Silica dispersed

Microporous insulation materials consist mainly of highly dispersed silica with a particle size of only 5-30 nm. The highly dispersed silica powder is pressed to plates, which receive heat treatment up to 800 °C, after which the plates are self-supporting and possess a micropore structure with pore diameter of 0.1pm. The addition of opacifiers to the highly dispersed silica starting material reduces the loss of heat by radiation. The dates for such insulation boards are shown in Table 18. 

Use of highly dispersible silica together with silanes and high vinyl S-SBR has met all critical magic triangle requirements like good dry and wet traction, reduction in tread wear, and low RR. 

O. K. Angelopulo, A. Kh. Ali, K. A. Dzhabarov, A. A. Rusaev, E. A. Konovalov, and I. V. Bojko. Plugging solution contains plugging Portland cement, waste from semiconductors production containing dispersed silica, chloride(s), carbonate(s), phosphate(s) and water. Patent SU 1700202-A, 1991. 

Well-dispersed silica and polymer/Co(salen) segments at a molecular level were obtained. Nondestructive immobilization of Co(salen) complexes within silica aero- and xerogels was also achieved with the sol-gel method using silylether-appended salen.1227... 

Instead of blending them either by dispersing silica powders as fillers within PE, which is a well-developed technology with many applications, or by polymerizing ethylene within the pores of modified9 or unmodified silica,10 now the nanometric physical blending... 

A. Bensalem, F. Bozon-Verduraz, M. Delamar, and G. Bugli, Preparation and characterization of highly dispersed silica-supported ceria, Appl. Catal. A Gen. 121, 81-93 (1995). 

It should be realized, at the outset, that colloidal solutions (unlike true solutions) will almost always be in a metastable state. That is, an electrostatic repulsion prevents the particles from combining into their most thermodynamically stable state, of aggregation into the macroscopic form, from which the colloidal dispersion was (artificially) created in the first place. On drying, colloidal particles will often remain separated by these repulsive forces, as illustrated by Figure 1.1, which shows a scanning electron microscope picture of mono-disperse silica colloids. 

Figure 1.1 Scanning electron microscope image of dried, mono-disperse silica colloids.

Alternatively, sodium nitro prusside gives a value, close to that of dispersed silica, and, in practice, could be used to determine the total excluded volume or the kinetic dead volume without incurring serious error. Values for the kinetic dead volume measured in this way could be... 

K3-Stoff (Ger). A highly dispersed silica, prepd by a special process, used during WW1I in some Tetan expls Ref G. Romer, Reports on Explosives (Germany) , PBL Rept No 85160 (1946), p 3... 

Nucleants. Although nylons crystallize quickly, it is often an advantage, particularly for small parts, to accelerate this process to reduce cycle time and increase productivity. Nylon-6, which crystallizes more slowly than nylon-6,6, also benefits from nudeation in unreinforced formulations. Nucleants are generally fine-particle-size solids or materials that crystallize as fine particles before the nylon. The materials, eg, finely dispersed silicas or talc, seed the molten nylon and result in a higher density of small uniformly sized spherulites in nylon-6 the crystalline form is also changed. Nudeation increases tensile strength and stiffness but makes the material more britde. Mold shrinkage is lower for nudeated resins. 

The active centers in silica are generated upon mechanical treatment not only due to the cleavage of the particles of material but also to their mutual contacts (so-called friction regime [11-13]). For this reason, the mechanical treatment can be used for generating defects at the surface of high-dispersed silica (aerosol). 

When silica with the developed specific surface (> 100m2/g) is used, the number of active sites per gram of material reaches 1018-1019. This amount is sufficient for their reliable detection by different methods EPR, IR and optical spectroscopy, microcalorimetry, and adsorption measurements. Using the thermo chemical method, one can activate the surface of powdered and semitransparent film Si02 samples with a thickness of several tens of microns obtained by pressing the high-dispersity silica powder (aerosil). These film samples are suitable for quantitative optical studies in the UV, visible, and IR regions. 

The hybrid materials having silica content below 50 wt% were composed of polyimide matrix with finely dispersed silica particles, and their hardness values were very close to that of the matrix polyimide. On the other hand, the hybrid materials having a silica content over 50 wt% were very hard and tough, and their hardness values increased with increasing silica content. In the latter hybrid materials, the silica formed a continuous phase with polyimide as the minor phase that probably acts as binder. This is a new type of polyimide-based composite, and may be referred to as polyimide-reinforced silica glass , al-... 

According to the results of our experiments in vitro, the highest adsorptive capacity with reference to proteins and protein-associated phospholipids and triglycerides of blood serum was characteristic of the highly disperse silica modified with aluminium oxide. The mechanism of the therapeutic effect of HDS on treatment for intestinal infections seems to involve the following major aspects. 

O. O. Chuiko and O. O. Pentyuk, Scientific Principles of Development of Medicinal Preparations on the Basis of Highly Disperse Silica, in Scientific Principles of Development of Medicinal Preparations (Osnova, Kharkiv, 1998), pp. 35-51. 

Highly disperse silica is widely used in pharmaceutical formulations as a filler, adsorbent, thickener etc.5 Their high hydrophilicity and the absence of emulsifying ability restrict their application. In contrast to hydroxylated silica, partially or fully hydrophobized silica may exhibit improved properties as a drug carrier. The main goal of this work is to study hydrophobized silica nanocomposites with immobilized vitamins C and E. Investigations of adsorption-desorption processes which involve silica nanoparticles and the antioxidants are described. Factors affecting the antioxidant stability have also been carefully considered. 

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... 

The process of chemical modification was carried out in a reactor with a mixer at 300°C for 1 h.7 Preliminary thermal treatment of the highly disperse silica surface was made at 200°C for 2 h. After the modification, samples were heated in airflow at 200°C for 2 h to remove the residual modifying agent, as well as the reaction products from the surface. 

Interaction of ascorbic acid (vitamin C) with the silica surface was complicated by the fast oxidation of ascorbic acid in aqueous and ethanol solutions because of dissolved oxygen.12,13 However, both unmodified and modified silica increase the oxidation resistance of vitamin C. In particular, the rate of ascorbic acid oxidation to dehydroascorbic acid was found to be much less in the presence of unmodified or modified silica (Figure 4). Vitamin C is stabilized in the presence of silica, apparently due to interaction of the vitamin with the surface of highly-disperse silica particles, as confirmed by the results... 

Partial silylation of the highly disperse silica surface enhances the adsorption of vitamin E from ethanol solution, and provides the ability to obtain water-soluble nanocomposites containing vitamin E. Immobilization of vitamin C on the silica surface prevents its oxidation. Its interaction with the adsorbent surface leads to a decrease in proton-donor ability of the OH-groups involved in the oxidation of ascorbic acid. Elydrophobized silica nanocomposites are characterized by a prolonged desorption of immobilized vitamins. It has been shown that vitamin C does not lose its antioxidant properties after desorption. 

P. O. Kuzema, Properties of chemically modified high-disperse silicas with hydrophilic-hydrophobic surface (PhD Thesis, Kyiv, 2004). 

Highly disperse silica was first applied in medical practice as an effective enterosorbent. It was then found to have a therapeutic influence, and that it can be used as a carrier for medicinal purposes.1,2... 

K3-Stoff (Ger). Ajhighly dispersed silica, prepd by a special process, used during Wwll in some Tetan expls... 

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