Silica particles migrate

These findings support the view that during the reaction ions are extracted from the surface of the glass particles, migrate to the aqueous phase where they form the matrix, and leave a silica gel relict. This explains why the glass particles appear to be unattacked when examined under the microscope. The presence of both A1 and P in the cementing matrix and the... 

The latest innovation is the introduction of ultra-thin silica layers. These layers are only 10 xm thick (compared to 200-250 pm in conventional plates) and are not based on granular adsorbents but consist of monolithic silica. Ultra-thin layer chromatography (UTLC) plates offer a unique combination of short migration distances, fast development times and extremely low solvent consumption. The absence of silica particles allows UTLC silica gel layers to be manufactured without any sort of binders, that are normally needed to stabilise silica particles at the glass support surface. UTLC plates will significantly reduce analysis time, solvent consumption and increase sensitivity in both qualitative and quantitative applications (Table 4.35). Miniaturised planar chromatography will rival other microanalytical techniques. 

Fine particle migration can occur in the absence of water-swelling clays. Migrating fines can include the migrating clays kaolinite, illite, chlorite, and some mixed layer clays and fine silica particles (162,163). Fine particle migration is promoted when the... 

Source of Silica. Silica can migrate either from free silica present in the cracking catalyst or from the silica alumina matrix but not as readily from the zeolite. Figure 11 shows SEM-EDAX silicon scans of cerium/alumina steamed in the presence of these three sources of silica. Again, the bright dots represent silicon. Qualitatively the sample steamed with pure silica contains more silicon than the sample steamed with silica-alumina. The sample steamed with zeolite shows silicon at the surface of the cross-sectioned particle but little in the interior. The surface silicon comes from dusting of the particle with very finely divided zeolite. 

Two more recent applications for amorphous silicas are expected to grow to large volumes. Precipitated silicas are used in the manufacture of separator sheets placed between cells in automotive batteries. Their function is to provide a controlled path for the migration of conductive ions as a result of the porosity of the silica particles. Additionally, both precipitated silicas and aerogels are being developed for use in low temperature insulation, where the low thermal conductivity of the dry silica powders makes them useful in consumer products such as refrigerators (83). 

Figure 15 Plots of the migration time of the EOF marker against the dimensionless length of the separating column, X. The conditions were 8 cm of separating column with varying lengths of (solid) open tubular or (dash) auxiliary columns packed with silica particles, pore size 300 A applied voltage, 10 kV. Eluent, (a) 2 mM, (b) 5 mM, (c) 10 mM Na-phosphate buffer, pH 7.0, in 7 3 ACN water. (Reprinted with permission from Ref. 77, copyright 2001, Wiley.)...

In the case of the VPO catalyst for the butane oxidation process and the MCM catalyst for the acrylonitrile process, the preferred precursor of the peripheral hard phase is polysilicic acid (PSA). The term "polysilicic acid" is generally reserved for those "silicic acids that have been formed and partially polymerized in the pH range 1-4 and consist of ultimate silica particles generally smaller than 3-4 nm diameter" (4). Small, discrete particles of colloidal silica also migrate to the periphery of the droplet, but they do not coalesce as extensively as PSA in drying. The larger the particle size, the lower the mechanical strength of the coalesced dry product. 

Evidence for particle migration of Pt on oxide supports is provided by three relatively recent studies." And and coworkers used in situ TEM to examine the sintering in vacuum of Pt on model alumina, silica, and carbon. They observed that at temperatures of 873 to 1023... 

The migration of energy between phases will also have an effect in the radiolysis of mixed polymeric systems not associated with transuranic waste. For instance, the radiolysis of polymers attached to silica particles or the radiolysis of rubber in steel belted tires will probably be affected by energy deposited in the non-organic phase. Energy migration to the polymeric phase may lead to the need for lower overall doses than initially anticipated for a... 

Reduction of surface unity All defoamers could be said to operate by disrupting the surface layer. Some defoamer chemistries are made of particles that migrate to the bubble surface and disrupt the regular packing of molecules at the water/ air interface. Some particles may absorb surfactant molecules onto their surface. This reduces the surface cohesion. Examples are hydrophobic silica particles, EBS particles, or silicone particles. 

Principle A glass column is packed with silica particles. A mobile phase is prepared that has the same refractive index as the silica particles. The migration of a dye through the invisible bed is observed. Defects in the bed are easily observed. 

When the removal of alkali metal ions is carried out by electrodialysis in any step of the process, it is essential that the sol-electrolyte contain an alkali metal salt of a nonsilic-eous anion to function as a supplementary elctrolyte, as is disclosed in U.S. Pat. No. 3,668,088 referred to herein above. The purpose of the supplementary electrolyte is to lower the electrical resistance of the sol-electrolyte by providing anions other than silicate and hydroxyl ions to carry the current toward the anode. In the absence of supplementary electrolyte, the current is carried by hydroxyl ions and silicate ions which are present only at very low concentrations in the pH range 8-9.5. Furthermore, when the current is carried by silicate ions, these ions migrate towards the anode and deposit sihca upon the membrane, thus further increasing the resistance and even-tuaUy terminating the process. There is an upper limit to the amount of supplementary electrolyte that can be present. If more than about 0.1 normal sodium salt such as sodium sulfate is present, the colloidal silica particles in the mixture tend to aggregate, even at the preferred pH of 9. 

Polyethylene sheets are widely used in automobile batteries to separate the individual electrochemical cells. The polyethylene is highly filled with porous silica particles to provide a path for the migration of conductive ions. This has become a major market for precipitated silicas because the filler loading can be as high as 70%. 

PA 6/ABS blends, the phase inversion was observed to shift towards higher ABS content due to increase in the viscosity ratio of ABS/PA 6 resulting from migration of silica particles from PA 6/ABS interface to ABS phase at higher ABS compositions in the blend (Liu et al. 2013). 

The properties of rubber-rubber blend composites depend on the size and shape and concentration of nano particles and their interactions with the individual mbber matrix. The interaction between the filler and the matrix are improved by surface modification. In the mbber industry the uniform distribution of nano particles is considered to be important as it affects the mechanical properties and performance of the composite. For mbber-mbber blend composites fillers like carbon black prefer to migrate to less polar, less viscous mbber phase whereas silica and clay particles migrate to more polar mbber phase. CNTs mainly reside in the highly polar and non-polar mbbers but not in weakly polar ones. The Tg remain unaltered for a completely incompatible blend. In the case of partially compatible blends, the Tgs of the blend components are expected to shift towards each other as compared with the pure components. Shifting of Tg of polymers to lower or higher values in a blend depends on the polarity difference and the difference in the thermal expansion coefficient of the respective polymers in the blend. 

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