Abstract
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.
Highlights
The production and use of copper and copper alloys is many thousands of years old and has been based on several different production technologies over the millennia [1]
Of them exhibit an elongated shape in the hammering rolling direction of the sheet, which was observed in historic copper materials from the Middle grey, Figuredirection
Considering the difference in microstructure between modern high-purity copper (e.g., DHP-Cu) and historic copper materials, and the fact that the protective properties of the patina layer mainly have been attributed to the inner cuprite layer [21], the results suggests that high-purity copper has a superior corrosion protective ability over historic ones
Summary
The production and use of copper and copper alloys is many thousands of years old and has been based on several different production technologies over the millennia [1]. Native copper and copper extracted from oxide ores was obtained through a reduction with charcoal These ores were rapidly exhausted in Europe, and ancient metallurgists had to learn to obtain the copper from a large variety of copper sulfide ores. They range from rather pure chalcopyrite (CuFeS2 ) to the Fahlerz ore with high antimony and arsenic contents. Oxygen became the agent that helped to reduce sulfur and other major and minor elements contained in the ore This explains why old copper samples contain larger amounts of oxygen (ranging from 400 to 4000 ppm by weight) and other metallic impurities.
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