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Distribution by Scientific Domains

Polymers and Materials Science	50%
Chemistry	50%

Selected Abstracts

Light-induced crosslinking polymerization,

POLYMER INTERNATIONAL, Issue 11 2002
Christian Decker
Abstract Light-induced polymerization of multifunctional monomers is a powerful method to transform a liquid resin into a solid polymer almost instantly, selectively in the illuminated areas. The reaction can conveniently be followed by real-time infrared spectroscopy, a technique which records directly conversion versus time curves in photosensitive resins undergoing ultrafast curing upon UV or laser exposure. The photoinitiator was shown to play a key role in laser-induced polymerization because of the monochromatic character of the emitted radiation. By using highly sensitive acrylate photoresists, relief images of micronic size were obtained by fast scanning with a focused laser beam. The laser direct imaging technology makes image transfer obsolete and eliminates the manufacture of photolithographic masks. Polymer networks of different architectures have been obtained by UV irradiation of various monomer blends: acrylate,epoxide, acrylate,vinyl ether, acrylate,polyene, vinyl ether,maleate and thiol,polyene. With monomers polymerizing by different mechanisms, ie radical and cationic types, interpenetrating polymer networks have been generated upon UV exposure in the presence of adequate photoinitiators. The crosslinking reaction was also performed in the solid state on polybutadiene which was plasticized with a multifunctional acrylate or thiol monomer. Thermoplastic elastomers were transformed within a fraction of a second into an insoluble material showing a greatly improved resistance to heat and chemicals, because of the tight polymer network formed. © 2002 Society of Chemical Industry [source]

High-Zirconium-Content Nano-Sized Bimodal Mesoporous Silicas

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2006
David Ortiz de Zárate
Abstract Silica-based nanoparticulated bimodal mesoporous materials with high Zr content (43 , Si/Zr , 4) have been synthesized by a one-pot surfactant-assisted procedure from a hydroalcoholic medium using a cationic surfactant (CTMABr = cetyltrimethylammonium bromide) as structure-directing agent, and starting from molecular atrane complexes of Zr and Si as hydrolytic inorganic precursors. This preparative technique allows optimization of the dispersion of the Zr guest species in the silica walls. The bimodal mesoporous nature of the final high surface area nano-sized materials is confirmed by XRD, TEM, and N2 adsorption,desorption isotherms. The small intraparticle mesopore system (with pore sizes around 2,3 nm) is due to the supramolecular templating effect of the surfactant, while the large mesopores (around 12,24 nm) have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. The basicity of the reaction medium seems to be a key parameter in the definition of this last pore system. The effects induced by the progressive incorporation of Zr atoms on the mesostructure have been examined, and the local environment of the Zr sites in the framework has been investigated by UV/Vis spectroscopy. Observations based on the consequences of post-treatments of the as-synthesized materials with HCl/ethanol mixtures corroborate that the atrane method leads to Zr-rich materials showing enhanced site accessibility and high chemical homogeneity throughout the pore walls. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

The influence of Metal Dusting on gas reactions

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2004
A. T. W. Kempen
Abstract Gas composition analysis measurements have been performed in the outlet gas stream of a laboratory metal dusting test furnace in order to study the influence of metal dusting on gas reactions. This analysis has shown that carbon deposition is associated with metal dusting, i.e. the material most severely attacked by metal dusting, catalyses the formation of carbon to the largest extent. Also, metal dusting has not been seen to influence the methanation reactions. A kinetic model has been used to interpret the obtained data with respect to the catalytic activity of several high temperature materials showing that the catalytic activity of the material can vary by orders of magnitude for different reactions. [source]

An evaluation of biological and abiotic controls for grapevine powdery mildew.

AUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 3 2006

Abstract Grapevine powdery mildew (Erysiphe necator) affects grape yield and fruit quality worldwide. Managers of conventional vineyards rely mainly on synthetic fungicides and sulfur to control powdery mildew, while in organic vineyards sulfur is the main control agent, often in rotation with canola-based oils, bicarbonates and biological control agents. The efficacy of those materials has not been evaluated critically under field conditions in Australia. Accordingly, a range of materials showing most promise in previous greenhouse trials (Crisp et al. 2006 Australian Journal of Grape and Wine Research12, pp. 192,202) were assessed via field trials in commercial vineyards. Applications of either milk or whey (alone, or mixed with a canola oil-based product), as well as applications of potassium bicarbonate (commercial formulation), all reduced the severity of powdery mildew compared with untreated vines. Eight applications of a 1:10 dilution of milk, 45 g/L whey powder or programs comprising rotations of potassium bicarbonate plus oil and whey, applied at 10,14 day intervals, reduced the severity of powdery mildew to levels not significantly different from that on vines sprayed with sulfur (wettable powder, 3,6 g/L). However, the relative control of powdery mildew by the test materials in field trials was dependent on the susceptibility of the grapevine cultivar and the extent of spray coverage achieved. In vineyards where highly susceptible cultivars were planted, and spray coverage was compromised, the resultant control of powdery mildew was reduced; and sometimes to commercially unacceptable levels. [source]