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An analysis of the black crusts from the Seville Cathedral: a challenge to deepen the understanding of the relationships among microstructure, microchemical features and pollution sources.

The Science of the total environment (2014-09-27)
Silvestro A Ruffolo, Valeria Comite, Mauro F La Russa, Cristina M Belfiore, Donatella Barca, Alessandra Bonazza, Gino M Crisci, Antonino Pezzino, Cristina Sabbioni
ABSTRACT

The Cathedral of Seville is one of the most important buildings in the whole of southern Spain. It suffers, like most of the historical buildings located in urban environments, from several degradation phenomena related to the high pollution level. Undoubtedly, the formation of black crusts plays a crucial role in the decay of the stone materials belonging to the church. Their formation occurs mainly on carbonate building materials, whose interaction with a sulfur oxide-enriched atmosphere leads to the transformation of calcium carbonate (calcite) into calcium sulfate dihydrate (gypsum) which, together with embedded carbonaceous particles, forms the black crusts on the stone surface. To better understand the composition and the formation dynamics of this degradation product and to identify the pollutant sources and evaluate their impact on the stone material, an analytical study was carried out on the black crust samples collected from different areas of the building. For a complete characterization of the black crusts, several techniques were used, including laser ablation inductively coupled plasma mass spectrometry, Fourier transform infrared spectroscopy, micro infrared spectroscopy, optical and scanning electron microscopy. This battery of tests provided information about the nature and distribution of the mineralogical phases and the elements within the crusts and the crust-substrate interface, contributing to the identification of the major pollution sources responsible for the deterioration of the monument over time. In addition, the results revealed a relation among the height of sampling, the surface exposure and the concentration of heavy metals. Finally, information has been provided about the origin of the concentration gradients of some metals.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Calcium carbonate, ≥99.995% trace metals basis
Sigma-Aldrich
Calcium carbonate, powder, ≤50 μm particle size, 98%
Sigma-Aldrich
Calcium sulfate, ≥99.99% trace metals basis
Sigma-Aldrich
Calcium carbonate, 99.999% trace metals basis
Supelco
Calcium carbonate, certified reference material for titrimetry, certified by BAM, ≥99.5%
Sigma-Aldrich
Calcium carbonate, BioUltra, precipitated, ≥99.0% (KT)
Sigma-Aldrich
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Calcium carbonate, BioXtra, ≥99.0%
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Sigma-Aldrich
Calcium carbonate, ACS reagent, chelometric standard, 99.95-100.05% dry basis
Supelco
Calcium carbonate, Pharmaceutical Secondary Standard; Certified Reference Material
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Calcium sulfate, Vetec, reagent grade
Sigma-Aldrich
Calcium carbonate, Vetec, reagent grade, 99%
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Calcium sulfate dihydrate, Vetec, reagent grade, 99%
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Calcium sulfate dihydrate, ACS reagent, 98%
Sigma-Aldrich
Calcium sulfate, −325 mesh, 99%
Sigma-Aldrich
Calcium carbonate, ACS reagent, ≥99.0%, powder
Sigma-Aldrich
Calcium sulfate dihydrate, puriss., meets analytical specification of NF, E 516, 99.0-101.0% (based on anhydrous substance)
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Calcium carbonate, puriss., meets analytical specification of Ph. Eur., BP, USP, FCC, E170, precipitated, 98.5-100.5% (based on anhydrous substance)
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Calcium carbonate, ReagentPlus®
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Calcium sulfate dihydrate, ReagentPlus®, ≥99%
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Drierite, without indicator, 4 mesh
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Drierite, with indicator, 8 mesh
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Drierite, with indicator, 4 mesh
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Drierite, without indicator, 8 mesh
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Drierite, with indicator, 6 mesh
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Calcium sulfate hemihydrate, purum, ≥97.0%
Sigma-Aldrich
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USP
Calcium Carbonate (AS), United States Pharmacopeia (USP) Reference Standard