Publication: Variability in sepiolite: Diffraction studies
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Publication Date
2011
Authors
Sánchez del Río, Manuel
Súarez Barrios, Mercedes
Silva, Iván da
Fuentes Montero, Luis
Martínez Críado, Gema
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Mineralogical Society of America
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Abstract
Twenty sepiolites of known composition from different origins were analyzed to quantify the
variability in structural parameters and its possible relationships with composition and morphology.
Morphology SEM analyses led to classify the sepiolites into several groups, beyond the two simple
macroscopic or clay groups. X-ray powder diffraction with synchrotron light was used to discuss the
variability of the a and b cell parameters with the nature of the cations and occupancy of the octahedral
shell. Rietveld refinement using the ideal sepiolite model is performed on sepiolites at two temperatures:
225 °C (for zeolitically dehydrated sepiolite) and 25 °C (for hydrated ambient sepiolite). The
latter permitted to locate ca. six molecules of the zeolitic H2O within the tunnels.
A few samples were selected to evaluate the feasibility and potential of single-crystal diffraction
methods: X-ray microdiffraction and electron diffraction. The macroscopic sepiolites gave wellstructured
and rich X-ray fiber diffraction patterns, in excellent agreement with ab initio simulations.
High-quality single-crystal electron diffraction patterns for three axis zones are indexed and compared
with simulations. The experimental and modeling results for X-ray microdiffraction and electron diffraction
open a new path for quantitative crystallography on sepiolite and other fibrous clays from
the sepiolite-palygorskite group.