Fumed silicas surface modification

Surface Sol-Gel Modification of Fumed Silica with Ti02/Al20s orAfO / T1O2 Double Layer. The basic procedure for functionalization of Cab-O-Sil silica... 

Fumed silica A-200 (Pilot plant at the Institute of Surface Chemistry, Kalush, Ukraine specific surface area Ascorbic acid (vitamin C) and all-rac-a-Tocopheryl acetate (vitamin E acetate) were used as adsorbates. Folin-Ciocalteu s phenol reagent (Merck) was used to measure the total polyphenolic index. Silica samples with different degree of surface silylation were obtained using gas-phase chemical modification of highly disperse silica (A-200) surface by trimethylchlorosilane.6... 

Fumed silica is always found to be amorphous, and therefore does not cause silicosis. The respective AI2O3 is crystalline and consists of the thermodynamically metastable S form instead of the stable a form. It can be transformed to the a-AI203 phase by heating to i200°C. This conversion is associated with a loss of surface area and an increase of hardness and abrasiveness. In the commercial Ti02 obtained by flame hydrolysis, the thermodynamically metastable modification anatase is the main phase, with about 30% rutile. The lattice transformation towards higher amounts of rutile becomes notable at temperatures above 700 °C. It is also associated with a decrease of... 

Primary aminoalkylsilanes are important compounds in application fields like adhesion promotion, surface modifying, and crosslinking, but are also used for endcapping of various substrates. Currently in focus is the recently developed endcapper (Fig. 1) which is the key molecule for the preparation of thermoplastic silicone elastomers (TPSE). Modification of silicone resins and fumed silica with 1 leads also to products with interesting economical potential. 

The amount of Si ions dissolution is found to be dependent on surface modification, which was confirmed by induchvely coupled plasma-atomic emission spectrometer (ICP-AES) analysis. Table 2.2 shows the dissolution amount of Si ions with and without surface modification of fumed silica slurry. Without surface modification, the amount of Si dissoluhon was 1.370 0.002 mol/L, whereas surfaces modified with poly(vinylpyrrolidone) (PVP) polymer yielded a dissoluhon of 0.070 0.001 mol/L, almost 20 hmes less than the unmodified surface. Figure 2.6 represents the electro-kinetic behavior of silica characterized by electrosonic amplitude (ESA) with and without surface modification. When PVP polymer modified the silica surface, d5mamic mobility of silica particles showed a reduchon from -9 to -7 mobility units (10 m /Vxs). Dynamic mobility of silica particles lacking this passivation layer shows that silica suspensions exhibit negative surface potentials at pH values above 3.5, and reach a maximum potential at pH 9.0. However, beyond pH 9.0, the electrokinetic potential decreases with an increasing suspension pH. This effect is attributed to a compression of the electrical double layer due to the dissolution of Si ions, which resulted in an increase of ionic silicate species in solution and the presence of alkali ionic species. When the silica surface was modified by... 

Surface modification was applied to hydrophilic fumed silica with a BET surface area of 300 mVg. Controlled surface coverage was realized using two different techniques. 

Chemical modification of the fiUer surface (transition from pure fumed silica to modified with dimethyl dichlorosilane) gives the same picture of the broadening of the relaxation spectra. These data allow for the conclusion that the conformational restrictions imposed by the solid surface, not the energetic interaction between alloy components and solid, play a m or role in the change of relaxation spectra. 

Disperse oxides unmodified or modified by organics (OC) or OSC are used as fillers, adsorbents, or additives [1-11]. OSCs are used as promoters of adhesion, inhibitors of corrosion, for the stabilization of monodisperse oxides and the formation of the nanoscaled particles. Oxide modification by alcohols or other OC is of interest for synthesis of polymer fillers, as such modification leads to plasticization and reinforcement of the filled coating, but in this case a question arises about hydrolyz-ability of the =M—O—C bonds between oxide surface and alkoxy groups, as those are less stable than =M—O— M= formed, for example, upon the silica modification by silanes or siloxanes. The high dispersity, high specific surface area, and high adsorption ability of fumed oxides have an influence on their efficiency as fillers of polymer systems. 

Modification of the cementitious binder with siiica fume The influences of silicafume in densification of the ITZ is well documented. The positive effect of the silica fume stems from its physical characteristics (where its small-sized particles can pack more readily at the surface of the reinforcing inclusion to diminish the wall effect as well as to reduce bleeding) and chemical nature which can promote pozzolanic reactions within the ITZ. Interfacial bond can be enhanced by 35% and more. 

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