High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces.

The mechanisms of bacterial contact killing induced by Cu surfaces were explored through high-resolution studies based on combinations of the focused ion beam (FIB), scanning transmission electron microscopy (STEM), high-resolution TEM, and nanoscale Fourier transform infrared spectroscopy (nano-FTIR) microscopy of individual bacterial cells of Gram-positive Bacillus subtilis in direct contact with Cu metal and Cu5Zn5Al1Sn surfaces after high-touch corrosion conditions. This approach permitted subcellular information to be extracted from the bioinorganic interface between a single bacterium and Cu/Cu5Zn5Al1Sn surfaces after complete contact killing. Early stages of interaction between individual bacteria and the metal/alloy surfaces include cell leakage of extracellular polymeric substances (EPSs) from the bacterium and changes in the metal/alloy surface composition upon adherence of bacteria. Three key observations responsible for Cu-induced contact killing include cell membrane damage, formation of nanosized copper-containing particles within the bacteria cell, and intracellular copper redox reactions. Direct evidence of cell membrane damage was observed upon contact with both Cu metal and Cu5Zn5Al1Sn surfaces. Cell membrane damage permits copper to enter into the cell interior through two possible routes, as small fragmentized Cu2O particles from the corrosion product layer and/or as released copper ions. This results in the presence of intracellular copper oxide nanoparticles inside the cell. The nanosized particles consist primarily of CuO with smaller amounts of Cu2O. The existence of two oxidation states of copper suggests that intracellular redox reactions play an important role. The nanoparticle formation can be regarded as a detoxification process of copper, which immobilizes copper ions via transformation processes within the bacteria into poorly soluble or even insoluble nanosized Cu structures. Similarly, the formation of primarily Cu(II) oxide nanoparticles could be a possible way for the bacteria to deactivate the toxic effects induced by copper ions via conversion of Cu(I) to Cu(II).

The nature of self-assembled octadecylphosphonic acid (ODPA) layers on copper substrates.

HYPOTHESIS: The self-assembly of amphiphilic molecules onto solid substrates can result both in the formation of monolayers and multilayers. However, on oxidized and non-oxidized copper (Cu), only monolayer formation was reported for phosphonic acids possessing one phosphate head group. Here, the adsorption of octadecylphosphonic acid (ODPA) on Cu substrates through a self-assembly process was investigated with the initial hypothesis of monolayer formation. EXPERIMENTS: The relative amount of ODPA adsorbed on a Cu substrate was determined by infrared reflection/absorption spectroscopy (IRRAS) and by atomic force microscopy (AFM) investigations before and after ODPA deposition. X-ray photoelectron spectroscopy (XPS) with sputtering was used to characterize the nature of the layers. FINDINGS: The results show that the thickness of the ODPA layer increased with deposition time, and after 1 h a multilayer film with a thickness of some tens of nm was formed. The film was robust and required long-time sonication for removal. The origin of the film robustness was attributed to the release of Cu ions, resulting in the formation of Cu-ODPA complexes with Cu ions in the form of Cu(I). Preadsorbing a monolayer of octadecylthiol (ODT) onto the Cu resulted in no ODPA adsorption, since the release of Cu(I) ions was abolished.

Co-Adsorption of H2O, OH, and Cl on Aluminum and Intermetallic Surfaces and Its Effects on the Work Function Studied by DFT Calculations.

The energetics of adsorption of H2O layers and H2O layers partially replaced with OH or Cl on an Al(111) surface and on selected surfaces of intermetallic phases, Mg2Si and Al2Cu, was studied by first-principle calculations using the density function theory (DFT). The results show that H2O molecules tended to bind to all investigated surfaces with an adsorption energy in a relatively narrow range, between -0.8 eV and -0.5 eV, at increased water coverage. This can be explained by the dominant role of networks of hydrogen bonds at higher H2O coverage. On the basis of the work function, the calculated Volta potential data suggest that both intermetallic phases became less noble than Al(111); also, the Volta potential difference was larger than 1 V when the coverage of the Cl-containing ad-layer reached one monolayer. The energetics of H2O dissociation and substitution by Cl as well as the corresponding work function of each surface were also calculated. The increase in the work function of the Al(111) surface was attributed to the oxidation effect during H2O adsorption, whereas the decrease of the work function for the Mg2Si(111)-Si surface upon H2O adsorption was explained by atomic and electronic rearrangements in the presence of H2O and Cl.

Analysis of Historic Copper Patinas. Influence of Inclusions on Patina Uniformity.

The morphology and elemental composition of cross sections of eight historic copper materials have been explored. The materials were taken from copper roofs installed in different middle and northern European environments from the 16th to the 19th century. All copper substrates contain inclusions of varying size, number and composition, reflecting different copper ores and production methods. The largest inclusions have a size of up to 40 µm, with most inclusions in the size ranging between 2 and 10 µm. The most common element in the inclusions is O, followed by Pb, Sb and As. Minor elements include Ni, Sn and Fe. All historic patinas exhibit quite fragmentized bilayer structures, with a thin inner layer of cuprite (Cu2O) and a thicker outer one consisting mainly of brochantite (Cu4SO4(OH)6). The extent of patina fragmentation seems to depend on the size of the inclusions, rather than on their number and elemental composition. The larger inclusions are electrochemically nobler than the surrounding copper matrix. This creates micro-galvanic effects resulting both in a profound influence on the homogeneity and morphology of historic copper patinas and in a significantly increased ratio of the thicknesses of the brochantite and cuprite layers. The results suggest that copper patinas formed during different centuries exhibit variations in uniformity and corrosion protection ability.

Kinetics and mechanisms of reactions between H2O2 and copper and copper oxides.

One of the main challenges for the nuclear power industry today is the disposal of spent nuclear fuel. One of the most developed methods for its long term storage is the Swedish KBS-3 concept where the spent fuel is sealed inside copper canisters and placed 500 meters down in the bedrock. Gamma radiation will penetrate the canisters and be absorbed by groundwater thereby creating oxidative radiolysis products such as hydrogen peroxide (H2O2) and hydroxyl radicals (HO˙). Both H2O2 and HO˙ are able to initiate corrosion of the copper canisters. In this work the kinetics and mechanism of reactions between the stable radiolysis product, H2O2, and copper and copper oxides were studied. Also the dissolution of copper into solution after reaction with H2O2 was monitored by ICP-OES. The experiments show that both H2O2 and HO˙ are present in the systems with copper and copper oxides. Nevertheless, these species do not appear to influence the dissolution of copper to the same extent as observed in recent studies in irradiated systems. This strongly suggests that aqueous radiolysis can only account for a very minor part of the observed radiation induced corrosion of copper.

Corrosion and runoff rates of Cu and three Cu-alloys in marine environments with increasing chloride deposition rate.

Bare copper sheet and three commercial Cu-based alloys, Cu15Zn, Cu4Sn and Cu5Al5Zn, have been exposed to four test sites in Brest, France, with strongly varying chloride deposition rates. The corrosion rates of all four materials decrease continuously with distance from the coast, i.e. with decreasing chloride load, and in the following order: Cu4Sn>Cu sheet>Cu15Zn>Cu5Al5Zn. The patina on all materials was composed of two main layers, Cu2O as the inner layer and Cu2(OH)3Cl as the outer layer, and with a discontinuous presence of CuCl in between. Additional minor patina constituents are SnO2 (Cu4Sn), Zn5(OH)6(CO3)2 (Cu15Zn and Cu5Al5Zn) and Zn6Al2(OH)16CO3·4H2O/Zn2Al(OH)6Cl·2H2O/Zn5Cl2(OH)8·H2O and Al2O3 (Cu5Al5Zn). The observed Zn- and Zn/Al-containing corrosion products might be important factors for the lower sensitivity of Cu15Zn and Cu5Al5Zn against chloride-induced atmospheric corrosion compared with Cu sheet and Cu4Sn. Decreasing corrosion rates with exposure time were observed for all materials and chloride loads and attributed to an improved adherence with time of the outer patina to the underlying inner oxide. Flaking of the outer patina layer was mainly observed on Cu4Sn and Cu sheet and associated with the gradual transformation of CuCl to Cu2(OH)3Cl of larger volume. After three years only Cu5Al5Zn remains lustrous because of a patina compared with the other materials that appeared brownish-reddish. Significantly lower release rates of metals compared with corresponding corrosion rates were observed for all materials. Very similar release rates of copper from all four materials were observed during the fifth year of marine exposure due to an outer surface patina that with time revealed similar constituents and solubility properties.

Combined in situ quartz crystal microbalance with dissipation monitoring, indirect nanoplasmonic sensing, and vibrational sum frequency spectroscopic monitoring of alkanethiol-protected copper corrosion.

In this study, we have applied three techniques to simultaneously and in situ study the initial stage of corrosion of copper protected by a self-assembled monolayer of octadecanethiol (ODT). We combined quartz crystal microbalance with dissipation monitoring (QCM-D), indirect nanoplasmonic sensing (INPS), and vibrational sum frequency spectroscopy (VSFS) and obtained complementary information about mass uptake and optical and spectroscopic changes taking place during the initial corrosion phase. All three techniques are very sensitive to the formation of a corrosion film (thickness in the range 0-0.41 nm) under mildly corrosive conditions (dry air, <0.5% relative humidity). The three techniques yield information about the viscoelasticity of the corrosion film (QCM-D), the homogeneity of the corrosion reaction on the surface (INPS), and the stability of the ODT protection layer (VSFS). Furthermore, by also studying the corrosion process in humid air (ca. 70% relative humidity), we illustrate how the combination of these techniques can be used to differentiate between simultaneously occurring processes, such as water adsorption and corrosion product formation.

Initial oxidation of brass induced by humidified air.

Complementary surface and near-surface analytical techniques have been used to explore a brass (Cu-20Zn) surface before, during, and after exposure in air at 90% relative humidity. Volta potential variations along the unexposed surface are attributed to variations in surface composition and resulted in an accelerated localized growth of ZnO and a retarded more uniform growth of an amorphous Cu2O-like oxide. After 3 days the duplex oxide has a total mass of 1.3 µg/cm2, with improved corrosion protective properties compared to the oxides grown on pure Cu or Zn. A schematic model for the duplex oxide growth on brass is presented.

Surface characteristics, copper release, and toxicity of nano- and micrometer-sized copper and copper(II) oxide particles: a cross-disciplinary study.

An interdisciplinary and multianalytical research effort is undertaken to assess the toxic aspects of thoroughly characterized nano- and micrometer-sized particles of oxidized metallic copper and copper(II) oxide in contact with cultivated lung cells, as well as copper release in relevant media. All particles, except micrometer-sized Cu, release more copper in serum-containing cell medium (supplemented Dulbecco's minimal essential medium) compared to identical exposures in phosphate-buffered saline. Sonication of particles for dispersion prior to exposure has a large effect on the initial copper release from Cu nanoparticles. A clear size-dependent effect is observed from both a copper release and a toxicity perspective. In agreement with greater released amounts of copper per quantity of particles from the nanometer-sized particles compared to the micrometer-sized particles, the nanometer particles cause a higher degree of DNA damage (single-strand breaks) and cause a significantly higher percentage of cell death compared to cytotoxicity induced by micrometer-sized particles. Cytotoxic effects related to the released copper fraction are found to be significantly lower than the effects related to particles. No DNA damage is induced by the released copper fraction.

Corrosion-induced release of the main alloying constituents of manganese-chromium stainless steels in different media.

The main focus of this paper is the assessment of release rates of chromium, nickel, iron and manganese from manganese-chromium stainless steel grades of low nickel content. The manganese content varied between 9.7 and 1.5 wt% and the corresponding nickel content between 1 and 5 wt%. All grades were exposed to artificial rain and two were immersed in a synthetic body fluid of similar pH but of different composition and exposure conditions. Surface compositional studies were performed using X-ray photoelectron spectroscopy (XPS) in parallel to correlate the metal release process with changes in surface oxide properties. All grades, independent of media, revealed a time-dependent metal release process with a preferential low release of iron and manganese compared to nickel and chromium while the chromium content of the surface oxide increased slightly. Manganese was detected in the surface oxide of all grades, except the grade of the lowest manganese bulk content. No nickel was observed in the outermost surface oxide. Stainless steel grades of the lowest chromium content (approximately 16 wt%) and highest manganese content (approximately 7-9 wt%), released the highest quantity of alloy constituents in total, and vice versa. No correlation was observed between the release rate of manganese and the alloy composition. Released main alloy constituents were neither proportional to the bulk alloy composition nor to the surface oxide composition.

Corrosion-induced release of Cu and Zn into rainwater from brass, bronze and their pure metals. A 2-year field study.

A 2-year field study has been conducted in an urban environment to provide annual release rates of copper and zinc from brass (20 wt% Zn) and copper and tin from bronze (6 wt% Sn) compared to sheets of their pure alloy constituents, copper and zinc. Despite relatively low nominal bulk alloy content, substantially more zinc was released from brass compared to copper. Both metals were released at a significantly slower rate from the brass alloy, compared to the pure metals. The proportion of release rates of copper and zinc from the alloy differed significantly from their proportions in the bulk alloy. Bronze showed relatively constant release rates of copper, being similar to that of pure copper sheet. The release of tin from bronze was negligible. The results clearly show that alloys and the pure metals behave very differently when exposed to rainwater. Accordingly, release rates from pure metals cannot be used to predict release rates of individual constituents from their alloys. Generated data are of importance within REACH, the new chemical policy of the European commission, where metal alloys erroneously are being treated as mixtures of chemical substances.

Nickel release from nickel particles in artificial sweat.

Nickel is widely used in a broad range of products, primarily made of alloys, used by humans on a daily basis. Previous assessments have shown that skin contact with some such products may cause nickel allergic contact dermatitis, induced by the release of nickel. However, data on nickel release from small nickel particles in artificial sweat for assessment of potential risks of workers in nickel-producing and nickel-using facilities are not available. The objective of this study was to fill this knowledge gap by determining nickel release from fine nickel powder ( approximately 4 microm diameter) of different loadings varying from 0.1 to 5 mg/cm(2), when immersed in artificial sweat. The amount of nickel released increased with increasing particle loading, whereas the highest release rate per surface area of particles was observed for the medium particle loading, 1 mg/cm(2), at current experimental conditions. All particle loadings showed time-dependent release rates, reaching a relative steady-state level of less than 0.1 microg/cm(2)/hr after 12 hr of immersion, whereby less than 0.5% of the nickel particle loading was released. Nickel release from particles was influenced by the surface composition, the active surface area for corrosion, particle size, and loading.

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(2)O 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 microg/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.

Occurrence and fate of corrosion-induced zinc in runoff water from external structures.

This paper comprises data from an extensive cross-disciplinary research project aiming to elucidate the environmental fate of corrosion-induced zinc release from external structures. It includes an exposure assessment that provide long-term runoff rates, concentrations and chemical speciation of zinc, from 14 zinc-based materials exposed during 5 years in Stockholm, Sweden, and an effect assessment including bioavailability and ecotoxicity measurements, both at the immediate release situation and after soil interaction. Runoff rates of total zinc ranged from 0.07 to 2.5 g Znm-2 yr-1 with zinc primarily released as the free ion for all materials investigated. The average effect concentration, causing a 50% growth reduction after 72 h to the green algae Raphidocelis subcapitata, was at the immediate release situation 69 microg ZnL-1. Upon interaction of runoff water with soil, which simulated 18 to 34 years of exposure, the total zinc concentration was significantly reduced, from milligram per litre to microgram per litre levels. Simultaneously, the most bioavailable fraction of zinc in runoff, the hydrated zinc(II)-ion, decreased from more than 95% to about 30%. The major fraction, 98-99%, of the introduced total zinc concentration in the runoff water was retained within the soil. As long as the soil retention capacity was not reached, this resulted in zinc concentrations in the percolate water transported through the soil layer, close to background values and below growth inhibition concentrations for the green algae investigated. Zinc retained in soil was to a large extent (85-99.9%) extractable with EDTA, and available for plant uptake after 5 to 7 months of ageing.

Long-term corrosion-induced copper runoff from natural and artificial patina and its environmental impact.

The overall objective of this paper is to present an extensive set of data for corrosion-induced copper dispersion and its environmental interaction with solid surfaces in the near vicinity of buildings. Copper dispersion is discussed in terms of total copper flows, copper speciation and bioavailability at the immediate release situation, and its changes during transport from source to recipient. Presented results are based on extensive field exposures (eight years) at an urban site, laboratory investigations of the runoff process, published field data, generated predictive site-specific runoff rate models, and reactivity investigations toward various natural and manmade surfaces, such as those in soil, limestone, and concrete. Emphasis is placed on the interaction of copper-containing runoff water with different soil systems through long-term laboratory column investigations. The fate of copper is discussed in terms of copper retention, copper chemical speciation, breakthrough capacities, and future mobilization based on changes in copper concentrations in the percolate water, computer modeling using the Windermere Humic Aqueous Model, and sequential extractions. The results illustrate that, for scenarios where copper comes in extensive contact with solid surfaces, such as soil and limestone, a large fraction of released copper is retained already in the immediate vicinity of the building. In all, both the total copper concentration in runoff water and its bioavailable part undergo a significant and rapid reduction.

A vibrational sum frequency spectroscopy study of the liquid-gas interface of acetic acid-water mixtures: 1. Surface speciation.

Aqueous acetic acid solutions have been studied by vibrational sum frequency spectroscopy (VSFS) in order to acquire molecular information about the liquid-gas interface. The concentration range 0-100% acetic acid has been studied in the CH/OH and the C-O/C=O regions, and in order to clarify peak assignments, experiments with deuterated acetic acid and water have also been performed. Throughout the whole concentration range, the acetic acid is proven to be protonated. It is explicitly shown that the structure of a water surface becomes disrupted even at small additions of acetic acid. Furthermore, the spectral evolution upon increasing the concentration of acetic acid is explained in terms of the different complexes of acetic acid molecules, such as the hydrated monomer, linear dimer, and cyclic dimer. In the C=O region, the hydrated monomer is concluded to give rise to the sum frequency (SF) signal, and in the CH region, the cyclic dimer contributes to the signal as well. The combination of results from the CH/OH and the C-O/C=O regions allows a thorough characterization of the behavior of the acetic acid molecules at the interface to be obtained.

A vibrational sum frequency spectroscopy study of the liquid-gas interface of acetic acid-water mixtures: 2. Orientation analysis.

Vibrational sum frequency spectroscopy has been used to investigate the surface of aqueous acetic acid solutions. By studying the methyl and carbonyl vibrations with different polarization combinations, an orientation analysis of the acetic acid molecules has been performed in the concentration range 0-100%. The surface tension of acetic acid solutions was also measured in order to obtain the surface concentration. The orientation of the interfacial acetic acid molecules was found to remain essentially constant in an upright position with the methyl group directed toward the gas phase in the whole concentration range. The tilt angle (theta(CH)3) of the symmetry axis of the methyl group with respect to the surface normal was found to be lower than 15 degrees when considering a delta distribution of angles or as narrow as 0 +/- 11 degrees when assuming a Gaussian distribution. Further investigations showed that the C=O bond tilt (theta(C)(=)(O)) of the acetic acid hydrated monomer was constant and close to 55 degrees in the concentration range where it was detected. Finally, the orientation information is discussed in terms of different species of acetic acid, where the formation of a surface layer of acetic acid cyclic dimers is proposed at high acid concentrations.

Predictive models of copper runoff from external structures.

A general model for annual runoff rate predictions of total copper from naturally patinated copper on buildings at specific urban or rural sites of low chloride influence has been deduced from laboratory and field data. All parameters within the model have a physical meaning and include the average annual rain acidity (pH), the annual rain quantity and the geometry of a building in terms of surface inclination. In 70% of all reported annual runoff rates, the predicted values are within 30% from the observed values. The individual and interactive effect of rain composition in terms of pH, sulfate, chloride and nitrate concentration was investigated in immersion experiments in artificial rain water representative of urban and rural sites of Europe. The results show pH to have a dominating effect on patina dissolution, nitrate to have a small inhibiting effect, whereas no significant effect was seen for chloride and sulfate. In case pH data are not available, a model has been statistically deduced from field data by considering SO2 as influencing parameter, rather than pH. The predictability with the SO2 model is not as good as with the pH model i.e. the pH model should preferentially be used since it is a better predictor and all parameters within the model can be physically explained.

Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy analysis of titanium surfaces cultured with osteoblast-like cells derived from human mandibular bone.

Variations in the oxide films on titanium surfaces blasted with TiO(2) particles of various sizes were analyzed after cultures with cells derived from human mandibular bone. Turned titanium surfaces and surfaces blasted with 63-90-, 106-180-, and 180-300-microm TiO(2) particles were cultured with osteoblast-like cells. The surfaces were characterized before and after the cell culture with electrochemical impedance spectroscopy (EIS). The surface chemical composition of selected samples was analyzed with X-ray photoelectron spectroscopy (XPS). EIS revealed that with respect to the turned surfaces, the effective surface area was about 5, 6, and 4 times larger on the surfaces blasted with 63-90-, 106-180-, and 180-300-microm particles, respectively. After 28 days of the cell culture, the corrosion resistance on all sample types was unaffected. The impedance characteristics suggest a considerable effect of ion incorporation and precipitation during culturing. XPS revealed that before the cell culture, a typical surface layer consisted of TiO(2). After the culture, the surface oxide film contained both phosphorus and calcium, along with large amounts of oxidized carbon (carbonate) and nitrogen. There were lower concentrations of carbon and nitrogen on the blasted surfaces. We concluded that the effective surface area was several times higher on blasted surfaces than on turned surfaces. Cells derived from human mandibular bone affected ion incorporation into the implant surface.