Use of temperature controlled stage confocal Raman microscopy to study phase transition of plattnerite

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Marco E. Ciriotti
Messaggi: 26747
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Use of temperature controlled stage confocal Raman microscopy to study phase transition of plattnerite

Messaggio da Marco E. Ciriotti » gio 21 mag, 2020 13:18

Referenza:
▪ Costantini, I., Lottici, P.P., Castro, K., Madariaga, J.M. (2020): Use of Temperature Controlled Stage Confocal Raman Microscopy to Study Phase Transition of Lead Dioxide (Plattnerite). Minerals, 10, 468; https://doi.org/10.3390/min10050468

Abstract:
The present work concerns the study of the phase transition of plattnerite [β-PbO2 lead (IV) oxide]-based samples when they are analysed by Raman spectroscopy. The laser-induced degradation process was carried out either on historical painting samples, where plattnerite was present as a degradation product of lead-based pigments, or commercial plattnerite samples as powder and pellets. The Raman spectra of plattnerite taken at low excitation power, to avoid phase transformations, are reported up to low wavenumbers, and they were characterized by the features at 159, 380, 515 and 653 cm−1 and a shoulder at 540 cm−1. The degradation of plattnerite was induced by increasing the laser power on the sample, and the formation of its secondary products red lead (Pb3O4), litharge (α-PbO) and massicot (β-PbO), when varying the laser power, is discussed. The analyses were performed in a controlled condition by coupling the Raman spectrometer to a temperature-controlled stage (Linkam THMS600- Renishaw), which allows for varying the sample temperature (from room temperature up to 600 °C) and keeping it constant inside the stage during the analysis. In this way, commercial plattnerite samples were heated by increasing the cell temperature to verify the temperature range at which the phase transitions of lead dioxide occur. In addition, thanks to the construction of temperature ramps, all the degradation pathways were shown, and other lead compounds were identified, generated by the laser power contribution. A different behaviour was found between pigments from historical painting samples and commercial samples under the effect of the laser. This information could be useful in order to recognize their nature when they are found in cultural heritage materials.
Marco E. Ciriotti

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TOSATO FABIO
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Iscritto il: ven 13 gen, 2006 11:39
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Re: Use of temperature controlled stage confocal Raman microscopy to study phase transition of plattnerite

Messaggio da TOSATO FABIO » gio 21 mag, 2020 14:08

Interessante lavoro.
Il raggio laser del Raman come tutti i raggi "scalda" il campione; per esempio analizzando una galena se si usa troppa potenza esce fuori uno spettro riconducibile alla leadhillite-susannite.
La strumentazione moderna consente di dosare la potenza del laser.
Per esempio quella che io utilizzo ha vari passaggi di erogazione: 100%, 50%, 25%, 10%, 1%, 0,1% di 17 mW
Tosato Fabio
"Il vero viaggio di scoperta non consiste nel cercare nuove terre, ma nell'avere nuovi occhi." M. Proust
Noi siamo anche quello che non siamo riusciti ad essere.
Sic transit gloria mundi.

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