Fumed silica/alumina

Figure 9. Surface content of (a) A1 in fumed silica/alumina and (b) Ti in titania/silica and the maximum adsorption of (a) Pb(II) and (b) Ni(II) as a function of the total (a) alumina or (b) titania content in mixed oxides.

Keywords fumed silica alumina/silica, titania/silica alumina/silica/titania Ni(II) Cd(II) Pb(II) polyethylene glycol) poly(vinyl alcohol) adsorption potentiometric titration surface charge density... 

In interpenetrating polymer networks, chemical crosslinking and phase separation and their timing affect properties. Fumed silica, alumina, and carbon fiber were used in a network developed Ifom polyurethane and polycslcracrylalc. The presence of fillers affected many properties. Conversion rates were higher in the presence of fillers. Also, microphase separation was affected. As a result of these two changes the filled material was unrecognizable from the unfilled material. 

FIGURE 37.1 OPTPD spectra of water desorbed from (a) fumed silica A-300 and fumed titania (b) fumed silica/titania and CVD-Ti02/fumed Si02 and (c) fumed silica/alumina re-hydration (R) time is 0.5 h. 

FIGURE 2.46 Surface content of (a) A1 in fumed silica/alumina and (b) Ti in titania/silica and the plateau adsorption (A) of (a) Pb(II) and (b) Ni(II) as a function of the total (a) alumina and (b) titania content in mixed nanooxides. (Adapted bom Appl. Surf. Sci., 253, Gun ko, V.M., Nychiporuk, Yu.M., Zarko, V.I. et ah, Relationships between surface compositions and properties of surfaces of mixed fumed oxides, 3215-3230, 2007b, Copyright 2007, with permission from Elsevier.)... 

The observation of individual AST particles with the hydrodynamic diameter of 10-20 nm (Figure 2.56), i.e., smaller than the average geometrical diameter of primary particles, is untypical for the aqueous suspensions of fumed silica, alumina, titania, or binary oxides (Gun ko et al. 2001e). This result can be caused by a very broad size distribution of primary particles of AST (broad primary particle size distribution is characteristic for nanooxides with a low specific surface area [vide supra Degussa 1997]). Therefore, one can assume that primary AST particles of strongly different sizes are characterized by different contributions of titania, alumina, and silica, since they can be formed in different zones of the flame during the synthesis. 

The above methods for obtaining D, as well as other ones, are reviewed in Refs. 3-12, and Refs. 7-9 give tables of D values for various adsorbents. For example, D is close to 3 for the highly porous silica gels and close to 2 for nonporous fumed silica and for graphitized carbon black coconut charcoal and alumina were found to have D values of 2.67 and 2.79, respectively [7]. 

All of the eommereial alkyl eyanoaerylate monomers are low-viseosity liquids, and for some applications this can be an advantage. However, there are instances where a viseous liquid or a gel adhesive would be preferred, sueh as for application to a vertical surface or on porous substrates. A variety of viscosity control agents, depending upon the desired properties, have been added to increase the viscosity of instant adhesives [21]. The materials, which have been utilized, include polymethyl methacrylate, hydrophobic silica, hydrophobic alumina, treated quartz, polyethyl cyanoacrylate, cellulose esters, polycarbonates, and carbon black. For example, the addition of 5-10% of amorphous, non-crystalline, fumed silica to ethyl cyanoacrylate changes the monomer viscosity from a 2-cps liquid to a gelled material [22]. Because of the sensitivity of cyanoacrylate esters to basic materials, some additives require treatment with an acid to prevent premature gelation of the product. 

These processes are very rapid and allow the preparation of inorganic supports in one step. This technique allows large-scale manufacturing of supports such as titania, fumed silica, and aluminas. Sometimes the properties of the material differ from the conventional preparation routes and make this approach unique. Multicomponent systems can be also prepared, either by multimetallic solutions or by using a two-nozzle system fed with monometallic solutions [22]. The as-prepared powder can be directly deposited onto substrates, and the process is termed combustion chemical vapor deposition [23]. 

Silica is the support of choice for catalysts used in processes operated at relatively low temperatures (below about 300 °C), such as hydrogenations, polymerizations or some oxidations. Its properties, such as pore size, particle size and surface area are easy to adjust to meet the specific requirements of particular applications. Compared with alumina, silica possesses lower thermal stability, and its propensity to form volatile hydroxides in steam at elevated temperatures also limits its applicability as a support. Most silica supports are made by one of two different preparation routes sol-gel precipitation to produce silica xerogels and flame hydrolysis to give so-called fumed silica. 

A number of reagents containing oxide components are used in zeolite manufacture [19]. Silica is provided by addihon of sodium or other alkali silicate solutions, precipitated, colloidal, or fumed silica, or tetraalkylorthosihcate (alkyl = methyl, ethyl) and certain mineral silicates such as clays and kaolin. Alumina is provided as sodium aluminate, aluminum sulfate soluhon, hydrous aluminum oxides such as pseudo boehmite, aluminum nitrate, or aluminum alkoxides. Additional alkali is added as hydroxide or as halide salts, while organic amines and/or... 

Nanooxides such as fumed silica, titania, alumina, etc. (with spherical primary nanoparticles) are used as fillers for complex drugs, enterosorbents, vaccine adjuvants, food additives, etc.1,2 In general nonporous spherical nanoparticles can adsorb solutes in low amounts because the desolvation effect causes an... 

Abrasive particles are a key component in CMP slurry. The most commonly used abrasive particles include silica, alumina, ceria, zirconia, titania, and diamond. Table 21.1 listed a set of information on each type of abrasive particles such as density, microhardness, and isoelectric points (lEP). It is important to point out that the specific values for these properties depend highly on the preparation techniques and the specific states of the samples. The values listed in the table represent an average of the most commonly reported data. For example, the isoelectric point for silica is a function of the number of hydroxyl groups, type and level of adsorbed species, metal impurity in the solid matrix, and the treatment history of the materials [1]. There are three major types of silica according to their preparation methods fumed, colloidal, and precipitated. The common sources for obtaining these abrasive particles are listed in Table 21.2. As examples, some of the more specific information on... 

The purpose of this study was to explore the interaction between slurry particles and wafer surfaces by the measurements of their zeta potentials. The zeta potentials of slurry particles such as fumed and colloidal silica, alumina, ceria and MnOj and substrates such as silicon, TEGS, W, and A1 have been measured by electrophoretic and electroosmosis method to evaluate the electrical properties of surfaces, respectively. The zeta potential of oxide and metal surfaces showed similar values to those of particles as a function of pH. The interaction energy between alumina and silica particles and TEOS, W and A1 substrate were calculated based on DLVO theory. No deposition of silica particles on TEOS and the heavy deposition of alumina particles on metal substrates were observed in the particle deposition test. Experimental results were well agreed with the theoretical calculation. 

The zeta potential of slurry particles was measured as shown in Figure 1. Fumed silica showed a higher isoelectric point (lEP) at which the net charge and electrophoretic mobility is zero, than that of colloidal silica as shown in Figure 1 (a). Also zeta potentials of colloidal silica were around 20mV lower than that of fumed silica. Figure 1 (b) shows the zeta potentials of alumina, ceria and Mn02 particles. Due to their lower hardness than alumina, ceria has been... 

The macroscopic properties of liquid suspensions of fumed powders of silica, alumina etc. are not only affected by the size and structure of primary particles and aggregates, which are determined by the particle synthesis, but as well by the size and structure of agglomerates or mesoscopic clusters, which are determined by the particle-particle interactions, hence by a variety of product- and process-specific factors like the suspending medium, solutes, the solid concentration, or the employed mechanical stress. However, it is still unclear how these secondary and tertiary particle structures can be adequately characterized, and we are a long way from calculating product properties from them [1,2]. 

Figure 8.66. Internal shrinkage stress vs. interpenetrating netu ork formation time for PU/PEA=10/90 network. (1) unfilled network, (2) alumina-filled, (3) fumed silica-filled. [Data from Sergeeva L M, Skiba S I,...

Reactants used were reagent grade lithium carbonate, lithium hydroxide, and sodium hydroxide, aluminum hydroxide (Grades C-31, C-730, Hydral 705, and 710 ALCOA), precipitated silicic acid (Fisher Scientific), and ammonium-stabilized aqueous colloidal silica sol (Ludox "AS, DuPont). Other reactants, which were used and found unsatisfactory to produce mordenite as a phase under the experimental conditions investigated, were fumed silica, silica gel, silica-alumina gels, diatomite, and sodium aluminate. 

In many cases, highly filled paste adhesives are inherently thixotropic due to the inorganic fillers used such as alumina, sihca, other metal oxides, or metals. However, small amounts (1-5%) of thixotropic agents can be added to further control the flow properties. A popular and widely used thixotropic agent is fumed silica, also known as... 

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