The complex stratified patina formed on Sn-bronze in chloride-rich atmospheres has been explored through long-term field exposures and short-term laboratory investigations using a multi-analytical approach. The stratified patina is composed of Cu2O- and Cu-2(OH)(3)Cl-rich sublayers intercalated by Sn-oxides, mainly SnO2. The stratification is triggered by events of high chloride deposition, resulting in repeated dissolution and solidification of sublayers, whereby redox reactions between the intermediate products of Sn- and Cu-chlorides play a crucial role. Sn-induced patina stratification is a major reason for enhanced patina flaking on Sn-bronze and its accelerated corrosion rate compared to Cu metal in marine environments.

The copper patina colour has been systematically explored through a large set of short- and long-term exposed copper metal samples. The initial brown-black appearance is attributed to semiconducting properties of cuprite (Cu2O) and fully attained at thickness 0.8 +/- 0.2 mu m. The characteristic green-blue appearance is due to the colour forming Cu(II)-ion in the outer patina layer which needs to be 12 +/- 2 mu m to fully cover the inner cuprite layer. No significant influence of atmospheric environment on patina colour is discerned. The green-blue patina colour on historic copper was attained after shorter exposures than in modem copper due to more inhomogeneous microstructure.

The role of Sn on the atmospheric corrosion performance of binary Cu-Sn bronze alloys (4–6 wt.% Sn) compared with Cu metal used in outdoor architecture is elucidated in terms of microstructure, native surface oxide composition, patina evolution, corrosion rates, appearance and metal release. Results are presented for non-exposed surfaces and surfaces exposed at different urban and marine sites in Europe up to 5 years and based on multi-analytical findings from microscopic, spectroscopic, electrochemical and chemical investigations. Alloying influenced the corrosion, aesthetic appearance and patina evolution, differently for urban and marine sites, whereas no effects were observed on the release pattern.

The influence of surface adsorption of benzotriazole (BTAH) and of chloride ions (Cl-) on the kinetics of copper electrodeposition/dissolution in copper sulfate solutions and on copper deposit characteristics have been investigated using electrochemical quartz crystal microbalance (EQCM) combined with cyclic voltammetry (CV). The addition of BTAH alone increases the overpotential of copper deposition, whereas a Cu(I)BTA complex forms at potentials higher than 0.08 V (vs. SCE) accompanied with the occurrence of copper anodic dissolution. With simultaneous addition of BTAH and Cl-, surface adsorption of Cl- competes with that of BTAH during the initial stage of copper nucleation. Different cuprous reaction intermediates form in the examined potential range -0.4 to 0.3 V (vs. SCE), which partly eliminate the favorable effect of BTAH on the deposited copper. A BTAH-containing adsorbed layer formed on the matte side of electrodeposited copper film in the presence of BTAH with or without Cl-, exhibiting a barrier surface property and an improved corrosion resistance compared with the copper film electrodeposited in the electrolyte without addition of BTAH.

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.

The golden alloy Cu-5Zn-5Al-1Sn has found many applications because of its appearance and resistance to tarnishing. The microstructure and multi-component surface oxide of Cu-5Zn-5Al-1Sn have been investigated through a multi-analytical approach. Compared to commercial Cu metal, Cu-5Zn-5Al-1Sn has significantly smaller grains and higher fraction of coherent twin boundaries. The 5-10 nm thick oxide formed after diamond polishing has four identified sub-oxides all contributing to the overall corrosion resistance. Cu2O is mainly located in the outer part, followed by ZnO, SnO2 and Al2O3 closer to the alloy substrate. The latter three possess barrier properties, while Cu2O exhibits a more complex structure.

This paper presents an in-depth characterisation study of the patina formed on a copper tile taken from the roof of Queen Anne's Summer Palace in Prague after close to 400 years of exposure to the action of the atmosphere. A wide variety of techniques have been performed, including metallographic and chemical analysis (electrogravimetry, AAS, XRF) of the copper matrix, and spectroscopic and microscopic investigations (GIXRD, TEM/EDS and SEM/EDS) to determine the composition and structure of the patina. The major conclusions of the study are: (a) the base copper contains abundant inclusions mainly of rosiaite (PbSb2O6); (b) the patina is formed by an inner sublayer of cuprite (Cu2O) and an outer sublayer of brochantite [Cu4SO4(OH)6] and antlerite [Cu3SO4(OH)4] and traces of azurite [Cu3(CO3)2(OH)2]; and (c) the brochantite/antlerite crystals are randomly doped with Fe and C.

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.

This paper presents an in-depth characterisation study of the patina formed on a copper tile taken from the roof of Queen Anne's Summer Palace in Prague after > 300 years of exposure to the action of the atmosphere. A wide variety of techniques have been used, including metallographic and chemical analysis (electrogravimetry, AAS, XRF) of the copper matrix, and spectroscopic and microscopic investigations (GIXRD, FTIR, TEM/EDS and SEM/ EDS) to determine the composition and structure of the patina. The major conclusions of the study are: (a) the base copper contains abundant inclusions mainly of rosiaite (PbSb2O6); (b) the patina is formed by an inner sublayer of cuprite (Cu2O) and an outer sublayer of brochantite [Cu4SO4(OH)(6)] and antlerite [Cu3SO4(OH)(4)] and traces of azurite [Cu-3(CO3)(2)(OH)(2)]; and (c) the brochantite/antlerite crystals are randomly doped with Fe and C.