Towards understanding the microstructural and structural changes in natural hierarchical materials for energy recovery: In-operando multi-scale X-ray scattering characterization of Na- and Ca-montmorillonite on heating to 1150 °C

Abstract

Understanding the changes in the microstructures and structures of clays with varying intercalated metal ions at elevated temperatures is of importance for many applications ranging from the recovery of shale gas from unconventional formations to developing effective nuclear waste containment technologies, and engineering materials such as ceramics for fuel cell applications. In this study, synchrotron-based in-operando multi-scale X-ray scattering analyses are used to determine dynamic microstructural and crystal structural changes in Na- and Ca-montmorillonite on heating from 30 °C to 1150 °C. Larger cations such as Ca2+ confer more defined morphological regimes compared to Na+ ions in compacted clays, as evident from the ultra-small-angle X-ray scattering results. The hierarchical morphology of clays is characterized to distinguish between nano-scale interlayer swelling porosity, meso-scale porosity, and intergranular pore spaces between powdered clay grains. On heating from ambient temperature to 200 °C, the removal of interlayer water reduced the basal distances to 9.6 Å. On further heating to 800 °C, gradual dehydroxylation of the clay sheets is evident from the structural changes. The effects of sintering at temperatures greater than 800 °C are evident from significant reductions in the intrinsic porosities of the clay sheets, and the formation of newer phases such as mullite. By connecting the in-operando microstructural and structural changes across spatial scales ranging from micrometers to Angstroms, the possibility of engineering high temperature processes for achieving morphologies and chemical compositions of interest is presented.

Multiscale X-Ray Scattering for Probing Chemo-Morphological Coupling in Pore-to-Field and Process Scale Energy and Environmental Applications

“…On the structural front, a significant reduction in the intensity of the characteristic beidellite peak that corresponds to q = 4.22 Å −1 , d = 1.49 Å (h k l: (0 6 0), (3 3 0)) [21] is noted (Figure 3). The trend in the reduction of the peak intensity of beidellite on heating is similar to that of Na-and Ca-montmorillonite reported in previous studies [17]. It was interesting to note the onset of significant structural changes in beidellite (Figure 3) after a reduction in the interlayer basal distance (Figure 2).…”

“…Other studies quantified the porosity in limestone and sandstone using ultra-small and small angle neutron scattering (USANS/SANS) measurements supported by complimentary electron microscopy imaging [12,13]. With the recent interest in energy recovery from unconventional formations, the non-invasive characterization of the porosity in shales [14][15][16] and its constituents such as clays [17][18][19] using USAXS/SAXS has received increased attention.…”

Phase Evolution and Textural Changes during the Direct Conversion and Storage of CO2 to Produce Calcium Carbonate from Calcium Hydroxide

“…The characteristic peak of calcium hydroxide which corresponds to the (1 0 0) reflection at q = 2.024 Å −1 undergoes significant changes with continuous CO 2 flow as the temperature increases ( Figure 2) [40]. The shift in the characteristic peak to lower q or larger d values corresponds to thermal expansion, as reported in previous studies [10,28,41]. Tracking the changes in the integrated intensity of calcium hydroxide peak yields important insights into the onset of carbon mineralization behavior.…”

“…In this paper, the evolution of calcium carbonate phases from calcium hydroxide and the corresponding changes in the roughness of the pore-solid interface are investigated using in-operando synchrotron ultrasmall, small, and wide angle X-ray scattering (USAXS/SAXS/WAXS) measurements [6,8,10,11,[28][29][30][31][32]. Wide angle X-ray scattering measurements provide unambiguous insights into the structural changes, while ultrasmall and small angle X-ray scattering measurements reveal the changes in the textures of the pore-solid interface during the carbon mineralization of calcium hydroxide to produce calcium carbonate.…”

In Situ Angstrom-to-Micrometer Characterization of the Structural and Microstructural Changes in Kaolinite on Heating Using Ultrasmall-Angle, Small-Angle, and Wide-Angle X-ray Scattering (USAXS/SAXS/WAXS)

“…From a structural point of view, heating kaolinite from ambient temperature up to 150 °C is accompanied by the removal of loosely bound water and nanoscale-confined interlayer water, 25 which does not significantly alter the interlayer basal distance or the structure, unlike in swelling clays such as Na-montmorillonite and Ca-montmorillonite. 23,26 The transformation of kaolinite to metakaolin on heating in the range of 400 °C to 700 °C has been extensively investigated. 11,15–18,20,27–30 These studies suggest that metakaolin retains the pseudo-hexagonal morphology of kaolinite without the crystallinity.…”