Micas, formation mechanism

Recently, there has been progress in the preparation and formation mechanisms of the fetroelectric (P and/or y) phases. For example, the p and/or y phases coirld be epitaxially grown on surfaces of KBr, NaCl, or mica [145]. Electrospinning, using polar solvents, was demonstrated to be a facile route to prepare ferroelectric PVDF phases [146-148]. The ferroelectric phases could be readily induced by the incorporation of organically modified clays [149-154] and mirlti-walled CNTs [155,156] in the PVDF matrix. A nearly pine p phase was observed in electrospun PVDF composite fibers with nanoclays [157], magnetic nanoparticles [158], or even CNTs [159]. A mechanism based on the ion-dipole... 

The mechanism of mica formation from feldspars is not yet completely understood. Obviously, part of the illite produced by weathering of feldspar originates from the finegrained sericites developed by metamorphic processes during the late phases of rock formation (Muller [1966a]). By mechanical or chemical action, feldspars are dispersed, and the included sericites released. Illites formed by this process are, thus, detrital in character. On the other hand, two mechanisms of pedogenic formation of mica from feldspar are discussed. 

While Pb is typically not a useful choice for device top contacts because of its low melting point and soft mechanical characteristics, it is of considerable interest for its superconducting characteristics. There appear to be, however, no reports on Pb deposition on SAMs. In our own preliminary experiments of Pb deposition on Cl6 alkanethiolate SAM on Au/mica from UHV AFM imaging, we observed complete penetration with no top surface cluster formation and continuing penetration into the underlying Au lattice. ... 

Although many soil scientists had considered the possible mechanisms which soils employ for the retention [fixation] of phosphorus, it remained for Haseman et al. (1950) to demonstrate that phosphorus could — and in experimental situations did — replace the silicon of micas and clay minerals in order to form crystalline hydrous aluminium phosphates of sodium, ammonium and potassium. Prior to experimentation by this group, associated with the laboratories of the Tennessee Valley Authority (TVA), most authors attributed the retention of phosphorus by soils to combination with calcium to produce fairly insoluble minerals to adsorptive, exchangeable combination with silicate minerals and to formation of phosphates of iron... 

Despite the unlikelihood of secondary mineral formation by ion substitution into or movement within an existing solid, some secondary 2 1 layer silicates apparently are formed by solid-phase changes of mica fragments inherited from the parent material. Hydrous mica, for example, is a product of chemical weathering as well as mechanical breakdown of mica. Hydrous mica, in turn, can be modified directly to vermiculite, montmorillonite, or chlorite. The process is not completely understood, but seemingly involves the outward diffusion of K+ from between the layer lattices and a subsequent or simultaneous reduction of charge within the layer lattice. 

Kaolinite, on the other hand, has no structural counterpart among the igneous minerals. It is also the most widespread of the crystalline clay mineral. The most likely mechanism for kaolinite formation is the complete breakdown of feldspar or mica particles and the precipitation of kaolinite from Al(OH)3 and Si(OH)4 from the soil solution or from amorphous, less stable intermediates. 

The effects of composite formation are not only restricted to the improvement of mechanical properties, such as toughness, tensile strength, and many other, but also include, improvement of thermal and electric conductivities (carbon black, pol yrrole), reduction of water migration (platelet fillers such as talc and mica), improvement fire resistance (alumina trihydrate), improvement of quality (wood-like feel with wood filler), and decorative value. 

In Section 3.2.2, data were presented which show that char formation, possibly from a catalytic reaction between the polymer (PS, PA6, or a polymer compati-bilizer, PP-g-MA) and the clay, is often present when low peak HRRs (or mass loss rates) are observed. However, data were also presented which show that in the absence of any substantial charring there can still be a 50 to 60% reduction in peak HRRs if synthetic mica is used in PP/PP-g-MA nanocomposites. It appears that at least two mechanisms may be important to the function of nanocomposites one involving char formation and a second involving the inorganic residue alone. This dual mechanism may explain why the effectiveness of clay nanocomposites varies from polymer to polymer. 

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