Solid state NMR characterisation of the thermal transformation of Fuller's Earth

Fuller's Earth, a dioctahedral calcium montmorillonite clay mineral of the smectite group, undergoes thermal transformation via a series of complex intermediate states that are highly structurally disordered. Fuller's Earth is a commercially significant material with considerable levels of paramagnetic iron (Fe3+) substitution into octahedrally coordinated metal sites. Despite the high iron-content (similar to 10% of the occupied octahedral metal sites) in these samples Si-29 and Al-27 magic angle spinning (MAS) NMR spectra of sufficient quality are obtained to reveal structural changes in samples that have been heated from room temperature to 1400 degrees C. Two major structural changes are clearly observed, initial dehydroxylation and then collapse of the layer structure into more highly connected silica-rich domains and an alumina-rich phase. (C) 1997 Elsevier Science B.V

Solid state NMR characterization of the thermal transformation of an illite-rich clay

Lode, a dioctahedral illite-rich clay from Latvia belonging to the mica group of clay minerals, undergoes thermal transformation via a series of structurally disordered intermediate phases. Despite containing high levels of paramagnetic Fe substituted into the octahedral sites. Si-29 and Al-27 magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of sufficient quality are obtained to resolve different structural units, showing clearly defined structural changes which occur in the sample during calcination to 1200 degrees C. However, Fe plays a significant role in broadening the Al signal, with integrated peak intensities decreasing as temperature increases. Significant differences are revealed in the thermal decomposition process by NMR spectra between pyrophyllite, Ca-montmorillonite and illite clays, possibly due to the different cations present in the interlayer. It has also been shown for illite that no structural differences at the atomic level occur when the dwell time at a particular temperature is varied and no difference is observed between samples that have different thermal histories: however, a minor effect of particle size and surface area is visible in the NMR data