Silica containing fibers

Solid Particles. Dust and fibers from coal, clay, glass, asbestos, and minerals can lead to scarring or fibrosis of the lung lining. Pneumoconiosis, a condition common among coal miners that breathe coal dust, silicosis caused by breathing silica-containing dusts, and asbestosis from asbestos fibers are all well-known industrial pollution diseases. 

Solid-phase microextraction (SPME) — is a procedure originally developed for sample preconcentration in gas chromatography (GC). In this procedure a small-diameter fused silica optical fiber, coated with a liquid polymer phase such as poly(dimethylsiloxane), is immersed in an aqueous sample solution. The -> analytes partition into the polymer phase and are then thermally desorbed in the GC injector on the column. The same polymer coating is used as a stationary phase of capillary GC columns. The extraction is a non-exhaustive liquid-liquid extraction with the convenience that the organic phase is attached to the fiber. This fiber is contained in a syringe, which protects it and simplifies introduction of the fiber into a GC injector. Both uncoated and coated fibers with films of different GC stationary phases can be used. SPME can be successfully applied to the analysis of volatile chlorinated organic compounds, such as chlorinated organic solvents and substituted benzenes as well as nonvolatile chlorinated biphenyls. 

Many other alumina or alumina-silica-type fibers are available. Most of these are made by the sol-gel process. Sumitomo Chemical company produces a fiber that is a mixture of alumina and silica. The flow diagram of this process is shown in Fig. 6.8. Starting from an organoaluminum (polyaluminoxanes or a mixture of polyaluminoxanes and one or more kinds of Si containing compounds), a pre-... 

Small diameter, structural silica glass fibers and large diameter, bicomponent optical silica fibers are downdrawn from the surface melt of a solid preform. The melt temperatures needed to contain the melt exceed the capability of practical ceramic and bushing materials. 

Temperatures above 1800°C would be required to contain a fiber forming silica melt in a bushing. A requirement like this would by far exceed the practical capability of most precious metal and/or other practical alloy materials. As a result, pure silica glass fibers are downdrawn from solid silica preform rods (Figure 14). Gas flame or electrical furnaces soften the ends of the quartz rods, and thereby facilitate the formation of continuous silica fibers. Preforms made from natural silica contain 99.99% Si02 and impurities include 20-50 ppm Al, <5 ppm OH", and <4 ppm Na. Preforms made by oxidation of SiCl4 in a plasma flame [60] afford even purer silica fibers (<1 ppm Al, <0.1 ppm OH, <1 ppm Na, and <50 ppm Cl). 

Pyrolysis of acetylene on the surface of MCM-41 silicas containing metaUic catalysts has been studied. Application of matrices with the supported metals as catalysts enabled us to attain rather high yields of carbon nanostructures (20-30% of the process product). The electron microscopy data provided evidence for formation of nanotubes with an external diameter of 42-84 nm in the case of the cobalt catalyst and 14-200 nm in the case of the iron catalyst Formation of carbon fibers with diameters in the interval 80-110 nm for the nickel catalyst was also observed. In the absence of a catalyst on such matrices small yields (up to 2%) of carbon nanotubes were attained. 

Water incorporated into fused silica is of considerable importance because the resulting silanol groups affect the NIR transmission of silica optical fibers and other optical components. Silanols are discussed in the OH section. In mixed glasses, such as those containing borosilicates, aluminosilicates, and so on, associated water OH groups give rise to diffuse absorption bands. The absorption bands of water molecules on silica surfaces have been described by Klier et al. " ... 

Matsuzaki K., Aral D., Tanabe N., Mukaiyama T., Ikemura M. Continuous silica glass fiber produced by sol-gel process. J. Non-Cryst. Solids 1989 112 437-441 Meyer Jr. R., Shrout T., Yoshikawa S. Lead zirconium titanate fine fibers derived from alkoxide-based sol-gel technology. J. Am. Ceram. Soc. 1998 81 861-868 Mizuno T., Phalippou J., Zarzyeki J. Evolution of the viscosity of solutions containing metal alkox-ides. Glass Technol. 1985 26 39-45... 

Straw has a more complicated constitution than wood. Straw contains a relatively large number of cell elements. It contains fiber, vessel elements, the parenchyma cells, and epidermic cells, having high amount of ash and silica. The epidermic cells form the outermost surface cells, which are covered by a very thin layer of wax. This surface layer reduces the moisture absorbance of straw. Wheat straw has higher cellulose, ash, and silica content as compared to that of wood. The wax content of straw is higher than that of wood. Rice straw has been found to possess higher wax content [24]. 

Even cationic species such as the (hydrated) hydrogen ion (H ) can be lured into the hydrophobic silicone films from water medium as long as they contain appropriate additives to allow penetration of the analyte. For instance, Nivens et al. [140,141] have reported fabrication of silicone/ sol-gel films using a hydroxy-terminated poly(dimethyl siloxane (PDMS-OH), tetraethoxysilane (TEOS) and 3-ami-nopropyltriethoxysilane (APTES) mixture in ethanol-water. Tetramethylammonium hydroxide (TMAOH) is added to the mixture to entrap the fluorescent pH indicator dye 8-hydroxypyrene-l,3,6-trisulfonic acid trisodium salt (HPTS) [102], after base-catalyzed polycondensation of the silanes and the PDMS-OH. Silica optical fibers are stripped from their jacket at the distal end and dip-coated with the indicator gel before the end of gelation (24 h). The optical fluorosensor is able to measure between pH 6.0 and 8.5 for 6 months if stored in buffer medium. 

FIGURE 12.10 Tapping mode atomic force microscopy (AFM) images of the section analyzes of ethylene-propylene-diene monomer (EPDM) rubber-melamine fiber composites. A, composite containing no dry bonding system B, composite containing resorcinol, hexamine, and silica in the concentrations 5, 3, and 15 phr, respectively. 

FIGURE 12.18 Stress-strain curves of rubber-fiber composites developed for solid rocket motor insulator A, ethylene-propylene-diene monomer (EPDM) rubber-carbon fiber composites B, EPDM mbber-melamine fiber composites C, EPDM mbber-aramid fiber composites and D, EPDM rubber-aramid pulp composites. 1 and 2 stands for unaged and aged composites respectively. Carbon fiber- and melamine fiber-reinforced composites contain resorcinol, hexamine, and silica in the concentrations 10, 6 and 15, respectively and aramid fiber- and aramid pulp-based composites contain resorcinol, hexamine, and silica in the concentrations 5, 3 and 15, respectively. (From Rajeev, R.S., Bhowmick, A.K., De, S.K., and John, B., Internal communication. Rubber Technology Center, Indian Institute of Technology, Kharagpur, India, 2002.)... 

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