Clay coatings Formation

The difficulties imposed by clay coatings on quartz nucleation probably explain why there are few reports of quartz cementation in shales. The oxygen in quartz silt is isotopically heavy (8 0 = 19%o) compared to sand-size quartz (5 0 = 14%o) (Blatt, 1987) suggesting that a substantial component of relatively low-temperature quartz resides in shales. The application of cathodoluminescence microscopy to shales has been quite limited. In Frio Formation shales of south Texas no convincing quartz cement is observed across a range of depths in which quartz cementation becomes important in associated... 

Hindrances to precipitation of quartz and hence inclusion formation is represented by clay coatings on minerals (cf. Tada Siever 1989 Nedkvitne et al. 1993 Ehrenberg et al. 1995 Storvoll 1999 Storvoll et al. 2002) and also extreme organic coatings (cf. Skalnes 1993 Storvoll 1999 Storvoll et al. 2002). In such extreme cases precipitation of quartz is clearly kinetically hindered due to a lack of nucleation sites (cf. Bjorkum 1996) and inclusion formation rate is reduced or halted. When quartz grains are more or less totally covered in asphaltenes, as in some of the sediment surfaces in the Hild Field discussed by Skalnes (1993), is it also likely that the pressure solution of quartz is kinetically hindered. 

Adsorption of Metal Ions and Ligands. The sohd—solution interface is of greatest importance in regulating the concentration of aquatic solutes and pollutants. Suspended inorganic and organic particles and biomass, sediments, soils, and minerals, eg, in aquifers and infiltration systems, act as adsorbents. The reactions occurring at interfaces can be described with the help of surface-chemical theories (surface complex formation) (25). The adsorption of polar substances, eg, metal cations, M, anions. A, and weak acids, HA, on hydrous oxide, clay, or organically coated surfaces may be described in terms of surface-coordination reactions ... 

Sometimes it may become necessary to shut-in a gas well when the demand for gas is low. In such instances, the well is shut-in for an indefinite period, after which it is reopened and production is resumed. It often has been found that the production rate of gas from the reopened well is substantially less than it was before the well was shut-in. During production, the inner wall of the production tubing will be coated with a film of condensed freshwater because of the geothermal gradient. This water flows down when production is interrupted and can cause formation damage. This may occur because clays are normally saturated with brine water and not with freshwater. This swelling can be prevented with the injection of some additive, for example, sodium chloride, potassium chloride, calcium chloride, or an alcohol or a similar organic material [1853]. 

Metal oxides have a significant role in influencing physical, chemical, and biological properties of soils. They may exist as ciystalline minerals, as short-range ordered (SRO) mineral colloids, or as surface coatings on clay minerals and organic matter. Organic compounds influence the formation, transformation, and surface properties of these metal oxides. The SRO A1... 

Fig. 2 shows how the aminoday -metal nanoparticle composites form clear transparent solutions in water. The solutions are pink and yellow for Au and Ag respectively and dark brown in the cases of both Pt and Pd. The reddish-brown colour observed for Au-clay nanoparticle composites immediately after the addition of NaBH4 changed to pink with time. The solutions exhibit characteristic piasmon bands for the Au- and Ag-day suspensions at 520 nm and 410 nm respectively as shown in Fig. 3. In the cases of Pt and Pd, the characteristic absorption band for the precursor s around 260 to 280 nm was absent thereby confirming the formation of Pt and Pd nanoparticles. 7,18 TEM images of the aminoday-metal nanoparticle composites deposited on a carbon coated copper grid are shown in Fig. 4. The histograms show the average particle sizes to be around 3.5 and 5 nm respectively in the cases of Au and Ag nanoparticles. We could see the layered arrangements in the cases of Pt and Pd with the interspacing of 1.5 nm commensurate with the bilayer arrangement of aminoclays (see top right inset of Fig. 4b).

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