Synchrotron powder X-ray diffraction study of the structure and dehydration behavior of palygorskite

Post, J. E.; Heaney, Peter J.

doi:10.2138/am.2008.2590

Cited by 101 publications

(86 citation statements)

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“…The associated endothermic peak is found around 470°C. These two structural water loss are consistent with literature 40,36,37,38 . Refinement results (full pattern matching) for palygorskite for different heating temperature and before rehydration are summarized in Table 1.…”

Section: Iii1 Palygorskite Claysupporting

confidence: 93%

“…From 25°C to 200°C, a decrease of the cell volume for the monoclinic (C2/m) and the orthorhombic (Pbmn) phases is observed (Table 1), mainly due to the decrease of the a parameter. Post et al 40 already report this structural evolution related to the departure of zeolitic water, but only for a purely monoclinic palygorskite. Departure of the first half of structural water (see TGA data) causes a structural change and the emergence of a new monoclinic phase (P2 1 /a).…”

Section: Iii1 Palygorskite Claymentioning

confidence: 95%

“…Departure of the first half of structural water (see TGA data) causes a structural change and the emergence of a new monoclinic phase (P2 1 /a). This phase transition is attributed to the folding of the structure by rotation of the phyllosilicate ribbons about an axis through the Si-O-Si corner bonds that link the ribbons 40,41,40 . At 250°C, cell volume for the two primary phases of palygorskite (monoclinic C2/m and orthorhombic Pbmn) is severely decreased compared with the ones refined at 25°C and 200°C, as the result of the a parameter evolution.…”

Section: Iii1 Palygorskite Claymentioning

confidence: 99%

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Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels

et al. 2011

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The search for durable dyes led several past civilizations to develop artificial pigments. Maya Blue (MB), manufactured in pre-Columbian Mesoamerica, is one of the best known examples of an organic-inorganic hybrid material. Its durability is due to the unique association of indigo molecule and palygorskite, a particular fibrous clay occurring in Yucatan. Despite 50 years of sustained interest, the microscopic structure of MB and its relation to the durability remain open questions. Combining new thermogravimetric and synchrotron X-ray diffraction analyses, we show that indigo molecules can diffuse into the channel of the palygorskite during the heating process, replacing zeolitic water and stabilizing the room temperature phases of the clay.

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Section: Iii1 Palygorskite Claysupporting

confidence: 93%

Section: Iii1 Palygorskite Claymentioning

confidence: 95%

Section: Iii1 Palygorskite Claymentioning

confidence: 99%

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Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels

et al. 2011

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“…Consistency of the refined structure was constantly checked through screening of the GOF (Goodness-Of-Fit) parameters, graphical fit between observed and calculated profiles and graphical representation of the refined model (Moldraw: Ugliengo et al, 1993). The lower soft-constraint weighting factor yielding reasonable bonds in tetrahedrons (F = 10) was kept to avoid unrealistic bond distances and polyhedrons distortions (Post et al, 2007;Post and Heaney, 2008;Giustetto et al, 2011a;Giustetto and Compagnoni, 2011).…”

Section: Methodsmentioning

confidence: 99%

“…The low-angular position and asymmetry of the strong (110) reflection (d110  12.2 Å), bringing information about the channel content (Ovarlez et al, 2009), prevent its adequate fit so that in Rietveld procedures it is generally excluded (Chiari et al, 2003;Post et al, 2007;Post and Heaney, 2008;Giustetto et al, 2011a). The refinement was first carried out in the 1.5-41.5° 2 range, including the strong (110) reflection, which was later excluded by maintaining the structural model refined so far.…”

Section: Crystal Structure Refinementmentioning

confidence: 99%

Asbestiform sepiolite coated by aliphatic hydrocarbons from Perletoa, Aosta Valley Region (Western Alps, Italy): characterization, genesis and possible hazards

Giustetto

Seenivasan²,

Belluso

2014

Mineral. mag.

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An atypical asbestiform sepiolite occurrence with exceptionally long fibres wrapped by a sheath of aliphatic hydrocarbons was found in the Gressoney Valley (Italian Western Alps) while monitoring asbestos presence in outcrops of serpentinite rocks. Microscopic and Fourier transform infrared analyses proved that these fibres, apparently up to several cm long, are formed by bundles of thinner fibrils (average length: 150 μm) potentially dispersible in the environment. When observed using transmission electron microscopy these fibrils show a rhomboidal to parallelogram cross section (<1 μm), of which surfaces are covered mostly by an aliphatic hydrocarbon film – an association not reported in the literature. The sepiolite fibrils and their organic coating probably originated in sequential steps from precipitation of Si/Mg rich hydrothermal fluids, resulting from serpentinization of olivine and clinopyroxene and a Fischer-Tropsch-type reaction. The presence of hydrocarbons has serious implications for the sepiolite habit, as the organic wrap interacts with the fibril’s surface reducing the amount of adsorbed water and favouring the fragmentation of thicker units into thinner ones, due to an ‘opening’ process implying separation along z and cleavage on (110). This defibrillation mechanism, coupled with the extraordinary length, further increases the aspect ratio of these fibrils (length/width ≫3) thus amplifying their potential danger for human health when dispersed in air and inhaled.

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