Antwerp, Belgium, EMC 2004 CD-Rom Conference Preprints; I.Z. Balta, L. Robbiola, Traditional artificial artistic bronze and copper patinas—an investigation by SEM–EDS and ATR/FT-IR, in: Proceedings of the 8th International Conference on Non Destructive Investigations and Microanalysis for the Diagnostics and Conservation of the Cultural and Environmental Heritage, 15–19 May 2005, Lecce, Italy, ART’05 CD-Rom Conference Preprints]. Differences in morphology (structure, thickness, porosity, adherence, compactity, uniformity, homogeneity) and also in composition, on both artistic cast bronze and pure copper patinas, were clearly evidenced. Further in-depth investigation is required to be carried out in order to better understand the patinas mechanisms of formation and the layers kinetics of growth. The elemental and chemical analysis, either on a surface monolayer or in a depth profile, by using the Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS) techniques, can provide this kind of information, unique at trace-level sensitivity. SIMS has proved to be a suitable analytical technique for analyzing small amounts of material with high atomic sensitivity (ppm or even ppb) and high depth/lateral resolution in the micron and sub-micron range [R.G. Wilson, F.A. Stevie, C.W. Magee, Secondary Ion Mass Spectrometry: A Practical Handbook for Depth Profiling and Bulk Impurity Analysis, Wiley & Sons, New York, 1989; M. Dowsett, A. Adriaens, The role of SIMS in cultural heritage studies, Nucl. Instr. Meth. Phys. Res. B 226 (2004) 38–52]. XPS has the ability to provide detailed chemical information on virtually each kind of solid sample, and elemental identification is therefore possible due to the core level photoemission. The most important advantage is the high surface sensitivity of the chemical information (a few monolayers) [E. Ciliberto, G. Spoto, Modern Analytical Methods in Art and Archaeology, John Wiley & Sons, Inc., New York, 2000]. In addition elements’ relative abundance can be made semi-quantitative or quantitative and information on chemical bonds can be derived. The aim of the present work is to highlight the advantages and the limits of XPS and Dynamic SIMS surface analytical techniques for the characterization of artistic bronze and copper artificial patinas. The results obtained on the analyzed samples allowed the distribution of the main elements in the corrosion patinas layers and the contribution of each elements present in bronze matrix to the color of the resulting patinas to be precisely revealed. This information could be used for comparative studies between artificial and natural patinas, and also for provenience and authentication studies for artistic and archaeological bronzes.

Calcium Carbonate on Bronze Finds

The removal of calcareous accretions from archaeological bronzes can be a difficult step in their conservation. Chemical cleaning with chelating agents might be an alternative to mechanical methods. In this study the use of the chelating agent sodium tripolyphosphate (STPP) was examined to determine whether it is effective in discriminating between calcium carbonate and copper patina, and non-corrosive to copper alloys in the presence of air. Comparative experiments with STPP and disodium ethylenediamine-tetraacetate (Na2-EDTA) were carried out on synthetic malachite, cuprite, calcium carbonate, naturally polished malachite surfaces and sheets of bronze and brass. In addition to the properties of the chelating agent, the solubility of the salts and the pH values of the solutions are crucial factors in the removal of compounds of low solubility. The quantity of metal ions dissolved, estimated by atomic absorption spectral analysis and scanning electron microscopy, showed that the calcareous accretions could be removed satisfactorily, but STPP also dissolved constituent parts of the patina, such as malachite and cuprite, and may harm bronze or brass. Compared to Na2-EDTA, STPP is less effective in dissolving calcium carbonate. It is less harmful to the patina and base metal, but may lead to patination of the underlying metal.

In vitro studies of copper release from powder particles in synthetic biological media

The aim of this paper is to provide quantitative data on copper release from powder particles of different copper materials, including artificial copper patina, Cu 2O and metallic Cu, when exposed to different synthetic biological media to simulate an inhalation scenario and/or skin contact. Generated data may contribute in risk assessment of potential health effects following exposure to and handling of various copper materials. All tests were performed in vitro to determine total copper concentrations, release rates of total copper, and to elucidate its time-dependence. The copper release process was interpreted in terms of specific surface area, surface morphology-, and composition. All powder materials show a time-dependent release process with total copper release rates less than 3 μg/cm 2 per hour at steady state conditions, for all media investigated. The importance of using relevant test media when simulating different interstitial lung conditions and difficulties encountered when comparing powder particles of essentially different properties are thoroughly discussed.

Surface Analysis of Copper Patinas Formed Outdoors by using Time-of-flight Secondary Ion Mass Spectrometry

Surface Analysis of Copper Patinas Formed Outdoors by using Time-of-flight Secondary Ion Mass Spectrometry

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.

Investigation of copper patinas using ion beam analysis and scanning electron microscopy

AbstractIon beam analysis (IBA) techniques were applied successfully to the investigation of non‐corroded and artificially corroded patina layers grown on copper substrates in order to explore their potential use in the study of degradation phenomena of copper and copper alloys subjected to chemical treatment and exposed to selected environmental conditions. Rutherford backscattering spectroscopy (RBS) with deuterons as projectiles and the nuclear reactions 16O(d,p)17O and 32S(p,p′γ)32S were applied to the investigation of the depth distribution of oxygen and sulphur in near‐surface layers of synthetic patina consisting of mineral phases corresponding to chalcanthite as well as to cuprite + chalcanthite and antlerite + brochantite + chalcanthite. Electrochemical techniques (potentiodynamic polarization and cyclic voltammetry in 0.5 M Na2SO4) were used for artificial acceleration and study of the corrosion processes, and scanning electron microscopy (SEM/EDS) was used for examination of the surface morphology of the samples. A patinated roof sample from the Vienna Hofburg also was investigated using the same techniques. The measurement showed that IBA can provide valuable information for the study of patina near‐surface layers of thickness up to a few micrometres and indicated that cuprite was the mineral phase primarily formed on the copper substrates and the main component of the interface between the patina layer and the metallic substrate. The investigated copper patinas looked rather heterogeneous and were characterized by high porosity. Mixed patinas exhibited considerable stability to further corrosive attack. Copyright © 2005 John Wiley & Sons, Ltd.

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 SO 2 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: Δ m= kt 0.6 and Δ m= 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 Δ m= 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.

Quantitative analysis of corroded copper patina by step scan and rapid scan photoacoustic Fourier transform infrared spectroscopy

Atmospheric corrosion enhanced by increasing air pollution causes increasing damage at valuable metallic monuments worthy of protection, e.g., the roof of the Stockholm City Hall. To explore the potential use of Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) in quantitative corrosion product analysis, the determination of the chemical composition of copper patina samples formed under atmospheric conditions was studied. As an experimental technique, we used a FTIR spectrometer in combination with sample-gas-microphone PAS using helium as the transfer gas at room temperature. The main components of the different samples—brochantite Cu4SO4(OH)6 and antlerite Cu3SO4(OH)4—were identified by their characteristic vibrational absorption bands. A quantitative analysis of these two components has been performed with rapid- and step-scan FTIR/PAS by using artificially corroded copper samples with differing ratios of composition. From these data, calibration curves were obtained allowing a nondestructive determination of the brochantite/antlerite ratio for quality control within an accuracy of about 10%.

Investigation of artificially produced and natural copper patina layers

Patina layers artificially produced by chemical treatment of copper and bronze were characterized using ion-beam analysis techniques. In order to simulate the corrosion process, the samples were electrochemically treated in 0.5 M Na2SO4 solution at ambient temperature. The corrosion behavior of artificial Cu patina layers prepared on copper and bronze substrates was studied using potentiodynamic, potentiostatic, and cyclic voltammetric techniques. The composition of the patina layers, which mainly consisted of phases corresponding to the minerals cuprite, antlerite, and brochantite, was determined by energy dispersive spectroscopy and scanning electron microscopy was used to examine their surface morphology prior to and after the corrosion tests. A natural patina sample was also investigated in the same way for comparison purposes. Characterization of the untreated and the electrochemically treated samples was also performed by Rutherford backscattering spectroscopy and nuclear reaction analysis techniques. Backscattering of protons and deuterons, as well as the 16O(d,p)17O, 32S(p,p′γ)32S and 63Cu(p,nγ)63Zn nuclear reactions were used for the profiling of oxygen, sulfur, and copper in the patina layers under investigation. The measurements indicate that the composition of the artificially prepared antlerite and brochantite patina layers is very close to that expected stoichiometrically. The antlerite patinas are transformed during the electrochemical treatment in 0.5 M Na2SO4 solution to brochantite, whereas the brochantite patinas seem to remain unchanged.

Microstructural Analysis of Artificially Formed Patinas on Copper

We analyzed artificially formed copper patinas to obtain microstructural information by means of transmission electron microscopy, energy dispersed X-ray spectroscopy, electron diffraction (ED), and X-ray diffraction (XRD). We found that there were two different phases in the patinas. One was a well-crystallized phase composed of copper, sulfur, and oxygen, and whose ED pattern exhibited many spots. The ED and XRD patterns revealed that this crystalline phase was antlerite The other phase was a noncrystalline phase with no spots but with a diffused pattern. This phase also contained copper, sulfur, and oxygen; however, the sulfur X-ray intensity was much stronger than that from the crystallized phase. We believe this phase to be composed of cuprite and sulfate. © 2002 The Electrochemical Society.

The evolution of outdoor copper patina

A general reaction scheme has been deduced which describes the evolution of the copper patina, including altogether eight compounds, formed upon exposure to outdoor atmospheric environments. The scheme is based on data obtained from altogether 39 exposure sites, using a recently developed method for quantitative X-ray powder diffraction analysis of up to 8 year old patina still adhering to the copper substrate. In all cases, cuprite forms initially and continuously throughout the atmospheric exposure. Three main sequences have been identified on sheltered copper, representing different reaction routes in sulfur- or chlorine-dominated environments. In less sulfur-polluted environments, posnjakite forms on the cuprite as a precursor to brochantite. In more sulfur-polluted environments, strandbergite is a precursor to antlerite. Both reaction routes may operate simultaneously and the main route may change from the more sulfur-polluted to the less polluted route, as a result of decreased pollutant levels. In chlorine-dominated environments the initial cuprite formation is followed by nantokite and atacamite. By far the most dominating sequence on unsheltered copper includes cuprite, followed by posnjakite and brochantite formation.

FTIR study of copper patinas in the urban atmosphere

This paper deals with the application of the FTIR and XPS spectroscopies in the chemical and phase analysis of patina layers. Relationship between the composition of copper patinas and the characteristics of the atmosphere in which they were formed has been clearly demonstrated. Since copper possesses an ability to interact with different atmospheric species retaining a variety of signatures of those interactions in a stable patina layer, it is the particularly appropriate material for a study of corrosion processes. The analysis of many samples demonstrate that copper roofs are covered with a complex patina reflecting corrosion stimulated by atmospheric pollutants, extraneous deposits from wind blown materials and birds.

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(H 2O) 6 2+.

Determination of sulphur and copper depth distribution in patina layers using nuclear reaction techniques

A method for Cu and S profiling in patina layers was developed by applying a combination of nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy (RBS). The copper profiling was performed by using the 1327 keV γ-ray deexciting the third excited state to the ground state of 63Cu produced by the reaction 63 Cu( p, p ′ γ) 63Cu. For the determination of sulphur the 2230 keV γ-ray was used deexciting the first excited state to the ground state of 32S formed through the reaction 32 S( p, p ′ γ) 32S, which exhibits three sharp resonances at projectile energies 3.094, 3.195 and 3.379 MeV. The relevant cross-sections were measured in the energy range between 3.0 and 3.7 MeV in steps of 20 keV at 125° to the incident proton beam direction. The technique was tested using artificially produced and natural copper patina layers. Supporting information on the depth distribution of the constituent elements of the patina samples was obtained by p-RBS ( E p: 1.5 MeV, θ: 160°).

Characterization of artificially produced copper and bronze patina by XPS

Characterization of artificially produced copper and bronze patina by XPS

Reactions of copper patina compounds—I. Influence of some air pollutants

Aged copper or bronze objects in outdoor environments exhibit patina layers containing several constituents. The influence of air pollutants on some of these compounds was studied, including cuprite (Cu 2O), tenorite (CuO), brochantite (Cu 4(OH) 6SO 4), antlerite, (Cu 3(OH) 4SO 4), Cu 2.5(OH) 3SO 4 · 2H 2O, and a mixture of atacamite/clinoatacamite (Cu 2(OH) 3Cl). The compounds were exposed to air containing ppb-levels of SO 2, O 3 and NO 2. The products were characterized by X-ray diffraction (XRD) after four weeks’ exposure. Deposition of SO 2 and consumption of O 3 were studied using on-line gas analysis. Mechanisms are suggested for the interaction of air pollutants with the patina compounds and the reactions are discussed in relation to outdoor conditions. The results are in agreement with observations from the field. Tenorite reacted rapidly with SO 2 in humid air, acting as an ideal absorber. This observation is in agreement with the rare occurrence of this corrosion product in outdoor environment. In the case of cuprite, sulfates were produced in a humid SO 2+O 3 environment while no sulfate formed when SO 2 was the only pollutant or when SO 2 and NO 2 were combined. However, active carbon on the cuprite surface enhanced the sulfation markedly in SO 2+NO 2 atmosphere. Cu 2.5(OH) 3SO 4 · 2H 2O, brochantite and antlerite formed on copper oxides. Cu 2.5(OH) 3SO 4 · 2H 2O, is suggested to be a metastable precursor in brochantite and antlerite formation and is slightly more soluble than these. Brochantite and antlerite did not react in any of the environments studied. In contrast, atacamite/clinoatacamite reacted rapidly with SO 2 in humid air, forming soluble CuSO 4 · xH 2O and a CuCl 2 · xH 2O solution.

Reactions of copper patina compounds—II. influence of sodium chloride in the presence of some air pollutants

The influence of NaCl on patina compounds occurring on outdoor copper and bronze objects was investigated. The laboratory study included cuprite (Cu 2O), tenorite (CuO), brochantite (Cu 4(OH) 6SO 4), and antlerite (Cu 3 (OH) 4SO 4), pretreated with 10 wt % NaCl. The pure compounds were exposed in humid air containing combinations of trace amounts of SO 2, O 3 and NO 2. Phase transformations were characterized by X-ray diffraction (XRD) after four weeks’ exposure. Deposition of SO 2 and consumption of O 3 were studied using on-line gas analysis. Mechanisms are suggested and reactions are discussed in relation to outdoor conditions. Tenorite did not react with NaCl in humid air. However, when SO 2 was added to the air, reaction was rapid, copper hydroxy chlorides and hydroxy sulfates forming. In addition, an unknown phase appeared in this environment. Cuprite pretreated with NaCl formed copper hydroxy chlorides in humid air. When SO 2 was added to the air, the mixture absorbed all SO 2 supplied. The rapid sulfation is suggested to be caused by the increased basicity due to oxidation of cuprite. Treating brochantite or antlerite with NaCl(aq) resulted in a remarkably fast conversion to copper hydroxy chlorides. The experiments demonstrate that copper hydroxy chlorides are expected to form on outdoor patina even in rain-exposed area. The lack of occurrence of hydroxy chlorides in these areas is suggested to be due to a progressing cyclic weathering; including the formation of hydroxy chlorides by salt deposition, the formation of soluble copper compounds by dry deposition of SO 2, and subsequent wash-out by the rain.

Studies of copper patina by photothermal beam deflection

Photothermal beam deflection (PBD) is a suitable method for three-dimensional, non-contact and non-destructive surface analysis. This method has been applied to the characterization of the thermal properties of natural and artificial patina and to the measurement of the thickness of the patina layers. The thickness of the outdoor and indoor patina of the roof of the Vienna Hofburg was measured to be about 22 μm and 10 μm, respectively. The thermal diffusivities of antlerite and chalcanthite were determined to 0.13 cm2/s and 0.04 cm2/s, respectively.

98/00170 Dual-functional NiMo sulfide catalysts on zeolite-alumina supports for hydrotreating and hydrocracking of heavy oils

The aim of this paper is to provide quantitative data on copper release from powder particles of different copper materials, including artificial copper patina, Cu2O and metallic Cu, when exposed to different synthetic biological media to simulate an inhalation scenario and/or skin contact. Generated data may contribute in risk assessment of potential health effects following exposure to and handling of various copper materials. All tests were performed in vitro to determine total copper concentrations, release rates of total copper, and to elucidate its time-dependence. The copper release process was interpreted in terms of specific surface area, surface morphology-, and composition. All powder materials show a time-dependent release process with total copper release rates less than 3 μg/cm2 per hour at steady state conditions, for all media investigated. The importance of using relevant test media when simulating different interstitial lung conditions and difficulties encountered when comparing powder particles of essentially different properties are thoroughly discussed.