Cinnabar use on painting is historically documented from ancient times, together with its tendency to darken. The most accepted mechanism for this kind of deterioration considers cinnabar (α-HgS) transformation into its polymorph metacinnabar, β-HgS, but recent studies have cast doubt on this hypothesis. On this background, an in situ high-temperature X-ray powder diffraction study of the thermal behaviour of cinnabar has been carried out. Data, measured in transmission geometry on a non-hermetically sealed capillary, indicate that the α-HgS (trigonal) → β-HgS (cubic) phase transition occurs at 673 K and is completed at 698 K due to kinetics reasons. The thermal expansion of cinnabar is fairly isotropic, the a-parameter being slightly softer against heating. A fast cooling of metacinnabar at room temperature (T) produced a mixture of both polymorphs. The analysis of the kinetics of the β-HgS → α-HgS transformation at room-T shows a low rate of conversion, but not low enough to be consistent with a persistence of metacinnabar for a time span of 2000 years as hypothesized in reference data for Pompeian frescoes. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung.

Thermal behaviour of cinnabar, α-HgS, and the kinetics of the β-HgS (metacinnabar) → α-HgS conversion at room temperature / Ballirano, Paolo; Botticelli, Michela; Maras, Adriana. - In: EUROPEAN JOURNAL OF MINERALOGY. - ISSN 0935-1221. - STAMPA. - 25:6(2013), pp. 957-965. [10.1127/0935-1221/2013/0025-2341]

Thermal behaviour of cinnabar, α-HgS, and the kinetics of the β-HgS (metacinnabar) → α-HgS conversion at room temperature

BALLIRANO, Paolo;BOTTICELLI, MICHELA;MARAS, Adriana
2013

Abstract

Cinnabar use on painting is historically documented from ancient times, together with its tendency to darken. The most accepted mechanism for this kind of deterioration considers cinnabar (α-HgS) transformation into its polymorph metacinnabar, β-HgS, but recent studies have cast doubt on this hypothesis. On this background, an in situ high-temperature X-ray powder diffraction study of the thermal behaviour of cinnabar has been carried out. Data, measured in transmission geometry on a non-hermetically sealed capillary, indicate that the α-HgS (trigonal) → β-HgS (cubic) phase transition occurs at 673 K and is completed at 698 K due to kinetics reasons. The thermal expansion of cinnabar is fairly isotropic, the a-parameter being slightly softer against heating. A fast cooling of metacinnabar at room temperature (T) produced a mixture of both polymorphs. The analysis of the kinetics of the β-HgS → α-HgS transformation at room-T shows a low rate of conversion, but not low enough to be consistent with a persistence of metacinnabar for a time span of 2000 years as hypothesized in reference data for Pompeian frescoes. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung.
2013
metacinnabar; rietveld method; β-hgs; cinnabar; α-hgs; high-temperature x-ray powder diffraction; sulfides; pigment; sulphides
01 Pubblicazione su rivista::01a Articolo in rivista
Thermal behaviour of cinnabar, α-HgS, and the kinetics of the β-HgS (metacinnabar) → α-HgS conversion at room temperature / Ballirano, Paolo; Botticelli, Michela; Maras, Adriana. - In: EUROPEAN JOURNAL OF MINERALOGY. - ISSN 0935-1221. - STAMPA. - 25:6(2013), pp. 957-965. [10.1127/0935-1221/2013/0025-2341]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/537260
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