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Uncovering lead formate crystallization in oil-based paintings

SYSNO ASEP	0524413
Document Type	J - Journal Article
R&D Document Type	Journal Article
Subsidiary J	Článek ve WOS
Title	Uncovering lead formate crystallization in oil-based paintings
Author(s)	Švarcová, Silvie (UACH-T)_{SAI, RID, ORCID} Kočí, Eva (UACH-T)_{SAI, RID} Bezdička, Petr (UACH-T)_{SAI, RID, ORCID} Garrappa, Silvia (UACH-T)_{ORCID, RID, SAI} Kobera, Libor (UMCH-V)_{RID, ORCID} Plocek, Jiří (UACH-T)_{RID, ORCID, SAI} Brus, Jiří (UMCH-V)_{RID, ORCID} Šťastný, Martin (UACH-T)_{SAI, RID} Hradil, David (UACH-T)_{RID, SAI}
Number of authors	9
Source Title	Dalton Transactions. - : Royal Society of Chemistry - ISSN 1477-9226 Roč. 49, č. 16 (2020), s. 5044-5054
Number of pages	12 s.
Language	eng - English
Country	GB - United Kingdom
Keywords	Pb-207 NMR ; seed oil ; oxidation ; formaldehyde ; autoxidation
Subject RIV	CA - Inorganic Chemistry
OECD category	Inorganic and nuclear chemistry
Subject RIV - cooperation	Institute of Macromolecular Chemistry - Macromolecular Chemistry
R&D Projects	GA17-15621S GA ČR - Czech Science Foundation (CSF)
	GA19-05259S GA ČR - Czech Science Foundation (CSF)
Method of publishing	Limited access
Institutional support	UACH-T - RVO:61388980 ; UMCH-V - RVO:61389013
UT WOS	000530357500009
EID SCOPUS	85084167965
DOI	10.1039/d0dt00327a
Annotation	Lead carboxylates are an extensive group of compounds studied for their promising industrial applications and for their risky behavior when they are formed in oil paintings as corrosion products of lead-based pigments, leading to serious deterioration of paintings. Although the processes leading to the formation of aggregates, protrusions or inclusions, affecting undesirably the appearance of paintings, are assumed to be long term, neo-formed lead carboxylates are detectable in the early stage of paint drying. To uncover the chemical changes in lead pigments during the drying of oil paint films, model systems consisting of minium (Pb3O4) and four common drying oils were studied by X-ray powder diffraction (XRPD), C-13 and Pb-207 solid state NMR (ssNMR) spectroscopy and Fourier-transformed infrared spectroscopy (FTIR). For the first time, a degradation mechanism of Pb(3)O(4)via the crystallization of lead formate (Pb(HCOO)(2)), at the end of oxidative polymerization of oil paint films, was uncovered. The formation of formic acid in oils was proved by gas chromatography-mass spectrometry (GC-MS). Vapor experiments evidenced the susceptibility of Pb3O4 to react with volatile formic acid released during the autoxidation of oils comparably to the direct pigment-binder interactions in paint films. The investigation of the local environment of lead atoms in the paint film by Pb-207 WURST-CPMG NMR spectroscopy showed that Pb(ii) atoms reacted with linseed oil preferentially to form highly crystalline Pb(HCOO)(2), while the local chemical environment of Pb(iv) atoms did not change. The results proved the co-existence of (i) highly crystalline Pb(HCOO)(2), (ii) a highly mobile amorphous phase corresponding to free carboxylic acids or a nascent lead soap phase and (iii) the remaining Pb3O4 in the polymeric/ionomeric network. Pb(HCOO)(2) is assumed to be an intermediate for the conversion of Pb3O4 to lead soaps and/or lead carbonates.
Workplace	Institute of Inorganic Chemistry
Contact	Jana Kroneislová, krone@iic.cas.cz, Tel.: 311 236 931
Year of Publishing	2021
Electronic address	https://doi.org/10.1039/D0DT00327A

Number of the records: 1