Silica components

Figura 2.9 Dse of th Grob test Mixture to compare tbe activity of various glass surfaces coated with ov-ioi. Surface types A > Untreated pyrex glass, B pyrex glass deactivated by thermal degradation of Ceurbowax 20M, C < SCOT column, prepared with Silanox 101, D pyrex glass column coated with a layer of barium carbonate and deactivated as in (B), and E - untreated fused silica. Components are identified in Table 2.7 with ac - 2-ethylhexanoic acid. (Reproduced with permission from ref. 152. Copyright Elsevier Scientific Publishing Co.)...

Silica analysis of water, 26 39 Silica-based glass fibers fabrication of, 77 136-137 transparency of, 77 132 Silica brick, ASTM classifications and specifications for, 27 509 Silica components, production of, 23 56 Silica fibers... 

The nuisance dust aspect of bauxite is in sharp contrast to the limited industrial situation where lung injury was reported in Canadian workers, who in the 1940s engaged in the manufacture of alumina abrasives in the virtual absence of fume control. Fusing of bauxite at 2000°C gave rise to a fume composed of freshly formed particles of amorphous silica and aluminum oxide. Despite the poor choice of the term—bauxite fume pneumoconiosis—sometimes used to describe the disease, scientific opinion favors the silica component as the probable toxic agent. It should be emphasized that bauxite from some sources may contain small amounts of silica. 

It has generally been believed that the capacity of inhaled natural graphite dust to cause a disease is largely the result of its crystalline silica component. ... 

Production of net-shape silica components serves as an example of sol-gel processing methods. A silica gel may be formed by network growth from an array of discrete colloidal particles (method 1) or by formation of an interconnected three-dimensional network by the simultaneous... 

In addition [103,104], a new type of composite that combines DNA with silica components via a sol-gel method was described. The DNA-silica hybrid material is advantageous with respect to its mechanical and chemical stability in both aqueous and organic solvents. Similar to the previously described hybrids, the specific functions of the DNA molecules were retained and maintained the DNA-silica hybrid materials adsorb DNA-interactive chemicals from diluted aqueous solution. In another series of reports [105-109], DNA-loaded PSf microspheres were fabricated by means of a liquid-liquid phase separation technique. The release rate of DNA from the microspheres can be controlled by manipulating the microsphere structure. Increasing the polymer concentration causes lower porosity and smaller pores on the outer surface of the microspheres, and leads to a low release rate of DNA from the microspheres. The DNA-loaded PSf microspheres could effectively accumulate harmful DNA-intercalating pollutants and endocrine disruptors, as described in previous reports. 

The method of Lentz (35,36) was adopted for trimethylsilylation of the aqueous silicate solutions. The mixture of cone, hydrochloric acid, water, 2-propanol and hexamethyldisiloxane was used as the trimethylsilylating reagent. Trimethylsilylated derivatives obtained were adaptable to gas-phase analysis. The distribution of silicate species in solutions, which was analyzed quantitatively by the trimethylsilylation technique combined with gas-liquid chromatography, was expressed as the Si(>2 recovery, that is, the percentage of silica as a silicate species in total silica component in the solutions. 

Zivanovic (1995) presented a description of clinkers made with silica fume, instead of quartz sand, as the primary silica component in the raw feed. The silica fume made up approximately 3.0 percent of the feed. Alite crystal size was reported to be from 50 to 200 pm and belite grains were said to be rounded and between 50 and 60 pm. No mention of belite nests was made. The cements made with silica fume or tuff and a particular marl, compared to other cements not made with these materials, did not require as much grinding and produced higher 28-day mortar strengths. 

The HBPI-silica hybrid membranes were prepared by thermal imidization and sol-gel reaction with two kinds of alkoxysilanes, TMOS and/or MTMS. Appropriate amounts of TMOS and/or MTMS and ion exchange water were added in the DMAc solution of the hyperbranched polyamic acids. For TMOS/MTMS combined system, TMOS and MTMS were added to achieve equivalent weight fraction of silica components arising from TMOS and MTMS. The mixed solutions were stirred for 24h and cast on PET films and... 

The surface of CS (Cc=5-13 wt%) was studied by the electron microscopy technique (Leboda 1987). In that case on the surface there were both portions of the parent silica and portions of silica covered by a carbon layer, but any uniform coverage of the starting surface by a carbon layer was not observed. This is typical picture for any silica substrates (Gun ko and Leboda 2002). With increasing concentration of carbon, the area of the silica component of the surface noticeably decreases and at the carbon concentration equal to 13 wt% it became relatively small. It can be anticipated that at the carbon concentration of 40 wt% (CS-2) practically all the surface is covered by a carbon layer. So, the surface of the CS-2 sample may be more homogeneous than that of the CS-1 sample and it can be concluded that the tendency of the adsorbent surface to undergo polarization increases as a function of the surface heterogeneity of a given material. 

This value remains relatively constant over a sevenfold range of concentration. It is assumed that 474 ppm is the equilibrium solubility of the postulated colloidal silica component in silicate of molar ratio 3.36. From the formulas in Chapter I relating particle diameter to solubility (Figure 1.101>), the solubility is that of silica particles about 11 A in diameter. From equations relating size to molecular weight, this corresponds to a molecular weight of 1.15 x 10 d x 6 x 10 , or 920, or about 15 silicon atoms per particle. 

In zinc-rich paints some early patents indicate the importance of a silica component. Colloidal silica was reacted with finely divided zinc to form a colloidal zinc silicate in which the excess zinc metal was suspended (654). A water-insoluble binder for zinc-containing coatings was produced by mixing alkali-stabilized colloidal silica with lithium hydroxide in suitable proportions (655). Evolution of gas from mixtures of colloidal silica with zinc powder is prevented by adding an indigoid compounds (656). Another formulation involves quaternary ammonium polysilicate solution milled with lead oxide as the binder for zinc (657). Some of the problems stem from the impurities in the zinc powder which promote reaction with the medium (658). Adhesion. of paints of this type of steel is improved by adding up to 2% of a styrene-acrylic resin dispersion (659). 

Titania powders not only with particulate morphology in different nano-sizes but also with fibrous morphology were synthesized. Even synthesis of nanotubes was reported under hydrothermal conditions from NaOH solution [26-30] and also nanofibers from KOH solution [31,32]. Both nanotubes and nanofibers thus prepared were later clarified to be protonated titania (titanate) [33-36]. A comprehensive review was published on protonated titanate nanotubes [37]. Effects of remnant sodium content and annealing temperature were studied on the structure and photoactivity of the nanotubes [38]. Titanate nanowires and nanoribbons were also reportedly formed [39,40]. Nano-sized Ti02 powders were obtained by annealing of titanate nanotubes and nanofibers [41]. Mesoporous anatase-type Ti02 powder was prepared by selective dissolution of silica component in Ti-Si binary oxides [42]. 

From Tables 124 and 12-5 we can conclude that incorporation of small amount of zirconia, in the matrix, slightly inproves the photostability of rhodamine B. In order to study the influence of zirconia incorporation on the photostability of rhodamine 6G, we should compare the results in sihca 1 with zirconia 3, since both matrices are - similar by their silica components and by their silica components and by the same reason, silica 2 with zirconia 2. In both cases, the incorporation of zirconia favors the photostability. 

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