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SiO2
Kinds of SiO2 Terms modified by SiO2 Selected AbstractsPreparation, structure and photoluminescence properties of SiO2,coated ZnS nanowiresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2010Changhyun Jin Abstract It is essential to passivate one-dimensional (1D) nanostructures with insulating materials to avoid crosstalking as well as to protect them from contamination and oxidation. The structure and influence of thermal annealing on the photoluminescence properties of ZnS-core/SiO2 -shell nanowires synthesized by the thermal evaporation of ZnS powders followed by the sputter deposition of SiO2 were investigated. Transmission electron microscopy and X-ray diffraction analyses revealed that the cores and shells of the core-shell nanowires were single crystal zinc blende-type ZnO and amorphous SiO2, respectively. Photoluminescence (PL) measurement showed that the core-shell nanowires had a green emission band centered at around 525 nm with a shoulder at around 385 nm. The PL emission of the core-shell nanowires was enhanced in intensity by annealing in an oxidative atmosphere and further enhanced by subsequently annealing in a reducing atmosphere. Also the origin of the enhancement of the green emission by annealing is discussed based on the energy-dispersive X-ray spectroscopy analysis results. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatially resolved X-ray diffraction as a tool for strain analysis in laterally modulated epitaxial structuresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2009A. Wierzbicka Abstract Spatially resolved X-ray diffraction (SRXRD) is applied for micro-imaging of strain in laterally modulated epitaxial structures. In GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2 -masked GaAs substrates a downward tilt of ELO wings caused by their interaction with the mask is observed. The distribution of the tilt magnitude across the wings width is determined with ,m-scale spatial resolution. This allows measuring of the shape of the lattice planes in individual ELO stripes. If a large area of the sample is studied the X-ray imaging provides precise information on the tilt of an individual wing and its distribution. In heteroepitaxial GaSb/GaAs ELO layers local mosaicity in the wing area is found. By the SRXRD the size of microblocks and their relative misorientation were analyzed. Finally, the SRXRD technique was applied to study distribution of localized strain in AlGaN epilayers grown by MOVPE on bulk GaN substrates with AlN mask. X-ray mapping proves that by mask patterning strain in AlGaN layer can be easily engineered, which opens a way to produce thicker, crack-free AlGaN layers with a higher Al content needed in GaN-based laser diodes. All these examples show that high spatial and angular resolutions offered by SRXRD makes the technique a powerful tool to study local lattice distortions in semiconductor microstructures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Morphological, structural and optical study of quasi-1D SnO2 nanowires and nanobeltsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005D. Calestani Abstract 0.1,0.3 mm thick entanglements of quasi-one-dimensional semiconducting Tin dioxide nanocrystals, in form of nanowires and nanobelts, are successfully grown by low cost Chemical Vapour Deposition directly on large area (100 mm2) Al2O3, SiO2 and Si substrates. Their lateral size ranges from 50 to 700 nm and their length can achieve several hundreds of micrometers. Transmission Electron Microscopy reveals either the nanowires and the nanobelts grow in the tetragonal Rutile structure. Diffraction contrast analyses and selected area diffraction investigations show the nanowires are single crystals without defects while the nanobelts sometimes present twins inside. An almost cylindrical shape and an average diameter of about 30,50 nm for the smallest nanowires is reported. X-ray diffraction investigations exclude the presence of spurious phases. A broad band structured in two emissions peaked at about 450 nm and 560 nm is revealed by large area Cathotoluminescence, while single nanocrystal spectroscopy shows that the reduction of the lateral dimension of the nanobelts from 1000 nm to 50 nm blue-shifts the main emission band at 560 nm of about 40 nm (at room temperature). These preliminary results suggest a possible role of oxygen vacancies and of the surface/volume ratio on the origin and the blue shift of Cathodoluminescence spectra. The near band edge emission, typical of bulk tin dioxide (,320 nm), is not found in nanobelts narrower than 1000 nm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Void formation in the Cu layer during thermal treatment of SiNx/Cu/Ta73Si27/SiO2/Si systemsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1-2 2005R. Hübner Abstract The thermal stability of a SiNx passivation layer and its influence on the annealing behavior of an amorphous Ta73Si27 diffusion barrier deposited between copper and SiO2 were analyzed by X-ray diffraction, glow discharge optical emission spectroscopy, Auger electron spectroscopy, scanning electron microscopy, and transmission electron microscopy. During heat treatment at a temperature Tan = 500 °C, diffusion of Cu atoms out of the Cu metallization into the SiNx passivation occurs. The Cu diffusion intensifies with increasing annealing temperature and annealing time and seems to be a necessary precondition for a defect formation process observed within the Cu metallization. Depending on the chemical composition of the SiNx/Cu interface, voids in the ,m-range can be formed within the Cu film. Compared to an unpassivated sample, heat treatment leads to a reduced diffusion of Ta atoms from the barrier through the copper into the SiNx/Cu interface. The barrier crystallization process into Ta5Si3 occurring during annealing at Tan = 600 °C is principally not affected by the presence of a SiNx passivation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] InN@SiO2 Nanomaterials as New Blue Light EmittersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2008Prabhakaran Munusamy Abstract In this article we report blue photoluminescence (, 450 nm) from InN@SiO2 nanomaterials. The InN@SiO2 nanomaterials were prepared by a simple precipitation reaction followed by a solid-state reaction. Various control experiments demonstrate that the interface between the InN and SiO2 seems to play a crucial role in the origin of the blue emission from the InN@SiO2 nanomaterial. The InN@SiO2 nanomaterial was characterized by using analytical methods such as TEM, XRD, Raman, XPS, and photoluminescence spectroscopy, which confirmed the existence of InN on SiO2 with a small excess of nitrogen relative to indium.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Aerogel and Xerogel Catalysts Based on ,-Alumina Doped with Silicon for High Temperature ReactionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2005Aurelien Florin Popa Abstract Numerous materials (supports and catalysts) based on alumina have been prepared using the sol-gel process and carbon dioxide supercritical drying. In this work two types of solids, i.e. xerogels and aerogels, were systematically compared and a way of introducing platinum metal with a content of 5% percent by weight was examined. The structural data, the surface area, Pt dispersion and catalytic activity for the decomposition of the propellant were measured for the various samples. The (Al2O3)0.88(SiO2)0.12 samples prepared show very interesting porosity values, especially for the aerogel. For this reason, they were chosen as supports for the synthesis of 5 wt% platinum on alumina catalysts. The results presented in this work allowed us to obtain an overall view of the influence of the preparation mode on the properties of platinum on alumina supported catalysts. The dispersion of the metal phase is directly dependent on the specific surface of the support. A significant value for the surface area implies a large amount of centers for interaction with the metal precursor and, consequently, the appearance of more centres of simultaneous germination. Although aerogels obtained by carbon dioxide supercritical drying always show superior properties compared with xerogels, for catalytic decompositions the xerogels still remain superior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] SiO2 -CaO Vitreous Films Deposited onto Ti6Al4V SubstratesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2003Isabel Izquierdo-Barba Abstract A sol-gel dipping method has been utilised to deposit SiO2 -CaO films onto Ti6Al4V alloy substrates. These layers were prepared by the dip-coating technique from a series of precursor solutions with different concentrations of glassy xSiO2 -(1 , x)CaO (x = 0.8 mol) diluted with absolute ethanol. The characterisation of the films by a variety of techniques reveals differences in the textural properties and in the films' thicknesses depending on the sol concentration in the precursor solution. Concentrated precursor solutions yield porous layers with a higher thickness and surface roughness than those obtained from the dilute ones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Microstructural Characteristics of an AZ91 Matrix-Glassy Carbon Particle Composite,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Anita Olszówka-Myalska This paper presents the results of a microstructural investigation of a new type of ultralight glassy carbon particles (Cp)-AZ91 magnesium alloy matrix composite manufactured by the powder metallurgy method. Glassy Cp with unmodified surfaces and surfaces modified with SiO2 amorphous nanocoating were used in the experiment. The composite microstructure, with an emphasis given on the interface, was characterized by scanning electron microscope (SEM), TEM, and HRTEM microscopy. Uniform distribution of the particles in the matrix and their good bonding with the metal matrix were observed. A continuous very thin MgO oxide layer containing needle-like Al2MgO4 phase was detected at the glassy carbon,AZ91 interface. An increase of aluminum concentration at the interface as a result of Mg and Al diffusion into the SiO2 nanolayer was observed in the case of particles modified with SiO2. Crystalline phases containing carbon were not detected at the interface. [source] Surface Activation of a Ferrimagnetic Glass,Ceramic for Antineoplastic Drugs GraftingADVANCED ENGINEERING MATERIALS, Issue 7 2010Enrica Vernè A ferrimagnetic glass,ceramic, belonging to the system SiO2,Na2O,CaO,P2O5,FeO,Fe2O3, has been studied as potential carrier for antineoplastic agents, in order to exploit the combination of hyperthermia and chemotherapy. Different material pre-treatments, such as ultrasonic washing, water, or simulated body fluid dipping, were evaluated to promote the surface activation of the glass,ceramic, i.e., the hydroxyl groups formation on it. X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersion spectrometry, and wettability measurements were performed to observe the samples surface modification. The best results in terms of free hydroxyl groups exposition were obtained by dipping the samples in distilled water for 7 days at 37,°C. Two different anticancer drugs were selected in order to test the reactivity of the activated surface: cisplatinum and doxorubicin. The uptake and release of doxorubicin and cisplatinum were evaluated on glass,ceramic powders, by using UV,Visible spectrometry and graphite furnace atomic absorption spectroscopy, respectively. After 1 day of uptake at 37,°C, the quantity of doxorubicin incorporated into the glass,ceramic is 77,±,7 wt%, while only 42,±,9.6 wt% of cisplatinum is grafted onto the material surface. For both antitumoral agents, the maximum drug release after soaking in aqueous solutions at 37,°C was obtained in few hours, with a randomly distributed kinetics trend. [source] Hydroxyapatite/SiO2 Composites via Freeze Casting for Bone Tissue Engineering,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Silke Blindow Freeze casting is a fabrication method that allows producing near-net-shaped ceramics with variable porosity. Hydroxyapatite (HA) was modified by the addition of different amounts of SiO2 nanoparticles during freeze cast preparation. The addition of SiO2 introduced a partial phase transformation of HA to , -tricalcium phosphate and improved the form stability due to less shrinkage after sintering. The impact of surface roughness of pure HA ceramics and the influence of SiO2 introduction during freeze casting on adhesion, proliferation, and differentiation of human osteoblast-like cells (MG-63) was investigated. While both cell attachment and proliferation of smooth pressed HA was significantly enhanced compared to rough freeze cast HA, the addition of SiO2 improved the cell numbers of the latter. The expression of cell differentiation markers osteocalcin and collagen I was found to be supported by rough surfaces (Ra,=,5,6,µm) in particular on ceramics containing SiO2 [source] Silica-Immobilized NHC,CuI Complex: An Efficient and Reusable Catalyst for A3 -Coupling (Aldehyde,Alkyne,Amine) under Solventless Reaction ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2008Min Wang Abstract A novel silica-immobilized NHC,CuI complex was developed and used as a highly efficient catalyst in the three-component coupling reactions of aldehydes, alkynes and amines (A3 -coupling). The reactions were applicable to aromatic and aliphatic aldehydes, alkynes and amines, and generated the corresponding propargylamines in good yields only in the presence of SiO2,NHC,CuI (2 mol-%) at room temp. under solvent-free reaction conditions. Moreover, the catalyst was quantitatively recovered from the reaction mixture by a simple filtration and reused for ten cycles with almost consistent activity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Crystallization of Highly Supercooled Silicate MeltsADVANCED ENGINEERING MATERIALS, Issue 12 2006M. Roskosz Crystallization of liquids in the system CaO-MgO-Al2O3 -SiO2 at one atmosphere has been studied at temperatures between the glass transition (Tg) and the solidus. To determine the textures, compositions and unit-cell parameters of the crystalline phases, the authors have characterized the experimental charges over a wide range of length scales by scanning and transmission electron microscopy, electron microprobe analyses, X-ray diffraction, and Raman spectroscopy. With increasing temperature, crystals tend to reach the equilibrium composition, but the relative importance of thermodynamic and kinetic factors is a single function of T - Tg, regardless of liquid composition. This feature is of considerable practical interest as it provides the possibility, not only to predict, but also to control the composition of the crystallizing phases. [source] Antireflective Nanoparticle Arrays Enhance the Efficiency of Silicon Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Dehui Wan Abstract In this study, the phenomenon of light trapping in Si solar cells coated with metal (Au) and dielectric (TiO2, SiO2) nanoparticles (NPs) is systematically investigated. In contrast to previous reports, herein it is proposed that the photocurrent enhancement of solar cells should be attributed to the limited antireflection ability of the Au NP arrays. In other words, the Au NP arrays might not enhance the absorption of the active layer in cells when no light is reflected from the air,substrate interface. Therefore, the Au NPs are replaced with dielectric NPs, which possess lower extinction coefficients, and then the antireflection property of the TiO2 NP arrays is optimized. A simple, rapid, and cheap solution-based method is used to prepare close-packed TiO2 NP films on Si solar cells; these devices exhibit a uniform and remarkable increase (ca. 30%) in their photocurrents. To the best of the authors' knowledge, this uniform photocurrent enhancement is greater than those obtained from previously reported metal and dielectric NP,enhanced Si wafer-based solar cells. [source] Construction and Characterization of Porous SiO2/Hydrogel Hybrids as Optical Biosensors for Rapid Detection of BacteriaADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Naama Massad-Ivanir Abstract The use of a new class of hybrid nanomaterials as label-free optical biosensors for bacteria detection (E. coli K12 as a model system) is demonstrated. The hybrids combine a porous SiO2 (PSiO2) optical nanostructure (a Fabry,Pérot thin film) used as the optical transducer element and a hydrogel. The hydrogel, polyacrylamide, is synthesized in situ within the nanostructure inorganic host and conjugated with specific monoclonal antibodies (IgGs) to provide the active component of the biosensor. The immobilization of the IgGs onto the hydrogel via a biotin-streptavidin system is confirmed by fluorescent labeling experiments and reflective interferometric Fourier transform spectroscopy (RIFTS). Additionally, the immobilized IgGs maintain their immunoactivity and specificity when attached to the sensor surface. Exposure of these modified-hybrids to the target bacteria results in "direct cell capture" onto the biosensor surface. These specific binding events induce predictable changes in the thin-film optical interference spectrum of the hybrid. Preliminary studies demonstrate the applicability of these biosensors for the detection of low bacterial concentrations in the range of 103,105 cell mL,1 within minutes. [source] High-Performance Air-Stable n-Type Organic Transistors Based on Core-Chlorinated Naphthalene Tetracarboxylic DiimidesADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Joon Hak Oh Abstract Core-chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are synthesized and employed for n-channel organic thin-film transistors (OTFTs). Structural analyses of the single crystals and thin films are performed and their charge-transport behavior is investigated in terms of structure,property relationships. NDIs with two chlorine substituents are shown to exhibit a herringbone structure with a very close ,-plane distance (3.3,3.4,Å), a large ,-stack overlap (slipping angle ca. 62°), and high crystal densities (2.046,2.091,g,cm,3). These features result in excellent field-effect mobilities of up to 1.43,cm2,V,1,s,1 with minimal hysteresis and high on,off ratios (ca. 107) in air. This is similar to the highest n-channel mobilities in air reported so far. Despite the repulsive interactions of bulky Cl substituents, tetrachlorinated NDIs adopt a slip-stacked face-to-face packing with an interplanar distance of around 3.4,Å, resulting in a high mobility (up to 0.44,cm2,V,1,s,1). The air-stability of dichlorinated NDIs is superior to that of tetrachlorinated NDIs, despite of their higher LUMO levels. This is closely related to the denser packing of the fluorocarbon chains of dichlorinated NDIs, which serves as a kinetic barrier to the diffusion of ambient oxidants. Interestingly, these NDIs show an optimal performance either on bare SiO2 or on octadecyltrimethoxysilane (OTS)-treated SiO2, depending on the carbon number of the fluoroalkyl chains. Their synthetic simplicity and processing versatility combined with their high performance make these semiconductors highly promising for practical applications in flexible electronics. [source] Remote extinguishing of large fires with powder aerosolsFIRE AND MATERIALS, Issue 5 2006Article first published online: 9 JAN 200, Mikhail Krasnyansky Abstract A new method for distant extinguishing of fire spreading in an extended closed volume such as a mine working, storehouse, subway tunnel, electric cable channels, etc. is proposed. A novel extinguishing agent based on a stable mixture of superfine ammonium phosphate [NH4H2PO4] and modified fumed silica [SiO2,CH3] is supplied to the fire by a powerful ventilator. The properties of the extinguishing agent (average particle size, airborne residence time, distance of transfer by the air stream) have been studied in an experimental chamber (100 m3). A test extinguishing of a large-scale fire has been performed in an experimental tunnel 180 m in length. Extinguishing agent consumption, dynamics of temperature change over the tunnel length and composition of fire gases were recorded in this test. The influence of foam concentration, addition of nitrogen and halons to aerosol, were also studied. Copyright © 2006 John Wiley & Sons, Ltd. [source] Preparation-Condition Dependence of Hybrid SiO2 -Coated CdTe Nanocrystals with Intense and Tunable PhotoluminescenceADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Ping Yang Abstract When aqueously prepared CdTe nanocrystals (NCs) are coated with a SiO2 shell containing Cd ions and a sulfur source, they show a drastic increase in photoluminescence (PL) efficiency with a significant red shift and spectral narrowing after reflux. This is ascribed to the creation of a hybrid structure characterized by the formation of CdS-like clusters in the vicinity of the NCs in the SiO2 shell. Since these clusters are close to the NCs, their effective size increases to reduce the quantum size effect. The dependences of the PL properties on the preparation conditions are systematically investigated. The PL efficiency increases from 28% to 80% in the best case with a red shift of 80,nm. The PL behaviors differ from those of normal CdTe NCs and include less temperature quenching and longer PL lifetime. The SiO2 coating enables bioconjugation with IgG without deterioration of PL efficiency, making hybrid NCs amenable for bioapplication. [source] Original Fuel-Cell Membranes from Crosslinked Terpolymers via a "Sol,gel" StrategyADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Ozlem Sel Abstract Hybrid organic/inorganic membranes that include a functionalized (-SO3H), interconnected silica network, a non-porogenic organic matrix, and a -SO3H-functionalized terpolymer are synthesized through a sol,gel-based strategy. The use of a novel crosslinkable poly(vinylidene fluoride- ter -perfluoro(4-methyl-3,6-dioxaoct-7-ene sulfonyl fluoride)- ter -vinyltriethoxysilane) (poly(VDF- ter -PFSVE- ter -VTEOS)) terpolymer allows a multiple tuning of the different interfaces to produce original hybrid membranes with improved properties. The synthesized terpolymer and the composite membranes are characterized, and the proton conductivity of a hybrid membrane in the absence of the terpolymer is promising, since 8,mS cm,1 is reached at room temperature, immersed in water, with an experimental ion-exchange-capacity (IECexp) value of 0.4,meq g,1. Furthermore, when the composite membranes contain the interfaced terpolymer, they exhibit both a higher proton conductivity (43,mS cm,1 at 65 °C under 100% relative humidity) and better stability than the standard hybrid membrane, arising from the occurrence of a better interface between the inorganic silica and the poly[(vinylidene fluoride)- co -hexafluoropropylene] (poly(VDF- co -HFP)) copolymer network. Accordingly, the hybrid SiO2 -SO3H/terpolymer/poly(VDF- co -HFP) copolymer membrane has potential use as an electrolyte in a polymer-electrolyte-membrane fuel cell operating at intermediate temperatures. [source] Supercritical-Fluid-Assisted One-Pot Synthesis of Biocompatible Core(, -Fe2O3)/Shell(SiO2) Nanoparticles as High Relaxivity T2 -Contrast Agents for Magnetic Resonance ImagingADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Elena Taboada Abstract Monodisperse iron oxide/microporous silica core/shell composite nanoparticles, core(, -Fe2O3)/shell(SiO2), with a diameter of approximately 100,nm and a high magnetization are synthesized by combining sol,gel chemistry and supercritical fluid technology. This one-step processing method, which is easily scalable, allows quick fabrication of materials with controlled properties and in high yield. The particles have a specific magnetic moment (per kg of iron) comparable to that of the bulk maghemite and show superparamagnetic behavior at room temperature. The nanocomposites are proven to be useful as T2 MRI imaging agent. They also have potential to be used in NMR proximity sensing, theranostic drug delivery, and bioseparation. [source] Re-creation of the 1744 Heylyn and Frye ceramic patent wares using Cherokee clay: Implications for raw materials, kiln conditions, and the earliest English porcelain productionGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2004W.R.H. Ramsay Porcelain wares have been produced following the directions contained in the Heylyn and Frye patent of 1744, using Cherokee clay and a lime-alkali glass frit. The wares were fired to the bisque (, 950°C), glazed using a clay-glass mixture, and then fired to a "heat-work" level of Orton cone 9,90° deflection at 150°C per hour (1279°C). Modal mineralogy comprises Caplagioclase and two glass phases, one relict frit and the other a melt phase. The bulk chemistry of the body comprises 64.3 wt % SiO2, 21.7 wt % Al2O3, and 5.6 wt % CaO. Molecular ratios are SiO2:Al2O3 5.0 and SiO2:CaO 10.7. It is concluded that the patent, whose significance has been questioned over many years, was a practical working recipe, that close comparison may be made with porcelains of the "A"-marked group, and that the patent represents a remarkable landmark in English ceramic history. © 2004 Wiley Periodicals, Inc. [source] From London to Liverpool: Evidence for a Limehouse,Reid porcelain connection based on the analysis of sherds from the Brownlow Hill (ca. 1755,1767) factory siteGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 8 2003J. Victor Owen The diversity of Brownlow Hill porcelains of the Wm Reid & Co. era is due to the remarkably wide range in the composition of their pastes and glazes and inferred firing conditions relative to the initial vitrification temperature. Sixteen of 21 analyzed sherds from the factory site are bone-ash wares that display large variations in their bulk chemical composition. The remaining samples have silicious-aluminous (akin to "stone china" sensu Richard Pococke in 1750) and silicious-aluminous-calcic ("S-A-C") compositions that resemble Limehouse (London) and Pomona (Staffordshire) porcelains produced during the 1740s. The mineralogy of the Brownlow Hill S-A-C sherds suggests firing at a relatively high temperature (Tmax approaching 1400°C, based on relations on the SiO2 -Al2O3 -CaO phase diagram), thereby obscuring the identity of some of the ingredients (e.g., the source of CaO) used in their manufacture. Limehouse and Brownlow Hill may have been linked through the activities of William Ball, who is mentioned in connection with both factories, or indirectly via former Limehouse staff later employed at the Pomona factory, located not far from a Wm Reid & Co. branch factory in Shelton, Stoke-on-Trent. In terms of a time line, knowledge of these pastes appears to have spread first from London to Staffordshire, and then to Liverpool. © 2003 Wiley Periodicals, Inc. [source] The major- and trace-element whole-rock fingerprints of Egyptian basalts and the provenance of Egyptian artefactsGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2001John D. Greenough Discrimination diagrams have been developed that source Egyptian basaltic artefacts using whole-rock major element geochemistry. These include K2O versus SiO2, TiO2 and P2O5 against MgO/Fe2O3t (total Fe as Fe2O3), and a discriminant analysis diagram using SiO2, Fe2O3t, CaO, and MnO. A complementary set of diagrams uses easily obtained trace element data (Nb/Y versus Zr/Nb; Zr [ppm] versus Rb/Sr; TiO2 [wt % volatile free] versus V; and Cr [ppm] versus Zr/Y) to determine the bedrock sources. These diagrams have been applied to seven First Dynasty basalt vessels (Abydos), two Fourth Dynasty basalt paving stones (Khufu's funerary temple, Giza), and two Fifth Dynasty paving stones (Sahure's complex, Abu Sir). They show that the bedrock source for all the artefacts was the Haddadin flow in northern Egypt. Multidimensional scaling and cluster analysis applied to the whole-rock data (major elements and trace elements together) and previously published mineral fingerprinting studies confirm these results. Comparing mineral versus whole-rock fingerprinting techniques, a major advantage of the former is the small sample size required (0.001 g compared to , 0.1 g). Analytical costs are similar for both methods assuming that a comparison (bedrock) database can be assembled from the literature. For most archaeological problems, a whole-rock bedrock database is more likely to exist than a mineral database, and whole-rock analyses on artefacts will generally be easier to obtain than mineral analyses. Whole-rock fingerprinting may be more sensitive than mineral-based fingerprinting. Thus, if sample quantity is not an issue, whole-rock analysis may have a slight cost, convenience, and technical advantage over mineral-based methods. Our results also emphasize that the Egyptians cherished their Haddadin basalt flow and used it extensively and exclusively for manufacturing basalt vessels and paving stones for at least 600 years (,3150 B.C. to 2500 B.C., approximate ages of the vessels and Abu Sir paving stones, respectively). © 2001 John Wiley & Sons, Inc. [source] Geochemical and mineralogical distinctions between Bonnin and Morris (Philadelphia, 1770,1772) porcelain and some contemporary British phosphatic waresGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2001J. Victor Owen The major element compositions of 15 ceramic sherds from the Bonnin and Morris factory site were determined by electron microprobe. Thirteen samples are phosphatic; the others consist of (a) "soapstone" (magnesian/plombian) and (b) true porcelain, and are interpreted as exotic artifacts, as is one compositionally distinct (relatively SiO2 -poor, P2O5+CaO-rich) phosphatic sample. Although long considered to be virtually indistinguishable from Bow porcelain (London: ca. 1747,1776), the phosphatic Philadelphia wares have a relatively low mean CaO/P2O5 ratio (3.3 versus 3.8; molecular proportions) and high alumina content (6.6 versus 5.4 wt % Al2O3). Furthermore, unlike Bow, the Bonnin and Morris samples contain calcic plagioclase (bytownite), and in some instances, an orthoclase-rich ternary feldspar. The preservation of calcic plagioclase indicates that Philadelphia porcelain was fired at (rather than above) the thermal minimum in the An-SiO2 -C3P system, although the presence of Na (and other fluxes) in these wares precludes the exact determination of the maximum firing temperature from this phase diagram. These wares are also distinctive insofar as the phosphate and melt phases can contain small amounts of lead; they have bulk lead contents of approximately 0.1,1.2 wt % PbO. This component has not been detected in the body of Bow or other contemporary British phosphatic porcelains. Their principal similarity lies in the fact that both wares contain sulfate. In addition, the glazes on Bonnin and Morris porcelain (e.g., PbO , 35,50 wt %; SnO2 , 1,2%) compositionally resemble those used at Bow. If feldspar is formed at all, then Al-poor phosphatic porcelain (or those with low CaO/P2O5 ratios) will have comparatively low modal calcic plagioclase contents, thereby allowing the rapid depletion of this mineral via resorption by the melt phase during vitrification. Such appears to have been the case for analyzed Bow porcelain, which is therefore interpreted to have been overfired (sensu lato) relative to its Philadelphia counterpart. Conceivably, calcic plagioclase could be preserved in low-Al wares that were fired only briefly at vitrification temperatures. Given the role of firing history in governing the mineralogy of porcelain, compositional criteria are more reliable for distinguishing these wares. © 2001 John Wiley & Sons, Inc. [source] Unravelling the microbial role in ooid formation , results of an in situ experiment in modern freshwater Lake Geneva in SwitzerlandGEOBIOLOGY, Issue 4 2008K. PLEE ABSTRACT The microbial role in the formation of the cortex of low-Mg calcite freshwater ooids in western part of Lake Geneva in Switzerland has been suggested previously, but not demonstrated conclusively. Early work mostly concentrated in hypersaline milieus, and hence little is known about their genesis in freshwater environments. We designed an in situ experiment to mimic the natural process of low-Mg calcite precipitation. A special device was placed in the ooid-rich bank of the lake. It contained frosted glass (SiO2) slides, while quartz (SiO2) is the most abundant mineral composition of ooid nuclei that acted as artificial substrates to favour microbial colonization. Microscopic inspection of the slides revealed a clear seasonal pattern of carbonate precipitates, which were always closely associated with biofilms that developed on the surface of the frosted slides containing extracellular polymeric substance, coccoid and filamentous cyanobacteria, diatoms and heterotrophic bacteria. Carbonate precipitation peaks during early spring and late summer, and low-Mg calcite crystals mostly occur in close association with filamentous and coccoid cyanobacteria (e.g. Tolypothrix, Oscillatoria and Synechococcus, Anacystis, respectively). Further scanning electron microscope inspection of the samples revealed low-Mg calcite with crystal forms varying from anhedral to euhedral rhombohedra, depending on the seasons. Liquid cultures corroborate the in situ observations and demonstrate that under the same physicochemical conditions the absence of biofilms prevents the precipitation of low-Mg calcite crystals. These results illustrate that biofilms play a substantial role in low-Mg calcite ooid cortex formation. It further demonstrates the involvement of microbes in the early stages of ooid development. Combined with ongoing microbial cultures under laboratory-controlled conditions, the outcome of our investigation favoured the hypothesis of external microbial precipitation of low-Mg calcite as the main mechanism involved in the early stage of ooid formation in freshwater Lake Geneva. [source] The genesis of the carbonatized and silicified ultramafics known as listvenites: a case study from the Mihal,çç,k region (Eski,ehir), NW TurkeyGEOLOGICAL JOURNAL, Issue 5 2006Mehmet Akbulut Abstract The Mihal,çç,k region (Eski,ehir) in NW Turkey includes an ophiolitic assemblage with a serpentinite-matrix mélange. The serpentinites of this mélange host silica-carbonate metasomatites which were previously named as listvenites. Our mineralogical and geochemical studies revealed that these alteration assemblages represent members of the listvenitic series, mainly the carbonate rocks, silica-carbonate rocks and birbirites, rather than true listvenites (sensu stricto). Tectonic activity and lithology are principal factors that control the formation of these assemblages. Carbonatization and silicification of the serpentinite host-rock is generated by CO2, SiO2 -rich H2O hydrothermal fluid which includes As, Ba, Sb and Sr. Low precious metal (Au, Ag) contents of the alteration assemblages indicate lack of these metals in the fluid. Primary assemblages of the alteration are carbonate rocks that are followed by silica-carbonate rocks and birbirites, respectively. Petrographic studies and chemical analyses suggested an alkaline and moderate to high temperature (350,400°C) fluid with low oxygen and sulphur fugacity for the carbonatization of the serpentinites. The low temperature phases observed in the subsequent silicification indicated that the fluid cooled during progressive alteration. The increasing Fe-oxide content and sulphur phases also suggested increasing oxygen and sulphur fugacity during this secondary process and silica-carbonate rock formation. The occurrence of birbirites is considered as a result of reactivation of tectonic features. These rocks are classified in two sub-groups; the Group 1 birbirites show analogous rare earth element (REE) trends with the serpentinite host-rock, and the Group 2 birbirites simulate the REE trends of the nearby tectonic granitoid slices. The unorthodox REE trend of Group 2 birbirites is interpreted to have resulted from a mobilization process triggered by the weathering solutions rather than being products of enrichment by the higher temperature hydrothermal activity. Copyright © 2006 John Wiley & Sons, Ltd. [source] Origin, age and petrogenesis of Neoproterozoic composite dikes from the Arabian-Nubian Shield, SW JordanGEOLOGICAL JOURNAL, Issue 2 2004G. Jarrar Abstract The evolution of a Pan-African (c. 900,550,Ma) suite of composite dikes, with latite margins and rhyolite interiors, from southwest Jordan is discussed. The dikes cut the Neoproterozoic calc-alkaline granitoids and high-grade metamorphic rocks (c. 800,600,Ma) of the northern Arabian-Nubian Shield in Jordan and have been dated by the Rb-Sr isochron method at 566±7,Ma. The symmetrically distributed latite margins constitute less than one-quarter of the whole dike thickness. The rhyolite intruded a median fracture within the latite, while the latter was still hot but completely solidified. The dikes are alkaline and bimodal in composition with a gap in SiO2 between 61 and 74,wt%. Both end members display similar chondrite-normalized rare earth element patterns. The rhyolites display the compositional signature of A-type granites. The (La/Lu)N values are 6.02 and 4.91 for latites and rhyolites, respectively, and the rhyolites show a pronounced negative Eu anomaly, in contrast to the slight negative Eu anomaly of the latites. The chemical variability (e.g. Zr/Y, Zr/Nb, K/Rb) within and between latites and rhyolites does not support a fractional crystallization relationship between the felsic and mafic members of the dikes. We interpret the magma genesis of the composite dikes as the result of intrusion of mantle-derived mafic magma into the lower crust in an extensional tectonic regime. The mafic magma underwent extensive fractional crystallization, which supplied the necessary heat for melting of the lower crust. The products of the initial stages of partial melting (5,10%) mixed with the fractionating mafic magma and gave rise to the latite melts. Further partial melting of the lower crust (up to 30%) produced a felsic melt, which upon 50% fractional crystallization (hornblende 15%, biotite 5%, feldspars 60%, and quartz 20%) gave rise to the rhyolitic magma. Copyright © 2004 John Wiley & Sons, Ltd. [source] Engineering LacI for Self-Assembly of Inorganic Nanoparticles on DNA Scaffold through the Understanding of LacI Binding to Solid SurfacesADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Haibin Chen Abstract The potential of utilizing the DNA binding protein lac repressor (LacI) to organize inorganic nanoparticles (NPs) is explored in this study. A peptide cognitive of both SiO2 and TiO2 simultaneously (STB1, -CHKKPSKSC-) is genetically engineered into the C-terminus of LacI to give LacI-STB1, and the inserted STB1 peptides in the context of LacI-STB1 molecules are shown to actively interact with both SiO2 and TiO2. Wild-type LacI is found to interact with the two surfaces at its flexible N-terminal DNA binding domain, and LacI-STB1 exhibits much stronger binding affinity to both surfaces by harnessing a second binding region (STB1 peptide) fused at its C-terminus. The quantitative analysis of binding kinetics reveals that, compared to wild-type LacI with one binding region (N-terminus), two remote binding regions (N-terminus and C-terminus) in LacI-STB1 do not lead to faster adsorption rates to the two surfaces, but remarkably slow down the desorption rates. Finally, using LacI-STB1 as a linker, the successful assembly of a sandwich nanostructure of DNA/LacI-STB1/TiO2 NPs is demonstrated using surface plasmon resonance (SPR) measurements and TEM. The demonstrated LacI-STB1-mediated assembly of TiO2 NPs on DNA scaffold may provide a generic platform for controlled spatial arrangement of various nanoparticles of engineering interest. [source] Chitosan Hydrogel-Capped Porous SiO2 as a pH Responsive Nano-Valve for Triggered Release of InsulinADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Jianmin Wu Abstract A pH responsive, chitosan-based hydrogel film is used to cap the pores of a porous SiO2 layer. The porous SiO2 layer is prepared by thermal oxidation of an electrochemically etched Si wafer, and the hydrogel film is prepared by reaction of chitosan with glycidoxypropyltrimethoxysilane (GPTMS). Optical reflectivity spectroscopy and scanning electron microscopy (SEM) confirm that the bio-polymer only partially infiltrates the porous SiO2 film, generating a double layer structure. The optical reflectivity spectrum displays Fabry,Pérot interference fringes characteristic of a double layer, which is characterized using reflective interferometric Fourier transform spectroscopy (RIFTS). Monitoring the position of the RIFTS peak corresponding to the hydrogel layer allows direct, real-time observation of the reversible volume phase transition of the hydrogel upon cycling of pH in the range 6.0,7.4. The swelling ratio and response time are controlled by the relative amount of GPTMS in the hydrogel. The pH-dependent volume phase transition can be used to release insulin trapped in the porous SiO2 layer underneath the hydrogel film. At pH 7.4, the gel in the top layer effectively blocks insulin release, while at pH 6.0 insulin penetrates the swollen hydrogel layer, resulting in a steady release into solution. [source] Self-Assembly of DNA-Templated Polypyrrole Nanowires: Spontaneous Formation of Conductive Nanoropes,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2008Stela Pruneanu Abstract Polypyrrole nanowires formed by polymerization of pyrrole on a DNA template self-assemble into rope-like structures. These ,nanoropes' may be quite smooth (diameters 5,30,nm) or may show frayed ends where individual strands are visible. A combination of electric force microscopy, conductive atomic force microscopy and two-terminal current,voltage measurements show that they are conductive. Nanoropes adhere more weakly to hydrophobic surfaces prepared by silanization of SiO2 than to the clean oxide; this effect can be used to aid the combing of the nanoropes across microelectrode devices for electrical characterization. [source] Atomic Layer Deposition of UV-Absorbing ZnO Films on SiO2 and TiO2 Nanoparticles Using a Fluidized Bed Reactor,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2008David M. King Atomic layer deposition (ALD) was used to apply conformal, nanothick ZnO coatings on particle substrates using a fluidized bed reactor. Diethylzinc (DEZ) and water were used as precursors at 177,°C. Observed growth rates were ca. 2.0 Å/cycle on primary particles as verified by HRTEM. ICP-AES and XPS were used to quantify Zn:substrate ratios. Layers of 6, 18, and 30 nm were deposited on 550 nm SiO2 spheres for UV blocking cosmetics particles. TiO2 nanoparticles were coated in the second part of this work by ZnO shells of 2, 5, and 10 nm thickness as novel inorganic sunscreen particles. The specific surface area of powders changed appropriately after nanothick film deposition using optimized conditions, signifying that high SA particles can be functionalized without agglomeration. The ZnO layers were polycrystalline as deposited and narrowing of the FWHM occurred upon annealing. Annealing the ZnO-TiO2 nanocomposite powder to 600,°C caused the formation of zinc titanate (Zn2TiO4) in both oxygen-rich and oxygen-deficient environments. The non-ideal surface behavior of the DEZ precursor became problematic for the much longer times required for high surface area nanoparticle processing and results in Zn-rich films at this growth temperature. In situ mass spectrometry provides process control capability to functionalize bulk quantities of nano- and ultrafine particles without significant precursor waste or process overruns. ZnO overlayers can be efficiently deposited on the surfaces of primary particles using ALD processing in a scalable fluidized bed reactor. [source] | |||||||||||||||||||||||||||||||||||||||||||