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A system for continuous monitoring of atmospheric corrosivity has been 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, aluminium, bronze, and brass at thicknesses from 50 nm to 250 m were tailored for environments with different corrosivities. The developed technology proved capable of providing high sensitivity, allowing for real-time corrosion monitoring even in low-corrosive indoor cultural heritage facilities. Laboratory tests showed good reproducibility with the standard deviation of parallel measurements at less than ±20% for metals which corrode uniformly in the tested environments. Several examples selected from a broad testing programme in partner museums, libraries, and other institut ions show successful applications of the logger system for characterization of air quality control in indoor locations, during transport and in temporary exhibitions; assessment of new buildings and storage facilities; and fundamental studies of optimal conservation and storage procedures. A first outline of a classification system for lead, which is particularly sensitive to the presence of carboxylic acids, is given. The technique has a large potential as an independent method for monitoring air quality in facilities displaying and storing valuable objects of cultural heritage.

The corrosion rate of copper and bronze Cu-8 wt.%Sn increased rapidly when the concentration of formic or acetic acid in air reached about 300 ppb at 80% relative humidity (RH) and a temperature of 20 °C. It decreased slowly during the several days after pollutant removal due to the slow rate of pollutant desorption from the metal surfaces. Corrosion of these metals was barely affected by the acids at RH up to 60%. For iron, the critical concentration of formic acid in air which led to surface activation at 80% RH was between 1000 and 1590 ppb.

Many ancient Chinese bronze mirrors have survived with a patina that leaves the delicate surface decorations intact. The microstructure of these mirrors is two-phase: Cu-rich α and Sn-rich δ. Although the mirrors have been labeled ‘corrosion-resistant’, the smooth surface includes a corroded layer up to 100 µm thick. In this ‘altered’ layer, there is selective attack of the α phase; the α-phase regions are replaced by tin oxide with the δ phase remaining metallic. Here, electrochemical polarization has been used to drive the dealloying process in modern, cast bronze duplicating the microstructure on ancient bronzes. Timed experiments were performed to investigate the growth of the ‘altered’ region on the model samples. The altered layer forms quickly but the rate of growth slows over time. Theoretical calculations show that dissolution of copper from the α phase leaves a large volume for the tin oxide corrosion product permitting retention of the smooth surface.

Many ancient Chinese bronze mirrors have survived with a patina that leaves the delicate relief surface decorations intact. The microstructure of these ancient mirrors is two-phase and consists of acicular α-phase (Cu-rich) regions encased in a δ-phase (Sn-rich) matrix. At the surface, there is evidence of selective dissolution of the α-phase; the α-phase regions are replaced pseudomorphically by a mineral product with the δ -phase remaining metallic. Electrochemical polarization has been used to drive the copper dealloying process in modern, cast bronze. Synchrotron x-ray diffraction was employed to compare the ancient samples with those that were prepared potentiostatically. Poorly crystallized tin oxide (SnO2) was found in the α - replacement products of both sample types. The corrosion-resistance of the potentiostatically-treated bronze samples was tested by atmospheric exposure. Comparison with exposed, untreated samples indicated that the treatment was protective.

Many ancient Chinese bronze mirrors have survived with their original surface decorationsintact, particularly those with “glassy” black surface coatings. The microstructures and compositions of cross-sectional samples from ancient mirrors have been analyzed with optical and electron microscopy and synchrotron x-ray fluorescence. The core has a two-phase metal structure while the surface shows evidence of selective dissolution of copper from the α (Curich) phase. The ci phase regions are replaced pseudomorphically by a mineral product with the δ (Sn-rich) phase remaining metallic. A fundamental study of the electrochemistry of the copper-tin system has given information on theconditions under which selective dissolution of copper takes place. Electrochemical polarization has been used to drive the copper dealloying process in cast high-tin bronze. Theresulting microstructure is similar to the dealloyed microstructure observed in the ancient samples.

The effectiveness of in situ multielement X-ray absorption near edge spectroscopy for studying the passivation of alloys is demonstrated. By simultaneously windowing the appropriate K{sub a} fluorescence lines with a 13-element energy-dispersive germanium detector it is possible to measure concurrently the behavior of different alloying elements during electrochemical polarization. A thin film of stainless steel was stepped between {minus}1.5 and +0.4 V (MSE) (the transpassive region of chromium) in a pH 8.4 borate buffer. On the first oxidation, no metal was lost and Fe and Ni showed some oxidation. On reduction, significant Fe and a barely detectable quantity of Ni dissolved. During the second oxidation, some Cr and a smaller fraction of Ni dissolved.