Showing papers on "Silane published in 2006"

High-pressure phases of silane.

Abstract: High-pressure phases of silane SiH4 are predicted using first-principles electronic structure methods. We search for low-enthalpy structures by relaxing from randomly chosen initial configurations, a strategy which is demonstrated to work well for unit cells containing up to at least ten atoms. We predict that silane will metallize at higher pressures than previously anticipated but might show high-temperature superconductivity at experimentally accessible pressures.

Applications of Pore-Expanded Mesoporous Silicas. 3. Triamine Silane Grafting for Enhanced CO2 Adsorption

Abstract: Conventional MCM-41 and pore-expanded MCM-41 (PE-MCM-41) silicas have been used as supports for grafting 3-[2-(2-aminoethylamino)ethylamino]propyl trimethoxysilane (TRI) and tested for CO2 adsorption. The effects of the quantity of triamine silane added to the grafting mixture on the CO2 adsorption capacity and apparent adsorption rate have been examined. The results showed that when both supports were grafted under the same conditions, PE-MCM-41 was grafted with slightly larger quantities of amine than MCM-41, for all controlled silane additions. Based on the adsorption performance of the materials using a dry 5% CO2/N2 feed mixture, the optimal quantity of triamine silane added to the grafting mixture was determined to be ca. 3.0 cm3/g(SiO2), for both MCM-41 and PE-MCM-41. The CO2 adsorption capacity of TRI−PE-MCM-41 was significantly higher than that of TRI−MCM-41. Furthermore, the dynamic adsorption performance of TRI−PE-MCM-41 was far superior to TRI−MCM-41. In comparison to 13X zeolite, TRI−PE-MCM-4...

Surface characterizations of mono-, di-, and tri-aminosilane treated glass substrates.

Abstract: The surface properties and structure of mono-, di-, and tri-aminosilane treated glass surfaces were investigated using surface analytical techniques including X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), and streaming potential. An optimized dip-coating process was demonstrated to produce roughly silane monolayer coverage on the glass surface. The surface charge measurements indicated that aminosilanization converts the glass surface from negative to positive potentials at neutral pH values. Higher positive streaming potential was observed for tri-compared with mono- and di-aminosilane treated glass surfaces. For all aminosilane treated glass samples, the high-resolution N 1s XPS spectra indicated a preferential orientation of the protonated amino-groups towards the glass surface whereas the free amino groups were protruding outward. This study aimed to obtain uniform, reproducibly thin, strongly adhering, internally cross-linked, and high positively charged aminosilane-coated glass surfaces for the attachment of DNA fragments used in microarraying experiments.

Structures and Potential Superconductivity in SiH 4 at High Pressure: En Route to “Metallic Hydrogen”

Abstract: A way to circumvent the high pressures needed to metallize hydrogen is to "precompress" it in hydrogen-rich molecules, a strategy probed theoretically for silane. We show that phases with tetrahedral SiH4 molecules should undergo phase transitions with sixfold- and eightfold-coordinate Si appearing above 25 GPa. The most stable structure found can be metallized at under a megabar and at a compression close to the prediction of Goldhammer-Herzfeld criterion. According to a BCS-like estimate, metallic silane should be a high-temperature superconductor.

The use of silane technology in crosslinking polyethylene/wood flour composites

Abstract: In this study, the use of silane technology in crosslinking polyethylene–wood flour composites have been investigated. Composites were produced in a one-step process using a co-rotating twin-screw extruder. The composites were stored in a sauna and at room temperature to study the effect of humidity on the degree of crosslinking. Crosslinked composites showed improved toughness and creep properties compared to non-crosslinked composites. The flexural modulus, on the other hand, was lower in the crosslinked samples than in the non-crosslinked ones. FTIR was used to study the crosslinking reaction in the samples. X-ray mapping of the silicon signal was also performed to locate the silane in the composites. This study provides a basis for proposing, that part of the silane is grafted onto polyethylene and wood thereby creating a crosslinked network in the matrix with chemical bonds (covalent and hydrogen bonding) to wood. The other part of the silane remains un-reacted and blends into the system.

The use of pre-treatments based on doped silane solutions for improved corrosion resistance of galvanised steel substrates

Abstract: The present work aims at evaluating the corrosion resistance of galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane doped with cerium nitrate or zirconium nitrate. The corrosion resistance of the pre-treated substrates was evaluated by electrochemical impedance spectroscopy, during immersion in NaCl solutions. The chemical composition of the surface was assessed by X-ray photoelectron spectroscopy and the surface morphology was studied by atomic force microscopy. The electrochemical results show that pre-treatments based on doped silane solutions provide good corrosion protection of the galvanised steel substrates. The work also aims at discussing the role of the dopants on the protective properties of the silane coatings formed on galvanised steel substrates.

Creating water-repellent effects on wood by treatment with silanes

Abstract: Three types of silanes were tested for their ability to impart hydrophobicity to solid wood samples: a tetraalkoxy silane bearing four hydrolysable alkoxy groups; two alkyl-trialkoxy silanes; and two multifunctional oligomeric silane systems. The first two types were applied as monomeric silane solutions and pre-condensed sols. The water uptake of treated wood was considerably reduced, especially after treatment with multifunctional waterborne silane systems, while uptake of gaseous water was not changed. Initial water repellence was most pronounced when a fluoro-alkyl functional oligomeric silane system was used; however, after a longer submersion time (24 h), the reduction in water uptake was strongly diminished. Wetting-drying cycles led to a reduction in hydrophobicity of samples treated with sols of alkoxysilanes, while aqueous functional silanes revealed enhanced water-repellent effects after these tests. This was explained by continued condensation of unreacted silanol groups in the aqueous functional silanes during the wetting-drying cycles. X-Ray mapping of silicon (SEM-EDX) showed that the reduction in water uptake due to the multifunctional silane HS 2909 is caused by plugging of the main penetration pathways such as pits, ray cells and ray tracheids.

The corrosion resistance of hot dip galvanized steel pretreated with Bis-functional silanes modified with microsilica

Abstract: The present work aims at understanding the corrosion behaviour of hot dip galvanized steel pretreated with either bis-1,2-[triethoxysilyl]ethane silane (BTSE) or bis-[triethoxysilylpropyl] tetrasulfide (BTESPT) modified with microparticles of SiO 2 . The corrosion resistance was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization and by the scanning vibrational electrode technique (SVET) during immersion in dilute NaCl solutions. The films formed on the galvanized steel substrate were characterized by X-ray photoelectron spectroscopy, Auger electron spectroscopy and atomic force microscopy. The results show that the pretreatments based on silane films modified with silica particles provide corrosion protection for hot dip galvanized steel during immersion in NaCl-containing solutions.

Flour rice husk as filler in block copolymer polypropylene : Effect of different coupling agents

Abstract: Flour rice husk (FRH) was employed as a filler in block copolymer polypropylene (PPB) in order to prepare polymer-based reinforced composites. Four coupling agents were selected to modify the surface of the rice husk in the composite materials, including two types of functionalized polymers [PP homopolymer grafted with maleic anhydride (MA-PP) and an elastomer styrene-ethylene-butadiene-styrene triblock copolymer grafted with MA (MA-SEBS)] and two bifunctional organometallic coupling agents (silane and titanate with linear low-density polyethylene as a carrier). The influence of each type of coupling agent on the interfacial bonding strength was studied by dynamic mechanical analysis, scanning electronic microscopy, and rheological tests. The results showed that strong interactions were formed between the coupling agents and the filler surface. The addition of a coupling agent with an elastomeric carrier (MA-SEBS) increased the loss tangent and reduced the storage modulus of the composite. A similar but less intense effect was observed for the titanate coupling agent. However, an antagonistic performance was obtained when MA-PP and silane were employed as coupling agents. In addition, when the percentage of MA-SEBS was increased, the impact properties of FRH/PPB blends were improved and the strength was reduced.

Silane/MoO2Cl2 as an efficient system for the reduction of esters

Abstract: The first method for the reduction of esters using a high oxidation state oxo complex as a catalyst is reported. The system silane/MoO2Cl2 (5 mol%) proved to be very efficient for the reduction of aliphatic and aromatic esters to the corresponding alcohols in good yields.

Mesoporous silicas functionalized with a high density of carboxylate groups as efficient absorbents for the removal of basic dyestuffs

Abstract: A novel silane bearing a reactive anhydride group was synthesized. Due to its special structure, the direct co-condensation of this synthesized functional silane with TEOS in the presence of different surfactant templates led to ordered mesoporous silicas with different pore sizes and a high density of carboxylic acid groups, which were used as adsorbents for the removal of three basic dyestuffs (methylene blue, phenosafranine and night blue) from waste water. The performed measurements showed that, probably due to their high surface area, good affinity of carboxylic groups and large number of binding sites, the obtained mesoporous materials exhibit a high adsorption capacity and an extremely rapid adsorption rate. Furthermore, these carboxylic-functionalized adsorbents can be regenerated by simple washing with acid solution to recover both the adsorbents and the adsorbed dyes. The experimental data for the adsorption of all three basic dyes were analyzed using Langmuir and Redlich–Peterson isotherm models. It is found that the Langmuir equation provides an accurate description of these adsorption data, suggesting that monolayer adsorption occurred in all cases of the performed sorption processes. In this work, the influences of the pH values of the treated solutions and the pore sizes of the prepared adsorbents on the adsorption behavior were also discussed.

Nanostructuration of phenylenevinylenediimide-bridged silsesquioxane: from electroluminescent molecular J-aggregates to photoresponsive polymeric H-aggregates.

Abstract: A new approach to control molecular aggregation of pi-conjugated chromophores in the solid state has been investigated. Our strategy was to use a modifiable bulky fragment which should induce a J-aggregation and offer the possibility to reach an H-aggregation upon its chemical modification by lateral slip of pi-conjugated molecules. The chosen fragment for that purpose was the hydrolyzable triethoxysilane function (Si(OEt)3). Our objective was to design and synthesize electroluminescent or solar cell hybrid organic-inorganic materials by the sol-gel process applied to a bifunctionalized silane. With this intention, the synthesis of the sol-gel processable phenylenevinylenediimide silsesquioxane 6 was accomplished and the study of spin-coated thin films of the pure silane precursor subjected or not to the sol-gel process has been carried out. Optical properties of 6 are consistent with the formation of J-aggregates in the solid state due to the steric hindrance introduced by the triethoxysilane units. Conversely, the spectroscopic behavior observed for the hybrid film 6F is attributed to an H-aggregation corresponding to a "card pack" orientation of the distyrylbenzeneimide chromophores in the compressed silicate network. Morevover, 6 and 6F also exhibited different electronic behaviors: light-emitting diodes exhibited high brightness with the native precursor 6 and almost no light output with the sol-gel processed silsesquioxane 6F. Photovoltaic cells showed the opposite behavior with low photocurrent generation in the precursor case and higher photocurrents with the sol-gel processed layers. These results provide a deeper understanding of the present self-assembly process that is strongly governed by the molecular packing of the oligosiloxane precursor.

The novel use of organo alkoxy silane for the synthesis of organic-inorganic hybrid coatings

Abstract: UV-curable, organic–inorganic hybrid coatings based on a UV-curable epoxyacrylate resin (EA) and methacryloxypropyl trimethoxysilane were prepared by the sol–gel method. 2,2′-Bis(4-β-hydroxy ethoxy) phenyl propane was modified by a coupling agent, 3-isocyanato propyl triethoxy silane, to improve the compatibility of the organic and inorganic phases. The formulations were applied onto Aluminum panels and cured by UV light to obtain a hard and clear coating with a good adhesion. The structural characterization of cured hybrid materials was performed using solid state 29Si NMR spectroscopy. The real time infrared technique was used to follow the degree of double bond conversion and photopolymerization rate. The thermal properties of the coatings are improved depends on the ‘component A’ composition in hybrid mixture which was composed of methacryloxy propyl trimethoxysilane (MAPTMS) and trimethoxysilane terminated HEPA urethane (TMSHU). The char yield of pure epoxy acrylate resin was 0.7 wt% and that of 30 wt% of component A containing hybrid coating was 4.6 wt% at 900 °C in air atmosphere. The morphology of the hybrid materials was examined by scanning electron microscopy. The hybrids were nanocomposites.