Silica Aerosil

It was prepared by incipient wetness impregnation using Co(N03)2, 6H20, 99.9%, as cobalt precursor. Silica Aerosil 380 was purchased from Degussa. The sample was then dried at 573 K (300°C) and subsequently calcined at 773 K (500°C) under synthetic air. The quantity of cobalt introduced was 2wt.%. 

The pyrogenic flame hydrolyzed silica Aerosil 200, a commercial product from Degussa, was used as a dispersion in doubly distilled water (1). The precipitated silica was prepared by hydrolysis of orthosilicic acid tetraethylester in ammoniacal solution according to the method of Stober, Fink and Bohn (11). The prepared suspension was purified by repeated centrifugation, separation from solvent and redispersion of the sediment in fresh water. Finally, the water was evaporated and the wet silica dried at 150°C for about half an hour. 

Table 11.2 Characteristics of silica Aerosil 200 as a function of the dehydration temperature [56]. ...

Figure 1 shows the crystallization kinetics of ZSM-48. A good agreement is shown between the crystallinity evaluated by X-ray and adsorption of n-hexane. These kinetic curves confirm the metastability of ZSM-48 zeolite. Indeed the conversion of ZSM-48 into cristobalite, a dense and stable phase, occurs for long reaction times. The difference between the two curves at start reaction times is due to the presence of hydrated silica (Aerosil) that also adsorbs n-hexane. 

In the samples 5 and 6 the source of Si and Al is different and respectively Silica Aerosil (Serva) and Aluminium hydroxide (Serva)... 

In chemical modifications of inorganic particles, the adsorbed water sometimes affects the reaction of the hydroxyl group with the modifier. According to Fripiat et al. (6), evacuation at 200°C and 10-7 mmHg for 24 h still leaves about 0.2 mmol/ g adsorbed water on silica (Aerosil 200). 

Hamann et al. (11) have prepared phenylazo-bound silica via four-step reactions from the starting silica (Aerosil 200) and carried out the polymerizations of styrene, methyl methacrylate, acrylamide, acrylonitrile, acrylic acid, and 4-vinylpyri-... 

If the number of polar sites on a hydrophobic surface is increased, at some point, a solid of profoundly different surface characteristics should emerge. The nonporous silica, Aerosil, with 75 % of its surface made up of... 

The silica Aerosil was from Degussa. Silica platelets for spectroscopic use were preheated in air at 800° C, as described elsewheer (16). The hydrogen and deuterium gases were from J. T. Baker. The purity was 99.95% and 99.50%, respectively. The gases were dried carefully before use. 

Figure 9.9 Left BET adsorption isotherms plotted as total number of moles adsorbed, n, divided by the number of moles in a complete monolayer, ri7non, versus the partial pressure, P, divided by the equilibrium vapor pressure, Po. Isotherms were calculated for different values of the parameter C. Right Adsorption isotherms of water on a sample of alumina (Baikowski CR 1) and silica (Aerosil 200) at 20°C (P0 = 2.7 kPa, redrawn from Ref. [379]). The BET curves were plotted using Eq. (9.37) with C = 28 (alumina) and C = 11 (silica). To convert from n/nmo to thickness, the factors 0.194 nm and 0.104 nm were used, which correspond to n-mon = 6.5 and 3.6 water molecules per nm2, respectively.

We have tried to specify the influence of different physico-chemical parameters upon the electrophoretic mobility, using model particles such as silica (Aerosil 380 - Degussa) which is characterized by a charge very close to that of natural suspended sediment from Loire and Gironde. 

Silica powder samples were as follows (a) pyrogenic amorphous silica Aerosil 50 (A50, Degussa) (b) tridymite (Tri), a kind gift of Dr. Stober (C.I.I.T.,... 

Synthesis mixtures prepared using amorphous silica (Aerosil 200, Degussa), 25% aq. TMAOH, aqueous solution of hydroxide and bromide of hexadeciltrimethylammonium. Source of Ti was TEOT. Gels with following molar compositions were prepared Si/Ti — 60, (CTMA)20 TMA2. 

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. 

Figure 3.9 FTIR and FTFIR skeletal spectra of amorphous silica (aerosil), a-quartz, silicalite-1 and kaolinite.

Figure 3.21 FTIR spectra of amorphous silica (Aerosil from Degussa), silica-alumina (Strem, AI2O3 13%), and H-MFI zeolite (Zeolyst, Si/AI = 25) after activation (full lines) and after contact with CO gas at 140 K (broken lines).

Figure 6.40 Storage modulus ver-sus frequency for suspension of fumed silica (Aerosil R972 surface area = 108 m /g aggregate size 200 nm) at a concentration of = 0.085 in PDMS Mw = 118,000). The modulus for the unfilled PDMS is also shown, as is the modulus for the suspension treated in two differ-ent ways (MSI, MS2) to remove the active silanol groups from the silica particle surface. (From Aranguren et al. 1992, with permission from the Journal of Rheology.)...

Colloidal silica (Aerosil , Cabosil ) Glidant 0.1-0.2 Excellent glidant... 

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