Characterization of Intercalated Smectites Using XRD Profile Analysis in the Low-Angle Region

Abstract

Abstract---X-ray diffraction (XRD) characterization of natural and intercalated smectites is usually limited to the apparent d-value estimated from the peak maxima in the raw data. This can lead to the misinterpretation of the measured data. In the case of XRD, the interference function is modulated by instrumental factors (Lorentz-polarization factor, diffraction geometry) and physical factors (structure factor, surface roughness effect). These effects lead to diffraction profile distortions, depending on the diffraction angle and peak full width at half maximum (FWHM). As a result, the diffraction profiles for structures with large line broadening (FWHM > 1 ~ exhibit a significant peak shift (Ad --1.5 A), especially at low angles (20 --< 10~ The present work deals with the detailed analysis of all these effects, their corrections and their consequences for the interpretation of diffraction patterns (including possible errors in determining lattice parameters or the structure model). The investigated materials were montmorillonites (MMT) intercalated with hydroxy-A1 polymers. Diffraction profile analysis revealed the corrected d-values and showed that the intercalated sample is not a mixed-layered structure. As a result a structural model of the interlayer is presented.

Molecular simulations of Zn-montmorillonite

“…The shape of the hydration curve agrees with the shapes for Na-MMT, Ca-MMT and Mg-MMT as presented by MacEwan & Wilson (1980) or Karaborni et al (1996). The differences in measured and calculated d-values for different hydration states may be partially caused by the inaccurate determination of d-values at lower diffraction angles (Janeba et al, 1997).…”

X‐ray powder diffraction of polymer/layered silicate nanocomposites: Model and practice

“…Roughness and alignment displace the sample from the perfect focusing geometry. If we consider the sample surface as a mosaic of small units, each with a finite angular deviation ω from the sample normal, the impact on the relative intensity, I / I o , can be expressed as follows:33 For example, ω = 0.5 and 1.0° results in an effective decrease in the relative intensity of 0.67 and 0.5 at 2θ = 2° and of 0.83 and 0.71 at 2θ = 5°, respectively. ω = 0.5° is only a relative vertical end–end displacement of a 4‐cm sample by 350 μm.…”

“…34,35 The data were collected on a -2 Rigaku powder diffractometer (rotating anode, 45 kV, 40 mA, Cu K␣). The extent of background 32,33 The position of the basal reflections and the extent of the background scattering depend on the source slits (0.5 and 1°) and sample alignment (sample surface removed 0, 250, and 500 m from the focal plane). (b) Summary of the apparent layer repeat distance determined from d 001 and d 002 reflections for the controlled displacement of the sample surface away from the focal plane.…”

Colloid Diffusion in Compacted Bentonite: Microstructural Constraints

“…The interlayer distances in water-saturated bentonite can be obtained from the basal spacing, d 001 , using low-angle X-ray diffraction (XRD) for example, where the interlayer distance is the basal spacing minus the thickness of one montmorillonite layer,~0.95 nm. Due to certain diffraction effects occurring for small interstratified particles at low angles (<5º2y), the true interlayer spacing might be slightly different than the interlayer distances obtained directly from Bragg's law (Moore and Reynolds, 1997;Janeba et al, 1988;Vaia and Liu, 2002). Note also that a certain distribution of basal spacings will always exist, even at small water contents (Ferrage et al, 2005).…”