Silica-like layer

RPECVD technique could be used with success to coat stainless-steel plates in a uniform way by a silica-like layer which is expected to protect the active phases from poisoning. After a proper treatment to enhance its wettability, this layer serves also as a carrier to Ti02-anatase, which is required to enhance the catalytic properties of the active polyvanadate phase. The optimised procedure could be appUed to cover stainless-steel foams for the first time. The catalytic properties of both plates and foams in the oxidative dehydrogenation of propane in specially designed reactors is in progress. 

A significant number of papers take advantage of the fact that oxidation of PDMS (either by exposure to UV-ozone or to oxygen plasma) can create a stiff silica-like material [17, 40, 43], During the oxidation process, up to 50% of PDMS in the topmost layer is converted into silica [40], Oxygen plasma treatment was first applied by B owden and coworkers [ 16] to create such a surface layer and use a thermal shrinkage process to create wrinkles. They found patterns with wavelengths between fractions of a micron and 10 p.m. They also reported the appearance of cracks which arise due to the brittle nature of the silica material. 

In order to explain the interactions between silica surfaces, the polarization model is adapted to poorly-organized surfaces. To account for the disorder induced in water by the rough surfaces of silica, the dipole correlation length Am, which is the main parameter of the polarization model, is allowed to decrease from Am=14.9A obtained for water perfectly organized in ice-like layers in the vicinity of a surface to smaller values. For Am=4A, good agreement with experiment is obtained for reasonable values of the parameters involved (such as surface dipole and charge densities) [7.9],... 

The optimal concentrations were determined at which iron and silica sediments separate rapidly from a mixed sol as it coagulates, forming banded jaspilite-like layers. In these experiments, differential deposition of iron... 

Layered silica clays are recognized for their ability to form a variety of pillared intercalated derivatives with properties for occluding organic compounds and metal complexes, including organometallic clusters (158). These materials consist of positive charged Mg(OH)2-like layers separated by hydrated gallery anions. 

The alumina layer, in which the aluminium ions are in octahedral positions, is sandwiched between two silica layers with the tetrahedral silicon ions partly replaced by aluminium ions, giving a net negative charge to the 2 1 layers. Since these systems contain both mica-like (non-watersweliable) and montmorilIonite-like layers, they have been called synthetic mica montmori1Ionite, SMM (M. After deammoniation the resulting proton gives SMM its acidic properties ... 

A polymer called latex , prepared from a monomer that contains organic groups, is deposited as an array of tiny beads (0.1-0.2 ptm in diameter) on an waterproof support to form a continuous film-like layer about 1-2 gum thickness. The support is made of micro-spheres of silica or glass or polystyrene of about 25 gum diameter (Figure 4.6) This gives rapid equilibriums between stationary and mobile phases. 

Example 5.4 The clay minerals are composed [46, 89] of sheets of tetrahedrally coordinated silica and sheets of octahedrally coordinated alumina or magnesia. These sheets occur stacked upon one another forming plate-like layers or particles. Montmorillonite, for example, clay occurs as relatively broad, thin platelets, typically about 0.3 pm across and about 2 nm thick. When dispersed in aqueous solutions of near-neutral pH to alkaline pH, the particles carry a net negative... 

Opium alkaloids are most commonly estimated by separating them on a chromatographic paper (PC) and/or on a thin layer chromatographic plate (TLC). The former needs a longer time for developing spots than on the silica gel layers of TLC. After the separation of different opium alkaloids with different mobile phase systems of PC and TLC, individual alkaloids are quantitatively measured by eluting the spot and using different procedures, like spot area measurement, spectrophotometry, IR spectroscopy, densitometry, etc. Important methods are described below ... 

Befahy, S. Lipnik, P. Pardoen, T. Nascimento, C. Patris, B. Bertrand, P. Yunus, S., Thickness and Elastic Modulus of Plasma Treated PDMS Silica-Like Surface Layer. Langmuir 2010, 26, 3372-3375. 

The most extremum behavior of all the characteristics is observed at low content of cells in the suspension (Figure 7.11). A minimum of Ys and C and a maximum of CZ are at Ch o = 98.4 wt% or Cy=C<-eii+Cicw=6.1 wt%. Notice that there is the extreme dependence of the Ys value on the total concentration of water in the aqueous suspensions of nanooxides (see Section 1.1.6) at a minimum at Chjo 93 wt%. This boundary concentration corresponds to transition from diluted suspensions to concentrated ones characterized by different particle-particle interactions. In the diluted suspensions, the systems can separate into a gel-like layer and upper layer with bulk, almost pure water. In the concentrated suspensions, the systems represent a continuous gel-like structure without separation of bulk water. With increasing size of particles, the critical concentration (CJ should increase. Therefore, one could expect a larger Q value for yeast S. cerevisiae cells (5-10 pm) than for nanosilica (primary particles 10 nm). However, the C<. values for yeast cells and nanosilica are relatively close due to the formation of silica nanoparticles aggregates 0.5-l pm and agglomerates >1 pm, which have sizes close to sizes of cells. Therefore, at Cy< 10 wt% (Cycolloidal dispersion with relatively weak intercell interactions. At these Cy values, the adhesion... 

Inverted raspberry-like morphologies (the mineral particles being located at the surface of the latex spheres) have also been discussed in Sections 4.4.2.2 and 4.4.2.4 about colloidal silica and layered silicates, respectively. These are mainly a consequence of the surfactant-like behavior of the inorganic particles in specific situations. This was clearly illustrated in a recent report by Landfester, who showed that silica or clays can be used as pickering stabilizers of miniemulsion jxjlymer-izations, resulting therefore in the formation of armored latexes, the surface of which was recovered by the small inorganic particles [99,131]. 

Dissolution is an equilibrium reaction. That is, the dissolution of the surface is accompanied by precipitation of the solute oxide species. Some authors argue that this results in transformation of the surface morphology. For instance. Vigil et al. (1994) proposed the formation of a gel-like layer on a silica surface, which results from re-precipitation of dissolved silica and that consists of polymeric -Si(0H)2-0-Si(0H)2-0H chains. The thickness of this layer is estimated with 10 A. A similar concept was stated by Adamczyk et al. (2004). 

The starting material K2Ti O, is nonporous, and has a fairly low BET surface area as 3.3 m /g. In contrast, the resulted silica-pillared layered titanate has a relatively high surface area of 45.9 m /g, indicating the existence of an appreciable intracrystal surface area. The M2 adsorption-desorption isotherm of the silica-pillared layered titanate is shown in Figure 3. The adsorption isotherm of the pillared sample is between type I and ZZ at low pressures[14]. This type of isotherm is characteristic of materials in which both micropores and mesopores are present. The hysteresis loop of the curve demonstrates that this material is porous. Moreover, the loop is somewhat like type H3 and H4 loops as classified by K.S.H. Sing, et al.[14]. This type of loop... 

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