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Uncovering lead formate crystallization in oil-based paintings
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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, SAINumber of authors 9 Source Title Dalton Transactions. - : Royal Society of Chemistry - ISSN 1477-9226
Roč. 49, č. 16 (2020), s. 5044-5054Number 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
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