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Microporous and Mesoporous Molecular Sieves
Published in Rolando M.A. Roque-Malherbe, Adsorption and Diffusion in Nanoporous Materials, 2018
Natural and synthetic zeolites belong to the group of molecular sieves existing in more than 1000 reported materials [34] that are three-dimensional microporous crystalline solids. In this regard, as an exemplification of how the zeolite structures are assembled, here, precisely, three of the most important framework types are shown: the LTA framework type (Figure 8.1a) corresponding to the following materials A, LZ-215, SAPO-42, ZK-4, ZK-21, ZK-22, and alpha, along with the framework-type FAU (Figure 8.1b) related to the natural zeolite faujasite and the synthetic ones: X, Y, EMC-2, EMT, ZSM-3, and ZSM-20. Finally, the HEU framework-type (Figure 8.1c) compatible with the natural zeolites heulandite and clinoptilolite and the synthetic zeolite LZ-219 is shown [2,24,34].
Silica and Silicates
Published in Shamil Shaikhutdinov, Introduction to Ultrathin Silica Films Silicatene and Others, 2022
At variance to STM, atomic force microscopy (AFM) does not suffer from electric conductivity constraints. To the best of our knowledge, the first AFM studies of silica were carried out not on silica polymorphs, which are structurally and compositionally more simple, but on easily cleaved (means, naturally clean) mica samples, with the aim to study low friction properties mica is famous for.53 AFM images recorded in the so called “frictional” mode revealed the periodicity of the hexagonal layer of SiO4 units that forms the cleavage plane of mica. AFM studies of silicate crystals were then extended towards adsorption of molecules on a zeolite, e.g., clinoptilolite (Na,K,Ca)2−3Al3(Al,Si)2Si13O36·12H2O, cut along the (010) plane.54 In particular, AFM images obtained in various media revealed that molecules could be bound to the surface in different ways: Neutral molecules of tert-butanol formed an ordered array, whereas tert-butyl ammonium ions formed clusters. These promising results triggered further AFM investigations of many other natural zeolite crystals, such as scolecite, stilbite, faujasite, heulandite, and mordenite, to name a few.55-58 In essence, the obtained AFM images were in good agreement with models derived from their bulk crystal structures, although really atomic resolution could not be achieved. AFM was also invoked to study feldspars, in this case albite (010) surface Na0.95Ca0.05Al1.05Si2.95O8.58 Again, the spatial resolution was not sufficient to draw solid conclusions on the atomic structure.
Natural Nanomaterials
Published in M. H. Fulekar, Bhawana Pathak, Environmental Nanotechnology, 2017
Zeolites are hydrated aluminosilicate minerals made of tetrahedral building blocks of AlO4 and SiO4 linked by rings. These units form a rigid, 3-D crystalline structure with a network of interconnected tunnels and cages. More than 40 naturally occurring zeolites are known. Natural zeolites are rock-forming, micro porous silicate minerals. An example is the mineral natrolite [Na2Al2Si3O10 ⋅ 2H2O]. In zeolite, the pore and channel sizes are nearly uniform, allowing the crystal to act as a nanoscale filter, or molecular sieve. Molecular sieves are materials that can be short molecules based on their size and chemical or electronic affinity. The size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the diameters of the tunnels. The types of molecules that can pass through the pores are influenced by their electrical charges and chemical interaction with the sieve matrix. Due to the strong electron charge inside the pores and high surface energy, zeolites can act a catalyst. The nanoscale architecture of the silicate and alumina in zeolites gives them their remarkable properties. Because of their powerful properties as filters and catalysts, zeolites are invaluable scientific tools. Zeolites have an ‘open’ structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+ and others. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution. Some of the more common mineral zeolites are analcime, chabazite, heulandite, natrolite, phillipsite and stilbite (Fuoco, 2012).
Correlation between the Warepan/Otapirian and the Norian/Rhaetian stage boundary: implications of a global negative δ13Corg perturbation
Published in New Zealand Journal of Geology and Geophysics, 2022
The Arawi Shellbeds and Ngutunui Formation are a succession of volcaniclastic sedimentary rocks dominated by thin sandstones, siltstones and shales, with minor but conspicuous conglomerates, tuffs and shellbeds (Figure 3). Limestones are not present, although the shellbeds approach coquina limestone composition in places within the Arawi Shellbeds (Grant-Mackie 1985), and there are no radiolarian cherts. Compositionally, the volcanic lithologies are broadly andesitic but range from basaltic andesite to dacite. The tuffs vary in vitric, crystal and lithic composition. In every respect, the sedimentary rocks in the Kiritehere section are typical of Murihiku Supergroup. They have been weakly metamorphosed to zeolite facies grade with conspicuous zeolite veining (laumontite, stilbite) and zeolite ‘cements’ (laumontite, heulandite, analcime). There are minor faults in places and also some ‘slumps’ (Grant-Mackie and Lowry 1964) but in general the stratigraphy is more or less ‘layer cake’, easy to recognise in the field, and the named formations and groups can be traced for many tens of kilometres. However, the sedimentary sequence as a whole has been folded, and a number of anticlines and synclines are recognised and named within a broader Kawhia Regional Syncline (e.g. Kear 1960; Edbrooke 2005). In the Kiritehere section, the sequence is dipping and younging to the east, and is part of a large homoclinal structure that may be interpreted as the west limb of a syncline (e.g. Kear 1960; Kear and Schofield 1964; Edbrooke 2005).
Metamorphism in the New England Orogen, eastern Australia: a review
Published in Australian Journal of Earth Sciences, 2020
K. Jessop, N. R. Daczko, S. Piazolo
In the SNEO, studies of metamorphism in the forearc basin of the passive-compressive Currabubula-Connors Arc phase show that metamorphism is very low grade. Illite crystallinity studies of K-white mica (Offler & Hand, 1988) revealed diagenetic (zeolite) to low sub-greenschist (prehnite–pumpellyite) facies. Offler, Roberts, Lennox, and Gibson (1997) studied rocks from the northern to the southeastern end of the Tamworth Belt (Figure 1) and recognised four zones increasing with stratigraphic depth from zeolite (heulandite–clinoptilolite ± stilbite) facies to sub-greenschist (prehnite ± pumpellyite ± epidote) facies with a calculated geothermal gradients of 9−12 °C/km. Offler et al. (1997) concluded that metamorphism resulted from burial and that relatively cold lithosphere was subducted at the time of basin sedimentation.
Upper Cretaceous rhyolitic ash beds from the Novaya Sibir Island (New Siberian Islands)
Published in GFF, 2019
V. Kostyleva, E. Shchepetova, A. Kotelnikov
Petrographical observations show very high content (more than 90%) of fresh unreworked (juvenile) pyroclastics (<0.2 mm in size) in the samples collected from the ash layers. The pyroclastic material is dominated (up to more than 90%) by very fine to fine-grained vitric components (0.005–0.15 mm in size), represented by colorless transparent (isotropic under the cross polarized light) glass shards of identical morphology showing curved stretched edges with sharp corners, Y-junctions and gas bubble holes that are typical for viscous acid volcanic glass of rhyolitic composition. Commonly (ab-1, ab-2 of Unit I and ab-4, Unit III) glass shards are mixed with low to high portion (10–50%) of brownish-green to slightly reddish fragments of biotite phenocrysts (0.01–0.2 mm, rarely up to 0.5 mm in size) (Fig. 4A, B), and fine-sized needle-like fragments of quartz and elongated zircon crystals are also present. The fine-dispersed matrix (<0.002 mm) in the samples of ab-1, ab-2 and ab-4 seems to be originally composed of very finely fragmented rhyolitic volcanic glass, now replaced by products of low-grade devitrification such as tridymite, zeolites of the heulandite-clinoptilolite group and the clay mineral smectite.