Coatings, smectites

Figure 4. SEM images of filamentous aggregates of faioct ech al smectite enveloping dolomite crystals in dolomite crust (Carlsbad Cavern). Image on die right was modified from Polyak and Guven (2000). Arrows point to coated dolomite rhombs.

Surfactant-coated interlayer sites in smectite have similar properties to detergents. A hydrophobic molecule or compound such as dioxin or other chlorinated phenol is attracted to the hydrophobic hydrocarbon tail projecting from the interlayer surface and immobilized. 

Chlorite replaces kaolinite, clay pseudomatrix, infiltrated clays, micas and heavy minerals. It occurs as rims composed of platelets oriented perpendicularly to grain surfaces. The rims were formed by replacing infiltrated smectitic clay coatings, which were originally oriented tangentially to grain surfaces (Fig. 14A) (see Moraes De Ros, 1990). These infiltrated clays were presumably introduced into the vadose zone of alluvial continental sediments under semi-arid conditions by episodic floods (Walker et al., 1978 Moraes De Ros,... 

Typically, mechanically infiltrated clays are originally detrital smectites formed under semi-arid weathering conditions (see Keller, 1970 Walker et al., 1978). This is evidenced by the dominance of smectitic clays in the mudstone samples and in the mud intraclasts. Infiltrated coatings and derived chloritized rims are conspicuous, particularly in medium-grained sheet-flood sandstones (up to 2.7 vol%). 

Illite is a minor diagenetic constituent occurring as fibres closely associated with chloritized pseudomatrix and infiltrated coatings. The presence of honeycombed mixed-layer illite/smectite (I/S) might indicate that illitization occurred via this intermediate stage. 

Although both cores display floodplain mudstones and sheet-flood sandstones, the Middle Lunde samples in 34/7-A-3H are dominated by fine- to medium-grained sheet-flood sandstones. The elevated initial porosity and permeability of these sandstones compared with the mudstones, siltstones and very fine to fine-grained sandstones has perhaps allowed larger amounts of mechanically infiltrated clays, which are preserved as smectitic coatings and/or transformed into chloritic or C/S and I/S rims in the sandstones. 

Authigenic clay minerals identified by SEM/EDS include minor amounts of kaolinite, chlorite, illite and mixed-layer illite/smectite, which form grain coatings, platelets or fibrous cements. 

Figure 8. Micro-XRF image of Pu sorbed onto manganese oxide coatings on smectite grains in Yucca Mountain tuff reacted with a Pu(V)-containing aqueous solution. Image was collected on the insertion device beam line 13- - at GSECARS (Advanced Photon Source), (after Duff et al. 1999a,b)...

Short-range-ordered or noncrystalline Al precipitation products are ubiquitous in soil environments (Parfitt, 1980 Kampf et al., 2000). They dominate the chemical reactions in soils because of their extremely small particle sizes and highly reactive surfaces. In pure form they are not stable, but in the presence of chelating anions they may remain unchanged indefinitely. Short-range-ordered Al precipitates and soluble OH-Al species often coat crystalline minerals in soils or may be interlayered into the interlamellar spaces of vermiculites or smectites, altering the surface properties of these phyllosificates. OH-Al interlayered vermiculites and smectites are particularly abundant in Ultisols and Alfisols (Bamhisel and Bertsch, 1989). 

Figure 1.11. Some effects of pedochemical weathering on phyllosilicate surfaces. Weathering produces interlayer hydroxy-polymers, interstratification, and external-surface organic and inorganic polymer coatings on smectite. On kaolinite, organic and iron oxide coatings are produced by weathering. After Jenne ...

Bentonite is a smectite clay, which has a lamellar stmcture. By adding water, the clay structure swells due to the adsorption of water molecules. The clay then becomes workable and can be spread to coat the sand grains during mixing. 

Chem. Descrip. Organophilic smectite CAS 53320-8 0 EINECS/ELINCS 250476-2 Uses Clay for use in paints/coatings, adhesives, caulks, sealants, agriculture, inks, paper, cosmetics, personal care, refractory, foundry, rubber, waste treatment, greases, gelcoats, oil field, household care, laminates, unsat. polyesters... 

Chem. Descrip. Smectite CAS 53320-86-8 EINECS/ELINCS 258-476-2 Uses Thixotrope, thickener for latex emulsion systems incl. coatings, sealants, and adhesives emulsion stabilizer for cosmetics and pharmaceuticals... 

PEG-5M PEG-7M PEG-9M PEG-23M PEG-45M PEG-12 ricinoleate PEG-2 stearate PVM/MA copolymer Smectite thickener, paper coatings Hydroxyethylcellulose thickener, paper finishes Beeswax, synthetic thickener, paper sizing Xanthan gum thickener, papermaking PEG-14M... 

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