Sepiolite–palygorskite: Textural study and genetic considerations

Romero, Emilia García; Suárez, M.

doi:10.1016/j.clay.2013.09.013

Cited by 107 publications

(42 citation statements)

References 35 publications

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“…1, this sample exhibits straight and rigid fibers in spheres, slightly curly intermediate fibers oriented in all directions, with lengths between 1 and 10 lm; it is in good agreement with the previous study performed by Garcia-Romero and Suarez [14]. This complex structure can be easily modified by the effect of the thermal treatments where a heating from RT to 500°C induces changes in the lattice that can be associated with the loss of (i) hygroscopic zeolitic water molecules (designated as H 2 O) and (ii) coordinated or crystallographically bound water molecules [designated as (OH 2 ) 4 ].…”

Section: Results and Discussion Esem And Xrd Characterizationsupporting

confidence: 90%

“…Supergenic sepiolite is found as a secondary mineral associated with serpentine and sedimentary sepiolite and appears linked to opal and palygorskite, e.g., in the Tagus river basin in which we collected samples (Batallones hill, Madrid). The sepiolite structure is formed by (i) tetrahedral silicon sheets, with an apical oxygen inverted, bound to octahedral magnesium sheets (typical T-O-T structure of phyllosilicates) [11,12], (ii) tunnels in the inner of the particle and (iii) channels (open tunnels in the external surface) [13,14]. This clay can be formed by hydrothermal processes or by sedimentation [15], although the most accepted mechanism for its formation is by the direct precipitation from solutions containing silica and magnesium [16].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of the irradiation dose on the luminescence emission of a Mg-rich phyllosilicate

Correcher¹,

Rodrı́guez-Lazcano²,

Gomesdarocha³

et al. 2015

J Radioanal Nucl Chem

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Section: Results and Discussion Esem And Xrd Characterizationsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Effect of the irradiation dose on the luminescence emission of a Mg-rich phyllosilicate

Correcher¹,

Rodrı́guez-Lazcano²,

Gomesdarocha³

et al. 2015

J Radioanal Nucl Chem

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“…This would be in accordance with the observation that dioctahedral palygorskite folds at lower temperatures than trioctahedral sepiolite (Frost and Ding 2003;Post and Heaney 2008), despite the smaller width of its tunnels that does not seem to impede the OH 2 desorption. By analogy, any type of structure involving sepiolite and/or palygorskite polysomes of different composition or octahedral character (Gionis et al 2007;Chryssikos et al 2009;García-Romero and Suárez 2010;Stathopoulou et al 2011;Suárez and García-Romero 2013) is expected to contribute to the complexity of the folding process.…”

Section: Structural Considerations Of Cooperative Foldingmentioning

confidence: 98%

Near-infrared investigation of folding sepiolite

Tsampodimou

Bukas

Stathopoulou

et al. 2014

American Mineralogist

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Sepiolite is an industrially important clay mineral of the palygorskite-sepiolite group with alternating 2:1 ribbons and hydrated tunnels. Dry sepiolite, Mg 8 Si 12 O 30 (OH) 4 (OH 2 ) 4 , loses half of its OH 2 content upon further heating and undergoes a structural collapse known as folding. This treatment is considered essential for enhancing the absorptive properties of the clay. In this paper, the folding process is studied by near-infrared (NIR) spectroscopy, mid-infrared attenuated total reflectance (ATR), and thermogravimetric analysis (TGA). The folded state, Mg 8 Si 12 O 30 (OH) 4 (OH 2 ) 2 , reveals a new spectrum of fundamental and higher-order OH 2 vibrations, as well as systematically split doublets of structural and surface O-H vibrations. Detailed assignments for the stretching, combination, and overtone O-H modes are proposed on the basis of the two non-degenerate populations of Mg 3 OH (and SiOH) present in the folded state. It is demonstrated that NIR is of particular diagnostic value in monitoring conveniently and non-invasively the folding process, which appears as a simple transition between well-defined dry-and folded-structures. At the level of elementary sepiolite particles (laths), folding is described as a cooperative process requiring the integrity of the ribbons and the inter-ribbon linkages (moderately acid-leached sepiolite does not fold). This is opposed to the skewed and sometimes complex OH 2 desorption trace observed by high-resolution TGA, which appears to indicate a multimodal distribution of laths. It is proposed that the rate-determining step for a sepiolite (also, palygorskite) lath to fold is the creation of a critical zone at mid-particle length, which is OH 2 -deficient and contains unstable, fivefold-coordinated Mg 2+ .

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“…As is known, the rods in natural PAL are existed as bundles or aggregates owing to the Van der Waals forces and hydrogen bonding interaction [19]. This means that natural PAL is only a precursor, instead of a real nanomaterial.…”

Section: Introductionmentioning

confidence: 99%