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Materials (Basel). 2017 Mar 16;10(3). pii: E298. doi: 10.3390/ma10030298.

Analysis of Historic Copper Patinas. Influence of Inclusions on Patina Uniformity.

Author information

1
KTH Royal Institute of Technology, Div. Surface and Corrosion Science, School of Chemical Science and Engineering, SE 10044 Stockholm, Sweden. tingru@kth.se.
2
KTH Royal Institute of Technology, Div. Surface and Corrosion Science, School of Chemical Science and Engineering, SE 10044 Stockholm, Sweden. ingero@kth.se.
3
National Centre for Metallurgical Research (CENIM-CSIC), 28040 Madrid, Spain. delafuente@cenim.csic.es.
4
National Centre for Metallurgical Research (CENIM-CSIC), 28040 Madrid, Spain. bchico@cenim.csic.es.
5
National Centre for Metallurgical Research (CENIM-CSIC), 28040 Madrid, Spain. morcillo@cenim.csic.es.
6
Independent scholar, Luxembourg-1361, Luxembourg. jean-marie.welter@pt.lu.
7
KTH Royal Institute of Technology, Div. Surface and Corrosion Science, School of Chemical Science and Engineering, SE 10044 Stockholm, Sweden. chrisl@kth.se.

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.

KEYWORDS:

Volta potential; antlerite; atmospheric corrosion; bilayer; brochantite; cuprite; historic copper; inclusions; micro-galvanic effect; patina

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