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)

Synchrotron-based in-operando multi-scale X-ray scattering analyses are used to connect microstructural changes to phase changes in kaolinite on heating from 30 °C to 1150 °C. Combined ultra-small-angle and small-angle X-ray scattering (USAXS and SAXS) data are modeled to determine the hierarchical morphology of kaolinite comprising nano-scale interlayer pores, meso-scale pores, and larger interparticle voids, while wide-angle X-ray scattering (WAXS) data reveal the simultaneous evolution of molecular phases in kaolinite. We found that the transformation of kaolinite to metakaolin corresponds to the disappearance of nano-scale porosity, and the onset of sintered phases such as mullite consistent with the overall reduction in porosity. The emergence of nanoscale particulate features on heating above 900 °C corresponds to the onset of sintered phases such as spinel and mullite. This study illustrates the application of multi-scale X-ray scattering measurements to connect the thermally induced phase changes with changes in pore structure and fine morphology evolution.