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[en] Commercially available poly(propylene)imine (DAB-Am-32 and DAB-Am-64) dendrimers were used as single-molecule templates to tailor the porosity of silicas via a nonacidic sol-gel method. X-ray diffraction on both the as-prepared (oven-dried at 373 K) and the calcined (833 K) materials revealed that modest contraction took place on template removal and that the cavities created did not achieve three-dimensional ordering under the current synthesis conditions. Transmission electron microscopy of ''Pt-stained'' samples supported this picture. A modified Horvath-Kawazoe analysis of the argon adsorption isotherms indicated that DAB-Am-64 is a much more effective template than DAB-Am-32. Pyrolysis and oxidation protocols for template removal are also presented. (c) 2000 Materials Research Society
[en] In this study, the properties of the vulcanizations based on NBR rubber mixtures and in the presence of low molecular weight reactive compounds (SKN-40 + DChDEAST, SKN-40 + DMPhM), vulcanized by the gamma rays and temperature were studied. The degree of crystallinity of the irradiated samples was determined in the presence of tension. An assumption is made about the relationship between the changes and the occurrence of thermo radiation - chemical processes leading to the formation of multifunctional nodes and a change in the number of active network chains in thermo radiation samples of SKN-40 rubber.
[en] Alternate fuel fabrication techniques are being developed at WNRE as part of the thorium fuel cycle program. The sol-gel techniques are attractive and this report assembles and summarizes information relating to thoria sol-gel fuels. Some background information on the behaviour and advantages of sol-gel fuel forms is presented, followed by a review of relevant colloid chemistry and an explanation of the fundamental steps of sol-gel processes. Finally, several variants to the basic process are reviewed and evaluated. (author)
[en] A jet is described which is suitable for the preparation of sorbents, catalysts and nuclear fuels in form of spherical particles of equal size. The jet comprises no moving parts and allows to produce particles in sizes from 0.1 to 1.0 mm. The advantage of the particles thus produced is, e.g., a reduction in the dust level from the production of nuclear fuels and the possibility of remote control of the process. (E.S.)
[en] A number of adsorbents are available commercially as coatings for SPME fibers but some analytical methodologies might demand specific properties for the extraction of selected compounds, special coatings that have particular volume and a selectivity towards particular analytes. This paper presents a simple, fast, effective and environmental friendly methodology for the determination of accelerants in arson samples using headspace solid-phase micro extraction coupled to gas chromatography. A new fiber prepared by sol-gel method, containing 1:1 molar ratio of octyltriethoxysilane (C8-TEOS): methyltrimethoxysilane (MTMOS) was employed in this technique. The efficiency of the new fiber coating prepared by sol-gel technology for the determination of accelerants was compared to that of commercial PDMS/ DVB fibers. Poly dimethylsiloxane divinylbenzene (PDMS/ DVB) is the most common fiber coating for the extraction of hydrocarbon compounds. Compared with commercial PDMS/ DVB fiber, the new homemade fiber exhibited higher extraction capability and good selectivity for accelerants. The homemade fiber was also applied for the simulated arson samples. The home-made SPME adsorbent was shown to be a good alternative to commercially available fiber for the determination of accelerants in arson cases. (author)
[en] Transparent and colourless silica coatings were deposited on anadosing and non-anodising substrates of aluminium-base alloys (series 6063). Coatings were prepared by sol-gel (dipping method) from a silica alkoxide and a mixture of both silica alkolide and silica alkylalkoxide. Preparations were optimised from viscosity, density, surface tension, and contact angle measurements. Densification was carried out at 60 and 120 degree centigree. Reflectance attenuation of coated samples was analysed by UV-VIS-NIR spectroscopy. The results indicated that -10% of attenuation is reached. Durability and resistance against degradation tests of the metal/coating system were undertaken by immersion into aqueous solutions. Electrochemical impedance measurements and potential corrosion of the metallic substrate for variable times were performed. (Author) 7 refs
[en] A new sol-gel hybrid material, methyltrimethoxysilane-cyanopropyltriethoxysilane (MTMOS-CNPrTEOS) was successfully synthesized and used as a coating material in stir bar sorptive extraction (SBSE) of selected non-steroidal anti-inflammatory drugs (NSAIDs) in urine samples. The MTMOS-CNPrTEOS hybrid was synthesized by hydrolysis and condensation of MTMOS and CNPrTEOS in the presence of trifluoroacetic acid as catalyst via sol-gel method. Several factors influencing the synthesized sol-gel hybrid MTMOS-CNPrTEOS process such as mole ratio of MTMOS-CNPrTEOS, NaOH concentrations as etching solution, etching time, coating time and water content were investigated and optimized in this study. The optimum synthesis conditions obtained were 1:1 mol ratio of MTMOS-CNPrTEOS, 1 M NaOH as etching solution, 60 min etching time, 2 h coating time and 6 mmol water. The sol-gel hybrid MTMOS-CNPrTEOS synthesized under the optimum conditions was used to determine selected NSAIDs in human urine samples using normal stacking mode capillary electrophoresis with ultraviolet detection. MTMOS-CNPrTEOS SBSE method demonstrated good linearity (60 to 20,000 μg L"-"1) with excellent coefficient of determination (r"2 > 0.9990). The sol-gel hybrid MTMOS-CNPrTEOS SBSE method showed low limit of detection (35 - 41 μg L"-"1) with good precision (RSD < 6 %, n = 3) and excellent extraction recoveries (83.5 - 98.9 %) for the selected NSAIDs. The sol-gel hybrid MTMOS-CNPrTEOS SBSE method demonstrated good potential as an alternative sorbent in SBSE method for NSAIDs. (author)
[en] Highlights: • RF aerogel flyer-plates with graded density were fabricated by sol-gel techniques without using any extra “glue”. • The interface effect between aerogels and environment was studied and the common troubles of dense layer was well solved. • The shrinkage effect of aerogel was studied and controlled, and cracking and curling of samples were avoided effectively. • A graded-density aerogel sample overwhelmed the single-density one by extending 50% in the rising edge of compression. Resorcinol formaldehyde (RF)/carbonized resorcinol formaldehyde (CRF) aerogel flyer-plates with graded density were fabricated via simple and optimized methods. The preparation of multilayer aerogel was studied, which included controlling the microstructure as well as the interface effect between aerogels and environment. Any extra glue was used in the preparation which included sol-gel techniques and supercritical drying. The problem of dense layer that always appeared on the surface of aerogel during the preparation was studied, and effectively overcome by modifying the mold with ammonia. Meanwhile the shrinkage effect of aerogel was studied and well controlled, as a result the cracking and curling of samples were avoided effectively. Finally, qualified samples with thickness of ~ hundreds μm and density of 0.20–1.56 g/cm3 were obtained. As a preliminary experiment, a two-layer aerogel graded density was used to impact Al target, and a piece of isopachous polystyrene with single density was used as contrast. Consequently the aerogel flyer-plate with graded density was accelerated by laser beam, and impacted Al target with extending the rising edge of ramp compression by 50% in comparison to the contrast. Further work is focusing on optimizing the density range of aerogels and improving their properties.