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 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nano-fibriform silica was extracted from chrysotile by the acid-leaching method. The acid-leached residue of chrysotile has been studied by TEM, XRD, FT-IR, and thermal analysis techniques, etc. When the magnesium leaching degree (MLD) is over 90%, the nano-fibriform silica consists of hydrous silicon dioxide (above 90%) with small amount of magnesium trapped inside the SiO network. The amount of hydroxyl on surface of nano-fibriform silica is 6 unit nm(-2). This value is between the values of fumed and precipitated silica. This study shows that nano-fibriform silica is a kind of amorphous matter with a high special surface area (368 m2/g), a high adsorption (330 cm3/g), and a larger pore volume (0.51 cm3/g). The diameter of a single silica fiber is 20-30 nm. The nitrogen adsorption isotherm is similar to Type IV curve. The nano-fibriform silica is one of mesopores materials.
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PMID:Nano-fibriform production of silica from natural chrysotile. 1621 72

As a way to control the surface properties of nanowires and nanotubes, we present a method for growing polymer from the surface of silicon/silica core/shell nanowires. After modification of nanowire surfaces with polymer initiators, Atom Transfer Radical Polymerization (ATRP) was used to grow methacrylate polymer chains from the surface. The resulting structures were characterized by SEM, TEM, and EELS. After etching the silicon cores, the resulting polymer-coated nanotubes will have hydrophilic silica cores with hydrophobic polymer shells.
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PMID:Synthesis of bifunctional polymer nanotubes from silicon nanowire templates via atom transfer radical polymerization. 1628 87

The gas to particle synthesis route is a relatively clean and efficient manner for the production of high-quality ceramic powders. These powders can be subsequently sintered in any wanted shape. The modeling of these production systems is difficult because several mechanisms occur in parallel. From theoretical considerations it can be determined, however, that coagulation and sintering are dominant mechanisms as far as shape and size of the particles are considered. In part I of this article an extensive theoretical analysis was given on the self-preserving size distribution theory for power law particles. In this second part, cumulative particle size distributions of silicon and silicon nitride agglomerates, produced in a laser reactor, were determined from TEM pictures and compared to the distributions calculated from this self-preserving theory for power law particles. The calculated distributions were in fair agreement with the measured results, especially at the high end of the distributions. Calculated and measured particle growth rates were also in fair agreement. Using the self-preserving theory an analysis was made on the distribution of annealed silicon agglomerates, of interest in applications to nanoparticle technology.
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PMID:The self-preserving size distribution theory. II. Comparison with experimental results for Si and Si3N4 aerosols. 1629 May 35

A significant challenge in materials characterization is the determination of the structure of nanoparticle assemblies that have been deposited on solid substrates, such as SiO2. The best method for obtaining quantitative information about structure, size, and spacing on the nanometer-length scale is TEM; however, commercially available TEM grids offer a limited range of substrate materials. In addition, the compositions of these grids do not permit much chemical processing. Here we describe silicon-based grids with electron-transparent SiO2 windows suitable for use as substrates for high-resolution TEM that can be easily fabricated using standard silicon microfabrication techniques. These grids are physically and chemically robust and exhibit the same surface chemistry and chemical stability as an oxide grown on a silicon wafer. Thus, the grids make possible the concurrent investigation of chemical and structural information on the same sample. Convenient modification of the surfaces of the grids provides access to a wide range of new substrates for the direct imaging of chemically modified surfaces by TEM. We demonstrate the utility of these grids by aligning DNA on the chemically modified SiO2 surface in order to direct the assembly of linear arrays of nanoparticles. Using these grids, we are able to quantify the effects of assembly conditions on nanoparticle size, spacing, and dispersity in the arrays.
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PMID:Substrates for direct imaging of chemically functionalized SiO2 surfaces by transmission electron microscopy. 1638 40

Phosphorus containing and octyl-terminated silicon nanoparticles (NPs) are generated by a solution reduction route under room temperature conditions for the first time and characterized by TEM, HRTEM, EDX, 1H/13C/31P NMR, EPR, and PL spectroscopy, then annealed to form a thin film with phosphorus doping confirmed by microprobe elemental analyses.
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PMID:The preparation of a phosphorus doped silicon film from phosphorus containing silicon nanoparticles. 1644 42

To reveal the possible mechanism of silica deposition in higher plants, lignin was isolated from rice straw following a modified method to conduct a simulation experiment in vitro. UV and infrared absorption spectra showed that the substance had the unique characteristics of pure lignin. The presence of silicon in the precipitation was revealed by TEM (transmission electron microscopy) with EDXA (energy dispersive X-ray analysis) device. It was found that in the borax solution where lignin precipitation occurred silica-lignin co-precipitation was produced but not in the DMSO solution where lignin was broken into its composition compounds and did not precipitate. This means that it is macromolecular lignin itself but not its compounds that could induce silica deposition in higher plants.
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PMID:In vitro simulation studies of silica deposition induced by lignin from rice. 1653 27

Cobalt-containing mesoporous materials that have been prepared using different procedures have been comparatively characterized by transmission electron microscopy/energy-dispersive X-ray spectroscopy (TEM/EDS), extended X-ray absorption fine structure spectroscopy (EXAFS), X-ray absorption near edge spectroscopy (XANES), and ultraviolet-visible (UV-vis), near-infrared (NIR), and mid-infrared (mid-IR) spectroscopies, and the results provide new insights into the local environment and properties of cobalt in this type of material. TEM/EDS analyses have shown that tetraethyl orthosilicate (TEOS) may be less appropriate as a silicon source during the syntheses of cobalt-containing mesoporous materials, because the distribution of cobalt throughout the framework may become uneven. EXAFS has been determined to be the most suitable method for direct verification of framework incorporation, by identifying silicon as the backscatterer in the second shell. Such a direct verification may not be obtained using UV-vis spectroscopy. From EXAFS analyses, it is also possible to distinguish between surface-bound and framework-incorporated cobalt. There is a good agreement between the results obtained from XANES and UV-vis regarding the coordination symmetry of cobalt in the samples. The presence of cobalt in the silica framework has been determined to create Lewis acid sites, and these acid sites are suggested to be located at tetrahedral cobalt sites at the surface.
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PMID:Spectroscopic characterization of cobalt-containing mesoporous materials. 1653 73

The significance of micrometer-sized strut porosity in promoting bone ingrowth into porous hydroxyapatite (HA) scaffolds has only recently been noted. In this study, silicon-substituted HA (0.8 wt % Si-HA) with approximately 8.5% of the total porosity present as microporosity within the struts of the implant was prepared for high-resolution transmission electron microscopy (HR-TEM) via both ultramicrotomy and focused ion beam milling. Between the struts of the porous Si-HA, pores with varying shapes and sizes (1-10 microm in diameter) were characterized. Within the struts, the Si-HA contained features such as grain boundaries and triple-junction grain boundaries. Bone ingrowth and dissolution from a Si-HA implant were studied using HR-TEM after 6 weeks in vivo. Minor local dissolution occurred within several pores within the struts. Organized, mineralized collagen fibrils had grown into the strut porosity at the interface between the porous Si-HA implant and the surface of the surrounding bone. In comparison, deeper within the implant, disorganized and poorly mineralized fibers were observed within the strut porosity. These findings provide valuable insight into the development of bone around porous Si-HA implants.
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PMID:The structure of the bond between bone and porous silicon-substituted hydroxyapatite bioceramic implants. 1659 83

Titania is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of its excellent UV light absorption properties. Its high photocatalytic activity, however, facilitates the generation of reactive oxygen species, which can oxidize and degrade other ingredients during its formulation, raising safety concerns. Dense coating of titania nanoparticles with a silica layer could help in depression of their photocatalytic activity by disturbing the formation of radicals produced by the reaction of oxygen and/or water with the electron-hole pair. Depression of the high photocatalytic activity of titania necessitates that the silica shell has to be thick, with minimum microporosity. Coating parameters were optimized to attain greater amounts of precipitated silica and thicker shells with lower microporosity, which in turn resulted in great depression of photocatalytic activity. Silica-coated titania nanoparticles were characterized by TEM, XPS, FT-IR, EDX, and microporosity measurements. The photocatalytic activity was evaluated for the coated powder to investigate the efficiency of the silica coating as well.
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PMID:Control of silica shell thickness and microporosity of titania-silica core-shell type nanoparticles to depress the photocatalytic activity of titania. 1669 69

A hot filament chemical vapor deposition method has been developed to grow vertical array single-walled carbon nanotubes (SWNTs). In this study, a hot filament (temperature greater than 2000 degrees C) was used to activate gas mixtures of hydrogen and carbon containing species at sub-atmospheric pressures. Silicon substrates decorated with islands of iron were directly inserted into a preheated furnace in which a hot filament is activating the gas. Vertical arrays of SWNTs are produced with diameters ranging from 0.78 to 1.6 nm. The samples were characterized with Raman and fluorescence spectroscopy and SEM and TEM microscopy.
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PMID:Vertical array growth of small diameter single-walled carbon nanotubes. 1670 47


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