Corrosion of 85-5-5-5 bronze in natural and synthetic acid rain

In order to investigate the decay of bronzes exposed to acid wet depositions, a comparative study has been performed by following the corrosion behaviour of different sets of bronze specimens exposed either to natural rain or to a similar solution, without organic compounds, artificially reproduced in laboratory. The as cast G85 bronze specimens were exposed to aggressive solutions for different periods through a wet-dry technique. The pH trend of the solutions and the amount of metals transferred into the solutions were periodically monitored. OM, SEM, XRD, RAMAN analyses and ac electrochemical measurements were performed on the artificially weathered specimens. Preliminary results, showing the difference between the ageing in natural and synthetic rain, suggest the influence of the organic components on the corrosion process. In particular, the growth of a more uniform protective layer of corrosion products on the metal surface exposed to the natural rain could be attributed to these components. PACS 82.45.Bb; 82.33.Tb     

Weathering properties of treated southern yellow pine wood examined by X-ray photoelectron spectroscopy, scanning electron microscopy and physical characterization

In this study the weathering behavior of southern yellow pine (SYP) wood samples pretreated in different solutions has been examined using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and various types of physical characterization regarding material loss and discoloration. The treatment solutions include water as a control, a commercially available water repellent (WR) wood treating additive and polyethylene glycol (PEG) products including PEG PLUS™, PEG 8000 solutions and Compound 20M in varying concentrations. All contained the wood preservative chromated copper arsenate (CCA). One sample was treated with a CCA solution only. The treatments were carried out at 20 °C and 150 psig for 1/2 h after exposure to vacuum (28 mmHg) for 15 min. Simulated weathering was achieved in an Atlas 65-W Weather-Ometer for 2000 h with both light and dark periods and rain. The temperature ranged from 23 °C during the dark cycle to 35 °C during the light cycle. With weathering the XPS O/C ratios increase due to oxidation of the surface. Exposure to UV light results in bond breakage and reaction with oxygen in the presence of air to form organic functional groups such as , , CO and/or O-C-O. These oxidized products can protect the underlying wood from deterioration if they are insoluble in water and remain on the surface as a protective coating. If soluble, rain washes the compounds away and assists in the degradation. Correlated changes are observed in the XPS O/C ratios, the high-resolution XPS C 1s spectra, the SEM micrographs and physical measurements including thickness alteration, weight loss, and discoloration by yellowing or whitening of the weathered wood. The PEG treatments are effective in protecting wood with the 2% PEG PLUS treatment providing the best weathering behavior similar to that of the CCA treatment. The WR and water treatments yield the poorest weathering properties.     

Efficiency and resistance of the artificial oxalate protection treatment on marble against chemical weathering

The artificial oxalate protection method was analyzed in laboratory experiments in order to achieve an optimum treatment application and concentration giving rise to its most effective protective nature. Spectroscopic (Fourier transform infrared, Micro-Raman and UV-vis colorimetry), microscopic (scanning electron microscope) and contact-angle analyses were carried out to characterize Carrara marble samples before and after application of the treatment to validate its efficiency. The resistance effects against chemical weathering were subsequently observed in a lab-controlled weak acid rain experiment. An acid spray at pH 5.5, representative of normal rain was used to provoke degrade of natural marble, marble treated with the artificial oxalate protective at concentrations of 0.4 and 5% and marble treated with a commercial organic silicon product. Run-off solutions sampled at timely intervals were tested for any change in pH followed by ion chromatography measurements for the presence of calcium ions in solution. The chromatography results of the oxalate treatment applied at a 5% concentration are analogous to an organic commercial product indicating its validity as a method for the conservation of carbonate substrates conferring protection to stone materials against acid environments.     

Effect of compressive stress on cavitation erosion-corrosion behavior of nickel-aluminum bronze alloy

The effect of compressive stress on cavitation erosion-corrosion behavior of nickel-aluminum bronze alloy was investigated, and the results showed that the alloy exhibited selective phase corrosion of eutectoid “α + κ_iii” and its destruction was aggravated with more cavitation mass loss up to 1.74 times of the specimen without stress. It was mainly owing to the enhanced corrosion-induced erosion caused by compressive stress, which led to lattice distortion of the alloy and the resulting accelerated selective phase corrosion with increasing surface roughness, and then intensified the synergistic effect of electrochemical corrosion and mechanical erosion.     

Studies on corrosion protection of Al2024 T6 alloy by electropolymerized polyaniline coating

Aqueous electropolymerized polymer coatings on aluminum alloys can replace the carcinogenic chromate coating. In this work, the corrosion protection ability of electropolymerized polyaniline coating on Al2024 T6 alloy has been found out. The polyaniline coatings on aluminum were formed by galvanostatic and potentiostatic methods from a bath of 0.5 M oxalic acid containing 0.1 M aniline. The corrosion protection ability of the coating was found out by Tafel polarization and EIS in 1% NaCl solution. It has been found that polyaniline coated aluminum alloy has exhibited higher corrosion activity due to the presence of pores in the coating. However, the corrosion resistant property of polyaniline coated aluminum has been found to be improved to 90% by post-treatment in cerium containing solution at 60 °C.     

Indoor atmospheric corrosion of conventional weathering steels in the tropical atmosphere of Panama

One year indoor atmospheric corrosion examinations have been carried out on two conventional weathering steels for a year, at two test sites, Tocumen and Sherman Breakwater in Panama. They are environmentally classified by ISO 9223 as S₁P₀ τ ₄ and S₃P₀ τ ₅, respectively. In this humid-tropical marine climate corrosion rates are rather high, especially at Sherman Breakwater test site, mainly due to the high deposition of chloride, among other environmental conditions. Our results indicate that indoor corrosion is highly determined by the time of wetness and chloride ions. A-588 weathering steel corroded at a generally lower rate than COR-420 weathering steel. Rust characterization was performed by XRD, FTIR, and Mössbauer spectroscopy. Lepidocrocite, goethite, maghemite and akaganeite were found as corrosion products. Akaganeite is only detected when high chlorides deposition rates are obtained, and no washing effect occurs. This phase, together with maghemite, is obtained when there is greater aggressiveness in the environment.     

Corrosion reaction of iron exposed to the open atmosphere in the Antarctic

Within a cooperative program for the elaboration of a Latin American Map of Atmospheric Corrosion, weathering steel and mild steel samples were exposed to the Antarctic atmosphere and the corrosion products analyzed by ICEMS, XPS and XRD. Superparamagnetic -FeOOH was the main corrosion product after 24 h of exposure. Cl^– ions are found on the surface of the corroded samples by XPS.     

Electrodeposition of polyaniline–carbon nanotubes composite films and investigation on their role in corrosion protection of austenitic stainless steel by SNIFTIR analysis

Composite films of polyaniline (PANI) and carbon nanotubes (CNTs) were prepared by electrochemical co-deposition from solutions of the corresponding monomer containing two different kinds of CNTs. The first type was commercial (diameter = 110–170 nm, length = 5–9 μm) and the second one was home-made (diameter = 30 nm, length = 5–20 μm). The electrochemical behaviour of PANI–CNTs composite films was investigated with Cyclic Voltammetry and the surface morphology was analysed by Scanning Electron Microscopy (SEM). Subtractively Normalised Interfacial FT-IR procedure was used to investigate the presence of corrosion products when the films were deposited on stainless steel substrates and exposed to acid environment. The spectral investigations were utilised to understand the role of composite films in the corrosion protection and to discriminate the best performance CNTs.     

The cleaning of early glasses: investigation about the reactivity of different chemical treatments on the surface of ancient glasses

X-ray photoelectron spectroscopy (XPS) has been used to evaluate the reactivity of different chemical cleaning procedures on the surface of archaeological glasses. Investigations were performed on a series of Roman glass samples coming from Sicilian excavations. The ancient freshly fractured glass samples were subjected to different cleaning protocols such as piranha solution (solution of sulphuric acid and hydrogen peroxide) and EDTA/ammonia and citric acid/ammonia solutions at different pH values. The atomic concentrations of alkaline and alkaline-earth ions, measured using XPS spectra acquired at the surface of all the samples, revealed that, in acid solution, the reactivities of the EDTA and citric acid solutions were higher than that of the piranha solution. Moreover, in alkaline conditions, the reactivities of the chelating agent/ammonia solutions seem to be very high and effective in taking out alkaline and alkaline-earth ions and in destroying the external glassy structure with the formation of a silica gel thin film. PACS  61.43.Fs; 81.65.Cf; 61.66.Fn; 82.80.Pv     

Investigation of the toxicity of aqueous media after high-energy exposure by the spectralluminescent methods

The spectral and luminescent characteristics of aqueous solutions in the presence of phenol and natural organic acids are investigated after high-energy exposure (to a diffuse barrier discharge or an electron beam) in comparison with conventional ozonization. The toxicity of solutions is determined by the bioluminescent methods. It is demonstrated that the pulsed diffuse barrier discharge causes efficient transformation of phenol (C = 10^–3 M) in water. After such exposure, the solutions possess extreme toxicity. Addition of humic acids to the aqueous phenol solution results in decreased rates of phenol transformation and reduces the degree of toxicity after the high-energy exposure.     

Zero resistance ammeter of metallic alloys in aqueous solutions

In the present work, the corrosion current density of a low carbon steel, a pure aluminum, a stainless steel, a copper–nickel alloy were obtained in 1 M NaOH, 1 M KCl, 1 M NaCl, 1 M H₂SO₄ solutions, respectively. The obtained corrosion data from the optical interferometry technique, as a zero resistance Ammeter were compared with corrosion data obtained on the same alloys, in the specified solutions, from an electronic zero resistance-Ammeter as well as from the linear polarization method. The comparison among the three techniques indicates that there is a contrast in the results among the investigated alloys. In general, the results of the optical interferometry were found to fall in between the corrosion values of the zero resistance ammeter and the linear polarization method, because the technique works based on the electromagnetic principle, in the absence of electronic noise. As a result, the optical interferometry can be considered as a useful zero resistance-Ammeter for measuring the corrosion current density of metallic electrodes in aqueous solutions, at the open circuit potential of the electrodes in the aqueous solutions.     

Formation processes of CuCl and regenerated Cu crystals on bronze surfaces in neutral and acidic media

The paper is devoted to investigating the formation of CuCl and regenerated Cu crystals on bronze. Electrochemical behaviour of bronze in simulated anoxic edaphic media and occluded cell (O.C.) solutions was studied with cycle voltammetry (CV) and X-ray diffraction (XRD). Within potential range of −800 to +800 mV, oxidation occurred was largely a process in which Cu is oxidized to CuCl and the reduction process was a reverse of it. An atomic force microscopy (AFM) was used to observe the morphology of CuCl crystals, regenerated Cu crystals and corrosion interface at nm level. The deposition of regenerated Cu on simulated archaeological bronzes was simulated under experimental conditions for the first time. CuCl could be thoroughly reduced to pure Cu if reduction time interval were sufficiently prolonged. This provided a theoretical and experimental basis for getting rid of harmful CuCl patina from archaeological bronzes with electrochemical means.     

In situ QCM and TM-AFM investigations of the early stages of degradation of silver and copper surfaces

The early stages of atmospheric corrosion of pure copper and pure silver specimens were investigated performing in situ tapping mode atomic force microscopy (TM-AFM), in situ quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). The information obtained by TM-AFM is the change of the topography of the sample surfaces with emphasis on the shape and lateral distribution of the corrosion products grown within the first hours of weathering. The simultaneously performed in situ QCM measurements are indicating the mass changes due to possibly occurring corrosive processes on the surface during weathering and are therefore a valuable tool for the determination of corrosion rates. Investigations were carried out in synthetic air at different levels of relative humidity (RH) with and without addition of 250 ppb SO₂ as acidifying agent. On a polished copper surface the growth of corrosion products could be observed by TM-AFM analysis at 60% RH without any addition of acidifying gases [M. Wadsak, M. Schreiner, T. Aastrup, C. Leygraf, Surf. Sci. 454-456 (2000) 246-250]. On a weathered copper surface the addition of SO₂ to the moist air stream leads to the formation of additional features as already described in the literature [M. Wadsak, M. Schreiner, T. Aastrup, C. Leygraf, Surf. Sci. 454-456 (2000) 246-250; Ch. Kleber, J. Weissenrieder, M. Schreiner, C. Leygraf, Appl. Surf. Sci. 193 (2002) 245-253]. Exposing a silver specimen to humidity leads to the degradation of the surface structure as well as to a formation of corrosion products, which could be detected by in situ QCM measurements. After addition of 250 ppb SO₂ to the moist gas stream an increase of the formed feature's volume on the silver surface could be observed by TM-AFM measurements. The results obtained additionally from the in situ QCM measurements confirm the influence of SO₂ due to a further increase of the mass of the formed corrosion layer (and therefore an increase of the calculated corrosion rates) compared to the data obtained from the experiment carried out in humidity only.     

Vibrational and electronic properties of painting lakes

Naturally occurring dyes have been used to produce painting pigments, called lakes, by precipitation or adsorption of an organic dyestuff onto an insoluble inorganic substrate. Most natural dyes link to metal cations, by means of coordination bonds. The stable complexes formed precipitate together with solid amorphous hydrous aluminum oxide in alkaline solutions, yielding a hybrid material called a lake. Conventional chromatographic methods for lake analysis require dye extraction from the substrate; as a consequence, they do not provide any information about the organo-metallic complexes. In this work a comprehensive investigation based on X-ray fluorescence, Fourier transform infrared and UV–visible absorption and emission spectroscopies was carried out on 13 organic pigments derived from eight different natural sources. Three different kinds of substrate containing aluminum hydroxide were distinguished dependent on different preparation procedures. Information concerning the recipe and the dye composition was obtained by UV–visible spectroscopies. Dyes from different sources (animal or vegetal) could be distinguished. This study shows that the combined use of different spectroscopic techniques provides complementary information to high-performance liquid chromatography and therefore can be proposed for a molecular non-invasive investigation of these materials on works of art. PACS  87.64.Ni; 87.64.Je     

The corrosion of weathering steel by SO2 polluted atmospheres at its very early stages

CEMS was used in conjunction with AES to study the protective film formed on a weathering steel by exposure to a highly SO₂-polluted atmosphere. Ferrous species (sulphite) and ferric oxyhydroxides (ferrihydrite and α-FeOOH) were identified as corrosion products. From the correlation of CEMS and AES results the evolution with time of the different compounds is obtained, and a possible reaction sequence is outlined.     

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.     

The corrosion products of weathering steel and pure iron in simulated wet-dry cycles

Mössbauer spectroscopy and X-ray diffraction were used to establish the composition of the rust formed on pure iron and weathering steel after exposure to several wet-dry cycles in an SO₂-polluted atmosphere. α-FeOOH poorly crystallized andquasi amorphous ferrihydrite are identified as the main corrosion products. The rust has different particle size for iron and weathering steel samples.     

Initiation of nuclear reactions under laser irradiation of Au nanoparticles in the aqueous solution of Uranium salt

Laser exposure of a suspension of either gold or palladium nanoparticles in aqueous solutions of UO₂Cl₂ of natural isotope abundance was experimentally studied. Picosecond Nd:YAG lasers at peak power of 10¹¹–10¹³ W/cm² at the wavelength of 1.06–0.355 μm were used as well as a visible-range Cu vapor laser at a peak power of 10¹⁰ W/cm². The composition of colloidal solutions before and after laser exposure was analyzed using atomic absorption and gamma spectroscopy in the 0.06–1 MeV range of photon energy. Real-time gamma spectroscopy was used to characterize the kinetics of nuclear reactions during laser exposure. It was found that laser exposure initiated nuclear reactions involving both ²³⁸U and ²³⁵U nuclei via different channels in H₂O and D₂O. The influence of saturation of both the liquid and nanoparticles by gaseous H₂ and D₂ on the kinetics of nuclear transformations was found. Possible mechanisms of observed processes are discussed.     

Comparative Mössbauer and sem study of the corrosion reaction of iron and weathering steel in SO2-polluted atmospheres

A kinetic CEMS study of the early corrosion stages of iron and weathering steel in low (LAC) and very low (VLAC) SO₂-polluted atmospheres has been carried out. The morphology and sulphur content of corrosion products were examined with SEM-EDAX.