Variability in sepiolite: Diffraction studies

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 H 2 O 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.

Physicochemical properties of Aquivion/fluorine grafted sepiolite electrolyte membranes for use in PEMFC

“…Rio's group reported that sepiolite does not contain any Fe 2þ ions, based on the analysis of twenty kinds of different sepiolites from various provenances such as Madrid, Toledo, Zaragoza, California and so on [56]. This is consistent with our observation.…”

Microwave-Assisted Acid Activation of Clays Composed of 2:1 Clay Minerals: A Comparative Study

“…Some differences in the profiles suggest differences in crystallinity and chemical compositions [44]. Small differences in the d-spacing of 110 reflections have been related to slight differences in the crystalline cell, since isomorphic substitution can produce compositional variations [48]. Therefore, the slightly higher d-spacing values of the 110 reflection of Sp2 suggest that this sepiolite sample could have small compositional differences from Sp1.…”

Authigenic Mg-Clay Minerals Formation in Lake Margin Deposits (the Cerro de los Batallones, Madrid Basin, Spain)

“…The method is cheap, straightforward and satisfactorily accurate. To establish the relative ordering ("crystallinity") of sepiolite, the FWHM (Full Width at Half Maximum) parameter was measured on the (110) reflection at 1.2 nm in bulk sample [24]. The method proposed by Christidis and Koutsopoulou [25] was used for smectite type determination in five selected samples.…”