| 1. |
- Chang, Tingru
(författare)
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Atmospheric corrosion of copper and copper-based alloys in architecture : from native surface oxides to fully developed patinas
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Copper and copper-based alloys are commonly used in both ancient and modern architecture. This requires an in-depth fundamental and applied understanding on their atmospheric corrosion behavior at different climatic, environmental and pollutant levels and how these parameters influence e.g. corrosion initiation, patina characteristics, aesthetic appearances, corrosion rates, and runoff rates. This doctoral thesis elucidates the role of native surface oxides on the corrosion performance, corrosion initiation, formation and evolution of corrosion products from hours to months, years and even centuries, to diffuse dispersion of metals from Cu metal/Cu alloy surfaces focusing on the roles of alloying elements, microstructure, and deposition of chlorides. In-depth investigations have been performed at both laboratory and field conditions on commercial Cu metal and copper-based alloys of a golden alloy (Cu5Zn5Al1Sn) and Sn-bronzes (Cu4Sn, Cu6Sn). Patina characteristics and relations to the presence of microstructural inclusions have in addition been investigated for historic patinas of Cu metal roofing of different age and origin, highlighted with data for a 400 years old Cu patina exposed at urban conditions.A multi-analytical approach comprising microscopic, spectroscopic and electrochemical methods was employed for in-depth investigations of surface characteristics and bulk properties. Electron backscattered diffraction (EBSD) was utilized to characterize the microstructure. Auger electron spectroscopy (scanning-AES), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES) were employed for surface chemical compositional analysis, and atomic absorption spectroscopy (AAS) to assess the amount of metal release from the patinas. Cathodic reduction (CR) and electrochemical impedance spectroscopy (EIS) were used to assess the amount and corrosion resistance of corrosion products formed at laboratory conditions. Confocal Raman micro-spectroscopy (CRM), infrared reflection absorption spectroscopy (IRAS) and grazing incidence X-ray diffraction (GIXRD) were used to identify the phases of corrosion products. Colorimetry was used to assess surface appearances.Cu5Zn5Al1Sn and Cu4Sn/Cu6Sn exhibit favorable bulk properties with respect to corrosion in terms of smaller grain size compared with Cu metal and show non-significant surface compositional variations. The presence of multi-component native oxides predominantly composed of Cu2O enriched with Sn-oxides on Cu4Sn/Cu6Sn, and with ZnO, SnO2 and Al2O3 on Cu5Zn5Al1Sn, improves the barrier properties of the native surface oxides and the overall corrosion resistance of Cu4Sn/Cu6Sn and Cu5Zn5Al1Sn. The formation of Zn/Al/Sn-containing corrosion products (e.g. Zn5(CO3)2(OH)6 and Zn6Al2(OH)16CO3·4H2O) significantly reduces the corrosion rate of Cu5Zn5Al1Sn in chloride-rich environments. Alloying with Sn reduces the corrosion rate of Sn-bronze at urban environments of low chloride levels but results in enhanced corrosion rates at chloride-rich marine conditions.A clear dual-layer structure patina was observed for centuries-old naturally patinated copper metal with an origin from the roof of Queen Anne's Summer Palace in Prague, the Czech Republic. The patina comprises an inner sub-layer of Cu2O and an outer sub-layer of Cu4SO4(OH)6/Cu3SO4(OH)4. Abundant relatively noble inclusions (mainly rosiaite (PbSb2O6)) were observed and incorporated in both the copper matrix and the patina. The largest inclusions of higher nobility than the surrounding material create significant micro-galvanic effects that result in a fragmentized patina and large thickness ratios between the Cu4SO4(OH)6/Cu3SO4(OH)4 and the Cu2O sub-layer, investigated via a statistical analysis of inclusions and patina characteristics of eight different historic urban copper patinas.
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| 2. |
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| 3. |
- Dubus, Michel, et al.
(författare)
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Monitoring copper and silver corrosion in different museum environments by electrical resistance measurement
- 2010
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Ingår i: Studies in Conservation. - : Int. Inst. for Conservation of Historic and Artistic Works. - 0039-3630 .- 2047-0584. ; 55:2, s. 121-133
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Tidskriftsartikel (refereegranskat)abstract
- The results are reported of a systematic programme of electrical resistance measurement (ERM) of copper and silver corrosion rates within various museum environments, directed towards developing preventive conservation understanding and practice. Electrical resistivity measurements were made using copper and silver probes for one month and one year in 33 locations, and these are interpreted in comparison with two standards. Advantages and drawbacks of different methods available for the evaluation of the corrosion aggressiveness of indoor air are discussed. Practical solutions are proposed for improving the protection of metal objects collections. Improvements are also proposed to maximize the efficiency and suitability of the measuring device to the very specific applications of cultural heritage collections.
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| 4. |
- Kouril, Milan, et al.
(författare)
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Corrosion monitoring in archives by the electrical resistance technique
- 2014
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Ingår i: Journal of Cultural Heritage. - : Elsevier Masson SAS. - 1296-2074 .- 1778-3674. ; 15:2, s. 99-103
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Tidskriftsartikel (refereegranskat)abstract
- It is essential that corrosion monitoring of indoor atmospheres should be highly sensitive, especially, when corrosion rates corresponding to the lowest standard corrosivity categories are supposed to be identified within one or a few days. The electrical resistance technique in combination with high-sensitivity electrical resistance sensors enabled detection of a corrosion loss on an atomic scale. Case studies have demonstrated the sensors' ability to timely inform the users about changes in the atmosphere quality. In confrontation with quartz crystal microbalance technique, resistometric sensors provided better explainable data.
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| 5. |
- Kouøil, M., et al.
(författare)
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Korozní monitoring v rukách restaurátorù a konzervátorù/Corrosion monitoring in the hands of restorers and conservators
- 2012
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Ingår i: Koroze a Ochrana Materialu. - 0452-599X. ; 56:3, s. 67-75
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Tidskriftsartikel (refereegranskat)abstract
- A technique for continuous monitoring of atmospheric corrosivity was developed. An electronic unit measures and records changes in the electrical resistance of a thin metal track applied on an insulating substrate. If the metal corrodes, the effective cross-sectional area of the track decreases and the electrical resistance increases. Sensors made of silver, copper, iron / steel, zinc, lead, tin, bronze and brass at thicknesses from 50 nm to 250 Êm were tailored for environments with different corrosivity. The developed technology proved to provide subAngstrom (<10-10 m) sensitivity allowing for real-time corrosion monitoring even in low-corrosive indoor cultural heritage facilities. Laboratory tests showed good reproducibility of the technique with standard deviation of parallel measurements up to ±20% for metals corroding in a given environment mostly uniformly. Since the technique measures the maximal depth of corrosion attack, the response is somewhat higher compared to methods measuring the average corrosion depth. Several examples from a wide testing programme in partner museums, archives, libraries and other institutions were selected to show successful applications of the technique for qualifi cation and comparison of air quality control in indoor premises, assessment of new buildings and storage facilities, air quality control during transport and temporary exhibitions and fundamental studies of optimal conservation and storage procedures. A fi rst outline of a classifi cation system for lead, which is particularly sensitive to presence of carboxylic acids, is given. The technique has a large potential as an independent method of air quality monitoring in facilities.
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| 6. |
- Nazarov, Andrej, et al.
(författare)
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Application of EIS and SKP methods for the study of the zinc/polymer interface
- 2008
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 53:25, s. 7531-7538
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical impedance spectroscopy (EIS) and Scanning Kelvin probe (SKP) were applied to study the zinc/polymer interface. The coating capacitance and the drop of potential across the zinc/epoxy interface are investigated as a function of water penetration and hydrolysis of adhesion bonds. Water penetrates to the interface, decreasing thus the potential drop and increasing the capacitance. Further removal of water leads to the restoration of bonds accompanied by a decrease in capacitance and the return to the initial potential distribution across the interface. Commercial high-performance coil coatings applied to galvanized steel were studied in order to correlate the interface stability and the tendency to blistering. EIS and SKP measurements allowed the evaluation of the electrochemical conditions at the interface. Local adhesion failures caused non-uniformity in the potential profile measured by SKP. Monitoring of changes in impedance at low frequency related to the interface during temperature cycling may be useful for the evaluation of the tendency to blistering.
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| 7. |
- Nazarov, Andrej, et al.
(författare)
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Formation of galvanic cells and localized corrosion of zinc and zinc alloys under atmospheric conditions
- 2017
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Ingår i: Corrosion. - : National Assoc. of Corrosion Engineers International. - 0010-9312 .- 1938-159X. ; 73:1, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric corrosion of Zn and Zn alloys with local NaCl contaminations was studied in situ by scanning Kelvin probe. The corrosion process was accompanied by the formation of clearly separated anodic and cathodic locations and local galvanic cells on the surface. The corrosion activity correlated to variations in Volta potential during air to nitrogen transients. The effect of dielectric and semiconducting solids on the efficiency of cathodic reaction on zinc was investigated. The rate of oxygen reduction was high on semiconducting ZnO films with defective structure, as they are effective donors of electrons. Mg, Ti, Cr, and Al were alloyed to zinc to modify the composition of surface oxide films. The addition of Mg provided the most effective corrosion inhibition, blocking completely the spreading of the cathodic area from NaCl contamination. The other elements had minor influence, but might be applied for further improvement of the Zn-Mg system. The effect of Mg is believed to be connected to semiconducting properties of the formed surface oxide film.
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| 8. |
- Nazarov, Andrej P., et al.
(författare)
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Protective action of vanadate at defected areas of organic coatings on zinc
- 2005
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 152:7, s. B220-B227
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of vanadate release from an organic coating and the stability and protective ability of the newly formed vanadate-based films on zinc surfaces have been studied with respect to self-healing ability of vanadate-pigmented organic coatings. The results were compared with those obtained with chromate. The kinetics of vanadate release from a polyester coating was comparable to that of chromate. The methods of X-ray absorption near edge spectroscopy (XANES) and scanning Kelvin probe were used for studying the mechanism of inhibition and the kinetics of vanadate reduction on bare zinc. XANES proved to be a powerful tool for determination of the oxidation state of vanadium in surface films. The experiments showed that vanadate was reduced more rapidly than chromate under the same atmospheric conditions. However, addition of magnesium phosphate resulted in a significantly lower reduction rate of vanadate. The results are discussed in light of the increased adsorption ability of the more negatively charged vanadium(V) species at higher pH, while the oxygen reduction process on zinc is inhibited due to the presence of phosphate. Thus, vanadate in combination with another inhibitor could provide corrosion protection at defects of organic coatings on zinc comparable to that of chromate.
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| 9. |
- Prosek, Tomas, et al.
(författare)
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Application of automated corrosion sensors for real-time monitoring in atmospheres polluted with organic acids
- 2011
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Ingår i: 18th International Corrosion Congress 2011. - 9781618393630 ; , s. 1477-1484
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Konferensbidrag (refereegranskat)abstract
- Loggers for continuous measurement of the corrosion rate of metals under atmospheric conditions were developed. The electronic unit measures and records changes in the electrical resistance of a thin metal track applied on an insulating substrate. If the metal corrodes, the effective cross-sectional area of the track decreases and the electrical resistance increases. Part of the metal track is protected by an organic coating and, thus, serves as a reference to compensate for resistivity changes due to varying temperature. Sensors made of silver, copper, iron / steel, zinc, bronze and lead with sensitivities tailored to different environments are available. Thin film metal sensors with the metal track thickness from 50 to 800 nm were made by physical vapour deposition (PVD). Examples of the logger application for continuous measurements of metal corrosion rates in air are given. Due to the sensitivity of the measurement as high as 0.1 nm, in terms of corrosion depth, changes in air corrosivity were registered within tens of minutes or hours even in low-corrosive environments. At relative humidities from 15 to 80 % and at the temperature of 20 °C, it was used for monitoring in the air polluted with controlled amounts of formic and acetic acids at concentrations from 0-1590 and 0- 870 ppb, respectively. Gases in these concentrations were reported to be found in museums and other cultural heritage institutions and are expected to cause accelerated deterioration of metal objects. Threshold limits of the formic acid concentration in air at 80 % RH and at 20 °C causing changes in the classification of indoor air corrosivity according to ISO 11844-1 are given.
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| 10. |
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