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Open AccessArticle

Characterization of Serpentines from Different Regions by Transmission Electron Microscopy, X-ray Diffraction, BET Specific Surface Area and Vibrational and Electronic Spectroscopy

1
Laboratorium für Organische Chemie, ETH Zürich, Vladimir-Prelog-Weg 3, HCI, 809 Zürich, Switzerland
2
Departamento de Geología, Facultad de Ciencias, Universidad de Salamanca, Pl. de la Merced s/n, 37008 Salamanca, Spain
3
Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad de Salamanca, Pl. de la Merced s/n, 37008 Salamanca, Spain
4
Laboratorio de altas presiones, Departamento de Química Inorgánica I, Universidad Complutense de Madrid, Avd. Complutense, s/n, 28040 Madrid, Spain
*
Author to whom correspondence should be addressed.
Fibers 2019, 7(5), 47; https://doi.org/10.3390/fib7050047
Received: 26 March 2019 / Revised: 3 May 2019 / Accepted: 14 May 2019 / Published: 20 May 2019
(This article belongs to the Special Issue Mineral Fibres)
Serpentinite powdered samples from four different regions were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), SBET and porosity measurements, UV-Vis and Infrared Spectroscopy of the skeletal region and surface OH groups. SEM micrographs of the samples showed a prismatic morphology when the lizardite was the predominant phase, while if antigorite phase prevailed, the particles had a globular morphology. The few fibrous-shaped particles, only observed by SEM and weakly detected by XRD on MO-9C and MO13 samples, were characteristic of the chrysotile phase. All diffraction XRD patterns showed characteristic peaks of antigorite and lizardite serpentine phases, with crystallite sizes in the range 310–250 Å and with different degrees and types of carbonation processes, one derived from the transformation of the serpentine, generating dolomite, and another by direct precipitation of calcite. The SBET reached values between 38–24 m2∙g−1 for the samples less crystalline, in agreement with the XRD patterns, while those with a higher degree of crystallinity gave values close to 8–9 m2∙g−1. In the UV region all electronic spectra were dominated by the absorption edge due to O2− → Si4+ charge transfer transition, with Si4+ in tetrahedral coordination, corresponding to a band gap energy of ca 4.7 eV. In the visible region, 800–350 nm, the spectra of all samples, except Donai, presented at least two weak and broad absorptions centred in the range 650–800 and 550–360 nm, associated with the presence of Fe3+ ions from the oxidation of structural Fe2+ ions in the serpentinites ((MgxFe2+1−x)3Si2O5(OH)4). The relative intensity of the IR bands corresponding to the stretching modes of the OH’s groups indicated the prevalence of one of the two phases, antigorite or lizardite, in the serpentinites. We proposed that the different relative intensity of these bands could be considered as diagnostic to differentiate the predominance of these phases in serpentinites. View Full-Text
Keywords: XRD; SEM; IR; RD-UV-Vis spectroscopy; chrysotile; antigorite; lizardite characterization XRD; SEM; IR; RD-UV-Vis spectroscopy; chrysotile; antigorite; lizardite characterization
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Rivero Crespo, M.A.; Pereira Gómez, D.; Villa García, M.V.; Gallardo Amores, J.M.; Sánchez Escribano, V. Characterization of Serpentines from Different Regions by Transmission Electron Microscopy, X-ray Diffraction, BET Specific Surface Area and Vibrational and Electronic Spectroscopy. Fibers 2019, 7, 47.

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