Authors:Szilvia Ormándi, Ildikó Cora, Zsolt Dallos, Ferenc Kristály, and István Dódony
Zeolites are crystalline microporous alumosilicates whose unique pore and channel systems are the reason for their important role in catalysis, separation, and ion exchange. This work focuses on the morphology and structure of a natural zeolite, mordenite. Our samples were collected at Lengyendi-galya (Gyökeres-tető) in the Mátra Mountains (NE-Hungary). Zeolite samples were investigated by X-ray powder diffraction, scanning, and transmission electron microscopy. Mordenite has typically fibrous appearance and occurs in association with other zeolites such as heulandite and chabazite. Based on intense streaks and superlattice reflections in selected area electron diffraction patterns, we identified planar faults in the structure. A single fault produces a dachiardite-type structural slab within the mordenite lattice, reducing its channel size.
Authors:István Dódony, Tibor Németh, and Viktória K. Kis
A natural occurrence of a silica/clay nanocomposite material was investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). High-resolution images show that this nanocomposite material consists of 5–20 nm thick slabs of smectite and tridymite/cristobalite layers with coincident normals. In spite of the brittle glass-like appearance of the nanocomposite material its colloidal properties are similar to those of pure smectite but partial loss of expansion capacity was detected upon glycerol solvation. The structural relationship between smectite and silica is interpreted based on the smectite structure model of Edelman and Favejee (1940) which supposes reversed tetrahedra in the SiO4 layer of the TOT structure. This structure model explains the presence of silica impurities in bentonites used as raw material and several geological standard montmorillonites.