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991.
Vijay Jain Arun K. Varshneya Peter P. Bihuniak 《Journal of the American Ceramic Society》1989,72(5):843-845
The steady-state dc ionic resistivity measurements on GE 124 commercial fused silica glass were carried cut in nonblocking mode between 300° and 650°C using fused Li+ , Na+ , and K+ nitrate salts as electrodes. The alkali ions were electrolyzed through a sample disk in a U-tube-type dc conductivity cell until steady state was achieved. Sequential conduction experiments at varying temperatures using various ions in a given sample showed that the resistivity of an ion could vary by as much as 1 order of magnitude depending upon the conduction history of the specimen, i.e., which ions had been electrolyzed through the specimen during prior experiments. 相似文献
992.
Reaction of Zirconia with Silica at the Stoichiometry of Zircon 总被引:2,自引:0,他引:2
Zirconia was combined with silica and halide mineralizers and fired in a nitrogen atmosphere. X-ray analysis showed zircon was formed, demonstrating that an oxygen atmosphere is not necessary for the formation of zircon. The reaction mechanism is the same as that forming zircon in air, involving transport of the silica as a volatile halide, followed by diffusion of silica and oxygen across the product layer to a reaction site on the zirconia. 相似文献
993.
A.J.J. van der Zanden 《Drying Technology》1997,15(3):1077-1081
A set-up and a method are described with which sorption isotherms of granular materials can be measured. The set-up uses a recirculating air flow through a fluidized bed of granular materials. The measuring procedure starts with drying the granular material completely. A known amount of water is added to the fluidized bed. At equilibrium between the amount of water in the granular material and the circulating air the air humidity is measured. The method is demonstrated using silica gel. 相似文献
994.
Janet L. Armstrong M. John Matthewson Charles R. Kurkjian 《Journal of the American Ceramic Society》2000,83(12):3100-3109
Strength and dynamic fatigue behavior of silica fibers has been measured as a function of ambient humidity. Bare and polymer-coated fibers were compared to determine the influence of the coating. The results verify earlier work that suggests the degradation reaction is approximately second order with respect to humidity. However, we verify this result using rigorous data analysis techniques and, unlike the earlier work, the result is shown to be independent of the form of the kinetic model for crack growth. Trends in the calculated fatigue parameters illustrate that a simple exponential crack growth law best describes the humidity data. No significant differences were found between coated and bare fibers, provided the coated fibers were properly equilibrated. A data analysis methodology is given for obtaining valid reaction orders independently of the crack growth law form. 相似文献
995.
Sol–gel films are actively investigated during the last decade as possible candidates for environmentally friendly pre-treatments. However, the important drawback in this case is the lack of active corrosion protection and self-healing ability. 相似文献
996.
Xiaohong S. Li Glen E. Fryxell Chongmin Wang Mark H. Engelhard 《Microporous and mesoporous materials》2008,111(1-3):639-642
Ag-doped mesoporous titanium oxide was prepared using non-ionic surfactants and easily handled titanium precursors, under mild reaction conditions. The structure of these materials was determined as a function of the concentration of the Ag dopant and calcination temperature. In contrast to the stabilizing effect of Cd-doping on mesoporous TiO2, Ag doping was found to significantly destabilize the mesoporous structure. 相似文献
997.
Periodic mesoporous silica was modified with metal organic reagents via direct surface substitution reactions, thus introducing functional groups into the channels of the structure. Using materials functionalised with basic aromatic molecules as catalysts, the efficient Michael addition of diethyl malonate to trans-β-nitrostyrene was achieved. The catalysts anchored to the silica surface show high activity in the catalytic process even at low concentrations and low temperatures. The catalysts also prove to be stable during many recycling procedures. In combination with the remarkably reduced cost for the synthesis of these solid bases, the new hybrid systems are promising candidates for a new generation of catalysts. 相似文献
998.
María Luisa Ojeda Antonio Campero Jos Guadalupe Lpez-Corts María Carmen Ortega-Alfaro Celso Velsquez Cecilio Alvarez 《Microporous and mesoporous materials》2008,111(1-3):178-187
A metal Fischer carbene [(CO)5WC(φ)OCH2CH3] was covalently linked for the first time to the silanol groups of the mesoporous channels of SBA15 by following two different synthetic anchoring routes. The first one goes through the reaction of the SBA15 mesoporous silica walls functionalized by aminopropyltriethoxysilane (APTES) with a tungsten carbene Wφ, while in the second approach a precursor synthesized by reacting APTES with the carbene Wφ is then anchored via a direct bond to the silanol groups in the interior pore channels of SBA-15.
This tethering is helpful to prevent the decomposition of the metallic complex. XRD, N2 adsorption–desorption, and TEM analysis provide strong evidence that the mesoporous support structure retains its long-range ordering after the grafting process, despite a significant reduction of its specific surface area, pore-volume and pore-size. The chemical bonding of the tungsten carbene to the silanol groups of SBA-15 materials was studied with solid-state NMR spectroscopy. Both 13C MAS NMR and 29Si CP MAS NMR spectra confirm the covalent linking of the carbene to the silica-pore system. 相似文献
999.
Jean Marcel R. Gallo Chiara Bisio Leonardo Marchese Heloise O. Pastore 《Microporous and mesoporous materials》2008,111(1-3):632-635
A novel SBA-16-related synthesis of mesostructured silica containing framework aluminum is reported here. This material was successfully synthesized using aluminum sulphate and the pH-adjusting method. The structural and porosity properties of this novel material were studied by X-ray diffraction and N2 adsorption at 77 K. The Al insertion was determined by 27Al-MAS-NMR and the acidity was monitored by infrared spectroscopy of CO adsorption at 100 K. 相似文献
1000.
The work focuses on the synthesis of a red ceramic pigment by inclusion of hematite in a fumed silica matrix with different specific surface areas. Iron(II) sulfate was used as hematite precursor. Mixtures of iron(II) sulfate and fumed silica with different mole ratios were heated at different temperatures from 1000 to 1300 °C for 4 h. 相似文献