Colloidal silica types

Figure 6.2. (a). Colloidal silica network on the surface of spores from Isoetes pantii (quill wort). Scale = 20 pm. (b). Polystyrene networks and foams produced as a biproduct of colloidal latex formation. Both types of colloidal system are typical of the diversity of patterns that can be derived from the interactions of minute particles. Scale (in (a)) = 50pm. 

Syntheses were run in modified Morey-type autoclaves of 15-ml capacity at autogenous pressure. For mordenite synthesis, the reactants were mixed in a mortar and pestle into a homogeneous mix and loaded into the autoclaves. For zeolite A and X synthesis, separate sodium aluminate solutions and colloidal silica sols were prepared and mixed in the autoclaves. 

The largest area of ignorance and therefore the most promising field far investigation lies in nucleation. Breck s synthesis required SiC>2 in die form of colloidal silica sol to make silica-rich type Y. We have since learned to seed the batch with a freshly prepared slurry (18), and use cheaper silica sources. But we are far from a chemical definition of the nucleating agent... 

Ceramic Ablators, Several types of subliming or melting ceramic ablators have been used or considered tor use in dielectric applications particulady with quartz or boron nitride [10043-11-5] fiber reinforcements to form a nonconductive char. Fused silica is available in both nonporous (optically transparent) and porous (slip cast) forms. Ford Aerospace manufactures a 3D silica- fiber-reinfo reed composite densified with colloidal silica (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see Composite materials, ceramic matrix). 

In emulsions, amine hydrochloride constitutes the aqueous phase and acrylic ester the organic phase. Cetyltrimethylanunonium bromide (CTAB) or span/twin (S/T)-type surfactants are used for emulsion polymerization. Solid dispersants such as talc and colloidal silica are often used to stabilize emulsions which are difficult to stabilize with usual surfactants. HydrophiUc colloidal silica (Aerosil 200) drastically increases the stability of some emulsions provided high amounts (up to 10%) of Aerosil are used. Random copolymers containing 10% hydroxyl groups can be used as polymeric dispersants for preparing w/o emulsions. 

The scratching mechanism described above is very typical for oxide CMP. In order to minimize the scratching level, slurry manufacturers have explored various abrasive types and formulations. Using ultrahigh-quality colloidal silica with the right combination of chemical additives, it is possible to produce scratch-free slurries. With such a slurry, the dilute HF has no effect on the scratch count as shown in Fig. 17.7. 

In the case of terrestrial effusions, when acid volcanic waters mixed with surface river waters and especially with sea waters in the near-shore zones, the pH value gradually increased due to dilution and neutralization and approached the equilibrium value, controlled by carbonate-silicate buffer reactions (pH within 6-8 depending on the type of buffer). As a result, colloidal silica already had begun to coagulate in the near-shore zones, and clots were deposited along with clastic components or were carried on by currents. However, maximum chemogenic deposition began some distance... 

Section 1 considers the methods of synthesis and physico-chemical properties of new types of inorganic sorbents (complex carbon-mineral sorbents, co-precipitated hydroxides, functional polysiloxane sorbents, porous glasses with controlled porosity, colloidal silicas, aluminium oxyhydroxide colloids, apatites). These sorbents are widely used in scientific investigations, in chemical practice and are important from a technological point of view. The presented results provide additional possibilities for the preparation of inorganic sorbents possessing unique adsorption and catalytic properties. Moreover, Section 1 presents the possibilities of the computational studies on the design of synthetic materials for selective adsorption of different substances. 

Si NMR Spectroscopy of Colloidal Silica. 29Si NMR spectroscopy has been used extensively to study aqueous solutions of silicates and has provided detailed information on the types of polymeric species in solution (3-5). However, despite the power of the technique it has not been exploited previously to investigate colloidal silica. The usefulness of the technique arises from the successive shift of the 29Si resonance to high field on replacement of Si-OH bonds in silicate species with siloxy bonds, Si-O-Si. Thus monomeric species are observed furthest downfield (Q°) and other resonances are observed at intervals of —10 ppm for end units (Q1), middle units (Q2), branching units (Q3), and tetrafunctional units (Q4). (Q refers to four possible coordination bonds the superscript refers to the actual number.) From the relative intensities of the different... 

Inorganic-organic composition uses are similar to coatings uses except that no substrate is involved. A variety of mixtures can be used in which the colloidal silica is added to impart strength. An example of this type of system was disclosed by Asahi Glass Company, Ltd. (35) colloidal silica was added to isophorone diisocyanate and a pentaerythritol triacetate-tetraacetate mixture to produce a material for a polycarbonate plate. 

Zeolite P-B (B or P Structure Type). Zeolite P-B was crystallized from coprecipitated gels using NaOH solution as the titrant and Ludox colloidal silica sol. The gel was crystallized at 150°-200°C for 45-72 hours. Phosphorus contents up to 23 wt % P203 were achieved in P-B zeolites. 

The hydrolysis of (EtO)4Si (and the subsequent polycondensation of Si-OH containing molecules) has been the subject of considerable investigation because of its importance in the fabrication of glasses and colloidal silica via the sol-gel process see Sol-Gel Synthesis of Solids). Hydrolysis of the Si-0 bond in alkoxysilanes is also very widely used to attach silicon compounds to surfaces and in coupling reactions. The fundamental reaction types involved in the formation of polymeric silica materials (via, for example, cyclic oligomers similar to those shown in Figures 4 and 5) from monomeric (RO)4Si compounds are shown in Scheme 43. 

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