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Alkoxide Precursors (alkoxide + precursor)
Selected AbstractsDeformation Mechanism of Fine-Grained Magnesium Aluminate Spinel Prepared Using an Alkoxide PrecursorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Takeshi Shiono Polycrystalline MgAl2O4 spinel with high purity and stoichiometric composition was prepared using alkoxide precursors. The average grain size of the polycrystal was fine (1.7 ,m). The deformation mechanism of the polycrystal was investigated in air at temperatures of 1300°,1400°C. At 1300°C, oxygen lattice diffusion controlled the deformation, despite the fine grain size; however, increases in the temperature and applied stress caused cavities to nucleate and grow. Spinel possessed better creep resistance than alumina of comparative grain size. The effective diffusion coefficient was determined as follows: [formula omitted] [source] Growth of Praseodymium Oxide Thin Films by Liquid Injection MOCVD Using a Novel Praseodymium Alkoxide Precursor.CHEMINFORM, Issue 52 2003Helen C. Aspinall Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Al2O3,SiO2 Films by Ar/O2 Plasma-Enhanced CVD from Alkoxide Precursors,CHEMICAL VAPOR DEPOSITION, Issue 5 2006Y. Li Amorphous Al2O3, SiO2, and Al2O3,SiO2 composite films have been produced at 800,°C from alkoxide solution precursors by liquid-injection oxygen plasma enhanced CVD. The films' structures and morphologies are affected by the feed rate of the liquid precursor and their compositions can be controlled by adjusting the Si/Al ratios in the starting source. Steel substrates coated with the above films gained excellent protection when they were exposed to high temperature atmosphere containing KCl vapor. [source] Growth of Hafnium Aluminate Thin Films by Liquid Injection MOCVD Using Alkoxide Precursors,CHEMICAL VAPOR DEPOSITION, Issue 5 2004P.A. Marshall Abstract Thin films of Hf aluminate, (HfO2)x(Al2O3)1,x (Al,=,8.4,38.5,at.-%) have been deposited by liquid injection MOCVD using the metal alkoxide precursors [Hf(mmp)4] (mmp,=,OCMe2CH2OMe) and [Al(OiPr)3]. (HfO2)x(Al2O3)1,x thin films deposited at 500,°C had a thickness range of 7,13,nm and were high purity, with no carbon detected by Auger electron spectroscopy (AES) at the estimated detection limit of 0.5,at.-%. Thick films of (HfO2)x(Al2O3)1,x containing more than ,7,at.-% Al were found by X-ray diffraction (XRD) to be amorphous. High frequency capacitance,voltage (C,V) measurements indicate strong electron trapping and a high density of interface states. [source] Yttrium Silicate Powders Produced by the Sol,Gel Method, Structural and Thermal CharacterizationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2003Damien Boyer Yttrium silicate (Y2SiO5) powders of high purity have been synthesized using the sol,gel method. Alkoxide precursors were used with commercial tetraethyl orthosilicate as the silica source and yttrium propoxide synthesized from YCl3. Powders calcined from the xerogel showed submicrometer crystal sizes. These powders were sintered at temperatures <1300°C and are suitable for coating applications such as a thermal barrier system for SiC/SiC composites. [source] Cover Picture: Functionalized Gold Nanoparticles Mimic Catalytic Activity of a Polysiloxane-Synthesizing Enzyme (Adv. Mater.ADVANCED MATERIALS, Issue 10 200510/2005) Abstract A system that acts as a biomimetic of the silica-synthesizing enzyme found in a marine sponge is reported by Morse and co-workers on p.,1234. Gold nanoparticles (GNPs) are functionalized with the same organic moieties that are found in the enzyme's catalytic site. Interaction between the nucleophilic (OH-terminated) and hydrogen-bonding (imidazole-terminated) GNPs, as shown on the cover, is required for the hydrolysis of a silicon alkoxide precursor and subsequent polycondensation to form silica at a low temperature and near-neutral pH. Replacement of either of the required functional groups by a non-reactive methyl group abolishes catalysis in this synthetic system, as it does in the biological enzyme. Cover art provided by Peter Allen. [source] Protective organic-inorganic hybrid coatings on mild steel derived from Ti(OC4H9)4 -modified precursorsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2004V. Nguyen Abstract Titania-poly(methyl methacrylate-co-butyl methacrylate-co-methacrylic acid) hybrids prepared by a sol-gel method were deposited by dip coating on mild steel. Transparent and defect free coatings with titania content ranging between 0 and 12.7 wt.% have been prepared. Barrier properties and dry adherence have been tested by electrochemical impedance spectroscopy (EIS) and the vertical pull-off test, respectively. The pull-off test results suggest that the titanium alkoxide precursor must intercede on the substrate/coating interphase during film formation to create specific adhesive bondings with the substrate. In this paper, two capacitance models are used to estimate the water uptake, one based on a uniform and one on a heterogeneous distribution of sorbed water. Water uptake determined from these two models is compared to the gravimetry results. It is suggested that a reliable determination of the actual water uptake in coatings from capacitance measurements require an extensive experimental work. The variations in the state of sorbed water with the specimen type or immersion time, the leaching of organics during immersion or the slow diffusion of ions are fundamental factors that must be considered when comparing the water uptake determined from gravimetry and capacitance models. [source] Reactions under Autogenic Pressure at Elevated Temperature (RAPET) of Various Alkoxides: Formation of Metals/Metal Oxides-Carbon Core-Shell StructuresCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2004Swati V. Pol Abstract The RAPET reaction at 700,°C, of different alkoxides (Ti, V, and Si) led to three different nanocomposites. Carbon is the element common to all three structures. Carbon was found as the core in the decomposition of TEOS, as the shell in the decomposition of VO(OEt)3 and embedded in, or mixed completely with, TiO2 in the decomposition of Ti(OiPr)4. This novel method using only metallic alkoxide precursor, in the absence of catalyst, leads in a one-step process to core-shell structures. [source] Functionalized Gold Nanoparticles Mimic Catalytic Activity of a Polysiloxane-Synthesizing Enzyme,ADVANCED MATERIALS, Issue 10 2005D. Kisailus A synthetic analogue of a naturally occurring enzyme has been produced by grafting appropriate nucleophilic and hydrogen-bonding functionalities to gold nanoparticles via self-assembled monolayers (see Figure and cover). The synthetic analogue mimics silicatein proteins, which act as both catalysts and templates for formation of silica needles in a marine sponge, converting silicon alkoxide precursors to silica at low temperatures and near-neutral pH. [source] Deformation Mechanism of Fine-Grained Magnesium Aluminate Spinel Prepared Using an Alkoxide PrecursorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Takeshi Shiono Polycrystalline MgAl2O4 spinel with high purity and stoichiometric composition was prepared using alkoxide precursors. The average grain size of the polycrystal was fine (1.7 ,m). The deformation mechanism of the polycrystal was investigated in air at temperatures of 1300°,1400°C. At 1300°C, oxygen lattice diffusion controlled the deformation, despite the fine grain size; however, increases in the temperature and applied stress caused cavities to nucleate and grow. Spinel possessed better creep resistance than alumina of comparative grain size. The effective diffusion coefficient was determined as follows: [formula omitted] [source] Growth of Hafnium Aluminate Thin Films by Liquid Injection MOCVD Using Alkoxide Precursors,CHEMICAL VAPOR DEPOSITION, Issue 5 2004P.A. Marshall Abstract Thin films of Hf aluminate, (HfO2)x(Al2O3)1,x (Al,=,8.4,38.5,at.-%) have been deposited by liquid injection MOCVD using the metal alkoxide precursors [Hf(mmp)4] (mmp,=,OCMe2CH2OMe) and [Al(OiPr)3]. (HfO2)x(Al2O3)1,x thin films deposited at 500,°C had a thickness range of 7,13,nm and were high purity, with no carbon detected by Auger electron spectroscopy (AES) at the estimated detection limit of 0.5,at.-%. Thick films of (HfO2)x(Al2O3)1,x containing more than ,7,at.-% Al were found by X-ray diffraction (XRD) to be amorphous. High frequency capacitance,voltage (C,V) measurements indicate strong electron trapping and a high density of interface states. [source] Microporous Niobia,Silica Membrane with Very Low CO2 PermeabilityCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 5 2008Vittorio Boffa Dr. Abstract A sol,gel-derived microporous ceramic membrane with an exceptionally low permeability for CO2 from gaseous streams was developed and characterized. The sols were prepared from a mixture of niobium and silicon alkoxide precursors by acid-catalyzed synthesis. Microporous films were formed by coating asymmetric ,-alumina disks with the polymeric sol (Si/Nb=3:1), followed by calcination at 500,°C. The membrane consists of a 150-nm-thick layer with a Si/Nb atomic ratio of about 1.5. The single-gas permeance of small gas molecules such as H2, CH4, N2, and SF6 decreases steadily with kinetic diameter. Hydrogen, helium, and carbon dioxide follow an activated transport mechanism through the membrane. The permeance of CO2 in this membrane is much lower than that in pure silica, and its behavior deviates strongly from the general trend observed with the other gases. This is attributed to a relatively strong interaction between CO2 and adsorption sites in the niobia,silica membrane. [source] | |||||||||||||