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Sample records for ge-doped amorphous silica

  1. Charge storage characteristics and tunneling mechanism of amorphous Ge-doped HfOx films

    NASA Astrophysics Data System (ADS)

    Qiu, X. Y.; Zhang, S. Y.; Zhang, T.; Wang, R. X.; Li, L. T.; Zhang, Y.; Dai, J. Y.

    2016-09-01

    Amorphous Ge-doped HfOx films have been deposited on p-Si(100) substrates by means of RF magnetron sputtering. Microstructural investigations reveal the partial oxidation of doped Ge atoms in the amorphous HfOx matrix and the existence of HfSiOx interfacial layer. Capacitance-voltage hysteresis of the Ag-/Ge-doped HfOx/Si/Ag memory capacitor exhibits a memory window of 3.15 V which can maintain for >5 × 104 cycles. Current-voltage characteristics reveal that Poole-Frenkel tunneling is responsible for electron transport in the Ge-doped HfOx film.

  2. Thermoluminescence Response of Ge-Doped Cylindrical-, Flat- and Photonic Crystal Silica-Fibres to Electron and Photon Radiation.

    PubMed

    Entezam, A; Khandaker, M U; Amin, Y M; Ung, N M; Bradley, D A; Maah, J; Safari, M J; Moradi, F

    2016-01-01

    Study has been made of the thermoluminescence (TL) response of silica-based Ge-doped cylindrical, flat and photonic crystal fibres (referred to herein as PCF-collapsed) to electron (6, 12 and 20 MeV) and photon (6, 10 MV) irradiation and 1.25 MeV γ-rays, for doses from 0.1 Gy to 100 Gy. The electron and photon irradiations were delivered through use of a Varian Model 2100C linear accelerator located at the University of Malaya Medical Centre and γ-rays delivered from a 60Co irradiator located at the Secondary Standard Dosimetry Laboratory (SSDL), Malaysian Nuclear Agency. Tailor-made to be of various dimensions and dopant concentrations (6-10% Ge), the fibres were observed to provide TL yield linear with radiation dose, reproducibility being within 1-5%, with insensitivity to energy and angular variation. The sensitivity dependency of both detectors with respect to field size follows the dependency of the output factors. For flat fibres exposed to 6 MV X-rays, the 6% Ge-doped fibre provided the greatest TL yield while PCF-collapsed showed a response 2.4 times greater than that of the 6% Ge-doped flat fibres. The response of cylindrical fibres increased with core size. The fibres offer uniform response, high spatial resolution and sensitivity, providing the basis of promising TL systems for radiotherapy applications. PMID:27149115

  3. Thermoluminescence Response of Ge-Doped Cylindrical-, Flat- and Photonic Crystal Silica-Fibres to Electron and Photon Radiation

    PubMed Central

    Entezam, A.; Khandaker, M. U.; Amin, Y. M.; Ung, N. M.; Bradley, D. A.; Maah, J.; Safari, M. J.; Moradi, F.

    2016-01-01

    Study has been made of the thermoluminescence (TL) response of silica-based Ge-doped cylindrical, flat and photonic crystal fibres (referred to herein as PCF-collapsed) to electron (6, 12 and 20 MeV) and photon (6, 10 MV) irradiation and 1.25 MeV γ-rays, for doses from 0.1 Gy to 100 Gy. The electron and photon irradiations were delivered through use of a Varian Model 2100C linear accelerator located at the University of Malaya Medical Centre and γ-rays delivered from a 60Co irradiator located at the Secondary Standard Dosimetry Laboratory (SSDL), Malaysian Nuclear Agency. Tailor-made to be of various dimensions and dopant concentrations (6–10% Ge), the fibres were observed to provide TL yield linear with radiation dose, reproducibility being within 1–5%, with insensitivity to energy and angular variation. The sensitivity dependency of both detectors with respect to field size follows the dependency of the output factors. For flat fibres exposed to 6 MV X-rays, the 6% Ge-doped fibre provided the greatest TL yield while PCF-collapsed showed a response 2.4 times greater than that of the 6% Ge-doped flat fibres. The response of cylindrical fibres increased with core size. The fibres offer uniform response, high spatial resolution and sensitivity, providing the basis of promising TL systems for radiotherapy applications. PMID:27149115

  4. Refractive index change dependence on Ge(1) defects in {gamma}-irradiated Ge-doped silica

    SciTech Connect

    Alessi, A.; Agnello, S.; Gelardi, F. M.; Grandi, S.; Parlato, A.

    2009-07-01

    We present an experimental study regarding the effects of the {gamma} radiation on silica glass doped with Ge up to 10 000 ppm molar produced by the sol-gel technique. We have determined the irradiation-induced changes in the refractive index ({delta}n) as a function of the oxygen deficiency of the samples, evaluated from the ratio between the germanium lone pair centers (GLPC) and the Ge content. {delta}n at 1500 nm have been estimated using optical-absorption spectra in the range 1.5-6 eV. We have found that {delta}n is independent of Ge differences for GLPC/Ge values <10{sup -4}, while it depends on Ge for larger oxygen deficiencies. In details, the oxygen deficiency can reduce the induced {delta}n of the investigated materials and our studies evidence that the photosensitivity of the GeO{sub 2}-SiO{sub 2} glass is reduced until the GLPC concentration reaches values of 2x10{sup 17}-5x10{sup 17} defects/cm{sup 3}. We have also investigated the induced concentration of paramagnetic point defects [Ge(1), Ge(2), and E'Ge] using the electron-paramagnetic-resonance (EPR) technique. From the comparison of the optical and EPR data we have further found a relation between the induced optical-absorption coefficient at 5.8 eV and Ge(1) defects, a linear correlation between Ge(1) and {delta}n and the absence of a correlation between the other paramagnetic defects and {delta}n. These findings suggest that the {delta}n phenomenology is closely related to the Ge(1) generation mechanisms and this latter is affected by the oxygen defic0011ien.

  5. Characterisation of the thermoluminescence (TL) properties of tailor-made Ge-doped silica glass fibre for applications in medical radiation therapy dosimetry

    NASA Astrophysics Data System (ADS)

    Zahaimi, N. A.; Zin, H.; Mahdiraji, G. A.; Rahman, A. L. Abdul; Bradley, D. A.; Rahman, A. T. Abdul

    2014-11-01

    We have investigated the characterisation of new fabricated material Ge doped silica glass thermoluminescence TL dosimeter (Photonic Research Centre, University of Malaya) for medical radiation dosimetry at therapy energy. Previously, the dosimeter has been studied to provide ideal dosimetry system, suitable to ensure an accurate delivery of radiation doses to tumour tissue while minimising the amount of radiation administrated to healthy tissue. Both energies of photon and electron were used in this experiment for a dose range of 1 to 5 Gy. The various sizes of core diameter Ge doped silica glass (120, 241, 362, 483 and 604 μm) were exposed by using linear accelerator at Pantai Medical Centre. For both energies, the optical fibres were found to produce a flat response to a fixed photon and electron doses to within 4% (S.D) of the mean of the TL distribution. In terms of dose response, the fibres provide linear response over the range investigated, from a fraction of 1-5 Gy. The finding shows 120 μm fibres have 1.82 greater dose response than 604 pm fibres irradiated at 6 MV photon with a fixed dose of 3 Gy. While for electron energy 12 MeV, the response shows 120 μm fibres have 1.58 greater dose response compared to 604 μm fibres. The good responses are suitable to make these tailor-made doped silica fibres a promising TL material for use as a dosimetric system in medical radiation therapy.

  6. Uranium incorporation into amorphous silica.

    PubMed

    Massey, Michael S; Lezama-Pacheco, Juan S; Nelson, Joey M; Fendorf, Scott; Maher, Kate

    2014-01-01

    High concentrations of uranium are commonly observed in naturally occurring amorphous silica (including opal) deposits, suggesting that incorporation of U into amorphous silica may represent a natural attenuation mechanism and promising strategy for U remediation. However, the stability of uranium in opaline silicates, determined in part by the binding mechanism for U, is an important factor in its long-term fate. U may bind directly to the opaline silicate matrix, or to materials such as iron (hydr)oxides that are subsequently occluded within the opal. Here, we examine the coordination environment of U within opaline silica to elucidate incorporation mechanisms. Precipitates (with and without ferrihydrite inclusions) were synthesized from U-bearing sodium metasilicate solutions, buffered at pH ∼ 5.6. Natural and synthetic solids were analyzed with X-ray absorption spectroscopy and a suite of other techniques. In synthetic amorphous silica, U was coordinated by silicate in a double corner-sharing coordination geometry (Si at ∼ 3.8-3.9 Å) and a small amount of uranyl and silicate in a bidentate, mononuclear (edge-sharing) coordination (Si at ∼ 3.1-3.2 Å, U at ∼ 3.8-3.9 Å). In iron-bearing synthetic solids, U was adsorbed to iron (hydr)oxide, but the coordination environment also contained silicate in both edge-sharing and corner-sharing coordination. Uranium local coordination in synthetic solids is similar to that of natural U-bearing opals that retain U for millions of years. The stability and extent of U incorporation into opaline and amorphous silica represents a long-term repository for U that may provide an alternative strategy for remediation of U contamination. PMID:24984107

  7. The Phagocytosis and Toxicity of Amorphous Silica

    PubMed Central

    Costantini, Lindsey M.; Gilberti, Renée M.; Knecht, David A.

    2011-01-01

    Background Inhalation of crystalline silica is known to cause an inflammatory reaction and chronic exposure leads to lung fibrosis and can progress into the disease, silicosis. Cultured macrophages bind crystalline silica particles, phagocytose them, and rapidly undergo apoptotic and necrotic death. The mechanism by which particles are bound and internalized and the reason particles are toxic is unclear. Amorphous silica has been considered to be a less toxic form, but this view is controversial. We compared the uptake and toxicity of amorphous silica to crystalline silica. Methodology/Principal Findings Amorphous silica particles are phagocytosed by macrophage cells and a single internalized particle is capable of killing a cell. Fluorescent dextran is released from endo-lysosomes within two hours after silica treatment and Caspase-3 activation occurs within 4 hours. Interestingly, toxicity is specific to macrophage cell lines. Other cell types are resistant to silica particle toxicity even though they internalize the particles. The large and uniform size of the spherical, amorphous silica particles allowed us to monitor them during the uptake process. In mCherry-actin transfected macrophages, actin rings began to form 1-3 minutes after silica binding and the actin coat disassembled rapidly following particle internalization. Pre-loading cells with fluorescent dextran allowed us to visualize the fusion of phagosomes with endosomes during internalization. These markers provided two new ways to visualize and quantify particle internalization. At 37°C the rate of amorphous silica internalization was very rapid regardless of particle coating. However, at room temperature, opsonized silica is internalized much faster than non-opsonized silica. Conclusions/Significance Our results indicate that amorphous and crystalline silica are both phagocytosed and both toxic to mouse alveolar macrophage (MH-S) cells. The pathway leading to apoptosis appears to be similar in both

  8. Is simulated amorphous'' silica really amorphous

    SciTech Connect

    Binggeli, N. , PHB Ecublens, 1015 Lausanne ); Chelikowsky, J.R. )

    1994-07-10

    We have carried out extensive molecular dynamics simulations for the pressure induced amorphization of quartz by means of a classical force-field model. In agreement with earlier simulations, we find that a phase transition occurs within the experimental pressure range of the amorphization. However, in contrast to the interpretation of previous simulations, we demonstrate that the new phase is [ital not] amorphous, since the correlation functions for the equilibrated structure can be shown to be consistent with those of a crystalline phase. In addition, two transformations to ordered structures are found to occur sequentially during the simulations. The first transformation is likely to be related to the recently discovered transition of quartz to an intermediate crystalline phase before its amorphization. The second transformation, instead, yields a compact, octahedrally coordinated Si sublattice. The latter may be an artifact of the pair-potential simulation. [copyright] 1994 American Institute of Physics

  9. Health hazards due to the inhalation of amorphous silica.

    PubMed

    Merget, R; Bauer, T; Küpper, H U; Philippou, S; Bauer, H D; Breitstadt, R; Bruening, T

    2002-01-01

    Occupational exposure to crystalline silica dust is associated with an increased risk for pulmonary diseases such as silicosis, tuberculosis, chronic bronchitis, chronic obstructive pulmonary disease (COPD) and lung cancer. This review summarizes the current knowledge about the health effects of amorphous (non-crystalline) forms of silica. The major problem in the assessment of health effects of amorphous silica is its contamination with crystalline silica. This applies particularly to well-documented pneumoconiosis among diatomaceous earth workers. Intentionally manufactured synthetic amorphous silicas are without contamination of crystalline silica. These synthetic forms may be classified as (1) wet process silica, (2) pyrogenic ("thermal" or "fumed") silica, and (3) chemically or physically modified silica. According to the different physicochemical properties, the major classes of synthetic amorphous silica are used in a variety of products, e.g. as fillers in the rubber industry, in tyre compounds, as free-flow and anti-caking agents in powder materials, and as liquid carriers, particularly in the manufacture of animal feed and agrochemicals; other uses are found in toothpaste additives, paints, silicon rubber, insulation material, liquid systems in coatings, adhesives, printing inks, plastisol car undercoats, and cosmetics. Animal inhalation studies with intentionally manufactured synthetic amorphous silica showed at least partially reversible inflammation, granuloma formation and emphysema, but no progressive fibrosis of the lungs. Epidemiological studies do not support the hypothesis that amorphous silicas have any relevant potential to induce fibrosis in workers with high occupational exposure to these substances, although one study disclosed four cases with silicosis among subjects exposed to apparently non-contaminated amorphous silica. Since the data have been limited, a risk of chronic bronchitis, COPD or emphysema cannot be excluded. There is no study

  10. Fabrication and characterization of amorphous silica nanostructures

    NASA Astrophysics Data System (ADS)

    Jin, Lei; Wang, Jianbo; Cao, Guangyi; Choy, Wallace C. H.

    2008-06-01

    Large-scale amorphous silica nanostructures, including nanowires, nanotubes and flowerlike nanowire bunches depending on the position, have been fabricated on silicon wafer through a cheap route under the assistance of gold and germanium. Accompanying the observation of blue-green light emission, comprehensive micro-structural characterization reveals that the growth of nanostructures is catalyzed only by gold whereas the final morphology of nanostructures depends on the location to germanium ball. Au 2Si, a compound of gold and silicon, is also disclosed as an intermediate state during the catalysis. Correspondingly, a growth scheme is proposed based on the experimental results and the vapor-liquid-solid mechanism.

  11. Dissolution and analysis of amorphous silica in marine sediments.

    USGS Publications Warehouse

    Eggimann, D.W.; Manheim, F. T.; Betzer, P.R.

    1980-01-01

    The analytical estimation of amorphous silica in selected Atlantic and Antarctic Ocean sediments, the U.S.G.S. standard marine mud (MAG-1), A.A.P.G. clays, and samples from cultures of a marine diatom, Hemidiscus, has been examined. Our values for amorphous silica-rich circum-Antarctic sediments are equal to or greater than literature values, whereas our values for a set of amorphous silica-poor sediments from a transect of the N. Atlantic at 11oN, after appropriate correction for silica released from clays, are significantly lower than previous estimates from the same region. -from Authors

  12. [Amorphous silica. Types, health effects of exposure, NDS].

    PubMed

    Woźniak, H; Wiecek, E

    1995-01-01

    Maximum allowable concentration (MAC) values for amorphous silica dust have not been identified in the Polish legal regulations up-to-date. In this work the authors review values of allowable (recommended) amorphous silica dust concentrations in other countries. Data on other types of amorphous silica (natural and synthetic) used in industry as well as data on health effects of exposure to these types of dust are presented. The work encompasses 42 entries in the references and one Table which includes the following proposed MAC values: Non-calcinate diatomaceous earth (diatomite) and synthetic silica: Total dust--10 mg/m3 Respirable dust--2 mg/m3 Calcinate diatomaceous earth (diatomite) and fused silica (vitreous silica): Total dust--2 mg/m3 Respirable dust--1 mg/m3. PMID:7637638

  13. Relationship between amorphous silica and precious metal in quartz veins

    NASA Astrophysics Data System (ADS)

    Harrichhausen, N.; Rowe, C. D.; Board, W. S.; Greig, C. J.

    2015-12-01

    Super-saturation of silica is common in fault fluids, due to pressure changes associated with fracture, fault slip, or temperature gradients in hydrothermal systems. These mechanisms lead to precipitation of amorphous silica, which will recrystallize to quartz under typical geologic conditions. These conditions may also promote the saturation of precious metals, such as gold, and the precipitation of nanoparticles. Previous experiments show that charged nanoparticles of gold can attach to the surface of amorphous silica nanoparticles. Thus, gold and silica may be transported as a colloid influencing mineralization textures during amorphous silica recrystallization to quartz. This may enrich quartz vein hosted gold deposits, but the instability of hydrous silica during subsequent deformation means that the microstructural record of precipitation of gold is lost. We investigate a recent, shallow auriferous hydrothermal system at Dixie Valley, Nevada to reveal the nano- to micro-scale relationships between gold and silica in fresh veins. Fault slip surfaces at Dixie Valley exhibit layers of amorphous silica with partial recrystallization to quartz. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) show amorphous silica can contain a few wt. % gold while areas recrystallized to quartz are barren. At the Jurassic Brucejack deposit in British Columbia, Canada we observe the cryptocrystalline quartz textures that may indicate recrystallization from amorphous silica within quartz-carbonate veins containing high grade gold. Comb quartz within syntaxial veins, vugs, and coating breccia clasts indicate structural dilation. Vein geometry is investigated to determine relative importance of fault slip in creating dilational sites. By comparing quartz-carbonate veins from the Dixie Valley to Brucejack, we can determine whether amorphous silica formed in different environments show similar potential to affect precious metal mineralization.

  14. Performance of Bragg and long-period gratings written in N- and Ge-doped silica fibers under {gamma}-radiation

    SciTech Connect

    Vasilev, S.A.; Dianov, E.M.; Golant, K.M.

    1998-06-01

    In-fiber Bragg and long-period gratings as well as Mach-Zehnder interferometers based on germanium- and nitrogen-doped silica fibers have been investigated under {gamma}-rays. The majority of the experimental results suggest that both types of gratings in both types of fibers are stable with respect to {gamma}-ray doses of up to 1.47 MGy.

  15. Physicochemical determinants in the cellular responses to nanostructured amorphous silicas.

    PubMed

    Gazzano, Elena; Ghiazza, Mara; Polimeni, Manuela; Bolis, Vera; Fenoglio, Ivana; Attanasio, Angelo; Mazzucco, Gianna; Fubini, Bice; Ghigo, Dario

    2012-07-01

    Amorphous silicas, opposite to crystalline polymorphs, have been regarded so far as nonpathogenic, but few studies have addressed the toxicity of the wide array of amorphous silica forms. With the advent of nanotoxicology, there has been a rising concern about the safety of silica nanoparticles to be used in nanomedicine. Here, we report a study on the toxicity of amorphous nanostructured silicas obtained with two different preparation procedures (pyrolysis vs. precipitation), the pyrogenic in two very different particle sizes, in order to assess the role of size and origin on surface properties and on the cell damage, oxidative stress, and inflammatory response elicited in murine alveolar macrophages. A quartz dust was employed as positive control and monodispersed silica spheres as negative control. Pyrogenic silicas were remarkably more active than the precipitated one as to cytotoxicity, reactive oxygen species production, lipid peroxidation, nitric oxide synthesis, and production of tumor necrosis factor-α, when compared both per mass and per unit surface. Between the two pyrogenic silicas, the larger one was the more active. Silanols density is the major difference in surface composition among the three silicas, being much larger than the precipitated one as indicated by joint calorimetric and infrared spectroscopy analysis. We assume here that full hydroxylation of a silica surface, with consequent stable coverage by water molecules, reduces/inhibits toxic behavior. The preparation route appears thus determinant in yielding potentially toxic materials, although the smallest size does not always correspond to an increased toxicity. PMID:22491428

  16. Fungus-mediated biotransformation of amorphous silica in rice husk to nanocrystalline silica.

    PubMed

    Bansal, Vipul; Ahmad, Absar; Sastry, Murali

    2006-11-01

    Rice husk is a cheap agro-based waste material, which harbors a substantial amount of silica in the form of amorphous hydrated silica grains. However, there have been no attempts at harnessing the enormous amount of amorphous silica present in rice husk and its room-temperature biotransformation into crystalline silica nanoparticles. In this study, we address this issue and describe how naturally deposited amorphous biosilica in rice husk can be bioleached and simultaneously biotransformed into high value crystalline silica nanoparticles. We show here that the fungus Fusarium oxysporum rapidly biotransforms the naturally occurring amorphous plant biosilica into crystalline silica and leach out silica extracellularly at room temperature in the form of 2-6 nm quasi-spherical, highly crystalline silica nanoparticles capped by stabilizing proteins; that the nanoparticles are released into solution is an advantage of this process with significant application and commercial potential. Calcination of the silica nanoparticles leads to loss of occluded protein and to an apparently porous structure often of cubic morphology. The room-temperature synthesis of oxide nanomaterials using microorganisms starting from potential cheap agro-industrial waste materials is an exciting possibility and could lead to an energy-conserving and economically viable green approach toward the large-scale synthesis of oxide nanomaterials. PMID:17061888

  17. A solubility model for amorphous silica in concentrated electrolytes

    SciTech Connect

    Felmy, A.R.; Schroeder, C.C.; Mason, M.J.

    1994-08-01

    Silica is one of the major constituents of the earth`s crust and is ubiquitously present in most natural materials. The solubility of silica and other silica-containing compounds is, therefore, of primary concern in geochemistry and in chemical processing applications where silica scale formation, resulting from changes in temperature and electrolyte composition, can cause problems in process design and operation. This paper describes the development of an aqueous thermodynamic model for accurately predicting the solubility of amorphous silica and other silica-containing compounds in the system Na{sup +}-H{sup +}-Mg{sup 2+}-NO{sub 3}{sup {minus}}-SO{sub 4}{sup 2{minus}}-Cl{sup {minus}}-H{sub 2}O to high concentration and across the temperature range 25--100 C. This model, which utilizes the aqueous thermodynamic model of Pitzer, includes only one dissolved silica species, H{sub 4}SiO{sub 4}(aq), and is valid in neutral to very acidic solutions. The model is parameterized from the extensive set of solubility data in the literature as well as from new experimental data on amorphous silica solubility in HNO{sub 3} and HCl developed as part of this study. The accuracy of the model is tested on solutions more complex than those used in model parameterization.

  18. Sodium diffusion through amorphous silica surfaces: a molecular dynamics study.

    PubMed

    Rarivomanantsoa, Michaël; Jund, Philippe; Jullien, Rémi

    2004-03-01

    We have studied the diffusion inside the silica network of sodium atoms initially located outside the surfaces of an amorphous silica film. We have focused our attention on structural and dynamical quantities, and we have found that the local environment of the sodium atoms is close to the local environment of the sodium atoms inside bulk sodo-silicate glasses obtained by quench. This is in agreement with recent experimental results. PMID:15267353

  19. Kinetics of amorphous silica dissolution and the paradox of the silica polymorphs

    PubMed Central

    Dove, Patricia M.; Han, Nizhou; Wallace, Adam F.; De Yoreo, James J.

    2008-01-01

    The mechanisms by which amorphous silica dissolves have proven elusive because noncrystalline materials lack the structural order that allows them to be studied by the classical terrace, ledge, kink-based models applied to crystals. This would seem to imply amorphous phases have surfaces that are disordered at an atomic scale so that the transfer of SiO4 tetrahedra to solution always leaves the surface free energy of the solid unchanged. As a consequence, dissolution rates of amorphous phases should simply scale linearly with increasing driving force (undersaturation) through the higher probability of detaching silica tetrahedra. By examining rate measurements for two amorphous SiO2 glasses we find, instead, a paradox. In electrolyte solutions, these silicas show the same exponential dependence on driving force as their crystalline counterpart, quartz. We analyze this enigma by considering that amorphous silicas present two predominant types of surface-coordinated silica tetrahedra to solution. Electrolytes overcome the energy barrier to nucleated detachment of higher coordinated species to create a periphery of reactive, lesser coordinated groups that increase surface energy. The result is a plausible mechanism-based model that is formally identical with the classical polynuclear theory developed for crystal growth. The model also accounts for reported demineralization rates of natural biogenic and synthetic colloidal silicas. In principle, these insights should be applicable to materials with a wide variety of compositions and structural order when the reacting units are defined by the energies of their constituent species. PMID:18632576

  20. TOXICITY OF AMORPHOUS SILICA NANOPARTICLES IN MOUSE KERATINOCYTES

    SciTech Connect

    Yu, Kyung; Wang, Wei; Gu, Baohua; Hussain, Saber

    2009-01-01

    The present study was designed to examine the uptake, localization and the cytotoxic effects of well-dispersed amorphous silica nanoparticles in mouse keratinocytes (HEL-30). Mouse keratinocytes were exposed for 24h to various concentrations of amorphous silica nanoparticles in homogeneous suspensions of average size distribution (30, 48, 118 and 535 nm SiO2) then assessed for uptake and biochemical changes. Results of transmission electron microscopy revealed all sizes of silica were taken up into the cells and localized into the cytoplasm. The lactate dehydrogenase (LDH) assay shows LDH leakage was dose- and size-dependent with exposure to 30 and 48 nm nanoparticles. However, no LDH leakage was observed for either 118 or 535 nm nanoparticles. The mitochondrial viability assay (MTT) showed significant toxicity for 30 and 48 nm at high concentrations (100 g/mL) compare to the 118 and 535 nm particles. Further studies were carried out to investigate if cellular reduced GSH and mitochondria membrane potential are involved in the mechanism of SiO2 toxicity. The redox potential of cells (GSH) was reduced significantly at concentrations of 50, 100 and 200 g/mL at 30 nm nanoparticle exposures. However, silica nanoparticles larger than 30 nm showed no changes in GSH levels. Reactive oxygen species (ROS) formation did not show any significant change between controls and the exposed cells. In summary, amorphous silica nanoparticles below 100 nm induced cytotoxicity suggest size-of the particles is critical to produce biological effects.

  1. Amorphous and nanostructured silica and aluminosilicate spray-dried microspheres

    NASA Astrophysics Data System (ADS)

    Todea, M.; Turcu, R. V. F.; Frentiu, B.; Tamasan, M.; Mocuta, H.; Ponta, O.; Simon, S.

    2011-08-01

    Amorphous silica and aluminosilicate microspheres with diameters in the 0.1-20 μm range were produced by spray drying method. SEM, TEM and AFM images showed the spherical shape of the obtained particles. Based on thermal analysis data, several heat treatments have been applied on the as-prepared samples in order to check the amorphous state stability of the microspheres and to develop nanosized crystalline phases. As-prepared microspheres remain amorphous up to 1400 °C. By calcination at 1400 °C, cristobalite type nanocrystals are developed on silica sample, while in aluminosilicate sample first are developed mullite type nanocrystals and only after prolonged treatment are developed also cristobalite type nanocrystals. 29Si and 27Al MAS NMR results show that the local order around aluminum and silicon atoms strongly depend on the thermal history of the microspheres.

  2. Occupational exposure to amorphous silica dust and pulmonary function.

    PubMed Central

    Choudat, D; Frisch, C; Barrat, G; el Kholti, A; Conso, F

    1990-01-01

    Respiratory manifestations among 41 workers exposed to amorphous silica dust were compared with a control group comprising 90 workers of equivalent socioeconomic state in the same plant. Flow volumes were determined, blood gas concentrations were measured at rest and during exercise, chest radiographs were obtained, and data about respiratory symptoms were collected by questionnaire. A dust exposure index was calculated for each exposed worker. It was not possible to differentiate between the two groups from the questionnaire, blood gas analysis, or chest radiographs. On the other hand, the tests of respiratory function showed a significant decrease in forced expiratory flow (FEF25-75, FEF50, and FEF75) in the exposed group compared with the controls, although no correlation was found between the exposure index and pulmonary function. It appears that smoking and exposure to amorphous silica synergise to induce small airway disease. PMID:2173947

  3. Xe in amorphous silica: A new thermometer in geothermal systems

    NASA Astrophysics Data System (ADS)

    Matsubara, Kayo; Matsuda, Jun-ichi; Nagao, Keisuke; Kita, Itsuro; Taguchi, Sachihiro

    1988-07-01

    We measured noble gases in amorphous silica of geothermal origin. These samples were formed by precipitation from geothermal water in neutral pH, and by the leaching of rocks in acid hot springs. The concentration of 132Xe has a negative correlation with the temperature of geothermal water although 36Ar and 84Kr show no such correlation. The relationship between 132Xe content A (×10-8cm³STP/g) and temperature T(°C) is approximated by the equation A=-(4.5×10-3)T +0.50. The obtained equation should be useful for estimating the silica-forming temperature that cannot be easily measured by other methods.

  4. Electron-beam-assisted superplastic shaping of nanoscale amorphous silica

    PubMed Central

    Zheng, Kun; Wang, Chengcai; Cheng, Yong-Qiang; Yue, Yonghai; Han, Xiaodong; Zhang, Ze; Shan, Zhiwei; Mao, Scott X; Ye, Miaomiao; Yin, Yadong; Ma, Evan

    2010-01-01

    Glasses are usually shaped through the viscous flow of a liquid before its solidification, as practiced in glass blowing. At or near room temperature (RT), oxide glasses are known to be brittle and fracture upon any mechanical deformation for shape change. Here, we show that with moderate exposure to a low-intensity (<1.8×10−2 A cm−2) electron beam (e-beam), dramatic shape changes can be achieved for nanoscale amorphous silica, at low temperatures and strain rates >10−4 per second. We show not only large homogeneous plastic strains in compression for nanoparticles but also superplastic elongations >200% in tension for nanowires (NWs). We also report the first quantitative comparison of the load-displacement responses without and with the e-beam, revealing dramatic difference in the flow stress (up to four times). This e-beam-assisted superplastic deformability near RT is useful for processing amorphous silica and other conventionally-brittle materials for their applications in nanotechnology. PMID:20975693

  5. Stability of amorphous silica-alumina in hot liquid water.

    PubMed

    Hahn, Maximilian W; Copeland, John R; van Pelt, Adam H; Sievers, Carsten

    2013-12-01

    Herein, the hydrothermal stability of amorphous silica-alumina (ASA) is investigated under conditions relevant for the catalytic conversion of biomass, namely in liquid water at 200 °C. The hydrothermal stability of ASA is much higher than that of pure silica or alumina. Interestingly, the synthetic procedure used plays a major role in its resultant stability: ASA prepared by cogelation (CG) lost its microporous structure, owing to hydrolysis of the siloxane bonds, but the resulting mesoporous material still had a considerable surface area. ASA prepared by deposition precipitation (DP) contained a silicon-rich core and an aluminum-rich shell. In hot liquid water, the latter structure was transformed into a layer of amorphous boehmite, which protected the particle from further hydrolysis. The surface area showed relatively minor changes during the transformation. Independent of the synthetic method used, the ASAs retained a considerable concentration of acid sites. The concentration of acid sites qualitatively followed the changes in surface area, but the changes were less pronounced. The performance of different ASAs for the hydrolysis of cellobiose into glucose is compared. PMID:24124062

  6. Synthesis of microforsterite using derived-amorphous-silica of silica sands

    NASA Astrophysics Data System (ADS)

    Nurbaiti, Upik; Triwikantoro, Zainuri, Mochamad; Pratapa, Suminar

    2016-04-01

    Synthesis of microforsterite (Mg2SiO4) has been successfully done by a simple method benefiting of the local silica sands from Tanah Laut, Indonesia. The starting material was amorphous silica powder which was processed using coprecipitation method from the sands. The silica powder was obtained from a series of stages of the purification process of the sands, namely magnetic separation, grinding and soaking with HCl. The microforsterite synthesis followed the reaction of stoichiometric mole ratio mixing of 1:2 of the amorphous silica and MgO powders with 3 wt% addion of PVA as a catalyst.The mixture was calcined at temperatures between 1150-1400°C with 4 hours holding time. XRD data showed that calcination at a temperature of 1150°C for 4 hours was optimum where the weight fraction of forsterite can reach as much as 93 wt% with MgO as the secondary phase and without MgSiO3. SEM photograph of the microforsterite showed tapered morphology with a relatively homogeneous distribution.

  7. Influence of amorphous silica on the hydration in ultra-high performance concrete

    SciTech Connect

    Oertel, Tina; Helbig, Uta; Hutter, Frank; Kletti, Holger; Sextl, Gerhard

    2014-04-01

    Amorphous silica particles (silica) are used in ultra-high performance concretes to densify the microstructure and accelerate the clinker hydration. It is still unclear whether silica predominantly increases the surface for the nucleation of C–S–H phases or dissolves and reacts pozzolanically. Furthermore, varying types of silica may have different and time dependent effects on the clinker hydration. The effects of different silica types were compared in this study by calorimetric analysis, scanning and transmission electron microscopy, in situ X-ray diffraction and compressive strength measurements. The silica component was silica fume, pyrogenic silica or silica synthesized by a wet-chemical route (Stoeber particles). Water-to-cement ratios were 0.23. Differences are observed between the silica for short reaction times (up to 3 days). Results indicate that silica fume and pyrogenic silica accelerate alite hydration by increasing the surface for nucleation of C–S–H phases whereas Stoeber particles show no accelerating effect.

  8. Ultra-wide bandwidth wavelength selective couplers based on the all solid multi-core Ge-doped fibre

    NASA Astrophysics Data System (ADS)

    Li, X.; Sun, B.; Yu, Y.

    2014-09-01

    A novel wavelength selective coupler based on the all solid nine-core Ge-doped fibre has been proposed. The wavelength selective coupler is based on the phenomenon of a multi-core coupling. All the cores are made of Ge-doped silica and the index of central core is larger than the outer core. At the fixed fibre length, the different wavelength can be selected. The performances of coupling and propagation characteristics have been numerically investigated by using a full beam propagation method (BPM). Simulation results show that the all solid nine-core Ge-doped fibre can achieve simultaneous shorter coupler length and wideband filtering characteristics. The 0.763 mm and 0.745 mm wavelength selective coupler are proposed to achieve different wavelength division and the bandwidth is up to the 400 nm, and 300 nm, respectively.

  9. HEALTH EFFECTS OF INHALED CRYSTALLINE AND AMORPHOUS SILICA

    EPA Science Inventory

    Recently, public concern regarding nonoccupational or ambient silica exposure, mainly to crystalline silica, has emerged making it important to evaluate background and ambient concentrations. Ambient emissions of silica rarely are estimated or measured in air pollution studies of...

  10. Radiotherapy dosimetry and the thermoluminescence characteristics of Ge-doped fibres of differing germanium dopant concentration and outer diameter

    NASA Astrophysics Data System (ADS)

    Noor, N. Mohd; Fadzil, M. S. Ahmad; Ung, N. M.; Maah, M. J.; Mahdiraji, G. A.; Abdul-Rashid, H. A.; Bradley, D. A.

    2016-09-01

    We examine the influence of elevated dopant concentration on the thermoluminescence characteristics of novel Ge-doped silica fibres. Basic dosimetric characteristics of the TL media were obtained, including linearity, reproducibility, energy dependence, fading, minimum detectable dose and glow curve analysis, use being made of a 60Co gamma irradiation facility (mean energy 1.25 MeV) and an electron linear accelerator producing photons at an accelerating potential of 6 and 10 MV. The 6 mol% Ge-doped fibres were found to provide TL response superior to that of 8- and 10 mol% Ge-doped fibres, both for fibres with outer diameter of 241 μm and 604 μm. Concerning reproducibility, obtained under three different test conditions, at <10% the 6 mol% Ge dopant concentration was observed to provide the superior coefficient of variation (CV). In regard to energy dependence, the 10 mol% Ge doped cylindrical fibres produced the largest gradient values at 0.364 and 0.327 for the 241 μm and 604 μm diameter cylindrical fibres respectively and thus the greatest energy dependency. Measured 33 days post irradiation; the 6 mol% Ge doped cylindrical fibres showed the least TL signal loss, at 21% for the 241 μm cylindrical fibre and <40% for the 604 μm cylindrical fibres. The results also revealed that the 6 mol% optical fibres provided the lowest minimum detectable dose, at 0.027 Gy for 6 MV photon beams. Evaluations of these characteristics are supporting development of novel Ge-doped optical fibres for dosimetry in radiotherapy.

  11. Implantation conditions for diamond nanocrystal formation in amorphous silica

    SciTech Connect

    Buljan, Maja; Radovic, Iva Bogdanovic; Desnica, Uros V.; Ivanda, Mile; Jaksic, Milko; Saguy, Cecile; Kalish, Rafi; Djerdj, Igor; Tonejc, Andelka; Gamulin, Ozren

    2008-08-01

    We present a study of carbon ion implantation in amorphous silica, which, followed by annealing in a hydrogen-rich environment, leads to preferential formation of carbon nanocrystals with cubic diamond (c-diamond), face-centered cubic (n-diamond), or simple cubic (i-carbon) carbon crystal lattices. Two different annealing treatments were used: furnace annealing for 1 h and rapid thermal annealing for a brief period, which enables monitoring of early nucleation events. The influence of implanted dose and annealing type on carbon and hydrogen concentrations, clustering, and bonding were investigated. Rutherford backscattering, elastic recoil detection analysis, infrared spectroscopy, transmission electron microscopy, selected area electron diffraction, ultraviolet-visible absorption measurements, and Raman spectroscopy were used to study these carbon formations. These results, combined with the results of previous investigations on similar systems, show that preferential formation of different carbon phases (diamond, n-diamond, or i-carbon) depends on implantation energy, implantation dose, and annealing conditions. Diamond nanocrystals formed at a relatively low carbon volume density are achieved by deeper implantation and/or lower implanted dose. Higher volume densities led to n-diamond and finally to i-carbon crystal formation. This observed behavior is related to damage sites induced by implantation. The optical properties of different carbon nanocrystal phases were significantly different.

  12. Carbothermic Reduction of Amorphous Silica Refined from Diatomaceous Earth

    NASA Astrophysics Data System (ADS)

    Hakamada, Masataka; Fukunaka, Yasuhiro; Oishi, Toshio; Nishiyama, Takashi; Kusuda, Hiromu

    2010-04-01

    Aimed at developing solar-grade Si (SOG-Si) resources, amorphous silica (AS) refined from diatomaceous earth was reduced carbothermically. The reactivity of quartz—typically crystalline silica—also was investigated for comparison. Preliminary experiments confirmed an intermediate phase of SiC during the carbothermic reaction. SiC was produced more easily by heating AS mixed with graphite within 2 hours at 1773 K in a resistance furnace, whereas quartz remained unreacted under the same condition. The AS mixed with SiC then was heated in an electrode impulse furnace. An Si peak was identified in the X-ray diffraction (XRD) pattern of the sample reacted within 30 seconds at 2273 K. Chemical analysis indicated that the mole ratio of reduced Si to initial SiO2 increased with a heating time of 15-30 seconds. It almost reached a constant depending on the heating temperature. The initial stage may correspond to a significant reduction from SiO2 to Si in the solid-solid or solid-gas reaction systems. The next stage probably is a slow vaporization of SiO(g). Once the reduced Si melts with SiO2 at the high temperature, the melt partially covers the surface of SiO2 to prevent contact with SiC. A better reactivity for refined AS is observed than for quartz.

  13. Processing pathway dependence of amorphous silica nanoparticle toxicity: colloidal vs pyrolytic.

    PubMed

    Zhang, Haiyuan; Dunphy, Darren R; Jiang, Xingmao; Meng, Huan; Sun, Bingbing; Tarn, Derrick; Xue, Min; Wang, Xiang; Lin, Sijie; Ji, Zhaoxia; Li, Ruibin; Garcia, Fred L; Yang, Jing; Kirk, Martin L; Xia, Tian; Zink, Jeffrey I; Nel, Andre; Brinker, C Jeffrey

    2012-09-26

    We have developed structure/toxicity relationships for amorphous silica nanoparticles (NPs) synthesized through low-temperature colloidal (e.g., Stöber silica) or high-temperature pyrolysis (e.g., fumed silica) routes. Through combined spectroscopic and physical analyses, we have determined the state of aggregation, hydroxyl concentration, relative proportion of strained and unstrained siloxane rings, and potential to generate hydroxyl radicals for Stöber and fumed silica NPs with comparable primary particle sizes (16 nm in diameter). On the basis of erythrocyte hemolytic assays and assessment of the viability and ATP levels in epithelial and macrophage cells, we discovered for fumed silica an important toxicity relationship to postsynthesis thermal annealing or environmental exposure, whereas colloidal silicas were essentially nontoxic under identical treatment conditions. Specifically, we find for fumed silica a positive correlation of toxicity with hydroxyl concentration and its potential to generate reactive oxygen species (ROS) and cause red blood cell hemolysis. We propose fumed silica toxicity stems from its intrinsic population of strained three-membered rings (3MRs) along with its chainlike aggregation and hydroxyl content. Hydrogen-bonding and electrostatic interactions of the silanol surfaces of fumed silica aggregates with the extracellular plasma membrane cause membrane perturbations sensed by the Nalp3 inflammasome, whose subsequent activation leads to secretion of the cytokine IL-1β. Hydroxyl radicals generated by the strained 3MRs in fumed silica, but largely absent in colloidal silicas, may contribute to the inflammasome activation. Formation of colloidal silica into aggregates mimicking those of fumed silica had no effect on cell viability or hemolysis. This study emphasizes that not all amorphous silicas are created equal and that the unusual toxicity of fumed silica compared to that of colloidal silica derives from its framework and surface

  14. Processing pathway dependence of amorphous silica nanoparticle toxicity - colloidal versus pyrolytic

    PubMed Central

    Zhang, Haiyuan; Dunphy, Darren R.; Jiang, Xingmao; Meng, Huan; Sun, Bingbing; Tarn, Derrick; Xue, Min; Wang, Xiang; Lin, Sijie; Ji, Zhaoxia; Li, Ruibin; Garcia, Fred L.; Yang, Jing; Kirk, Martin L.; Xia, Tian; Zink, Jeffrey I; Nel, Andre; Brinker, C. Jeffrey

    2012-01-01

    We have developed structure/toxicity relationships for amorphous silica nanoparticles (NPs) synthesized through low temperature, colloidal (e.g. Stöber silica) or high temperature pyrolysis (e.g. fumed silica) routes. Through combined spectroscopic and physical analyses, we have determined the state of aggregation, hydroxyl concentration, relative proportion of strained and unstrained siloxane rings, and potential to generate hydroxyl radicals for Stöber and fumed silica NPs with comparable primary particle sizes (16-nm in diameter). Based on erythrocyte hemolytic assays and assessment of the viability and ATP levels in epithelial and macrophage cells, we discovered for fumed silica an important toxicity relationship to post-synthesis thermal annealing or environmental exposure, whereas colloidal silicas were essentially non-toxic under identical treatment conditions. Specifically, we find for fumed silica a positive correlation of toxicity with hydroxyl concentration and its potential to generate reactive oxygen species (ROS) and cause red blood cell hemolysis. We propose fumed silica toxicity stems from its intrinsic population of strained three-membered rings (3MRs) along with its chain-like aggregation and hydroxyl content. Hydrogen-bonding and electrostatic interactions of the silanol surfaces of fumed silica aggregates with the extracellular plasma membrane cause membrane perturbations sensed by the Nalp3 inflammasome, whose subsequent activation leads to secretion of the cytokine IL-1β. Hydroxyl radicals generated by the strained 3MRs in fumed silica but largely absent in colloidal silicas may contribute to the inflammasome activation. Formation of colloidal silica into aggregates mimicking those of fumed silica had no effect on cell viability or hemolysis. This study emphasizes that not all amorphous silica is created equal and that the unusual toxicity of fumed silica compared to colloidal silica derives from its framework and surface chemistry along

  15. Anthropogenic impact on amorphous silica pools in temperate soils

    NASA Astrophysics Data System (ADS)

    Clymans, W.; Struyf, E.; Govers, G.; Vandevenne, F.; Conley, D. J.

    2011-08-01

    Human land use changes perturb biogeochemical silica (Si) cycling in terrestrial ecosystems. This directly affects Si mobilisation and Si storage and influences Si export from the continents, although the magnitude of the impact is unknown. A major reason for our lack of understanding is that very little information exists on how land use affects amorphous silica (ASi) storage in soils. We have quantified and compared total alkali-extracted (PSia) and easily soluble (PSie) Si pools at four sites along a gradient of anthropogenic disturbance in southern Sweden. Land use clearly affects ASi pools and their distribution. Total PSia and PSie for a continuous forested site at Siggaboda Nature Reserve (66 900 ± 22 800 kg SiO2 ha-1 and 952 ± 16 kg SiO2 ha-1) are significantly higher than disturbed land use types from the Råshult Culture Reserve including arable land (28 800 ± 7200 kg SiO2 ha-1 and 239 ± 91 kg SiO2 ha-1), pasture sites (27 300 ± 5980 kg SiO2 ha-1 and 370 ± 129 kg SiO2 ha-1) and grazed forest (23 600 ± 6370 kg SiO2 ha-1 and 346 ± 123 kg SiO2 ha-1). Vertical PSia and PSie profiles show significant (p < 0.05) variation among the sites. These differences in size and distribution are interpreted as the long-term effect of reduced ASi replenishment, as well as changes in ecosystem specific pedogenic processes and increased mobilisation of the PSia in disturbed soils. We have also made a first, though rough, estimate of the magnitude of change in temperate continental ASi pools due to human disturbance. Assuming that our data are representative, we estimate that total ASi storage in soils has declined by ca. 10 % since the onset of agricultural development (3000 BCE). Recent agricultural expansion (after 1700 CE) may have resulted in an average additional export of 1.1 ± 0.8 Tmol Si yr-1 from the soil reservoir to aquatic ecosystems. This is ca. 20 % to the global land-ocean Si flux carried by rivers. It is necessary to update this estimate in future

  16. Ge-doped GaSb thin films with zero mass density change upon crystallization for applications in phase change memories

    NASA Astrophysics Data System (ADS)

    Putero, Magali; Coulet, Marie-Vanessa; Muller, Christophe; Baehtz, Carsten; Raoux, Simone; Cheng, Huai-Yu

    2016-03-01

    In order to optimize materials for phase change random access memories (PCRAM), the effect of Ge doping on Ga-Sb alloy crystallization was studied using combined in situ synchrotron x-ray techniques, electrical measurements, and static laser testing. The present data emphasize that the crystallization temperature can be increased up to 390 °C with subsequent higher thermal stability of the amorphous phase; phase segregation is evidenced with GaSb, Sb, and Ge phases that crystallize in a two-step crystallization process. The Ge-doped GaSb films exhibit a larger electrical contrast as compared to undoped GaSb alloy (up to ×100). The optical contrast measured by laser testing is shown to follow the mass density change variations upon crystallization, with a negative contrast (higher value in amorphous state) whatever Ge-doping levels. In situ x-ray reflectivity measurements show that zero mass density change can be achieved by low Ge-doping. Ge-doped GaSb alloys look promising since a phase change material with zero mass density change and higher crystallization temperature satisfactorily fulfills the specifications for reliable PCRAM cells in terms of endurance and data retention.

  17. Variability of biological effects of silicas: different degrees of activation of the fifth component of complement by amorphous silicas.

    PubMed

    Governa, Mario; Amati, Monica; Fenoglio, Ivana; Valentino, Matteo; Coloccini, Sabrina; Bolognini, Lucia; Carlo Botta, Gian; Emanuelli, Monica; Pierella, Francesca; Volpe, Anna Rita; Astolfi, Paola; Carmignani, Marco; Fubini, Bice

    2005-10-01

    A biogenic and a pyrogenic amorphous silica were incubated in normal human plasma and compared on a per unit surface basis for their ability to split C5 molecules and yield small C5a peptides. Since C5a peptides induce selective chemotactic attraction of polymorphonuclear leukocytes (PMN), measurement of PMN-induced chemotaxis was used as an index of C5 activation. Though to a lesser extent than the crystalline forms, amorphous silicas can promote the cleavage of C5 protein and generation of C5a-like fragment. The biogenic silica, which differs from the pyrogenic variety in particle shape, level of contaminants, and degree of surface hydrophilicity, besides specific surface, induced a greater response. Both silicas activated C5 through a process which seems to involve multiple events similar to those induced by crystalline silica. C5 molecules are adsorbed and hydroxyl radicals are generated through Haber Weiss cycles catalyzed by the redox-active iron present at the particle surface either as trace impurities or chelated from plasma by silanol groups. In turn, these radicals convert native C5 to an oxidized C5-like form C5(H2O2). Finally, C5(H2O2) is cleaved by protease enzymatic action of plasma kallikrein activated by the same silica dusts, yielding a product, C5a(H2O2), having the same functional characteristic as C5a. PMID:16164962

  18. Strong strain rate effect on the plasticity of amorphous silica nanowires

    SciTech Connect

    Yue, Yonghai; Zheng, Kun

    2014-06-09

    With electron-beam (e-beam) off, in-situ tensile experiments on amorphous silica nanowires (NWs) were performed inside a transmission electron microscope (TEM). By controlling the loading rates, the strain rate can be adjusted accurately in a wide range. The result shows a strong strain rate effect on the plasticity of amorphous silica NWs. At lower strain rate, the intrinsic brittle materials exhibit a pronounced elongation higher than 100% to failure with obvious necking near ambient temperature. At the strain rate higher than 5.23 × 10{sup −3}/s, the elongation of the NW decreased dramatically, and a brittle fracture feature behavior was revealed. This ductile feature of the amorphous silica NWs has been further confirmed with the in-situ experiments under optical microscopy while the effect of e-beam irradiation could be eliminated.

  19. Flat Ge-doped optical fibres for food irradiation dosimetry

    SciTech Connect

    Noor, N. Mohd; Jusoh, M. A.; Razis, A. F. Abdull; Alawiah, A.; Bradley, D. A.

    2015-04-24

    Exposing food to radiation can improve hygiene quality, germination control, retard sprouting, and enhance physical attributes of the food product. To provide for food safety, radiation dosimetry in irradiated food is required. Herein, fabricated germanium doped (Ge-doped) optical fibres have been used. The fibres have been irradiated using a gamma source irradiator, doses in the range 1 kGy to 10 kGy being delivered. Using Ge-doped optical fibres of variable size, type and dopant concentration, study has been made of linearity, reproducibility, and fading. The thermoluminescence (TL) yield of the fibres were obtained and compared. The fibres exhibit a linear dose response over the investigated range of doses, with mean reproducibility to within 2.69 % to 8.77 %, exceeding the dose range of all commercial dosimeters used in evaluating high doses for the food irradiation industry. TL fading of the Ge-doped flat fibres has been found to be < 13%.

  20. Flat Ge-doped optical fibres for food irradiation dosimetry

    NASA Astrophysics Data System (ADS)

    Noor, N. Mohd; Jusoh, M. A.; Razis, A. F. Abdull; Alawiah, A.; Bradley, D. A.

    2015-04-01

    Exposing food to radiation can improve hygiene quality, germination control, retard sprouting, and enhance physical attributes of the food product. To provide for food safety, radiation dosimetry in irradiated food is required. Herein, fabricated germanium doped (Ge-doped) optical fibres have been used. The fibres have been irradiated using a gamma source irradiator, doses in the range 1 kGy to 10 kGy being delivered. Using Ge-doped optical fibres of variable size, type and dopant concentration, study has been made of linearity, reproducibility, and fading. The thermoluminescence (TL) yield of the fibres were obtained and compared. The fibres exhibit a linear dose response over the investigated range of doses, with mean reproducibility to within 2.69 % to 8.77 %, exceeding the dose range of all commercial dosimeters used in evaluating high doses for the food irradiation industry. TL fading of the Ge-doped flat fibres has been found to be < 13%.

  1. Molecular dynamics study of the mechanical loss in amorphous pure and doped silica

    SciTech Connect

    Hamdan, Rashid; Trinastic, Jonathan P.; Cheng, H. P.

    2014-08-07

    Gravitational wave detectors and other precision measurement devices are limited by the thermal noise in the oxide coatings on the mirrors of such devices. We have investigated the mechanical loss in amorphous oxides by calculating the internal friction using classical, atomistic molecular dynamics simulations. We have implemented the trajectory bisection method and the non-local ridge method in the DL-POLY molecular dynamics simulation software to carry out those calculations. These methods have been used to locate the local potential energy minima that a system visits during a molecular dynamics trajectory and the transition state between any two consecutive minima. Using the numerically calculated barrier height distributions, barrier asymmetry distributions, relaxation times, and deformation potentials, we have calculated the internal friction of pure amorphous silica and silica mixed with other oxides. The results for silica compare well with experiment. Finally, we use the numerical calculations to comment on the validity of previously used theoretical assumptions.

  2. Observations of Nucleation and Early Stage Growth of Amorphous Silica on Carboxyl-Terminated Model Biosubstrates

    NASA Astrophysics Data System (ADS)

    Wallace, A. F.; Dove, P. M.

    2005-12-01

    Over Earth history, organisms have developed the ability to control the nucleation and growth of a broad range of nanocrystalline and amorphous materials. The formation of amorphous biosilica is of particular interest because silicifiers sequester gigatons of silica annually, and suppress dissolved silica levels in the ocean to current low levels. The ecological success of marine diatoms, which are arguably the most important silicifiers, places them alongside marine calcifiers as major players in the sequestration of organic carbon. Thus, the biologically mediated formation of amorphous silica plays a key role in the global cycling of silicon and carbon. During controlled biomineralization, nucleation typically occurs in designated locations. There is a substantial body of evidence suggesting that macromolecules in the cellular environment determine these locations by acting as templates to provide energetically favorable sites for the onset of mineral and amorphous material nucleation. In diatoms, silica formation is likely initiated through heterogeneous nucleation on functional portions of macromolecules inside the Silica Deposition Vesicle (SDV). Previous studies of silica nucleation have implicated multiple chemical moieties associated with the constituent amino acids and sugars of polysaccharides, proteins, and glycoproteins as probable sites for in vivo surface nucleation and patterning. These investigations have usually employed complex macromolecules that exhibit multiple functionalities, and un-characterized solution compositions, thus rendering a quantitative analysis of kinetic and thermodynamic processes impossible. The objective of this research is to experimentally test kinetic and thermodynamic controls exercised by surface moieties on silica nucleation. Our experimental model system uses synthetic organic substrates designed to mimic key features of the interfacial regions between the surrounding cellular environment and the amorphous silica

  3. Ion-irradiation-induced preferential amorphization of Ge nanocrystals in silica

    SciTech Connect

    Ridgway, M.C.; Azevedo, G. de M; Elliman, R.G.; Glover, C.J.; Llewellyn, D.J.; Miller, R.; Wesch, W.; Foran, G.J.; Hansen, J.; Nylandsted-Larsen, A.

    2005-03-01

    Extended x-ray absorption fine structure (EXAFS) measurements have been used to characterize the ion-irradiation-induced crystalline-to-amorphous phase transformation in Ge nanocrystals. The atomic-scale structure of Ge nanocrystals in a silica matrix is first shown to deviate from that of bulk crystalline material with an increase in both Gaussian and non-Gaussian forms of structural disorder. The magnitude of the disorder in the bond-length distribution is comparable to that of relaxed amorphous Ge. The amorphization of such nanocrystals is then demonstrated at an ion dose {approx}100 times less than that required for bulk crystalline material irradiated simultaneously. Specifically, Ge nanocrystals irradiated at -196 deg. C are rendered amorphous at {approx}0.01 displacements per atom. Finally, we show the atomic-scale structure of amorphized nanocrystals and bulk amorphous material is comparable. The rapid amorphization of Ge nanocrystals is potentially the result of several factors including (i) the preferential nucleation of the amorphous phase at the nanocrystal/matrix interface (ii) the preirradiation, higher-energy structural state of the nanocrystals themselves (iii) an enhanced vacancy concentration within the nanocrystals due to inhibited Frenkel pair recombination when Ge interstitials are recoiled into the matrix, and (iv) ion-beam mixing and the subsequent increase in nanocrystal impurity concentrations.

  4. Molecular dynamics study of oil detachment from an amorphous silica surface in water medium

    NASA Astrophysics Data System (ADS)

    Chen, Jiaxuan; Si, Hao; Chen, Wenyang

    2015-10-01

    In this paper, the mechanism of oil detachment from optical glass in water medium is studied by using molecular dynamics simulation. At the beginning, some undecane molecules are adsorbed on the amorphous silica surface to get contaminated glass. Upon addition of 6000 water molecules, most of the undecane molecules on the substrate surface can be detached from an amorphous silica surface through three stages. The formation of different directions of water channels is vital for oil detachment. The electrostatic interaction of water substrate contributes to disturbing the aggregates of undecane molecules and the H-bonding interaction between the water molecules is helpful for the oil puddle away from the substrate. However, there is still some oil molecules residue on the substrate surface after water cleaning. The simulation results showed that the specific ring potential well of amorphous silica surface will hinder the detachment of oil molecules. We also find that the formation of the specific ring potential well is related to the number of atoms and the average radius in silica atomic rings. Increasing the upward lift force, which acts on the hydrocarbon tail of oil molecules, will be benefit to clear the oil pollution residues from the glass surface.

  5. Dielectric breakdown in silica-amorphous polymer nanocomposite films: the role of the polymer matrix.

    PubMed

    Grabowski, Christopher A; Fillery, Scott P; Westing, Nicholas M; Chi, Changzai; Meth, Jeffrey S; Durstock, Michael F; Vaia, Richard A

    2013-06-26

    The ultimate energy storage performance of an electrostatic capacitor is determined by the dielectric characteristics of the material separating its conductive electrodes. Polymers are commonly employed due to their processability and high breakdown strength; however, demands for higher energy storage have encouraged investigations of ceramic-polymer composites. Maintaining dielectric strength, and thus minimizing flaw size and heterogeneities, has focused development toward nanocomposite (NC) films; but results lack consistency, potentially due to variations in polymer purity, nanoparticle surface treatments, nanoparticle size, and film morphology. To experimentally establish the dominant factors in broad structure-performance relationships, we compare the dielectric properties for four high-purity amorphous polymer films (polymethyl methacrylate, polystyrene, polyimide, and poly-4-vinylpyridine) incorporating uniformly dispersed silica colloids (up to 45% v/v). Factors known to contribute to premature breakdown-field exclusion and agglomeration-have been mitigated in this experiment to focus on what impact the polymer and polymer-nanoparticle interactions have on breakdown. Our findings indicate that adding colloidal silica to higher breakdown strength amorphous polymers (polymethyl methacrylate and polyimide) causes a reduction in dielectric strength as compared to the neat polymer. Alternatively, low breakdown strength amorphous polymers (poly-4-vinylpyridine and especially polystyrene) with comparable silica dispersion show similar or even improved breakdown strength for 7.5-15% v/v silica. At ∼15% v/v or greater silica content, all the polymer NC films exhibit breakdown at similar electric fields, implying that at these loadings failure becomes independent of polymer matrix and is dominated by silica. PMID:23639183

  6. Amorphous silica in ultra-high performance concrete: First hour of hydration

    SciTech Connect

    Oertel, Tina; Hutter, Frank; Helbig, Uta; Sextl, Gerhard

    2014-04-01

    Amorphous silica in the sub-micrometer size range is widely used to accelerate cement hydration. Investigations including properties of silica which differ from the specific surface area are rare. In this study, the reactivity of varying types of silica was evaluated based on their specific surface area, surface silanol group density, content of silanol groups and solubility in an alkaline suspension. Pyrogenic silica, silica fume and silica synthesized by hydrolysis and condensation of alkoxy silanes, so-called Stoeber particles, were employed. Influences of the silica within the first hour were further examined in pastes with water/cement ratios of 0.23 using in-situ X-ray diffraction, cryo scanning electron microscopy and pore solution analysis. It was shown that Stoeber particles change the composition of the pore solution. Na{sup +}, K{sup +}, Ca{sup 2+} and silicate ions seem to react to oligomers. The extent of this reaction might be highest for Stoeber particles due to their high reactivity.

  7. Surface modification of zinc oxide nanoparticles with amorphous silica alters their fate in the circulation.

    PubMed

    Konduru, Nagarjun V; Murdaugh, Kimberly M; Swami, Archana; Jimenez, Renato J; Donaghey, Thomas C; Demokritou, Philip; Brain, Joseph D; Molina, Ramon M

    2016-08-01

    Nanoparticle (NP) pharmacokinetics and biological effects are influenced by many factors, especially surface physicochemical properties. We assessed the effects of an amorphous silica coating on the fate of zinc after intravenous (IV) injection of neutron activated uncoated (65)ZnO or silica-coated (65)ZnO NPs in male Wistar Han rats. Groups of IV-injected rats were sequentially euthanized, and 18 tissues were collected and analyzed for (65)Zn radioactivity. The protein coronas on each ZnO NP after incubation in rat plasma were analyzed by SDS-PAGE gel electrophoresis and mass spectrometry of selected gel bands. Plasma clearance for both NPs was biphasic with rapid initial and slower terminal clearance rates. Half-lives of plasma clearance of silica-coated (65)ZnO were shorter (initial - <1 min; terminal - 2.5 min) than uncoated (65)ZnO (initial - 1.9 min; terminal - 38 min). Interestingly, the silica-coated (65)ZnO group had higher (65)Zn associated with red blood cells and higher initial uptake in the liver. The (65)Zn concentrations in all the other tissues were significantly lower in the silica-coated than uncoated groups. We also found that the protein corona formed on silica-coated ZnO NPs had higher amounts of plasma proteins, particularly albumin, transferrin, A1 inhibitor 3, α-2-hs-glycoprotein, apoprotein E and α-1 antitrypsin. Surface modification with amorphous silica alters the protein corona, agglomerate size, and zeta potential of ZnO NPs, which in turn influences ZnO biokinetic behavior in the circulation. This emphasizes the critical role of the protein corona in the biokinetics, toxicology and nanomedical applications of NPs. PMID:26581431

  8. Synthesis and characterization of large specific surface area nanostructured amorphous silica materials.

    PubMed

    Marquez-Linares, Francisco; Roque-Malherbe, Rolando M A

    2006-04-01

    Large specific surface area materials attract wide attention because of their applications in adsorption, catalysis, and nanotechnology. In the present study, we describe the synthesis and characterization of nanostructured amorphous silica materials. These materials were obtained by means of a modification of the Stobe-Fink-Bohn (SFB) method. The morphology and essential features of the synthesized materials have been studied using an automated surface area and pore size analyzer and scanning electron microscopy. The existence of a micro/mesoporous structure in the obtained materials has been established. It was also found that the obtained particle packing materials show large specific surface area up to 1,600 m2/g. (To our best knowledge, there is no any reported amorphous silica material with such a higher specific surface area.) The obtained materials could be useful in the manufacture of adsorbents, catalyst supports, and other nanotechnological applications. PMID:16736774

  9. Coating of calcia-doped ceria with amorphous silica shell by seeded polymerization technique

    SciTech Connect

    El-Toni, Ahmed Mohamed . E-mail: el-toni@mail.tagen.tohoku.ac.jp; Yin, Shu; Yabe, Shinryo; Sato, Tsugio

    2005-07-12

    Calcia-doped ceria is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products. However, its high catalytic ability for oxidation of organic materials makes it difficult to use as a sunscreen material. Therefore, calcia-doped ceria was coated with amorphous silica by means of seeded polymerization technique in order to depress its oxidation catalytic ability. The catalytic ability as well as UV-shielding ability was investigated for coated particles.

  10. Novel 3-hydroxypropyl bonded phase by direct hydrosilylation of allyl alcohol on amorphous hydride silica

    PubMed Central

    Gómez, Jorge E.; Navarro, Fabián H.; Sandoval, Junior E.

    2015-01-01

    A novel 3-hydroxypropyl (propanol) bonded silica phase has been prepared by hydrosilylation of allyl alcohol on a hydride silica intermediate, in the presence of platinum (0)-divinyltetramethyldisiloxane (Karstedt's catalyst). The regio-selectivity of this synthetic approach had been correctly predicted by previous reports involving octakis(dimethylsiloxy)octasilsesquioxane (Q8M8H) and hydrogen silsesquioxane (T8H8), as molecular analogs of hydride amorphous silica. Thus, C-silylation predominated (~ 94%) over O-silylation, and high surface coverages of propanol groups (5±1 µmol/m2) were typically obtained in this work. The propanol-bonded phase was characterized by spectroscopic (IR and solid state NMR on silica microparticles), contact angle (on fused-silica wafers) and CE (on fused-silica tubes) techniques. CE studies of the migration behavior of pyridine, caffeine, tris(2,2’-bipyridine)Ru(II) chloride and lysozyme on propanol-modified capillaries were carried out. The adsorption properties of these select silanol-sensitive solutes were compared to those on the unmodified and hydride-modified tubes. It was found that hydrolysis of the SiH species underlying the immobilized propanol moieties leads mainly to strong ion-exchange based interactions with the basic solutes at pH 4, particularly with lysozyme. Interestingly, and in agreement with water contact angle and electroosmotic mobility figures, the silanol-probe interactions on the buffer-exposed (hydrolyzed) hydride surface are quite different from those of the original unmodified tube. PMID:24934906

  11. Intestinal absorption and biological effects of orally administered amorphous silica particles

    PubMed Central

    2014-01-01

    Although amorphous silica nanoparticles are widely used in the production of food products (e.g., as anticaking agents), there is little information available about their absorption and biological effects after oral exposure. Here, we examined the in vitro intestinal absorption and in vivo biological effects in mice of orally administered amorphous silica particles with diameters of 70, 300, and 1,000 nm (nSP70, mSP300, and mSP1000, respectively) and of nSP70 that had been surface-modified with carboxyl or amine groups (nSP70-C and nSP70-N, respectively). Analysis of intestinal absorption by means of the everted gut sac method combined with an inductively coupled plasma optical emission spectrometer showed that the intestinal absorption of nSP70-C was significantly greater than that of nSP70. The absorption of nSP70-N tended to be greater than that of nSP70; however, the results were not statistically significant. Our results indicate that silica nanoparticles can be absorbed through the intestine and that particle diameter and surface properties are major determinants of the degree of absorption. We also examined the biological effects of the silica particles after 28-day oral exposure in mice. Hematological, histopathological, and biochemical analyses showed no significant differences between control mice and mice treated with the silica particles, suggesting that the silica nanoparticles evaluated in this study are safe for use in food production. PMID:25288919

  12. Morphology controlling method for amorphous silica nanoparticles and jellyfish-like nanowires and their luminescence properties

    NASA Astrophysics Data System (ADS)

    Liu, Haitao; Huang, Zhaohui; Huang, Juntong; Xu, Song; Fang, Minghao; Liu, Yan-Gai; Wu, Xiaowen; Zhang, Shaowei

    2016-03-01

    Uniform silica nanoparticles and jellyfish-like nanowires were synthesized by a chemical vapour deposition method on Si substrates treated without and with Ni(NO3)2, using silicon powder as the source material. Composition and structural characterization using field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and fourier-transform infrared spectroscopy showed that the as-prepared products were silica nanoparticles and nanowires which have amorphous structures. The form of nanoparticles should be related to gas-phase nucleation procedure. The growth of the nanowires was in accordance with vapour-liquid-solid mechanism, followed by Ostwald ripening to form the jellyfish-like morphology. Photoluminescence and cathodoluminescence measurements showed that the silica products excited by different light sources show different luminescence properties. The emission spectra of both silica nanoparticles and nanowires are due to the neutral oxygen vacancies (≡Si-Si≡). The as-synthesized silica with controlled morphology can find potential applications in future nanodevices with tailorable photoelectric properties.

  13. Morphology controlling method for amorphous silica nanoparticles and jellyfish-like nanowires and their luminescence properties.

    PubMed

    Liu, Haitao; Huang, Zhaohui; Huang, Juntong; Xu, Song; Fang, Minghao; Liu, Yan-Gai; Wu, Xiaowen; Zhang, Shaowei

    2016-01-01

    Uniform silica nanoparticles and jellyfish-like nanowires were synthesized by a chemical vapour deposition method on Si substrates treated without and with Ni(NO3)2, using silicon powder as the source material. Composition and structural characterization using field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and fourier-transform infrared spectroscopy showed that the as-prepared products were silica nanoparticles and nanowires which have amorphous structures. The form of nanoparticles should be related to gas-phase nucleation procedure. The growth of the nanowires was in accordance with vapour-liquid-solid mechanism, followed by Ostwald ripening to form the jellyfish-like morphology. Photoluminescence and cathodoluminescence measurements showed that the silica products excited by different light sources show different luminescence properties. The emission spectra of both silica nanoparticles and nanowires are due to the neutral oxygen vacancies (≡Si-Si≡). The as-synthesized silica with controlled morphology can find potential applications in future nanodevices with tailorable photoelectric properties. PMID:26940294

  14. Morphology controlling method for amorphous silica nanoparticles and jellyfish-like nanowires and their luminescence properties

    PubMed Central

    Liu, Haitao; Huang, Zhaohui; Huang, Juntong; Xu, Song; Fang, Minghao; Liu, Yan-gai; Wu, Xiaowen; Zhang, Shaowei

    2016-01-01

    Uniform silica nanoparticles and jellyfish-like nanowires were synthesized by a chemical vapour deposition method on Si substrates treated without and with Ni(NO3)2, using silicon powder as the source material. Composition and structural characterization using field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and fourier-transform infrared spectroscopy showed that the as-prepared products were silica nanoparticles and nanowires which have amorphous structures. The form of nanoparticles should be related to gas-phase nucleation procedure. The growth of the nanowires was in accordance with vapour-liquid-solid mechanism, followed by Ostwald ripening to form the jellyfish-like morphology. Photoluminescence and cathodoluminescence measurements showed that the silica products excited by different light sources show different luminescence properties. The emission spectra of both silica nanoparticles and nanowires are due to the neutral oxygen vacancies (≡Si-Si≡). The as-synthesized silica with controlled morphology can find potential applications in future nanodevices with tailorable photoelectric properties. PMID:26940294

  15. Amorphization of quartz by friction: Implication to silica-gel lubrication of fault surfaces

    NASA Astrophysics Data System (ADS)

    Nakamura, Yu; Muto, Jun; Nagahama, Hiroyuki; Shimizu, Ichiko; Miura, Takashi; Arakawa, Ichiro

    2012-11-01

    To understand physico-chemical processes at real contacts (asperities) on fault surfaces, we conducted pin-on-disk friction experiments at room temperature, using single crystalline quartz disks and quartz pins. Velocity weakening from friction coefficient μ ˜ 0.6 to 0.4 was observed under apparent normal stresses of 8-19 (18 > 19), when the slip rate was increased from 0.003 to 2.6 m/s. Frictional surfaces revealed ductile deformation of wear materials. The Raman spectra of frictional tracks showed blue shifts and broadening of quartz main bands, and appearance of new peaks at 490-520 and 610 cm-1. All these features are indicative of pressure- and strain-induced amorphization of quartz. The mapping analyses of Fourier transform infrared (FT-IR) spectroscopy at room dry conditions suggest selective hydration of wear materials. It is possible that the strained Si-O-Si bridges in amorphous silica preferentially react with water to form silica-gel. In natural fault systems, amorphous materials would be produced at real fault contacts and accumulate over the fault surfaces with displacements. Subsequent hydration would lead to significant reduction of fault strength during slip.

  16. Consecutively Preparing D-Xylose, Organosolv Lignin, and Amorphous Ultrafine Silica from Rice Husk

    PubMed Central

    Zhang, Hongxi; Ding, Xuefeng; Wang, Zichen; Zhao, Xu

    2014-01-01

    Rice husk is an abundant agricultural by-product reaching the output of 80 million tons annually in the world. The most common treatment method of rice husk is burning or burying, which caused serious air pollution and resource waste. In order to solve this problem, a new method is proposed to comprehensively utilize the rice husk in this paper. Firstly, the D-xylose was prepared from the semicellulose via dilute acid hydrolysis. Secondly, the lignin was separated via organic solvent pulping from the residue. Finally, the amorphous ultrafine silica was prepared via pyrolysis of the residue produced in the second process. In this way, the three main contents of rice husk (semicellulose, lignin, and silica) are consecutively converted to three fine chemicals, without solid waste produced. The yields of D-xylose and organosolv lignin reach 58.2% and 58.5%, respectively. The purity and specific surface of amorphous ultrafine silica reach 99.92% and 225.20 m2/g. PMID:25140120

  17. Consecutively preparing d-xylose, organosolv lignin, and amorphous ultrafine silica from rice husk.

    PubMed

    Zhang, Hongxi; Ding, Xuefeng; Wang, Zichen; Zhao, Xu

    2014-01-01

    Rice husk is an abundant agricultural by-product reaching the output of 80 million tons annually in the world. The most common treatment method of rice husk is burning or burying, which caused serious air pollution and resource waste. In order to solve this problem, a new method is proposed to comprehensively utilize the rice husk in this paper. Firstly, the D-xylose was prepared from the semicellulose via dilute acid hydrolysis. Secondly, the lignin was separated via organic solvent pulping from the residue. Finally, the amorphous ultrafine silica was prepared via pyrolysis of the residue produced in the second process. In this way, the three main contents of rice husk (semicellulose, lignin, and silica) are consecutively converted to three fine chemicals, without solid waste produced. The yields of D-xylose and organosolv lignin reach 58.2% and 58.5%, respectively. The purity and specific surface of amorphous ultrafine silica reach 99.92% and 225.20 m(2)/g. PMID:25140120

  18. Gamma irradiated thermoluminescence response of Ge-doped SiO2 fibre.

    PubMed

    Wahib, Norfadira; Zulkepely, Nurul Najua; Mat Nawi, Siti Nurasiah; Amin, Yusoff Mohd; Ling, Yap Seong; Abdul Sani, Siti Fairus; Maah, Mohd Jamil; Bradley, D A

    2015-11-01

    Over the past decade and more, considerable interest has been shown in the thermoluminescence (TL) properties of silica-based single-mode optical fibres, in particular investigating potential ionising radiation dosimetry applications. Herein, study has been made of TL glow curve, dose response, reproducibility and fading of 6mol% Ge-doped silica, fabricated in-house and produced in the form of cylindrical fibres. Three different pairings of doped-core and silica cladding diameters were produced: (40, 241)µm, (80, 483)µm and (100, 604)µm. The TL results were compared against that of TLD-100, one of the most sensitive commercially available LiF-based TL media. For all three pairings of diameters, closely similar TL glow curve were obtained, formed of a single peaked structure with a maximum TL yield located between the temperatures 250 and 310°C. The TL yield of the fibres were linear over the range of doses investigated, from 1Gy up to 10Gy, their dose response exceeding that of TLD-100, the samples also being found to be reusable, without evidence of degradation. PMID:26313622

  19. Cohesion of Amorphous Silica Spheres: Toward a Better Understanding of The Coagulation Growth of Silicate Dust Aggregates

    NASA Astrophysics Data System (ADS)

    Kimura, Hiroshi; Wada, Koji; Senshu, Hiroki; Kobayashi, Hiroshi

    2015-10-01

    Adhesion forces between submicrometer-sized silicate grains play a crucial role in the formation of silicate dust agglomerates, rocky planetesimals, and terrestrial planets. The surface energy of silicate dust particles is the key to their adhesion and rolling forces in a theoretical model based on contact mechanics. Here we revisit the cohesion of amorphous silica spheres by compiling available data on the surface energy for hydrophilic amorphous silica in various circumstances. It turned out that the surface energy for hydrophilic amorphous silica in a vacuum is a factor of 10 higher than previously assumed. Therefore, the previous theoretical models underestimated the critical velocity for the sticking of amorphous silica spheres, as well as the rolling friction forces between them. With the most plausible value of the surface energy for amorphous silica spheres, theoretical models based on the contact mechanics are in harmony with laboratory experiments. Consequently, we conclude that silicate grains with a radius of 0.1 μm could grow to planetesimals via coagulation in a protoplanetary disk. We argue that the coagulation growth of silicate grains in a molecular cloud is advanced either by organic mantles rather than icy mantles or, if there are no mantles, by nanometer-sized grain radius.

  20. Ab initio simulation of photoinduced transformation of small rings in amorphous silica

    NASA Astrophysics Data System (ADS)

    Donadio, Davide; Bernasconi, Marco

    2005-02-01

    We have studied the photoinduced transformation of small rings (three membered) in amorphous silica by Car-Parrinello simulations. The process of ring opening leading to the formation of a couple of paramagnetic centers, namely an E' and a nonbridging-oxygen hole center (NBOHC), has been proposed experimentally to occur in silica exposed to F2 laser irradiation (at 7.9eV ). By using a scheme for the simulation of rare events in ab initio molecular dynamics [M. Iannuzzi, A. Laio, and M. Parrinello, Phys. Rev. Lett. 90, 238303 (2003)], we have identified a transformation path for the opening of a three-membered ring induced by a self-trapped triplet exciton, the migration of NBOHC and formation of a couple of stable E' and NBOHC paramagnetic defects.

  1. Oxidative Damage and Energy Metabolism Disorder Contribute to the Hemolytic Effect of Amorphous Silica Nanoparticles.

    PubMed

    Jiang, Lizhen; Yu, Yongbo; Li, Yang; Yu, Yang; Duan, Junchao; Zou, Yang; Li, Qiuling; Sun, Zhiwei

    2016-12-01

    Amorphous silica nanoparticles (SiNPs) have been extensively used in biomedical applications due to their particular characteristics. The increased environmental and iatrogenic exposure of SiNPs gained great concerns on the biocompatibility and hematotoxicity of SiNPs. However, the studies on the hemolytic effects of amorphous SiNPs in human erythrocytes are still limited. In this study, amorphous SiNPs with 58 nm were selected and incubated with human erythrocytes for different times (30 min and 2 h) at various concentrations (0, 10, 20, 50, and 100 μg/mL). SiNPs induced a dose-dependent increase in percent hemolysis and significantly increased the malondialdehyde (MDA) content and decreased the superoxide dismutase (SOD) activity, leading to oxidative damage in erythrocytes. Hydroxyl radical (·OH) levels were detected by electron spin resonance (ESR), and the decreased elimination rates of ·OH showed SiNPs induced low antioxidant ability in human erythrocytes. Na(+)-K(+) ATPase activity and Ca(2+)-Mg(2+) ATPase activity were found remarkably inhibited after SiNP treatment, possibly causing energy sufficient in erythrocytes. Percent hemolysis of SiNPs was significantly decreased in the presence of N-acetyl-cysteine (NAC) and adenosine diphosphate (ADP). It was concluded that amorphous SiNPs caused dose-dependent hemolytic effects in human erythrocytes. Oxidative damage and energy metabolism disorder contributed to the hemolytic effects of SiNPs in vitro. PMID:26831695

  2. Oxidative Damage and Energy Metabolism Disorder Contribute to the Hemolytic Effect of Amorphous Silica Nanoparticles

    NASA Astrophysics Data System (ADS)

    Jiang, Lizhen; Yu, Yongbo; Li, Yang; Yu, Yang; Duan, Junchao; Zou, Yang; Li, Qiuling; Sun, Zhiwei

    2016-02-01

    Amorphous silica nanoparticles (SiNPs) have been extensively used in biomedical applications due to their particular characteristics. The increased environmental and iatrogenic exposure of SiNPs gained great concerns on the biocompatibility and hematotoxicity of SiNPs. However, the studies on the hemolytic effects of amorphous SiNPs in human erythrocytes are still limited. In this study, amorphous SiNPs with 58 nm were selected and incubated with human erythrocytes for different times (30 min and 2 h) at various concentrations (0, 10, 20, 50, and 100 μg/mL). SiNPs induced a dose-dependent increase in percent hemolysis and significantly increased the malondialdehyde (MDA) content and decreased the superoxide dismutase (SOD) activity, leading to oxidative damage in erythrocytes. Hydroxyl radical (·OH) levels were detected by electron spin resonance (ESR), and the decreased elimination rates of ·OH showed SiNPs induced low antioxidant ability in human erythrocytes. Na+-K+ ATPase activity and Ca2+-Mg2+ ATPase activity were found remarkably inhibited after SiNP treatment, possibly causing energy sufficient in erythrocytes. Percent hemolysis of SiNPs was significantly decreased in the presence of N-acetyl-cysteine (NAC) and adenosine diphosphate (ADP). It was concluded that amorphous SiNPs caused dose-dependent hemolytic effects in human erythrocytes. Oxidative damage and energy metabolism disorder contributed to the hemolytic effects of SiNPs in vitro.

  3. Amorphous silica nanoparticles enhance cross-presentation in murine dendritic cells

    SciTech Connect

    Hirai, Toshiro; Yoshioka, Yasuo; Takahashi, Hideki; Ichihashi, Ko-ichi; Yoshida, Tokuyuki; Tochigi, Saeko; Nagano, Kazuya; Abe, Yasuhiro; Nabeshi, Hiromi; Yoshikawa, Tomoaki; Tsutsumi, Yasuo

    2012-10-26

    Highlights: Black-Right-Pointing-Pointer Silica nanoparticles enhanced cross-presentation. Black-Right-Pointing-Pointer Silica nanoparticles induced endosomal release of exogenous antigens. Black-Right-Pointing-Pointer Silica nanoparticle-induced cross-presentation was mediated by scavenger receptors. Black-Right-Pointing-Pointer Surface-modification may enable the manufacture of safer silica nanoparticles. -- Abstract: Nanomaterials (NMs) exhibit unique physicochemical properties and innovative functions, and they are increasingly being used in a wide variety of fields. Ensuring the safety of NMs is now an urgent task. Recently, we reported that amorphous silica nanoparticles (nSPs), one of the most widely used NMs, enhance antigen-specific cellular immune responses and may therefore aggravate immune diseases. Thus, to ensure the design of safer nSPs, investigations into the effect of nSPs on antigen presentation in dendritic cells, which are central orchestrators of the adaptive immune response, are now needed. Here, we show that nSPs with diameters of 70 and 100 nm enhanced exogenous antigen entry into the cytosol from endosomes and induced cross-presentation, whereas submicron-sized silica particles (>100 nm) did not. Furthermore, we show that surface modification of nSPs suppressed cross-presentation. Although further studies are required to investigate whether surface-modified nSPs suppress immune-modulating effects in vivo, the current results indicate that appropriate regulation of the characteristics of nSPs, such as size and surface properties, will be critical for the design of safer nSPs.

  4. Size and spatial homogeneity of SiGe quantum dots in amorphous silica matrix

    SciTech Connect

    Buljan, Maja; Pinto, Sara R. C.; Rolo, Anabela G.; Levichev, Sergey; Gomes, Maria J. M.; Kashtiban, Reza J.; Bangert, Ursel; Chahboun, Adil; Holy, Vaclav

    2009-10-15

    In this paper, we present a study of structural properties of SiGe quantum dots formed in amorphous silica matrix by magnetron sputtering technique. We investigate deposition conditions leading to the formation of dense and uniformly sized quantum dots, distributed homogeneously in the matrix. X-ray and Raman spectroscopy were used to estimate the Si content. A detailed analysis based on grazing incidence small angle x-ray scattering revealed the influence of the deposition conditions on quantum dot sizes, size distributions, spatial arrangement, and concentration of quantum dots in the matrix, as well as the Si:Ge content.

  5. Classical molecular dynamics simulations of hypervelocity nanoparticle impacts on amorphous silica

    SciTech Connect

    Samela, Juha; Nordlund, Kai

    2010-02-01

    We have investigated the transition from the atomistic to the macroscopic impact mechanism by simulating large Argon cluster impacts on amorphous silica. The transition occurs at cluster sizes less than 50 000 atoms at hypervelocity regime (22 km/s). After that, the crater volume increases linearly with the cluster size opposite to the nonlinear scaling typical of small cluster impacts. The simulations demonstrate that the molecular dynamics method can be used to explore atomistic mechanisms that lead to damage formation in small particle impacts, for example, in impacts of micrometeorites on spacecraft.

  6. Classical molecular dynamics simulations of hypervelocity nanoparticle impacts on amorphous silica

    NASA Astrophysics Data System (ADS)

    Samela, Juha; Nordlund, Kai

    2010-02-01

    We have investigated the transition from the atomistic to the macroscopic impact mechanism by simulating large Argon cluster impacts on amorphous silica. The transition occurs at cluster sizes less than 50000 atoms at hypervelocity regime (22 km/s). After that, the crater volume increases linearly with the cluster size opposite to the nonlinear scaling typical of small cluster impacts. The simulations demonstrate that the molecular dynamics method can be used to explore atomistic mechanisms that lead to damage formation in small particle impacts, for example, in impacts of micrometeorites on spacecraft.

  7. Cellular Recognition and Trafficking of Amorphous Silica Nanoparticles by Macrophage Scavenger Receptor A

    SciTech Connect

    Orr, Galya; Chrisler, William B.; Cassens, Kaylyn J.; Tan, Ruimin; Tarasevich, Barbara J.; Markillie, Lye Meng; Zangar, Richard C.; Thrall, Brian D.

    2011-09-01

    The internalization of engineered nanoparticles (ENPs) into cells is known to involve active transport mechanisms, yet the precise biological molecules involved are poorly understood. We demonstrate that the uptake of amorphous silica ENPs (92 nm) by macrophage cells is strongly inhibited by silencing expression of scavenger receptor A (SR-A). In addition, ENP uptake is augmented by introducing SR-A expression into human cells that are normally non-phagocytic. Confocal fluorescent microscopy analyses show that the majority of single or small clusters of silica ENPs co-localize intracellularly with SR-A and are internalized through a pathway characteristic of clathrin-dependent endocytosis. In contrast, larger silica NP agglomerates (>500 nm) are poorly co-localized with the receptor, suggesting independent trafficking or internalization pathways are involved. SR-A silencing also caused decreased cellular secretion of pro-inflammatory cytokines in response to silica ENPs. As SR-A is expressed in macrophages throughout the reticulo-endothelial system, this pathway is likely an important determinant of the biodistribution of, and cellular response to ENPs.

  8. Grafting Strategy to Develop Single Site Titanium on an Amorphous Silica Surface

    SciTech Connect

    Capel-Sanchez, M.; Blanco-Brieva, G; Campos-Martin, J; de Frutos, M; Wen, W; Rodriguez, J; Fierro, J

    2009-01-01

    Titanium/silica systems were prepared by grafting a titanium alkoxide (titanium isopropoxide and titanium (triethanolaminate) isopropoxide) precursor onto amorphous silica. The grafting process, which consisted of the hydrolysis of the Ti precursor by the hydroxyl groups on the silica surface, yielded samples containing Ti-loadings of 1-1.6 wt %. The as synthesized and calcined TiO2-SiO2 samples were characterized by UV-vis, FTIR, XPS, and XANES spectroscopic techniques. These systems were tested in the liquid-phase epoxidation of oct-1-ene with hydrogen peroxide reaction. Spectroscopic data indicated that titanium anchoring takes place by reaction between the alkoxide precursor and surface OH groups of the silica substrate. The nature of surface titanium species generated by chemical grafting depends largely on the titanium precursor employed. Thus, the titanium isopropoxide precursor yields tetrahedrally coordinated polymeric titanium species, which give rise to a low-efficiency catalyst. However, if an atrane precursor (titanium (triethanolaminate) isopropoxide) is employed, isolated titanium species are obtained. The fact that these species remain isolated even after calcination is due to the protective effect of the triethanolaminate ligand that avoids titanium polymerization. These differences in the titanium environment have a pivotal role in the performance of these systems in the epoxidation of alkenes with hydrogen peroxide.

  9. Fast response in-line gas sensor using C-type fiber and Ge-doped ring defect photonic crystal fiber.

    PubMed

    Kassani, Sahar Hosseinzadeh; Park, Jiyoung; Jung, Yongmin; Kobelke, Jens; Oh, Kyunghwan

    2013-06-17

    An in-line chemical gas sensor was proposed and experimentally demonstrated using a new C-type fiber and a Ge-doped ring defect photonic crystal fiber (PCF). The C-type fiber segment served as a compact gas inlet/outlet directly spliced to PCF, which overcame previous limitations in packaging and dynamic responses. C-type fiber was prepared by optimizing drawing process for a silica tube with an open slot. Splicing conditions for SMF/C-type fiber and PCF/C-type fiber were experimentally established to provide an all-fiber sensor unit. To enhance the sensitivity and light coupling efficiency we used a special PCF with Ge-doped ring defect to further enhance the sensitivity and gas flow rate. Sensing capability of the proposed sensor was investigated experimentally by detecting acetylene absorption lines. PMID:23787597

  10. The Thermoluminescence Response of Ge-Doped Flat Fibers to Gamma Radiation.

    PubMed

    Nawi, Siti Nurasiah Binti Mat; Wahib, Nor Fadira Binti; Zulkepely, Nurul Najua Binti; Amin, Yusoff Bin Mohd; Min, Ung Ngie; Bradley, David Andrew; Nor, Roslan Bin Md; Maah, Mohd Jamil

    2015-01-01

    Study has been undertaken of the thermoluminescence (TL) yield of various tailor-made flat cross-section 6 mol% Ge-doped silica fibers, differing only in respect of external dimensions. Key TL dosimetric characteristics have been investigated, including glow curves, dose response, sensitivity, fading and reproducibility. Using a (60)Co source, the samples were irradiated to doses within the range 1 to 10 Gy. Prior to irradiation, the flat fibers were sectioned into 6 mm lengths, weighed, and annealed at 400 °C for 1 h. TL readout was by means of a Harshaw Model 3500 TLD reader, with TLD-100 chips (LiF:Mg, Ti) used as a reference dosimeter to allow the relative response of the fibers to be evaluated. The fibers have been found to provide highly linear dose response and excellent reproducibility over the range of doses investigated, demonstrating high potential as TL-mode detectors in radiation medicine applications. Mass for mass, the results show the greatest TL yield to be provided by fibers of the smallest cross-section, analysis indicating this to be due to minimal light loss in transport of the TL through the bulk of the silica medium. PMID:26307987

  11. The Thermoluminescence Response of Ge-Doped Flat Fibers to Gamma Radiation

    PubMed Central

    Mat Nawi, Siti Nurasiah Binti; Wahib, Nor Fadira Binti; Zulkepely, Nurul Najua Binti; Amin, Yusoff Bin Mohd; Min, Ung Ngie; Bradley, David Andrew; Md Nor, Roslan Bin; Maah, Mohd Jamil

    2015-01-01

    Study has been undertaken of the thermoluminescence (TL) yield of various tailor-made flat cross-section 6 mol% Ge-doped silica fibers, differing only in respect of external dimensions. Key TL dosimetric characteristics have been investigated, including glow curves, dose response, sensitivity, fading and reproducibility. Using a 60Co source, the samples were irradiated to doses within the range 1 to 10 Gy. Prior to irradiation, the flat fibers were sectioned into 6 mm lengths, weighed, and annealed at 400 °C for 1 h. TL readout was by means of a Harshaw Model 3500 TLD reader, with TLD-100 chips (LiF:Mg, Ti) used as a reference dosimeter to allow the relative response of the fibers to be evaluated. The fibers have been found to provide highly linear dose response and excellent reproducibility over the range of doses investigated, demonstrating high potential as TL-mode detectors in radiation medicine applications. Mass for mass, the results show the greatest TL yield to be provided by fibers of the smallest cross-section, analysis indicating this to be due to minimal light loss in transport of the TL through the bulk of the silica medium. PMID:26307987

  12. Cytotoxic and genotoxic evaluation of different synthetic amorphous silica nanomaterials in the V79 cell line.

    PubMed

    Guichard, Y; Fontana, C; Chavinier, E; Terzetti, F; Gaté, L; Binet, S; Darne, C

    2016-09-01

    The nature of occupational risks and hazards in industries that produce or use synthetic amorphous silica (SAS) nanoparticles is still under discussion. Manufactured SAS occur in amorphous form and can be divided into two main types according to the production process, namely, pyrogenic silica (powder) and precipitated silica (powder, gel or colloid). The physical and chemical properties of SAS may vary in terms of particle size, surface area, agglomeration state or purity, and differences in their toxicity potential might therefore be expected. The aim of this study was to compare the cytotoxicity and genotoxicity of representative manufactured SAS samples in Chinese hamster lung fibroblasts (V79 cells). Five samples from industrial SAS producers were evaluated, that is, two pyrogenic SAS powders (with primary particle sizes of 20 nm and 25/70 nm), one precipitated SAS powder (20 nm) and two precipitated SAS colloids (15 and 40/80 nm). V79 cell cultures were treated with different concentrations of SAS pre-dispersed in bovine serum albumin -water medium. Pyr (pyrogenic) 20, Pre (precipitated) 20 and Col (colloid) 15 significantly decreased the cell viability after 24 h of exposure, whilst Pyr 25/70 and Col 40/80 had negligible effects. The cytotoxicity of Pyr 20, Pre 20 and Col 15 was revealed by the induction of apoptosis, and Pyr 20 and Col 15 also produced DNA damage. However, none of the SAS samples generated intracellular reactive oxidative species, micronuclei or genomic mutations in V79 cells after 24 h of exposure. Overall, the results of this study show that pyrogenic, precipitated and colloidal manufactured SAS of around 20 nm primary particle size can produce significant cytotoxic and genotoxic effects in V79 cells. In contrast, the coarser-grained pyrogenic and colloid SAS (approximately 50 nm) yielded negligible toxicity, despite having been manufactured by same processes as their finer-grained equivalents. To explain these differences, the influence

  13. Amorphous silica nanoparticles aggregate human platelets: potential implications for vascular homeostasis

    PubMed Central

    Corbalan, J Jose; Medina, Carlos; Jacoby, Adam; Malinski, Tadeusz; Radomski, Marek W

    2012-01-01

    Background Amorphous silica nanoparticles (SiNP) can be used in medical technologies and other industries leading to human exposure. However, an increased number of studies indicate that this exposure may result in cardiovascular inflammation and damage. A high ratio of nitric oxide to peroxynitrite concentrations ([NO]/[ONOO−]) is crucial for cardiovascular homeostasis and platelet hemostasis. Therefore, we studied the influence of SiNP on the platelet [NO]/[ONOO−] balance and platelet aggregation. Methods Nanoparticle–platelet interaction was examined using transmission electron microscopy. Electrochemical nanosensors were used to measure the levels of NO and ONOO− released by platelets upon nanoparticle stimulation. Platelet aggregation was studied using light aggregometry, flow cytometry, and phase contrast microscopy. Results Amorphous SiNP induced NO release from platelets followed by a massive stimulation of ONOO− leading to an unfavorably low [NO]/[ONOO−] ratio. In addition, SiNP induced an upregulation of selectin P expression and glycoprotein IIb/IIIa activation on the platelet surface membrane, and led to platelet aggregation via adenosine diphosphate and matrix metalloproteinase 2-dependent mechanisms. Importantly, all the effects on platelet aggregation were inversely proportional to nanoparticle size. Conclusions The exposure of platelets to amorphous SiNP induces a critically low [NO]/[ONOO−] ratio leading to platelet aggregation. These findings provide new insights into the pharmacological profile of SiNP in platelets. PMID:22334785

  14. In Situ Crystallization of Al-Containing Silicate Nanosheets on Monodisperse Amorphous Silica Microspheres.

    PubMed

    Okada, Tomohiko; Sueyoshi, Mai; Minamisawa, Hikari M

    2015-12-29

    The fine crystals of an Al-containing layered silicate, whose negative layer charge is generated by an isomorphous substitution in the tetrahedral SiO4 framework, successfully grew on monodisperse amorphous silica microspheres with diameters of 1.0 and 2.6 μm. The fine, plate-like crystals were observed to thoroughly cover the surface of the silica spheres, irrespective of their size, by the hydrothermal reactions of the silica powder in aqueous alkali solution containing Al and Mg ions in a rotating Teflon-lined autoclave. The crystal size increased when the concentration of the precursors was low. The presence of fluorine in the reaction media enlarged the crystalline phase in the direction of the layer stacking while reducing the plate size. The difference in the crystal size affected the kinetics on the hinokitiol desorption in n-hexane from the layered silicates modified with organoammonium ions. The organically modified layered silicate behaved as an exfoliated nanosheet in the nonpolar solvent. The less harmful elements in this hybrid suggest that it can be used in cosmetic and pharmaceutical applications as a drug support, without flaking off the fine layers on the microspherical substrates. PMID:26639090

  15. Structural, thermodynamic, electronic, and magnetic characterization of point defects in amorphous silica

    NASA Astrophysics Data System (ADS)

    Anderson, Nathan L.

    A completely first-principles procedure for the creation of experimentally validated amorphous silicon dioxide structures via a combination of molecular dynamics and density functional theory is presented. Point defects are analyzed within a statistical ensemble of these structures and overcoordinated silicon and oxygen defects are found to have similar formation energies to undercoordinated silicon atoms and oxygen vacancies. The formation of E' centers is found to occur in the absence of oxygen vacancies, and a single oxygen vacancy is found to lead to two isolated E' center precursors. Density functional techniques that properly account for the electrostatics in the presence of periodic boundary conditions are then used to add and remove electrons from each defect and the trapping level distributions are identified. These distributions are the result of the inherent local atomic variability in the amorphous network. The distribution energies are in good agreement with trap spectroscopy experiments where defect contributions are experimentally indistinguishable. This ability to distinguish defect contributions is used to provide a physical explanation of the atomic relaxations which occur upon electron or hole capture. The paramagnetic E'γ and E'β defects are shown to exist in the neutral charge state and are capable of trapping both electrons and holes. Statistical support for the oxygen vacancy originated dimerized model of the positively charged E'δ defect is demonstrated. An overlap of distributions for different defects is also found suggesting the existence of less known trapping mechanisms involving positively charged overcoordinated oxygen defects and overcoordinated silicon floating bond defects. Further, the uncertainty from the model form that results from exchange-correlation functional choice in density functional theory is quantified and found to be much less than the inherent atomic variability in the amorphous network. Extending these amorphous

  16. Molecular-dynamics simulations of thin polyisoprene films confined between amorphous silica substrates.

    PubMed

    Guseva, D V; Komarov, P V; Lyulin, Alexey V

    2014-03-21

    Constant temperature-constant pressure (NpT) molecular-dynamics computer simulations have been carried out for the united-atom model of a non-crosslinked (1,4) cis-polyisoprene (PI) melt confined between two amorphous, fully coordinated silica surfaces. The Lennard-Jones 12-6 potential was implemented to describe the polymer-silica interactions. The thickness H of the produced PI-silica film has been varied in a wide range, 1 < H/R(g) < 8, where R(g) is the individual PI chain radius of gyration measured under the imposed confinement. After a thorough equilibration, the PI film stratified structure and polymer segmental dynamics have been studied. The chain structure in the middle of the films resembles that in a corresponding bulk, but the polymer-density profile shows a pronounced ordering of the polymer segments in the vicinity of silica surfaces; this ordering disappears toward the film middles. Tremendous slowing down of the polymer segmental dynamics has been observed in the film surface layers, with the segmental relaxation more than 150 times slower as compared to that in a PI bulk. This effect increases with decreasing the polymer-film thickness. The segmental relaxation in the PI film middles shows additional relaxation process which is absent in a PI bulk. Even though there are fast relaxation processes in the film middle, its overall relaxation is slower as compared to that in a bulk sample. The interpretation of the results in terms of polymer glassy bridges has been discussed. PMID:24655202

  17. Molecular-dynamics simulations of thin polyisoprene films confined between amorphous silica substrates

    SciTech Connect

    Guseva, D. V.; Komarov, P. V.; Lyulin, Alexey V.

    2014-03-21

    Constant temperature–constant pressure (NpT) molecular-dynamics computer simulations have been carried out for the united-atom model of a non-crosslinked (1,4) cis-polyisoprene (PI) melt confined between two amorphous, fully coordinated silica surfaces. The Lennard-Jones 12-6 potential was implemented to describe the polymer–silica interactions. The thickness H of the produced PI–silica film has been varied in a wide range, 1 < H/R{sub g} < 8, where R{sub g} is the individual PI chain radius of gyration measured under the imposed confinement. After a thorough equilibration, the PI film stratified structure and polymer segmental dynamics have been studied. The chain structure in the middle of the films resembles that in a corresponding bulk, but the polymer-density profile shows a pronounced ordering of the polymer segments in the vicinity of silica surfaces; this ordering disappears toward the film middles. Tremendous slowing down of the polymer segmental dynamics has been observed in the film surface layers, with the segmental relaxation more than 150 times slower as compared to that in a PI bulk. This effect increases with decreasing the polymer-film thickness. The segmental relaxation in the PI film middles shows additional relaxation process which is absent in a PI bulk. Even though there are fast relaxation processes in the film middle, its overall relaxation is slower as compared to that in a bulk sample. The interpretation of the results in terms of polymer glassy bridges has been discussed.

  18. Proinflammatory Effects of Pyrogenic and Precipitated Amorphous Silica Nanoparticles in Innate Immunity Cells.

    PubMed

    Di Cristo, Luisana; Movia, Dania; Bianchi, Massimiliano G; Allegri, Manfredi; Mohamed, Bashir M; Bell, Alan P; Moore, Caroline; Pinelli, Silvana; Rasmussen, Kirsten; Riego-Sintes, Juan; Prina-Mello, Adriele; Bussolati, Ovidio; Bergamaschi, Enrico

    2016-03-01

    Amorphous silica nanoparticles (ASNP) can be synthetized via several processes, 2 of which are the thermal route (to yield pyrogenic silica) and the wet route from a solution containing silicate salts (to obtain precipitated, colloidal, mesoporous silica, or silica gel). Both methods of synthesis lead to ASNP that are applied as food additive (E551). Current food regulation does not require that production methods of additives are indicated on the product label, and, thus, the ASNP are listed without mentioning the production method. Recent results indicate, however, that pyrogenic ASNP are more cytotoxic than ASNP synthesized through the wet route. The present study was aimed at clarifying if 2 representative preparations of ASNP, NM-203 (pyrogenic) and NM-200 (precipitated), of comparable size, specific surface area, surface charge, and hydrodynamic radius in complete growth medium, had different effects on 2 murine macrophage cell lines (MH-S and RAW264.7 cells). Our results show that, when incubated in protein-rich fluids, NM-203 adsorbed on their surface more proteins than NM-200 and, once incubated with macrophages, elicited a greater oxidative stress, assessed from Hmox1 induction and ROS production. Flow cytometry and helium ion microscopy indicated that pyrogenic NM-203 interacted with macrophages more strongly than the precipitated NM-200 and triggered a more evident inflammatory response, evaluated with Nos2 induction, NO production and the secretion of TNF-α, IL-6 and IL-1β. Moreover, both ASNP synergized macrophage activation by bacterial lipopolysaccharide (LPS), with a higher effect observed for NM-203. In conclusion, the results presented here demonstrate that, compared to precipitated, pyrogenic ASNP exhibit enhanced interaction with serum proteins and cell membrane, and cause a larger oxidative stress and stronger proinflammatory effects in macrophages. Therefore, these 2 nanomaterials should not be considered biologically equivalent. PMID

  19. Surface complexation model for strontium sorption to amorphous silica and goethite

    PubMed Central

    Carroll, Susan A; Roberts, Sarah K; Criscenti, Louise J; O'Day, Peggy A

    2008-01-01

    Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25°C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy standard state; unless stated otherwise all strontium complexes are mononuclear. Strontium sorption to amorphous silica in the presence and absence of dissolved carbonate can be fit with tetradentate Sr2+ and SrOH+ complexes on the β-plane and a monodentate Sr2+complex on the diffuse plane to account for strontium sorption at low ionic strength. Strontium sorption to goethite in the absence of dissolved carbonate can be fit with monodentate and tetradentate SrOH+ complexes and a tetradentate binuclear Sr2+ species on the β-plane. The binuclear complex is needed to account for enhanced sorption at hgh strontium surface loadings. In the presence of dissolved carbonate additional monodentate Sr2+ and SrOH+ carbonate surface complexes on the β-plane are needed to fit strontium sorption to goethite. Modeling strontium sorption as outer-sphere complexes is consistent with quantitative analysis of extended X-ray absorption fine structure (EXAFS) on selected sorption samples that show a single first shell of oxygen atoms around strontium indicating hydrated surface complexes at the amorphous silica and goethite surfaces. Strontium surface complexation equilibrium constants determined in this study combined with other alkaline earth surface complexation constants are used to recalibrate a predictive model based on Born solvation and crystal-chemistry theory. The model is accurate to about 0.7 log K units. More studies are needed to determine the dependence of alkaline earth sorption on ionic strength and dissolved carbonate and sulfate concentrations for the development of a robust surface

  20. Surface Complexation Model for Strontium Sorption to Amorphous Silica and Goethite

    SciTech Connect

    Carroll, S; Robers, S; Criscenti, L; O'Day, P

    2007-11-30

    Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25 C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy standard state; unless stated otherwise all strontium complexes are mononuclear. Strontium sorption to amorphous silica in the presence and absence of dissolved carbonate can be fit with tetradentate Sr{sup 2+} and SrOH{sup +} complexes on the {beta}-plane and a monodentate Sr{sup 2+} complex on the diffuse plane to account for strontium sorption at low ionic strength. Strontium sorption to goethite in the absence of dissolved carbonate can be fit with monodentate and tetradentate SrOH{sup +} complexes and a tetradentate binuclear Sr{sup 2+} species on the {beta}-plane. The binuclear complex is needed to account for enhanced sorption at high strontium surface loadings. In the presence of dissolved carbonate additional monodentate Sr{sup 2+} and SrOH{sup +} carbonate surface complexes on the {beta}-plane are needed to fit strontium sorption to goethite. Modeling strontium sorption as outer-sphere complexes is consistent with quantitative analysis of extended X-ray absorption fine structure (EXAFS) on selected sorption samples that show a single first shell of oxygen atoms around strontium indicating hydrated surface complexes at the amorphous silica and goethite surfaces. Strontium surface complexation equilibrium constants determined in this study combined with other alkaline earth surface complexation constants are used to recalibrate a predictive model based on Born solvation and crystal-chemistry theory. The model is accurate to about 0.7 log K units. More studies are needed to determine the dependence of alkaline earth sorption on ionic strength and dissolved carbonate and sulfate

  1. Synthesis and characterization of amorphous mesoporous silica using TEMPO-functionalized amphiphilic templates

    NASA Astrophysics Data System (ADS)

    de Vries, Wilke; Doerenkamp, Carsten; Zeng, Zhaoyang; de Oliveira, Marcos; Niehaus, Oliver; Pöttgen, Rainer; Studer, Armido; Eckert, Hellmut

    2016-05-01

    Inorganic-organic hybrid materials based on amorphous mesoporous silica containing organized nitroxide radicals within its mesopores have been prepared using the micellar self-assembly of TEOS solutions containing the nitroxide functionalized amphiphile (4-(N,N-dimethyl-N-hexadecylammonium)-2,2,6,6-tetramethyl-piperidin-N-oxyl-iodide) (CAT-16). This template has been used both in its pure form and in various mixtures with cetyl trimethylammonium bromide (CTAB). The samples have been characterized by chemical analysis, N2 sorption studies, magnetic susceptibility measurements, and various spectroscopic methods. While electron paramagnetic resonance (EPR) spectra indicate that the strength of the intermolecular spin-spin interactions can be controlled via the CAT-16/CTAB ratio, nuclear magnetic resonance (NMR) data suggest that these interactions are too weak to facilitate cooperative magnetism.

  2. In situ catalytic pyrolysis of lignocellulose using alkali-modified amorphous silica alumina.

    PubMed

    Zabeti, M; Nguyen, T S; Lefferts, L; Heeres, H J; Seshan, K

    2012-08-01

    Canadian pinewood was pyrolyzed at 450 °C in an Infrared oven and the pyrolysis vapors were converted by passing through a catalyst bed at 450 °C. The catalysts studied were amorphous silica alumina (ASA) containing alkali metal or alkaline earth metal species including Na, K, Cs, Mg and Ca. The catalysts effectiveness to reduce the bio-oil oxygen content, to enhance the bio-oil energy density and to change the liquid and gas product distribution were evaluated using different techniques including gravimetric analysis, elemental analysis, Karl-Fischer titration, GC/MS and micro-GC analysis. According to the results K/ASA found to be the most effective catalysts for conversion of hollocellulose (hemicellulose and cellulose)-derived vapors of pinewood while Cs/ASA catalyst was the most effective catalyst for conversion of lignin-derived vapors and production of hydrocarbons. PMID:22705959

  3. A novel composite material based on antimony(III) oxide and amorphous silica

    SciTech Connect

    Zemnukhova, Ludmila A.; Panasenko, Alexander E.

    2013-05-01

    The composite material nSb₂O₃·mSiO₂·xH₂O was prepared by hydrolysis of SbCl₃ and Na₂SiO₃ in an aqueous medium. It has been shown that the composition of the material is influenced by the ratio of the initial components and the acidity of the reaction medium. The morphology of the material particles and its specific surface area have been determined. The thermal and optic properties were also investigated. - Graphical abstract: Novel composite material containing amorphous silica and crystal antimony(III) oxide has been synthesized by hydrolysis of SbCl₃ and Na₂SiO₃ in an aqueous medium. Highlights: • The composite material nSb₂O₃·mSiO₂·xH₂O was prepared in an aqueous medium. • The composition of the material is controllable by a synthesis conditions. • The morphology of the material and its optic properties have been determined.

  4. Photo-induced changes in a hybrid amorphous chalcogenide/silica photonic crystal fiber

    SciTech Connect

    Markos, Christos

    2014-01-06

    Photostructural changes in a hybrid photonic crystal fiber with chalcogenide nanofilms inside the inner surface of the cladding holes are experimentally demonstrated. The deposition of the amorphous chalcogenide glass films inside the silica capillaries of the fiber was made by infiltrating the nanocolloidal solution-based As{sub 25}S{sub 75}, while the photoinduced changes were performed by side illuminating the fiber near the bandgap edge of the formed glass nanofilms. The photoinduced effect of the chalcogenide glass directly red-shifts the transmission bandgap position of the fiber as high as ∼20.6 nm at around 1600 nm wavelength, while the maximum bandgap intensity change at ∼1270 nm was −3 dB.

  5. Giant Seebeck effect in Ge-doped SnSe

    PubMed Central

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  6. Giant Seebeck effect in Ge-doped SnSe.

    PubMed

    Gharsallah, M; Serrano-Sánchez, F; Nemes, N M; Mompeán, F J; Martínez, J L; Fernández-Díaz, M T; Elhalouani, F; Alonso, J A

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  7. Giant Seebeck effect in Ge-doped SnSe

    NASA Astrophysics Data System (ADS)

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-06-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit.

  8. In vitro platelet aggregation and oxidative stress caused by amorphous silica nanoparticles

    PubMed Central

    Nemmar, Abderrahim; Yuvaraju, Priya; Beegam, Sumaya; Yasin, Javed; Dhaheri, Rauda Al; Fahim, Mohamed A; Ali, Badreldin H

    2015-01-01

    Amorphous silica nanoparticles (SiNP) are being investigated for their potential use in various industrial and medical fields. Therefore, the assessment of their possible pathophysiological effect on circulating cells such as platelets is essential. We recently showed that intraperitoneal administration of SiNP causes proinflammatory and prothrombotic responses in vivo. However, little is known about the interaction of amorphous SiNP with platelets in vitro. Presently, we investigated the in vitro effects of SiNP (1, 5 and 25 μg/ml) on platelet aggregation, oxidative stress and intracellular calcium in mouse platelets. Incubation of platelets with SiNP caused a significant and dose-dependent platelet aggregation. Similarly, the activity of lactate dehydrogenase (as a marker of cell membrane integrity) was significantly increased by SiNP. Total antioxidant activity and lipid platelets vulnerability to in vitro peroxidation (measured by malondialdehyde production) were significantly increased after SiNP exposure. Additionally, SiNP exposure significantly increased the cytosolic calcium concentration. In conclusion, our in vitro data show that incubation of platelets with SiNP caused platelet aggregation, oxidative stress and increased intracellular calcium. This finding provides evidence on the toxicity of SiNP on platelet physiology. PMID:26069526

  9. Ion-specific adsorption and electroosmosis in charged amorphous porous silica.

    PubMed

    Hartkamp, Remco; Siboulet, Bertrand; Dufrêche, Jean-François; Coasne, Benoit

    2015-10-14

    Monovalent and divalent aqueous electrolytes confined in negatively charged porous silica are studied by means of molecular simulations including free energy calculations. Owing to the strong cation adsorption at the surface, surface charge overcompensation (overscreening) occurs which leads to an effective positive surface next to the Stern layer, followed by a negatively charged diffuse layer. A simple Poisson-Boltzmann model in which the single-ion potential of mean force is introduced is shown to capture the most prominent features of ion density profiles near an amorphous silica surface. Nevertheless, due to its mean-field nature, which fails to account for correlations, this simple model does not predict overscreening corresponding to charge inversion at the surface. Such an overscreening drastically affects the transport of confined electrolytes as it leads to flow reversal when subjected to an electric field. A simple continuum theory is shown to capture how the electro-osmotic flow is affected by overscreening and by the apparent enhanced viscosity of the confined electrolytes. Comparison with available experimental data is discussed, as well as the implications of these phenomena for ζ-potential measurements. PMID:26343799

  10. Photosensitivity of Ge-doped phosphate glass to 244 nm irradiation

    SciTech Connect

    Suzuki, S.; Schuelzgen, A.; Sabet, S.; Moloney, J. V.; Peyghambarian, N.

    2006-10-23

    UV photosensitivity of Ge-doped phosphate glasses is examined by writing photoinduced gratings in bulk glass samples. Radiation-induced index changes up to {approx}3.5x10{sup -5} were obtained by diffraction efficiency measurements of UV written gratings. In contrast to phosphate glasses without intentional doping, no significant photodarkening at visible wavelength was observed in Ge-doped phosphate glasses after UV exposure. The measured index changes demonstrate the potential of Ge-doped phosphate glasses for the fabrication of a fiber Bragg grating, a key component for phosphate-glass-based photonic devices.

  11. Ge-doped optical fibres as thermoluminescence dosimeters for kilovoltage X-ray therapy irradiations

    NASA Astrophysics Data System (ADS)

    Issa, Fatma; Latip, Nur Atiqah Abd; Bradley, David A.; Nisbet, Andrew

    2011-10-01

    We investigate key dosimetric parameters for the thermoluminescence (TL) of Ge-doped silica optical fibres irradiated by X-rays generated at 90 and 300 kVp. The parameters include dose response, reproducibility and fading. Relative dose measurements were performed, obtaining central axis percentage depth dose (PDD) values, use being made of doped fibres irradiated in water and solid water phantoms. TL yields were compared with published data and ionisation chamber measurements. Linearity to dose was demonstrated over the investigated range (0.1-6 Gy), with reproducibility to within±2%. TL fading was found to be minimal, at <1.5% over a 12 h period. The RMI 457 solid water phantom correction factor was found to be 1.155±0.152 and 0.955±0.221 at 90 and 300 kVp, respectively. The maximum discrepancy between PDD values obtained using optical fibres and ionisation chamber measurements was 2.1% at 90 kVp, while the maximum discrepancy between tabulated data and measurements was 1.1% at 300 kVp.

  12. Surface and bulk infrared modes of crystalline and amorphous silica particles: a study of the relation of surface structure to cytotoxicity of respirable silica.

    PubMed Central

    Pandurangi, R S; Seehra, M S; Razzaboni, B L; Bolsaitis, P

    1990-01-01

    Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity. Images FIGURE 2. A FIGURE 2. B FIGURE 2. C FIGURE 2. D PMID:2169410

  13. Surface-enhanced Raman scattering of amorphous silica gel adsorbed on gold substrates for optical fiber sensors

    NASA Astrophysics Data System (ADS)

    Degioanni, S.; Jurdyc, A. M.; Cheap, A.; Champagnon, B.; Bessueille, F.; Coulm, J.; Bois, L.; Vouagner, D.

    2015-10-01

    Two kinds of gold substrates are used to produce surface-enhanced Raman scattering (SERS) of amorphous silica obtained via the sol-gel route using tetraethoxysilane Si(OC2H5)4 (TEOS) solution. The first substrate consists of a gold nanometric film elaborated on a glass slide by sputter deposition, controlling the desired gold thickness and sputtering current intensity. The second substrate consists of an array of micrometer-sized gold inverted pyramidal pits able to confine surface plasmon (SP) enhancing electric field, which results in a distribution of electromagnetic energy inside the cavities. These substrates are optically characterized to observe SPR with, respectively, extinction and reflectance spectrometries. Once coated with thin layers of amorphous silica (SiO2) gel, these samples show Raman amplification of amorphous SiO2 bands. This enhancement can occur in SERS sensors using amorphous SiO2 gel as shells, spacers, protective coatings, or waveguides, and represents particularly a potential interest in the field of Raman distributed sensors, which use the amorphous SiO2 core of optical fibers as a transducer to make temperature measurements.

  14. Multimethod approach for the detection and characterisation of food-grade synthetic amorphous silica nanoparticles.

    PubMed

    Barahona, Francisco; Ojea-Jimenez, Isaac; Geiss, Otmar; Gilliland, Douglas; Barrero-Moreno, Josefa

    2016-02-01

    Synthetic amorphous silica (SAS) has been used as food additive under the code E551 for decades and the agrifood sector is considered a main exposure vector for humans and environment. However, there is still a lack of detailed methodologies for the determination of SAS' particle size and concentration. This work presents the detection and characterization of NPs in eleven different food-grade SAS samples, following a reasoned and detailed sequential methodology. Dynamic Light Scattering (DLS), Multiangle Light Scattering (MALS), Asymmetric Flow-Field Flow Fractionation (AF4), Inductively Coupled Plasma Mass Spectrometry (ICPMS) and Transmission Electron Microscopy (TEM) were used. The suitability and limitations, information derived from each type of analytical technique and implications related to current EC Regulation 1169/2011 on the provision of food information to consumers are deeply discussed. In general the z-average, AF4 hydrodynamic diameters and root mean square (rms) radii measured were in good agreement. AF4-ICPMS coupling and pre channel calibration with silica NPs standards allowed the reliable detection of NPs below 100nm for ten of eleven samples (AF4 diameters between 20.6 and 39.8nm) and to quantify the mass concentration in seven different samples (at mgL(-1) concentration level). TEM characterisation included the determination of the minimum detectable size and subsequent measurement of the equivalent circle diameter (ECD) of primary particles and small aggregates, which were between 10.3 and 20.3nm. Because of the dynamic size application range is limited by the minimum detectable size, all the techniques in this work can be used only as positive tests. PMID:26787162

  15. Mast cell accumulation precedes tissue fibrosis induced by intravenously administered amorphous silica nanoparticles.

    PubMed

    Zhuravskii, Serge; Yukina, Galina; Kulikova, Olga; Panevin, Alexey; Tomson, Vladimir; Korolev, Dmitry; Galagudza, Michael

    2016-05-01

    Despite the increasing use of amorphous silica nanoparticles (SNPs) in biomedical applications, their toxicity after intravenous administration remains a major concern. We investigated the effects of single 7 mg/kg intravenous infusions of 13 nm SNPs on hemodynamic parameters in rats. Hematological and biochemical parameters were assessed at 7, 30, and 60 d post treatment. Silicon content in the liver, lungs, heart, and kidney was analyzed, as well as tissue histology with special emphasis on mast cell (MC) content. SNP infusion had no effect on hemodynamics, nor did it alter hematological or biochemical parameters. SNP retention in the liver was conspicuous for up to 60 d. Among the other organs analyzed, silicon content was significantly increased only in the lung at 1-h post infusion. Despite the relatively low dose, SNP administration caused extensive liver remodeling, including the formation of multiple foreign body-type granulomas starting 7 d post treatment, and subsequent development of fibrosis. Histopathological changes in the liver were not preceded by hepatocyte necrosis. We found increased MC abundance in the liver, lungs, and heart starting on day 30 post treatment. MC recruitment in the liver preceded fibrosis, suggesting that MCs are involved in liver tissue remodeling elicited by intravenously administered SNPs. PMID:27055490

  16. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    SciTech Connect

    Pinto, S.; Roldan Gutierrez, Manuel A; Ramos, M. M.D.; Gomes, M.J.M.; Molina, S. I.; Pennycook, Stephen J; Varela del Arco, Maria; Buljan, M.; Barradas, N.; Alves, E.; Chahboun, A.; Bernstorff, S.

    2012-01-01

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  17. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    SciTech Connect

    Pinto, S. R. C.; Ramos, M. M. D.; Gomes, M. J. M.; Buljan, M.; Chahboun, A.; Roldan, M. A.; Molina, S. I.; Bernstorff, S.; Varela, M.; Pennycook, S. J.; Barradas, N. P.; Alves, E.

    2012-04-01

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  18. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    NASA Astrophysics Data System (ADS)

    Pinto, S. R. C.; Buljan, M.; Chahboun, A.; Roldan, M. A.; Bernstorff, S.; Varela, M.; Pennycook, S. J.; Barradas, N. P.; Alves, E.; Molina, S. I.; Ramos, M. M. D.; Gomes, M. J. M.

    2012-04-01

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO2)/SiO2 multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO2) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  19. Reactive wetting of amorphous silica by molten Al-Mg alloys and their interfacial structures

    NASA Astrophysics Data System (ADS)

    Shi, Laixin; Shen, Ping; Zhang, Dan; Jiang, Qichuan

    2016-07-01

    The reactive wetting of amorphous silica substrates by molten Al-Mg alloys over a wide composition range was studied using a dispensed sessile drop method in a flowing Ar atmosphere. The effects of the nominal Mg concentration and temperature on the wetting and interfacial microstructures were discussed. The initial contact angle for pure Al on the SiO2 surface was 115° while that for pure Mg was 35° at 1073 K. For the Al-Mg alloy drop, it decreased with increasing nominal Mg concentration. The reaction zone was characterized by layered structures, whose formation was primarily controlled by the variation in the alloy concentration due to the evaporation of Mg and the interfacial reaction from the viewpoint of thermodynamics as well as by the penetration or diffusion of Mg, Al and Si from the viewpoint of kinetics. In addition, the effects of the reaction and the evaporation of Mg on the movement of the triple line were examined. The spreading of the Al-Mg alloy on the SiO2 surface was mainly attributed to the formation of Mg2Si at the interface and the recession of the triple line to the diminishing Mg concentration in the alloy.

  20. Amorphous silica nanoparticles trigger nitric oxide/peroxynitrite imbalance in human endothelial cells: inflammatory and cytotoxic effects

    PubMed Central

    Corbalan, J Jose; Medina, Carlos; Jacoby, Adam; Malinski, Tadeusz; Radomski, Marek W

    2011-01-01

    Background The purpose of this study was to investigate the mechanism of noxious effects of amorphous silica nanoparticles on human endothelial cells. Methods Nanoparticle uptake was examined by transmission electron microscopy. Electrochemical nanosensors were used to measure the nitric oxide (NO) and peroxynitrite (ONOO−) released by a single cell upon nanoparticle stimulation. The downstream inflammatory effects were measured by an enzyme-linked immunosorbent assay, real-time quantitative polymerase chain reaction, and flow cytometry, and cytotoxicity was measured by lactate dehydrogenase assay. Results We found that the silica nanoparticles penetrated the plasma membrane and rapidly stimulated release of cytoprotective NO and, to a greater extent, production of cytotoxic ONOO−. The low [NO]/[ONOO−] ratio indicated increased nitroxidative/oxidative stress and correlated closely with endothelial inflammation and necrosis. This imbalance was associated with nuclear factor κB activation, upregulation of key inflammatory factors, and cell death. These effects were observed in a nanoparticle size-dependent and concentration-dependent manner. Conclusion The [NO]/[ONOO−] imbalance induced by amorphous silica nanoparticles indicates a potentially deleterious effect of silica nanoparticles on vascular endothelium. PMID:22131828

  1. The protein corona protects against size- and dose-dependent toxicity of amorphous silica nanoparticles

    PubMed Central

    Bantz, Christoph; Westmeier, Dana; Galla, Hajo J; Wang, Qiangbin; Kirkpatrick, James C; Nielsen, Peter; Maskos, Michael; Stauber, Roland H

    2014-01-01

    Summary Besides the lung and skin, the gastrointestinal (GI) tract is one of the main targets for accidental exposure or biomedical applications of nanoparticles (NP). Biological responses to NP, including nanotoxicology, are caused by the interaction of the NP with cellular membranes and/or cellular entry. Here, the physico-chemical characteristics of NP are widely discussed as critical determinants, albeit the exact mechanisms remain to be resolved. Moreover, proteins associate with NP in physiological fluids, forming the protein corona potentially transforming the biological identity of the particle and thus, adding an additional level of complexity for the bio–nano responses. Here, we employed amorphous silica nanoparticles (ASP) and epithelial GI tract Caco-2 cells as a model to study the biological impact of particle size as well as of the protein corona. Caco-2 or mucus-producing HT-29 cells were exposed to thoroughly characterized, negatively charged ASP of different size in the absence or presence of proteins. Comprehensive experimental approaches, such as quantifying cellular metabolic activity, microscopic observation of cell morphology, and high-throughput cell analysis revealed a dose- and time-dependent toxicity primarily upon exposure with ASP30 (Ø = 30 nm). Albeit smaller (ASP20, Ø = 20 nm) or larger particles (ASP100; Ø = 100 nm) showed a similar zeta potential, they both displayed only low toxicity. Importantly, the adverse effects triggered by ASP30/ASP30L were significantly ameliorated upon formation of the protein corona, which we found was efficiently established on all ASP studied. As a potential explanation, corona formation reduced ASP30 cellular uptake, which was however not significantly affected by ASP surface charge in our model. Collectively, our study uncovers an impact of ASP size as well as of the protein corona on cellular toxicity, which might be relevant for processes at the nano–bio interface in general. PMID:25247121

  2. Estimated storage of amorphous silica in soils of the circum-Arctic tundra region

    NASA Astrophysics Data System (ADS)

    Alfredsson, H.; Clymans, W.; Hugelius, G.; Kuhry, P.; Conley, D. J.

    2016-03-01

    We investigated the vertical distribution, storage, landscape partitioning, and spatial variability of soil amorphous silica (ASi) at four different sites underlain by continuous permafrost and representative of mountainous and lowland tundra, in the circum-Arctic region. Based on a larger set of data, we present the first estimate of the ASi soil reservoir (0-1 m depth) in circum-Arctic tundra terrain. At all sites, the vertical distribution of ASi concentrations followed the pattern of either (1) declining concentrations with depth (most common) or (2) increasing/maximum concentrations with depth. Our results suggest that a set of processes, including biological control, solifluction and other slope processes, cryoturbation, and formation of inorganic precipitates influence vertical distributions of ASi in permafrost terrain, with the capacity to retain stored ASi on millennial timescales. At the four study sites, areal ASi storage (0-1 m) is generally higher in graminoid tundra compared to wetlands. Our circum-Arctic upscaling estimates, based on both vegetation and soil classification separately, suggest a storage amounting to 219 ± 28 and 274 ± 33 Tmol Si, respectively, of which at least 30% is stored in permafrost. This estimate would account for about 3% of the global soil ASi storage while occupying an equal portion of the global land area. This result does not support the hypothesis that the circum-Arctic tundra soil ASi reservoir contains relatively higher amounts of ASi than other biomes globally as demonstrated for carbon. Nevertheless, climate warming has the potential to significantly alter ASi storage and terrestrial Si cycling in the Arctic.

  3. Advanced treatment of swine wastewater using an agent synthesized from amorphous silica and hydrated lime.

    PubMed

    Tanaka, Yasuo; Hasegawa, Teruaki; Sugimoto, Kiyomi; Miura, Keiichi; Aketo, Tsuyoshi; Minowa, Nobutaka; Toda, Masaya; Kinoshita, Katsumi; Yamashita, Takahiro; Ogino, Akifumi

    2014-01-01

    Advanced treatment using an agent synthesized from amorphous silica and hydrated lime (M-CSH-lime) was developed and applied to swine wastewater treatment. Biologically treated wastewater and M-CSH-lime (approximately 6 w/v% slurry) were fed continuously into a column-shaped reactor from its bottom. Accumulated M-CSH-lime gradually formed a bed layer. The influent permeated this layer and contacted the M-CSH-lime, and the treatment reaction progressed. Treated liquid overflowing from the top of the reactor was neutralized with CO₂gas bubbling. The colour removal rate approximately exceeded 50% with M-CSH-lime addition rates of > 0.15 w/v%. The removal rate of PO(3⁻)(4) exceeded 80% with the addition of>0.03 w/v% of M-CSH-lime. The removal rates of coliform bacteria and Escherichia coli exceeded 99.9% with > 0.1 w/v%. Accumulated M-CSH-lime in the reactor was periodically withdrawn from the upper part of the bed layer. The content of citric-acid-soluble P₂O₅ in the recovered matter was>15% when the weight ratio of influent PO(3⁻)(4) -P to added M-CSH-lime was > 0.15. This content was comparable with commercial phosphorus fertilizer. The inhibitory effect of recovered M-CSH-lime on germination and growth of leafy vegetable komatsuna (Brassica rapa var. perviridis) was evaluated by an experiment using the Neubauer's pot. The recovered M-CSH-lime had no negative effect on germination and growth. These results suggest that advanced water treatment with M-CSH-lime was effective for simultaneous removal of colour, [Formula: see text] and coliform bacteria at an addition rate of 0.03-0.15 w/v%, and that the recovered M-CSH-lime would be suitable as phosphorus fertilizer. PMID:25189846

  4. The amorphous silica-liquid water interface studied by ab initio molecular dynamics (AIMD): local organization in global disorder.

    PubMed

    Cimas, Álvaro; Tielens, Frederik; Sulpizi, Marialore; Gaigeot, Marie-Pierre; Costa, Dominique

    2014-06-18

    The structural organization of water at a model of amorphous silica-liquid water interface is investigated by ab initio molecular dynamics (AIMD) simulations at room temperature. The amorphous surface is constructed with isolated, H-bonded vicinal and geminal silanols. In the absence of water, the silanols have orientations that depend on the local surface topology (i.e. presence of concave and convex zones). However, in the presence of liquid water, only the strong inter-silanol H-bonds are maintained, whereas the weaker ones are replaced by H-bonds formed with interfacial water molecules. All silanols are found to act as H-bond donors to water. The vicinal silanols are simultaneously found to be H-bond acceptors from water. The geminal pairs are also characterized by the formation of water H-bonded rings, which could provide special pathways for proton transfer(s) at the interface. The first water layer above the surface is overall rather disordered, with three main domains of orientations of the water molecules. We discuss the similarities and differences in the structural organization of the interfacial water layer at the surface of the amorphous silica and at the surface of the crystalline (0 0 0 1) quartz surface. PMID:24863440

  5. Characterization of amorphous thermoluminescence dosimeters for patient dose measurement in X-ray diagnostic procedures

    NASA Astrophysics Data System (ADS)

    Ramli, N. N. H.; Salleh, H.; Mahdiraji, G. A.; Zulkifli, M. I.; Hashim, S.; Bradley, D. A.; M. Noor, N.

    2015-11-01

    We investigate the use of novel Ge-doped amorphous silica flat fibers as thermoluminescence dosimeters (TLDs) in verifying patient entrance surface-dose (ESD) in diagnostic examinations. Selected fibers with established dosimetric characteristics (including energy dependence, linearity, reproducibility, and fading) were loaded into plastic capsules in groups of six. The fibers have been calibrated against a parallel plate ionization chamber, use being made of x-rays generated at 70 kVp, accessing a Secondary Standards Dosimetry Laboratory (SSDL) facility. The fiber characterization measurements were made using a Toshiba X-ray machine operating within the nominal energies range 40 kVp to 150 kVp, for doses in the range 0.02 mGy up to 3 mGy. For doses from 2 mGy up to 150 mGy, the flat fibers exhibit linearity between TL yield and dose, reproducible to better than 3% standard deviation following repeat measurements (n=3). A marked energy-dependent response is observed for photons generated at potentials from 40 kVp to 150 kVp. From present results, it is concluded that Ge-doped fibers represent a viable system for use in diagnostic dosimetry, corrections being made for the various factors influencing TL yield.

  6. Photochemical hole-burning study of 1,4-dihydroxyanthraquinone doped in amorphous silica prepared by alcoholate method

    NASA Astrophysics Data System (ADS)

    Tani, T.; Namikawa, H.; Arai, K.; Makishima, A.

    1985-11-01

    The preparation of 1,4-dihydroxyanthraquinone, an amorphous silica doped with organic dye molecules, is described. The amorphous structure of this system is studied using photochemical hole burning (PHB), and the results are reported together with absorption and fluorescence spectra measured at room temperature. The PHB results for this material are compared with those for alcoholic organic glass, and mechanisms which dominate the temperature dependence of the holewidth are discussed. The introduction of various organic molecules into inorganic oxide glasses may provide a new field in material science. These materials are promising for various optical and optoelectronic applications, including PHB memory, due to the rigidity and stability of the glassy matrices preserving the function of the organic molecules. These materials may also be highly significant for molecular electronic materials.

  7. Loading amorphous Asarone in mesoporous silica SBA-15 through supercritical carbon dioxide technology to enhance dissolution and bioavailability.

    PubMed

    Zhang, Zhengzan; Quan, Guilan; Wu, Qiaoli; Zhou, Chan; Li, Feng; Bai, Xuequn; Li, Ge; Pan, Xin; Wu, Chuanbin

    2015-05-01

    The aim of this study was to load amorphous hydrophobic drug into ordered mesoporous silica (SBA-15) by supercritical carbon dioxide technology in order to improve the dissolution and bioavailability of the drug. Asarone was selected as a model drug due to its lipophilic character and poor bioavailability. In vitro dissolution and in vivo bioavailability of the obtained Asarone-SBA-15 were significantly improved as compared to the micronized crystalline drug. This study offers an effective, safe, and environmentally benign means of solving the problems relating to the solubility and bioavailability of hydrophobic molecules. PMID:25720818

  8. Type 1 diabetes epidemic in Finland is triggered by zinc-containing amorphous silica nanoparticles.

    PubMed

    Junnila, S K

    2015-04-01

    Type 1 diabetes (T1D), an autoimmune disease, breaks out in some of the children who has genetic susceptibility to T1D. Besides genetic susceptibility some environmental factor(s) are required to trigger the disease. The incidence of T1D in Finland is highest in the world, so we must seek an environmental factor, that is typical for Finland and can declare many aspects of T1D epidemiology and biology. In the literature most popular trigger has been enterovirus infections. It is difficult however to find why enteroviruses would be in this role in Finland in contrary to neighbouring countries e.g. Sweden. Colloidal amorphous silica (ASi) is typical for Finnish environment in consequency of the geohistory of Finland, great part of Finland is an ancient lake and sea bottom. ASi concentrations in natural waters are high in April-June and in November, only traces can be found in the rest of months. Pure colloidal ASi is not a strong trigger for T1D, but ASi particle which has surface adsorbed tetrahedrally coordinated zinc (ASiZn) is probably the trigger which has kept it's secret up to date. Zn functions as address label which conducts the ASiZn particle to the beta cell, whose content of zinc is highest in the body. ASi particle adheres to membrane proteins distorting their tertiary structure revealing new epitopes. If the fetus has not met these epitopes at proper time during intrauterine development, the consequence is that the negative selection of lymphocytes in the thymus and bone marrow and fetal liver is not perfect. When a child later in postnatal life becomes predisposed to ASiZn particles the immune system reacts to these as to nonself proteins. As a consequence the insulin producing beta cells are destroyed. Many observations from diabetes research support the hypothesis, some to mentioned. 1. Three common autoantigens (ZnT8, ICA512/IA-2, GAD65) are membrane proteins whose function zinc regulates. 2. Geographical variation in Finland is convergent with

  9. The toxicological mode of action and the safety of synthetic amorphous silica-a nanostructured material.

    PubMed

    Fruijtier-Pölloth, Claudia

    2012-04-11

    Synthetic amorphous silica (SAS), in the form of pyrogenic (fumed), precipitated, gel or colloidal SAS, has been used in a wide variety of industrial and consumer applications including food, cosmetics and pharmaceutical products for many decades. Based on extensive physico-chemical, ecotoxicology, toxicology, safety and epidemiology data, no environmental or health risks have been associated with these materials if produced and used under current hygiene standards and use recommendations. With internal structures in the nanoscale size range, pyrogenic, precipitated and gel SAS are typical examples of nanostructured materials as recently defined by the International Organisation for Standardisation (ISO). The manufacturing process of these SAS materials leads to aggregates of strongly (covalently) bonded or fused primary particles. Weak interaction forces (van der Waals interactions, hydrogen bonding, physical adhesion) between aggregates lead to the formation of micrometre (μm)-sized agglomerates. Typically, isolated nanoparticles do not occur. In contrast, colloidal SAS dispersions may contain isolated primary particles in the nano-size range which can be considered nano-objects. The size of the primary particle resulted in the materials often being considered as "nanosilica" and in the inclusion of SAS in research programmes on nanomaterials. The biological activity of SAS can be related to the particle shape and surface characteristics interfacing with the biological milieu rather than to particle size. SAS adsorbs to cellular surfaces and can affect membrane structures and integrity. Toxicity is linked to mechanisms of interactions with outer and inner cell membranes, signalling responses, and vesicle trafficking pathways. Interaction with membranes may induce the release of endosomal substances, reactive oxygen species, cytokines and chemokines and thus induce inflammatory responses. None of the SAS forms, including colloidal nano-sized particles, were shown

  10. Modeling the Adsorption of Mercury(II) on (Hydr)oxides II: alpha-FeOOH (Goethite) and Amorphous Silica.

    PubMed

    Bonnissel-Gissinger; Alnot; Lickes; Ehrhardt; Behra

    1999-07-15

    The surface complexation model is used to describe sorption experiments of inorganic mercury(II) in the presence of an amorphous silica, Aerosil 200, or an iron (hydr)oxide, the goethite alpha-FeOOH (Bayferrox 910). In the simulations, one assumes the formation of a monodentate surface complex &tbond;S&bond;OHg(+) and of ternary surface complexes with OH(-) surface groups, &tbond;S&bond;OHgOH and &tbond;S&bond;OHgCl, when chlorides are present in solution. Participation of the complex &tbond;S&bond;OHgCl has been especially evidenced. The mercury(II) surface complexation on oxides can be described by the following equilibria (298.15 K, I = 0): with log 5.8 and 8.0 for amorphous silica and goethite, respectively. Comparisons with other data from the literature have been made to investigate the influence of the nature of the oxide on the mechanism of mercury(II) adsorption. X-ray photoelectron spectroscopy was used to characterize the surface of the (hydr)oxides prior to adsorption and to observe when possible the mercury surface compounds. Copyright 1999 Academic Press. PMID:10419666

  11. Amorphous silica nanoparticles size-dependently aggravate atopic dermatitis-like skin lesions following an intradermal injection

    PubMed Central

    2012-01-01

    Background Due to the rising use of nanomaterials (NMs), there is concern that NMs induce undesirable biological effects because of their unique physicochemical properties. Recently, we reported that amorphous silica nanoparticles (nSPs), which are one of the most widely used NMs, can penetrate the skin barrier and induce various biological effects, including an immune-modulating effect. Thus, it should be clarified whether nSPs can be a risk factor for the aggravation of skin immune diseases. Thus, in this study, we investigated the relationship between the size of SPs and adjuvant activity using a model for atopic dermatitis. Results We investigated the effects of nSPs on the AD induced by intradermaly injected-mite antigen Dermatophagoides pteronyssinus (Dp) in NC/Nga mice. Ear thickness measurements and histopathological analysis revealed that a combined injection of amorphous silica particles (SPs) and Dp induced aggravation of AD in an SP size-dependent manner compared to that of Dp alone. In particular, aggravation was observed remarkably in nSP-injected groups. Furthermore, these effects were correlated with the excessive induction of total IgE and a stronger systemic Th2 response. We demonstrated that these results are associated with the induction of IL-18 and thymic stromal lymphopoietin (TSLP) in the skin lesions. Conclusions A particle size reduction in silica particles enhanced IL-18 and TSLP production, which leads to systemic Th2 response and aggravation of AD-like skin lesions as induced by Dp antigen treatment. We believe that appropriate regulation of nanoparticle physicochemical properties, including sizes, is a critical determinant for the design of safer forms of NMs. PMID:22296706

  12. Study of ice cluster impacts on amorphous silica using the ReaxFF reactive force field molecular dynamics simulation method

    NASA Astrophysics Data System (ADS)

    Rahnamoun, A.; van Duin, A. C. T.

    2016-03-01

    We study the dynamics of the collisions between amorphous silica structures and amorphous and crystal ice clusters with impact velocities of 1 km/s, 4 km/s, and 7 km/s using the ReaxFF reactive molecular dynamics simulation method. The initial ice clusters consist of 150 water molecules for the amorphous ice cluster and 128 water molecules for the crystal ice cluster. The ice clusters are collided on the surface of amorphous fully oxidized and suboxide silica. These simulations show that at 1 km/s impact velocities, all the ice clusters accumulate on the surface and at 4 km/s and 7 km/s impact velocities, some of the ice cluster molecules bounce back from the surface. At 4 km/s and 7 km/s impact velocities, few of the water molecules dissociations are observed. The effect of the second ice cluster impacts on the surfaces which are fully covered with ice, on the mass loss/accumulation is studied. These studies show that at 1 km/s impacts, the entire ice cluster accumulates on the surface at both first and second ice impacts. At higher impact velocities, some ice molecules which after the first ice impacts have been attached to the surface will separate from the surface after the second ice impacts at 7 km/s impact velocity. For the 4 km/s ice cluster impact, ice accumulation is observed for the crystal ice cluster impacts and ice separation is observed for the amorphous ice impacts. Observing the temperatures of the ice clusters during the collisions indicates that the possibility of electron excitement at impact velocities less than 10 km/s is minimal and ReaxFF reactive molecular dynamics simulation can predict the chemistry of these hypervelocity impacts. However, at impact velocities close to 10 km/s the average temperature of the impacting ice clusters increase to about 2000 K, with individual molecules occasionally reaching temperatures of over 8000 K and thus it will be prudent to consider the concept of electron excitation at these higher impact velocities

  13. Cr(VI) adsorption on functionalized amorphous and mesoporous silica from aqueous and non-aqueous media

    SciTech Connect

    Perez-Quintanilla, Damian . E-mail: isabel.sierra@urjc.es

    2007-08-07

    A mesoporous silica (SBA-15) and amorphous silica (SG) have been chemically modified with 2-mercaptopyridine using the homogeneous route. This synthetic route involved the reaction of 2-mercaptopyridine with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry and elemental analysis. The solid was employed as a Cr(VI) adsorbent from aqueous and non-aqueous solutions at room temperature. The effect of several variables (stirring time, pH, metal concentration and solvent polarity) has been studied using the batch technique. The results indicate that under the optimum conditions, the maximum adsorption value for Cr(VI) was 1.83 {+-} 0.03 mmol/g for MP-SBA-15, whereas the adsorption capacity of the MP-SG was 0.86 {+-} 0.02 mmol/g. On the basis of these results, it can be concluded that it is possible to modify chemically SBA-15 and SG with 2-mercaptopyridine and to use the resulting modified silicas as effective adsorbents for Cr(VI)

  14. Pressure-induced amorphizations of silica analogues: A probe of the relationship between order and disorder

    SciTech Connect

    Hammack, W.S.

    1993-02-01

    Purpose of these of high pressure investigations is to determine the relationship between order and disorder in amorphous materials using high pressure techniques were used. High pressure x-ray diffraction, electron transmission microscopy, and Raman scattering. Cornell High Energy Synchrotron Source (CHESS) at Ithaca was used to measure x-ray diffraction patterns using Energy-Dispersive X-ray Diffraction. It was shown that the structural ordering in pressure-amorphized solids can be described as defects in curved-space. High-resolution transmissions electron microscopy showed that pressure-amorphized alpha-quartz lacks periodicity at the atomic level. Study of a silicate mineral shows that pressure-induced amorphizations occur because of an impeded phase transition.

  15. The structure of amorphous bulk and silica-supported copper(II) hydroxides

    SciTech Connect

    Kriventsov, V.V.; Kochubey, D.I.; Elizarova, G.L.; Matvienko, L.G.; Parmon, V.N.

    1999-07-01

    Determination of the structure of surface hydroxocompounds is one of the most delicate areas of environmental chemistry, geochemistry, and catalysis. In nature, these compounds are formed everywhere, mostly by absorption of multicharged metal cations on different soil constitutents from water solutions. The data obtained show that at pH 7 copper(II) ions are adsorbed on a SiO{sub 2} surface as polymeric species of hydroxide nature. The structure of these species is similar to that of the bulk amorphous copper hydroxide. The amorphous state of supported Cu(OH){sub 2} is caused by a small (ca. 11 {angstrom}) size of the surface particles. In contrast, the overstoichiometric water molecules seem to act as ``amorphizers`` of the bulk copper hydroxide. The structures of the bulk and dispersed amorphous copper(II) hydroxide were determined. The amorphous Cu(OH){sub 2} has a layered structure close to the structure of the crystalline hydroxide, but the layers in the amorphous hydroxide are shifted toward one another approximately for {1/4} of the c period of the lattice.

  16. Adsorption of Amorphous Silica Nanoparticles onto Hydroxyapatite Surfaces Differentially Alters Surfaces Properties and Adhesion of Human Osteoblast Cells.

    PubMed

    Kalia, Priya; Brooks, Roger A; Kinrade, Stephen D; Morgan, David J; Brown, Andrew P; Rushton, Neil; Jugdaohsingh, Ravin

    2016-01-01

    Silicon (Si) is suggested to be an important/essential nutrient for bone and connective tissue health. Silicon-substituted hydroxyapatite (Si-HA) has silicate ions incorporated into its lattice structure and was developed to improve attachment to bone and increase new bone formation. Here we investigated the direct adsorption of silicate species onto an HA coated surface as a cost effective method of incorporating silicon on to HA surfaces for improved implant osseointegration, and determined changes in surface characteristics and osteoblast cell adhesion. Plasma-sprayed HA-coated stainless steel discs were incubated in silica dispersions of different concentrations (0-42 mM Si), at neutral pH for 12 h. Adsorbed Si was confirmed by XPS analysis and quantified by ICP-OES analysis following release from the HA surface. Changes in surface characteristics were determined by AFM and measurement of surface wettability. Osteoblast cell adhesion was determined by vinculin plaque staining. Maximum Si adsorption to the HA coated disc occurred after incubation in the 6 mM silica dispersion and decreased progressively with higher silica concentrations, while no adsorption was observed with dispersions below 6 mM Si. Comparison of the Si dispersions that produced the highest and lowest Si adsorption to the HA surface, by TEM-based analysis, revealed an abundance of small amorphous nanosilica species (NSP) of ~1.5 nm in diameter in the 6 mM Si dispersion, with much fewer and larger NSP in the 42 mM Si dispersions. 29Si-NMR confirmed that the NSPs in the 6 mM silica dispersion were polymeric and similar in composition to the larger NSPs in the 42 mM Si dispersion, suggesting that the latter were aggregates of the former. Amorphous NSP adsorbed from the 6 mM dispersion on to a HA-coated disc surface increased the surface's water contact angle by 53°, whereas that adsorbed from the 42 mM dispersion decreased the contact angle by 18°, indicating increased and decreased

  17. Adsorption of Amorphous Silica Nanoparticles onto Hydroxyapatite Surfaces Differentially Alters Surfaces Properties and Adhesion of Human Osteoblast Cells

    PubMed Central

    Kalia, Priya; Brooks, Roger A.; Kinrade, Stephen D.; Morgan, David J.; Brown, Andrew P.; Rushton, Neil; Jugdaohsingh, Ravin

    2016-01-01

    Silicon (Si) is suggested to be an important/essential nutrient for bone and connective tissue health. Silicon-substituted hydroxyapatite (Si-HA) has silicate ions incorporated into its lattice structure and was developed to improve attachment to bone and increase new bone formation. Here we investigated the direct adsorption of silicate species onto an HA coated surface as a cost effective method of incorporating silicon on to HA surfaces for improved implant osseointegration, and determined changes in surface characteristics and osteoblast cell adhesion. Plasma-sprayed HA-coated stainless steel discs were incubated in silica dispersions of different concentrations (0–42 mM Si), at neutral pH for 12 h. Adsorbed Si was confirmed by XPS analysis and quantified by ICP-OES analysis following release from the HA surface. Changes in surface characteristics were determined by AFM and measurement of surface wettability. Osteoblast cell adhesion was determined by vinculin plaque staining. Maximum Si adsorption to the HA coated disc occurred after incubation in the 6 mM silica dispersion and decreased progressively with higher silica concentrations, while no adsorption was observed with dispersions below 6 mM Si. Comparison of the Si dispersions that produced the highest and lowest Si adsorption to the HA surface, by TEM-based analysis, revealed an abundance of small amorphous nanosilica species (NSP) of ~1.5 nm in diameter in the 6 mM Si dispersion, with much fewer and larger NSP in the 42 mM Si dispersions. 29Si-NMR confirmed that the NSPs in the 6 mM silica dispersion were polymeric and similar in composition to the larger NSPs in the 42 mM Si dispersion, suggesting that the latter were aggregates of the former. Amorphous NSP adsorbed from the 6 mM dispersion on to a HA-coated disc surface increased the surface’s water contact angle by 53°, whereas that adsorbed from the 42 mM dispersion decreased the contact angle by 18°, indicating increased and decreased

  18. First-Principles Investigation of Low Energy E' Center Precursors in Amorphous Silica

    SciTech Connect

    Anderson, Nathan L.; Vedula, Ravi P.; Schultz, Peter A.; Van Ginhoven, Renee M.; Strachan, Alejandro

    2011-05-17

    We show that oxygen vacancies are not necessary for the formation of E’ centers in amorphous SiO2 and that a single O-deficiency can lead to two charge traps. Employing molecular dynamics with a reactive potential and density functional theory we generate an ensemble of stoichiometric and oxygen-deficient amorphous SiO2 atomic structures and identify low-energy network defects. Three-coordinated Si atoms appear in several low-energy defects both in stoichiometric and O-deficient samples where, in addition to the neutral oxygen vacancy, they appear as isolated defects.

  19. Modeling the adsorption of mercury(II) on (hydr)oxides. 2: {alpha}-FeOOH (goethite) and amorphous silica

    SciTech Connect

    Bonnissel-Gissinger, P.; Alnot, M.; Ehrhardt, J.J.; Lickes, J.P.; Behra, P.

    1999-07-15

    The surface complexation model is used to describe sorption experiments of inorganic mercury(II) in the presence of an amorphous silica, Aerosil 200, or an iron (hydr)oxide, the goethite {alpha}-FeOOH (Bayferrox 910). In the simulations, one assumes the formation of a monodentate surface complex {triple_bond}S{single_bond}OHgOH and {triple_bond}S{single_bond}OHgCl, when chlorides are present in solution. Participation of the complex {triple_bond}S{single_bond}OHgCl has been especially evidenced. Comparisons with other data from the literature have been made to investigate the influence of the nature of the oxide on the mechanism of mercury(II) adsorption. X-ray photoelectron spectroscopy was used to characterize the surface of the (hydr)oxides prior to adsorption and to observe when possible the mercury surface compounds.

  20. Thermally stimulated glow peaks in Ge-doped cultured quartz crystals and their radiation response

    SciTech Connect

    Bahadur, Harish

    2007-02-01

    Ge-doped crystalline quartz has been examined for its thermally stimulated luminescence and has been found to exhibit TL-glow peaks at 100, 200, and 310 degree sign C. While the peaks at 100 and 310 degree sign C have already been noticed in conventionally grown quartz, the new peak at 200 degree sign C, observed in the present studies, appears to be due to the presence of Ge in quartz lattice. The radiation dependence of this peak upon irradiation at 300 K by high energy electrons (1.75 MeV) has been presented and the results have been compared and discussed in terms of the hydroxyl defects in natural, cultured, and Ge-doped cultured quartz.

  1. Amorphous Silica- and Carbon- rich nano-templated surfaces as model interstellar dust surfaces for laboratory astrochemistry

    NASA Astrophysics Data System (ADS)

    Pascual, Natalia; Dawes, Anita; González-Posada, Fernando; Thompson, Neil; Chakarov, Dinko; Mason, Nigel J.; Fraser, Helen Jane

    2015-08-01

    Experimental studies on surface astrochemistry are vital to our understanding of chemical evolution in the interstellar medium (ISM). Laboratory surface-astrochemists have recently begun to study chemical reactions on interstellar dust-grain mimics, ranging from graphite, HOPG and graphene (representative of PAHs or large C-grains in the ISM) to amorphous olivine (representative of silicate dust) and ablated meteoritic samples (representative of interplanetary dust). These pioneering experiments show that the nature of the surface fundamentally affects processes at the substrate surface, substrate-ice interface, and ice over-layer. What these experiments are still lacking is the ability to account for effects arising from the discrete nano-scale of ISM grains, which might include changes to electronic structure, optical properties and surface-kinetics in comparison to bulk materials. The question arises: to what extent are the chemical and optical properties of interstellar ices affected by the size, morphology and material of the underlying ISM dust?We have designed, fabricated and characterised a set of nano-structured surfaces, where nanoparticles, representative of ISM grains, are adhered to an underlying support substrate. Here we will show the nanoparticles that have been manufactured from fused-silica (FS), glassy carbon (GC) and amorphous-C (aC). Our optical characterisation data shows that the nanostructured surfaces have different absorption cross-sections and significant scattering in comparison to the support substrates, which has implications for the energetic processing of icy ISM dust. We have been able to study how water-ice growth differs on the nanoparticles in comparison to the “flat” substrates, indicating increased ice amorphicity when nanoparticles are present, and on C-rich surfaces, compared to Si-rich particles. These data will be discussed in the context of interstellar water-ice features.

  2. Assessment of Ge-doped optical fibres subjected to x-ray irradiation

    NASA Astrophysics Data System (ADS)

    Ibrahim, S. A.; Che Omar, S. S.; Hashim, S.; Mahdiraji, G. A.; Bradley, D. A.; Kadir, A. B.; Isa, N. M.

    2014-11-01

    We have reported the thermoluminescence (TL) response of five different diameters ~120, 241, 362, 483, and 604 μm of 6 mol percent Ge-doped optical fibres. The perfomance of the Ge-doped optical fibre are compared with commercially available TLD-100 chips (LiF:Mg,Ti) in terms of their sensitivity and minimum detectable dose (MDD). The irradiation was performed using X-ray machine (Model ISO 'Narrow Spectrum Series') provided by the Malaysian Nuclear Agency (MNA) at 60 kV X-ray irradiation in low doses ranging from 1-10 mGy. The results show the linear TL dose response from the fibres up to 10 mGy. The smallest diameter of 120 pm optical fibre shows the highest TL dose response compared to above mentioned fibres. The minimum detectable dose (MDD) is 0.82, 0.20, 0.14, 0.08, and 0.13 mGy for Ge-doped with diameters of 120, 241, 362, 483 and 604 μm. All TL materials show the MDD value within the delivered dose 0.01-1.00 mGy subjected to x-ray irradiation. The Ge-doped fibre with diameter of 483 pm was matched the MDD value of TLD-100 chips that equivalent to 0.08 mGy at the same irradiation. We have observed that among the five different diameters of optical fibre, 120 μm shows the best results and its better response than TLD-100 chips (by a factor of 5). The linear response at low dose levels makes this optical fibre most suitable for medical application.

  3. How ge Doping Affects the Superconducting Properties of (Cu, Tl)-1234 Superconductors

    NASA Astrophysics Data System (ADS)

    Irfan, M.; Khan, Nawazish A.

    Ge-doped (Cu0.5Tl0.5)Ba2Ca3(Cu4-yGey)O12-δ (y = 0, 0.3, 0.6 and 0.9) superconductors have been synthesized at normal pressure through solid state reaction method. Ge has been doped in the CuO2 planes constituting the superconducting block of these structures. In the as-prepared samples, a suppression of the critical temperature is observed with increased Ge concentration. The suppression of the critical temperature can be attributed to the decreased number of carriers due to their localization at Ge4+ ions. Ge-doped post-annealed samples have shown enhancement in the critical temperature as well as magnitude of diamagnetism. Oxygen annealing seems to have replenished the charge carries through the process of hole doping in CuO2/GeO2 planes, thereby bringing the carrier density closer to the optimum level. Oxygen related phonon modes have also been investigated. A shift in peak positions of the apical and planar oxygen related modes have been observed while modes associated with Oδ oxygen atoms seem stable in both cases of Ge doping and oxygen annealing.

  4. Simulation of Forces between Humid Amorphous Silica Surfaces: A Comparison of Empirical Atomistic Force Fields

    PubMed Central

    2012-01-01

    Atmospheric humidity strongly influences the interactions between dry granular particles in process containers. To reduce the energy loss in industrial production processes caused by particle agglomeration, a basic understanding of the dependence of particle interactions on humidity is necessary. Hence, in this study, molecular dynamic simulations were carried out to calculate the adhesion between silica surfaces in the presence of adsorbed water. For a realistic description, the choice of force field is crucial. Because of their frequent use and transferability to biochemical systems, the Clay and CWCA force fields were investigated with respect to their ability to describe the water–silica interface in comparison to the more advanced Reax force field, ab initio calculations, and experiments. PMID:23378869

  5. Mechanism of amorphous silica particles precipitation: simulation approach compared to experimental results

    NASA Astrophysics Data System (ADS)

    Noguera, Claudine; Fritz, Bertrand; Clement, Alain

    2015-04-01

    Despite its importance in numerous industrial and natural processes, many unsolved questions remain regarding the mechanism of silica precipitation in aqueous solutions: order of the reaction, role of silica oligomers, existence of an induction time and characteristics of the particle population. Beyond empirical approaches used in the past, we demonstrate that the classical nucleation theory associated to a size dependent growth law, as embedded in the NANOKIN code (1-3), allows a quantitative description of precipitation occurring under largely different experimental conditions : preexisting initial supersaturation in a large domain of temperature (5-150°C) and chemical composition (4), supersaturation reached by neutralization of a high pH silica solution (5) or by fast cooling (6). In that way, the mechanism of silica precipitation can be unraveled. We are able to discard the hypothesis of an induction time as an explanation for the plateaus observed in the saturation curves in these experiments. We challenge the role of oligomer incorporation at the growth stage to account for the observed rate laws and we stress the difference between the order of the growth law and the order of the total reaction rate. We also demonstrate that the characteristics of the particle population are strongly dependent on the way supersaturation is reached (7). Such a microscopic approach thus proves to be well suited to elucidate the mechanism of nanoparticle formation in natural and industrial contexts, involving silica, but also other mineral phases produced as nanoparticles (8). (1) Noguera C., Fritz B., Clément A. and Barronet A., J. Cryst. Growth, 2006, 297, 180. (2) Noguera C., Fritz B., Clément A. and Barronet A., J. Cryst. Growth, 2006, 297, 187. (3) Fritz B., Clément A., Amal Y. and Noguera C., Geochim. Cosmochim. Acta, 2009, 73, 1340. (4) Rothbaum, H.P. and Rohde A.G., J. Colloid Interf. Sci., 1979,71, 533. (5) Tobler D.J., Shaw S. and Benning L.G., Geochim

  6. Amorphous Silica Based Nanomedicine with Safe Carrier Excretion and Enhanced Drug Efficacy

    NASA Astrophysics Data System (ADS)

    Zhang, Silu

    With recent development of nanoscience and nanotechnology, a great amount of efforts have been devoted to nanomedicine development. Among various nanomaterials, silica nanoparticle (NP) is generally accepted as non-toxic, and can provide a versatile platform for drug loading. In addition, the surface of the silica NP is hydrophilic, being favorable for cellular uptake. Therefore, it is considered as one of the most promising candidates to serve as carriers for drugs. The present thesis mainly focuses on the design of silica based nanocarrier-drug systems, aiming at achieving safe nanocarrier excretion from the biological system and enhanced drug efficacy, which two are considered as most important issues in nanomedicine development. To address the safe carrier excretion issue, we have developed a special type of selfdecomposable SiO2-drug composite NPs. By creating a radial concentration gradient of drug in the NP, the drug release occurred simultaneously with the silica carrier decomposition. Such unique characteristic was different from the conventional dense SiO2-drug NP, in which drug was uniformly distributed and can hardly escape the carrier. We found that the controllable release of the drug was primarily determined by diffusion, which was caused by the radial drug concentration gradient in the NP. Escape of the drug molecules then triggered the silica carrier decomposition, which started from the center of the NP and eventually led to its complete fragmentation. The small size of the final carrier fragments enabled their easy excretion via renal systems. Apart from the feature of safe carrier excretion, we also found the controlled release of drugs contribute significantly to the drug efficacy enhancement. By loading an anticancer drug doxorubicin (Dox) to the decomposable SiO 2-methylene blue (MB) NPs, we achieved a self-decomposable SiO 2(MB)-Dox nanomedicine. The gradual escape of drug molecules from NPs and their enabled cytosolic release by optical

  7. Oxidative stress, inflammation, and DNA damage in multiple organs of mice acutely exposed to amorphous silica nanoparticles

    PubMed Central

    Nemmar, Abderrahim; Yuvaraju, Priya; Beegam, Sumaya; Yasin, Javed; Kazzam, Elsadig E; Ali, Badreldin H

    2016-01-01

    The use of amorphous silica (SiO2) in biopharmaceutical and industrial fields can lead to human exposure by injection, skin penetration, ingestion, or inhalation. However, the in vivo acute toxicity of amorphous SiO2 nanoparticles (SiNPs) on multiple organs and the mechanisms underlying these effects are not well understood. Presently, we investigated the acute (24 hours) effects of intraperitoneally administered 50 nm SiNPs (0.25 mg/kg) on systemic toxicity, oxidative stress, inflammation, and DNA damage in the lung, heart, liver, kidney, and brain of mice. Lipid peroxidation was significantly increased by SiNPs in the lung, liver, kidney, and brain, but was not changed in the heart. Similarly, superoxide dismutase and catalase activities were significantly affected by SiNPs in all organs studied. While the concentration of tumor necrosis factor α was insignificantly increased in the liver and brain, its increase was statistically significant in the lung, heart, and kidney. SiNPs induced a significant elevation in pulmonary and renal interleukin 6 and interleukin-1 beta in the lung, liver, and brain. Moreover, SiNPs caused a significant increase in DNA damage, assessed by comet assay, in all the organs studied. SiNPs caused leukocytosis and increased the plasma activities of lactate dehydrogenase, creatine kinase, alanine aminotranferase, and aspartate aminotransferase. These results indicate that acute systemic exposure to SiNPs causes oxidative stress, inflammation, and DNA damage in several major organs, and highlight the need for thorough evaluation of SiNPs before they can be safely used in human beings. PMID:27022259

  8. Controlling Ethylene Hydrogenation Reactivity on Pt13 Clusters by Varying the Stoichiometry of the Amorphous Silica Support.

    PubMed

    Crampton, Andrew S; Rötzer, Marian D; Schweinberger, Florian F; Yoon, Bokwon; Landman, Uzi; Heiz, Ueli

    2016-07-25

    Ethylene hydrogenation was investigated on size-selected Pt13 clusters supported on three amorphous silica (a-SiO2 ) thin films with different stoichiometries. Activity measurements of the reaction at 300 K revealed that on a silicon-rich and a stoichiometric film, Pt13 exhibits a similar activity to that of Pt(111), in line with the known structure insensitivity of the reaction. On an oxygen-rich film, a threefold increased rate was measured. Pulsing ethylene at 400 K, then measuring the activity at 300 K, resulted in complete loss of activity on the silicon-rich surface compared to only marginal losses on the other surfaces. The measured reactivity trends correlate with charging characteristics of a Pt13 cluster on the SiO2 films, predicted through first-principle calculations. The results reveal that the stoichiometry-dependent charging by the support can be used to tune the selectivity of reaction pathways during a catalytic hydrogenation reaction. PMID:27356301

  9. Simultaneous removal of colour, phosphorus and disinfection from treated wastewater using an agent synthesized from amorphous silica and hydrated lime.

    PubMed

    Yamashita, Takahiro; Aketo, Tsuyoshi; Minowa, Nobutaka; Sugimoto, Kiyomi; Yokoyama, Hiroshi; Ogino, Akifumi; Tanaka, Yasuo

    2013-01-01

    An agent synthesized from amorphous silica and hydrated lime (CSH-lime) was investigated for its ability to simultaneously remove the colour, phosphorus and disinfection from the effluents from wastewater treatment plants on swine farms. CSH-lime removed the colour and phosphate from the effluents, with the colour-removal effects especially high at pH 12, and phosphorous removal was more effective in strongly alkaline conditions (pH > 10). Colour decreased from 432 +/-111 (mean +/- SD) to 107 +/- 41 colour units and PO4(3-)P was reduced from 45 +/- 39 mg/L to undetectable levels at the CSH-lime dose of 2.0% w/v. Moreover, CSH-lime reduced the total organic carbon from 99.0 to 37.9 mg/L at the dose of 2.0% w/v and was effective at inactivating total heterotrophic and coliform bacteria. However, CSH-lime did not remove nitrogen compounds such as nitrite, nitrate and ammonium. Colour was also removed from dye solutions by CSH-lime, at the same dose. PMID:23837353

  10. The effects of size and surface modification of amorphous silica particles on biodistribution and liver metabolism in mice

    NASA Astrophysics Data System (ADS)

    Lu, Xiaoyan; Ji, Cai; Jin, Tingting; Fan, Xiaohui

    2015-05-01

    Engineered nanoparticles, with unconventional properties, are promising platforms for biomedical applications. Since they may interact with a wide variety of biomolecules, it is critical to understand the impact of the physicochemical properties of engineered nanoparticles on biological systems. In this study, the effects of particle size and surface modification alone or in combination of amorphous silica particles (SPs) on biological responses were determined using a suite of general toxicological assessments and metabonomics analysis in mice model. Our results suggested that amino or carboxyl surface modification mitigated the liver toxicity of plain-surface SPs. 30 nm SPs with amino surface modification were found to be the most toxic SPs among all the surface-modified SP treatments at the same dosage. When treatment dose was increased, submicro-sized SPs with amino or carboxyl surface modification also induced liver toxicity. Biodistribution studies suggested that 70 nm SPs were mainly accumulated in liver and spleen regardless of surface modifications. Interestingly, these two organs exhibited different uptake trends. Furthermore, metabonomics studies indicated that surface modification plays a more dominant role to affect the liver metabolism than particle size.

  11. Ge doped GaN with controllable high carrier concentration for plasmonic applications

    SciTech Connect

    Kirste, Ronny; Hoffmann, Marc P.; Sachet, Edward; Bobea, Milena; Bryan, Zachary; Bryan, Isaac; Maria, Jon-Paul; Collazo, Ramón; Sitar, Zlatko; Nenstiel, Christian; Hoffmann, Axel

    2013-12-09

    Controllable Ge doping in GaN is demonstrated for carrier concentrations of up to 2.4 × 10{sup 20} cm{sup −3}. Low temperature luminescence spectra from the highly doped samples reveal band gap renormalization and band filling (Burstein-Moss shift) in addition to a sharp transition. Infrared ellipsometry spectra demonstrate the existence of electron plasma with an energy around 3500 cm{sup −1} and a surface plasma with an energy around 2000 cm{sup −1}. These findings open possibilities for the application of highly doped GaN for plasmonic devices.

  12. First-Principles Study of Electronic Structure and Thermoelectric Properties of Ge-Doped Tin Clathrates

    NASA Astrophysics Data System (ADS)

    Akai, K.; Kishimoto, K.; Koyanagi, T.; Kono, Y.; Yamamoto, S.

    2014-06-01

    We calculated the electronic structure and thermoelectric properties of the Ge-doped quaternary clathrate Ba-Ga-Sn-Ge. The electronic structure was calculated by using the WIEN2k code, which is based on the full-potential augmented plane-wave method. Using this method, we calculated the total energies for several Ge configurations to determine the positions of Ge atoms in the unit cell. The calculated Ge positions were in good agreement with the experimental results. Based on the resulting Ge positions, the band structure and thermoelectric properties of the Ba-Ga-Sn-Ge clathrates were calculated.

  13. Thermoluminescence characteristics of Ge-doped optical fibers with different dimensions for radiation dosimetry.

    PubMed

    Begum, Mahfuza; Rahman, A K M Mizanur; Abdul-Rashid, H A; Yusoff, Z; Begum, Mahbuba; Mat-Sharif, K A; Amin, Y M; Bradley, D A

    2015-06-01

    Important thermoluminescence (TL) properties of five (5) different core sizes Ge-doped optical fibers have been studied to develop new TL material with better response. These are drawn from same preform applying different speed and tension during drawing phase to produce Ge-doped optical fibers with five (5) different core sizes. The results of the investigations are also compared with most commonly used standard TLD-100 chips (LiF:Mg,Ti) and commercial multimode Ge-doped optical fiber (Yangtze Optical Fiber, China). Scanning Electron Microscope (SEM) and EDX analysis of the fibers are also performed to map Ge distribution across the deposited region. Standard Gamma radiation source in Secondary Standard Dosimetry Lab (SSDL) was used for irradiation covering dose range from 1Gy to 10Gy. The essential dosimetric parameters that have been studied are TL linearity, reproducibility and fading. Prior to irradiation all samples ∼0.5cm length are annealed at temperature of 400°C for 1h period to standardize their sensitivities and background. Standard TLD-100 chips are also annealed for 1h at 400°C and subsequently 2h at 100°C to yield the highest sensitivity. TL responses of these fibers show linearity over a wide gamma radiation dose that is an important property for radiation dosimetry. Among all fibers used in this study, 100μm core diameter fiber provides highest response that is 2.6 times than that of smallest core (20μm core) optical fiber. These fiber-samples demonstrate better response than commercial multi-mode optical fiber and also provide low degree of fading about 20% over a period of fifteen days for gamma radiation. Effective atomic number (Zeff) is found in the range (13.25-13.69) which is higher than soft tissue (7.5) however within the range of human-bone (11.6-13.8). All the fibers can also be re-used several times as a detector after annealing. TL properties of the Ge-doped optical fibers indicate promising applications in ionizing radiation

  14. Temperature dependence dielectric behavior of Ge-doped lead scandium tantalate single crystals

    NASA Astrophysics Data System (ADS)

    Dixit, Chandra Kumar; Srivastava, Anil Kumar

    2012-07-01

    The doping of Pb2SeTaO6 with Ge ferroelectrics was produced by a high-temperature solution method. We measure dielectric constant, dielectric loss and conductivity in the temperature range -30°C to 200°C and frequency range 1 to 100 KHz. The value of dielectric constant of the Pb2SeTaO6 (PST) crystal remained the same after thermal annealing whereas they decreased after Ge doping in the phase transition temperature range of the PST single crystal. All samples were investigated for conductivity with increasing temperature.

  15. Detection of Amorphous Silica in Air-Oxidized Ti3SiC2 at 500-1000°C by NMR and SIMS

    SciTech Connect

    Pang, Wei Kong; Low, I M; Hanna, J V

    2010-11-12

    The use of secondary-ion mass spectrometry (SIMS), nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) to detect the existence of amorphous silica in Ti3SiC2 oxidised at 500-1000 ºC is described. The formation of an amorphous SiO2 layer and its growth in thickness with temperature was monitored using dynamic SIMS. Results of NMR and TEM verify for the first time the direct evidence of amorphous silica formation during the oxidation of Ti3SiC2 at 1000 ºC.

  16. Comparison of thermoluminescence response of different sized Ge-doped flat fibers as a dosimeter

    NASA Astrophysics Data System (ADS)

    Begum, Mahfuza; Mizanur Rahman, A. K. M.; Abdul-Rashid, H. A.; Yusoff, Z.; Mat-Sharif, K. A.; Zulkifli, M. I.; Muhamad-Yasin, S. Z.; Ung, N. M.; Kadir, A. B. A.; Amin, Y. M.; Bradley, D. A.

    2015-11-01

    Prime dosimetric properties, including dose-response, linearity with dose, energy response, fading and threshold doses were investigated for three different dimension Ge-doped flat fibers. The results of measurement were also compared with two of the more commonly used standard TLD media, TLD-100 (LiF:Mg,Ti-7.5%6LiF) and TLD-700 (7LiF:Mg,Ti-99.9%7LiF) chips. The flat cross-section samples (60×180) μm2, (100×350) μm2 and (200×750) μm2 were fabricated using the Modified Chemical Vapor Deposition (MCVD) process and pulled from the same "preform." In the study, all flat fiber samples provided good linear dose-response for the photon and electron beams generated using a medical linear accelerator (LINAC), for doses in the range 0.5-8 Gy. Among the samples, the smallest dimension flat fiber provided the best response, with a sensitivity of some 61% and 54%, respectively of that of the TLD-100 and TLD-700 chips. The energy responses of the samples were studied for various photon (6 MV, 10 MV) and electron (6 MeV, 9 MeV) beam energies. TL fading of around 20% was observed over a period of thirty (30) days. These favorable TL characteristics point towards promising development of Ge-doped flat fibers for use in radiotherapy dosimetry.

  17. Characterization of Ge-doped optical fibres for MV radiotherapy dosimetry

    NASA Astrophysics Data System (ADS)

    Noor, Noramaliza M.; Hussein, M.; Kadni, T.; Bradley, D. A.; Nisbet, A.

    2014-05-01

    Ge-doped optical fibres offer promising thermoluminescence (TL) properties together with small physical size and modest cost. Their use as dosimeters for postal radiotherapy dose audits of megavoltage photon beams has been investigated. Key dosimetric characteristics including reproducibility, linearity, dose rate, temperature and angular dependence have been established. A methodology of measuring absorbed dose under reference conditions was developed. The Ge-doped optical fibres offer linearity between TL yield and dose, with a reproducibility of better than 5%, following repeated measurements (n=5) for doses from 5 cGy to 1000 cGy. The fibres also offer dose rate, angular and temperature independence, while an energy-dependent response of 7% was found over the energy range 6 MV to 15 MV (TPR20,10 of 0.660, 0.723 and 0.774 for 6, 10 and 15 MV respectively). The audit methodology has been developed with an expanded uncertainty of 4.22% at 95% confidence interval for the photon beams studied.

  18. Comparison of the TL fading characteristics of Ge-doped optical fibres and LiF dosimeters.

    PubMed

    Noor, Noramaliza M; Shukor, Nasiha A; Hussein, M; Nisbet, A; Bradley, D A

    2012-07-01

    Fading is important in choosing appropriate thermoluminescence (TL) materials for particular applications. Comparison is made herein of changes due to fading in the TL yield of Ge-doped fibres and lithium fluoride (LiF) dosimeters, for varying temperature and dose. The fading is independent of dose for all investigated dosimeters while the loss in TL yield reduces for lower storage temperatures. At room temperature and for 133 days of storage, a maximum signal loss of 5% has been observed for both forms of LiF dosimeter, while 9 and 50 μm core diameter Ge-doped fibres produced a loss of 11% and 8%, respectively. PMID:22134025

  19. Effects of amorphous silica coating on cerium oxide nanoparticles induced pulmonary responses

    PubMed Central

    Ma, Jane; Mercer, Robert R.; Barger, Mark; Schwegler-Berry, Diane; Cohen, Joel M.; Demokritou, Philip; Castranova, Vincent

    2015-01-01

    Recently cerium compounds have been used in a variety of consumer products, including diesel fuel additives, to increase fuel combustion efficiency and decrease diesel soot emissions. However, cerium oxide (CeO2) nanoparticles have been detected in the exhaust, which raises a health concern. Previous studies have shown that exposure of rats to nanoscale CeO2 by intratracheal instillation (IT) induces sustained pulmonary inflammation and fibrosis. In the present study, male Sprague–Dawley rats were exposed to CeO2 or CeO2 coated with a nano layer of amorphous SiO2 (aSiO2/CeO2) by a single IT and sacrificed at various times post-exposure to assess potential protective effects of the aSiO2 coating. The first acellular bronchoalveolar lavage (BAL) fluid and BAL cells were collected and analyzed from all exposed animals. At the low dose (0.15 mg/kg), CeO2 but not aSiO2/CeO2 exposure induced inflammation. However, at the higher doses, both particles induced a dose-related inflammation, cytotoxicity, inflammatory cytokines, matrix metalloproteinase (MMP)-9, and tissue inhibitor of MMP at 1 day post-exposure. Morphological analysis of lung showed an increased inflammation, surfactant and collagen fibers after CeO2 (high dose at 3.5 mg/kg) treatment at 28 days post-exposure. aSiO2 coating significantly reduced CeO2-induced inflammatory responses in the airspace and appeared to attenuate phospholipidosis and fibrosis. Energy dispersive X-ray spectroscopy analysis showed Ce and phosphorous (P) in all particle-exposed lungs, whereas Si was only detected in aSiO2/CeO2-exposed lungs up to 3 days after exposure, suggesting that aSiO2 dissolved off the CeO2 core, and some of the CeO2 was transformed to CePO4 with time. These results demonstrate that aSiO2 coating reduce CeO2-induced inflammation, phospholipidosis and fibrosis. PMID:26210349

  20. Effects of amorphous silica coating on cerium oxide nanoparticles induced pulmonary responses.

    PubMed

    Ma, Jane; Mercer, Robert R; Barger, Mark; Schwegler-Berry, Diane; Cohen, Joel M; Demokritou, Philip; Castranova, Vincent

    2015-10-01

    Recently cerium compounds have been used in a variety of consumer products, including diesel fuel additives, to increase fuel combustion efficiency and decrease diesel soot emissions. However, cerium oxide (CeO2) nanoparticles have been detected in the exhaust, which raises a health concern. Previous studies have shown that exposure of rats to nanoscale CeO2 by intratracheal instillation (IT) induces sustained pulmonary inflammation and fibrosis. In the present study, male Sprague-Dawley rats were exposed to CeO2 or CeO2 coated with a nano layer of amorphous SiO2 (aSiO2/CeO2) by a single IT and sacrificed at various times post-exposure to assess potential protective effects of the aSiO2 coating. The first acellular bronchoalveolar lavage (BAL) fluid and BAL cells were collected and analyzed from all exposed animals. At the low dose (0.15mg/kg), CeO2 but not aSiO2/CeO2 exposure induced inflammation. However, at the higher doses, both particles induced a dose-related inflammation, cytotoxicity, inflammatory cytokines, matrix metalloproteinase (MMP)-9, and tissue inhibitor of MMP at 1day post-exposure. Morphological analysis of lung showed an increased inflammation, surfactant and collagen fibers after CeO2 (high dose at 3.5mg/kg) treatment at 28days post-exposure. aSiO2 coating significantly reduced CeO2-induced inflammatory responses in the airspace and appeared to attenuate phospholipidosis and fibrosis. Energy dispersive X-ray spectroscopy analysis showed Ce and phosphorous (P) in all particle-exposed lungs, whereas Si was only detected in aSiO2/CeO2-exposed lungs up to 3days after exposure, suggesting that aSiO2 dissolved off the CeO2 core, and some of the CeO2 was transformed to CePO4 with time. These results demonstrate that aSiO2 coating reduce CeO2-induced inflammation, phospholipidosis and fibrosis. PMID:26210349

  1. Characterization of in vitro genotoxic, cytotoxic and transcriptomic responses following exposures to amorphous silica of different sizes.

    PubMed

    Decan, Nathalie; Wu, Dongmei; Williams, Andrew; Bernatchez, Stéphane; Johnston, Michael; Hill, Myriam; Halappanavar, Sabina

    2016-01-15

    The objectives of the present study were to investigate the underlying mechanisms of genetic and cellular toxicity induced by silica nanoparticles (SiNPs) and determine if such toxicity is influenced by particle size. Commercially available amorphous SiNPs (12 nm, 5-10 nm, and 10-15 nm) and micrometer sized (SiP2 μm) silica were characterised for size, chemical composition, and aggregation state. Mouse lung epithelial (FE1) cells derived from Muta™Mouse were exposed to various concentrations (12.5, 25, 50, 100 μg/ml) of SiNPs and SiP2 μm. Cellular viability, clonogenic potential, oxidative stress, micronucleus formation, and mutant frequency were measured at different post-exposure time points. Cellular internalization of particles was assessed using nanoscale hyperspectral microscopy. Biological pathway and functional perturbations were assessed using DNA microarrays. Detailed characterization of particles confirmed their size, purity, and uniform dispersion in the exposure medium. Decreased cellular viability was observed acutely at 24h at concentrations higher than 25 μg/ml for all particle types, with SiNPs being the most sensitive; loss of viability was surface area dependent at the lowest concentration tested. However, only SiNP12 showed poor long-term survival. A size-dependent increase in micronucleus formation was also observed for SiNPs. In contrast to the viability results, SiP2 μm exhibited the highest potential to induce oxidative stress compared to the SiNPs at all tested concentrations. Gene ontology and biological pathway analysis revealed significant changes in the expression of genes implicated in lysosomal functions in SiNP12-treated cells, which appear closely associated with higher SiNP12 internalization and lysosomal rearrangements in the cytoplasm of these cells. These results suggest that SiNPs induce cellular and genetic toxicity in a size-dependent manner and that the observed toxicity may be the results of higher particle

  2. Discrete Slip, Amorphous Silica and Pore Structure of Slickensided Gouge Layers in 2004-2006 Mt. St. Helens Lava Domes

    NASA Astrophysics Data System (ADS)

    White, J. C.; Kennedy, L. A.; Russell, J. K.; Friedlander, B.

    2012-12-01

    Spines of dacite lava formed during the 2004-2006 Mt. St. Helens (MSH) effusion event are enveloped by extrusion gouges created during upward movement of crystallized magma. Multiple slickenside sets form one of the most distinctive feature types within this gouge carapace. Macroscopically, slickenside surfaces are seen to be composite features composed of discrete slip surfaces in Y- and R-shear orientations. In general, the spacing between the slip surfaces decreases toward the outer, exposed slickensided surface until they appear to coalesce. Slickensides are formed in association with all MSH spines, unlike some other fault rock fabrics within the gouge; therefore, their morphology can be inferred to be independent of syn-faulting residence time. As a significant record of the extrusion process, the MSH slickensides have been characterized by analytical scanning/transmission electron microscopy (STEM) to elucidate the mechanisms of energy dissipation and material transport. At the scale of these observations, the individual surfaces within a slickenside set comprise comminution bands (10-20 μm wide), each bounded by a discrete slip surface. The internal structure of these shear bands consists of a consistent sense of decreasing grain size toward the slip surface away and away from the spire core; grain size is routinely less than 100nm within the bands. The 1-5 μm wide slip layers that bound comminution bands are variously composed of amorphous silica or polycrystalline aggregates of sub-100nm grain size plagioclase, k-feldspar and quartz. Grain aggregates in the slip layer form an extended fabric parallel to the displacement direction, creating a "flow" foliation at edges of the shears. Specific to the slip bands are nano-scale pores, often silica-filled, whose circular cross-sections indicate the presence of fluids throughout slickenside formation. It is contended that the development of discrete slip surfaces is consistent with formation of the gouge by

  3. Size and surface modification of amorphous silica particles determine their effects on the activity of human CYP3A4 in vitro

    NASA Astrophysics Data System (ADS)

    Imai, Shunji; Yoshioka, Yasuo; Morishita, Yuki; Yoshida, Tokuyuki; Uji, Miyuki; Nagano, Kazuya; Mukai, Yohei; Kamada, Haruhiko; Tsunoda, Shin-ichi; Higashisaka, Kazuma; Tsutsumi, Yasuo

    2014-12-01

    Because of their useful chemical and physical properties, nanomaterials are widely used around the world - for example, as additives in food and medicines - and such uses are expected to become more prevalent in the future. Therefore, collecting information about the effects of nanomaterials on metabolic enzymes is important. Here, we examined the effects of amorphous silica particles with various sizes and surface modifications on cytochrome P450 3A4 (CYP3A4) activity by means of two different in vitro assays. Silica nanoparticles with diameters of 30 and 70 nm (nSP30 and nSP70, respectively) tended to inhibit CYP3A4 activity in human liver microsomes (HLMs), but the inhibitory activity of both types of nanoparticles was decreased by carboxyl modification. In contrast, amine-modified nSP70 activated CYP3A4 activity. In HepG2 cells, nSP30 inhibited CYP3A4 activity more strongly than the larger silica particles did. Taken together, these results suggest that the size and surface characteristics of the silica particles determined their effects on CYP3A4 activity and that it may be possible to develop silica particles that do not have undesirable effects on metabolic enzymes by altering their size and surface characteristics.

  4. Rapid transport and high accumulation of amorphous silica in the Congo deep-sea fan: A preliminary budget

    NASA Astrophysics Data System (ADS)

    Raimonet, Mélanie; Ragueneau, Olivier; Jacques, Vincent; Corvaisier, Rudolph; Moriceau, Brivaëla; Khripounoff, Alexis; Pozzato, Lara; Rabouille, Christophe

    2015-01-01

    Mechanisms controlling the transfer and retention of silicon (Si) along continental margins are poorly understood, but play a major role in the functioning of coastal ecosystems and the oceanic biological pump of carbon. Deep-sea fans are well recognized as carbon sink spots, but we lack knowledge about the importance of the fans in the global Si cycle. Here, we provide a first estimate of the role played by the Congo deep-sea fan, one of the biggest in the world, in the Si cycle. Sediment cores sampled in the deep-sea fan were analyzed to build a Si mass balance. An exceptionally high accumulation rate of amorphous silica aSiO2 (2.29 ± 0.58 mol Si m- 2 y- 1) was found, due to a high sedimentation rate and the presence of aluminum in the sediments. Although favored by bioirrigation, recycling fluxes remained low (0.3 mol Si m- 2 y- 1) and reconstructed input fluxes could only be explained by lateral inputs coming from the canyon. Preliminary calculations show that the rapid transport of aSiO2 through the canyon and the excellent preservation efficiency in the sediments imply that 50% of aSiO2 river inputs from the Congo River accumulate annually in the deep-sea fan. Si:C ratios in deep-sea fan sediments were very low (0.2) and only three times as high as those measured in the river itself, which suggests that material from the river and the continental shelf was delivered directly through the canyon, with very little time for Si and C cycle decoupling to take place.

  5. Enhancement of ovalbumin-specific Th1, Th2, and Th17 immune responses by amorphous silica nanoparticles.

    PubMed

    Toda, Tsuguto; Yoshino, Shin

    2016-09-01

    Nanomaterials present in cosmetics and food additives are used for industrial applications. However, their safety profile is unclear. Amorphous silica nanoparticles (nSPs) are a widely used nanomaterial and have been shown to induce inflammatory cytokines following intratracheal administration in mice. The current study investigated the adjuvant effect of nSP30 (nSP with a diameter of 33 nm) on T helper (Th)1, Th2, and Th17 immune responses as well as immunoglobulin (Ig) levels in mice. BALB/c mice were intraperitoneally administered ovalbumin (OVA) with or without varying doses and varying sizes of nSPs. The adjuvant effect of nSPs was investigated by measuring OVA-specific IgG antibodies in sera, OVA-specific proliferative responses of splenocytes, and the production of Th1, Th2, and Th17 cytokines. Aluminum hydroxide was used as a positive adjuvant control. Anti-OVA IgG production, splenocyte proliferative responses, and secretion of IFN-γ, IL-2, IL-4, IL-5, and IL-17 were increased significantly in mice receiving a combined injection of nSP30 (30 or 300 µg) with OVA compared with OVA alone or a combined injection with nSP30 (3 µg). The responses were nSP30 dose-dependent. When different sized nSPs were used (with 30, 100, and 1000 nm diameters), the responses to OVA were enhanced and were size-dependent. The smaller sized nSP particles had a greater adjuvant effect. nSPs appear to exert a size-dependent adjuvant effect for Th1, Th2, and Th17 immune responses. Understanding the mechanisms of nSP adjuvanticity might lead to the development of novel vaccine adjuvants and therapies for allergic diseases caused by environmental factors. PMID:27343242

  6. Genotoxicity of synthetic amorphous silica nanoparticles in rats following short-term exposure. Part 1: oral route.

    PubMed

    Tarantini, Adeline; Huet, Sylvie; Jarry, Gérard; Lanceleur, Rachelle; Poul, Martine; Tavares, Ana; Vital, Nádia; Louro, Henriqueta; João Silva, Maria; Fessard, Valérie

    2015-03-01

    Synthetic amorphous silica (SAS) in its nanosized form is now used in food applications although the potential risks for human health have not been evaluated. In this study, genotoxicity and oxidative DNA damage of two pyrogenic (NM-202 and 203) and two precipitated (NM-200 and -201) nanosized SAS were investigated in vivo in rats following oral exposure. Male Sprague Dawley rats were exposed to 5, 10, or 20 mg/kg b.w./day for three days by gavage. DNA strand breaks and oxidative DNA damage were investigated in seven tissues (blood, bone marrow from femur, liver, spleen, kidney, duodenum, and colon) with the alkaline and the (Fpg)-modified comet assays, respectively. Concomitantly, chromosomal damage was investigated in bone marrow and in colon with the micronucleus assay. Additionally, malondialdehyde (MDA), a lipid peroxidation marker, was measured in plasma. When required, a histopathological examination was also conducted. The results showed neither obvious DNA strand breaks nor oxidative damage with the comet assay, irrespective of the dose and the organ investigated. Similarly, no increases in chromosome damage in bone marrow or lipid peroxidation in plasma were detected. However, although the response was not dose-dependent, a weak increase in the percentage of micronucleated cells was observed in the colon of rats treated with the two pyrogenic SAS at the lowest dose (5 mg/kg b.w./day). Additional data are required to confirm this result, considering in particular, the role of agglomeration/aggregation of SAS NMs in their uptake by intestinal cells. PMID:25504566

  7. Genotoxicity of synthetic amorphous silica nanoparticles in rats following short-term exposure. Part 2: intratracheal instillation and intravenous injection.

    PubMed

    Guichard, Yves; Maire, Marie-Aline; Sébillaud, Sylvie; Fontana, Caroline; Langlais, Cristina; Micillino, Jean-Claude; Darne, Christian; Roszak, Joanna; Stępnik, Maciej; Fessard, Valérie; Binet, Stéphane; Gaté, Laurent

    2015-03-01

    Synthetic amorphous silica nanomaterials (SAS) are extensively used in food and tire industries. In many industrial processes, SAS may become aerosolized and lead to occupational exposure of workers through inhalation in particular. However, little is known about the in vivo genotoxicity of these particulate materials. To gain insight into the toxicological properties of four SAS (NM-200, NM-201, NM-202, and NM-203), rats are treated with three consecutive intratracheal instillations of 3, 6, or 12 mg/kg of SAS at 48, 24, and 3 hrs prior to tissue collection (cumulative doses of 9, 18, and 36 mg/kg). Deoxyribonucleic acid (DNA) damage was assessed using erythrocyte micronucleus test and the standard and Fpg-modified comet assays on cells from bronchoalveolar lavage fluid (BALF), lung, blood, spleen, liver, bone marrow, and kidney. Although all of the SAS caused increased dose-dependent changes in lung inflammation as demonstrated by BALF neutrophilia, they did not induce any significant DNA damage. As the amount of SAS reaching the blood stream and subsequently the internal organs is probably to be low following intratracheal instillation, an additional experiment was performed with NM-203. Rats received three consecutive intravenous injections of 5, 10, or 20 mg/kg of SAS at 48, 24, and 3 hrs prior to tissue collection. Despite the hepatotoxicity, thrombocytopenia, and even animal death induced by this nanomaterial, no significant increase in DNA damage or micronucleus frequency was observed in SAS-exposed animals. It was concluded that under experimental conditions, SAS induced obvious toxic effects but did cause any genotoxicity following intratracheal instillation and intravenous injection. PMID:25451515

  8. High temperature stability testing of Ge-doped and F-doped Fabry-Perot fibre optical sensors

    NASA Astrophysics Data System (ADS)

    Polyzos, Dimitrios; Mathew, Jinesh; MacPherson, William N.; Maier, Robert R...

    2016-05-01

    We present high temperature (~1100°C) stability tests of, Ge-doped and F-doped, optical fibre sensors. Our analysis includes the variation in their behaviours within high temperature environments and how the dopant diffusion affects their long term stability.

  9. Hugoniot and mean ionization of laser-shocked Ge-doped plastic

    SciTech Connect

    Huser, G.; Salin, G.; Galmiche, D.; Ozaki, N.; Kodama, R.; Sano, T.; Sakawa, Y.; Miyanishi, K.; Asaumi, Y.; Kita, M.; Kondo, Y.; Nakatsuka, K.; Uranishi, H.; Yang, T.; Yokoyama, N.

    2013-12-15

    Pressure, density, temperature, and reflectivity measurements along the principal Hugoniot of Ge-doped plastics used in Inertial Confinement Fusion capsules surrogates were obtained to pressures reaching up to 7 Mbar and compared to Quotidian Equation of State models. The experiment was performed using the GEKKO XII laser at the Institute of Laser Engineering at Osaka University in Japan. High precision measurements of pressure and density were obtained using a quartz standard and found to be in good agreement with theoretical Hugoniot curves. Modeling of reflectivity measurements show that shocked samples can be described as poor metals and that mean ionization calculated within the frame of QEOS is overestimated. Similarly, shock temperatures were found to be below theoretical Hugoniot curves.

  10. Thermoluminescence response of Ge-doped SiO2 fibres to electrons, X- and γ-radiation

    NASA Astrophysics Data System (ADS)

    Entezam, A.; Khandaker, M. U.; Amin, Y. M.; Ung, N. M.; Maah, J.; Bradley, D. A.

    2016-04-01

    For doses from 10 cGy to 80 Gy, we investigate the thermoluminescence (TL) response of tailor-made Ge-doped SiO2 fibres for accelerated electrons (6, 12 and 20 MeV), megavoltage X-rays (6, 10 MV) and 1.25 MeV γ-rays, delivered by a linear accelerator (LINAC) and a Co-60 irradiator respectively. Fibres of various dimensions were fabricated, obtained with doping concentrations from 6% to 10% Ge. The fibres are observed to provide a linear response with radiation dose, an overall reproducibility of 1-5%, and inappreciable dependence on energy, field-size and angular variation. For fibres exposed to 6 MV X-rays, the response increases with core size, the 6% Ge-doped fibres providing the greatest TL yield. The fibres exhibit uniformity of response and provide the basis of a promising TL system for radiotherapy applications, offering high spatial resolution and sensitivity.

  11. Au-catalyzed synthesis and characterisation of phase change Ge-doped Sb-Te nanowires by MOCVD

    NASA Astrophysics Data System (ADS)

    Longo, M.; Stoycheva, T.; Fallica, R.; Wiemer, C.; Lazzarini, L.; Rotunno, E.

    2013-05-01

    The interest in the Ge doped Sb-Te chalcogenide alloy is mainly related to phase change memory applications. In view of phase change device scaling and reduction of programming energy, Sb-Te nanowires (NWs) become an attractive option. In this work, in order to investigate their potential transferability to industrial implementation, the self-assembly of Sb2Te3 NWs and Ge-Sb-Te NWs with Ge content in the range of 1-13% (Ge doping) was studied by coupling the advantages of MOCVD and the Vapour-Liquid-Solid (VLS) mechanism. The results show the structural and compositional gradual changes occurring from pure Sb2Te3 NWs to the previously reported, stoichiometric Ge1Sb2Te4 NWs [[12] M. Longo et al., Nano Lett., 12 (2012) 1509]. The typical diameter of the obtained NWs resulted to be 50 nm, with lengths up to 3 μm. The typology of Au catalyst nanoislands influenced both the NW morphology and the Ge incorporation during the VLS self-assembly; the Ge metalorganic precursor partial pressure affected the NW morphology and their structure. Finally, TEM observations revealed that defect-free, monocrystalline Sb2Te3 and Ge-doped Sb-Te phase change NWs could be obtained.

  12. Intraband absorption in self-assembled Ge-doped GaN/AlN nanowire heterostructures.

    PubMed

    Beeler, M; Hille, P; Schörmann, J; Teubert, J; de la Mata, M; Arbiol, J; Eickhoff, M; Monroy, E

    2014-03-12

    We report the observation of transverse-magnetic-polarized infrared absorption assigned to the s-p(z) intraband transition in Ge-doped GaN/AlN nanodisks (NDs) in self-assembled GaN nanowires (NWs). The s-p(z) absorption line experiences a blue shift with increasing ND Ge concentration and a red shift with increasing ND thickness. The experimental results in terms of interband and intraband spectroscopy are compared to theoretical calculations of the band diagram and electronic structure of GaN/AlN heterostructured NWs, accounting for their three-dimensional strain distribution and the presence of surface states. From the theoretical analysis, we conclude that the formation of an AlN shell during the heterostructure growth applies a uniaxial compressive strain which blue shifts the interband optical transitions but has little influence on the intraband transitions. The presence of surface states with density levels expected for m-GaN plane charge-deplete the base of the NWs but is insufficient to screen the polarization-induced internal electric field in the heterostructures. Simulations show that the free-carrier screening of the polarization-induced internal electric field in the NDs is critical to predicting the photoluminescence behavior. The intraband transitions, on the other hand, are blue-shifted due to many-body effects, namely, the exchange interaction and depolarization shift, which exceed the red shift induced by carrier screening. PMID:24502703

  13. Vacancy-donor complexes in highly n-type Ge doped with As, P and Sb

    NASA Astrophysics Data System (ADS)

    Kujala, J.; Südkamp, T.; Slotte, J.; Makkonen, I.; Tuomisto, F.; Bracht, H.

    2016-08-01

    Positron annihilation spectroscopy was performed to study defects in Ge doped with As, P and Sb. In each case, the samples had approximately the same dopant concentration  ∼1019 cm‑3. Results from the Doppler broadening and positron lifetime spectroscopies were compared to electronic structure calculations. The positron lifetime results show that the open volume related to the defect centers is not larger than a monovacancy. The results suggest that in the As doped sample the dominant trap at room temperature is a complex consisting of a vacancy and at least three dopant atoms. In the case of P doped Ge the results indicate that two defect complexes compete in positron trapping. Complexes with a higher number of P atoms around the vacancy seem to dominate at room temperature whereas at low temperature positron trapping at centers with fewer P atoms around the vacancy becomes more significant. The complexes with fewer P atoms are more negatively charged. In Sb doped Ge the results suggest that several types of traps are simultaneously competing in positron trapping at all measurement temperatures.

  14. Ionizing Radiation Detectors Based on Ge-Doped Optical Fibers Inserted in Resonant Cavities

    PubMed Central

    Avino, Saverio; D’Avino, Vittoria; Giorgini, Antonio; Pacelli, Roberto; Liuzzi, Raffaele; Cella, Laura; De Natale, Paolo; Gagliardi, Gianluca

    2015-01-01

    The measurement of ionizing radiation (IR) is a crucial issue in different areas of interest, from environmental safety and industrial monitoring to aerospace and medicine. Optical fiber sensors have recently proven good candidates as radiation dosimeters. Here we investigate the effect of IR on germanosilicate optical fibers. A piece of Ge-doped fiber enclosed between two fiber Bragg gratings (FBGs) is irradiated with gamma radiation generated by a 6 MV medical linear accelerator. With respect to other FBG-based IR dosimeters, here the sensor is only the bare fiber without any special internal structure. A near infrared laser is frequency locked to the cavity modes for high resolution measurement of radiation induced effects on the fiber optical parameters. In particular, we observe a variation of the fiber thermo-optic response with the radiation dose delivered, as expected from the interaction with Ge defect centers, and demonstrate a detection limit of 360 mGy. This method can have an impact in those contexts where low radiation doses have to be measured both in small volumes or over large areas, such as radiation therapy and radiation protection, while bare optical fibers are cheap and disposable. PMID:25686311

  15. Ionizing radiation detectors based on Ge-doped optical fibers inserted in resonant cavities.

    PubMed

    Avino, Saverio; D'Avino, Vittoria; Giorgini, Antonio; Pacelli, Roberto; Liuzzi, Raffaele; Cella, Laura; De Natale, Paolo; Gagliardi, Gianluca

    2015-01-01

    The measurement of ionizing radiation (IR) is a crucial issue in different areas of interest, from environmental safety and industrial monitoring to aerospace and medicine. Optical fiber sensors have recently proven good candidates as radiation dosimeters. Here we investigate the effect of IR on germanosilicate optical fibers. A piece of Ge-doped fiber enclosed between two fiber Bragg gratings (FBGs) is irradiated with gamma radiation generated by a 6 MV medical linear accelerator. With respect to other FBG-based IR dosimeters, here the sensor is only the bare fiber without any special internal structure. A near infrared laser is frequency locked to the cavity modes for high resolution measurement of radiation induced effects on the fiber optical parameters. In particular, we observe a variation of the fiber thermo-optic response with the radiation dose delivered, as expected from the interaction with Ge defect centers, and demonstrate a detection limit of 360 mGy. This method can have an impact in those contexts where low radiation doses have to be measured both in small volumes or over large areas, such as radiation therapy and radiation protection, while bare optical fibers are cheap and disposable. PMID:25686311

  16. Vacancy-donor complexes in highly n-type Ge doped with As, P and Sb.

    PubMed

    Kujala, J; Südkamp, T; Slotte, J; Makkonen, I; Tuomisto, F; Bracht, H

    2016-08-24

    Positron annihilation spectroscopy was performed to study defects in Ge doped with As, P and Sb. In each case, the samples had approximately the same dopant concentration  ∼10(19) cm(-3). Results from the Doppler broadening and positron lifetime spectroscopies were compared to electronic structure calculations. The positron lifetime results show that the open volume related to the defect centers is not larger than a monovacancy. The results suggest that in the As doped sample the dominant trap at room temperature is a complex consisting of a vacancy and at least three dopant atoms. In the case of P doped Ge the results indicate that two defect complexes compete in positron trapping. Complexes with a higher number of P atoms around the vacancy seem to dominate at room temperature whereas at low temperature positron trapping at centers with fewer P atoms around the vacancy becomes more significant. The complexes with fewer P atoms are more negatively charged. In Sb doped Ge the results suggest that several types of traps are simultaneously competing in positron trapping at all measurement temperatures. PMID:27351231

  17. Upgrading the rice husk char obtained by flash pyrolysis for the production of amorphous silica and high quality activated carbon.

    PubMed

    Alvarez, Jon; Lopez, Gartzen; Amutio, Maider; Bilbao, Javier; Olazar, Martin

    2014-10-01

    The overall valorization of rice husk char obtained by flash pyrolysis in a conical spouted bed reactor (CSBR) has been studied in a two-step process. Thus, silica has been recovered in a first step and the remaining carbon material has been subjected to steam activation. The char samples used in this study have been obtained by continuous flash pyrolysis in a conical spouted bed reactor at 500°C. Extraction with Na2CO3 allows recovering 88% of the silica contained in the rice husk char. Activation of the silica-free rice husk char has been carried out in a fixed bed reactor at 800°C using steam as activating agent. The porous structure of the activated carbons produced includes a combination of micropores and mesopores, with a BET surface area of up to 1365m(2)g(-1) at the end of 15min. PMID:25127010

  18. Sol-gel combustion synthesis, particle shape analysis and magnetic properties of hematite (α-Fe2O3) nanoparticles embedded in an amorphous silica matrix

    NASA Astrophysics Data System (ADS)

    Kopanja, Lazar; Milosevic, Irena; Panjan, Matjaz; Damnjanovic, Vesna; Tadic, Marin

    2016-01-01

    We report the synthesis and magnetic properties of hematite/amorphous silica nanostructures. Raman spectroscopy showed the formation of a hematite phase. A transmission electron microscopy (TEM) revealed spherically shaped hematite nanoparticles, well-dispersed in an amorphous silica matrix. In order to quantitatively describe morphological properties of nanoparticles, we use the circularity of shapes as a measure of how circular a shape is. Diameters of about 5 nm and a narrow size distribution of nanoparticles are observed. The obtained hematite nanoparticles exhibit superparamagnetic properties at room temperature (SPION). The sample does not display the Morin transition. The FC hysteresis loop at 5 K has shown an exchange bias effect. These results have been compared to those previously reported for α-Fe2O3/SiO2 nanosystems in the literature. These comparisons reveal that the sol-gel combustion method yields hematite nanoparticles with a higher magnetization and magnetic moment. These data indicate the existence of an additional factor that contributes to magnetization. We suggest that the increased magnetization is due to an increased number of the surface spins caused by the breaking of large numbers of exchange bonds between surface atoms (disordered structure). This leads to an increase in the magnetic moment per a hematite nanoparticle and an exchange bias effect. We have concluded that the combustion-related part of this synthesis method enhances surface effects, i.e. it promotes the breaking of bonds and surface disordered layers, which results in these magnetic properties. Such interesting structural and magnetic properties of hematite might be important in future practical applications and fundamental research.

  19. Biocompatibility of core@shell particles: cytotoxicity and genotoxicity in human osteosarcoma cells of colloidal silica spheres coated with crystalline or amorphous zirconia.

    PubMed

    Di Virgilio, A L; Arnal, P M; Maisuls, I

    2014-08-01

    The cytotoxicity and genotoxicity of novel colloidal silica spheres coated with crystalline or amorphous zirconia (SiO2@ZrO2(cryst) or SiO2@ZrO2(am)) have been studied in a human osteosarcoma cell line (MG-63), after 24 h exposure. SiO2@ZrO2(cryst) and SiO2@ZrO2(am) had mean diameters of 782±19 and 891±34 nm, respectively. SiO2@ZrO2(cryst) exposure reduced cell viability, with an increase in reactive oxygen species (ROS) and a decrease of the GSH/GSSG ratio. The comet and micronucleus (MN) assays detected DNA damage at 5 and 25 μg/mL, respectively. SiO2@ZrO2(am) induced genotoxic action only at 10 and 50 μg/mL (comet and MN assays), along with a decrease of the GSH/GSSG ratio at 50 μg/mL. Both particles were found inside the cells, forming vesicles; however, none of them entered the nucleus. Our findings show that crystallization of the shell of the amorphous ZrO2 increases both cytotoxicity and genotoxicity. PMID:25344169

  20. Amorphous Fe²⁺-rich FeOx loaded in mesoporous silica as a highly efficient heterogeneous Fenton catalyst.

    PubMed

    Wang, Min; Shu, Zhu; Zhang, Lingxia; Fan, Xiangqian; Tao, Guiju; Wang, Yongxia; Chen, Lisong; Wu, Meiying; Shi, Jianlin

    2014-06-28

    A simple physical-vapor-infiltration (PVI) method using ferrocene as the iron source, has been developed to load FeOx into the pore channels of mesoporous silica SBA-15. The obtained FeOx/SBA-15 composite has a high loading amount of FeOx (e.g. 26.64 wt% Fe content obtained at PVI duration 17 h and calcination temperature 450 °C) but unblocked pore channels thanks to the unique preparation strategy. The FeOx species are amorphous, rich of Fe(2+) and have been highly dispersed as a nanocoating onto the pore channel surface. The FeOx/SBA-15 composite was used as a heterogeneous Fenton catalyst to degrade Acid orange 7 (AO7). It showed a high catalytic activity and degradation efficiency, which was attributed to the high proportion of Fe(2+) in the amorphous FeOx and their favorable adsorption capability for the dye. The influences of the PVI duration, the calcination temperature and the Fenton reaction conditions (FeOx/SBA-15 dosages, H2O2 dosages and initial pH value) on the catalytic activity were investigated in detail. PMID:24816279

  1. Interactions between DPPC as a component of lung surfactant and amorphous silica nanoparticles investigated by HILIC-ESI-MS.

    PubMed

    Silina, Yuliya E; Welck, Jennifer; Kraegeloh, Annette; Koch, Marcus; Fink-Straube, Claudia

    2016-09-01

    This paper reports a rapid HILIC-ESI-MS assay to quantify dipalmitoylphosphatidylcholine (DPPC) as component of lung surfactant for nanosafety studies. The technique was used to investigate the concentration-dependent sorption of DPPC to two-sizes of amorphous SiO2 nanoparticles (SiO2-NPs) in a MeOH:H2O (50/50v/v) mixture and in cell culture medium. In MeOH:H2O (50/50v/v), the sorption of DPPC was positively correlated with the nanoparticles concentration. A substantial affinity of small amorphous SiO2-NPs (25nm) to DPPC standard solution compared to bigger SiO2-NPs (75nm) was not confirmed for biological specimens. After dispersion of SiO2-NPs in DPPC containing cell culture medium, the capacity of the SiO2-NPs to bind DPPC was reduced in comparison to a mixture of MeOH:H2O (50/50v/v) regardless from the nanoparticles size. Furthermore, HILIC-ESI-MS revealed that A549 cells internalized DPPC during growth in serum containing medium complemented with DPPC. This finding was in a good agreement with the potential of alveolar type II cells to recycle surfactant components. Binding of lipids present in the cell culture medium to amorphous SiO2-NPs was supported by means of HILIC-ESI-MS, TEM and ICP-MS independently. PMID:27442798

  2. Specific features of erbium ion photoluminescence in structures with amorphous and crystalline silicon nanoclusters in silica matrix

    SciTech Connect

    Dyakov, S. A. Zhigunov, D. M.; Timoshenko, V. Yu.

    2010-04-15

    Photoluminescence properties of the structures of amorphous and crystalline silicon nanoclusters with average sizes no larger than 4 nm in an erbium-doped silicon dioxide matrix were studied. It was found that the photoluminescence lifetime of Er{sup 3+} ions at a wavelength of 1.5 {mu}m decreases from 5.7 to 2.0 ms and from 3.5 to 1.5 ms in samples with amorphous nanoclusters and with nanocrystals, respectively, as the Er{sup 3+} concentration increases from 10{sup 19} to 10{sup 21} cm{sup -3}. The decrease in the erbium photoluminescence lifetime with the ion concentration is attributed to the effects of concentration-related quenching and residual implantation-induced defects. The difference between lifetimes for samples with amorphous and crystalline nanoclusters is interpreted as the effect of different probabilities of energy back transfer from Er{sup 3+} ions to the solid-state matrix in the structures under consideration.

  3. Effect of divalent ions on electroosmotic transport in a sodium chloride aqueous solution confined in an amorphous silica nanochannel

    NASA Astrophysics Data System (ADS)

    Conlisk, A. T.; Zambrano, Harvey; Cevheri, Necmettin; Yoda, Minami; Computational Micro-; Nanofluidics Lab Team; The Fluids, Optical; Interfacial Diagnostics Lab Team

    2012-11-01

    A critical enabling technology for the next generation of nanoscale devices, such as nanoscale ``lab on a chip'' systems, is controlling electroosmotic flow (EOF) in nanochannels. In this work, we control EOF in an aqueous sodium chloride (NaCl) solution confined in a silica nanochannel by systematically adding different amounts of divalent ions. Multivalent ions have a different affinity for the silica surface and different hydration characteristics in comparison to monovalent ions. Therefore by adding Mg++ and Ca++ to the sodium chloride solution, the electroosmotic velocity and the structure of the electrical double layer will be modified. The effects of adding Mg++ and Ca++ will be compared using non-equilibrium molecular dynamics simulations of the EOF at different electric fields of a NaCl solution in a silica nanochannel with different fractions of Ca++ and Mg++ ions. In general, the wall zeta-potential magnitude, and hence the EOF velocity, decreases as the Ca++ or Mg++ concentration increases. The system responds linearly with electric field. We will compare the computational results with the experimental data of Cevheri and Yoda (2012). This work is supported by Army Research Office (ARO) grant number W911NF1010290.

  4. A new method of utilizing rice husk: consecutively preparing D-xylose, organosolv lignin, ethanol and amorphous superfine silica.

    PubMed

    Zhang, Hongxi; Ding, Xuefeng; Chen, Xue; Ma, Yuejia; Wang, Zichen; Zhao, Xu

    2015-06-30

    Rice husk is an abundant agricultural by-product with the annual output of 120 and 40 million tons in the world and China, respectively. The common disposal method of rice husk in China has caused the pollution. This manuscript deals with a new method of comprehensively utilizing rice husk, by which hazardous materials are avoided to release. 100.3, 219.4, 50.1 and 170.5 g of D-xylose, organosolv lignin, ethanol and superfine silica are consecutively prepared from 1000 g of rice husk. This new method is helpful to resolving the problem of pollution and waste aroused by rice husk. PMID:25768989

  5. Five-day inhalation toxicity study of three types of synthetic amorphous silicas in Wistar rats and post-exposure evaluations for up to 3 months.

    PubMed

    Arts, Josje H E; Muijser, Hans; Duistermaat, Evert; Junker, Karin; Kuper, C Frieke

    2007-10-01

    Evidence suggests that short-term animal exposures to synthetic amorphous silicas (SAS) and crystalline silica can provide comparable prediction of toxicity to those of 90-day studies, therefore providing the opportunity to screen these types of substances using short-term rather than 90-day studies. To investigate this hypothesis, the inhalation toxicity of three SAS, precipitated silica Zeosil 45, silica gel Syloid 74, and pyrogenic silica Cab-O-Sil M5 was studied in Wistar rats. Rats were exposed nose-only to concentrations of 1, 5 or 25mg/m(3) of one of the SAS 6h a day for five consecutive days. Positive controls were exposed to 25mg/m(3) crystalline silica (quartz dust), negative controls to clean air. Animals were necropsied the day after the last exposure or 1 or 3 months later. All exposures were tolerated without serious clinical effects, changes in body weight or food intake. Differences in the effects associated with exposure to the three types of SAS were limited and almost exclusively confined to the 1-day post-exposure time point. Silicon levels in tracheobronchial lymph nodes were below the detection limit in all groups at all time points. Silicon was found in the lungs of all high concentration SAS groups 1-day post-exposure, and was cleared 3 months later. Exposure to all three SAS at 25mg/m(3) induced elevations in biomarkers of cytotoxicity in bronchoalveolar lavage fluid (BALf), increases in lung and tracheobronchial lymph node weight and histopathological lung changes 1-day post-exposure. Exposure to all three SAS at 5mg/m(3) induced histopathological changes and changes in BALf only. With all three SAS these effects were transient and, with the exception of slight histopathological lung changes at the higher exposure levels, were reversible during the 3-month recovery period. No adverse changes were observed in animals exposed to any of the SAS at 1mg/m(3). In contrast, with quartz-exposed animals the presence of silicon in the lungs was

  6. Track formation in two amorphous insulators, vitreous silica and diamond like carbon: Experimental observations and description by the inelastic thermal spike model

    NASA Astrophysics Data System (ADS)

    Rotaru, C.; Pawlak, F.; Khalfaoui, N.; Dufour, C.; Perrière, J.; Laurent, A.; Stoquert, J. P.; Lebius, H.; Toulemonde, M.

    2012-02-01

    Vitreous silica thin film (a-SiO 2) and mixed deuterated and hydrogenated amorphous carbon thin film (a-C:D,H), grown or deposited, respectively, on silicon, have been irradiated at GANIL in the MeV/u energy range with ions between C and U in order to reach electronic energy loss between 0.7 and 25 keV/nm. The evolution of Si-O bonds and C-D bonds contents was determined by infrared absorption spectroscopy. Complementary physico-chemical characterization was performed for a-C:D,H using Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA). For a-SiO 2, the band at 1076 cm -1 decreases with the appearance of a band at 1046 cm -1. In the case of the diamond like amorphous carbon, the main effects due to MeV/u ion irradiations are the decrease of sp 3 bonding content and of deuterium relative concentration (D/C atomic ratio) as a function of fluence with the appearance of the sp 1 bond. The cylinder radii in which these physical phenomena are confined can be deduced from a statistical analysis. Using the inelastic thermal spike model (i-TS) these track radii can be described using the electron-phonon mean free path which takes values equal to 3 and 0.9 nm for a-SiO 2 and a-C:D, respectively. Extrapolation to low energy range (˜1 MeV in total or ˜0.02 MeV/u) will be made.

  7. Preliminary results on the photo-transferred thermoluminescence from Ge-doped SiO2 optical fiber

    NASA Astrophysics Data System (ADS)

    Zulkepely, Nurul Najua; Amin, Yusoff Mohd; Md Nor, Roslan; Bradley, D. A.; Maah, Mohd Jamil; Mat Nawi, Siti Nurasiah; Wahib, Nur Fadira

    2015-12-01

    A study is made of photo-transferred thermoluminescence (PTTL), the TL being induced by transferring charge carriers from deeper to more superficial traps through energetic light exposure. Potential applications include dose reassessment in radiation dosimetry and also as a useful tool for dating. With incomplete emptying of deep traps following first readout, subsequent UV exposure is shown to lead to charge transfer to more shallow traps. Using Ge-doped SiO2 optical fibers exposed to 60Co gamma rays, the PTTL from the medium has been characterized in terms of the stimulation provided by exposure to a UV lamp and duration of exposure, maximum read-out temperature and pre-gamma irradiation dose. Ge-doped SiO2 optical fibers of flat cross-sectional shape have been used in this study. The efficiency of dose reassessment was compared to that of the highly popular phosphor-based TL detector TLD-100. Results show the maximum temperature of readout to have no measurable effect on the PTTL signal. For doses from 20 to 500 cGy, the method is shown to be effective using a UV lamp of wavelength 254 nm, also being indicative of potential application for doses on either side of the range currently investigated. A study was also made of the effect of UV exposure time on PTTL, seeking to determine the greatest accessible sensitivity and lowest measurable dose.

  8. Protein corona changes mediated by surface modification of amorphous silica nanoparticles suppress acute toxicity and activation of intrinsic coagulation cascade in mice

    NASA Astrophysics Data System (ADS)

    Yoshida, Tokuyuki; Yoshioka, Yasuo; Morishita, Yuki; Aoyama, Michihiko; Tochigi, Saeko; Hirai, Toshiro; Tanaka, Kota; Nagano, Kazuya; Kamada, Haruhiko; Tsunoda, Shin-ichi; Nabeshi, Hiromi; Yoshikawa, Tomoaki; Higashisaka, Kazuma; Tsutsumi, Yasuo

    2015-06-01

    Recently, nanomaterial-mediated biological effects have been shown to be governed by the interaction of nanomaterials with some kinds of proteins in biological fluids, and the physical characteristics of the nanomaterials determine the extent and type of their interactions with proteins. Here, we examined the relationships between the surface properties of amorphous silica nanoparticles with diameters of 70 nm (nSP70), their interactions with some proteins in biological fluids, and their toxicity in mice after intravenous administration. The surface modification of nSP70 with amino groups (nSP70-N) prevented acute lethality and abnormal activation of the coagulation cascade found in the nSP70-treated group of mice. Since our previous study showed that coagulation factor XII played a role in the nSP70-mediated abnormal activation of the coagulation cascade, we examined the interaction of nSP70 and nSP70-N with coagulation factor XII. Coagulation factor XII bonded to the surface of nSP70 to a greater extent than that observed for nSP70-N, and consequently more activation of coagulation factor XII was observed for nSP70 than for nSP70-N. Collectively, our results suggest that controlling the interaction of nSP70 with blood coagulation factor XII by modifying the surface properties would help to inhibit the nSP70-mediated abnormal activation of the blood coagulation cascade.

  9. Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application.

    PubMed

    Zhao, Wangen; Pan, Daocheng; Liu, Shengzhong Frank

    2016-05-21

    Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm(2) without an anti-reflection layer. PMID:27121893

  10. Calculation of amorphous silica solubilities at 25° to 300°C and apparent cation hydration numbers in aqueous salt solutions using the concept of effective density of water

    USGS Publications Warehouse

    Fournier, Robert O.; Williams, Marshall L.

    1983-01-01

    The solubility of amorphous silica in aqueous salt solutions at 25° to 300°C can be calculated using information on its solubility in pure water and a model in which the activity of water in the salt solution is defined to equal the effective density. pe, of “free” water in that solution. At temperatures of 100°C and above, pe closely equals the product of the density of the solution times the weight fraction of water in the solution. At 25°C, a correction parameter must be applied to pe that incorporates a term called the apparent cation hydration number, h. Because of the many assumptions and other uncertainties involved in determining values of h, by the model used here, the reported numbers are not necessarily real hydration numbers even though they do agree with some published values determined by activity and diffusion methods. Whether or not h is a real hydration number, it would appear to be useful in its inclusion within a more extensive activity coefficient term that describes the departure of silica solubilities in concentrated salt solutions from expected behavior according to the model presented here. Values of h can be calculated from measured amorphous silica solubilities in salt solutions at 25°C provided there is no complexing of dissolved silica with the dissolved salt, or if the degree of complexing is known. The previously postulated aqueous silica-sulfate complexing in aqueous Na2SO4 solutions is supported by results of the present effective density of water model

  11. Experimental studies of oxalate complexation at 80 °C: Gibbsite, amorphous silica, and quartz solubilities in oxalate-bearing fluids

    NASA Astrophysics Data System (ADS)

    Fein, Jeremy B.; Hestrin, Jacqueline E.

    1994-11-01

    Experimental measurements of amorphous silica, quartz, and gibbsite solubilities in oxalatebearing solutions at 80°C over a wide pH range reveal that aqueous Si-oxalate complexation is of negligible importance in natural fluid-rock systems, but that Al-oxalate complexation can dramatically affect aqueous Al concentrations. The data indicate the presence of at least two Al-oxalate complexes, and the data place quantitative constraints on the stoichiometry and stability of the Al-oxalate aqueous species. However, the data do not uniquely define the stoichiometries of the important Al-oxalate complexes. The two most likely possibilities are (1) Al(Ox) 33- and Al(Ox) + as the important complexes or (2) Al(OH) 2Ox -1 and Al(OH)Ox 0. For the first speciation, the observed solubilities constrain the values for the log of the dissociation constants for Al(Ox) 33- and Al(Ox) + to be -18.1 ± 0.5 and -8.3 ± 0.7, respectively. If Al(OH) 2Ox - and Al(OH)Ox 0 are dominant, the data define the dissociation constants for these complexes to be -24.5 ± 0.2 and -15.8 ± 0.5, respectively. Thermodynamic modeling, using these results, indicates that Al-oxalate complexation can dominate the Al budget of formation waters. Calculations suggest that with Al(Ox) 33- and Al(Ox) + dominant, the presence of a significant concentration of Ca (on the order of 200-300 ppm) does not imply a sequestering of oxalate by a Ca-oxalate precipitate. However, if Al(OH)Ox 0 and Al(OH) 2Ox - are the dominant Al-oxalate complexes, Ca-oxalate precipitation will occur at much lower Ca concentrations.

  12. Application of silica nanoparticles for increased silica availability in maize

    NASA Astrophysics Data System (ADS)

    Suriyaprabha, R.; Karunakaran, G.; Yuvakkumar, R.; Prabu, P.; Rajendran, V.; Kannan, N.

    2013-02-01

    Silica nanoparticles were extracted from rice husk and characterised comprehensively. The synthesised silica powders were amorphous in size with 99.7% purity (20-40 nm). Nanosilica was amended with red soil at 15 kg ha-1 along with micron silica. The influence of nanoscale on silica uptake, accumulation and nutritional variations in maize roots were evaluated through the studies such as root sectioning, elemental analysis and physiological parameters (root length and silica content) and compared with micron silica and control. Nanosilica treated soil reveals enhanced silica uptake and elongated roots which make the plant to resist in stress conditions like drought.

  13. 21 CFR 584.700 - Hydrophobic silicas.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...: (i) Amorphous fumed hydrophobic silica: Not less than 99.0 percent silicon dioxide after ignition... dichlorodimethylsilane. (ii) Precipated hydrophobic silica: Not less than 94.0 percent silicon dioxide after...

  14. 21 CFR 584.700 - Hydrophobic silicas.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Hydrophobic silicas. 584.700 Section 584.700 Food... DRINKING WATER OF ANIMALS Listing of Specific Substances Affirmed as GRAS § 584.700 Hydrophobic silicas. (a) Product. Amorphous fumed hydrophobic silica or precipitated hydrophobic silica (CAS Reg. No....

  15. 21 CFR 584.700 - Hydrophobic silicas.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Hydrophobic silicas. 584.700 Section 584.700 Food... DRINKING WATER OF ANIMALS Listing of Specific Substances Affirmed as GRAS § 584.700 Hydrophobic silicas. (a) Product. Amorphous fumed hydrophobic silica or precipitated hydrophobic silica (CAS Reg. No....

  16. 21 CFR 584.700 - Hydrophobic silicas.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Hydrophobic silicas. 584.700 Section 584.700 Food... DRINKING WATER OF ANIMALS Listing of Specific Substances Affirmed as GRAS § 584.700 Hydrophobic silicas. (a) Product. Amorphous fumed hydrophobic silica or precipitated hydrophobic silica (CAS Reg. No....

  17. 21 CFR 584.700 - Hydrophobic silicas.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Hydrophobic silicas. 584.700 Section 584.700 Food... DRINKING WATER OF ANIMALS Listing of Specific Substances Affirmed as GRAS § 584.700 Hydrophobic silicas. (a) Product. Amorphous fumed hydrophobic silica or precipitated hydrophobic silica (CAS Reg. No....

  18. Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application

    NASA Astrophysics Data System (ADS)

    Zhao, Wangen; Pan, Daocheng; Liu, Shengzhong (Frank)

    2016-05-01

    Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm2 without an anti-reflection layer.Cu2ZnSn(S,Se)4 (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe2 as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS2 : GeSe2 used. In addition, the Cu2Zn(Sn,Ge)(S,Se)4 thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm2 without an anti-reflection layer. Electronic supplementary information (ESI) available: The XRD patterns, chemical component analysis, top-view and cross-sectional images, and XPS of CZTGSSe thin films with different Ge content are exhibited. See DOI: 10.1039/c6nr00959j

  19. Synthesis and photoluminescence properties of aligned Zn{sub 2}GeO{sub 4} coated ZnO nanorods and Ge doped ZnO nanocombs

    SciTech Connect

    Su Yong; Meng Xia Chen Yiqing; Li Sen; Zhou Qingtao; Liang Xuemei; Feng Yi

    2008-07-01

    Aligned Zn{sub 2}GeO{sub 4} coated ZnO nanorods and Ge doped ZnO nanocombs were synthesized on a silicon substrate by a simple thermal evaporation method. The structure and morphology of the as-synthesized nanostructure were characterized using scanning electron microscopy and transmission electron microscopy. The growth of aligned Zn{sub 2}GeO{sub 4} coated ZnO nanorods and Ge doped ZnO nanocombs follows a vapor-solid (VS) process. Photoluminescence properties were also investigated at room temperature. The photoluminescence spectrum reveals the nanostructures have a sharp ultraviolet luminescence peak centered at 382 nm and a broad green luminescence peak centered at about 494 nm.

  20. Structural Modelling of Two Dimensional Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Kumar, Avishek

    The continuous random network (CRN) model of network glasses is widely accepted as a model for materials such as vitreous silica and amorphous silicon. Although it has been more than eighty years since the proposal of the CRN, there has not been conclusive experimental evidence of the structure of glasses and amorphous materials. This has now changed with the advent of two-dimensional amorphous materials. Now, not only the distribution of rings but the actual atomic ring structure can be imaged in real space, allowing for greater charicterization of these types of networks. This dissertation reports the first work done on the modelling of amorphous graphene and vitreous silica bilayers. Models of amorphous graphene have been created using a Monte Carlo bond-switching method and MD method. Vitreous silica bilayers have been constructed using models of amorphous graphene and the ring statistics of silica bilayers has been studied.

  1. Pack cementation Cr-Al coating of steels and Ge-doped silicide coating of Cr-Nb alloy

    SciTech Connect

    He, Y.R.; Zheng, M.H.; Rapp, R.A.

    1995-08-01

    Carbon steels or low-alloy steels used in utility boilers, heat exchangers, petrochemical plants and coal gasification systems are subjected to high temperature corrosion attack such as oxidation, sulfidation and hot corrosion. The pack cementation coating process has proven to be an economical and effective method to enhance the corrosion resistance by modifying the surface composition of steels. With the aid of a computer program, STEPSOL, pack cementation conditions to produce a ferrite Cr-Al diffusion coating on carbon-containing steels by using elemental Cr and Al powders have been calculated and experimentally verified. The cyclic oxidation kinetics for the Cr-Al coated steels are presented. Chromium silicide can maintain high oxidation resistance up to 1100{degrees}C by forming a SiO{sub 2} protective scale. Previous studies at Ohio State University have shown that the cyclic oxidation resistance of MOSi{sub 2} and TiSi{sub 2} can be further improved by Ge addition introduced during coating growth. The halide-activated pack cementation process was modified to produce a Ge-doped silicide diffusion coating in a single processing step for the ORNL-developed Cr-Nb advanced intermetallic alloy. The oxidation behavior of the silicide-coated Cr-Nb alloy was excellent: weight gain of about 1 mg/cm{sup 2} upon oxidation at 1100{degrees}C in air for 100 hours.

  2. Surficial Siloxane-to-Silanol Interconversion during Room-Temperature Hydration/Dehydration of Amorphous Silica Films Observed by ATR-IR and TIR-Raman Spectroscopy.

    PubMed

    Warring, Suzanne L; Beattie, David A; McQuillan, A James

    2016-02-16

    Silica has been frequently studied using infrared and Raman spectroscopy due to its importance in many practical contexts where its surface chemistry plays a vital role. The majority of these studies have utilized chemical-vapor-deposited films in vacuo after high-temperature calcination. However, room-temperature hydration and dehydration of thin silica particle films has not been well characterized in spite of the importance of such films as substrates for polymer and surfactant adsorption. The present study has utilized ATR-IR spectroscopy and thin silica particle films exposed to varying humidity to clearly show reversible conversion between surface siloxanes and hydrogen-bonded silanols without the need for semiempirical peak deconvolution. The IR spectra from corresponding hydration experiments on deuterated silica films has confirmed the vibrational mode assignments. The variation of humidity over silica films formed from silica suspensions of differing pH gave IR spectra consistent with the change in the relative populations of siloxide to silanol surface groups. In addition, total internal reflection Raman spectroscopy has been used to provide further evidence of room-temperature dehydroxylation, with spectral evidence for the presence of three-membered siloxane rings when films are dehydrated under argon. The confirmation of room-temperature siloxane-to-silanol interconversion is expected to benefit understanding in many silica surface chemical contexts. PMID:26804934

  3. Pressure-induced amorphizations of silica analogues: A probe of the relationship between order and disorder. Progress report, August 1, 1992--July 31, 1993

    SciTech Connect

    Hammack, W.S.

    1993-02-01

    Purpose of these of high pressure investigations is to determine the relationship between order and disorder in amorphous materials using high pressure techniques were used. High pressure x-ray diffraction, electron transmission microscopy, and Raman scattering. Cornell High Energy Synchrotron Source (CHESS) at Ithaca was used to measure x-ray diffraction patterns using Energy-Dispersive X-ray Diffraction. It was shown that the structural ordering in pressure-amorphized solids can be described as defects in curved-space. High-resolution transmissions electron microscopy showed that pressure-amorphized alpha-quartz lacks periodicity at the atomic level. Study of a silicate mineral shows that pressure-induced amorphizations occur because of an impeded phase transition.

  4. Reactive molecular dynamics simulation on the disintegration of Kapton, POSS polyimide, amorphous silica, and teflon during atomic oxygen impact using the ReaxFF reactive force-field method.

    PubMed

    Rahnamoun, A; van Duin, A C T

    2014-04-17

    Atomic oxygen (AO) is the most abundant element in the low Earth orbit (LEO). It is the result of the dissociation of molecular oxygen by ultraviolet radiation from the sun. In the LEO, it collides with the materials used on spacecraft surfaces and causes degradation of these materials. The degradation of the materials on the surface of spacecrafts at LEO has been a significant problem for a long time. Kapton polyimide, polyhedral oligomeric silsesquioxane (POSS), silica, and Teflon are the materials extensively used in spacecraft industry, and like many other materials used in spacecraft industry, AO collision degradation is an important issue in their applications on spacecrafts. To investigate the surface chemistry of these materials in exposure to space AO, a computational chemical evaluation of the Kapton polyimide, POSS, amorphous silica, and Teflon was performed in separate simulations under similar conditions. For performing these simulations, the ReaxFF reactive force-field program was used, which provides the computational speed required to perform molecular dynamics (MD) simulations on system sizes sufficiently large to describe the full chemistry of the reactions. Using these simulations, the effects of AO impact on different materials and the role of impact energies, the content of material, and temperature of material on the behavior of the materials are studied. The ReaxFF results indicate that Kapton is less resistant than Teflon toward AO damage. These results are in good agreement with experiment. These simulations indicate that the amorphous silica shows the highest stability among these materials before the start of the highly exothermic silicon oxidation. We have verified that adding silicon to the bulk of the Kapton structure enhances the stability of the Kapton against AO impact. Our canonical MD simulations demonstrate that an increase in the heat transfer in materials during AO impact can provide a considerable decrease in the

  5. Conversion of geothermal waste to commercial products including silica

    DOEpatents

    Premuzic, Eugene T.; Lin, Mow S.

    2003-01-01

    A process for the treatment of geothermal residue includes contacting the pigmented amorphous silica-containing component with a depigmenting reagent one or more times to depigment the silica and produce a mixture containing depigmented amorphous silica and depigmenting reagent containing pigment material; separating the depigmented amorphous silica and from the depigmenting reagent to yield depigmented amorphous silica. Before or after the depigmenting contacting, the geothermal residue or depigmented silica can be treated with a metal solubilizing agent to produce another mixture containing pigmented or unpigmented amorphous silica-containing component and a solubilized metal-containing component; separating these components from each other to produce an amorphous silica product substantially devoid of metals and at least partially devoid of pigment. The amorphous silica product can be neutralized and thereafter dried at a temperature from about 25.degree. C. to 300.degree. C. The morphology of the silica product can be varied through the process conditions including sequence contacting steps, pH of depigmenting reagent, neutralization and drying conditions to tailor the amorphous silica for commercial use in products including filler for paint, paper, rubber and polymers, and chromatographic material.

  6. Simultaneous aluminizing and chromizing of steels to form (Fe,Cr){sub 3}Al coatings and Ge-doped silicide coatings of Cr-Zr base alloys

    SciTech Connect

    Zheng, M.; He, Y.R.; Rapp, R.A.

    1997-12-01

    A halide-activated cementation pack involving elemental Al and Cr powders has been used to achieve surface compositions of approximately Fe{sub 3}Al plus several percent Cr for low alloy steels (T11, T2 and T22) and medium carbon steel (1045 steel). A two-step treatment at 925 C and 1150 C yields the codeposition and diffusion of aluminum and chromium to form dense and uniform ferrite coatings of about 400 {micro}m thickness, while preventing the formation of a blocking chromium carbide at the substrate surfaces. Upon cyclic oxidation in air at 700 C, the coated steel exhibits a negligible 0.085 mg/cm{sup 2} weight gain for 1900 one-hour cycles. Virtually no attack was observed on coated steels tested at ABB in simulated boiler atmospheres at 500 C for 500 hours. But coatings with a surface composition of only 8 wt% Al and 6 wt% Cr suffered some sulfidation attack in simulated boiler atmospheres at temperatures higher than 500 C for 1000 hours. Two developmental Cr-Zr based Laves phase alloys (CN129-2 and CN117(Z)) were silicide/germanide coated. The cross-sections of the Ge-doped silicide coatings closely mimicked the microstructure of the substrate alloys. Cyclic oxidation in air at 1100 C showed that the Ge-doped silicide coating greatly improved the oxidation resistance of the Cr-Zr based alloys.

  7. A novel solid-state NMR method for the investigation of trivalent lanthanide sorption on amorphous silica at low surface loadings.

    PubMed

    Mason, H E; Begg, J D; Maxwell, R S; Kersting, A B; Zavarin, M

    2016-07-13

    The modelling of radionuclide transport in the subsurface depends on a comprehensive understanding of their interactions with mineral surfaces. Spectroscopic techniques provide important insight into these processes directly, but at high concentrations are sometimes hindered by safety concerns and limited solubilities of many radionuclides, especially the actinides. Here we use Eu(iii) as a surrogate for trivalent actinide species, and study Eu(iii) sorption on the silica surface at pH 5 where sorption is fairly limited. We have applied a novel, surface selective solid-state nuclear magnetic resonance (NMR) technique to provide information about Eu binding at the silica surface at estimated surface loadings ranging from 0.1 to 3 nmol m(-2) (<0.1% surface loading). The NMR results show that inner sphere Eu(iii) complexes are evenly distributed across the silica surface at all concentrations, but that at the highest surface loadings there are indications that precipitates may form. These results illustrate that this NMR technique may be applied in solubility-limited systems to differentiate between adsorption and precipitation to better understand the interactions of radionuclides at solid surfaces. PMID:27291345

  8. Removal of dissolved and colloidal silica

    DOEpatents

    Midkiff, William S.

    2002-01-01

    Small amorphous silica particles are used to provide a relatively large surface area upon which silica will preferentially adsorb, thereby preventing or substantially reducing scaling caused by deposition of silica on evaporative cooling tower components, especially heat exchange surfaces. The silica spheres are contacted by the cooling tower water in a sidestream reactor, then separated using gravity separation, microfiltration, vacuum filtration, or other suitable separation technology. Cooling tower modifications for implementing the invention process have been designed.

  9. Kinetics of silica polymerization

    SciTech Connect

    Weres, O.; Yee, A.; Tsao, L.

    1980-05-01

    The polymerization of silicic acid in geothermal brine-like aqueous solutions to produce amorphous silica in colloidal form has been studied experimentally and theoretically. A large amount of high quality experimental data has been generated over the temperature rang 23 to 100{sup 0}C. Wide ranges of dissolved silica concentration, pH, and sodium chloride concentration were covered. The catalytic effects of fluoride and the reaction inhibiting effects of aluminum and boron were studied also. Two basic processes have been separately studied: the formation of new colloidal particles by the homogeneous nucleation process and the deposition of dissolved silica on pre-existing colloidal particles. A rigorous theory of the formation of colloidal particles of amorphous silica by homogeneous nucleation was developed. This theory employs the Lothe-Pound formalism, and is embodied in the computer code SILNUC which quantitatively models the homogeneous nucleation and growth of colloidal silica particles in more than enough detail for practical application. The theory and code were extensively used in planning the experimental work and analyzing the data produced. The code is now complete and running in its final form. It is capable of reproducing most of the experimental results to within experimental error. It is also capable of extrapolation to experimentally inaccessible conditions, i.e., high temperatures, rapidly varying temperature and pH, etc.

  10. The destruction of quartz, amorphous silica minerals, and feldspars in model experiments and in soils: Possible mechanisms, rates, and diagnostics (the analysis of literature)

    NASA Astrophysics Data System (ADS)

    Sokolova, T. A.

    2013-01-01

    The dissolution of quartz and amorphous SiO2 proceeds via the adsorption of water molecules on the surface of these minerals with the further formation of four silanol groups around the silicon atom and the detachment of the molecules of orthosilicic acid from the surface. The rates of quartz dissolution at pH 7 and 3 constitute 10-15.72 and 10-16.12 mol/m2 s, respectively. They increase by three orders of magnitude upon the rise in pH from 7 to 10; they also increase in the solutions of strong electrolytes and in the presence of the anions of polybasic organic acids. The dissolution of feldspars begins from the release of alkali metals and calcium from the surface of crystal lattices of these minerals into the solution in the course of the cation exchange reaction. This is a fast process, and it does not control the rate of the feldspar dissolution that depends on the concentrations of protonated (in the acid medium) and deprotonated (in the alkaline medium) complexes with participation of the surface Si-O-Si and Al-O-Si groups of the mineral lattices. The rate of dissolution of K-Na feldspars decreases from n × 10-11 to n × 10-12 mol/m2 s upon the rise in pH from 3 to 5; it also increases in the plagioclase series with an increase in the portion of anorthite molecules and in the presence of the anions of polybasic organic acids in the solution. The rate of dissolution of feldspars in the model experiments is by 1-3 orders of magnitude higher than that obtained by different methods for native soils. This may be related to the adequacy of determination of the specific surface and its changes with time in native soils.

  11. Silica in alkaline brines

    USGS Publications Warehouse

    Jones, B.F.; Rettig, S.L.; Eugster, H.P.

    1967-01-01

    Analysis of sodium carbonate-bicarbonate brines from closed basins in volcanic terranes of Oregon and Kenya reveals silica contents of up to 2700 parts per million at pH's higher than 10. These high concentrations of SiO 2 can be attributed to reaction of waters with silicates, and subsequent evaporative concentration accompanied by a rise in pH. Supersaturation with respect to amorphous silica may occur and persist for brines that are out of contact with silicate muds and undersaturated with respect to trona; correlation of SiO2 with concentration of Na and total CO2 support this interpretation. Addition of moredilute waters to alkaline brines may lower the pH and cause inorganic precipitation of substantial amounts of silica.

  12. Second harmonic generation from Ge doped SiO{sub 2} (Ge{sub x}(SiO{sub 2}){sub 1−x}) thin films grown by sputtering

    SciTech Connect

    Kawamura, Ibuki; Imakita, Kenji; Fujii, Minoru; Hayashi, Shinji

    2013-11-11

    Second-order nonlinear optical properties of sputter-deposited Ge-doped SiO{sub 2} thin films were investigated. It was shown that the second-order nonlinearity of SiO{sub 2}, which vanishes in the electric-dipole approximation due to the centrosymmetric structure, can be significantly enhanced by Ge doping. The observed maximum value of d{sub 33} was 8.2 pm/V, which is 4 times larger than d{sub 22} of β-BaB{sub 2}O{sub 4} crystal. Strong correlation was observed between the d{sub eff} values and the electron spin resonance signals arising from GeP{sub b} centers, suggesting that GeP{sub b} centers are the most probable origin of the large second-order nonlinearity.

  13. Water-Silica Force Field for Simulating Nanodevices

    PubMed Central

    Cruz-Chu, Eduardo R.; Aksimentiev, Aleksei; Schulten, Klaus

    2008-01-01

    Amorphous silica is an inorganic material that is central for many nanotechnology appplications, such as nanoelectronics, microfluidics, and nanopore technology. In order to use molecular dynamics (MD) simulations to study the behavior of biomolecules with silica, we developed a force field for amorphous silica surfaces based on their macroscopic wetting properties that is compatible with the CHARMM force field and TIP3P water model. The contact angle of a water droplet with silica served as a criterion to tune the intermolecular interactions. The resulting force field was used to study the permeation of water through silica nanopores, illustrating the influence of the surface topography and the intermolecular parameters on permeation kinetics. We find that minute modeling of the amorphous surface is critical for MD studies, since the particular arrangement of surface atoms controls sensitively electrostatic interactions between silica and water. PMID:17064100

  14. Precipitated silica as flow regulator.

    PubMed

    Müller, Anne-Kathrin; Ruppel, Joanna; Drexel, Claus-Peter; Zimmermann, Ingfried

    2008-08-01

    Flow regulators are added to solid pharmaceutical formulations to improve the flow properties of the powder mixtures. The primary particles of the flow regulators exist in the form of huge agglomerates which are broken down into smaller aggregates during the blending process. These smaller aggregates adsorb at the surface of the solid's grains and thus diminish attractive Van-der-Waals-forces by increasing the roughness of the host's surface. In most cases amorphous silica is used as flow additive but material properties like particle size or bond strength influence the desagglomeration tendency of the agglomerates and thus the flow regulating potency of each silica. For some silica types we will show that the differences in their flow regulating potency are due to the rate and extent by which they are able to cover the surface of the host particles. Binary powder mixtures consisting of a pharmaceutical excipient and an added flow regulator were blended in a Turbula mixer for a defined period of time. As pharmaceutical excipient corn starch was used. The flow regulators were represented by a selection of amorphous silicon dioxide types like a commercial fumed silica and various types of SIPERNAT precipitated silica provided by Evonik-Degussa GmbH, Hanau, Germany. Flowability parameters of the mixtures were characterized by means of a tensile strength tester. The reduction of tensile strength with the blending time can be correlated with an increase in fragmentation of the flow regulator. PMID:18595668

  15. Positron probing of gamma-irradiated Ge doped with P, As, Sb, and Bi: Changes in atomic structures of defects due to n→ p conversion

    NASA Astrophysics Data System (ADS)

    Arutyunov, N. Yu.; Emtsev, V. V.

    2009-12-01

    The emission of the high-momentum annihilation radiation from the subvalent ion core shells and electron density around a positron localized at a vacancy-group-V-impurity atom complexes produced in oxygen-lean Ge doped with P, As, Sb, and Bi by irradiation with 60Co gamma-rays at room temperature have been investigated with the help of the angular correlation of annihilation radiation (ACAR) before and after n→ p conversion. The probability of positron annihilation in the subvalent shells of atoms incorporated in dominant radiation centers was found to be dependent on the ratio of the ion core radii ri(P 5+, As 5+)/ ri(Ge 4+)<1 and ri(Sb 5+, Bi 5+)/ ri(Ge 4+)>1, respectively. In passing from P to As impurity atoms the activation energy Δ Ee of electron emission to be detected by DLTS measurements is increased by ~(+0.017 eV) vs. the increase of the electron density parameter to be reconstructed by ACAR data, Δ r‧ s= r‧ s(As)- r‧ s(P)≈0.029 a.u. On the contrary, in passing from Sb to Bi impurity atoms, Δ Ee value is decreased by ~(-0.028 eV) whereas the electron density parameter rises by Δ r‧ s= r‧ s(Bi)- r‧ s(Sb)≈0.04 a.u. After n→ p conversion a marked decrease in both the electron density and the number of ion cores around the positron points to the fact that the radiation-produced complexes with group-V-impurity atoms (P, As, Sb, Bi) are of a multi-vacancy character. The deep acceptor states in the forbidden gap ( Ev+0.1), ( Ev+0.12), ( Ev+0.16) eV to be attributed to the P-, As-, Sb-, and Bi-containing multi-vacancy centers, respectively, were found to contribute to lessening the electron density around the trapped positron. It is argued that a close similarity of the As 5+ and Ge 4+ ion cores results in a small (but marked) augmentation in the electron density around the positron in As-containing multi-vacancy centers after n→ p conversion. A trend for inward relaxation of the ion cores is observed in all radiation-produced centers

  16. Amorphic complexity

    NASA Astrophysics Data System (ADS)

    Fuhrmann, G.; Gröger, M.; Jäger, T.

    2016-02-01

    We introduce amorphic complexity as a new topological invariant that measures the complexity of dynamical systems in the regime of zero entropy. Its main purpose is to detect the very onset of disorder in the asymptotic behaviour. For instance, it gives positive value to Denjoy examples on the circle and Sturmian subshifts, while being zero for all isometries and Morse-Smale systems. After discussing basic properties and examples, we show that amorphic complexity and the underlying asymptotic separation numbers can be used to distinguish almost automorphic minimal systems from equicontinuous ones. For symbolic systems, amorphic complexity equals the box dimension of the associated Besicovitch space. In this context, we concentrate on regular Toeplitz flows and give a detailed description of the relation to the scaling behaviour of the densities of the p-skeletons. Finally, we take a look at strange non-chaotic attractors appearing in so-called pinched skew product systems. Continuous-time systems, more general group actions and the application to cut and project quasicrystals will be treated in subsequent work.

  17. Fracture-induced amorphization of polycrystalline SiO2 stishovite: a potential platform for toughening in ceramics

    PubMed Central

    Nishiyama, Norimasa; Wakai, Fumihiro; Ohfuji, Hiroaki; Tamenori, Yusuke; Murata, Hidenobu; Taniguchi, Takashi; Matsushita, Masafumi; Takahashi, Manabu; Kulik, Eleonora; Yoshida, Kimiko; Wada, Kouhei; Bednarcik, Jozef; Irifune, Tetsuo

    2014-01-01

    Silicon dioxide has eight stable crystalline phases at conditions of the Earth's rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced amorphization of stishovite that is a high-pressure polymorph. The amorphization accompanies a huge volume expansion of ~100% and occurs in a thin layer whose thickness from the fracture surface is several tens of nanometers. Amorphous silica materials that look like strings or worms were observed on the fracture surfaces. The amount of amorphous silica near the fracture surfaces is positively correlated with indentation fracture toughness. This result indicates that the fracture-induced amorphization causes toughening of stishovite polycrystals. The fracture-induced solid-state amorphization may provide a potential platform for toughening in ceramics. PMID:25297473

  18. The Structure and Properties of Amorphous Indium Oxide

    PubMed Central

    2015-01-01

    A series of In2O3 thin films, ranging from X-ray diffraction amorphous to highly crystalline, were grown on amorphous silica substrates using pulsed laser deposition by varying the film growth temperature. The amorphous-to-crystalline transition and the structure of amorphous In2O3 were investigated by grazing angle X-ray diffraction (GIXRD), Hall transport measurement, high resolution transmission electron microscopy (HRTEM), electron diffraction, extended X-ray absorption fine structure (EXAFS), and ab initio molecular dynamics (MD) liquid-quench simulation. On the basis of excellent agreement between the EXAFS and MD results, a model of the amorphous oxide structure as a network of InOx polyhedra was constructed. Mechanisms for the transport properties observed in the crystalline, amorphous-to-crystalline, and amorphous deposition regions are presented, highlighting a unique structure–property relationship. PMID:25678743

  19. Simulation of Peptide Binding to Silica and Silica Mineralization

    NASA Astrophysics Data System (ADS)

    Emami, F. S.; Heinz, H.; Berry, R. J.; Varshney, V.; Farmer, B. L.; Naik, R. R.; Patwardhan, S. V.; Perry, C. C.

    2009-03-01

    The purpose of this study is to identify the nature of the interaction of peptides with silica surfaces and their effect on mineralization. Classical force fields (CVFF, PCFF) have been extended for silica aiming at the computation of surface properties in quantitative agreement with experiment, taking explicitly into account water molecules, pH, and surface coverage with peptides. We focus on the interaction of five short peptides (pep1, pep4, 82-4, H4, R5) identified by biopanning with regular and amorphous silica surfaces (Q3 and Q2) to understand the relation between peptide sequence and affinity to the surface. Results of the atomistic molecular dynamics simulation indicate adsorption energies, binding constants and conformational changes upon adsorption. The comparison of NMR chemical shifts in solution and on the surface in computation and experiment further aids in understanding the mechanism of binding.

  20. Improvements in geothermal electric power and silica production

    DOEpatents

    Hill, J.H.; Fulk, M.M.

    Electricity is generated from hot geothermal solution by extracting heat therefrom, mineral solids which form in a so cooled geothermal solution are separated to recover minerals and facilitate reinjection of the solution into the ground. The separated solids are treated to recover silica by addition of an acid (amorphous silica precipitates) or a base (other minerals precipitate and soulble silicates are formed which are subsequently precipitated by acid neutralization). If desired, after silica is separated, other minerals can be separated and recovered.

  1. Silica nephropathy.

    PubMed

    Ghahramani, N

    2010-07-01

    Occupational exposure to heavy metals, organic solvents and silica is associated with a variety of renal manifestations. Improved understanding of occupational renal disease provides insight into environmental renal disease, improving knowledge of disease pathogenesis. Silica (SiO2) is an abundant mineral found in sand, rock, and soil. Workers exposed to silica include sandblasters, miners, quarry workers, masons, ceramic workers and glass manufacturers. New cases of silicosis per year have been estimated in the US to be 3600-7300. Exposure to silica has been associated with tubulointerstitial disease, immune-mediated multisystem disease, chronic kidney disease and end-stage renal disease. A rare syndrome of painful, nodular skin lesions has been described in dialysis patients with excessive levels of silicon. Balkan endemic nephropathy is postulated to be due to chronic intoxication with drinking water polluted by silicates released during soil erosion. The mechanism of silica nephrotoxicity is thought to be through direct nephrotoxicity, as well as silica-induced autoimmune diseases such as scleroderma and systemic lupus erythematosus. The renal histopathology varies from focal to crescentic and necrotizing glomerulonephritis with aneurysm formation suggestive of polyarteritis nodosa. The treatment for silica nephrotoxicity is non-specific and depends on the mechanism and stage of the disease. It is quite clear that further research is needed, particularly to elucidate the pathogenesis of silica nephropathy. Considering the importance of diagnosing exposure-related renal disease at early stages, it is imperative to obtain a thorough occupational history in all patients with renal disease, with particular emphasis on exposure to silica, heavy metals, and solvents. PMID:23022796

  2. Amorphous Phases on the Surface of Mars

    NASA Technical Reports Server (NTRS)

    Rampe, E. B.; Morris, R. V.; Ruff, S. W.; Horgan, B.; Dehouck, E.; Achilles, C. N.; Ming, D. W.; Bish, D. L.; Chipera, S. J.

    2014-01-01

    Both primary (volcanic/impact glasses) and secondary (opal/silica, allophane, hisingerite, npOx, S-bearing) amorphous phases appear to be major components of martian surface materials based on orbital and in-situ measurements. A key observation is that whereas regional/global scale amorphous components include altered glass and npOx, local scale amorphous phases include hydrated silica/opal. This suggests widespread alteration at low water-to-rock ratios, perhaps due to snow/ice melt with variable pH, and localized alteration at high water-to-rock ratios. Orbital and in-situ measurements of the regional/global amorphous component on Mars suggests that it is made up of at least three phases: npOx, amorphous silicate (likely altered glass), and an amorphous S-bearing phase. Fundamental questions regarding the composition and the formation of the regional/global amorphous component(s) still remain: Do the phases form locally or have they been homogenized through aeolian activity and derived from the global dust? Is the parent glass volcanic, impact, or both? Are the phases separate or intimately mixed (e.g., as in palagonite)? When did the amorphous phases form? To address the question of source (local and/or global), we need to look for variations in the different phases within the amorphous component through continued modeling of the chemical composition of the amorphous phases in samples from Gale using CheMin and APXS data. If we find variations (e.g., a lack of or enrichment in amorphous silicate in some samples), this may imply a local source for some phases. Furthermore, the chemical composition of the weathering products may give insight into the formation mechanisms of the parent glass (e.g., impact glasses contain higher Al and lower Si [30], so we might expect allophane as a weathering product of impact glass). To address the question of whether these phases are separate or intimately mixed, we need to do laboratory studies of naturally altered samples made

  3. H 3SiOH and F 3SiOH as models for isolated hydroxyl groups of amorphous silica: an ab initio study of the adducts with dihydrogen and carbon monoxide

    NASA Astrophysics Data System (ADS)

    Senchenya, I. N.; Civalleri, B.; Ugliengo, P.; Garrone, E.

    1998-09-01

    Ab initio calculations have been performed at both the self-consistent field (SCF) and the second-order Møller-Plesset (MP2) levels of theory, using both double-zeta plus polarisation functions basis sets and augmented correlation-consistent valence-polarised (aug-cc-pVDZ and aug-cc-pVTZ) ones, to compare the acidic and vibration features and the geometry of H 3SiOH, the model usually adopted for the isolated hydroxyls of silica, with those of its fluorinated analogue, F 3SiOH. Their complexes with H 2 and CO have also been studied. Passing from the MP2/DZP level of computation to MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ levels results in a considerable improvement of calculated data for H 3SiOH and its complexes when compared with experimental data. H 3SiOH is, however, less acidic than isolated hyroxyls of silica. In contrast, the use of F 3SiOH as a model yields an overestimation of the acidic properties; e.g., the stretching O-H mode frequency shifts caused by hydrogen-bond interaction with the base molecules. The combined use of both models may provide guidelines for prediction of the adducts of the isolated hydroxyl of silica with small molecules.

  4. Silica substrate or portion formed from oxidation of monocrystalline silicon

    DOEpatents

    Matzke, Carolyn M.; Rieger, Dennis J.; Ellis, Robert V.

    2003-07-15

    A method is disclosed for forming an inclusion-free silica substrate using a monocrystalline silicon substrate as the starting material and oxidizing the silicon substrate to convert it entirely to silica. The oxidation process is performed from both major surfaces of the silicon substrate using a conventional high-pressure oxidation system. The resulting product is an amorphous silica substrate which is expected to have superior etching characteristics for microfabrication than conventional fused silica substrates. The present invention can also be used to convert only a portion of a monocrystalline silicon substrate to silica by masking the silicon substrate and locally thinning a portion the silicon substrate prior to converting the silicon portion entirely to silica. In this case, the silica formed by oxidizing the thinned portion of the silicon substrate can be used, for example, as a window to provide optical access through the silicon substrate.

  5. Earthquake lubrication and healing explained by amorphous nanosilica

    NASA Astrophysics Data System (ADS)

    Rowe, C. D.; Lamothe, K. G.; Rempe, M.; Andrews, M.; Mitchell, T. M.; Di Toro, G.; White, J. C.

    2015-12-01

    Earthquake slip and rupture propagation require fault strength to decrease during slip. Extreme shear weakening observed in laboratory friction experiments on silica-rich rocks has been explained by the formation of a hydrated amorphous 'silica gel' on the slip surface, but the mode of formation and deformation behavior of this material are not known. In addition, the wear material displays time-dependent strengthening on timescales of hours to days. We performed shearing experiments on chert rocks and analyzed the wear material formed at a range of slip rates from 10-4 - 10-1 m/s. We show by transmission electron microscopy (TEM) and X-ray diffraction that silica lubrication is the result of the formation of amorphous nanopowder rather than a gel. The nanopowder has distinct structure and properties when compared to commercially available amorphous silica nanoparticles, which result from the degree and distribution of hydration and the style of bond strain within particles (observed by Raman spectroscopy and FTIR). The lubrication effect is due to intra-particle plasticity, even at low temperature and interparticle lubrication caused by trapping of water layers between hydrated surfaces. The hours to days timescale of healing may be explained by the natural time-dependent sintering between the hydrated surfaces of the nanopowder. Formation of amorphous silica nanopowders during slip can explain the general characteristics of earthquake ruptures, including the timescales of coseismic weakening and post-seismic healing.

  6. Amorphous metal composites

    DOEpatents

    Byrne, Martin A.; Lupinski, John H.

    1984-01-01

    An improved amorphous metal composite and process of making the composite. The amorphous metal composite comprises amorphous metal (e.g. iron) and a low molecular weight thermosetting polymer binder. The process comprises placing an amorphous metal in particulate form and a thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

  7. DNA Binding to the Silica Surface.

    PubMed

    Shi, Bobo; Shin, Yun Kyung; Hassanali, Ali A; Singer, Sherwin J

    2015-08-27

    We investigate the DNA-silica binding mechanism using molecular dynamics simulations. This system is of technological importance, and also of interest to explore how negatively charged DNA can bind to a silica surface, which is also negatively charged at pH values above its isoelectric point near pH 3. We find that the two major binding mechanisms are attractive interactions between DNA phosphate and surface silanol groups and hydrophobic bonding between DNA base and silica hydrophobic region. Umbrella sampling and the weighted histogram analysis method (WHAM) are used to calculate the free energy surface for detachment of DNA from a binding configuration to a location far from the silica surface. Several factors explain why single-stranded DNA (ssDNA) has been observed to be more strongly attracted to silica than double-stranded (dsDNA): (1) ssDNA is more flexible and therefore able to maximize the number of binding interactions. (2) ssDNA has free unpaired bases to form hydrophobic attachment to silica while dsDNA has to break hydrogen bonds with base partners to get free bases. (3) The linear charge density of dsDNA is twice that of ssDNA. We devise a procedure to approximate the atomic forces between biomolecules and amorphous silica to enable large-scale biomolecule-silica simulations as reported here. PMID:25966319

  8. Silica Transport and Cementation in Quartz Aggregates

    NASA Astrophysics Data System (ADS)

    Pebble, C.; Farver, J.; Onasch, C.; Winslow, D.

    2008-12-01

    Silica transport and cementation in quartz aggregates have been experimentally investigated. Starting materials include a natural quartz arenite (Pocono sandstone), sized clasts of synthetic quartz, and sized grains of disaggregated natural sandstones. Experimental charges consisted of amorphous silica powder (~25 mg), AlCl3 powder (~3 mg), 25 wt% NaCl brine solution (~20 mg), and the starting material (~150 mg). The charges were weld-sealed in gold capsules and run in cold-seal pressure vessels at 300°C to 600°C at 150 MPa confining pressure for up to 4 weeks. Detailed calibrations of the furnaces indicate the maximum temperature variation across the length of the sample charges (3-7mm) was <5°C, and typically <3°C. After the experiments, samples were vacuum impregnated with epoxy containing a blue dye and sawn in half along the long axis of the sample charge. The nature and amount of silica transport and cementation in the samples was determined by a combination of Cathodoluminescence (CL), Light Microscopy (LM), and Scanning Electron Microscopy (SEM). Photomosaics of the samples were collected and the amount of cement, porosity, and average grain sizes were determined by point-counting. The cement was easily recognized from the quartz grains by the difference in luminescence. The experiments indicate that the presence of amorphous silica results in rapid silica cementation in quartz aggregates (e.g., up to 12% cement by volume in 4 weeks at 450°C). The amount of cementation is a function of substrate type, time, temperature, and ionic strength of the brine. The rate of silica transport through the length of the experimental charge appears to be limited by the silica solubility and its rapid depletion by cementation. Although most of the cement was derived from the amorphous silica, evidence for local dissolution-precipitation was observed. The experiments demonstrate that the mobility of silica, and consequent precipitation of cement, does not require a

  9. Three-dimensional fabrication and characterisation of core-shell nano-columns using electron beam patterning of Ge-doped SiO{sub 2}

    SciTech Connect

    Gontard, Lionel C.; Jinschek, Joerg R.; Ou Haiyan; Verbeeck, Jo; Dunin-Borkowski, Rafal E.

    2012-06-25

    A focused electron beam in a scanning transmission electron microscope (STEM) is used to create arrays of core-shell structures in a specimen of amorphous SiO{sub 2} doped with Ge. The same electron microscope is then used to measure the changes that occurred in the specimen in three dimensions using electron tomography. The results show that transformations in insulators that have been subjected to intense irradiation using charged particles can be studied directly in three dimensions. The fabricated structures include core-shell nano-columns, sputtered regions, voids, and clusters.

  10. Nanoparticle-doped radioluminescent silica optical fibers

    NASA Astrophysics Data System (ADS)

    Mrazek, J.; Nikl, M.; Kasik, I.; Podrazky, O.; Aubrecht, J.; Beitlerova, A.

    2014-05-01

    This contribution deals with the preparation and characterization of the silica optical fibers doped by nanocrystalline zinc silicate. The sol-gel approach was employed to prepare colloidal solution of zinc silicate precursors. Prepared sol was thermally treated to form nanocrystalline zinc silicate disperzed inside amorphous silica matrix or soaked inside the porous silica frit deposed inside the silica substrate tube which was collapsed into preform and drawn into optical fiber. Single mode optical fiber with the core diameter 15 μm and outer diamer 125 μm was prepared. Optical and waveguiding properties of the fiber were analyzed. Concentration of the zinc silicate in the fiber was 0.93 at. %. Radioluminescence properties of nanocrystalline zinc silicate powder and of the prepared optical fiber were investigated. The nanoparticle doped samples appear a emission maximum at 390 nm.

  11. Amorphous Computing

    NASA Astrophysics Data System (ADS)

    Sussman, Gerald

    2002-03-01

    agents constructed by engineered cells, but we have few ideas for programming them effectively: How can one engineer prespecified, coherent behavior from the cooperation of immense numbers of unreliable parts that are interconnected in unknown, irregular, and time-varying ways? This is the challenge of Amorphous Computing.

  12. Pulsed amplified spontaneous Raman emission at 2.2 μm in silica-based fiber

    NASA Astrophysics Data System (ADS)

    Jiang, Huawei; Zhang, Lei; Yang, Xuezong; Yu, Ting; Feng, Yan

    2016-04-01

    All-fiber source at 2.2 μm is investigated with amplified spontaneous Raman scattering process in highly Ge-doped silica fiber. By optimizing the gain fiber length, the second-order Raman Stokes light at 2.43 μm is suppressed and 3 W first-order Raman Stokes light at 2.2 μm is obtained with a homemade 2-μm Q-switched Tm3+-doped fiber laser as pump source. The conversion efficiency is 35.9 % from 2.0 to 2.2 μm, and the peak power of the 2.2-μm laser is about 400 W.

  13. Comparison of methods for the measurement of radiation dose distributions in high dose rate (HDR) brachytherapy: Ge-doped optical fiber, EBT3 Gafchromic film, and PRESAGE{sup Registered-Sign} radiochromic plastic

    SciTech Connect

    Palmer, A. L.; Di Pietro, P.; Alobaidli, S.; Issa, F.; Doran, S.; Bradley, D.; Nisbet, A.

    2013-06-15

    Purpose: Dose distribution measurement in clinical high dose rate (HDR) brachytherapy is challenging, because of the high dose gradients, large dose variations, and small scale, but it is essential to verify accurate treatment planning and treatment equipment performance. The authors compare and evaluate three dosimetry systems for potential use in brachytherapy dose distribution measurement: Ge-doped optical fibers, EBT3 Gafchromic film with multichannel analysis, and the radiochromic material PRESAGE{sup Registered-Sign} with optical-CT readout. Methods: Ge-doped SiO{sub 2} fibers with 6 {mu}m active core and 5.0 mm length were sensitivity-batched and their thermoluminescent properties used via conventional heating and annealing cycles. EBT3 Gafchromic film of 30 {mu}m active thickness was calibrated in three color channels using a nominal 6 MV linear accelerator. A 48-bit transmission scanner and advanced multichannel analysis method were utilized to derive dose measurements. Samples of the solid radiochromic polymer PRESAGE{sup Registered-Sign }, 60 mm diameter and 100 mm height, were analyzed with a parallel beam optical CT scanner. Each dosimetry system was used to measure the dose as a function of radial distance from a Co-60 HDR source, with results compared to Monte Carlo TG-43 model data. Each system was then used to measure the dose distribution along one or more lines through typical clinical dose distributions for cervix brachytherapy, with results compared to treatment planning system (TPS) calculations. Purpose-designed test objects constructed of Solid Water and held within a full-scatter water tank were utilized. Results: All three dosimetry systems reproduced the general shape of the isolated source radial dose function and the TPS dose distribution. However, the dynamic range of EBT3 exceeded those of doped optical fibers and PRESAGE{sup Registered-Sign }, and the latter two suffered from unacceptable noise and artifact. For the experimental

  14. Uniform and continuous silica nanocoatings on ZnS phosphors

    NASA Astrophysics Data System (ADS)

    Yuan, Jiongliang

    2008-04-01

    The penetration depth of the primary electrons into amorphous silica, anatase titania, Y2O3, ZnO, In2O3, indium and tin oxides is compared at lower voltages. It shows that amorphous silica has the largest penetration depth, thus the silica coatings will lead to minimal energy loss and maximal cathodoluminescence intensity. Almost uniform and continuous silica coatings on ZnS phosphors have successfully been obtained by a sol-gel method with the catalysis of ammonia. Zeta potential analysis shows that the ZnS phosphors are covered almost completely. An adsorption-catalysis-growth mechanism is suggested, and used to explain other ammonia-catalyzed coating processes.

  15. Generation of crystalline silica from sugarcane burning.

    PubMed

    Le Blond, Jennifer S; Horwell, Claire J; Williamson, Ben J; Oppenheimer, Clive

    2010-07-01

    Sugarcane leaves contain amorphous silica, which may crystallise to form crystalline silica polymorphs (cristobalite or quartz), during commercial sugarcane harvesting where sugarcane plants are burned. Respirable airborne particulate containing these phases may present an occupational health hazard. Following from an earlier pilot study (J. S. Le Blond, B. J. Williamson, C. J. Horwell, A. K. Monro, C. A. Kirk and C. Oppenheimer, Atmos. Environ., 2008, 42, 5558-5565) in which experimental burning of sugarcane leaves yielded crystalline silica, here we report on actual conditions during sugarcane burning on commercial estates, investigate the physico-chemical properties of the cultivated leaves and ash products, and quantify the presence of crystalline silica. Commercially grown raw sugarcane leaf was found to contain up to 1.8 wt% silica, mostly in the form of amorphous silica bodies (with trace impurities e.g., Al, Na, Mg), with only a small amount of quartz. Thermal images taken during several pre-harvest burns recorded temperatures up to 1056 degrees C, which is sufficient for metastable cristobalite formation. No crystalline silica was detected in airborne particulate from pre-harvest burning, collected using a cascade impactor. The sugarcane trash ash formed after pre-harvest burning contained between 10 and 25 wt% SiO(2), mostly in an amorphous form, but with up to 3.5 wt% quartz. Both quartz and cristobalite were identified in the sugarcane bagasse ash (5-15 wt% and 1-3 wt%, respectively) formed in the processing factory. Electron microprobe analysis showed trace impurities of Mg, Al and Fe in the silica particles in the ash. The absence of crystalline silica in the airborne emissions and lack of cristobalite in trash ash suggest that high temperatures during pre-harvest burning were not sustained long enough for cristobalite to form, which is supported by the presence of low temperature sylvite and calcite in the residual ash. The occurrence of quartz and

  16. Crystallization of hollow mesoporous silica nanoparticles.

    PubMed

    Drisko, Glenna L; Carretero-Genevrier, Adrian; Perrot, Alexandre; Gich, Martí; Gàzquez, Jaume; Rodriguez-Carvajal, Juan; Favre, Luc; Grosso, David; Boissière, Cédric; Sanchez, Clément

    2015-03-11

    Complex 3D macrostructured nanoparticles are transformed from amorphous silica into pure polycrystalline α-quartz using catalytic quantities of alkaline earth metals as devitrifying agent. Walls as thin as 10 nm could be crystallized without losing the architecture of the particles. The roles of cation size and the mol% of the incorporated devitrifying agent in crystallization behavior are studied, with Mg(2+), Ca(2+), Sr(2+) and Ba(2+) all producing pure α-quartz under certain conditions. PMID:25503642

  17. A new parameter-free soft-core potential for silica and its application to simulation of silica anomalies

    NASA Astrophysics Data System (ADS)

    Izvekov, Sergei; Rice, Betsy M.

    2015-12-01

    A core-softening of the effective interaction between oxygen atoms in water and silica systems and its role in developing anomalous thermodynamic, transport, and structural properties have been extensively debated. For silica, the progress with addressing these issues has been hampered by a lack of effective interaction models with explicit core-softening. In this work, we present an extension of a two-body soft-core interatomic force field for silica recently reported by us [S. Izvekov and B. M. Rice, J. Chem. Phys. 136(13), 134508 (2012)] to include three-body forces. Similar to two-body interaction terms, the three-body terms are derived using parameter-free force-matching of the interactions from ab initio MD simulations of liquid silica. The derived shape of the O-Si-O three-body potential term affirms the existence of repulsion softening between oxygen atoms at short separations. The new model shows a good performance in simulating liquid, amorphous, and crystalline silica. By comparing the soft-core model and a similar model with the soft-core suppressed, we demonstrate that the topology reorganization within the local tetrahedral network and the O-O core-softening are two competitive mechanisms responsible for anomalous thermodynamic and kinetic behaviors observed in liquid and amorphous silica. The studied anomalies include the temperature of density maximum locus and anomalous diffusivity in liquid silica, and irreversible densification of amorphous silica. We show that the O-O core-softened interaction enhances the observed anomalies primarily through two mechanisms: facilitating the defect driven structural rearrangements of the silica tetrahedral network and modifying the tetrahedral ordering induced interactions toward multiple characteristic scales, the feature which underlies the thermodynamic anomalies.

  18. A new parameter-free soft-core potential for silica and its application to simulation of silica anomalies

    SciTech Connect

    Izvekov, Sergei Rice, Betsy M.

    2015-12-28

    A core-softening of the effective interaction between oxygen atoms in water and silica systems and its role in developing anomalous thermodynamic, transport, and structural properties have been extensively debated. For silica, the progress with addressing these issues has been hampered by a lack of effective interaction models with explicit core-softening. In this work, we present an extension of a two-body soft-core interatomic force field for silica recently reported by us [S. Izvekov and B. M. Rice, J. Chem. Phys. 136(13), 134508 (2012)] to include three-body forces. Similar to two-body interaction terms, the three-body terms are derived using parameter-free force-matching of the interactions from ab initio MD simulations of liquid silica. The derived shape of the O–Si–O three-body potential term affirms the existence of repulsion softening between oxygen atoms at short separations. The new model shows a good performance in simulating liquid, amorphous, and crystalline silica. By comparing the soft-core model and a similar model with the soft-core suppressed, we demonstrate that the topology reorganization within the local tetrahedral network and the O–O core-softening are two competitive mechanisms responsible for anomalous thermodynamic and kinetic behaviors observed in liquid and amorphous silica. The studied anomalies include the temperature of density maximum locus and anomalous diffusivity in liquid silica, and irreversible densification of amorphous silica. We show that the O–O core-softened interaction enhances the observed anomalies primarily through two mechanisms: facilitating the defect driven structural rearrangements of the silica tetrahedral network and modifying the tetrahedral ordering induced interactions toward multiple characteristic scales, the feature which underlies the thermodynamic anomalies.

  19. A new parameter-free soft-core potential for silica and its application to simulation of silica anomalies.

    PubMed

    Izvekov, Sergei; Rice, Betsy M

    2015-12-28

    A core-softening of the effective interaction between oxygen atoms in water and silica systems and its role in developing anomalous thermodynamic, transport, and structural properties have been extensively debated. For silica, the progress with addressing these issues has been hampered by a lack of effective interaction models with explicit core-softening. In this work, we present an extension of a two-body soft-core interatomic force field for silica recently reported by us [S. Izvekov and B. M. Rice, J. Chem. Phys. 136(13), 134508 (2012)] to include three-body forces. Similar to two-body interaction terms, the three-body terms are derived using parameter-free force-matching of the interactions from ab initio MD simulations of liquid silica. The derived shape of the O-Si-O three-body potential term affirms the existence of repulsion softening between oxygen atoms at short separations. The new model shows a good performance in simulating liquid, amorphous, and crystalline silica. By comparing the soft-core model and a similar model with the soft-core suppressed, we demonstrate that the topology reorganization within the local tetrahedral network and the O-O core-softening are two competitive mechanisms responsible for anomalous thermodynamic and kinetic behaviors observed in liquid and amorphous silica. The studied anomalies include the temperature of density maximum locus and anomalous diffusivity in liquid silica, and irreversible densification of amorphous silica. We show that the O-O core-softened interaction enhances the observed anomalies primarily through two mechanisms: facilitating the defect driven structural rearrangements of the silica tetrahedral network and modifying the tetrahedral ordering induced interactions toward multiple characteristic scales, the feature which underlies the thermodynamic anomalies. PMID:26723691

  20. Nanocrystal dispersed amorphous alloys

    NASA Technical Reports Server (NTRS)

    Perepezko, John H. (Inventor); Allen, Donald R. (Inventor); Foley, James C. (Inventor)

    2001-01-01

    Compositions and methods for obtaining nanocrystal dispersed amorphous alloys are described. A composition includes an amorphous matrix forming element (e.g., Al or Fe); at least one transition metal element; and at least one crystallizing agent that is insoluble in the resulting amorphous matrix. During devitrification, the crystallizing agent causes the formation of a high density nanocrystal dispersion. The compositions and methods provide advantages in that materials with superior properties are provided.

  1. New transformations between crystalline and amorphous ice

    NASA Technical Reports Server (NTRS)

    Hemley, R. J.; Chen, L. C.; Mao, H. K.

    1989-01-01

    High-pressure optical and spectroscopic techniques were used to obtain directly the ice I(h) - hda-ice transformation in a diamond-anvil cell, and the stability of the amorphous form is examined as functions of pressure and temperature. It is demonstrated that hda-ice transforms abruptly at 4 GPa and 77 K to a crystalline phase close in structure to orientationally disordered ice-VII and to a more highly ordered, ice-VIII-like structure at higher temperatures. This is the first time that an amorphous solid is observed to convert to a crystalline solid at low temperatures by compression alone. Phase transitions of this type may be relevant on icy planetary satellites, and there may also be implications for the high-pressure behavior of silica.

  2. Size- and structure-dependent toxicity of silica particulates

    NASA Astrophysics Data System (ADS)

    Hanada, Sanshiro; Miyaoi, Kenichi; Hoshino, Akiyoshi; Inasawa, Susumu; Yamaguchi, Yukio; Yamamoto, Kenji

    2011-03-01

    Nano- and micro-particulates firmly attach with the surface of various biological systems. In some chronic pulmonary disease such as asbestosis and silicosis, causative particulates will induce chronic inflammatory disorder, followed by poor prognosis diseases. However, nano- and micro-scale specific toxicity of silica particulates is not well examined enough to recognize the risk of nano- and micro-particulates from the clinical aspect. To clarify the effect of the size and structure of silica particulates on the cellular damage and the biological response, we assessed the cytotoxicity of the various kinds of silica particles including amorphous and crystalline silica, in mouse alveolar macrophage culture, focusing on the fibrotic and inflammatory response. Our study showed that the cytotoxicity, which depends on the particle size and surface area, is correlated with their inflammatory response. By contrast, production of TGF-β, which is one of the fibrotic agents in lung, by addition of crystal silica was much higher than that of amorphous silica. We conclude that fibrosis and inflammation are induced at different phases and that the size- and structure-differences of silica particulates affect the both biological responses, caused by surface activity, radical species, and so on.

  3. Facile Fabrication of Ultrafine Hollow Silica and Magnetic Hollow Silica Nanoparticles by a Dual-Templating Approach

    NASA Astrophysics Data System (ADS)

    Wu, Wei; Xiao, Xiangheng; Zhang, Shaofeng; Fan, Lixia; Peng, Tangchao; Ren, Feng; Jiang, Changzhong

    2010-01-01

    The development of synthetic process for hollow silica materials is an issue of considerable topical interest. While a number of chemical routes are available and are extensively used, the diameter of hollow silica often large than 50 nm. Here, we report on a facial route to synthesis ultrafine hollow silica nanoparticles (the diameter of ca. 24 nm) with high surface area by using cetyltrimethylammmonium bromide (CTAB) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as co-templates and subsequent annealing treatment. When the hollow magnetite nanoparticles were introduced into the reaction, the ultrafine magnetic hollow silica nanoparticles with the diameter of ca. 32 nm were obtained correspondingly. Transmission electron microscopy studies confirm that the nanoparticles are composed of amorphous silica and that the majority of them are hollow.

  4. In vitro comet and micronucleus assays do not predict morphological transforming effects of silica particles in Syrian Hamster Embryo cells.

    PubMed

    Darne, Christian; Coulais, Catherine; Terzetti, Francine; Fontana, Caroline; Binet, Stéphane; Gaté, Laurent; Guichard, Yves

    2016-01-15

    Crystalline silica particles and asbestos have both been classified as carcinogenic by the International Agency for Research on Cancer (IARC). However, because of the limited data available, amorphous silica was not classifiable. In vitro, the carcinogenic potential of natural crystalline and amorphous silica particles has been revealed by the Syrian Hamster Embryo (SHE) cell transformation assay. On the other hand, the genotoxic potential of those substances has not been investigated in SHE cells. And yet, genotoxicity assays are commonly used for hazard evaluation and they are often used as in vitro assays of reference to predict a possible carcinogenic potential. The main objective of this study was to compare the genotoxic potential and the carcinogenic potential of different crystalline and amorphous silica particles in SHE cells. Three silica samples of different crystallinity were used: natural amorphous silica, partially crystallized silica and quartz silica particles. Their genotoxicity were tested through the in vitro micronucleus assay and the comet assay in SHE, and their carcinogenic potential through the SHE transformation assay. In addition, silica samples were also tested with the same genotoxicity assays in V79 hamster-lung cells, a common in vitro model for particle exposure. Results obtained in the micronucleus and the comet assays show that none of the silica was capable of inducing genotoxic effects in SHE cells and only the amorphous silica induced genotoxic effects in V79 cells. However in the SHE cell transformation assays, the partially crystallized and quartz silica were able to induce morphological cell transformation. Together, these data suggest that, in vitro, the short-term genotoxic assays alone are not sufficient to predict the hazard and the carcinogenic potential of this type of particles; SHE transformation assay appears a more reliable tool for this purpose and should be included in the "in vitro battery assays" for hazard

  5. Hydrogen in amorphous silicon

    SciTech Connect

    Peercy, P. S.

    1980-01-01

    The structural aspects of amorphous silicon and the role of hydrogen in this structure are reviewed with emphasis on ion implantation studies. In amorphous silicon produced by Si ion implantation of crystalline silicon, the material reconstructs into a metastable amorphous structure which has optical and electrical properties qualitatively similar to the corresponding properties in high-purity evaporated amorphous silicon. Hydrogen studies further indicate that these structures will accomodate less than or equal to 5 at.% hydrogen and this hydrogen is bonded predominantly in a monohydride (SiH/sub 1/) site. Larger hydrogen concentrations than this can be achieved under certain conditions, but the excess hydrogen may be attributed to defects and voids in the material. Similarly, glow discharge or sputter deposited amorphous silicon has more desirable electrical and optical properties when the material is prepared with low hydrogen concentration and monohydride bonding. Results of structural studies and hydrogen incorporation in amorphous silicon were discussed relative to the different models proposed for amorphous silicon.

  6. Characterization of zirconia- and niobia-silica mixture coatings produced by ion-beam sputtering

    SciTech Connect

    Melninkaitis, Andrius; Tolenis, Tomas; Mazule, Lina; Mirauskas, Julius; Sirutkaitis, Valdas; Mangote, Benoit; Fu Xinghai; Zerrad, Myriam; Gallais, Laurent; Commandre, Mireille; Kicas, Simonas; Drazdys, Ramutis

    2011-03-20

    ZrO{sub 2}-SiO{sub 2} and Nb{sub 2}O{sub 5}-SiO{sub 2} mixture coatings as well as those of pure zirconia (ZrO{sub 2}), niobia (Nb{sub 2}O{sub 5}), and silica (SiO{sub 2}) deposited by ion-beam sputtering were investigated. Refractive-index dispersions, bandgaps, and volumetric fractions of materials in mixed coatings were analyzed from spectrophotometric data. Optical scattering, surface roughness, nanostructure, and optical resistance were also studied. Zirconia-silica mixtures experience the transition from crystalline to amorphous phase by increasing the content of SiO{sub 2}. This also results in reduced surface roughness. All niobia and silica coatings and their mixtures were amorphous. The obtained laser-induced damage thresholds in the subpicosecond range also correlates with respect to the silica content in both zirconia- and niobia-silica mixtures.

  7. Hard magnetism in structurally engineered silica nanocomposite.

    PubMed

    Song, Hyon-Min; Zink, Jeffrey I

    2016-09-21

    Creation of structural complexity by simple experimental control will be an attractive approach for the preparation of nanomaterials, as a classical bottom-up method is supplemented by a more efficient and more direct artificial engineering method. In this study, structural manipulation of MCM-41 type mesoporous silica is investigated by generating and imbedding hard magnetic CoFe2O4 nanoparticles into mesoporous silica. Depending on the heating rate and target temperature, mesoporous silica undergoes a transformation in shape to form hollow silica, framed silica with interior voids, or melted silica with intact mesostructures. Magnetism is governed by the major CoFe2O4 phase, and it is affected by antiferromagnetic hematite (α-Fe2O3) and olivine-type cobalt silicate (Co2SiO4), as seen in its paramagnetic behavior at the annealing temperature of 430 °C. The early formation of Co2SiO4 than what is usually observed implies the effect of the partial substitution of Fe in the sites of Co. Under slow heating (2.5 °C min(-1)) mesostructures are preserved, but with significantly smaller mesopores (d100 = 1.5 nm). In addition, nonstoichiometric CoxFe1-xO with metal vacancies at 600 °C, and spinel Co3O4 at 700 °C accompany major CoFe2O4. The amorphous nature of silica matrix is thought to contribute significantly to these structurally diverse and rich phases, enabled by off-stoichiometry between Si and O, and accelerated by the diffusion of metal cations into SiO4 polyhedra at an elevated temperature. PMID:27537252

  8. Evaluation of silica nanoparticle toxicity after topical exposure for 90 days

    PubMed Central

    Ryu, Hwa Jung; Seong, Nak-won; So, Byoung Joon; Seo, Heung-sik; Kim, Jun-ho; Hong, Jeong-Sup; Park, Myeong-kyu; Kim, Min-Seok; Kim, Yu-Ri; Cho, Kyu-Bong; Seo, Mu Yeb; Kim, Meyoung-Kon; Maeng, Eun Ho; Son, Sang Wook

    2014-01-01

    Silica is a very common material that can be found in both crystalline and amorphous forms. Well-known toxicities of the lung can occur after exposure to the crystalline form of silica. However, the toxicities of the amorphous form of silica have not been thoroughly studied. The majority of in vivo studies of amorphous silica nanoparticles (NPs) were performed using an inhalation exposure method. Since silica NPs can be commonly administered through the skin, a study of dermal silica toxicity was necessary to determine any harmful effects from dermal exposures. The present study focused on the results of systemic toxicity after applying 20 nm colloidal silica NPs on rat skin for 90 days, in accordance with the Organization for Economic Cooperation and Development test guideline 411 with a good laboratory practice system. Unlike the inhalation route or gastrointestinal route, the contact of silica NPs through skin did not result in any toxicity or any change in internal organs up to a dose of 2,000 mg/kg in rats. PMID:25565831

  9. Evaluation of silica nanoparticle toxicity after topical exposure for 90 days.

    PubMed

    Ryu, Hwa Jung; Seong, Nak-won; So, Byoung Joon; Seo, Heung-sik; Kim, Jun-ho; Hong, Jeong-Sup; Park, Myeong-kyu; Kim, Min-Seok; Kim, Yu-Ri; Cho, Kyu-Bong; Seo, Mu Yeb; Kim, Meyoung-Kon; Maeng, Eun Ho; Son, Sang Wook

    2014-01-01

    Silica is a very common material that can be found in both crystalline and amorphous forms. Well-known toxicities of the lung can occur after exposure to the crystalline form of silica. However, the toxicities of the amorphous form of silica have not been thoroughly studied. The majority of in vivo studies of amorphous silica nanoparticles (NPs) were performed using an inhalation exposure method. Since silica NPs can be commonly administered through the skin, a study of dermal silica toxicity was necessary to determine any harmful effects from dermal exposures. The present study focused on the results of systemic toxicity after applying 20 nm colloidal silica NPs on rat skin for 90 days, in accordance with the Organization for Economic Cooperation and Development test guideline 411 with a good laboratory practice system. Unlike the inhalation route or gastrointestinal route, the contact of silica NPs through skin did not result in any toxicity or any change in internal organs up to a dose of 2,000 mg/kg in rats. PMID:25565831

  10. Ordered nanoporous silica as carriers for improved delivery of water insoluble drugs: a comparative study between three dimensional and two dimensional macroporous silica

    PubMed Central

    Wang, Ying; Zhao, Qinfu; Hu, Yanchen; Sun, Lizhang; Bai, Ling; Jiang, Tongying; Wang, Siling

    2013-01-01

    The goal of the present study was to compare the drug release properties and stability of the nanoporous silica with different pore architectures as a matrix for improved delivery of poorly soluble drugs. For this purpose, three dimensional ordered macroporous (3DOM) silica with 3D continuous and interconnected macropores of different sizes (200 nm and 500 nm) and classic mesoporous silica (ie, Mobil Composition of Matter [MCM]-41 and Santa Barbara Amorphous [SBA]-15) with well-ordered two dimensional (2D) cylindrical mesopores were successfully fabricated and then loaded with the model drug indomethacin (IMC) via the solvent deposition method. Scanning electron microscopy (SEM), N2 adsorption, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were applied to systematically characterize all IMC-loaded nanoporous silica formulations, evidencing the successful inclusion of IMC into nanopores, the reduced crystallinity, and finally accelerated dissolution of IMC. It was worth mentioning that, in comparison to 2D mesoporous silica, 3DOM silica displayed a more rapid release profile, which may be ascribed to the 3D interconnected pore networks and the highly accessible surface areas. The results obtained from the stability test indicated that the amorphous state of IMC entrapped in the 2D mesoporous silica (SBA-15 and MCM-41) has a better physical stability than in that of 3DOM silica. Moreover, the dissolution rate and stability of IMC loaded in 3DOM silica was closely related to the pore size of macroporous silica. The colorimetric 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Cell Counting Kit (CCK)-8 assays in combination with direct morphology observations demonstrated the good biocompatibility of nanoporous silica, especially for 3DOM silica and SBA-15. The present work encourages further study of the drug release properties and stability of drug entrapped in different pore architecture of silica in order to realize

  11. Multifunctional mesoporous silica catalyst

    DOEpatents

    Lin, Victor Shang-Yi; Tsai, Chih-Hsiang; Chen, Hung-Ting; Pruski, Marek; Kobayashi, Takeshi

    2015-03-31

    The present invention provides bifunctional silica mesoporous materials, including mesoporous silica nanoparticles ("MSN"), having pores modified with diarylammonium triflate and perfluoroaryl moieties, that are useful for the acid-catalyzed esterification of organic acids with organic alcohols.

  12. What Is Crystalline Silica?

    MedlinePlus

    ... silica, and requires a repirator protection program until engineering controls are implemented. Additionally, OSHA has a National ... silica materials with safer substitutes, whenever possible. ■ Provide engineering or administrative controls, where feasible, such as local ...

  13. Amorphous diamond films

    DOEpatents

    Falabella, S.

    1998-06-09

    Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

  14. Silica extraction from geothermal water

    SciTech Connect

    Bourcier, William L; Bruton, Carol J

    2014-09-23

    A method of producing silica from geothermal fluid containing low concentration of the silica of less than 275 ppm includes the steps of treating the geothermal fluid containing the silica by reverse osmosis treatment thereby producing a concentrated fluid containing the silica, seasoning the concentrated fluid thereby producing a slurry having precipitated colloids containing the silica, and separating the silica from the slurry.

  15. Amorphous metal alloy

    DOEpatents

    Wang, R.; Merz, M.D.

    1980-04-09

    Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

  16. Inhibition of Recrystallization of Amorphous Lactose in Nanocomposites Formed by Spray-Drying.

    PubMed

    Hellrup, Joel; Alderborn, Göran; Mahlin, Denny

    2015-11-01

    This study aims at investigating the recrystallization of amorphous lactose in nanocomposites. In particular, the focus is on the influence of the nano- to micrometer length scale nanofiller arrangement on the amorphous to crystalline transition. Further, the relative significance of formulation composition and manufacturing process parameters for the properties of the nanocomposite was investigated. Nanocomposites of amorphous lactose and fumed silica were produced by co-spray-drying. Solid-state transformation of the lactose was studied at 43%, 84%, and 94% relative humidity using X-ray powder diffraction and microcalorimetry. Design of experiments was used to analyze spray-drying process parameters and nanocomposite composition as factors influencing the time to 50% recrystallization. The spray-drying process parameters showed no significant influence. However, the recrystallization of the lactose in the nanocomposites was affected by the composition (fraction silica). The recrystallization rate constant decreased as a function of silica content. The lowered recrystallization rate of the lactose in the nanocomposites could be explained by three mechanisms: (1) separation of the amorphous lactose into discrete compartments on a micrometer length scale (compartmentalization), (2) lowered molecular mobility caused by molecular interactions between the lactose molecules and the surface of the silica (rigidification), and/or (3) intraparticle confinement of the amorphous lactose. PMID:26182904

  17. Determination of silica coating efficiency on metal particles using multiple digestion methods.

    PubMed

    Wang, Jun; Topham, Nathan; Wu, Chang-Yu

    2011-10-15

    Nano-sized metal particles, including both elemental and oxidized metals, have received significant interest due to their biotoxicity and presence in a wide range of industrial systems. A novel silica technology has been recently explored to minimize the biotoxicity of metal particles by encapsulating them with an amorphous silica shell. In this study, a method to determine silica coating efficiency on metal particles was developed. Metal particles with silica coating were generated using gas metal arc welding (GMAW) process with a silica precursor tetramethylsilane (TMS) added to the shielding gas. Microwave digestion and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) were employed to solubilize the metal content in the particles and analyze the concentration, respectively. Three acid mixtures were tested to acquire the appropriate digestion method targeting at metals and silica coating. Metal recovery efficiencies of different digestion methods were compared through analysis of spiked samples. HNO(3)/HF mixture was found to be a more aggressive digestion method for metal particles with silica coating. Aqua regia was able to effectively dissolve metal particles not trapped in the silica shell. Silica coating efficiencies were thus calculated based on the measured concentrations following digestion by HNO(3)/HF mixture and aqua regia. The results showed 14-39% of welding fume particles were encapsulated in silica coating under various conditions. This newly developed method could also be used to examine the silica coverage on particles of silica shell/metal core structure in other nanotechnology areas. PMID:21962698

  18. Cytotoxic and transforming effects of silica particles with different surface properties in Syrian hamster embryo (SHE) cells.

    PubMed

    Elias, Z; Poirot, O; Danière, M C; Terzetti, F; Marande, A M; Dzwigaj, S; Pezerat, H; Fenoglio, I; Fubini, B

    2000-10-01

    Several crystalline and amorphous silica dusts (two quartz of natural origin, one cristobalite of natural and two of biogenic origin, three amorphous diatomite earths and one pyrogenic amorphous silica) were studied in the SHE cell transformation assay, in order to compare their cytotoxic and transforming potencies and examine the role of the structure and of the state of the surface on these effects. Some samples were modified by grinding, etching and heating with the aim of establishing relationships between single surface properties and biological responses. The results showed that some quartz and cristobalite dusts (crystalline) as well as the diatomaceous earths (amorphous), but not the pyrogenic amorphous silica, were cytotoxic and induced morphological transformation of SHE cells in a concentration-dependent manner. The ranking in cytotoxicity was different from that in transforming potency, suggesting two separate molecular mechanisms for the two effects. The cytotoxic and transforming potencies were different from one dust to another, even among the same structural silicas. The type of crystalline structure (quartz vs cristobalite) and the crystalline vs biogenic amorphous form did not correlate with cytotoxic or transforming potency of silica dusts. Comparison of cellular effects induced by original and surface modified samples revealed that several surface functionalities modulate cytotoxic and transforming potencies. The cytotoxic effects appeared to be related to the distribution and abundance of silanol groups and to the presence of trace amounts of iron on the silica surface. Silica particles with fractured surfaces and/or iron-active sites, able to generate reactive oxygen species, induced SHE cell transformation. The results show that the activity of silica at the cellular level is sensitive to the composition and structure of surface functionalities and confirm that the biological response to silica is a surface originated phenomenon. PMID

  19. Inhomogeneous Elastic Response of Silica Glass

    NASA Astrophysics Data System (ADS)

    Léonforte, F.; Tanguy, A.; Wittmer, J. P.; Barrat, J.-L.

    2006-08-01

    Using large scale molecular dynamics simulations we investigate the properties of the nonaffine displacement field induced by macroscopic uniaxial deformation of amorphous silica, a strong glass according to Angell’s classification. We demonstrate the existence of a length scale ξ characterizing the correlations of this field (corresponding to a volume of about 1000 atoms), and compare its structure to the one observed in a standard fragile model glass. The “boson-peak” anomaly of the density of states can be traced back in both cases to elastic inhomogeneities on wavelengths smaller than ξ where classical continuum elasticity becomes simply unapplicable.

  20. Cell viability in a wet silica gel.

    PubMed

    Nieto, Alejandra; Areva, Sami; Wilson, Timothy; Viitala, Reeta; Vallet-Regi, Maria

    2009-11-01

    A modified two-step sol-gel route using silicon ethoxide (TEOS) has been used to synthesize amorphous sol-gel-derived silica, which has been successfully used as a cell encapsulation matrix for 3T3 mouse fibroblasts and CRL-2595 epithelial cells due to its non-toxicity. The sol-gel procedure comprised a first, low pH hydrolysis step, followed by a neutral condensation-gelation step. A high water-to-TEOS ratio and the addition of d-glucose as a porogen and source of nutrients were chosen to minimize silica dissolution and improve the biocompatibility of the process. Indeed, the cell integrity in the encapsulation process was preserved by alcohol removal from the starting solution. Cells were then added in a buffered medium, causing rapid gelation and entrapment of the cells within a randomly structured siloxane matrix in the shape of a monolith, which was maintained in the wet state. MTT and alamarBlue assays were used to check the cytotoxicity of the silica gels and the viability of entrapped cells at initial times in contact with silica. To improve cell attachment, cell clumping experiments - where groups of cells were formed - were designed, rendering improved viability. The obtained materials are therefore excellent candidates for designing tissue-culture scaffolds and implantable bioreactors for biomedical applications. PMID:19481618

  1. Formation of amorphous materials

    DOEpatents

    Johnson, William L.; Schwarz, Ricardo B.

    1986-01-01

    Metastable amorphous or fine crystalline materials are formed by solid state reactions by diffusion of a metallic component into a solid compound or by diffusion of a gas into an intermetallic compound. The invention can be practiced on layers of metals deposited on an amorphous substrate or by intermixing powders with nucleating seed granules. All that is required is that the diffusion of the first component into the second component be much faster than the self-diffusion of the first component. The method is practiced at a temperature below the temperature at which the amorphous phase transforms into one or more crystalline phases and near or below the temperature at which the ratio of the rate of diffusion of the first component to the rate of self-diffusion is at least 10.sup.4. This anomalous diffusion criteria is found in many binary, tertiary and higher ordered systems of alloys and appears to be found in all alloy systems that form amorphous materials by rapid quenching. The method of the invention can totally convert much larger dimensional materials to amorphous materials in practical periods of several hours or less.

  2. Structural Amorphous Steels

    NASA Astrophysics Data System (ADS)

    Lu, Z. P.; Liu, C. T.; Thompson, J. R.; Porter, W. D.

    2004-06-01

    Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist’s dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.

  3. Enhanced stab resistance of armor composites with functionalized silica nanoparticles

    NASA Astrophysics Data System (ADS)

    Mahfuz, Hassan; Clements, Floria; Rangari, Vijaya; Dhanak, Vinod; Beamson, Graham

    2009-03-01

    Traditionally shear thickening fluid (STF) reinforced with Kevlar has been used to develop flexible armor. At the core of the STF-Kevlar composites is a mixture of polyethylene glycol (PEG) and silica particles. This mixture is often known as STF and is consisted of approximately 45 wt % PEG and 55 wt % silica. During rheological tests, STF shows instantaneous spike in viscosity above a critical shear rate. Fabrication of STF-Kevlar composites requires preparation of STF, dilution with ethanol, and then impregnation with Kevlar. In the current approach, nanoscale silica particles were dispersed directly into a mixture of PEG and ethanol through a sonic cavitation process. Two types of silica nanoparticles were used in the investigation: 30 nm crystalline silica and 7 nm amorphous silica. The admixture was then reinforced with Kevlar fabric to produce flexible armor composites. In the next step, silica particles are functionalized with a silane coupling agent to enhance bonding between silica and PEG. The performance of the resulting armor composites improved significantly. As evidenced by National Institute of Justice spike tests, the energy required for zero-layer penetration (i.e., no penetration) jumped twofold: from 12 to 25 J cm2/g. The source of this improvement has been traced to the formation of siloxane (Si-O-Si) bonds between silica and PEG and superior coating of Kevlar filaments with particles. Fourier transform infrared, x-ray photoemission spectroscopy, and scanning electron microscopy studies were performed to examine chemical bonds, elemental composition, and particle dispersion responsible for such improvement. In summary, our experiments have demonstrated that functionalization of silica particles followed by direct dispersion into PEG resulted in superior Kevlar composites having much higher spike resistance.

  4. Silica-Ceria Hybrid Nanostructures

    SciTech Connect

    Munusamy, Prabhakaran; Sanghavi, Shail P.; Nachimuthu, Ponnusamy; Baer, Donald R.; Thevuthasan, Suntharampillai

    2012-04-25

    A new hybrid material system that consists of ceria attached silica nanoparticles has been developed. Because of the versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and versatile properties of silica and antioxidant properties of ceria nanoparticles, this material system is ideally suited for biomedical applications. The silica particles of size ~50nm were synthesized by the Stöber synthesis method and ceria nanoparticles of size ~2-3nm was attached to the silica surface using a hetrocoagulation method. The presence of silanol groups on the surface of silica particles mediated homogenous nucleation of ceria which were attached to silica surface by Si-O-Ce bonding. The formations of silica-ceria hybrid nanostructures were characterized by X-photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The HRTEM image confirms the formation of individual crystallites of ceria nanoparticles attached to the silica surface. The XPS analysis indicates that ceria nanoparticles are chemically bonded to surface of silica and possess mixture of +3 and +4 chemical states.

  5. Silazane to silica

    NASA Technical Reports Server (NTRS)

    Harvey, Gale A.

    1992-01-01

    Thin film silica and/or methyl silicone were detected on most external surfaces of the retrieved LDEF. Known sources of silicone in or on the LDEF appear inadequate to explain the ubiquitous presence of the silica and silicone films. Hexamethyldisilazane (HMDS) was used as the Challenger tile waterproofing compound for the Challenger/LDEF deployment mission. HMDS releases NH3 which depolymerizes silicone RTV's. Polyurethanes were also attacked. Much of the silica/silicone contamination of LDEF resulted from HMDS.

  6. Amorphous semiconductor solar cell

    DOEpatents

    Dalal, Vikram L.

    1981-01-01

    A solar cell comprising a back electrical contact, amorphous silicon semiconductor base and junction layers and a top electrical contact includes in its manufacture the step of heat treating the physical junction between the base layer and junction layer to diffuse the dopant species at the physical junction into the base layer.

  7. Disorder-induced amorphization

    SciTech Connect

    Lam, N.Q.; Okamoto, P.R.; Li, Mo

    1997-03-01

    Many crystalline materials undergo a crystalline-to-amorphous (c-a) phase transition when subjected to energetic particle irradiation at low temperatures. By focusing on the mean-square static atomic displacement as a generic measure of chemical and topological disorder, we are led quite naturally to a generalized version of the Lindemann melting criterion as a conceptual framework for a unified thermodynamic approach to solid-state amorphizing transformations. In its simplest form, the generalized Lindemann criterion assumes that the sum of the static and dynamic mean-square atomic displacements is constant along the polymorphous melting curve so that c-a transformations can be understood simply as melting of a critically-disordered crystal at temperatures below the glass transition temperature where the supercooled liquid can persist indefinitely in a configurationally-frozen state. Evidence in support of the generalized Lindemann melting criterion for amorphization is provided by a large variety of experimental observations and by molecular dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds.

  8. Amorphous silicon photovoltaic devices

    SciTech Connect

    Carlson, David E.; Lin, Guang H.; Ganguly, Gautam

    2004-08-31

    This invention is a photovoltaic device comprising an intrinsic or i-layer of amorphous silicon and where the photovoltaic device is more efficient at converting light energy to electric energy at high operating temperatures than at low operating temperatures. The photovoltaic devices of this invention are suitable for use in high temperature operating environments.

  9. Silazine to silica

    NASA Technical Reports Server (NTRS)

    Harvey, Gale A.

    1993-01-01

    Thin film silica and/or methyl silicone were detected on most external surfaces of the retrieved LDEF. Both solar ultraviolet radiation and atomic oxygen can convert silicones to silica. Known sources of silicone in or on the LDEF appear inadequate to explain the ubiquitous presence of the silica and silicone films. Hexamethyldisilazane (HMDS) was used as the Challenger tile waterproofing compound for the Challenger/LDEF deployment mission. HMDS is both volatile and chemically reactive at STP. In addition, HMDS releases NH3 which depolymerizes silicone RTV's. Polyurethanes are also depolymerized. Experiments are reported that indicate much of the silicone and silica contamination of LDEF resulted directly or indirectly from HMDS.

  10. Silica Debris Disk Evidence for Giant Planet Forming Impacts

    NASA Astrophysics Data System (ADS)

    Lisse, C.

    2014-04-01

    Giant impacts are major formation events in the history of our solar system. The final assembly of the planets, as we understand it, had to include massive fast collision events as the planets grew to objects with large escape velocities or in regions of high Keplerian velocities (Chambers 2004; Kenyon & Bromley 2004a,b, 2006; Fegley & Schaefer 2005). These massive impact events should create large amounts of glassy silica material derived from the rapid melting, vaporization, and refreezing of normal silicate rich primitive rocky material. We report here the detection of 4 bright silica-rich debris disks in the Spitzer IRS spectral archive, and the possible identification of 7 others. The stellar types of the system primaries span from A5V to G0V, their ages are 10 - 100 Myr, and the dust is warm, 280 - 480 K, and is located between 1.5 and 6 AU, well inside the systems' terrestrial planet regions. The minimum amount of detected 0.1 - 20 dust mass ranges from 10^21 - 10^23 kg; assuming < 10% dust formation efficiency (Benz 2009, 2011) this implies collisions involving impactors massing at least 10^22 - 10^24 kg, i.e. from Moon to Earth mass. We find possible trends in the mineralogy of the silica, with predominantly amorphous silica found in the 2 younger systems, and crystalline silica in the older systems. We speculate this is due higher velocity impacts found in younger, hotter systems, coupled with the effects of energetic photon annealing of small amorphous silica grains. All of these measures are consistent with the creation of silica rich rubble, or construction debris, during the terrestrial planet formation era of giant impacts.

  11. Solid dispersions of carvedilol with porous silica.

    PubMed

    Kovačič, Borut; Vrečer, Franc; Planinšek, Odon

    2011-01-01

    Solid dispersion particles of carvedilol (CAR) were prepared with porous silica (Sylysia 350) by the solvent evaporation method in a vacuum evaporator to ensure an effective pore-filling procedure. Two sets were prepared, each with various amounts of CAR in solid dispersions, and with the pore-filling process differing each time. Set A was prepared by a one-step filling method and set B by a multiple-step pore-filling method of CAR into porous silica. The solid dispersions were then characterized using thermal analysis, X-ray diffraction, and nitrogen adsorption experiments. The results showed that the drug release can be significantly improved compared with the dissolution of the drug in its pure crystalline or amorphous state. Drug release from solid dispersion was faster when the drug content in the solid dispersion was low, which enabled the drug to be finely dispersed along the hydrophilic carrier's surface. The results also showed that a multiple-step pore-filling procedure is more effective for drug loading as indicated by the absence of a crystalline drug state, greatly reduced porosity, and improved wettability and physical stability of the amorphous CAR. PMID:21467668

  12. Unveiling the complex electronic structure of amorphous metal oxides

    PubMed Central

    Århammar, C.; Pietzsch, Annette; Bock, Nicolas; Holmström, Erik; Araujo, C. Moyses; Gråsjö, Johan; Zhao, Shuxi; Green, Sara; Peery, T.; Hennies, Franz; Amerioun, Shahrad; Föhlisch, Alexander; Schlappa, Justine; Schmitt, Thorsten; Strocov, Vladimir N.; Niklasson, Gunnar A.; Wallace, Duane C.; Rubensson, Jan-Erik; Johansson, Börje; Ahuja, Rajeev

    2011-01-01

    Amorphous materials represent a large and important emerging area of material’s science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today’s integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5–10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

  13. Fused Silica Surface Coating for a Flexible Silica Mat Insulation System

    NASA Technical Reports Server (NTRS)

    Rhodes, W. H.

    1973-01-01

    Fused silica insulation coatings have been developed for application to a flexible mat insulation system. Based on crystalline phase nucleation and growth kinetics, a 99+% SiO2 glass was selected as the base composition. A coating was developed that incorporated the high emissivity phase NiCr2O4 as a two phase coating with goals of high emittance and minimum change in thermal expansion. A second major coating classification has a plasma sprayed emittance coating over a sealed pure amorphous SiO2 layer. A third area of development centered on extremely thin amorphous SiO2 coatings deposited by chemical vapor deposition. The coating characterization studies presented are mechanical testing of thin specimens extracted from the coatings, cyclic arc exposures, and emittance measurements before and after arc exposures.

  14. Enhanced photoacoustic stability of gold nanorods by silica matrix confinement

    NASA Astrophysics Data System (ADS)

    Chen, Leng-Chun; Wei, Chen-Wei; Souris, Jeffrey S.; Cheng, Shih-Hsun; Chen, Chin-Tu; Yang, Chung-Shi; Li, Pai-Chi; Lo, Leu-Wei

    2010-01-01

    Photoacoustic tomography (PAT) has garnered much attention for its high contrast and excellent spatial resolution of perfused tissues. Gold nanorods (GNRs) have been employed to further enhance the imaging contrast of PAT. However, the photon fluences typically needed for PA wave induction often also result in GNR shape changes that significantly reduce the efficiency of acoustic wave generation. In this work, we propose, synthesize, and evaluate amorphous silica-coated gold nanorods (GNR-Si) in an effort to improve contrast agent stability and ameliorate efficiency loss during photoacoustic (PA) wave induction. TEM and optical absorption spectra measurements of GNR and GNR-Si show that encasing GNRs within amorphous silica provides substantial protection of nanorod conformation from thermal deformation. PA signals generated by GNR-Si demonstrate considerably greater resistance to degradation of signal intensity with repetitive pulsing than do uncoated GNRs, thereby enabling much longer, high-contrast imaging sessions than previously possible. The prolongation of high-contrast imaging, and biocompatibility and easy surface functionalization for targeting ligands afforded by amorphous silica, suggest GNR-Si to be potentially significant for the clinical translation of PAT.

  15. Hierarchical structures of amorphous solids characterized by persistent homology

    PubMed Central

    Hiraoka, Yasuaki; Nakamura, Takenobu; Hirata, Akihiko; Escolar, Emerson G.; Matsue, Kaname; Nishiura, Yasumasa

    2016-01-01

    This article proposes a topological method that extracts hierarchical structures of various amorphous solids. The method is based on the persistence diagram (PD), a mathematical tool for capturing shapes of multiscale data. The input to the PDs is given by an atomic configuration and the output is expressed as 2D histograms. Then, specific distributions such as curves and islands in the PDs identify meaningful shape characteristics of the atomic configuration. Although the method can be applied to a wide variety of disordered systems, it is applied here to silica glass, the Lennard-Jones system, and Cu-Zr metallic glass as standard examples of continuous random network and random packing structures. In silica glass, the method classified the atomic rings as short-range and medium-range orders and unveiled hierarchical ring structures among them. These detailed geometric characterizations clarified a real space origin of the first sharp diffraction peak and also indicated that PDs contain information on elastic response. Even in the Lennard-Jones system and Cu-Zr metallic glass, the hierarchical structures in the atomic configurations were derived in a similar way using PDs, although the glass structures and properties substantially differ from silica glass. These results suggest that the PDs provide a unified method that extracts greater depth of geometric information in amorphous solids than conventional methods. PMID:27298351

  16. Hierarchical structures of amorphous solids characterized by persistent homology.

    PubMed

    Hiraoka, Yasuaki; Nakamura, Takenobu; Hirata, Akihiko; Escolar, Emerson G; Matsue, Kaname; Nishiura, Yasumasa

    2016-06-28

    This article proposes a topological method that extracts hierarchical structures of various amorphous solids. The method is based on the persistence diagram (PD), a mathematical tool for capturing shapes of multiscale data. The input to the PDs is given by an atomic configuration and the output is expressed as 2D histograms. Then, specific distributions such as curves and islands in the PDs identify meaningful shape characteristics of the atomic configuration. Although the method can be applied to a wide variety of disordered systems, it is applied here to silica glass, the Lennard-Jones system, and Cu-Zr metallic glass as standard examples of continuous random network and random packing structures. In silica glass, the method classified the atomic rings as short-range and medium-range orders and unveiled hierarchical ring structures among them. These detailed geometric characterizations clarified a real space origin of the first sharp diffraction peak and also indicated that PDs contain information on elastic response. Even in the Lennard-Jones system and Cu-Zr metallic glass, the hierarchical structures in the atomic configurations were derived in a similar way using PDs, although the glass structures and properties substantially differ from silica glass. These results suggest that the PDs provide a unified method that extracts greater depth of geometric information in amorphous solids than conventional methods. PMID:27298351

  17. Amorphous silicon radiation detectors

    DOEpatents

    Street, R.A.; Perez-Mendez, V.; Kaplan, S.N.

    1992-11-17

    Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification. 13 figs.

  18. Amorphous silicon radiation detectors

    DOEpatents

    Street, Robert A.; Perez-Mendez, Victor; Kaplan, Selig N.

    1992-01-01

    Hydrogenated amorphous silicon radiation detector devices having enhanced signal are disclosed. Specifically provided are transversely oriented electrode layers and layered detector configurations of amorphous silicon, the structure of which allow high electric fields upon application of a bias thereby beneficially resulting in a reduction in noise from contact injection and an increase in signal including avalanche multiplication and gain of the signal produced by incoming high energy radiation. These enhanced radiation sensitive devices can be used as measuring and detection means for visible light, low energy photons and high energy ionizing particles such as electrons, x-rays, alpha particles, beta particles and gamma radiation. Particular utility of the device is disclosed for precision powder crystallography and biological identification.

  19. Making silica rock coatings in the lab: synthetic desert varnish

    NASA Astrophysics Data System (ADS)

    Perry, Randall S.; Kolb, Vera M.; Philip, Ajish I.; Lynne, Bridget Y.; McLoughlin, Nicola; Sephton, Mark; Wacey, David; Green, Owen R.

    2005-09-01

    Desert varnish and silica rock coatings have perplexed investigators since Humboldt and Darwin. They are found in arid regions and deserts on Earth but the mechanism of their formation remains challenging (see Perry et al. this volume). One method of researching this is to investigate natural coatings, but another way is to attempt to produce coatings in vitro. Sugars, amino acids, and silicic acid, as well as other organic and (bio)organic compounds add to the complexity of naturally forming rock coatings. In the lab we reduced the complexity of the natural components and produced hard, silica coatings on basaltic chips obtained from the Mojave Desert. Sodium silicate solution was poured over the rocks and continuously exposed to heat and/or UV light. Upon evaporation the solutions were replenished. Experiments were performed at various pH's. The micro-deposits formed were analyzed using optical, SEM-EDAX, and electron microprobe. The coatings formed are similar in hardness and composition to silica glazes found on basalts in Hawaii as well as natural desert varnish found in US southwest deserts. Thermodynamic mechanisms are presented showing the theoretical mechanisms for overcoming energy barriers that allow amorphous silica to condense into hard coatings. This is the first time synthetic silica glazes that resemble natural coatings in hardness and chemical composition have been successfully reproduced in the laboratory, and helps to support an inorganic mechanism of formation of desert varnish as well as manganese-deficient silica glazes.

  20. Silica, Silicosis, and Autoimmunity

    PubMed Central

    Pollard, Kenneth Michael

    2016-01-01

    Inhalation of dust containing crystalline silica is associated with a number of acute and chronic diseases including systemic autoimmune diseases. Evidence for the link with autoimmune disease comes from epidemiological studies linking occupational exposure to crystalline silica dust with the systemic autoimmune diseases systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis. Although little is known regarding the mechanism by which silica exposure leads to systemic autoimmune disease, there is a voluminous literature on silica exposure and silicosis that may help identify immune processes that precede development of autoimmunity. The pathophysiology of silicosis consists of deposition of silica particles in the alveoli of the lung. Ingestion of these particles by macrophages initiates an inflammatory response, which stimulates fibroblasts to proliferate and produce collagen. Silica particles are encased by collagen leading to fibrosis and the nodular lesions characteristic of the disease. The steps in the development of silicosis, including acute and chronic inflammation and fibrosis, have different molecular and cellular requirements, suggesting that silica-induced inflammation and fibrosis may be mechanistically separate. Significantly, it is unclear whether silica-induced inflammation and fibrosis contribute similarly to the development of autoimmunity. Nonetheless, the findings from human and animal model studies are consistent with an autoimmune pathogenesis that begins with activation of the innate immune system leading to proinflammatory cytokine production, pulmonary inflammation leading to activation of adaptive immunity, breaking of tolerance, and autoantibodies and tissue damage. The variable frequency of these immunological features following silica exposure suggests substantial genetic involvement and gene/environment interaction in silica-induced autoimmunity. However, numerous questions remain unanswered. PMID:27014276

  1. Silica, Silicosis, and Autoimmunity.

    PubMed

    Pollard, Kenneth Michael

    2016-01-01

    Inhalation of dust containing crystalline silica is associated with a number of acute and chronic diseases including systemic autoimmune diseases. Evidence for the link with autoimmune disease comes from epidemiological studies linking occupational exposure to crystalline silica dust with the systemic autoimmune diseases systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis. Although little is known regarding the mechanism by which silica exposure leads to systemic autoimmune disease, there is a voluminous literature on silica exposure and silicosis that may help identify immune processes that precede development of autoimmunity. The pathophysiology of silicosis consists of deposition of silica particles in the alveoli of the lung. Ingestion of these particles by macrophages initiates an inflammatory response, which stimulates fibroblasts to proliferate and produce collagen. Silica particles are encased by collagen leading to fibrosis and the nodular lesions characteristic of the disease. The steps in the development of silicosis, including acute and chronic inflammation and fibrosis, have different molecular and cellular requirements, suggesting that silica-induced inflammation and fibrosis may be mechanistically separate. Significantly, it is unclear whether silica-induced inflammation and fibrosis contribute similarly to the development of autoimmunity. Nonetheless, the findings from human and animal model studies are consistent with an autoimmune pathogenesis that begins with activation of the innate immune system leading to proinflammatory cytokine production, pulmonary inflammation leading to activation of adaptive immunity, breaking of tolerance, and autoantibodies and tissue damage. The variable frequency of these immunological features following silica exposure suggests substantial genetic involvement and gene/environment interaction in silica-induced autoimmunity. However, numerous questions remain unanswered. PMID:27014276

  2. Solid State Electrolytes Prepared from PEO (360) Silanated Silica

    NASA Technical Reports Server (NTRS)

    Maitra, P.; Ding, J.; Liu, B.; Wunder, S. L.; Lin, H.-P.; Chua, D.; Salomon, M.

    2002-01-01

    All solid state composite electrolytes were prepared using fumed silica (SiO2) silanated with an oligomeric polyethylene oxide (PEO) silane containing 6-9 ethylene oxide repeat units, a PEO matrix and LiClO4 (8/1 O/Li). The PEO-silane covalently attached to the silica was amorphous, with a T(sub g) that increased from -90 C to -53 C after attachment. The conductivity of films prepared using the PEO-silanated silica increased to approx. 6 x 10(exp -5) S/cm at RT compared with approx. 1 x 10(-5) S/cm for films prepared with unsilanated SiO2.

  3. Size and distribution controllable silica microballs fabricated by electrospraying

    NASA Astrophysics Data System (ADS)

    Xu, Bojing; Wu, Pan; Jiang, Qi; Gu, Wenhua

    2015-10-01

    Silica microballs have a wide range of applications in the field of optics, electronics, biotechnology chemical industry, and so on. In this work, a new approach, electrospraying, was used to coat the silica microballs onto the glass substrate, and the coating results were compared to spin-coating and dip-coating. Good microball size control could be achieved using the electrospraying method. X-Ray Diffraction (XRD) results showed that amorphous silica microballs were obtained. From Scanning Electron Microscopy (SEM) images, we can see that uniform microball size was achieved. In general, the results are better than what can be achieved by spin-coating, and comparable to that of dip-coating. However, electrospraying has great potential in mass production, especially for large-area fabrication.

  4. Crystallized alkali-silica gel in concrete from the late 1890s

    SciTech Connect

    Peterson, Karl . E-mail: cee@mtu.edu; Gress, David . E-mail: dlgress@unh.edu; Van Dam, Tom . E-mail: cee@mtu.edu; Sutter, Lawrence . E-mail: cee@mtu.edu

    2006-08-15

    The Elon Farnsworth Battery, a concrete structure completed in 1898, is in an advanced state of disrepair. To investigate the potential for rehabilitation, cores were extracted from the battery. Petrographic examination revealed abundant deposits of alkali silica reaction products in cracks associated with the quartz rich metasedimentary coarse aggregate. The products of the alkali silica reaction are variable in composition and morphology, including both amorphous and crystalline phases. The crystalline alkali silica reaction products are characterized by quantitative X-ray energy dispersive spectrometry (EDX) and X-ray diffraction (XRD). The broad extent of the reactivity is likely due to elevated alkali levels in the cements used.

  5. Nanobubble collapse on a silica surface in water: billion-atom reactive molecular dynamics simulations.

    PubMed

    Shekhar, Adarsh; Nomura, Ken-ichi; Kalia, Rajiv K; Nakano, Aiichiro; Vashishta, Priya

    2013-11-01

    Cavitation bubbles occur in fluids subjected to rapid changes in pressure. We use billion-atom reactive molecular dynamics simulations on a 163,840-processor BlueGene/P supercomputer to investigate damage caused by shock-induced collapse of nanobubbles in water near an amorphous silica surface. Collapse of an empty bubble generates a high-speed nanojet, which causes pitting on the silica surface. We find pit radii are close to bubble radii, and experiments also indicate linear scaling between them. The gas-filled bubbles undergo partial collapse and, consequently, the damage on the silica surface is mitigated. PMID:24237524

  6. Nanobubble Collapse on a Silica Surface in Water: Billion-Atom Reactive Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Shekhar, Adarsh; Nomura, Ken-ichi; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2013-11-01

    Cavitation bubbles occur in fluids subjected to rapid changes in pressure. We use billion-atom reactive molecular dynamics simulations on a 163 840-processor BlueGene/P supercomputer to investigate damage caused by shock-induced collapse of nanobubbles in water near an amorphous silica surface. Collapse of an empty bubble generates a high-speed nanojet, which causes pitting on the silica surface. We find pit radii are close to bubble radii, and experiments also indicate linear scaling between them. The gas-filled bubbles undergo partial collapse and, consequently, the damage on the silica surface is mitigated.

  7. New antifouling silica hydrogel.

    PubMed

    Beltrán-Osuna, Ángela A; Cao, Bin; Cheng, Gang; Jana, Sadhan C; Espe, Matthew P; Lama, Bimala

    2012-06-26

    In this work, a new antifouling silica hydrogel was developed for potential biomedical applications. A zwitterionic polymer, poly(carboxybetaine methacrylate) (pCBMA), was produced via atom-transfer radical polymerization and was appended to the hydrogel network in a two-step acid-base-catalyzed sol-gel process. The pCBMA silica aerogels were obtained by drying the hydrogels under supercritical conditions using CO(2). To understand the effect of pCBMA on the gel structure, pCBMA silica aerogels with different pCBMA contents were characterized using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) spectroscopy, and the surface area from Brauner-Emmet-Teller (BET) measurements. The antifouling property of pCBMA silica hydrogel to resist protein (fibrinogen) adsorption was measured using enzyme-linked immunosorbent assay (ELISA). SEM images revealed that the particle size and porosity of the silica network decreased at low pCBMA content and increased at above 33 wt % of the polymer. The presence of pCBMA increased the surface area of the material by 91% at a polymer content of 25 wt %. NMR results confirmed that pCBMA was incorporated completely into the silica structure at a polymer content below 20 wt %. A protein adsorption test revealed a reduction in fibrinogen adsorption by 83% at 25 wt % pCBMA content in the hydrogel compared to the fibrinogen adsorption in the unmodified silica hydrogel. PMID:22607091

  8. Does the crystal habit modulate the genotoxic potential of silica particles? A cytogenetic evaluation in human and murine cell lines.

    PubMed

    Guidi, P; Nigro, M; Bernardeschi, M; Lucchesi, P; Scarcelli, V; Frenzilli, G

    2015-10-01

    Crystalline silica inhaled from occupational sources has been classified by IARC as carcinogenic to humans; in contrast, for amorphous silica, epidemiological and experimental evidence remains insufficient. The genotoxicity of crystalline silica is still debated because of the inconsistency of experimental results ("variability of silica hazard"), often related to the features of the particle surfaces. We have assessed the role of crystal habit in the genotoxicity of silica powders. Pure quartz (crystalline) and vitreous silica (amorphous), sharing the same surface features, were used in an in vitro study with human pulmonary epithelial (A549) and murine macrophage (RAW264.7) cell lines, representative of occupational and environmental exposures. Genotoxicity was evaluated by the comet and micronucleus assays, and cytotoxicity by the trypan blue method. Cells were treated with silica powders for 4 and 24h. Quartz but not vitreous silica caused cell death and DNA damage in RAW264.7 cells. A549 cells were relatively resistant to both powders. Our results support the view that crystal habit per se plays a pivotal role in modulating the biological responses to silica particles. PMID:26433261

  9. Silica Embedded Metal Hydrides

    SciTech Connect

    Heung, L.K.; Wicks, G.G.

    1998-08-01

    A method to produce silica embedded metal hydride was developed. The product is a composite in which metal hydride particles are embedded in a matrix of silica. The silica matrix is highly porous. Hydrogen gas can easily reach the embedded metal hydride particles. The pores are small so that the metal hydride particles cannot leave the matrix. The porous matrix also protects the metal hydride particles from larger and reactive molecules such as oxygen, since the larger gas molecules cannot pass through the small pores easily. Tests show that granules of this composite can absorb hydrogen readily and withstand many cycles without making fines.

  10. Oxygen configurations in silica

    SciTech Connect

    Chelikowsky, James R.; Chadi, D. J.; Binggeli, N.

    2000-07-15

    We propose a transition state for oxygen in silica. This state is produced by the insertion of an oxygen molecule into the Si-O-Si bond, i.e., it consists of producing a Si-O-O-O-Si bond. This state allows molecular oxygen diffusion in silica without breaking the molecular O{sub 2} bond and it is energetically more stable than a peroxy configuration. This configuration may allow for exchange of molecular oxygen with the oxygen in the silica framework. (c) 2000 The American Physical Society.

  11. Baking black opal in the desert sun: The importance of silica in desert varnish

    NASA Astrophysics Data System (ADS)

    Perry, Randall S.; Lynne, Bridget Y.; Sephton, Mark A.; Kolb, Vera M.; Perry, Carole C.; Staley, James T.

    2006-07-01

    Desert varnish, a widespread black manganese-rich rock coating, contains labile organic compounds, but a mechanism for its formation and for their preservation remains unproven. Using Raman spectroscopy, X-ray diffraction, and scanning transmission electron microscopy, we analyzed varnish and found amorphous hydrated silica (opal) and the silica mineral moganite, similar to findings we have reported from siliceous hot-spring deposits. We suggest that the slow dissolution of silica from anhydrous and hydrous minerals, and its subsequent gelling, condensation, and hardening, provides a simple explanation of a formation mechanism for desert varnish and silica glazes and the incorporation of organic material from local environments. These chemical signatures, sequestered in silica, provide valuable information about terrestrial and extraterrestrial paleoenvironments.

  12. Shock-wave equation-of-state measurements in fused silica up to 1600 GPa

    DOE PAGESBeta

    McCoy, C. A.; Gregor, M. C.; Polsin, D. N.; Fratanduono, D. E.; Celliers, P. M.; Boehly, T. R.; Meyerhofer, D. D.

    2016-06-02

    The properties of silica are important to geophysical and high-pressure equation of state research. The most prevalent crystalline form, α-quartz, has been extensively studied to TPa pressures. Recent experiments with amorphous silica, commonly referred to as fused silica, provided Hugoniot and reflectivity data up to 630 GPa using magnetically-driven aluminum impactors. This article presents measurements of the fused silica Hugoniot over the range from 200 to 1600 GPa using laser-driven shocks with a quartz standard. These results extend the measured Hugoniot of fused silica to higher pressures, but more importantly, in the 200-600 GPa range, the data are very goodmore » agreement with those obtained with a different driver and standard material. As a result, a new shock velocity-particle velocity relation is derived to fit the experimental data.« less

  13. Coaxial carbon plasma gun deposition of amorphous carbon films

    NASA Technical Reports Server (NTRS)

    Sater, D. M.; Gulino, D. A.; Rutledge, S. K.

    1984-01-01

    A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented.

  14. First-principles study of the amorphization of stishovite by isotropic volume expansion

    NASA Astrophysics Data System (ADS)

    Misawa, Masaaki; Shimojo, Fuyuki; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    Simple synthesis of ceramics with high hardness and high toughness from Earth-abundant materials is one of the most important issues in materials science. Nishiyama et al. synthesized nano-crystalline stishovite with extremely high toughness and high hardness via compression and decompression of silica, and proposed fracture-induced amorphization mechanisms for the toughning. Furthermore, it was shown that the toughening mechanisms are effective even in nanoscale order. Our first-principles molecular dynamics simulations have shown rapid amorphization of stishovite within picoseconds under increasing volume, thus substantiating the proposed amorphization mechanisms. Furthermore, we have calculated the critical stress, energy difference, and energy barrier for the crystalline-to-amorphous structural transition.

  15. Resolving amorphous solid-liquid interfaces by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Burson, Kristen M.; Gura, Leonard; Kell, Burkhard; Büchner, Christin; Lewandowski, Adrian L.; Heyde, Markus; Freund, Hans-Joachim

    2016-05-01

    Recent advancements in liquid atomic force microscopy make it an ideal technique for probing the structure of solid-liquid interfaces. Here, we present a structural study of a two-dimensional amorphous silica bilayer immersed in an aqueous solution utilizing liquid atomic force microscopy with sub-nanometer resolution. Structures show good agreement with atomically resolved ultra-high vacuum scanning tunneling microscopy images obtained on the same sample system, owing to the structural stability of the silica bilayer and the imaging clarity from the two-dimensional sample system. Pair distance histograms of ring center positions are utilized to develop quantitative metrics for structural comparison, and the physical origin of pair distance histogram peaks is addressed by direct assessment of real space structures.

  16. Cellulose-silica aerogels.

    PubMed

    Demilecamps, Arnaud; Beauger, Christian; Hildenbrand, Claudia; Rigacci, Arnaud; Budtova, Tatiana

    2015-05-20

    Aerogels based on interpenetrated cellulose-silica networks were prepared and characterised. Wet coagulated cellulose was impregnated with silica phase, polyethoxydisiloxane, using two methods: (i) molecular diffusion and (ii) forced flow induced by pressure difference. The latter allowed an enormous decrease in the impregnation times, by almost three orders of magnitude, for a sample with the same geometry. In both cases, nanostructured silica gel was in situ formed inside cellulose matrix. Nitrogen adsorption analysis revealed an almost threefold increase in pores specific surface area, from cellulose aerogel alone to organic-inorganic composite. Morphology, thermal conductivity and mechanical properties under uniaxial compression were investigated. Thermal conductivity of composite aerogels was lower than that of cellulose aerogel due to the formation of superinsulating mesoporous silica inside cellulose pores. Furthermore, composite aerogels were stiffer than each of reference aerogels. PMID:25817671

  17. Coagulated silica - a-SiO2 admixture in cement paste

    NASA Astrophysics Data System (ADS)

    Pokorný, Jaroslav; Pavlíková, Milena; Záleská, Martina; Rovnaníková, Pavla; Pavlík, Zbyšek

    2016-07-01

    Amorphous silica (a-SiO2) in fine-grained form possesses a high pozzolanic activity which makes it a valuable component of blended binders in concrete production. The origin of a-SiO2 applied in cement-based composites is very diverse. SiO2 in amorphous form is present in various amounts in quite a few supplementary cementing materials (SCMs) being used as partial replacement of Portland cement. In this work, the applicability of a commercially produced coagulated silica powder as a partial replacement of Portland cement in cement paste mix design is investigated. Portland cement CEM I 42.5R produced according to the EU standard EN 197-1 is used as a reference binder. Coagulated silica is applied in dosages of 5 and 10 % by mass of cement. The water/binder ratio is kept constant in all the studied pastes. For the applied silica, specific surface area, density, loss on ignition, pozzolanic activity, chemical composition, and SiO2 amorphous phase content are determined. For the developed pastes on the basis of cement-silica blended binder, basic physical properties as bulk density, matrix density, and total open porosity are accessed. Pore size distribution is determined using MIP analysis. Initial and final setting times of fresh mixtures are measured by automatic Vicat apparatus. Effect of silica admixture on mechanical resistivity is evaluated using compressive strength, bending strength, and dynamic Young's modulus measurement. The obtained data gives evidence of a decreased workability of paste mixtures with silica, whereas the setting process is accelerated. On the other hand, reaction activity of silica with Portland cement minerals results in a slight decrease of porosity and improvement of mechanical resistivity of cement pastes containing a-SiO2.

  18. Paleozoic and Mesozoic silica-rich seawater: Evidence from hematitic chert (jasper) deposits

    NASA Astrophysics Data System (ADS)

    Grenne, Tor; Slack, John F.

    2003-04-01

    Laterally extensive beds of highly siliceous, hematitic chert (jasper) are associated with many volcanogenic massive sulfide (VMS) deposits of Late Cambrian to Early Cretaceous age, yet are unknown in analogous younger (including modern) settings. Textural studies suggest that VMS-related jaspers in the Ordovician Løkken ophiolite of Norway were originally deposited as Si- and Fe-rich gels that precipitated from hydrothermal plumes as colloidal silica and iron-oxyhydroxide particles. Rare earth element patterns and Ge/Si ratios of the jaspers reflect precipitation from plumes having seawater dilution factors of 103 to 104, similar to modern examples. We propose that silica in the ancient jaspers is not derived from submarine hydrothermal fluids—as suggested by previous workers—but instead was deposited from silica-rich seawater. Flocculation and precipitation of the silica were triggered inorganically by the bridging effect of positively charged iron oxyhydroxides in the hydrothermal plume. A model involving amorphous silica (opal-A) precursors to the jaspers suggests that silica contents of Cambrian Early Cretaceous oceans were at least 110 mg/L SiO2, compared to values of 40 60 mg/L SiO2 estimated in other studies. The evolution of ancient silica-rich to modern Fe-rich precipitates in submarine-hydrothermal plumes reflects a changeover from silica-saturated to silica-depleted seawater through Phanerozoic time, due mainly to ocean-wide emergence of diatoms in the Cretaceous.

  19. Crystalline Silica Primer

    USGS Publications Warehouse

    Staff- Branch of Industrial Minerals

    1992-01-01

    substance and will present a nontechnical overview of the techniques used to measure crystalline silica. Because this primer is meant to be a starting point for anyone interested in learning more about crystalline silica, a list of selected readings and other resources is included. The detailed glossary, which defines many terms that are beyond the scope of this publication, is designed to help the reader move from this presentation to a more technical one, the inevitable next step.

  20. Impact of pressure on plastic yield in amorphous solids with open structure

    NASA Astrophysics Data System (ADS)

    Mantisi, B.; Kermouche, G.; Barthel, E.; Tanguy, A.

    2016-03-01

    Plasticity in amorphous silica is unusual: The yield stress decreases with hydrostatic pressure, in contrast to the Mohr-Coulomb response commonly found in more compact materials such as bulk metallic glasses. To better understand this response, we have carried out molecular dynamics simulations of plastic response in a model glass with open structure. The simulations reproduce the anomalous dependence of yield stress with pressure and also correctly predict that the plastic response turns to normal once the material has been fully compacted. We also show that the overall shape of the yield surface is consistent with a quadratic behavior predicted assuming local buckling of the structure, a point of view that fits well into the present understanding of the deformation mechanisms of amorphous silica. The results also confirm that free volume is an adequate internal variable for a continuum scale description of the plastic response of amorphous silica. Finally, we also investigate the long-range correlations between rearrangement events. We find that strong intermittency is observed when the structure remains open, while compaction results in more homogeneous rearrangements. These findings are in agreement with recent results on the effect of compression on the middle range order in silicate glasses and also suggest that the well-known volume recovery of densified silica at relatively low temperatures is in fact a form of aging.

  1. Silica, hybrid silica, hydride silica and non-silica stationary phases for liquid chromatography.

    PubMed

    Borges, Endler M

    2015-04-01

    Free silanols on the surface of silica are the "villains", which are responsible for detrimental interactions of those compounds and the stationary phase (i.e., bad peak shape, low efficiency) as well as low thermal and chemical stability. For these reasons, we began this review describing new silica and hybrid silica stationary phases, which have reduced and/or shielded silanols. At present, in liquid chromatography for the majority of analyses, reversed-phase liquid chromatography is the separation mode of choice. However, the needs for increased selectivity and increased retention of hydrophilic bases have substantially increased the interest in hydrophilic interaction chromatography (HILIC). Therefore, stationary phases and this mode of separation are discussed. Then, non-silica stationary phases (i.e., zirconium oxide, titanium oxide, alumina and porous graphitized carbon), which afford increased thermal and chemical stability and also selectivity different from those obtained with silica and hybrid silica, are discussed. In addition, the use of these materials in HILIC is also reviewed. PMID:25234386

  2. Nanomoulding with amorphous metals.

    PubMed

    Kumar, Golden; Tang, Hong X; Schroers, Jan

    2009-02-12

    Nanoimprinting promises low-cost fabrication of micro- and nano-devices by embossing features from a hard mould onto thermoplastic materials, typically polymers with low glass transition temperature. The success and proliferation of such methods critically rely on the manufacturing of robust and durable master moulds. Silicon-based moulds are brittle and have limited longevity. Metal moulds are stronger than semiconductors, but patterning of metals on the nanometre scale is limited by their finite grain size. Amorphous metals (metallic glasses) exhibit superior mechanical properties and are intrinsically free from grain size limitations. Here we demonstrate direct nanopatterning of metallic glasses by hot embossing, generating feature sizes as small as 13 nm. After subsequently crystallizing the as-formed metallic glass mould, we show that another amorphous sample of the same alloy can be formed on the crystallized mould. In addition, metallic glass replicas can also be used as moulds for polymers or other metallic glasses with lower softening temperatures. Using this 'spawning' process, we can massively replicate patterned surfaces through direct moulding without using conventional lithography. We anticipate that our findings will catalyse the development of micro- and nanoscale metallic glass applications that capitalize on the outstanding mechanical properties, microstructural homogeneity and isotropy, and ease of thermoplastic forming exhibited by these materials. PMID:19212407

  3. Organic-modified and biological silica studied by synchrotron x-ray pair distribution function measurements

    NASA Astrophysics Data System (ADS)

    Dimasi, Elaine; Jeffryes, Clayton; Rorrer, Gregory; Belton, David; Perry, Carole

    2007-03-01

    Biomineralization is a process by which living organisms create composite organic/mineral tissues which have hierarchical structures on micron and submicron scales. Fine control over mineral phase and morphology make biomineralization an important inspiration for materials science. It is often not appreciated that even amorphous minerals such as silica can exhibit hierarchical structure and special properties. One difficulty is that the molecular structures of amorphous phases can be hard to elucidate. We are exploring the use of pair distribution function measurements from synchrotron x-ray scattering to study silica structures, comparing both synthetic organic-modifed silicas and germanium-containing biosilica from diatoms. The raw scattering patterns show clear differences. We will discuss how these data can be scrutinized to determine what differences may be created at the molecular level by different silicification processes.

  4. Mechanism of cellular uptake of genotoxic silica nanoparticles

    PubMed Central

    2012-01-01

    Mechanisms for cellular uptake of nanoparticles have important implications for nanoparticulate drug delivery and toxicity. We have explored the mechanism of uptake of amorphous silica nanoparticles of 14 nm diameter, which agglomerate in culture medium to hydrodynamic diameters around 500 nm. In HT29, HaCat and A549 cells, cytotoxicity was observed at nanoparticle concentrations ≥ 1 μg/ml, but DNA damage was evident at 0.1 μg/ml and above. Transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy confirmed entry of the silica particles into A549 cells exposed to 10 μg/ml of nanoparticles. The particles were observed in the cytoplasm but not within membrane bound vesicles or in the nucleus. TEM of cells exposed to nanoparticles at 4°C for 30 minutes showed particles enter cells when activity is low, suggesting a passive mode of entry. Plasma lipid membrane models identified physical interactions between the membrane and the silica NPs. Quartz crystal microbalance experiments on tethered bilayer lipid membrane systems show that the nanoparticles strongly bind to lipid membranes, forming an adherent monolayer on the membrane. Leakage assays on large unilamellar vesicles (400 nm diameter) indicate that binding of the silica NPs transiently disrupts the vesicles which rapidly self-seal. We suggest that an adhesive interaction between silica nanoparticles and lipid membranes could cause passive cellular uptake of the particles. PMID:22823932

  5. Kinetics of silica deposition from simulated geothermal brines

    SciTech Connect

    Bohlmann, E.G.; Mesmer, R.E.; Berlinski, P.

    1980-03-01

    Supersaturated brines were passed through columns packed with several forms of silica (crystalline ..cap alpha.. quartz, polycrystalline ..cap alpha.. quartz, and porous Vycor). Also, silica deposition on ThO/sub 2/ microspheres and titanium powder was studied under controlled conditions of supersaturation, pH, temperature, and salinity. The residence time was varied by adjustments of flow rate and column length. The silica contents of the input and effluent solutions were determined colorimetrically by a molybdate method which does not include polymers without special pretreatment. Essentially identical deposition behavior was observed once the substrate was thoroughly coated with amorphous silica and the BET surface area of the coated particles was taken into account. The reaction rate is not diffusion limited in the columns. The silica deposition is a function of the monomeric Si(OH)/sub 4/ concentration in the brine. The deposition on all surfaces examined was spontaneously nucleated. The dependence on the supersaturation concentration, hydroxide ion concentration, surface area, temperature and salinity were examined. Fluoride was shown to have no effect at pH 5.94 and low salinity. The empirical rate law which describes the data in 1 m NaCl in the pH range 5-7 and temperatures from 60 to 120/sup 0/C is given.

  6. Nanospherical silica as luminescent markers obtained by sol-gel.

    PubMed

    Azevedo, Caroline B; Batista, TúlioM; de Faria, Emerson H; Rocha, Lucas A; Ciuffi, Katia J; Nassar, Eduardo J

    2015-03-01

    Hybrid nanosilicas constitute a broad study field. They find application as catalysts, pigments, drug delivery systems, and biomaterials, among others, and it is possible to obtain them via the sol-gel methodology. Lanthanide ions present special properties like light emission. Their incorporation into a silica matrix can enhance their luminescent properties, which enables their application as luminescent markers. This work reports on (i) the preparation of luminescent spherical hybrid silica nanoparticles by the hydrolytic sol-gel methodology, (ii) doping of the resulting matrix with the europium(III) ion or its complex with 1,10-phenanthroline, and (iii) characterization of the final powders by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, and europium(III) ion photoluminescence. The synthesized materials consisted of hybrid, amorphous, polydispersed nonspherical silicas with average size of 180 nm. Photoluminescence confirmed incorporation of the europium(III) ion and its complex into the silica matrix-the ligand-metal charge transfer band emerged in the excitation spectra. The emission spectra presented the bands corresponding to the transition of the excited state (5)D0 level to (7)FJ (J = 0, 1, 2, 3 and 4). The main emission occurred in the red region; the lifetime was long. These characteristics indicated that the prepared nanospherical hybrid silicas could act as luminescent markers. PMID:25686772

  7. The radiolysis and radioracemization of amino acids on silica surfaces

    NASA Technical Reports Server (NTRS)

    Bonner, W. A.; Lemmon, R. M.

    1981-01-01

    Results are presented of experiments on the radioracemization of amino acids in the presence of silica surfaces such as may have been found on the prebiotic earth. L-leucine and a DL-leucine mixture deposited on samples of 1-quartz and an amorphous silica preparation (Syloid 63) was subjected to Co-60 gamma-ray irradiation, then analyzed by gas chromatography to determine the radiolysis and racemization rates. The quartz surface is found to have a marginal efficacy in enhancing radiolysis when compared with a crystalline L-leucine control, although enhancing radioracemization symmetrically by a factor of two. Both the radiolysis and radioracemization of L-leucine and DL-leucine on a Syloid-63 silica surface are observed to increase with increasing radiation dose, and to be substantially greater than in the crystalline controls. Additional experiments with the nonprotein amino acid isovaline deposited on Syloid 63 confirm the greater radiolysis susceptibility of amino acids deposited on silica with respect to the crystalline state, although racemization is not observed. The observations suggest that the presence of a silica surface would have a deleterious effect on any mechanism for the origin of molecular chirality relying on stereoselective beta-radiolysis.

  8. Amorphous silicon ionizing particle detectors

    DOEpatents

    Street, R.A.; Mendez, V.P.; Kaplan, S.N.

    1988-11-15

    Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation. 15 figs.

  9. Amorphous silicon ionizing particle detectors

    DOEpatents

    Street, Robert A.; Mendez, Victor P.; Kaplan, Selig N.

    1988-01-01

    Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation.

  10. Compensated amorphous silicon solar cell

    DOEpatents

    Devaud, Genevieve

    1983-01-01

    An amorphous silicon solar cell including an electrically conductive substrate, a layer of glow discharge deposited hydrogenated amorphous silicon over said substrate and having regions of differing conductivity with at least one region of intrinsic hydrogenated amorphous silicon. The layer of hydrogenated amorphous silicon has opposed first and second major surfaces where the first major surface contacts the electrically conductive substrate and an electrode for electrically contacting the second major surface. The intrinsic hydrogenated amorphous silicon region is deposited in a glow discharge with an atmosphere which includes not less than about 0.02 atom percent mono-atomic boron. An improved N.I.P. solar cell is disclosed using a BF.sub.3 doped intrinsic layer.

  11. From lime to silica and alumina: systematic modeling of cement clinkers using a general force-field.

    PubMed

    Freitas, A A; Santos, R L; Colaço, R; Bayão Horta, R; Canongia Lopes, J N

    2015-07-28

    Thirteen different cement-clinker crystalline phases present in the lime-silica-alumina system have been systematically modeled using a simple and general force field. This constitutes a new type of approach towards the study of lime-silica-alumina systems, where the simpler and more transferable Lennard-Jones potential was used instead of the more traditional Buckingham potential. The results were validated using experimental density and structural data. The elastic properties were also considered. Six amorphous phases (corresponding to calcium/silicon ratios corresponding to belite, rankinite, wollastonite and alumina-doped amorphous wollastonite with 5%, 10% and 15% alumina content) were also studied using molecular dynamics simulations. The obtained MD trajectories were used to characterize the different crystalline and amorphous phases in terms of the corresponding radial distribution functions, aggregate analyses and connectivity among silica groups. These studies allowed a direct comparison between the crystalline and amorphous phases and revealed how the structure of the silica network was modified in the amorphous materials or by the inclusion of other structural units such as alumina. The knowledge at an atomistic level of such modifications is paramount for the formulation of new cement-clinker phases. PMID:26109081

  12. In vivo penetration of bare and lipid-coated silica nanoparticles across the human stratum corneum.

    PubMed

    Iannuccelli, Valentina; Bertelli, Davide; Romagnoli, Marcello; Scalia, Santo; Maretti, Eleonora; Sacchetti, Francesca; Leo, Eliana

    2014-10-01

    Skin penetration of silica nanoparticles (NP) currently used in pharmaceutical and cosmetic products is a topic of interest not only to evaluate their possible toxicity, but also to understand their behaviour upon contact with the skin and to exploit their potential positive effects in drug or cosmetic delivery field. Therefore, the present work aimed to elucidate the in vivo mechanism by which amorphous hydrophilic silica NP enter human stratum corneum (SC) through the evaluation of the role played by the nanoparticle surface polarity and the human hair follicle density. Two silica samples, bare hydrophilic silica (B-silica, 162±51nm in size) and hydrophobic lipid-coated silica (LC-silica, 363±74nm in size) were applied on both the volar and dorsal side of volunteer forearms. Twelve repetitive stripped tapes were removed from the human skin and evaluated for elemental composition by Energy Dispersive X-ray (EDX) analysis and for silicon content by Inductively Coupled Plasma quadrupole Mass Spectrometry (ICP-MS). All the stripped tapes revealed nanosized structures generally located in the broad spaces between corneocytes and characterized by the same elemental composition (relative weight percentage of silicon and silicon to oxygen weight ratio) than that of the applied samples. However, only about 10% B-silica permeated until the deepest SC layers considered in the study indicating a silica retention in the upper layers of SC, regardless of the hair follicle density. Otherwise, the exposure to LC-silica led to a greater silica skin penetration extent into the deeper SC layers (about 42% and 18% silica following volar and dorsal forearm application, respectively) indicating that the NP surface polarity played a predominant role on that of their size in determining the route and the extent of penetration. PMID:25139292

  13. Silica Transport, Deposition and Porosity Evolution in a Fracture : Insights from Hydrothermal Flow-through Experiments

    NASA Astrophysics Data System (ADS)

    Okamoto, A.; Yamada, R.; Saishu, H.; Tsuchiya, N.

    2014-12-01

    Geofluids contain a large amount of silica, which solubility changes depending on temperature and pressure. Ubiquitous occurrences of various silica deposits (quartz veins, silica sinter, scales) suggest that silica precipitation plays an important role on temporal and spatial variation of hydrological properties of the Earth's crusts. A pressure drop, for example, induced by seismicity, is one of the driving forces for silica precipitation within the crusts. In spite of the importance of silica depositions in fractures, how porosity and permeability evolution during silica precipitation is still poorly understood. In this study, we conducted the hydrothermal experiments for silica precipitation from supersaturated solutions in vapor (370˚C, 20 MPa) and supercritical (420 ˚C, 30 MPa) conditions with flow rate of 1 g/min. After the experiments, we analyzed the 3-D porosity structures by X-ray CT, and then by making thin section. We developed a tube-in-tube vessel, which is composed of main vessel (made of SUS316), and inner alumina tube (6 mm inner diameter), to make a horizontal flow path. We did not used rock/mineral substrates, and alumina balls (1 mm diameter) are closely packed in the inner tube. In both situations, a significant amount of silica deposited within a week, showing contrasting porosity structures between vapor and supercritical conditions. In vapor conditions, the precipitates are fine-grained quartz aggregate, and the most deposited at around 38 mm from the inlet. The pores were filled from the bottom to the top in the tube. In contrast, in the supercritical conditions, the precipitates are composites of amorphous silica and quartz; which accumulated around the alumina balls uniformly. Quartz grains are formed in amorphous silica layers, and the most porosity reduction occurred at around 25 mm from the inlet. A simple model of cellular automaton involving particle flow, adsorption, settling and deposition reveals that the relative magnitude of

  14. Diatomite releases silica during spirit filtration.

    PubMed

    Gómez, J; Gil, M L A; de la Rosa-Fox, N; Alguacil, M

    2014-09-15

    The purpose of this study was to ascertain whether diatomite is an inert filter aid during spirit filtration. Surely, any compound with a negative effect on the spirit composition or the consumer's health could be dissolved. In this study different diatomites were treated with 36% vol. ethanol/water mixtures and the amounts and structures of the extracted compounds were determined. Furthermore, Brandy de Jerez was diatomite- and membrane-filtered at different temperatures and the silicon content was analysed. It was found that up to 0.36% by weight of diatomite dissolved in the aqueous ethanol and amorphous silica, in the form of hollow spherical microparticles, was the most abundant component. Silicon concentrations in Brandy de Jerez increased by up to 163.0% after contact with diatomite and these changes were more marked for calcined diatomite. In contrast, reductions of more than 30% in silicon concentrations were achieved after membrane filtration at low temperatures. PMID:24767070

  15. SnO{sub 2} nanoparticles in silica: Nanosized tools for femtosecond-laser machining of refractive index patterns

    SciTech Connect

    Paleari, A.; Franchina, E.; Chiodini, N.; Lauria, A.; Bricchi, E.; Kazansky, P.G.

    2006-03-27

    We show that SnO{sub 2} nanoclusters in silica interact with ultrashort infrared laser pulses focused inside the material generating a hydrostatic compression and photoelastic response of the surrounding glass. This effect, together with the laser-induced nanocluster amorphization, gives rise to positive or negative refractive-index changes, up to 10{sup -2}, depending on the beam-power density. This result points out a wide tuning of the refractive index patterns obtainable in silica-based optical technology.

  16. Silica fractionation and reactivity in soils

    NASA Astrophysics Data System (ADS)

    Unzué Belmonte, Dácil; Barão, Lúcia; Vandevenne, Floor; Schoelynck, Jonas; Struyf, Eric; Meire, Patrick

    2014-05-01

    550°C burnings. The first results showed differences in silica fractions between treatments and between soil types. This project is a close collaboration with University of Dresden. -Fertilization. Humans use fertilizers to increase crops growth and to avoid plagues affecting soil biogeochemistry. We set up a greenhouse experiment where olivine (a relatively easily weatherable silicate mineral) fertilization is applied to two crops (barley and wheat), at two rain application regimes (daily rain and weekly heavy rain) and with different fertilizer grain sizes. The aim of this project is to investigate how olivine application affects Si fractionation and reactivity in the soil profile. Barão, L., Clymans, W., Vandevenne, F., Meire, P., Conley, D.J. and Struyf, E. Pedogenic and biogenic amorphous Si distribution along a temperate land use gradient. Submitted, European Journal of Soil Science, 2013. Koning, E., Epping, E., and Van Raaphorst, W.: Determining bio- genic silica in marine samples by tracking silicate and aluminium concentrations in alkaline leaching solutions, Aquat. Geochem., 8, 37-67, 2002. Vandevenne, F.I., Struyf, E., Clymans, W. & Meire, P. 2012. Agricultural silica harvest: have humans created a new and important loop in the global silica cycle? Frontiers in Ecology and the Environment 10: 243-248.

  17. Bulk amorphous materials

    SciTech Connect

    Schwarz, R.B.; Archuleta, J.I.; Sickafus, K.E.

    1998-12-01

    This is the final report for a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The objective of this work was to develop the competency for the synthesis of novel bulk amorphous alloys. The authors researched their synthesis methods and alloy properties, including thermal stability, mechanical, and transport properties. The project also addressed the development of vanadium-spinel alloys for structural applications in hostile environments, the measurement of elastic constants and thermal expansion in single-crystal TiAl from 300 to 750 K, the measurement of elastic constants in gallium nitride, and a study of the shock-induced martensitic transformations in NiTi alloys.

  18. Amorphous and Cellular Computing

    NASA Astrophysics Data System (ADS)

    Abelson, Harold; Sussman, Gerald J.; Knight, Thomas F., Jr

    2001-08-01

    The objective of this research is to create the architectural, algorithmic, and technological foundations for exploiting programmable materials. These are materials that incorporate vast numbers of programmable elements that react to each other and to their environment. Such materials can be fabricated economically, provided that the computing elements are amassed in bulk without arranging for precision interconnect and testing. In order to exploit programmable materials we must identify engineering principles for organizing and instructing myriad programmable entities to cooperate to robustly achieve pre-established goals, even though the individual entities are unreliable and interconnected in unknown, irregular, and time-varying ways. Progress in microfabrication and in bioengineering will make it possible to assemble such amorphous systems at almost no cost, provided that (1) the units need not all work correctly; (2) the units are identically programmed; and (3) there is no need to manufacture precise geometrical arrangements of the units or precise interconnections among them.

  19. Separation of silica from spent geothermal fluids by adsorptive bubble techniques

    SciTech Connect

    De Carlo, E.H.; Ronay, C.

    1987-01-01

    A method is described for the separation of amorphous silica from super-saturated high ionic strength geothermal fluids produced by the Hawaii Geothermal Project Well-A. A bench-scale technique which makes use of adsorptive bubble flotation is employed to remove silica after flocculation by the addition of polyvalent metal ions to hot (60-90/sup 0/C) spent brine discharge. Ferric and aluminum salts are evaluated as flocculants under varying conditions. The anionic surfactant sodium lauryl sulfate and the cationic surfactant lauryl amine hydrochloride (LA) are utilized as the collectors below and above the isoelectric point, respectively. Efficiency of removal of the silica is pH, metal concentration, and surfactant-type dependent. Best results are achieved under slightly alkaline conditions (pH = 8), using 3.75 x 10E/sup -4/ M ferric ion present as its sulfate, La as the collector, and with a gas flow of 15 +/- 3 mL/min. Under these conditions, approximately 70 +/- 2% of the total silica is separated from the brine discharge; this value, although not quantitative, represents more than 85% removal of the silica present above its amorphous solubility at the operating temperature. After the separation process, fluids contain residual concentrations of silica which are not expected to result in scale deposition and which can then be passed through heat exchangers to extract further energy for secondary uses.

  20. Perspective on photovoltaic amorphous silicon

    SciTech Connect

    Luft, W.; Stafford, B.; von Roedern, B.

    1992-05-01

    Amorphous silicon is a thin film option that has the potential for a cost-effective product for large-scale utility photovoltaics application. The initial efficiencies for single-junction and multijunction amorphous silicon cells and modules have increased significantly over the past 10 years. The emphasis of research and development has changed to stabilized efficiency, especially that of multijunction modules. NREL has measured 6.3%--7.2% stabilized amorphous silicon module efficiencies for US products, and 8.1% stable efficiencies have been reported by Fuji Electric. This represents a significant increase over the stabilized efficiencies of modules manufactured only a few years ago. An increasing portion of the amorphous silicon US government funding is now for manufacturing technology development to reduce cost. The funding for amorphous silicon for photovoltaics by Japan over the last 5 years has been about 50% greater than that in the United State, and by Germany in the last 2--3 years more than twice that of the US Amorphous silicon is the only thin-film technology that is selling large-area commercial modules. The cost for amorphous silicon modules is now in the $4.50 range; it is a strong function of plant production capacity and is expected to be reduced to $1.00--1.50/W{sub p} for plants with 10 MW/year capacities. 10 refs.

  1. Perspective on photovoltaic amorphous silicon

    SciTech Connect

    Luft, W.; Stafford, B.; von Roedern, B. )

    1992-12-01

    Amorphous silicon is a thin film option that has the potential for a cost-effective product for large-scale utility photovoltaics application. The initial efficiencies for single-junction and multijunction amorphous silicon cells and modules have increased significantly over the past 10 years. The emphasis of research and development has changed to stabilized efficiency, especially that of multijunction modules. NREL has measured 6.3%--7.2% stabilized amorphous silicon module efficiencies for U.S. products, and 8.1% stable efficiencies have been reported by Fuji Electric. This represents a significant increase over the stabilized efficiencies of modules manufactured only a few years ago. An increasing portion of the amorphous silicon U.S. government funding is now for manufacturing technology development to reduce cost. The funding for amorphous silicon for photovoltaics by Japan over the last 5 years has been about 50% greater than that in the United States, and by Germany in the last 2--3 years more than twice that of the U.S. Amorphous silicon is the only thin-film technology that is selling large-area commercial modules. The cost for amorphous silicon modules is now in the $4.50 range; it is a strong function of plant production capacity and is expected to be reduced to $1.00--1.50/W[sub [ital p

  2. Stability and migration of small copper clusters in amorphous dielectrics

    SciTech Connect

    Guzman, David M.; Onofrio, Nicolas; Strachan, Alejandro

    2015-05-21

    We use density functional theory (DFT) to study the thermodynamic stability and migration of copper ions and small clusters embedded in amorphous silicon dioxide. We perform the calculations over an ensemble of statistically independent structures to quantify the role of the intrinsic atomic-level variability in the amorphous matrix affect the properties. The predicted formation energy of a Cu ion in the silica matrix is 2.7 ± 2.4 eV, significantly lower the value for crystalline SiO{sub 2}. Interestingly, we find that Cu clusters of any size are energetically favorable as compared to isolated ions; showing that the formation of metallic clusters does not require overcoming a nucleation barrier as is often assumed. We also find a broad distribution of activation energies for Cu migration, from 0.4 to 1.1 eV. This study provides insights into the stability of nanoscale metallic clusters in silica of interest in electrochemical metallization cell memories and optoelectronics.

  3. Resolving 2D Amorphous Materials with Scanning Probe Microscopy

    NASA Astrophysics Data System (ADS)

    Burson, Kristen M.; Buechner, Christin; Lewandowski, Adrian; Heyde, Markus; Freund, Hans-Joachim

    Novel two-dimensional (2D) materials have garnered significant scientific interest due to their potential technological applications. Alongside the emphasis on crystalline materials, such as graphene and hexagonal BN, a new class of 2D amorphous materials must be pursued. For amorphous materials, a detailed understanding of the complex structure is necessary. Here we present a structural study of 2D bilayer silica on Ru(0001), an insulating material which is weakly coupled to the substrate. Atomic structure has been determined with a dual mode atomic force microscopy (AFM) and scanning tunneling microscopy (STM) sensor in ultra-high vacuum (UHV) at low temperatures, revealing a network of different ring sizes. Liquid AFM measurements with sub-nanometer resolution bridge the gap between clean UHV conditions and the environments that many material applications demand. Samples are grown and characterized in vacuum and subsequently transferred to the liquid AFM. Notably, the key structural features observed, namely nanoscale ring networks and larger holes to the substrate, show strong quantitative agreement between the liquid and UHV microscopy measurements. This provides direct evidence for the structural stability of these silica films for nanoelectronics and other applications. KMB acknowledges support from the Alexander von Humboldt Foundation.

  4. Silica Precipitation and Lithium Sorption

    SciTech Connect

    Jay Renew

    2015-09-20

    This file contains silica precipitation and lithium sorption data from the project. The silica removal data is corrected from the previous submission. The previous submission did not take into account the limit of detection of the ICP-MS procedure.

  5. Paleozoic and Mesozoic silica-rich seawater: Evidence from hematitic chert (jasper) deposits

    USGS Publications Warehouse

    Grenne, Tor; Slack, J.F.

    2003-01-01

    Laterally extensive beds of highly siliceous, hematitic chert (jasper) are associated with many volcanogenic massive sulfide (VMS) deposits of Late Cambrian to Early Cretaceous age, yet are unknown in analogous younger (including modern) settings. Textural studies suggest that VMS-related jaspers in the Ordovician L??kken ophiolite of Norway were originally deposited as Si- and Fe-rich gels that precipitated from hydrothermal plumes as colloidal silica and iron-oxyhydroxide particles. Rare earth element patterns and Ge/Si ratios of the jaspers reflect precipitation from plumes having seawater dilution factors of 103 to 104, similar to modern examples. We propose that silica in the ancient jaspers is not derived from submarine hydrothermal fluids-as suggested by previous workers-but instead was deposited from silic-rich sea-water. Flocculation and precipitation of the silica were triggered inorganically by the bridging effect of positively charged iron oxyhydroxides in the hydrothermal plume. A model involving amorphous silica (opal-A) precursors to the jaspers suggests that silica contents of Cambrian-Early Cretaceous oceans were at least 110 mg/L SiO2, compared to values of 40-60 mg/L SiO2 estimated in other studies. The evolution of ancient silica-rich to modern Fe-rich precipitates in submarine-hydrothermal plumes reflects a changeover from silica-saturated to silica-depleted seawater through Phanerozoic time, due mainly to ocean-wide emergence of diatoms in the Cretaceous.

  6. Monitoring the recrystallisation of amorphous xylitol using Raman spectroscopy and wide-angle X-ray scattering.

    PubMed

    Palomäki, Emmi; Ahvenainen, Patrik; Ehlers, Henrik; Svedström, Kirsi; Huotari, Simo; Yliruusi, Jouko

    2016-07-11

    In this paper we present a fast model system for monitoring the recrystallization of quench-cooled amorphous xylitol using Raman spectroscopy and wide-angle X-ray scattering. The use of these two methods enables comparison between surface and bulk crystallization. Non-ordered mesoporous silica micro-particles were added to the system in order to alter the rate of crystallization of the amorphous xylitol. Raman measurements showed that adding silica to the system increased the rate of surface crystallization, while X-ray measurements showed that the rate of bulk crystallization decreased. Using this model system it is possible to measure fast changes, which occur in minutes or within a few hours. Raman-spectroscopy and wide-angle X-ray scattering were found to be complementary techniques when assessing surface and bulk crystallization of amorphous xylitol. PMID:27163527

  7. Containerless processing of amorphous ceramics

    NASA Technical Reports Server (NTRS)

    Weber, J. K. Richard; Krishnan, Shankar; Schiffman, Robert A.; Nordine, Paul C.

    1990-01-01

    The absence of gravity allows containerless processing of materials which could not otherwise be processed. High melting point, hard materials such as borides, nitrides, and refractory metals are usually brittle in their crystalline form. The absence of dislocations in amorphous materials frequently endows them with flexibility and toughness. Systematic studies of the properties of many amorphous materials have not been carried out. The requirements for their production is that they can be processed in a controlled way without container interaction. Containerless processing in microgravity could permit the control necessary to produce amorphous forms of hard materials.

  8. Nanomanufacturing of silica nanowires: Synthesis, characterization and applications

    NASA Astrophysics Data System (ADS)

    Sekhar, Praveen Kumar

    In this research, selective and bottom-up manufacturing of silica nanowires on silicon (Si) and its applications has been investigated. Localized synthesis of these nanowires on Si was achieved by metal thin film catalysis and metal ion implantation based seeding approach. The growth mechanism of the nanowires followed a vapor-liquid-solid (VLS) mechanism. Mass manufacturing aspects such as growth rate, re-usability of the substrate and experimental growth model were also investigated. Further, silica nanowires were explored as surface enhanced Raman (SER) substrate and immunoassay templates towards optical and electrochemical detection of cancer biomarkers respectively. Investigating their use in photonic applications, optically active silica nanowires were synthesized by erbium implantation after nanowire growth and implantation of erbium as a metal catalyst in Si to seed the nanowires. Ion implantation of Pd in Si and subsequent annealing in Ar at 1100 0 C for 60 mins in an open tube furnace resulted in silica nanowires of diameters ranging from 15 to 90 nm. Similarly, Pt was sputtered on to Si and further annealed to obtain silica nanowires of diameters ranging from 50 to 500 nm. Transmission electron microscopy studies revealed the amorphous nature of the wires. In addition, nano-sized Pd catalyst was found along the body of the nanowires seeded by Pd implantation into Si. After functionalization of the wires with 3 - AminoPropylTriMethoxySilane (APTMS), the Pd decorated silica nanowires served as an SER substrate exhibiting a sensitivity of 10 7 towards the detection of interleukin-10 (IL-10, a cancer biomarker) with higher spatial resolution. Voltammetric detection of IL-10 involved silica nanowires synthesized by Pd thin film catalysis on Si as an immunoassay template. Using the electrochemical scheme, the presence of IL-10 was detected down to 1fg/mL in ideal pure solution and 1 pg/mL in clinically relevant samples. Time resolved photoluminescence (PL

  9. Epoxy Grout With Silica Thickener

    NASA Technical Reports Server (NTRS)

    Mcclung, C. E.

    1984-01-01

    Grout cures quickly, even in presence of hydraulic oil. Grout is mixture of aggregate particles, finely-divided silica, epoxy resin, and triethylenetetramine curing agent, with mixture containing about 85 percent silica and aggregate particle sand 15 percent resin and curing agent. Silica is thickening agent and keeps grout from sagging.

  10. Apatite Formation from Amorphous Calcium Phosphate and Mixed Amorphous Calcium Phosphate/Amorphous Calcium Carbonate.

    PubMed

    Ibsen, Casper J S; Chernyshov, Dmitry; Birkedal, Henrik

    2016-08-22

    Crystallization from amorphous phases is an emerging pathway for making advanced materials. Biology has made use of amorphous precursor phases for eons and used them to produce structures with remarkable properties. Herein, we show how the design of the amorphous phase greatly influences the nanocrystals formed therefrom. We investigate the transformation of mixed amorphous calcium phosphate/amorphous calcium carbonate phases into bone-like nanocrystalline apatite using in situ synchrotron X-ray diffraction and IR spectroscopy. The speciation of phosphate was controlled by pH to favor HPO4 (2-) . In a carbonate free system, the reaction produces anisotropic apatite crystallites with large aspect ratios. The first formed crystallites are highly calcium deficient and hydrogen phosphate rich, consistent with thin octacalcium phosphate (OCP)-like needles. During growth, the crystallites become increasingly stoichiometric, which indicates that the crystallites grow through addition of near-stoichiometric apatite to the OCP-like initial crystals through a process that involves either crystallite fusion/aggregation or Ostwald ripening. The mixed amorphous phases were found to be more stable against phase transformations, hence, the crystallization was inhibited. The resulting crystallites were smaller and less anisotropic. This is rationalized by the idea that a local phosphate-depletion zone formed around the growing crystal until it was surrounded by amorphous calcium carbonate, which stopped the crystallization. PMID:27460160

  11. Effect of silica forms in rice husk ash on the properties of concrete

    NASA Astrophysics Data System (ADS)

    Bui, Le Anh-Tuan; Chen, Chun-Tsun; Hwang, Chao-Lung; Wu, Wei-Sheng

    2012-03-01

    The strength and durability properties of concrete with or without three types of rice husk ash (RHA), namely, amorphous, partial crystalline, and crystalline RHA, were investigates. The three types of RHA were added into concrete at a 20% replacement level. Consequently, the pozzolanic reactivity of amorphous RHA was higher than that of partial crystalline and crystalline RHA. Concrete added with amorphous RHA showed excellent characteristics in its mechanical and durability properties. The results showed that the higher the amount of crystalline silica in RHA, the lower the concrete resistivity value became. When compared with each other, concretes with 20% of the cement replaced with these types of RHA achieved similar ultrasonic pulse velocity values, but all were lower than that of the control concrete. The incorporation of these kinds of RHA significantly reduced chloride penetration. The results not only encourage the use of amorphous materials, they also support the application of crystalline or partial crystalline RHA as mineral and pozzolanic admixtures for cement.

  12. Fabrication of amorphous diamond films

    DOEpatents

    Falabella, S.

    1995-12-12

    Amorphous diamond films having a significant reduction in intrinsic stress are prepared by biasing a substrate to be coated and depositing carbon ions thereon under controlled temperature conditions. 1 fig.

  13. Raman Spectroscopy of Amorphous Carbon

    SciTech Connect

    Tallant, D.R.; Friedmann, T.A.; Missert, N.A.; Siegal, M.P.; Sullivan, J.P.

    1998-01-01

    Amorphous carbon is an elemental form of carbon with low hydrogen content, which may be deposited in thin films by the impact of high energy carbon atoms or ions. It is structurally distinct from the more well-known elemental forms of carbon, diamond and graphite. It is distinct in physical and chemical properties from the material known as diamond-like carbon, a form which is also amorphous but which has a higher hydrogen content, typically near 40 atomic percent. Amorphous carbon also has distinctive Raman spectra, whose patterns depend, through resonance enhancement effects, not only on deposition conditions but also on the wavelength selected for Raman excitation. This paper provides an overview of the Raman spectroscopy of amorphous carbon and describes how Raman spectral patterns correlate to film deposition conditions, physical properties and molecular level structure.

  14. Formation of long-range ordered quantum dots arrays in amorphous matrix by ion beam irradiation

    SciTech Connect

    Buljan, M.; Bogdanovic-Radovic, I.; Karlusic, M.; Desnica, U. V.; Radic, N.; Dubcek, P.; Drazic, G.; Salamon, K.; Bernstorff, S.; Holy, V.

    2009-08-10

    We demonstrate the production of a well ordered three-dimensional array of Ge quantum dots in amorphous silica matrix. The ordering is achieved by ion beam irradiation and annealing of a multilayer film. Structural analysis shows that quantum dots nucleate along the direction of the ion beam used for irradiation, while the mutual distance of the quantum dots is determined by the diffusion properties of the multilayer material rather than the distances between traces of ions that are used for irradiation.

  15. Silica-based nanocomposites via reverse microemulsions: classifications, preparations, and applications.

    PubMed

    Wang, Jiasheng; Shah, Zameer Hussain; Zhang, Shufen; Lu, Rongwen

    2014-05-01

    Silica-based nanocomposites with amorphous silica as the matrix or carrier along with a functional component have been extensively investigated. These nanocomposites combine the advantages of both silica and the functional components, demonstrating great potential for various applications. To synthesize such composites, one of the most frequently used methods is reverse microemulsion due to its convenient control over the size, shape, and structures. The structures of the composites have a decisive significance for their properties and applications. In this review, we tried to categorize the silica-based nanocomposites via reverse microemulsions based on their structures, discussed the syntheses individually for each structure, summarized their applications, and made some perspectives based on the current progress of this field. PMID:24562100

  16. The preparation and properties of monodisperse core-shell silica magnetic microspheres.

    PubMed

    Lou, Min-yi; Jia, Qiu-ling; Wang, De-ping; Liu, Bing; Huang, Wen-hai

    2008-01-01

    The monodisperse core-shell silica magnetic microspheres (MMS) were synthesized by sol-gel method gelling in the emulsion. Optical microscope (OM), field emission scanning electron microscope (FESEM), nitrogen adsorption and desorption Brunauer Emmett Teller Procedure (BET) isotherms and Barrett-Joyner-Halenda (BJH) pore size distribution measurements, X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and vibrating sample magnetometer (VSM) were used to characterize the appearance, size distribution, phase, specific surface area, chemical composition and magnetic property of silica MMS. The results showed that silica MMS prepared through sol-gel method with acid-alkali two-step catalyze and gelling in emulsion exhibited the superior core-shell structure and size distribution of the microspheres concentrated in about 20 mum. The main phase of microspheres was amorphous silica and spinel ferroferric oxide. Meanwhile, the microspheres remained the superparamagnetic behavior and could be used as biomaterials. PMID:17597357

  17. Shock-wave equation-of-state measurements in fused silica up to 1600 GPa

    NASA Astrophysics Data System (ADS)

    McCoy, C. A.; Gregor, M. C.; Polsin, D. N.; Fratanduono, D. E.; Celliers, P. M.; Boehly, T. R.; Meyerhofer, D. D.

    2016-06-01

    The properties of silica are important to geophysical and high-pressure equation-of-state research. Its most-prevalent crystalline form, α-quartz, has been extensively studied to TPa pressures. This article presents Hugoniot measurements on amorphous silica, commonly referred to as fused silica, over a range from 200 to 1600 GPa using laser-driven shocks and an α-quartz standard. These results extend the measured Hugoniot of fused silica to higher pressures. In the 200- to 600-GPa range, the data are in very good agreement with those obtained by Qi et al. [Phys. Plasmas 22, 062706 (2015)] using magnetically driven aluminum impactors and aluminum as a standard material. A new shock velocity/particle velocity relation is derived to fit the experimental data.

  18. Comparison of analytical methods for the determination of silica in geothermal waters

    USGS Publications Warehouse

    Chemerys, J.C.

    1983-01-01

    The silica concentration of 26 Guatemalan geothermal waters were analyzed colorimetrically (spectrophotometrically) and by atomic absorption. Results by the atomic absorption method were less affected by polymerization and precipitation of silica from supersaturated solutions. Shaking the samples prior to analysis improves the accuracy of the atomic absorption results. The advantages of colorimetric analysis over atomic absorption are better sensitivity and precision. However, for accurate colorimetric results, geothermal samples must be sufficiently diluted in the field, which ensures that no further polymerization occurs and that amorphous silica that may be present will redissolve. If the samples are not diluted in the field they should be diluted in the laboratory and left standing for at least a month to allow the silica to redissolve. If analyzed immediately the diluted samples should be made alkaline and heated overnight in a 90?? oven. ?? 1983.

  19. Linear and Nonlinear Wave Dynamics in Amorphous Photonic Lattices

    NASA Astrophysics Data System (ADS)

    Rechtsman, Mikael; Szameit, Alexander; Segev, Mordechai

    Conventional intuition in solid-state physics holds that in order for a solid to have an electronic band-gap, it must be periodic, allowing the use of Bloch's theorem. Indeed, the free-electron approximation seems to imply that Bragg scattering in periodic potentials is a necessary condition for the formation of a band-gap. But this is obviously untrue: looking through a window reveals that glassy silica (SiO2), although possessing no order at all, still displays a band-gap spanning the entire photon energy range of visible light, without absorption. Several experimental studies have probed the properties of the band-gap in such "amorphous" electronic systems using spectroscopic techniques [1], time-of-flight measurements [2], and others. With the major progress in photonic crystals [3, 4], it is natural to explore amorphous photonic structures with band-gaps, where the actual wavefunction can be observed directly, and hence, many physical issues can be studied at an unprecedented level. Indeed, amorphous photonic media have been studied theoretically in several pioneering papers (e.g., [5, 6]), and experiments in the microwave regime have demonstrated the existence of a band-gap [5]. However, amorphous band-gap media have never been studied experimentally in the optical regime. Particularly in optics, the full beauty of disorder can be revealed: optics offers the possibility to precisely engineer the potential strength and period, as well as the unique opportunity to employ nonlinearity under controlled conditions, which could unravel unknown features that are much harder to access experimentally in other systems. Here, we present the first experimental study of amorphous photonic lattices: a two-dimensional array of randomly organized evanescently coupled waveguides. We demonstrate that the bands in this medium, comprising inherently localized Anderson states, are separated by gaps, despite the total lack of Bragg scattering. We find that amorphous photonic

  20. Amorphous metal alloy and composite

    DOEpatents

    Wang, Rong; Merz, Martin D.

    1985-01-01

    Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

  1. Age hardening of 6061/alumina-silica fiber composite

    SciTech Connect

    Khangaonkar, P.R.; Shamsul, J.B.; Azmi, R.

    1994-12-31

    Continuous alumina-silica fiber (Altex of Sumitomo) which yields high performance composites with some aluminium alloys was tried for squeeze cast 6061 based composites with volume fractions of 0.5 and 0.32, and the matrix microhardness and resistivity changes during age hardening were studied. The matrix in the composites hardened much more than the unreinforced alloy. Microhardness increases of up to 70 VPN above the solution treated condition at various aging temperatures were observed. The resistivity variation indicated an appreciable state of internal stress which continued to persist even when hardness fell by overaging. Energy dispersive X-ray analysis indicated that the regions close to the fibers had a higher silicon content than the matrix, and amorphous silica in the fiber may have a role in the formation of an enriched layer which may help the bonding and strength in the composite.

  2. The mechanism of growth of quartz crystals into fused silica

    NASA Technical Reports Server (NTRS)

    Fratello, V. J.; Hays, J. F.; Spaepen, F.; Turnbull, D.

    1980-01-01

    It is proposed that the growth of quartz crystals into fused silica is effected by a mechanism involving the breaking of an Si-O bond and its association with an OH group, followed by cooperative motion of the nonbridging oxygen and the hydroxyl group which results in the crystallization of a row of several molecules along a crystalline-amorphous interfacial ledge. This mechanism explains, at least qualitatively, all the results of the earlier experimental study of the dependence of quartz crystal growth upon applied pressure: large negative activation volume; single activation enthalpy below Si-O bond energy; growth velocity constant in time, proportional to the hydroxyl and chlorine content, decreasing with increasing degree of reduction, and enhanced by nonhydrostatic stresses; lower pre-exponential for the synthetic than for the natural silica.

  3. The Radiolysis and Radioracemization of Amino Acids on Silica Surfaces

    NASA Astrophysics Data System (ADS)

    Bonner, William A.; Lemmon, Richard M.

    1981-12-01

    L-Leucine, deposited on both 1-quartz powder and on a commercial amorphous silica preparation (Syloid 63), has been subjected to irradiation in a60Co γ-ray source, and the ensuing radiolysis and radioracemization have been determined gas chromatographically. The radiolysis and radioracemization observed for leucine on 1-quartz were rather similar to those noted for a crystalline L-leucine control. L-Leucine on Syloid 63, however, was vastly more susceptible to radiolysis as compared to the L-leucine control, and radioracemization was also markedly enhanced—each increasing with larger radiation dosage. L-Isovaline showed a similar, but diminished, enhancement of radiolysis sensitivity when adsorbed on the Syloid surface, but underwent no radioracemization whatsoever. The divergent results of the control and quartz-leucine irradiationsversus the Syloid-leucine and Syloid-isovaline irradiations are interpreted qualitatively in terms of the surface area parameters of the two silica adsorbents and the amino acid adsorbates.

  4. Silica-based nanocomposites via reverse microemulsions: classifications, preparations, and applications

    NASA Astrophysics Data System (ADS)

    Wang, Jiasheng; Shah, Zameer Hussain; Zhang, Shufen; Lu, Rongwen

    2014-04-01

    Silica-based nanocomposites with amorphous silica as the matrix or carrier along with a functional component have been extensively investigated. These nanocomposites combine the advantages of both silica and the functional components, demonstrating great potential for various applications. To synthesize such composites, one of the most frequently used methods is reverse microemulsion due to its convenient control over the size, shape, and structures. The structures of the composites have a decisive significance for their properties and applications. In this review, we tried to categorize the silica-based nanocomposites via reverse microemulsions based on their structures, discussed the syntheses individually for each structure, summarized their applications, and made some perspectives based on the current progress of this field.Silica-based nanocomposites with amorphous silica as the matrix or carrier along with a functional component have been extensively investigated. These nanocomposites combine the advantages of both silica and the functional components, demonstrating great potential for various applications. To synthesize such composites, one of the most frequently used methods is reverse microemulsion due to its convenient control over the size, shape, and structures. The structures of the composites have a decisive significance for their properties and applications. In this review, we tried to categorize the silica-based nanocomposites via reverse microemulsions based on their structures, discussed the syntheses individually for each structure, summarized their applications, and made some perspectives based on the current progress of this field. Electronic supplementary information (ESI) available: The structures of all the surfactants included in this review are listed. See DOI: 10.1039/c3nr06025j

  5. Stable single-layer honeycomblike structure of silica.

    PubMed

    Özçelik, V Ongun; Cahangirov, S; Ciraci, S

    2014-06-20

    Silica or SiO(2), the main constituent of Earth's rocks has several 3D complex crystalline and amorphous phases, but it does not have a graphitelike layered structure in 3D. Our theoretical analysis and numerical calculations from the first principles predict a single-layer honeycomblike allotrope, hα silica, which can be viewed to be derived from the oxidation of silicene and it has intriguing atomic structure with reentrant bond angles in hexagons. It is a wide band gap semiconductor, which attains remarkable electromechanical properties showing geometrical changes under an external electric field. In particular, it is an auxetic metamaterial with a negative Poisson's ratio and has a high piezoelectric coefficient. While it can form stable bilayer and multilayer structures, its nanoribbons can show metallic or semiconducting behavior depending on their chirality. Coverage of dangling Si orbitals by foreign adatoms can attribute new functionalities to hα silica. In particular, Si(2)O(5), where Si atoms are saturated by oxygen atoms from top and bottom sides alternatingly can undergo a structural transformation to make silicatene, another stable, single layer structure of silica. PMID:24996101

  6. Stable Single-Layer Honeycomblike Structure of Silica

    NASA Astrophysics Data System (ADS)

    Özçelik, V. Ongun; Cahangirov, S.; Ciraci, S.

    2014-06-01

    Silica or SiO2, the main constituent of Earth's rocks has several 3D complex crystalline and amorphous phases, but it does not have a graphitelike layered structure in 3D. Our theoretical analysis and numerical calculations from the first principles predict a single-layer honeycomblike allotrope, hα silica, which can be viewed to be derived from the oxidation of silicene and it has intriguing atomic structure with reentrant bond angles in hexagons. It is a wide band gap semiconductor, which attains remarkable electromechanical properties showing geometrical changes under an external electric field. In particular, it is an auxetic metamaterial with a negative Poisson's ratio and has a high piezoelectric coefficient. While it can form stable bilayer and multilayer structures, its nanoribbons can show metallic or semiconducting behavior depending on their chirality. Coverage of dangling Si orbitals by foreign adatoms can attribute new functionalities to hα silica. In particular, Si2O5, where Si atoms are saturated by oxygen atoms from top and bottom sides alternatingly can undergo a structural transformation to make silicatene, another stable, single layer structure of silica.

  7. Study of interaction in silica glass via model potential approach

    NASA Astrophysics Data System (ADS)

    Mann, Sarita; Rani, Pooja

    2016-05-01

    Silica is one of the most commonly encountered substances in daily life and in electronics industry. Crystalline SiO2 (in several forms: quartz, cristobalite, tridymite) is an important constituent of many minerals and gemstones, both in pure form and mixed with related oxides. Cohesive energy of amorphous SiO2 has been investigated via intermolecular potentials i.e weak Van der Waals interaction and Morse type short-range interaction. We suggest a simple atom-atom based Van der Waals as well as Morse potential to find cohesive energy of glass. It has been found that the study of silica structure using two different model potentials is significantly different. Van der Waals potential is too weak (P.E =0.142eV/molecule) to describe the interaction between silica molecules. Morse potential is a strong potential, earlier given for intramolecular bonding, but if applied for intermolecular bonding, it gives a value of P.E (=-21.92eV/molecule) to appropriately describe the structure of silica.

  8. Amorphous carbon for photovoltaics

    NASA Astrophysics Data System (ADS)

    Risplendi, Francesca; Grossman, Jeffrey C.

    2015-03-01

    All-carbon solar cells have attracted attention as candidates for innovative photovoltaic devices. Carbon-based materials such as graphene, carbon nanotubes (CNT) and amorphous carbon (aC) have the potential to present physical properties comparable to those of silicon-based materials with advantages such as low cost and higher thermal stability.In particular a-C structures are promising systems in which both sp2 and sp3 hybridization coordination are present in different proportions depending on the specific density, providing the possibility of tuning their optoelectronic properties and achieving comparable sunlight absorption to aSi. In this work we employ density functional theory to design suitable device architectures, such as bulk heterojunctions (BHJ) or pn junctions, consisting of a-C as the active layer material.Regarding BHJ, we study interfaces between aC and C nanostructures (such as CNT and fullerene) to relate their optoelectronic properties to the stoichiometry of aC. We demonstrate that the energy alignment between the a-C mobility edges and the occupied and unoccupied states of the CNT or C60 can be widely tuned by varying the aC density to obtain a type II interface.To employ aC in pn junctions we analyze the p- and n-type doping of a-C focusingon an evaluation of the Fermi level and work function dependence on doping.Our results highlight promising features of aC as the active layer material of thin-film solar cells.

  9. Vis-NIR Spectroscopy of Mineral Mixtures with Montmorillonite and Silica: Implications for Detecting Alteration Products on Mars

    NASA Astrophysics Data System (ADS)

    Rampe, E. B.; Kraft, M. D.; Sharp, T. G.

    2009-12-01

    Introduction. A variety of secondary silicates have been identified on Mars using Vis-NIR spectroscopic data from the Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite (OMEGA) on Mars Express and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter, including smectite, chlorite, kaolinite, and illite clay minerals and hydrous amorphous silica [1-4]. The detection of these materials is significant because they provide important information about past aqueous environments on Mars. Vis-NIR spectra of specific secondary silicates can be distinguished by the positions and shapes of hydration features. Here, we investigate the detection of secondary silicates by vis-NIR spectroscopy of mixtures with basaltic igneous minerals and either hydrous amorphous silica or montmorillonite. Experimental Procedure. Minor amounts of <2 μm amorphous silica or montmorillonite clay (2.5, 5, 10, and 20 wt%) were physically mixed with augite, andesine, or olivine (75-106 μm). A portion of each mixture was compressed into a pellet. Vis-NIR spectra (0.32-2.55 μm) of particulate and pellet mixtures were measured at RELAB at Brown University, and each spectrum was visually inspected to determine detection limits of secondary silicates based on hydration features. Preliminary Results. Absorptions at 1.4 and 1.9 μm (OH stretch overtone and H2O bend and stretch, respectively) occur in almost all mixture spectra; however, the strength, shape, and position are dependent on the igneous mineral and secondary silicate abundance in the mixture. The morphology of absorptions at ~2.2 μm (from metal-OH bonds) differs between amorphous silica and montmorillonite [3,4], so we use these absorptions to determine the detection limits of amorphous silica and montmorillonite. The 2.2 μm absorption is present in all montmorillonite-mixture spectra, indicating the montmorillonite detection limit is <2.5 wt%; however, the 2.2 μm absorption is

  10. Surface characterization of zirconia-coated alumina and silica carriers

    SciTech Connect

    Damyanova, S.; Grange, P.; Delmon, B.

    1997-06-01

    Silica- and alumina-supported zirconia samples have been prepared by impregnation of the supports with a solution of zirconium alkoxide (n-propoxide) in n-propanol containing ZrO{sub 2} in the ranges 1.2-28.6 and 2.2-23.2 wt%, respectively. The samples were characterized by the SBET method, XRD, XPS, and FTIR. The x-ray diffraction showed that zirconia on silica was amorphous for all concentrations of ZrO{sub 2}. Zirconia on alumina was amorphous up to 17.1 wt% ZrO{sub 2}; beyond this value crystallites were formed. The increase in the XPS IZr 3d/ISi 2p indicates that ZrO{sub 2} appears as a monolayer on silica near the theoretical monolayer coverage (about 28.6 wt%), whereas for alumina-supported zirconia samples the monolayer is formed at lower ZrO{sub 2} content (between 12.9 and 17.1 wt%). It was observed by pyridine adsorption that the strong Lewis acid sites on alumina decreased after deposition of zirconia. However, the number of Lewis acid sites on silica-supported zirconia samples, evoked by an increase of the positive charge on Zr atoms compared to pure zirconia, increases with increasing ZrO{sub 2} content. Some Bronsted acid sites were detected on ZrO{sub 2}/SiO{sub 2} samples due to the slightly higher electron density on the oxygen associated with Si atoms detected by XPS. 42 refs., 8 figs., 4 tabs.

  11. Simultaneous utilization of soju industrial waste for silica production and its residue ash as effective cationic dye adsorbent

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soju industrial waste is an important biomass resource. The present study is aimed to utilize soju industrial waste for silica extraction, and residual ash as a low cost adsorbent for the removal of Methylene Blue (MB) from aqueous solution. High percentage of pure amorphous nanosilica was obtained ...

  12. Hydrated silica on Mars: Global comparison and in-depth analysis at Antoniadi Crater

    NASA Astrophysics Data System (ADS)

    Smith, Matthew R.

    Hydrated silica is found in a variety of Martian deposits within suites of minerals that indicate aqueous alteration, mostly because hydrated silica forms easily in different environments. Because of its relative ubiquity on Mars, it makes a good tracer mineral to compare otherwise dissimilar deposits and relate their relative degrees of aqueous alteration. The first portion of this dissertation uses near-infrared and thermal-infrared spectroscopy to determine the relative degree of crystallinity of hydrated silica and the bulk SiO2 abundance of hydrated-silica-bearing surfaces. This analysis reveals that Martian hydrated silicas exhibit a range of crystalline structures, from noncrystalline (opal-A or hydrated glass) to crystalline (quartz), implying a range in the maturity of these silica deposits. However, bulk SiO2 abundances show less diversity, with most Martian silica deposits having relatively low SiO2 abundances, similar to a basaltic andesitic composition that exists over much of the surface and that suggests little interaction with water. The second portion of this dissertation focuses on one location that contains the only detected quartz on the planet. High-resolution satellite imagery and thermal and near-infrared spectroscopy is used to construct a geologic history of these deposits and their local context. The quartz-bearing deposits are consistently found co-located with hydrated silica, and this spatial coherence suggests that the quartz formed as a diagenetic product of amorphous silica, rather than as a primary igneous mineral. Diagenetic quartz is a mature alteration product of hydrated amorphous silica, and indicates more persistent water and/or higher temperatures at this site. There is also spectral evidence for smectites beneath the silica-bearing rocks, in the lowermost exposed Noachian-aged breccia. A similar stratigraphic sequence---smectite-bearing breccias beneath deposits containing minerals indicating a greater degree of alteration

  13. A thermodynamic and kinetic model for paste–aggregate interactions and the alkali–silica reaction

    SciTech Connect

    Guthrie, George D. Carey, J. William

    2015-10-15

    A new conceptual model is developed for ASR formation based on geochemical principles tied to aqueous speciation, silica solubility, kinetically controlled mineral dissolution, and diffusion. ASR development is driven largely by pH and silica gradients that establish geochemical microenvironments between paste and aggregate, with gradients the strongest within the aggregate adjacent to the paste boundary (i.e., where ASR initially forms). Super-saturation of magadiite and okenite (crystalline ASR surrogates) occurs in the zone defined by gradients in pH, dissolved silica, Na{sup +}, and Ca{sup 2} {sup +}. This model provides a thermodynamic rather than kinetic explanation of why quartz generally behaves differently from amorphous silica: quartz solubility does not produce sufficiently high concentrations of H{sub 4}SiO{sub 4} to super-saturate magadiite, whereas amorphous silica does. The model also explains why pozzolans do not generate ASR: their fine-grained character precludes formation of chemical gradients. Finally, these gradients have interesting implications beyond the development of ASR, creating unique biogeochemical environments.

  14. Geology of quartz and hydrated silica-bearing deposits near Antoniadi Crater, Mars

    NASA Astrophysics Data System (ADS)

    Smith, Matthew R.; Bandfield, Joshua L.

    2012-06-01

    The only area on Mars where crystalline quartz has been identified from orbit is near Antoniadi Crater, on the northern edge of the Syrtis Major shield volcano. However, the method of quartz formation has remained unknown. In this study, we use high-resolution satellite imagery as well as thermal and near-infrared spectroscopy to construct a geologic history of these deposits and their local context. We find that the quartz-bearing deposits are consistently co-located with hydrated silica. This spatial coherence suggests that the quartz formed as a diagenetic product of amorphous silica, rather than as a primary igneous mineral. Diagenetic quartz is a mature alteration product of hydrated amorphous silica, and indicates more persistent water and/or higher temperatures at this site. Beneath the silica-bearing rocks, we also find spectral evidence for smectites in the lowermost exposed Noachian-aged breccia. A similar stratigraphic sequence — smectite-bearing breccias beneath deposits containing minerals suggesting a greater degree of alteration — has also been found at nearby exposures at Nili Fossae and Toro Crater, suggesting a widespread sequence of alteration. By merging the mineral detections of thermal infrared (quartz, feldspar) and near-infrared spectroscopy (hydrated silica, smectite clays) we are able to construct a more complete geologic history from orbit.

  15. Coherent anti-Stokes Raman scattering microscopy driving the future of loaded mesoporous silica imaging.

    PubMed

    Fussell, Andrew L; Mah, Pei Ting; Offerhaus, Herman; Niemi, Sanna-Mari; Salonen, Jarno; Santos, Hélder A; Strachan, Clare

    2014-11-01

    This study reports the use of variants of coherent anti-Stokes Raman scattering (CARS) microscopy as a novel method for improved physicochemical characterization of drug-loaded silica particles. Ordered mesoporous silica is a biomaterial that can be loaded to carry a number of biochemicals, including poorly water-soluble drugs, by allowing the incorporation of drug into nanometer-sized pores. In this work, the loading of two poorly water-soluble model drugs, itraconazole and griseofulvin, in MCM-41 silica microparticles is characterized qualitatively, using the novel approach of CARS microscopy, which has advantages over other analytical approaches used to date and is non-destructive, rapid, label free, confocal and has chemical and physical specificity. The study investigated the effect of two solvent-based loading methods, namely immersion and rotary evaporation, and microparticle size on the three-dimensional (3-D) distribution of the two loaded drugs. Additionally, hyperspectral CARS microscopy was used to confirm the amorphous nature of the loaded drugs. Z-stacked CARS microscopy suggested that the drug, but not the loading method or particle size range, affected 3-D drug distribution. Hyperspectral CARS confirmed that the drug loaded in the MCM-41 silica microparticles was in an amorphous form. The results show that CARS microscopy and hyperspectral CARS microscopy can be used to provide further insights into the structural nature of loaded mesoporous silica microparticles as biomaterials. PMID:25064000

  16. Imaging atomic rearrangements in two-dimensional silica glass: watching silica's dance.

    PubMed

    Huang, Pinshane Y; Kurasch, Simon; Alden, Jonathan S; Shekhawat, Ashivni; Alemi, Alexander A; McEuen, Paul L; Sethna, James P; Kaiser, Ute; Muller, David A

    2013-10-11

    Structural rearrangements control a wide range of behavior in amorphous materials, and visualizing these atomic-scale rearrangements is critical for developing and refining models for how glasses bend, break, and melt. It is difficult, however, to directly image atomic motion in disordered solids. We demonstrate that using aberration-corrected transmission electron microscopy, we can excite and image atomic rearrangements in a two-dimensional silica glass-revealing a complex dance of elastic and plastic deformations, phase transitions, and their interplay. We identified the strain associated with individual ring rearrangements, observed the role of vacancies in shear deformation, and quantified fluctuations at a glass/liquid interface. These examples illustrate the wide-ranging and fundamental materials physics that can now be studied at atomic-resolution via transmission electron microscopy of two-dimensional glasses. PMID:24115436

  17. Nanoporous silica-based protocells at multiple scales for designs of life and nanomedicine

    DOE PAGESBeta

    Sun, Jie; Jakobsson, Eric; Wang, Yingxiao; Brinker, C. Jeffrey

    2015-01-19

    In this study, various protocell models have been constructed de novo with the bottom-up approach. Here we describe a silica-based protocell composed of a nanoporous amorphous silica core encapsulated within a lipid bilayer built by self-assembly that provides for independent definition of cell interior and the surface membrane. In this review, we will first describe the essential features of this architecture and then summarize the current development of silica-based protocells at both micro- and nanoscale with diverse functionalities. As the structure of the silica is relatively static, silica-core protocells do not have the ability to change shape, but their interiormore » structure provides a highly crowded and, in some cases, authentic scaffold upon which biomolecular components and systems could be reconstituted. In basic research, the larger protocells based on precise silica replicas of cells could be developed into geometrically realistic bioreactor platforms to enable cellular functions like coupled biochemical reactions, while in translational research smaller protocells based on mesoporous silica nanoparticles are being developed for targeted nanomedicine. Ultimately we see two different motivations for protocell research and development: (1) to emulate life in order to understand it; and (2) to use biomimicry to engineer desired cellular interactions.« less

  18. Water Contact Angle Dependence with Hydroxyl Functional Groups on Silica Surfaces under CO2 Sequestration Conditions.

    PubMed

    Chen, Cong; Zhang, Ning; Li, Weizhong; Song, Yongchen

    2015-12-15

    Functional groups on silica surfaces under CO2 sequestration conditions are complex due to reactions among supercritical CO2, brine and silica. Molecular dynamics simulations have been performed to investigate the effects of hydroxyl functional groups on wettability. It has been found that wettability shows a strong dependence on functional groups on silica surfaces: silanol number density, space distribution, and deprotonation/protonation degree. For neutral silica surfaces with crystalline structure (Q(3), Q(3)/Q(4), Q(4)), as silanol number density decreases, contact angle increases from 33.5° to 146.7° at 10.5 MPa and 318 K. When Q(3) surface changes to an amorphous structure, water contact angle increases 20°. Water contact angle decreases about 12° when 9% of silanol groups on Q(3) surface are deprotonated. When the deprotonation degree increases to 50%, water contact angle decreases to 0. The dependence of wettability on silica surface functional groups was used to analyze contact angle measurement ambiguity in literature. The composition of silica surfaces is complicated under CO2 sequestration conditions, the results found in this study may help to better understand wettability of CO2/brine/silica system. PMID:26509282

  19. Characterisation of silica derived from rice husk (Muar, Johor, Malaysia) decomposition at different temperatures

    NASA Astrophysics Data System (ADS)

    Azmi, M. A.; Ismail, N. A. A.; Rizamarhaiza, M.; W. M. Hasif. A. A., K.; Taib, H.

    2016-07-01

    Rice husk was thermally decomposed to yield powder composed of silica (SiO2). Temperatures of 700°C and 1000°C were chosen as the decomposition temperatures. X-Ray Diffraction (XRD), X-Ray Florescence (XRF), Fourier Transform Infrared (FTIR), and Field Emission Scanning Electron Microscope (FESEM) analyses were conducted on a synthetic silica powder (SS-SiO2) and the rice husk ash as for the comparative characterisation study. XRD analyses clearly indicated that the decomposed rice husk yielded silica of different nature which are Crystalline Rice Husk Silica (C-RHSiO2) and Amorphous Rice Husk Silica (A-RHSiO2). Moreover, it was found that SS-SiO2 was of Quartz phase, C-RHSiO2 was of Trydimite and Cristobalite. Through XRF detection, the highest SiO2 purity was detected in SS-SiO2 followed by C-RHSiO2 and A-RHSiO2 with purity percentages of 99.60%, 82.30% and 86.30% respectively. FTIR results clearly indicated silica (SiO2) bonding 1056, 1064, 1047, 777, 790 and 798 cm-1) increased as the crystallinity silica increased. The Cristobalite phase was detected in C-RH SiO2 at the wavelength of 620 cm-1. Morphological features as observed by FESEM analyses confirmed that, SS-SiO2 and C-RH SiO2 showed prominent coarse granular morphology.

  20. Nanoporous silica-based protocells at multiple scales for designs of life and nanomedicine

    SciTech Connect

    Sun, Jie; Jakobsson, Eric; Wang, Yingxiao; Brinker, C. Jeffrey

    2015-01-19

    In this study, various protocell models have been constructed de novo with the bottom-up approach. Here we describe a silica-based protocell composed of a nanoporous amorphous silica core encapsulated within a lipid bilayer built by self-assembly that provides for independent definition of cell interior and the surface membrane. In this review, we will first describe the essential features of this architecture and then summarize the current development of silica-based protocells at both micro- and nanoscale with diverse functionalities. As the structure of the silica is relatively static, silica-core protocells do not have the ability to change shape, but their interior structure provides a highly crowded and, in some cases, authentic scaffold upon which biomolecular components and systems could be reconstituted. In basic research, the larger protocells based on precise silica replicas of cells could be developed into geometrically realistic bioreactor platforms to enable cellular functions like coupled biochemical reactions, while in translational research smaller protocells based on mesoporous silica nanoparticles are being developed for targeted nanomedicine. Ultimately we see two different motivations for protocell research and development: (1) to emulate life in order to understand it; and (2) to use biomimicry to engineer desired cellular interactions.

  1. Nanoporous silica-based protocells at multiple scales for designs of life and nanomedicine.

    PubMed

    Sun, Jie; Jakobsson, Eric; Wang, Yingxiao; Brinker, C Jeffrey

    2015-01-01

    Various protocell models have been constructed de novo with the bottom-up approach. Here we describe a silica-based protocell composed of a nanoporous amorphous silica core encapsulated within a lipid bilayer built by self-assembly that provides for independent definition of cell interior and the surface membrane. In this review, we will first describe the essential features of this architecture and then summarize the current development of silica-based protocells at both micro- and nanoscale with diverse functionalities. As the structure of the silica is relatively static, silica-core protocells do not have the ability to change shape, but their interior structure provides a highly crowded and, in some cases, authentic scaffold upon which biomolecular components and systems could be reconstituted. In basic research, the larger protocells based on precise silica replicas of cells could be developed into geometrically realistic bioreactor platforms to enable cellular functions like coupled biochemical reactions, while in translational research smaller protocells based on mesoporous silica nanoparticles are being developed for targeted nanomedicine. Ultimately we see two different motivations for protocell research and development: (1) to emulate life in order to understand it; and (2) to use biomimicry to engineer desired cellular interactions. PMID:25607812

  2. Nanoporous Silica-Based Protocells at Multiple Scales for Designs of Life and Nanomedicine

    PubMed Central

    Sun, Jie; Jakobsson, Eric; Wang, Yingxiao; Brinker, C. Jeffrey

    2015-01-01

    Various protocell models have been constructed de novo with the bottom-up approach. Here we describe a silica-based protocell composed of a nanoporous amorphous silica core encapsulated within a lipid bilayer built by self-assembly that provides for independent definition of cell interior and the surface membrane. In this review, we will first describe the essential features of this architecture and then summarize the current development of silica-based protocells at both micro- and nanoscale with diverse functionalities. As the structure of the silica is relatively static, silica-core protocells do not have the ability to change shape, but their interior structure provides a highly crowded and, in some cases, authentic scaffold upon which biomolecular components and systems could be reconstituted. In basic research, the larger protocells based on precise silica replicas of cells could be developed into geometrically realistic bioreactor platforms to enable cellular functions like coupled biochemical reactions, while in translational research smaller protocells based on mesoporous silica nanoparticles are being developed for targeted nanomedicine. Ultimately we see two different motivations for protocell research and development: (1) to emulate life in order to understand it; and (2) to use biomimicry to engineer desired cellular interactions. PMID:25607812

  3. Modeling vitreous silica bilayers

    NASA Astrophysics Data System (ADS)

    Kumar, Avishek; Wilson, Mark; Sherrington, David; Thorpe, Michael

    2014-03-01

    The recent synthesis and imaging of bilayers of vitreous silica has led to a wealth of new information. We have modeled the experimentally-observed bilayer using a computer assembly procedure to form a network of corner-sharing tetrahedra, which is then mirror-reflected to form a bilayer. We show that the vitreous silica bilayer has additional macroscopic degrees of freedom iff there is a symmetry plane through the center of the bilayer going through the central layer of oxygen ions that join the upper and lower monolayers. We have computer-refined the experimental coordinates to determine the density, and other structural characteristics such as the Si-Si pair distribution function, Si-O-Si bond angle distribution and the Aboav-Weaire law.

  4. Viscoelasticity of silica gels

    SciTech Connect

    Scherer, G.W.

    1995-12-01

    The response of silica gels to mechanical loads depends on the properties of the solid phase and the permeability of the network. Understanding this behavior is essential for modeling of stresses developed during drying or heating of gels. The permeability and the mechanical properties are readily determined from a simple beam-bending experiment, by measuring the load relaxation that occurs at constant deflection. Load decay results from movement of the liquid within the network; in addition, there may be viscoelastic relaxation of the network itself. Silica gel is viscoelastic in chemically aggressive media, but in inert liquids (such as ethanol or acetone) it is elastic. Experiments show that the viscoelastic relaxation time decreases as the concentration and pH of the water in the pore liquid increase. During drying, the permeability decreases and the viscosity increases, both exhibiting a power-law dependence on density of the gel network.

  5. Physical characteristics of chitosan-silica composite of rice husk ash

    NASA Astrophysics Data System (ADS)

    Sumarni, Woro; Sri Iswari, Retno; Marwoto, Putut; Rahayu, Endah F.

    2016-02-01

    Some previous studies showed that the characteristics of chitosan membranes have a very rigid and non-porous structure so that its utilization is not maximized, particularly in the filtration process. Hence, it needs modification to improve the quality of the chitosan membranes. Adding the silica into the chitosan membranes is one of the offered solutions to overcome the problems of physical and mechanical properties of chitosan. This study aims to investigate the effect of variations in the silica composition to the physical characteristics of the chitosan-silica membranes of rice husk ash that were synthesized. The chitosan used is derived from the chitin of Vannamei shrimps’ shell with 82% degree of de-acetylation, while the silica was synthesized from rice husk ash with rendering of silica (SiO2) by 5% and the results of XRD analysis showed an amorphous phase. Membrane synthesis was performed using the phase inversion method with chitosan-silica mass ratios of rice husk ash, which were 1:0.0; 1:0.5; 1:1.0; 1:1.5 and 1:2.0. The results showed that the addition of silica increases the swelling index and the membrane permeability. The results of the analysis, FTIR spectra, obtained a new functional group after the addition of silica, they are Si-OH, Si-O-Si, and CO- NH2. The morphology test using CCD Microscope MS-804 results in the very tight chitosan membranes without the silica surface, it has no pores, smooth and homogeneous, while the chitosan-silica composite membrane of rice husk ash obviously has cracks and small cavities that seemed to spread out.

  6. Strain-modulated electronic and thermal transport properties of two-dimensional O-silica.

    PubMed

    Han, Yang; Qin, Guangzhao; Jungemann, Christoph; Hu, Ming

    2016-07-01

    Silica is one of the most abundant materials in the Earth's crust and is a remarkably versatile and important engineering material in various modern science and technology. Recently, freestanding and well-ordered two-dimensional (2D) silica monolayers with octahedral (O-silica) building blocks were found to be theoretically stable by (Wang G et al 2015 J. Phys. Chem. C 119 15654-60). In this paper, by performing first-principles calculations, we systematically investigated the electronic and thermal transport properties of 2D O-silica and also studied how these properties can be tuned by simple mechanical stretching. Unstrained 2D O-silica is an insulator with an indirect band gap of 6.536 eV. The band gap decreases considerably with bilateral strain up to 29%, at which point a semiconductor-metal transition occurs. More importantly, the in-plane thermal conductivity of freestanding 2D O-silica is found to be unusually high, which is around 40 to 50 times higher than that of bulk α-quartz and more than two orders of magnitude higher than that of amorphous silica. The thermal conductivity of O-silica decreases by almost two orders of magnitude when the bilateral stretching strain reaches 10%. By analyzing the mode-dependent phonon properties and phonon-scattering channel, the phonon lifetime is found to be the dominant factor that leads to the dramatic decrease of the lattice thermal conductivity under strain. The very sensitive response of both band gap and phonon transport properties to the external mechanical strain will enable 2D O-silica to easily adapt to the different environment of realistic applications. Our study is expected to stimulate experimental exploration of further physical and chemical properties of 2D silica systems, and offers perspectives on modulating the electronic and thermal properties of related low-dimensional structures for applications such as thermoelectric, photovoltaic, and optoelectronic devices. PMID:27199352

  7. Strain-modulated electronic and thermal transport properties of two-dimensional O-silica

    NASA Astrophysics Data System (ADS)

    Han, Yang; Qin, Guangzhao; Jungemann, Christoph; Hu, Ming

    2016-07-01

    Silica is one of the most abundant materials in the Earth’s crust and is a remarkably versatile and important engineering material in various modern science and technology. Recently, freestanding and well-ordered two-dimensional (2D) silica monolayers with octahedral (O-silica) building blocks were found to be theoretically stable by (Wang G et al 2015 J. Phys. Chem. C 119 15654–60). In this paper, by performing first-principles calculations, we systematically investigated the electronic and thermal transport properties of 2D O-silica and also studied how these properties can be tuned by simple mechanical stretching. Unstrained 2D O-silica is an insulator with an indirect band gap of 6.536 eV. The band gap decreases considerably with bilateral strain up to 29%, at which point a semiconductor–metal transition occurs. More importantly, the in-plane thermal conductivity of freestanding 2D O-silica is found to be unusually high, which is around 40 to 50 times higher than that of bulk α-quartz and more than two orders of magnitude higher than that of amorphous silica. The thermal conductivity of O-silica decreases by almost two orders of magnitude when the bilateral stretching strain reaches 10%. By analyzing the mode-dependent phonon properties and phonon-scattering channel, the phonon lifetime is found to be the dominant factor that leads to the dramatic decrease of the lattice thermal conductivity under strain. The very sensitive response of both band gap and phonon transport properties to the external mechanical strain will enable 2D O-silica to easily adapt to the different environment of realistic applications. Our study is expected to stimulate experimental exploration of further physical and chemical properties of 2D silica systems, and offers perspectives on modulating the electronic and thermal properties of related low-dimensional structures for applications such as thermoelectric, photovoltaic, and optoelectronic devices.

  8. The deposition of boron nitride and carbon films on silica glass fibers

    SciTech Connect

    Smith, W.L.; Michalske, T.A.; Rye, R.R.

    1993-11-01

    A chemical vapor deposition technique is used to produce amorphous boron nitride and carbon thin films on high strength silica glass fibers. In this method, the fiber is drawn under ultra high vacuum conditions and low pressure process gases, in the presence of a hot tungsten filament, are used to grow films at low substrate temperatures. Films deposited with this technique do not degrade the intrinsic pristine strength of the silica fibers under dry conditions and, when stressed in chemically aggressive environments, act as effective barrier coatings.

  9. Mechanochemistry of shock-induced nanobubble collapse near silica in water

    NASA Astrophysics Data System (ADS)

    Nomura, K.; Kalia, R. K.; Nakano, A.; Vashishta, P.; van Duin, A. C. T.

    2012-08-01

    We have performed million-atom reactive molecular dynamics simulations to study shock-induced bubble collapse near an amorphous silica surface. We observe the formation of water jet during the bubble collapse, which collides on to the silica surface causing a hemispherical pit. Fragment analysis reveals substantial ionization activities in water followed by rapid increase in H3O+ population during the pit formation. We have identified a shock-induced H3O+ ion formation mechanism, in which transient five-coordinated silicon atoms play a pivotal role.

  10. Carboxymethyl cellulose/silica hybrids as templates for calcium phosphate biomimetic mineralization.

    PubMed

    Salama, Ahmed; Abou-Zeid, Ragab E; El-Sakhawy, Mohamed; El-Gendy, Ahmed

    2015-03-01

    Multiphase hybrid materials were synthesized using carboxymethyl cellulose (CMC) as bioactive polymer, silica gel as matrix assisted networks and calcium phosphate as inorganic mineral phase. These hybrids were investigated with infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. Biomimetic crystal growth nucleated from the CMC/silica hybrids was suggested as amorphous calcium phosphate with an evidence that hydroxyapatite, the mineralized component of bone, may be formed at high CMC content. This study provides an efficient approach toward bone-like hybrids with potential bone healing applications. PMID:25526694

  11. 21 CFR 182.1711 - Silica aerogel.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Silica aerogel. 182.1711 Section 182.1711 Food and... GENERALLY RECOGNIZED AS SAFE Multiple Purpose GRAS Food Substances § 182.1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of...

  12. 21 CFR 582.1711 - Silica aerogel.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 6 2010-04-01 2010-04-01 false Silica aerogel. 582.1711 Section 582.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  13. 21 CFR 582.1711 - Silica aerogel.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 6 2012-04-01 2012-04-01 false Silica aerogel. 582.1711 Section 582.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  14. 21 CFR 182.1711 - Silica aerogel.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Silica aerogel. 182.1711 Section 182.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  15. 21 CFR 582.1711 - Silica aerogel.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 6 2014-04-01 2014-04-01 false Silica aerogel. 582.1711 Section 582.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  16. 21 CFR 582.1711 - Silica aerogel.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 6 2011-04-01 2011-04-01 false Silica aerogel. 582.1711 Section 582.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  17. 21 CFR 182.1711 - Silica aerogel.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Silica aerogel. 182.1711 Section 182.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  18. 21 CFR 182.1711 - Silica aerogel.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 3 2012-04-01 2012-04-01 false Silica aerogel. 182.1711 Section 182.1711 Food and....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam having a minimum silica content of 89.5 percent. (b) (c) Limitations, restrictions, or explanation....

  19. Nanostructures having crystalline and amorphous phases

    SciTech Connect

    Mao, Samuel S; Chen, Xiaobo

    2015-04-28

    The present invention includes a nanostructure, a method of making thereof, and a method of photocatalysis. In one embodiment, the nanostructure includes a crystalline phase and an amorphous phase in contact with the crystalline phase. Each of the crystalline and amorphous phases has at least one dimension on a nanometer scale. In another embodiment, the nanostructure includes a nanoparticle comprising a crystalline phase and an amorphous phase. The amorphous phase is in a selected amount. In another embodiment, the nanostructure includes crystalline titanium dioxide and amorphous titanium dioxide in contact with the crystalline titanium dioxide. Each of the crystalline and amorphous titanium dioxide has at least one dimension on a nanometer scale.

  20. Amorphous-diamond electron emitter

    DOEpatents

    Falabella, Steven

    2001-01-01

    An electron emitter comprising a textured silicon wafer overcoated with a thin (200 .ANG.) layer of nitrogen-doped, amorphous-diamond (a:D-N), which lowers the field below 20 volts/micrometer have been demonstrated using this emitter compared to uncoated or diamond coated emitters wherein the emission is at fields of nearly 60 volts/micrometer. The silicon/nitrogen-doped, amorphous-diamond (Si/a:D-N) emitter may be produced by overcoating a textured silicon wafer with amorphous-diamond (a:D) in a nitrogen atmosphere using a filtered cathodic-arc system. The enhanced performance of the Si/a:D-N emitter lowers the voltages required to the point where field-emission displays are practical. Thus, this emitter can be used, for example, in flat-panel emission displays (FEDs), and cold-cathode vacuum electronics.

  1. Generalized melting criterion for amorphization

    SciTech Connect

    Devanathan, R. |; Lam, N.Q.; Okamoto, P.R.; Meshii, M.

    1992-12-01

    We present a thermodynamic model of solid-state amorphization based on a generalization of the well-known Lindemann criterion. The original Lindemann criterion proposes that melting occurs when the root-mean-square amplitude of thermal displacement exceeds a critical value. This criterion can be generalized to include solid-state amorphization by taking into account the static displacements. In an effort to verify the generalized melting criterion, we have performed molecular dynamics simulations of radiation-induced amorphization in NiZr, NiZr{sub 2}, NiTi and FeTi using embedded-atom potentials. The average shear elastic constant G was calculated as a function of the total mean-square atomic displacement following random atom-exchanges and introduction of Frenkel pairs. Results provide strong support for the generalized melting criterion.

  2. Nanoscale plasticity in silica glass

    SciTech Connect

    Glosli, J.N.; Boercker, D.B.; Tesar, A.; Belak, J.

    1993-10-01

    Mechanisms of nano-scale plasticity and damage initiation in silica glass is examined using molecular dynamics simulation. Computer experiments are carried out by indenting a sharp diamond-like tool, containing 4496 atoms, into a silica slab consisting of 12288 atoms. Both elastic and plastic deformation of silica is observed during nanoindentation simulation; this transition occurs at an indentation of 1.25 nm, and the calculated hardness (15GPa for 1.5 nm indentation) agrees with experiment.

  3. Ice formation in amorphous cellulose

    NASA Astrophysics Data System (ADS)

    Czihak, C.; Müller, M.; Schober, H.; Vogl, G.

    2000-03-01

    We investigate the formation of ice in wet amorphous cellulose in the temperature range of 190 K⩽T⩽280 K. Due to voids and pores in the cellulose film, water molecules are able to form crystalline aggregates. Beyond that, water is able to penetrate between cellulose chains where it can adsorb to hydroxyl side groups. From diffraction data we suggest an aggregation of low-density amorphous (lda) ice at cellulose surfaces. The formation of lda ice shows a clear temperature dependence which will be discussed together with recent inelastic neutron scattering results.

  4. Exploring Silica Chemistry at Biological Interfaces: Kinetic and Thermodynamic Drivers of Surface Nucleation

    NASA Astrophysics Data System (ADS)

    Wallace, A. F.; Dove, P. M.

    2006-12-01

    Biochemical investigations have begun to yield information about structural and chemical properties of organic macromolecules involved in biosilicification processes. However, the mechanisms by which these molecules mediate biosilica formation remain unclear. The formation of mineralized structures in organisms is rooted in processes taking place at the nanoscale, and therefore, molecular level investigative probes are required. Insights into how mineral formation occurs within living organisms can be gained by conducting experimental studies with simple model systems that emulate key features of biological systems. Our approach utilizes a novel AFM-based approach to measure the dependence of amorphous silica nucleation kinetics on the chemical and structural nature of the underlying substrate. Model biological surfaces terminated with carboxyl, hydroxyl, and amine moieties were generated through the spontaneous adsorption of {ω}-alkanethiol self-assembled monolayers onto ultra-flat (111) surfaces of gold. Silica nucleation experiments used supersaturated solutions of silicic acid that were produced by the acid catalyzed hydrolysis of tetramethyl orthosilicate. Measurements of surface nucleation rate were conducted under conditions that simulate current views of conditions within silica deposition vesicles of major diatom species, (e.g. ambient temperature, pH = 5.0, NaCl = 0.1 mol/kg). Aqueous silicate levels were varied to examine dependencies on saturation state. Analysis of the kinetic data within the framework of nucleation theory quantifies the height of the kinetic barrier to silica formation, and the net energy of silica-substrate solution interfaces. By conducting experiments for COOH, NH3+, and OH-functionalized substrates, we determine the kinetic and thermodynamic controls of functional chemistry on heterogeneous nucleation of amorphous silica. The findings are providing new insights into how biochemical interfaces mediate the onset of silica formation.

  5. Cellular uptake, evolution, and excretion of silica nanoparticles in human cells

    NASA Astrophysics Data System (ADS)

    Chu, Zhiqin; Huang, Yuanjie; Tao, Qian; Li, Quan

    2011-08-01

    A systematic study on the interaction of silica nanoparticles (NPs) with human cells has been carried out in the present work. Endocytosis and exocytosis are identified as major pathways for NPs entering, and exiting the cells, respectively. Most of the NPs are found to be enclosed in membrane bounded organelles, which are fairly stable (against rupture) as very few NPs are released into the cytoplasm. The nanoparticle-cell interaction is a dynamic process, and the amount of NPs inside the cells is affected by both the amount and morphology (degree of aggregation) of NPs in the medium. These interaction characteristics determine the low cytotoxicity of SiO2 NPs at low feeding concentration.A systematic study on the interaction of silica nanoparticles (NPs) with human cells has been carried out in the present work. Endocytosis and exocytosis are identified as major pathways for NPs entering, and exiting the cells, respectively. Most of the NPs are found to be enclosed in membrane bounded organelles, which are fairly stable (against rupture) as very few NPs are released into the cytoplasm. The nanoparticle-cell interaction is a dynamic process, and the amount of NPs inside the cells is affected by both the amount and morphology (degree of aggregation) of NPs in the medium. These interaction characteristics determine the low cytotoxicity of SiO2 NPs at low feeding concentration. Electronic supplementary information (ESI) available: Low magnification TEM image of 400 nm amorphous silica NPs; TEM images depicting the evolution process of 50 nm silica NPs inside cells; Confocal microscopy images showing the interaction of silica NPs with cells; ζ potential of NPs in dispersion with different pH value; MTT results of H1299 and NE083 cells incubated with 400 nm and 10-20 nm amorphous silica NPs and light microscopy images of H1299 cells treated with 50 nm silica NPs. See DOI: 10.1039/c1nr10499c

  6. High-Silica Rocks and Soils at Gusev Crater, Mars: Distribution, Spectra, and Implications for Past Hydrothermal Activity

    NASA Astrophysics Data System (ADS)

    Rice, M. S.; Bell, J. F.; Wang, A.; Cloutis, E. A.

    2008-12-01

    The Mars Exploration Rover (MER) Spirit has discovered surprisingly high concentrations of amorphous silica in the Inner Basin of the Columbia Hills. As described by Squyres et al. (2008, Science, 320, 1063), within a topographic lowland called Eastern Valley, Spirit's Alpha Particle X-Ray Spectrometer (APXS) measured a composition of >90 wt.% silica at the soil feature "Gertrude Weise", a record high for Mars. The Mössbauer spectrum of this target is featureless. APXS measurements of light-toned nodular outcrops also show high silica concentrations (up to ~72 wt.%), which in some locations co-exist with sulfur-rich soils. Miniature Thermal Emission Spectrometer (Mini-TES) results from the soils and nodules are consistent with opal-A. These deposits have been found adjacent to "Home Plate", a layered plateau interpreted as the product of explosive volcanism. The silica-rich soils and nodules are consistent with sinters and/or residues formed in a hydrothermal system, and may be related to the same hydrovolcanic activity that produced Home Plate. We have begun to map the distribution of high-silica materials in Gusev Crater more extensively using remote sensing, in order to understand the regional extent of possible hydrothermal activity. Spirit's Pancam instrument has collected visible to near-infrared relative reflectance spectra of the region in 11 unique wavelengths. We find that a distinct absorption feature at the longest Pancam wavelength (1009 nm) appears to be characteristic of the high-silica soils and nodules. By mapping the occurrence of this feature with other spectral parameters in Pancam images, we can remotely identify potential amorphous silica deposits elsewhere in the Columbia Hills. Here we present a map with our proposed regional distribution of silica-rich materials within the rover's Gusev Crater traverse area. The mineralogic origin of the 1009nm feature is enigmatic; reflectance spectra of amorphous silica are typically featureless in near

  7. Amorphous SiO2 surface models: energetics of the dehydroxylation process, strain, ab initio atomistic thermodynamics and IR spectroscopic signatures.

    PubMed

    Comas-Vives, Aleix

    2016-03-14

    In this contribution, realistic amorphous SiO2 models of 2.1 × 2.1 nm with silanol densities ranging 1.1-7.2 OH per nm(2) are obtained by means of ab initio calculations via the dehydroxylation of a fully hydroxylated silica surface. The dehydroxyation process is considered to take place via direct condensation of adjacent silanol groups and silica migration steps. The latter reconstructions are needed in order to obtain highly dehydroxylated silica surfaces with favorable energetics and without the formation of defects. The obtained surface phase diagram of different silica models as a function of temperature and PH2O is able to correctly describe the silanol density under different conditions, and the IR spectroscopic signatures of the silanols are in qualitative agreement with the experiment. The amorphous silica models presented here have a high degree of heterogeneity as found from the big variability obtained in the energetics of the dehydroxylation steps. It was also found that the resulting average Si-O distance of the newly formed siloxane bridges serves as a descriptor of the strain introduced in the silica surface. All these factors can be crucial in order to simulate the activity of catalysts grafted onto silica with different silanol densities, especially the one containing ca. 1 OH per nm(2), which can serve as a model for the SiO2 surface pretreated under high vacuum and at 700 °C. PMID:26898649

  8. Spectral Evidence for Silica in Eos Chasma, Mars

    NASA Astrophysics Data System (ADS)

    Hamilton, V. E.

    2006-12-01

    Thermal Emission Imaging System (THEMIS) data in Eos Chasma have revealed spatially small areas, typically mounds or knobs, with materials having significant (>~35%) fractions of silica in one or more as-of-yet unidentified phases [1]. Silica, SiO2, occurs geologically in both crystalline (e.g., quartz) and amorphous (e.g., opal, glass) forms. The identification of associated minerals and the specific silica phase(s) observed in the thermal infrared data is critical to constraining the abundance estimate further. New results from THEMIS multispectral data show that if the silica is present as quartz or one of its polymorphs (e.g., tridymite, cristobalite, coesite), it is probably equal to or less than ~35% of the modal mineralogy. If the silica is present in an amorphous form with different spectral character, such as opal, this number could increase by several tens of percent. Cherts, which are quartz in rock form, exhibit a variety of microscopic textures (e.g., microcrystalline, fibrous, and "megaquartz") [2] and contain contaminating phases that produce variations in their spectra; we have identified several chert samples that also are candidate components and could be present at abundances of several tens of percent or greater. Primary and secondary silica phases are formed by a wide array of geologic processes, many of which include interactions with ambient or hydrothermal fluids and some of which are well-known preservers of biomarkers on Earth. Thus, silica enrichments on the Martian surface are likely to be important recorders of aqueous processes, and possibly biomarkers as well. As such, an area in Eos Chasma adjacent to silica-bearing deposits has been proposed as a landing site for NASA's 2009 Mars Science Laboratory rover [3]. The majority of silica-bearing deposits are a few hundred m2 in size, and there is a paucity of high- resolution visible images with which they can be investigated. A 3-m/pixel Mars Orbiter Camera (MOC) image of a relatively

  9. Petrography study on altered flint aggregate by alkali-silica reaction

    SciTech Connect

    Bulteel, D. . E-mail: bulteel@ensm-douai.fr; Rafai, N.; Degrugilliers, P.; Garcia-Diaz, E.

    2004-11-15

    The aim of our study is to improve our understanding of an alkali-silica reaction (ASR) via petrography. We used a chemical concrete subsystem: flint aggregate, portlandite and KOH. The altered flint aggregate is followed by optical microscopy and scanning electron microscopy (SEM) before and after acid treatment at different intervals. After acid treatment, the observations showed an increase in aggregate porosity and revealed internal degradation of the aggregate. This degradation created amorphous zones. Before acid treatment, the analyses on polished sections by scanning electron microscopy coupled with energy dispersive spectroscopy (EDS) enabled visualization of K{sup +} and Ca{sup 2+} penetration into the aggregate. The appearance of amorphous zones and penetration of positive ions into the aggregate are correlated with the increase in the molar fraction of silanol sites. This degradation is specific to the alkali-silica reaction.

  10. Spectroscopy of silica and the remote detection of astrobiologically rich environments

    NASA Astrophysics Data System (ADS)

    Michalski, J. R.; Sharp, T. G.; Kraft, M. D.; Christensen, P. R.

    2003-04-01

    Fundamental to the exploration of Mars and other solid planets for astrobiology is the desire to locate sites where rocks have been aqueously altered or where aqueous sediments exist. One material that is common and abundant on Earth, and that is likely to occur in any environment where silicate rocks have interacted with water, is silica. Silica is an important material for astrobiology because of its long crustal residence time and relative abundance on Earth, and because most of the early terrestrial microfossils are entombed in it. Presumably, if opaline deposits or microcrystalline silica are discovered on Mars, they will be high priority sites for further investigation. Not only is silica important in preserving biological materials directly, it is also an important mineralogical indicator of geological environment. For example, remote detection of the high temperature polymorphs tridymite or cristobalite would be suggestive of volcanic or hydrothermal-fumarolic activity. Discovery of various silica polymorphs on Mars would be important for understanding the geologic context of deposits, as well as for identification of astrobiologically interesting materials. Given the availability of thermal infrared spectra of Mars from the NASA TES and THEMIS experiments, and the anticipated results of Mini-TES from the surface of Mars, an investigation of the thermal emission spectra of silica minerals and siliceous materials is timely. We present results of a thermal infrared spectral analysis of silica polymorphs and some siliceous rocks. The spectral effects of crystal structure, crystallinity, composition, and surface roughness are examined. All amorphous forms, including silica glass, hyalite (opal-AN), and opal (A), exhibit very similar emission spectra. Partially crystalline silica, such as opal-CT is distinguishable from amorphous forms by the depth and shape of the major reststrahlen feature. Spectra of cristobalite and tridymite bear unique Si-O vibrational

  11. Biogeochemistry: Silica cycling over geologic time

    NASA Astrophysics Data System (ADS)

    Conley, Daniel J.; Carey, Joanna C.

    2015-06-01

    The Earth's long-term silica cycle is intimately linked to weathering rates and biogenic uptake. Changes in weathering rates and the retention of silica on land have altered silica availability in the oceans for hundreds of millions of years.

  12. Amorphous-silicon cell reliability testing

    NASA Technical Reports Server (NTRS)

    Lathrop, J. W.

    1985-01-01

    The work on reliability testing of solar cells is discussed. Results are given on initial temperature and humidity tests of amorphous silicon devices. Calibration and measurement procedures for amorphous and crystalline cells are given. Temperature stress levels are diagrammed.

  13. Imprinting bulk amorphous alloy at room temperature

    SciTech Connect

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.

  14. Imprinting bulk amorphous alloy at room temperature

    PubMed Central

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-01-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment. PMID:26563908

  15. Imprinting bulk amorphous alloy at room temperature.

    PubMed

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T; Lograsso, Thomas A; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-01-01

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. Our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment. PMID:26563908

  16. ZBLAN, Silica Fiber Comparison

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This graph depicts the increased signal quality possible with optical fibers made from ZBLAN, a family of heavy-metal fluoride glasses (fluorine combined zirconium, barium, lanthanum, aluminum, and sodium) as compared to silica fibers. NASA is conducting research on pulling ZBLAN fibers in the low-g environment of space to prevent crystallization that limits ZBLAN's usefulness in optical fiber-based communications. In the graph, a line closer to the black theoretical maximum line is better. Photo credit: NASA/Marshall Space Flight Center

  17. Amorphous rare earth magnet powders

    SciTech Connect

    Sellers, C.H.; Branagan, D.J.; Hyde, T.A.; Lewis, L.H.; Panchanathan, V.

    1996-08-01

    Gas atomization (GA) processing does not generally have a high enough cooling rate to produce the initial amorphous microstructure needed to obtain optimal magnetic properties in RE{sub 2}Fe{sub 14}B alloys. Phase separation and an underquenched microstructure result from detrimental {alpha}-Fe precipitation, and the resulting magnetic domain structure is very coarse. Additionally, there is a dramatic dependence of the magnetic properties on the cooling rate (and therefore the particle size) and the powders can be sensitive to environmental degradation. Alloy compositions designed just for GA (as opposed to melt spinning) are necessary to produce an amorphous structure that can be crystallized to result in a fine structure with magnetic properties which are independent of particle size. The addition of titanium and carbon to the melt has been found to change the solidification process sufficiently to result in an ``overquenched`` state in which most of the powder size fractions have an amorphous component. Crystallization with a brief heat treatment produces a structure which has improved magnetic properties, in part due to the ability to use compositions with higher Fe contents without {alpha}-Fe precipitation. Results from magnetometry, magnetic force microscopy, and x-ray analyses will be used to contrast the microstructure, domain structure, and magnetic properties of this new generation of amorphous powders with their multiphase predecessors.

  18. Model for amorphous aggregation processes

    NASA Astrophysics Data System (ADS)

    Stranks, Samuel D.; Ecroyd, Heath; van Sluyter, Steven; Waters, Elizabeth J.; Carver, John A.; von Smekal, Lorenz

    2009-11-01

    The amorphous aggregation of proteins is associated with many phenomena, ranging from the formation of protein wine haze to the development of cataract in the eye lens and the precipitation of recombinant proteins during their expression and purification. While much literature exists describing models for linear protein aggregation, such as amyloid fibril formation, there are few reports of models which address amorphous aggregation. Here, we propose a model to describe the amorphous aggregation of proteins which is also more widely applicable to other situations where a similar process occurs, such as in the formation of colloids and nanoclusters. As first applications of the model, we have tested it against experimental turbidimetry data of three proteins relevant to the wine industry and biochemistry, namely, thaumatin, a thaumatinlike protein, and α -lactalbumin. The model is very robust and describes amorphous experimental data to a high degree of accuracy. Details about the aggregation process, such as shape parameters of the aggregates and rate constants, can also be extracted.

  19. Terahertz-induced Kerr effect in amorphous chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Zalkovskij, M.; Strikwerda, A. C.; Iwaszczuk, K.; Popescu, A.; Savastru, D.; Malureanu, R.; Lavrinenko, A. V.; Jepsen, P. U.

    2013-11-01

    We have investigated the terahertz-induced third-order (Kerr) nonlinear optical properties of the amorphous chalcogenide glasses As2S3 and As2Se3. Chalcogenide glasses are known for their high optical Kerr nonlinearities which can be several hundred times greater than those of fused silica. We use high-intensity, single-cycle terahertz pulses with a maximum electrical field strength exceeding 400 kV/cm and frequency content from 0.2 to 3.0 THz. By optical Kerr-gate sampling, we measured the terahertz-induced nonlinear refractive indices at 800 nm to be n2=1.746×10-14cm2/W for As2S3 and n2=3.440×10-14 cm2/W for As2Se3.

  20. Isolated catalyst sites on amorphous supports: A systematic algorithm for understanding heterogeneities in structure and reactivity

    NASA Astrophysics Data System (ADS)

    Goldsmith, Bryan R.; Sanderson, Evan D.; Bean, Daniel; Peters, Baron

    2013-05-01

    Methods for modeling catalytic sites on amorphous supports lag far behind methods for modeling catalytic sites on metal surfaces, zeolites, and other crystalline materials. One typical strategy for amorphous supports uses cluster models with arbitrarily chosen constraints to model the rigid amorphous support, but these constraints arbitrarily influence catalyst site activity. An alternative strategy is to use no constraints, but this results in catalytic sites with unrealistic flexibility. We present a systematic ab initio method to model isolated active sites on insulating amorphous supports using small cluster models. A sequential quadratic programming framework helps us relate chemical properties, such as the activation energy, to active site structure. The algorithm is first illustrated on an empirical valence bond model energy landscape. We then use the algorithm to model an off-pathway kinetic trap in olefin metathesis by isolated Mo sites on amorphous SiO2. The cluster models were terminated with basis set deficient fluorine atoms to mimic the properties of an extended silica framework. We also discuss limitations of the current algorithm formulation and future directions for improvement.

  1. Tandem junction amorphous silicon solar cells

    DOEpatents

    Hanak, Joseph J.

    1981-01-01

    An amorphous silicon solar cell has an active body with two or a series of layers of hydrogenated amorphous silicon arranged in a tandem stacked configuration with one optical path and electrically interconnected by a tunnel junction. The layers of hydrogenated amorphous silicon arranged in tandem configuration can have the same bandgap or differing bandgaps.

  2. Synthesis, characterization and catalytic activity of carbon-silica hybrid catalyst from rice straw

    NASA Astrophysics Data System (ADS)

    Janaun, J.; Safie, N. N.; Siambun, N. J.

    2016-07-01

    The hybrid-carbon catalyst has been studied because of its promising potential to have high porosity and surface area to be used in biodiesel production. Silica has been used as the support to produce hybrid carbon catalyst due to its mesoporous structure and high surface area properties. The chemical synthesis of silica-carbon hybrid is expensive and involves more complicated preparation steps. The presence of natural silica in rice plants especially rice husk has received much attention in research because of the potential as a source for solid acid catalyst synthesis. But study on rice straw, which is available abundantly as agricultural waste is limited. In this study, rice straw undergone pyrolysis and functionalized using fuming sulphuric acid to anchor -SO3H groups. The presence of silica and the physiochemical properties of the catalyst produced were studied before and after sulphonation. The catalytic activity of hybrid carbon silica acid catalyst, (H-CSAC) in esterification of oleic acid with methanol was also studied. The results showed the presence of silica-carbon which had amorphous structure and highly porous. The carbon surface consisted of higher silica composition, had lower S element detected as compared to the surface that had high carbon content but lower silica composition. This was likely due to the fact that Si element which was bonded to oxygen was highly stable and unlikely to break the bond and react with -SO3H ions. H-CSAC conversions were 23.04 %, 35.52 % and 34.2 7% at 333.15 K, 343.15 K and 353.15 K, respectively. From this research, rice straw can be used as carbon precursor to produce hybrid carbon-silica catalyst and has shown catalytic activity in biodiesel production. Rate equation obtained is also presented.

  3. Characteristics, distribution, origin, and significance of opaline silica observed by the Spirit rover in Gusev crater, Mars

    USGS Publications Warehouse

    Ruff, S.W.; Farmer, J.D.; Calvin, W.M.; Herkenhoff, K. E.; Johnson, J. R.; Morris, R.V.; Rice, M.S.; Arvidson, R. E.; Bell, J.F., III; Christensen, P.R.; Squyres, S. W.

    2011-01-01

    The presence of outcrops and soil (regolith) rich in opaline silica (???65-92 wt % SiO2) in association with volcanic materials adjacent to the "Home Plate" feature in Gusev crater is evidence for hydrothermal conditions. The Spirit rover has supplied a diverse set of observations that are used here to better understand the formation of silica and the activity, abundance, and fate of water in the first hydrothermal system to be explored in situ on Mars. We apply spectral, chemical, morphological, textural, and stratigraphic observations to assess whether the silica was produced by acid sulfate leaching of precursor rocks, by precipitation from silica-rich solutions, or by some combination. The apparent lack of S enrichment and the relatively low oxidation state of the Home Plate silica-rich materials appear inconsistent with the originally proposed Hawaiian analog for fumarolic acid sulfate leaching. The stratiform distribution of the silica-rich outcrops and their porous and brecciated microtextures are consistent with sinter produced by silica precipitation. There is no evidence for crystalline quartz phases among the silica occurrences, an indication of the lack of diagenetic maturation following the production of the amorphous opaline phase. Copyright ?? 2011 by the American Geophysical Union.

  4. Silica Fillers for elastomer Reinforement

    SciTech Connect

    Kohls, D.J.; Schaefer, D.W.

    2012-09-10

    This article summarizes recent work on the structure of precipitated silica used in the reinforcement of elastomers. Silica has a unique morphology, consisting of multiple structural levels that can be controlled through processing. The ability to control and characterize the multiple structures of precipitated silica is an example of morphological engineering for reinforcement applications. In this summary of some recent research efforts using precipitated silica, small-angle scattering techniques are described and their usefulness for determining the morphology of silica in terms of primary particles, aggregates, and agglomerates are discussed. The structure of several different precipitated silica powders is shown as well as the mechanical properties of elastomers reinforced with these silica particles. The study of the mechanical properties of filled elastomer systems is a challenging and exciting topic for both fundamental science and industrial application. It is known that the addition of hard particulates to a soft elastomer matrix results in properties that do not follow a straightforward rule of mixtures. Research efforts in this area have shown that the properties of filled elastomers are influenced by the nature of both the filler and the matrix, as well as the interactions between them. Several articles have reviewed the influence of fillers like silica and carbon black on the reinforcement of elastomers. In general, the structure-property relationships developed for filled elastomers have evolved into the following major areas: Filler structure, hydrodynamic reinforcement, and interactions between fillers and elastomers.

  5. Silica Fillers for elastomer Reinforement

    SciTech Connect

    Kohls, D.J.; Schaefer, D.W.

    2009-08-26

    This article summarizes recent work on the structure of precipitated silica used in the reinforcement of elastomers. Silica has a unique morphology, consisting of multiple structural levels that can be controlled through processing. The ability to control and characterize the multiple structures of precipitated silica is an example of morphological engineering for reinforcement applications. In this summary of some recent research efforts using precipitated silica, small-angle scattering techniques are described and their usefulness for determining the morphology of silica in terms of primary particles, aggregates, and agglomerates are discussed. The structure of several different precipitated silica powders is shown as well as the mechanical properties of elastomers reinforced with these silica particles. The study of the mechanical properties of filled elastomer systems is a challenging and exciting topic for both fundamental science and industrial application. It is known that the addition of hard particulates to a soft elastomer matrix results in properties that do not follow a straightforward rule of mixtures. Research efforts in this area have shown that the properties of filled elastomers are influenced by the nature of both the filler and the matrix, as well as the interactions between them. Several articles have reviewed the influence of fillers like silica and carbon black on the reinforcement of elastomers. In general, the structure-property relationships developed for filled elastomers have evolved into the following major areas: Filler structure, hydrodynamic reinforcement, and interactions between fillers and elastomers.

  6. Vapor Pressure and Evaporation Coefficient of Silicon Monoxide over a Mixture of Silicon and Silica

    NASA Technical Reports Server (NTRS)

    Ferguson, Frank T.; Nuth, Joseph A., III

    2012-01-01

    The evaporation coefficient and equilibrium vapor pressure of silicon monoxide over a mixture of silicon and vitreous silica have been studied over the temperature range (1433 to 1608) K. The evaporation coefficient for this temperature range was (0.007 plus or minus 0.002) and is approximately an order of magnitude lower than the evaporation coefficient over amorphous silicon monoxide powder and in general agreement with previous measurements of this quantity. The enthalpy of reaction at 298.15 K for this reaction was calculated via second and third law analyses as (355 plus or minus 25) kJ per mol and (363.6 plus or minus 4.1) kJ per mol respectively. In comparison with previous work with the evaporation of amorphous silicon monoxide powder as well as other experimental measurements of the vapor pressure of silicon monoxide gas over mixtures of silicon and silica, these systems all tend to give similar equilibrium vapor pressures when the evaporation coefficient is correctly taken into account. This provides further evidence that amorphous silicon monoxide is an intimate mixture of small domains of silicon and silica and not strictly a true compound.

  7. Amine modification of nonporous silica nanoparticles reduces inflammatory response following intratracheal instillation in murine lungs.

    PubMed

    Morris, Angie S; Adamcakova-Dodd, Andrea; Lehman, Sean E; Wongrakpanich, Amaraporn; Thorne, Peter S; Larsen, Sarah C; Salem, Aliasger K

    2016-01-22

    Amorphous silica nanoparticles (NPs) possess unique material properties that make them ideal for many different applications. However, the impact of these materials on human and environmental health needs to be established. We investigated nonporous silica NPs both bare and modified with amine functional groups (3-aminopropyltriethoxysilane (APTES)) in order to evaluate the effect of surface chemistry on biocompatibility. In vitro data showed there to be little to no cytotoxicity in a human lung cancer epithelial cell line (A549) for bare silica NPs and amine-functionalized NPs using doses based on both mass concentration (below 200μg/mL) and exposed total surface area (below 14m(2)/L). To assess lung inflammation, C57BL/6 mice were administered bare or amine-functionalized silica NPs via intra-tracheal instillation. Two doses (0.1 and 0.5mg NPs/mouse) were tested using the in vivo model. At the higher dose used, bare silica NPs elicited a significantly higher inflammatory response, as evidence by increased neutrophils and total protein in bronchoalveolar lavage (BAL) fluid compared to amine-functionalized NPs. From this study, we conclude that functionalization of nonporous silica NPs with APTES molecules reduces murine lung inflammation and improves the overall biocompatibility of the nanomaterial. PMID:26562768

  8. Effect of Sintering Temperature on the Properties of Fused Silica Ceramics Prepared by Gelcasting

    NASA Astrophysics Data System (ADS)

    Wan, Wei; Huang, Chun-e.; Yang, Jian; Zeng, Jinzhen; Qiu, Tai

    2014-07-01

    Fused silica ceramics were fabricated by gelcasting, by use of a low-toxicity N' N-dimethylacrylamide gel system, and had excellent properties compared with those obtained by use of the low-toxicity 2-hydroxyethyl methacrylate and toxic acrylamide systems. The effect of sintering temperature on the microstructure, mechanical and dielectric properties, and thermal shock resistance of the fused silica ceramics was investigated. The results showed that sintering temperature has a critical effect. Use of an appropriate sintering temperature will promote densification and improve the strength, thermal shock resistance, and dielectric properties of fused silica ceramics. However, excessively high sintering temperature will greatly facilitate crystallization of amorphous silica and result in more cristobalite in the sample, which will cause deterioration of these properties. Fused silica ceramics sintered at 1275°C have the maximum flexural strength, as high as 81.32 MPa, but, simultaneously, a high coefficient of linear expansion (2.56 × 10-6/K at 800°C) and dramatically reduced residual flexural strength after thermal shock (600°C). Fused silica ceramics sintered at 1250°C have excellent properties, relatively high and similar flexural strength before (67.43 MPa) and after thermal shock (65.45 MPa), a dielectric constant of 3.34, and the lowest dielectric loss of 1.20 × 10-3 (at 1 MHz).

  9. In search of the chemical basis of the hemolytic potential of silicas.

    PubMed

    Pavan, Cristina; Tomatis, Maura; Ghiazza, Mara; Rabolli, Virginie; Bolis, Vera; Lison, Dominique; Fubini, Bice

    2013-08-19

    The membranolytic activity of silica particles toward red blood cells (RBCs) has been known for a long time and is sometimes associated with silica pathogenicity. However, the molecular mechanism and the reasons why hemolysis differs according to the silica form are still obscure. A panel of 15 crystalline (pure and commercial) and amorphous (pyrogenic, precipitated from aqueous solutions, vitreous) silica samples differing in size, origin, morphology, and surface chemical composition were selected and specifically prepared. Silica particles were grouped into six groups to compare their potential in disrupting RBC membranes so that one single property differed in each group, while other features were constant. Free radical production and crystallinity were not strict determinants of hemolytic activity. Particle curvature and morphology modulated the hemolytic effect, but silanols and siloxane bridges at the surface were the main actors. Hemolysis was unrelated to the overall concentration of silanols as fully rehydrated surfaces (such as those obtained from aqueous solution) were inert, and one pyrogenic silica also lost its membranolytic potential upon progressive dehydration. Overall results are consistent with a model whereby hemolysis is determined by a defined surface distribution of dissociated/undissociated silanols and siloxane groups strongly interacting with specific epitopes on the RBC membrane. PMID:23819533

  10. Silaffins in Silica Biomineralization and Biomimetic Silica Precipitation

    PubMed Central

    Lechner, Carolin C.; Becker, Christian F. W.

    2015-01-01

    Biomineralization processes leading to complex solid structures of inorganic material in biological systems are constantly gaining attention in biotechnology and biomedical research. An outstanding example for biomineral morphogenesis is the formation of highly elaborate, nano-patterned silica shells by diatoms. Among the organic macromolecules that have been closely linked to the tightly controlled precipitation of silica in diatoms, silaffins play an extraordinary role. These peptides typically occur as complex posttranslationally modified variants and are directly involved in the silica deposition process in diatoms. However, even in vitro silaffin-based peptides alone, with and without posttranslational modifications, can efficiently mediate biomimetic silica precipitation leading to silica material with different properties as well as with encapsulated cargo molecules of a large size range. In this review, the biomineralization process of silica in diatoms is summarized with a specific focus on silaffins and their in vitro silica precipitation properties. Applications in the area of bio- and nanotechnology as well as in diagnostics and therapy are discussed. PMID:26295401

  11. Silaffins in Silica Biomineralization and Biomimetic Silica Precipitation.

    PubMed

    Lechner, Carolin C; Becker, Christian F W

    2015-08-01

    Biomineralization processes leading to complex solid structures of inorganic material in biological systems are constantly gaining attention in biotechnology and biomedical research. An outstanding example for biomineral morphogenesis is the formation of highly elaborate, nano-patterned silica shells by diatoms. Among the organic macromolecules that have been closely linked to the tightly controlled precipitation of silica in diatoms, silaffins play an extraordinary role. These peptides typically occur as complex posttranslationally modified variants and are directly involved in the silica deposition process in diatoms. However, even in vitro silaffin-based peptides alone, with and without posttranslational modifications, can efficiently mediate biomimetic silica precipitation leading to silica material with different properties as well as with encapsulated cargo molecules of a large size range. In this review, the biomineralization process of silica in diatoms is summarized with a specific focus on silaffins and their in vitro silica precipitation properties. Applications in the area of bio- and nanotechnology as well as in diagnostics and therapy are discussed. PMID:26295401

  12. Terrestrial ecosystems and the global biogeochemical silica cycle

    NASA Astrophysics Data System (ADS)

    Conley, Daniel J.

    2002-12-01

    Most research on the global Si cycle has focused nearly exclusively on weathering or the oceanic Si cycle and has not explored the complexity of the terrestrial biogeochemical cycle. The global biogeochemical Si cycle is of great interest because of its impact on global CO2 concentrations through the combined processes of weathering of silicate minerals and transfer of CO2 from the atmosphere to the lithosphere. A sizable pool of Si is contained as accumulations of amorphous silica, or biogenic silica (BSi), in living tissues of growing plants, known as phytoliths, and, after decomposition of organic material, as remains in the soil. The annual fixation of phytolith silica ranges from 60-200 Tmol yr-1 and rivals that fixed in the oceanic biogeochemical cycle (240 Tmol yr-1). Internal recycling of the phytolith pool is intense with riverine fluxes of dissolved silicate to the oceans buffered by the terrestrial biogeochemical Si cycle, challenging the ability of weathering models to predict rates of weathering and consequently, changes in global climate. Consideration must be given to the influence of the terrestrial BSi pool on variations in the global biogeochemical Si cycle over geologic time and the influence man has had on modifying both the terrestrial and aquatic biogeochemical cycles.

  13. Amorphous metal-organic frameworks.

    PubMed

    Bennett, Thomas D; Cheetham, Anthony K

    2014-05-20

    Crystalline metal-organic frameworks (MOFs) are porous frameworks comprising an infinite array of metal nodes connected by organic linkers. The number of novel MOF structures reported per year is now in excess of 6000, despite significant increases in the complexity of both component units and molecular networks. Their regularly repeating structures give rise to chemically variable porous architectures, which have been studied extensively due to their sorption and separation potential. More recently, catalytic applications have been proposed that make use of their chemical tunability, while reports of negative linear compressibility and negative thermal expansion have further expanded interest in the field. Amorphous metal-organic frameworks (aMOFs) retain the basic building blocks and connectivity of their crystalline counterparts, though they lack any long-range periodic order. Aperiodic arrangements of atoms result in their X-ray diffraction patterns being dominated by broad "humps" caused by diffuse scattering and thus they are largely indistinguishable from one another. Amorphous MOFs offer many exciting opportunities for practical application, either as novel functional materials themselves or facilitating other processes, though the domain is largely unexplored (total aMOF reported structures amounting to under 30). Specifically, the use of crystalline MOFs to detect harmful guest species before subsequent stress-induced collapse and guest immobilization is of considerable interest, while functional luminescent and optically active glass-like materials may also be prepared in this manner. The ion transporting capacity of crystalline MOFs might be improved during partial structural collapse, while there are possibilities of preparing superstrong glasses and hybrid liquids during thermal amorphization. The tuning of release times of MOF drug delivery vehicles by partial structural collapse may be possible, and aMOFs are often more mechanically robust than

  14. Silica Deposits Within Gusev Crater: Clear Evidence for Martian Water

    NASA Astrophysics Data System (ADS)

    Yen, A.; Ming, D.; Morris, R.; Clark, B.; Gellert, R.; Hurowitz, J.; Athena Science Team

    2007-12-01

    dominated by silica. This alternative is supported by the association with Ti, as acid-sulfate weathered analogs from Kilauea Volcano (Hawaii) are enriched in both amorphous silica and anatase. It is likely that a combination of these processes, both of which involve localized aqueous interactions, have been active along the eastern margin of Home Plate.

  15. Study of thermal conductivity of ice clusters after impact deposition on the silica surfaces using the ReaxFF reactive force field.

    PubMed

    Rahnamoun, A; van Duin, A C T

    2016-01-21

    During aircraft or spacecraft missions, ice accumulates on different parts of their surface elements. An important parameter affecting the ability to remove this ice from the surface is the heat transfer characteristics of the accumulated ice. The ice heat transfer is related to the process of ice formation and its density and internal structure. In this study we investigate the effects of the ice and silica structure and the ice cluster attachment mechanism to the silica surface on the thermal conductivity (TC) of the attached ice cluster using the ReaxFF reactive force field. The purpose of this study is to investigate the thermal transport in amorphous and crystalline ice after high-velocity deposition on the silica surfaces. A dual thermostat method has been applied for the calculation of TC values. The validity of this method has been verified by comparing the calculated values of TC for crystal and amorphous ice with available experimental values. Our calculations show that the TC values of both crystal and amorphous ice drop after deposition on the silica surfaces. This decrease in the TC is more significant for the ice deposition on suboxide silica surfaces. Furthermore, crystal ice shows higher TC values than amorphous ice after accumulation. However, when crystal ice impacts on the silica surface at 1 km s(-1) impact speed, the crystalline shape of the ice cluster is lost to a considerable level and the TC values obtained for the ice clusters in such cases are closer to amorphous ice TC values. We observed a decrease in the TC values when ionic species are added inside the ice clusters. PMID:26670950

  16. Chemical interactions of aluminum with aqueous silica at 25 degrees Celsius

    USGS Publications Warehouse

    Hem, John David; Roberson, C.E.; Lind, Carol J.; Polxer, W.L.

    1973-01-01

    Solutions containing from 10 -5 to 10 -2 moles per liter of aluminum and dissolved silica in various ratios were aged at pH levels between 4 and 10 at 25?C. A colloidal amorphous product having the composition of halloysite was produced in most solutions. It had a consistent and reversible equilibrium solubility equivalent to a standard free energy of formation of -8974 ? 1.0 kcal per mole for the formula A12Si2O5(OH)4. Some aging times were longer than 4 years, but most solutions gave consistent solubilities after only a few months of aging. Where silica concentrations were below about 10 -4 molar, microcrystalline gibbsite was formed below pH 6.0 and crystalline bayerite above pH 7.0, but only after much longer aging than was required for crystallization in silica-free solutions. Electron micrographs and diffraction patterns of the synthesized material indicate some crystallinity in the aluminosilicate, but no X-ray diffraction patterns could be obtained even in the material aged 4 years. Solubility relationships for solutions containing fluoride as well as silica and aluminum are explainable by using cryolite stabilities determined in previous work. Aluminum contents of 51 samples of water analyzed for other purposes are in reasonable agreement with the assumption of equilibrium with amorphous clay mineral species similar to the material synthesized in this work. Solubility calculations are summarized graphically for solutions of ionic strength of 0.01 and 0.10.

  17. Altered Gene Transcription in Human Cells Treated with Ludox® Silica Nanoparticles

    PubMed Central

    Fede, Caterina; Millino, Caterina; Pacchioni, Beniamina; Celegato, Barbara; Compagnin, Chiara; Martini, Paolo; Selvestrel, Francesco; Mancin, Fabrizio; Celotti, Lucia; Lanfranchi, Gerolamo; Mognato, Maddalena; Cagnin, Stefano

    2014-01-01

    Silica (SiO2) nanoparticles (NPs) have found extensive applications in industrial manufacturing, biomedical and biotechnological fields. Therefore, the increasing exposure to such ultrafine particles requires studies to characterize their potential cytotoxic effects in order to provide exhaustive information to assess the impact of nanomaterials on human health. The understanding of the biological processes involved in the development and maintenance of a variety of pathologies is improved by genome-wide approaches, and in this context, gene set analysis has emerged as a fundamental tool for the interpretation of the results. In this work we show how the use of a combination of gene-by-gene and gene set analyses can enhance the interpretation of results of in vitro treatment of A549 cells with Ludox® colloidal amorphous silica nanoparticles. By gene-by-gene and gene set analyses, we evidenced a specific cell response in relation to NPs size and elapsed time after treatment, with the smaller NPs (SM30) having higher impact on inflammatory and apoptosis processes than the bigger ones. Apoptotic process appeared to be activated by the up-regulation of the initiator genes TNFa and IL1b and by ATM. Moreover, our analyses evidenced that cell treatment with Ludox® silica nanoparticles activated the matrix metalloproteinase genes MMP1, MMP10 and MMP9. The information derived from this study can be informative about the cytotoxicity of Ludox® and other similar colloidal amorphous silica NPs prepared by solution processes. PMID:25170680

  18. Anisotropic surroundings effects on photo absorption of partially embedded Au nanospheroids in silica glass substrate

    SciTech Connect

    Meng, Xuan; Shibayama, Tamaki Watanabe, Seiichi; Yu, Ruixuan; Ishioka, Junya

    2015-02-15

    The influence of a directly adjacent or an anisotropic surrounding medium alters the plasmonic properties of a nanoparticle because it provides a mechanism for symmetry breaking of the scattering. Given the success of ion irradiation induced embedment of rigid metallic nanospheroids into amorphous substrate, it is possible to examine the effect of the silica glass substrate on the plasmonic properties of these embedded nanospheroids. In this work presented here, discrete dipole approximation (DDA) calculations for the Au nanospheroids’ optical properties were performed based on 3–dimensional (3D) configuration extracted from planar SEM micrographs and cross–sectional TEM micrographs of the Au nanospheroids partially embedded in the silica glass, and the well–matched simulations with respect to the experimental measurements could demonstrate the dielectric constant at the near surface of silica glass decreased after Ar–ion irradiation.

  19. Temperature dependent thermal conductivity of pure silica MEL and MFI zeolite thin films

    NASA Astrophysics Data System (ADS)

    Fang, Jin; Huang, Yi; Lew, Christopher M.; Yan, Yushan; Pilon, Laurent

    2012-03-01

    This paper reports the temperature dependent cross-plane thermal conductivity of pure silica zeolite (PSZ) MFI and MEL thin films measured using the 3ω method between 30 and 315 K. PSZ MFI thin films were b-oriented, fully crystalline, and had a 33% microporosity. PSZ MEL thin films consisted of MEL nanoparticles embedded in a nonuniform and porous silica matrix. They featured porosity, relative crystallinity, and particle size ranging from 40% to 59%, 23% to 47%, and 55 to 80 nm, respectively. Despite their crystallinity, MFI films had smaller thermal conductivity than that of amorphous silica due to strong phonon scattering by micropores. In addition, the effects of increased relative crystallinity and particle size on thermal conductivity of MEL thin films were compensated by the simultaneous increase in porosity. Finally, thermal conductivity of MFI zeolite was predicted and discussed using the Callaway model based on the Debye approximation.

  20. Electron spin resonance identification of a methyl associated organic radical in irradiated amorphous SiO{sub 2}

    SciTech Connect

    Austin, W.R.; Leisure, R.G.

    1996-12-01

    An electron spin resonance (ESR) signal comprised of three resolved lines of equal 19.3 Gauss separation (3{times}19.3 G), but unequal amplitude, is observed in x-irradiated amorphous silicon dioxide. The radical appears exclusively in silica samples which also exhibit the methyl radical, a familiar indicator of trace carbon and hydrogen contamination. The 3{times}19.3 G signal is observed to grow most rapidly versus irradiation dose when methyl radical concentration is near maximum. This evidence suggests that the ESR signal is due to a radiolytic, organic radical which evolves after the methyl radical and, like the methyl radical, is trapped and stabilized in the amorphous silica network. Experimental methods of radical generation are presented, followed by discussion of models for the chemical structure of the 3{times}19.3 G radical. {copyright} {ital 1996 American Institute of Physics.}

  1. Exoelectron analysis of amorphous silicon

    NASA Astrophysics Data System (ADS)

    Dekhtyar, Yu. D.; Vinyarskaya, Yu. A.

    1994-04-01

    The method based on registration of photothermostimulated exoelectron emission (PTSE) is used in the proposed new field of investigating the structural defects in amorphous silicon (a-Si). This method can be achieved if the sample under investigation is simultaneously heated and illuminated by ultraviolet light. The mechanism of PTSE from a-Si has been studied in the case of a hydrogenized amorphous silicon (a-Si:H) film grown by glow discharge method. The electronic properties and annealing of defects were analyzed in the study. It has been shown from the results that the PTSE from a-Si:H takes place as a prethreshold single-photon external photoeffect. The exoemission spectroscopy of a-Si:H was shown to be capable in the study of thermally and optically stimulated changes in the electronic structure of defects, their annealing, as well as diffusion of atomic particles, such as hydrogen.

  2. Silica research in Glasgow

    NASA Astrophysics Data System (ADS)

    Barr, B. W.; Cagnoli, G.; Casey, M. M.; Clubley, D.; Crooks, D. R. M.; Danzmann, K.; Elliffe, E. J.; Goßler, S.; Grant, A.; Grote, H.; Heptonstall, A.; Hough, J.; Jennrich, O.; Lück, H.; McIntosh, S. A.; Newton, G. P.; Palmer, D. A.; Plissi, M. V.; Robertson, D. I.; Robertson, N. A.; Rowan, S.; Skeldon, K. D.; Sneddon, P.; Strain, K. A.; Torrie, C. I.; Ward, H.; Willems, P. A.; Willke, B.; Winkler, W.

    2002-04-01

    The Glasgow group is involved in the construction of the GEO600 interferometer as well as in R&D activity on technology for advanced gravitational wave detectors. GEO600 will be the first GW detector using quasi-monolithic silica suspensions in order to decrease thermal noise significantly with respect to steel wire suspensions. The results concerning GEO600 suspension mounting and performance will be shown in the first section. Section 2 is devoted to the present results from the direct measurement of thermal noise in mirrors mounted in the 10 m interferometer in Glasgow which has a sensitivity limit of 4 × 10-19 m Hz-1/2 above 1 kHz. Section 3 presents results on the measurements of coating losses. R&D activity has been carried out to understand better how thermal noise in the suspensions affects the detector sensitivity, and in section 4 a discussion on the non-linear thermoelastic effect is presented.

  3. Silica aerogel core waveguide.

    PubMed

    Grogan, M D W; Leon-Saval, S G; England, R; Birks, T A

    2010-10-11

    We have selectively filled the core of hollow photonic crystal fibre with silica aerogel. Light is guided in the aerogel core, with a measured attenuation of 0.2 dB/cm at 1540 nm comparable to that of bulk aerogel. The structure guides light by different mechanisms depending on the wavelength. At long wavelengths the effective index of the microstructured cladding is below the aerogel index of 1.045 and guidance is by total internal reflection. At short wavelengths, where the effective cladding index exceeds 1.045, a photonic bandgap can guide the light instead. There is a small region of crossover, where both index- and bandgap-guided modes were simultaneously observed. PMID:20941148

  4. 21 CFR 582.1711 - Silica aerogel.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 6 2013-04-01 2013-04-01 false Silica aerogel. 582.1711 Section 582.1711 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) ANIMAL DRUGS....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam...

  5. 21 CFR 182.1711 - Silica aerogel.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 3 2013-04-01 2013-04-01 false Silica aerogel. 182.1711 Section 182.1711 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN....1711 Silica aerogel. (a) Product. Silica aerogel as a finely powdered microcellular silica foam...

  6. Silica/Polymer and Silica/Polymer/Fiber Composite Aerogels

    NASA Technical Reports Server (NTRS)

    Ou, Danny; Stepanian, Christopher J.; Hu, Xiangjun

    2010-01-01

    Aerogels that consist, variously, of neat silica/polymer alloys and silica/polymer alloy matrices reinforced with fibers have been developed as materials for flexible thermal-insulation blankets. In comparison with prior aerogel blankets, these aerogel blankets are more durable and less dusty. These blankets are also better able to resist and recover from compression . an important advantage in that maintenance of thickness is essential to maintenance of high thermal-insulation performance. These blankets are especially suitable as core materials for vacuum- insulated panels and vacuum-insulated boxes of advanced, nearly seamless design. (Inasmuch as heat leakage at seams is much greater than heat leakage elsewhere through such structures, advanced designs for high insulation performance should provide for minimization of the sizes and numbers of seams.) A silica/polymer aerogel of the present type could be characterized, somewhat more precisely, as consisting of multiply bonded, linear polymer reinforcements within a silica aerogel matrix. Thus far, several different polymethacrylates (PMAs) have been incorporated into aerogel networks to increase resistance to crushing and to improve other mechanical properties while minimally affecting thermal conductivity and density. The polymethacrylate phases are strongly linked into the silica aerogel networks in these materials. Unlike in other organic/inorganic blended aerogels, the inorganic and organic phases are chemically bonded to each other, by both covalent and hydrogen bonds. In the process for making a silica/polymer alloy aerogel, the covalent bonds are introduced by prepolymerization of the methacrylate monomer with trimethoxysilylpropylmethacrylate, which serves as a phase cross-linker in that it contains both organic and inorganic monomer functional groups and hence acts as a connector between the organic and inorganic phases. Hydrogen bonds are formed between the silanol groups of the inorganic phase and the

  7. Visual Observations of the Amorphous-Amorphous Transition in H2O Under Pressure.

    PubMed

    Mishima, O; Takemura, K; Aoki, K

    1991-10-18

    The vapor-deposited low-density amorphous phase of H(2)O was directly compressed at 77 kelvin with a diamond-anvil cell, and the boundary between the low-density amorphous phase and the high-density amorphous phase was observed while the sample was warmed under compression. The transition from the low-density amorphous phase to the high-density amorphous phase was distinct and reversible in an apparently narrow pressure range at approximately 130 to approximately 150 kelvin, which provided experimental evidence for polymorphism in amorphous H(2)O. PMID:17742228

  8. Study of Cell Division Aberrations Induced by Some Silica Dusts in Mammalian Cells in Vitro.

    PubMed

    Béna, F; Danière, M C; Terzetti, F; Poirot, O; Elias, Z

    2000-01-01

    Previously we observed that some crystalline and amorphous (diatomaceous earths) silicas (but not pyrogenic amorphous silica) induced morphological transformation of Syrian hamster embryo (SHE) cells. In order to explore the mechanisms of the silica-induced cell transformation, in this study we have examined the possibility that silica may cause genomic changes by interfering with the normal events of mitotic division. The SHE cells were exposed to transforming samples of Min-U-Sil 5 quartz and amorphous diatomite earth (DE) as well as to inactive amorphous synthetic Aerosil 0X50 at concentrations between 9 and 36 μg/cm(2) of culture slide. Effects on the mitotic spindle and on chromosome congression and segregation through the mitotic stages were concurrently examined by differential and indirect immunofluorescence stainings using anti-β-tubulin antibody. Min-U-Sil 5 and DE dusts induced a significant increase in the number of aberrant mitotic cells detected by differential staining. Increased frequencies of monopolar mitoses and scattered chromosomes as well as a small incidence of lagging chromosomes in DE-treated cells were observed. The immunostaining was more efficient in the detection of spindle disturbances. Min-U-Sil induced a significantly concentration-dependent increase of monopolar spindles. At the highest concentration, highly disorganized prophase spindles and prometaphase multipolars were observed. These damages caused a concentration-dependent decrease in metaphase to anaphase transition. DE-induced spindle aberrations did not reach significant levels over control, although increase in monopolar and multipolar spindles were recorded. Exposure to OX50 particles did not disrupt spindle integrity. To determine whether micronuclei (MN) arise from divisional abnormalities induced by the active samples, we performed in SHE and human bronchial epithelial cells kinetochore (K)-specific and centromere (C)-specific staining, respectively. A concentration

  9. Skin penetration of silica microparticles.

    PubMed

    Boonen, J; Baert, B; Lambert, J; De Spiegeleer, B

    2011-06-01

    Knowledge about skin penetration of nano- and microparticles is essential for the development of particle-core drug delivery systems and toxicology. A large number of studies have been devoted to metallic particle penetration. However, little work has been published about the importance of chemical material properties of the particles and the skin penetration effect of the applied formulation. Here, we investigated the penetration of 3 microm silica particles in water and in a 65% ethanolic plant extract on ex vivo human skin using scanning electron microscopy. Contrary to most other microsphere skin studies, we observed for the first time that 3 microm silica particles can penetrate the living epidermis. Moreover, when formulated in the ethanolic medium, particles even reach the dermis. The deviating chemical properties of silica compared to previously investigated microparticles (titanium dioxide, zinc oxide) and confounding effect of the formulation in which the silica microparticles are presented, is thus demonstrated. PMID:21699089

  10. A Significant Amount of Crystalline Silica in Returned Cometary Samples: Bridging the Gap between Astrophysical and Meteoritical Observations

    NASA Astrophysics Data System (ADS)

    Roskosz, Mathieu; Leroux, Hugues

    2015-03-01

    Crystalline silica (SiO2) is recurrently identified at the percent level in the infrared spectra of protoplanetary disks. By contrast, reports of crystalline silica in primitive meteorites are very unusual. This dichotomy illustrates the typical gap existing between astrophysical observations and meteoritical records of the first solids formed around young stars. The cometary samples returned by the Stardust mission in 2006 offer an opportunity to have a closer look at a silicate dust that experienced a very limited reprocessing since the accretion of the dust. Here, we provide the first extended study of silica materials in a large range of Stardust samples. We show that cristobalite is the dominant form. It was detected in 5 out of 25 samples. Crystalline silica is thus a common minor phase in Stardust samples. Furthermore, olivine is generally associated with this cristobalite, which put constraints on possible formation mechanisms. A low-temperature subsolidus solid-solid transformation of an amorphous precursor is most likely. This crystallization route favors the formation of olivine (at the expense of pyroxenes), and crystalline silica is the natural byproduct of this transformation. Conversely, direct condensation and partial melting are not expected to produce the observed mineral assemblages. Silica is preserved in cometary materials because they were less affected by thermal and aqueous alterations than their chondritic counterparts. The common occurrence of crystalline silica therefore makes the cometary material an important bridge between the IR-based mineralogy of distant protoplanetary disks and the mineralogy of the early solar system.

  11. Narrow band gap amorphous silicon semiconductors

    DOEpatents

    Madan, A.; Mahan, A.H.

    1985-01-10

    Disclosed is a narrow band gap amorphous silicon semiconductor comprising an alloy of amorphous silicon and a band gap narrowing element selected from the group consisting of Sn, Ge, and Pb, with an electron donor dopant selected from the group consisting of P, As, Sb, Bi and N. The process for producing the narrow band gap amorphous silicon semiconductor comprises the steps of forming an alloy comprising amorphous silicon and at least one of the aforesaid band gap narrowing elements in amount sufficient to narrow the band gap of the silicon semiconductor alloy below that of amorphous silicon, and also utilizing sufficient amounts of the aforesaid electron donor dopant to maintain the amorphous silicon alloy as an n-type semiconductor.

  12. Multi-Length Scale Analysis of the Effect of Fused-Silica Pre-shocking on its Tendency for Devitrification

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Snipes, J. S.; Ramaswami, S.

    2016-03-01

    Recent studies have suggested that impact-induced devitrification of fused silica, or more specifically formation of high-density stishovite, can significantly improve ballistic-penetration resistance of fused silica, the material which is used in transparent armor. The studies have also shown that in order for stishovite to form during a ballistic impact event, very high projectile kinetic energy normalized by the projectile/fused-silica target-plate contact area must accompany such an event. Otherwise fused-silica devitrification, if taking place, does not substantially improve the material ballistic-penetration resistance. In the present work, all-atom molecular-level computations are carried out in order to establish if pre-shocking of fused-silica target-plates (to form stishovite) and subsequent unloading (to revert stishovite to the material amorphous structure) can increase fused silica's propensity for stishovite formation during a ballistic impact. Towards that end, molecular-level computational procedures are developed to simulate both the pre-shocking treatment of the fused-silica target-plate and its subsequent impact by a solid right-circular cylindrical projectile. The results obtained clearly revealed that when strong-enough shockwaves are used in the fused-silica target-plate pre-shocking procedure, the propensity of fused silica for stishovite formation during the subsequent ballistic impact is increased, as is the associated ballistic-penetration resistance. To rationalize these findings, a detailed post-processing microstructural analysis of the pre-shocked material is employed. The results obtained suggest that fused silica pre-shocked with shockwaves of sufficient strength retain some memory/embryos of stishovite, and these embryos facilitate stishovite formation during the subsequent ballistic impact.

  13. The power of light: Self-organized formation of macroscopic amounts of silica melts controlled by laser light

    NASA Astrophysics Data System (ADS)

    Günster, J.; Oelgardt, C.; Heinrich, J. G.; Melcher, J.

    2009-01-01

    CO2 laser systems with a power output of up to 12kW continuous wave have been employed for melting high purity amorphous silica (SiO2) powders. Under the intense light irradiation, the migration of matter on the silica sample has been observed. A net mass transport results in the formation of macroscopic structures in the liquid phase. Protrusions of up to 7mm height are formed against gravitational force and surface tension. For the first time, this work reports on the self-organized formation of macroscopic structures by viscous flow of a dielectric melt driven by laser light.

  14. The power of light: Self-organized formation of macroscopic amounts of silica melts controlled by laser light

    SciTech Connect

    Guenster, J.; Oelgardt, C.; Heinrich, J. G.; Melcher, J.

    2009-01-12

    CO{sub 2} laser systems with a power output of up to 12 kW continuous wave have been employed for melting high purity amorphous silica (SiO{sub 2}) powders. Under the intense light irradiation, the migration of matter on the silica sample has been observed. A net mass transport results in the formation of macroscopic structures in the liquid phase. Protrusions of up to 7 mm height are formed against gravitational force and surface tension. For the first time, this work reports on the self-organized formation of macroscopic structures by viscous flow of a dielectric melt driven by laser light.

  15. Amorphous silicon solar cell allowing infrared transmission

    DOEpatents

    Carlson, David E.

    1979-01-01

    An amorphous silicon solar cell with a layer of high index of refraction material or a series of layers having high and low indices of refraction material deposited upon a transparent substrate to reflect light of energies greater than the bandgap energy of the amorphous silicon back into the solar cell and transmit solar radiation having an energy less than the bandgap energy of the amorphous silicon.

  16. Amorphous powders for inhalation drug delivery.

    PubMed

    Chen, Lan; Okuda, Tomoyuki; Lu, Xiang-Yun; Chan, Hak-Kim

    2016-05-01

    For inhalation drug delivery, amorphous powder formulations offer the benefits of increased bioavailability for poorly soluble drugs, improved biochemical stability for biologics, and expanded options of using various drugs and their combinations. However, amorphous formulations usually have poor physicochemical stability. This review focuses on inhalable amorphous powders, including the production methods, the active pharmaceutical ingredients and the excipients with a highlight on stabilization of the particles. PMID:26780404

  17. Graphene as a transparent electrode for amorphous silicon-based solar cells

    SciTech Connect

    Vaianella, F. Rosolen, G.; Maes, B.

    2015-06-28

    The properties of graphene in terms of transparency and conductivity make it an ideal candidate to replace indium tin oxide (ITO) in a transparent conducting electrode. However, graphene is not always as good as ITO for some applications, due to a non-negligible absorption. For amorphous silicon photovoltaics, we have identified a useful case with a graphene-silica front electrode that improves upon ITO. For both electrode technologies, we simulate the weighted absorption in the active layer of planar amorphous silicon-based solar cells with a silver back-reflector. The graphene device shows a significantly increased absorbance compared to ITO-based cells for a large range of silicon thicknesses (34.4% versus 30.9% for a 300 nm thick silicon layer), and this result persists over a wide range of incidence angles.

  18. Role of Amorphous Boundary Layer in Enhancing Ionic Conductivity of Lithium–lanthanum–titanate Electrolyte

    SciTech Connect

    Mei, A.; Wang, X.; Lana, J.-L.; Fenga, Y.-C.; Genga, H.-X.; Lina, Y.-H.; Nana, C.-W.

    2010-03-01

    The low ionic conductivity is a bottleneck of the inorganic solid state electrolyte used for lithium ion battery. In ceramic electrolytes, grain boundary usually dominates the total conductivity. In order to improve the grain boundary effect, an amorphous silica layer is introduced into grain boundary of ceramic electrolytes based on lithium-lanthanum-titanate, as evidenced by electron microscopy. The results showed that the total ionic conductivity could be to be enhanced over 1 x 10{sup -4} S/cm at room temperature. The reasons can be attributed to removing the anisotropy of outer-shell of grains, supplement of lithium ions in various sites in grain boundary and close bindings among grains by the amorphous boundary layer among grains.

  19. Investigating the Origin of Silica Occurrences on Mars through Laboratory Observations

    NASA Astrophysics Data System (ADS)

    Ruff, S. W.; Milliken, R. E.; Farmer, J. D.; Mills, V. W.; Robertson, K.

    2012-12-01

    Natural amorphous "opaline" silica is a non-crystalline, typically hydrated phase of nearly pure SiO2 that is a common product of aqueous alteration of basaltic materials [e.g., 1]. It has been identified on Mars with orbital spectral data [2] and in situ measurements from the Spirit rover [3]. On Earth, opaline silica is produced over a range of temperature, pH, and water-to-rock ratio conditions that occur in hot springs, fumaroles, volcanic exhalations, low temperature weathering, and diagenesis [e.g., 4 and references therein]. The mere identification of silica on Mars therefore does not indicate a unique geologic environment or setting. However, various attributes of a given silica occurrence can be used to narrow or perhaps uniquely define the conditions in which it formed. Field relationships, microtexture, bulk and trace element chemistry, and spectral characteristics provide clues to the geologic environment in which the silica formed. Here we focus on the opaline silica in outcrops and soil at the Home Plate feature in Gusev crater where there is good evidence for past hydrothermal processes [3]. Unresolved is whether fumaroles, hot springs, geysers, or some combination of these features were present and responsible for the emplacement of opaline silica there. Knowing the answer has implications for understanding ancient climate and habitability of Mars. We have begun an investigation involving a range of laboratory measurements on natural silica-rich samples collected from various settings in Yellowstone and Hawaii Volcanoes National Parks. Visible and near infrared (VNIR) and thermal infrared (TIR) spectral measurements are supplemented with X-ray powder diffraction, scanning electron microscopy, petrographic microscopy, and ultimately with bulk and trace element measurements. Among our emerging results: 1) both VNIR and TIR spectra can detect the presence of <2 μm silica coatings on altered basalts; 2) VNIR spectra of silica from different

  20. Petrologic Constraints on Amorphous and Crystalline Magnesium Silicates: Dust Formation and Evolution in Selected Herbig Ae/Be Systems

    NASA Astrophysics Data System (ADS)

    Rietmeijer, Frans J. M.; Nuth, Joseph A.

    2013-07-01

    The Infrared Space Observatory, Spitzer Space Telescope, and Herschel Space Observatory surveys provided a wealth of data on the Mg-silicate minerals (forsterite, enstatite), silica, and "amorphous silicates with olivine and pyroxene stoichiometry" around Herbig Ae/Be stars. These incredible findings do not resonate with the mainstream Earth Sciences because of (1) disconnecting "astronomical nomenclature" and the long existing mineralogical and petrologic terminology of minerals and amorphous materials, and (2) the fact that Earth scientists (formerly geologists) are bound by the "Principle of Actualism" that was put forward by James Hutton (1726-1797). This principle takes a process-oriented approach to understanding mineral and rock formation and evolution. This paper will (1) review and summarize the results of laboratory-based vapor phase condensation and thermal annealing experiments, (2) present the pathways of magnesiosilica condensates to Mg-silicate mineral (forsterite, enstatite) formation and processing, and (3) present mineralogical and petrologic implications of the properties and compositions of the infrared-observed crystalline and amorphous dust for the state of circumstellar disk evolution. That is, the IR-observation of smectite layer silicates in HD142527 suggests the break-up of asteroid-like parent bodies that had experienced aqueous alteration. We discuss the persistence of amorphous dust around some young stars and an ultrafast amorphous to crystalline dust transition in HD 163296 that leads to forsterite grains with numerous silica inclusions. These dust evolution processes to form forsterite, enstatite ± tridymite could occur due to amorphous magnesiosilica dust precursors with a serpentine- or smectite-dehydroxylate composition.

  1. PETROLOGIC CONSTRAINTS ON AMORPHOUS AND CRYSTALLINE MAGNESIUM SILICATES: DUST FORMATION AND EVOLUTION IN SELECTED HERBIG Ae/Be SYSTEMS

    SciTech Connect

    Rietmeijer, Frans J. M.; Nuth, Joseph A.

    2013-07-01

    The Infrared Space Observatory, Spitzer Space Telescope, and Herschel Space Observatory surveys provided a wealth of data on the Mg-silicate minerals (forsterite, enstatite), silica, and ''amorphous silicates with olivine and pyroxene stoichiometry'' around Herbig Ae/Be stars. These incredible findings do not resonate with the mainstream Earth Sciences because of (1) disconnecting ''astronomical nomenclature'' and the long existing mineralogical and petrologic terminology of minerals and amorphous materials, and (2) the fact that Earth scientists (formerly geologists) are bound by the ''Principle of Actualism'' that was put forward by James Hutton (1726-1797). This principle takes a process-oriented approach to understanding mineral and rock formation and evolution. This paper will (1) review and summarize the results of laboratory-based vapor phase condensation and thermal annealing experiments, (2) present the pathways of magnesiosilica condensates to Mg-silicate mineral (forsterite, enstatite) formation and processing, and (3) present mineralogical and petrologic implications of the properties and compositions of the infrared-observed crystalline and amorphous dust for the state of circumstellar disk evolution. That is, the IR-observation of smectite layer silicates in HD142527 suggests the break-up of asteroid-like parent bodies that had experienced aqueous alteration. We discuss the persistence of amorphous dust around some young stars and an ultrafast amorphous to crystalline dust transition in HD 163296 that leads to forsterite grains with numerous silica inclusions. These dust evolution processes to form forsterite, enstatite {+-} tridymite could occur due to amorphous magnesiosilica dust precursors with a serpentine- or smectite-dehydroxylate composition.

  2. Hydrogen-induced rupture of strained Si─O bonds in amorphous silicon dioxide.

    PubMed

    El-Sayed, Al-Moatasem; Watkins, Matthew B; Grasser, Tibor; Afanas'ev, Valery V; Shluger, Alexander L

    2015-03-20

    Using ab initio modeling we demonstrate that H atoms can break strained Si─O bonds in continuous amorphous silicon dioxide (a-SiO(2)) networks, resulting in a new defect consisting of a threefold-coordinated Si atom with an unpaired electron facing a hydroxyl group, adding to the density of dangling bond defects, such as E' centers. The energy barriers to form this defect from interstitial H atoms range between 0.5 and 1.3 eV. This discovery of unexpected reactivity of atomic hydrogen may have significant implications for our understanding of processes in silica glass and nanoscaled silica, e.g., in porous low-permittivity insulators, and strained variants of a-SiO(2). PMID:25839289

  3. Plasma Deposition of Amorphous Silicon

    NASA Technical Reports Server (NTRS)

    Calcote, H. F.

    1982-01-01

    Strongly adhering films of silicon are deposited directly on such materials as Pyrex and Vycor (or equivalent materials) and aluminum by a non-equilibrium plasma jet. Amorphous silicon films are formed by decomposition of silicon tetrachloride or trichlorosilane in the plasma. Plasma-jet technique can also be used to deposit an adherent silicon film on aluminum from silane and to dope such films with phosphorus. Ability to deposit silicon films on such readily available, inexpensive substrates could eventually lead to lower cost photovoltaic cells.

  4. Preparation of amorphous sulfide sieves

    DOEpatents

    Siadati, Mohammad H.; Alonso, Gabriel; Chianelli, Russell R.

    2006-11-07

    The present invention involves methods and compositions for synthesizing catalysts/porous materials. In some embodiments, the resulting materials are amorphous sulfide sieves that can be mass-produced for a variety of uses. In some embodiments, methods of the invention concern any suitable precursor (such as thiomolybdate salt) that is exposed to a high pressure pre-compaction, if need be. For instance, in some cases the final bulk shape (but highly porous) may be same as the original bulk shape. The compacted/uncompacted precursor is then subjected to an open-flow hot isostatic pressing, which causes the precursor to decompose and convert to a highly porous material/catalyst.

  5. Plasma deposition of amorphous hydrogenated carbon films on III-V semiconductors

    NASA Technical Reports Server (NTRS)

    Pouch, John J.; Warner, Joseph D.; Liu, David C.; Alterovitz, Samuel A.

    1988-01-01

    Amorphous hydrogenated carbon films were grown on GaAs, InP and fused silica substrates using plasmas generated from hydrocarbon gases. Methane and n-butane sources were utilized. The effects of flow rate and power density on film growth were investigated. Carbon was the major constituent in the films. The degree of asymmetry at the carbon-semiconductor interface was approximately independent of the power density. Different H-C bonding configurations were detected by the technique of secondary-ion mass spectrometry. Band gaps up to 3 eV were obtained from optical absorption studies. Breakdown strengths as high as 600 MV/m were measured.

  6. High-pressure-induced structural changes, amorphization and molecule penetration in MFI microporous materials: a review.

    PubMed

    Vezzalini, Giovanna; Arletti, Rossella; Quartieri, Simona

    2014-06-01

    This is a comparative study on the high-pressure behavior of microporous materials with an MFI framework type (i.e. natural mutinaite, ZSM-5 and the all-silica phase silicalite-1), based on in-situ experiments in which penetrating and non-penetrating pressure-transmitting media were used. Different pressure-induced phenomena and deformation mechanisms (e.g. pressure-induced over-hydration, pressure-induced amorphization) are discussed. The influence of framework and extra-framework composition and of the presence of silanol defects on the response to the high pressure of MFI-type zeolites is discussed. PMID:24892591

  7. Biomimetic synthesized bimodal nanoporous silica: Bimodal mesostructure formation and application for ibuprofen delivery.

    PubMed

    Li, Jing; Xu, Lu; Zheng, Nan; Wang, Hongyu; Lu, Fangzheng; Li, Sanming

    2016-01-01

    The present paper innovatively reports bimodal nanoporous silica synthesized using biomimetic method (B-BNS) with synthesized polymer (C16-L-serine) as template. Formation mechanism of B-BNS was deeply studied and exploration of its application as carrier of poorly water-soluble drug ibuprofen (IBU) was conducted. The bimodal nanopores and curved mesoscopic channels of B-BNS were achieved due to the dynamic self-assembly of C16-L-serine induced by silane coupling agent (3-aminopropyltriethoxysilane, APTES) and silica source (tetraethoxysilane, TEOS). Characterization results confirmed the successful synthesis of B-BNS, and particularly, nitrogen adsorption/desorption measurement demonstrated that B-BNS was meso-meso porous silica material. In application, B-BNS loaded IBU with high drug loading content due to its enlarged nanopores. After being loaded, IBU presented amorphous phase because nanoporous space and curved mesoscopic channels of B-BNS prevented the crystallization of IBU. In vitro release result revealed that B-BNS controlled IBU release with two release phases based on bimodal nanopores and improved dissolution in simulated gastric fluid due to crystalline conversion of IBU. It is convincible that biomimetic method provides novel theory and insight for synthesizing bimodal nanoporous silica, and unique functionalities of B-BNS as drug carrier can undoubtedly promote the application of bimodal nanoporous silica and development of pharmaceutical science. PMID:26478410

  8. Biocompatibility assessment of rice husk-derived biogenic silica nanoparticles for biomedical applications.

    PubMed

    Alshatwi, Ali A; Athinarayanan, Jegan; Periasamy, Vaiyapuri Subbarayan

    2015-02-01

    Synthetic forms of silica have low biocompatibility, whereas biogenic forms have myriad beneficial effects in current toxicological applications. Among the various sources of biogenic silica, rice husk is considered a valuable agricultural biomass material and a cost-effective resource that can provide biogenic silica for biomedical applications. In the present study, highly pure biogenic silica nanoparticles (bSNPs) were successfully harvested from rice husks using acid digestion under pressurized conditions at 120°C followed by a calcination process. The obtained bSNPs were subjected to phase identification analysis using X-ray diffraction, which revealed the amorphous nature of the bSNPs. The morphologies of the bSNPs were observed using transmission electron microscopy (TEM), which revealed spherical particles 10 to 30 nm in diameter. Furthermore, the biocompatibility of the bSNPs with human lung fibroblast cells (hLFCs) was investigated using a viability assay and assessing cellular morphological changes, intracellular ROS generation, mitochondrial transmembrane potential and oxidative stress-related gene expression. Our results revealed that the bSNPs did not have any significant incompatibility in these in vitro cell-based approaches. These preliminary findings suggest that bSNPs are biocompatible, could be the best alternative to synthetic forms of silica and are applicable to food additive and biomedical applications. PMID:25492167

  9. Effect of concentrated epoxidised natural rubber and silica masterbatch for tyre application

    NASA Astrophysics Data System (ADS)

    Azira, A. A.; Verasamy, D.; Kamal, M. M.

    2016-07-01

    The availability of concentrated epoxidised natural rubber (ENR-LC) has provided a better opportunity for using epoxidised natural rubber (ENR) with silica to reinforce natural rubber for tyre application. ENR-LC mixed directly with silica to rubber by high speed stirrer without using any coupling agent. Some rubber compounds were prepared by mixing a large amount of precipitated amorphous white silica with natural rubber. The silica was prepared in aqueous dispersion and the filler was perfectly dispersed in the ENR-LC. The performance of the composites was evaluated in this work for the viability of ENR-LC/Si in tyre compounding. Compounding was carried out on a two roll mill, where the additives and curing agents was later mixed. Characterization of these composites was performed by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) for dispersion as well as mechanical testing. C-ENR/Si showed efficient as primary reinforcing filler in ENR with regard to modulus and tensile strength, resulting on an increase in the stiffness of the rubbers compared to ENR latex. Overall improvement in the mechanical properties for the ENR-LC over the control crosslinked rubber sample was probably due to synergisms of silica reinforcement and crosslinking of the polymeric matrix phase.

  10. Synthesis of silica nanoparticles from Vietnamese rice husk by sol-gel method

    NASA Astrophysics Data System (ADS)

    Le, Van Hai; Thuc, Chi Nhan Ha; Thuc, Huy Ha

    2013-02-01

    Silica powder at nanoscale was obtained by heat treatment of Vietnamese rice husk following the sol-gel method. The rice husk ash (RHA) is synthesized using rice husk which was thermally treated at optimal condition at 600°C for 4 h. The silica from RHA was extracted using sodium hydroxide solution to produce a sodium silicate solution and then precipitated by adding H2SO4 at pH = 4 in the mixture of water/butanol with cationic presence. In order to identify the optimal condition for producing the homogenous silica nanoparticles, the effects of surfactant surface coverage, aging temperature, and aging time were investigated. By analysis of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the silica product obtained was amorphous and the uniformity of the nanosized sample was observed at an average size of 3 nm, and the BET result showed that the highest specific surface of the sample was about 340 m2/g. The results obtained in the mentioned method prove that the rice husk from agricultural wastes can be used for the production of silica nanoparticles.

  11. Synthesis of silica nanoparticles from Vietnamese rice husk by sol–gel method

    PubMed Central

    2013-01-01

    Silica powder at nanoscale was obtained by heat treatment of Vietnamese rice husk following the sol–gel method. The rice husk ash (RHA) is synthesized using rice husk which was thermally treated at optimal condition at 600°C for 4 h. The silica from RHA was extracted using sodium hydroxide solution to produce a sodium silicate solution and then precipitated by adding H2SO4 at pH = 4 in the mixture of water/butanol with cationic presence. In order to identify the optimal condition for producing the homogenous silica nanoparticles, the effects of surfactant surface coverage, aging temperature, and aging time were investigated. By analysis of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the silica product obtained was amorphous and the uniformity of the nanosized sample was observed at an average size of 3 nm, and the BET result showed that the highest specific surface of the sample was about 340 m2/g. The results obtained in the mentioned method prove that the rice husk from agricultural wastes can be used for the production of silica nanoparticles. PMID:23388152

  12. Synthesis of silica nanoparticles from Vietnamese rice husk by sol-gel method.

    PubMed

    Le, Van Hai; Thuc, Chi Nhan Ha; Thuc, Huy Ha

    2013-01-01

    Silica powder at nanoscale was obtained by heat treatment of Vietnamese rice husk following the sol-gel method. The rice husk ash (RHA) is synthesized using rice husk which was thermally treated at optimal condition at 600°C for 4 h. The silica from RHA was extracted using sodium hydroxide solution to produce a sodium silicate solution and then precipitated by adding H2SO4 at pH = 4 in the mixture of water/butanol with cationic presence. In order to identify the optimal condition for producing the homogenous silica nanoparticles, the effects of surfactant surface coverage, aging temperature, and aging time were investigated. By analysis of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the silica product obtained was amorphous and the uniformity of the nanosized sample was observed at an average size of 3 nm, and the BET result showed that the highest specific surface of the sample was about 340 m2/g. The results obtained in the mentioned method prove that the rice husk from agricultural wastes can be used for the production of silica nanoparticles. PMID:23388152

  13. How is Physical Depositional Setting Related to Silica Chemistry in the Platte River, USA?

    NASA Astrophysics Data System (ADS)

    Van Orsdel, Z. R.; Mohr, R. C.; Ford, E.; Wagner, Z.; Kettenring, K. M.; Triplett, L.

    2013-12-01

    Beginning in 2003, a non-native subspecies of Phragmites australis, a wetland grass, invaded the Platte River in Nebraska, USA. The plants' dense root and rhizome structures caused channel narrowing and increased deposition of fine sediment. We hypothesized that a significant proportion of the fine sediment was comprised of biogenic silica particles including terrestrial plant phytoliths. In this study, we determined a relationship between particle size and biogenic silica content in Platte River sediments to help characterize when and where silica is sequestered in the riparian areas of rivers. Historically a wide, braided, largely unvegetated sand-bed river, the Platte has undergone several major changes since the early 1900s. The main anthropogenic impact on the Platte has been a ~75 percent reduction in flow, leading to channel narrowing and more vegetation occupying riparian areas. Phragmites is particularly effective at building islands and extending river banks because its roots add cohesion to sediment. We suspect that the presence of Phragmites in the Platte River has resulted in a reduction of bioavailable silica (dissolved and particulate amorphous particles) being exported to the downstream receiving waters, ultimately including the Gulf of Mexico. We want to better understand silica sequestration in riverine environments, because silicon is often a limiting nutrient for some phytoplankton (e.g., diatoms and radiolaria) in coastal oceans. In the Platte, lower water levels and increased vegetation density cause reduced flow velocity, allowing more silica particles to settle out of suspension. We hypothesized that silica content in the riparian sediments of the Platte River negatively correlate with particle size, and that the non-native subspecies of Phragmites uses more silica than the native variety. In order to quantify the effect Phragmites is having on the Platte's silica load, plant and sediment samples were prepared using a timed NaOH digestion

  14. Laser surface treatment of amorphous metals

    NASA Astrophysics Data System (ADS)

    Katakam, Shravana K.

    Amorphous materials are used as soft magnetic materials and also as surface coatings to improve the surface properties. Furthermore, the nanocrystalline materials derived from their amorphous precursors show superior soft magnetic properties than amorphous counter parts for transformer core applications. In the present work, laser based processing of amorphous materials will be presented. Conventionally, the nanocrystalline materials are synthesized by furnace heat treatment of amorphous precursors. Fe-based amorphous/nanocrystalline materials due to their low cost and superior magnetic properties are the most widely used soft magnetic materials. However, achieving nanocrystalline microstructure in Fe-Si-B ternary system becomes very difficult owing its rapid growth rate at higher temperatures and sluggish diffusion at low temperature annealing. Hence, nanocrystallization in this system is achieved by using alloying additions (Cu and Nb) in the ternary Fe-Si-B system. Thus, increasing the cost and also resulting in reduction of saturation magnetization. laser processing technique is used to achieve extremely fine nanocrystalline microstructure in Fe-Si-B amorphous precursor. Microstructure-magnetic Property-laser processing co-relationship has been established for Fe-Si-B ternary system using analytical techniques. Laser processing improved the magnetic properties with significant increase in saturation magnetization and near zero coercivity values. Amorphous materials exhibit excellent corrosion resistance by virtue of their atomic structure. Fe-based amorphous materials are economical and due to their ease of processing are of potential interest to synthesize as coatings materials for wear and corrosion resistance applications. Fe-Cr-Mo-Y-C-B amorphous system was used to develop thick coatings on 4130 Steel substrate and the corrosion resistance of the amorphous coatings was improved. It is also shown that the mode of corrosion depends on the laser processing

  15. Silica-rich deposits and hydrated minerals at Gusev Crater, Mars: Vis-NIR spectral characterization and regional mapping

    USGS Publications Warehouse

    Rice, M.S.; Bell, J.F., III; Cloutis, E.A.; Wang, A.; Ruff, S.W.; Craig, M.A.; Bailey, D.T.; Johnson, J. R.; De Souza, P.A., Jr.; Farrand, W. H.

    2010-01-01

    The Mars Exploration Rover (MER) Spirit has discovered surprisingly high concentrations of amorphous silica in soil and nodular outcrops in the Inner Basin of the Columbia Hills. In Pancam multispectral observations, we find that an absorption feature at the longest Pancam wavelength (1009 nm) appears to be characteristic of these silica-rich materials; however, spectral analyses of amorphous silica suggest that the ???1009 nm spectral feature is not a direct reflection of their silica-rich nature. Based on comparisons with spectral databases, we hypothesize that the presence of H2O or OH, either free (as water ice), adsorbed or bound in a mineral structure, is responsible for the spectral feature observed by Pancam. The Gertrude Weise soil, which is nearly pure opaline silica, may have adsorbed water cold-trapped on mineral grains. The origin of the ???1009 nm Pancam feature observed in the silica-rich nodular outcrops may result from the presence of additional hydrated minerals (specific sulfates, halides, chlorides, sodium silicates, carbonates or borates). Using the ???1009 nm feature with other spectral parameters as a "hydration signature" we have mapped the occurrence of hydrated materials along the extent of Spirit's traverse across the Columbia Hills from West Spur to Home Plate (sols 155-1696). We have also mapped this hydration signature across large panoramic images to understand the regional distribution of materials that are spectrally similar to the silica-rich soil and nodular outcrops. Our results suggest that hydrated materials are common in the Columbia Hills. ?? 2009 Elsevier Inc.

  16. Studies of hydrogenated amorphous silicon

    SciTech Connect

    Bishop, S G; Carlos, W E

    1984-07-01

    This report discusses the results of probing the defect structure and bonding of hydrogenated amorphous silicon films using both nuclear magnetic resonance (NMR) and electron spin resonance (ESR). The doping efficiency of boron in a-Si:H was found to be less than 1%, with 90% of the boron in a threefold coordinated state. On the other hand, phosphorus NMR chemical shift measurements yielded a ration of threefold to fourfold P sites of roughly 4 to 1. Various resonance lines were observed in heavily boron- and phosphorus-doped films and a-SiC:H alloys. These lines were attributed to band tail states on twofold coordinated silicon. In a-SiC:H films, a strong resonance was attributed to dangling bonds on carbon atoms. ESR measurements on low-pressure chemical-vapor-deposited (LPCVD) a-Si:H were performed on samples. The defect density in the bulk of the films was 10/sup 17//cc with a factor of 3 increase at the surface of the sample. The ESR spectrum of LPCVD-prepared films was not affected by prolonged exposure to strong light. Microcrystalline silicon samples were also examined. The phosphorus-doped films showed a strong signal from the crystalline material and no resonance from the amorphous matrix. This shows that phosphorus is incorporated in the crystals and is active as a dopant. No signal was recorded from the boron-doped films.

  17. Ductile crystalline-amorphous nanolaminates.

    PubMed

    Wang, Yinmin; Li, Ju; Hamza, Alex V; Barbee, Troy W

    2007-07-01

    It is known that the room-temperature plastic deformation of bulk metallic glasses is compromised by strain softening and shear localization, resulting in near-zero tensile ductility. The incorporation of metallic glasses into engineering materials, therefore, is often accompanied by complete brittleness or an apparent loss of useful tensile ductility. Here we report the observation of an exceptional tensile ductility in crystalline copper/copper-zirconium glass nanolaminates. These nanocrystalline-amorphous nanolaminates exhibit a high flow stress of 1.09 +/- 0.02 GPa, a nearly elastic-perfectly plastic behavior without necking, and a tensile elongation to failure of 13.8 +/- 1.7%, which is six to eight times higher than that typically observed in conventional crystalline-crystalline nanolaminates (<2%) and most other nanocrystalline materials. Transmission electron microscopy and atomistic simulations demonstrate that shear banding instability no longer afflicts the 5- to 10-nm-thick nanolaminate glassy layers during tensile deformation, which also act as high-capacity sinks for dislocations, enabling absorption of free volume and free energy transported by the dislocations; the amorphous-crystal interfaces exhibit unique inelastic shear (slip) transfer characteristics, fundamentally different from those of grain boundaries. Nanoscale metallic glass layers therefore may offer great benefits in engineering the plasticity of crystalline materials and opening new avenues for improving their strength and ductility. PMID:17592136

  18. Action of colloidal silica films on different nano-composites

    NASA Astrophysics Data System (ADS)

    Abdalla, S.; Al-Marzouki, F.; Obaid, A.; Gamal, S.

    Nano-composite films have been the subject of extensive work to develop the energy-storage efficiency of electrostatic capacitors. Factors such as polymer purity, nano-particles size, and film morphology drastically affect the electrostatic efficiency of the dielectric material that form an insulating film between conductive electrodes of a capacitor. This in turn affects the energy storage performance of the capacitor. In the present work, we have studied the dielectric properties of 4 high pure amorphous polymer films: polymethylmethacrylate (PMMA), polystyrene, polyimide and poly-4-vinylpyridine. Comparison between the dielectric properties of these polymers has revealed that the higher break down performance is a character of polyimide PI and PMMA. Also, our experimental data shows that adding colloidal silica to PMMA and PI leads to a net decrease in the dielectric properties compared to the pure polymer.

  19. Surface modification of silica nanoparticles

    NASA Astrophysics Data System (ADS)

    Ranjan, Rajesh

    Surface modification of nanosized silica particles by polymer grafting is gaining attention. This can be attributed to the fact that it provides a unique opportunity to engineer the interfacial properties of these modified particles; at the same time the mechanical and thermal properties of the polymers can be improved. Controlled free radical polymerization is a versatile technique which affords control over molecular weight, molecular weight distribution, architecture and functionalities of the resulting polymer. Three commonly used controlled free radical polymerizations include nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and reversible addition fragmentation transfer (RAFT) polymerization. ATRP and RAFT polymerization were explored in order to modify the silica surface with well-defined polymer brushes. A novel click-functionalized RAFT chain transfer agent (RAFT CTA) was synthesized which opened up the possibility of using RAFT polymerization and click chemistry together in surface modification. Using this RAFT CTA, the surface of silica nanoparticles was modified with polystyrene and polyacrylamide brushes via the "grafting to" approach. Both tethered polystyrene and polyacrylamide chains were found in the brush regime. The combination of ATRP and click chemistry was also explored for surface modification. A combination of RAFT polymerization and click chemistry was also studied to modify the surface via the "grafting from" approach. Our strategy included the (1) "grafting from" approach for brush formation (2) facile click reaction to immobilize the RAFT agent (3) synthesis of R-supported chain transfer agent and (4) use of the more active trithiocarbonate RAFT agent. Grafting density obtained by this method was significantly higher than reported values in the literature. Polystyrene (PS) grafted silica nanoparticles were also prepared by a tandem process that simultaneously employs reversible addition fragmentation

  20. Fluorination of amorphous thin-film materials with xenon fluoride

    DOEpatents

    Weil, R.B.

    1987-05-01

    A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.

  1. Fluorination of amorphous thin-film materials with xenon fluoride

    DOEpatents

    Weil, Raoul B.

    1988-01-01

    A method is disclosed for producing fluorine-containing amorphous semiconductor material, preferably comprising amorphous silicon. The method includes depositing amorphous thin-film material onto a substrate while introducing xenon fluoride during the film deposition process.

  2. Method of making amorphous metal composites

    DOEpatents

    Byrne, Martin A.; Lupinski, John H.

    1982-01-01

    The process comprises placing an amorphous metal in particulate form and a low molecular weight (e.g., 1000-5000) thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

  3. Electron tunnelling into amorphous germanium and silicon.

    NASA Technical Reports Server (NTRS)

    Smith, C. W.; Clark, A. H.

    1972-01-01

    Measurements of tunnel conductance versus bias, capacitance versus bias, and internal photoemission were made in the systems aluminum-oxide-amorphous germanium and aluminium-oxide-amorphous silicon. A function was extracted which expresses the deviation of these systems from the aluminium-oxide-aluminium system.

  4. Electron beam recrystallization of amorphous semiconductor materials

    NASA Technical Reports Server (NTRS)

    Evans, J. C., Jr.

    1968-01-01

    Nucleation and growth of crystalline films of silicon, germanium, and cadmium sulfide on substrates of plastic and glass were investigated. Amorphous films of germanium, silicon, and cadmium sulfide on amorphous substrates of glass and plastic were converted to the crystalline condition by electron bombardment.

  5. Imprinting bulk amorphous alloy at room temperature

    DOE PAGESBeta

    Kim, Song-Yi; Park, Eun-Soo; Ott, Ryan T.; Lograsso, Thomas A.; Huh, Moo-Young; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

    2015-11-13

    We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the abilitymore » of amorphous alloys or metallic glasses to precisely replicate patterning features onto both conventional metals and the other amorphous alloys. In conclusion, our work presents an avenue for avoiding the embrittlement of amorphous alloys associated with thermoplastic forming and yields new insight the forming application of bulk amorphous alloys at room temperature without using heat treatment.« less

  6. Effect of Micromorphology and Surface Reactivity of Several Unusual forms of Crystalline Silica on the toxicity to a Monocyte-Macrophage Tumor Cell Line.

    PubMed

    Fenoglio, I; Fubini, B; Tiozzo, R; Di Renzo, F

    2000-01-01

    The fibrogenic or carcinogenic response to the inhalation of crystalline silica dusts is strictly related to the physicochemical properties of the particles, which, in turn, are mostly determined by the "origin" and the history of the dust. Several physicochemical properties have been reported to modulate silica pathogenicity. None of them simply correlate with the reported toxicity in all the systems used to study silica pathogenicity. This confirms, on the one hand, that several properties are implicated at the same time, and on the other that pathogenicity is the result of a multistage process. There is a general consensus on the key role played by alveolar macrophages in silica-related diseases. For this article the cytotoxicity of a large variety of silicas, including rather unusual forms, with controlled micromorphology and surface properties, has been studied on a mouse monocyte-machrophage tumor cell line successfully employed in previous studies on cristobalite (Fubini et al., 1999). When compared on a per unit surface basis, crystalline silicas were more cytotoxic than amorphous ones, with the notable exception of stishovite, the nonpathogenic crystalline polymorph, with octahedrally coordinated silicon atoms. Among the amorphous ones, a diatomaceous earth and a powdered silica glass exhibited an intermediate toxicity, higher than what was elicited by a pyrogenic silica. In this study a new class of crystalline silicas have been considered, pure-silica zeolites, which constitute a new morphological entity with which cells may be confronted. The cytotoxicity of these samples varies from inert to highly cytotoxic, covering all the range of toxicity covered by the traditional silica dusts. We discuss the influence of morphological properties and surface reactivity on the cytotoxicity of several pure-silica zeolites. The extent of exposed surface and the shape of the particles correlate with cell toxicity. The lower cytotoxicity of one "non-pathogenic quartz

  7. Exposure to crystalline silica in abrasive blasting operations where silica and non-silica abrasives are used.

    PubMed

    Radnoff, Diane L; Kutz, Michelle K

    2014-01-01

    Exposure to respirable crystalline silica is a hazard common to many industries in Alberta but particularly so in abrasive blasting. Alberta occupational health and safety legislation requires the consideration of silica substitutes when conducting abrasive blasting, where reasonably practicable. In this study, exposure to crystalline silica during abrasive blasting was evaluated when both silica and non-silica products were used. The crystalline silica content of non-silica abrasives was also measured. The facilities evaluated were preparing metal products for the application of coatings, so the substrate should not have had a significant contribution to worker exposure to crystalline silica. The occupational sampling results indicate that two-thirds of the workers assessed were potentially over-exposed to respirable crystalline silica. About one-third of the measurements over the exposure limit were at the work sites using silica substitutes at the time of the assessment. The use of the silica substitute, by itself, did not appear to have a large effect on the mean airborne exposure levels. There are a number of factors that may contribute to over-exposures, including the isolation of the blasting area, housekeeping, and inappropriate use of respiratory protective equipment. However, the non-silica abrasives themselves also contain silica. Bulk analysis results for non-silica abrasives commercially available in Alberta indicate that many contain crystalline silica above the legislated disclosure limit of 0.1% weight of silica per weight of product (w/w) and this information may not be accurately disclosed on the material safety data sheet for the product. The employer may still have to evaluate the potential for exposure to crystalline silica at their work site, even when silica substitutes are used. Limited tests on recycled non-silica abrasive indicated that the silica content had increased. Further study is required to evaluate the impact of product recycling

  8. High-pressure infrared sepctra of alpha-quartz, coesite, stishovite and silica glass

    NASA Technical Reports Server (NTRS)

    Williams, Q.; Hemley, R. J.; Kruger, M. B.; Jeanloz, R.

    1993-01-01

    High-pressure infrared absorption spectra of alpha-quatz, coesite, stishovite, and SiO2 glass are consistent with the primary compression mechanism of the initially tetrahedrally bonded phases being the bending of the Si-O-Si angle at pressures less than 10-20 GPa. At higher pressures, up to 40 GPa, we observe a decline in the intensity of the infrared SiO4 asymmetric-stretching vibrations of all three phases, with an increase in the relative amplitude between 700 and 900/cm. This change in intensities is attributed to an increase in the average coordination number of silicon through extreme distortion of tetrahedra. At pressures above approximately 20 GPa, the low-pressure crystalline polymorphs gradually become amorphous, and the infrared spectra provide evidence for an increase in silicon coordination in these high-density amorphous phases. The pressure-amorphized samples prepared from quartz and coesite differ structurally both from each other and from silica glass that has been compressed, and the high pressure spectra indicate that these materials are considerably more disordered than stishovite under comparable pressure conditions. Average mode Grueneisen parameters calculated for quartz, stishovite and fused silica from both infrared and Raman spectra are compatible with the corresponding thermodynamic value of the Grueneisen parameter, however, that of coesite is significantly discrepant.

  9. Interfacial Effect on Confined Crystallization of Poly(ethylene oxide)/Silica Composites

    NASA Astrophysics Data System (ADS)

    Su, Yunlan; Zhao, Weiwei; Gao, Xia; Xu, Jianjun; Wang, Dujin

    The impact of nanoconfinement introduced by nanoparticles on polymer crystallization has attracted extensive attention because it plays the decisive role in the ultimate properties of polymer nanocomposites. In this study, interfacial and spatial confinement effects of silica (SiO2) nanoparticles on the crystallization behaviors of poly(ethylene oxide) (PEO)/SiO2 composites were systematically investigated by changing the size and concentration of SiO2 in PEO matrix. The composites with high silica loadings exhibit two crystallization peaks of PEO as determined by differential scanning calorimetry (DSC). The first peak at 7-43 °C is related to the bulk PEO, while the second peak at -20 to -30 °C is attributed to the restricted PEO segments. Three-layer (amorphous, interfacial and bulk) model is proposed to interpret the confined crystallization of PEO/SiO2 composites, which is supported by the results of thermogravimetric analysis (TGA) and solid-state 1H nuclear magnetic resonance (NMR). In amorphous layer, most PEO segments are directly adsorbed on SiO2 surface via hydrogen bonding. The interfacial PEO layer, which is nonuniform, is composed of crystallizable loops and tails extending from amorphous layer. National Natural Science Foundation of China (NSFC) under Contract 21274156.

  10. Structure, thermodynamics, and crystallization of amorphous hafnia

    NASA Astrophysics Data System (ADS)

    Luo, Xuhui; Demkov, Alexander A.

    2015-09-01

    We investigate theoretically amorphous hafnia using the first principles melt and quench method. We identify two types of amorphous structures of hafnia. Type I and type II are related to tetragonal and monoclinic hafnia, respectively. We find type II structure to show stronger disorder than type I. Using the phonon density of states, we calculate the specific heat capacity for type II amorphous hafnia. Using the nudged elastic band method, we show that the averaged transition barrier between the type II amorphous hafnia and monoclinic phase is approximately 0.09 eV/HfO2. The crystallization temperature is estimated to be 421 K. The calculations suggest an explanation for the low thermal stability of amorphous hafnia.

  11. Solid-state diffusion in amorphous zirconolite

    SciTech Connect

    Yang, C.; Dove, M. T.; Trachenko, K.; Zarkadoula, E.; Todorov, I. T.; Geisler, T.; Brazhkin, V. V.

    2014-11-14

    We discuss how structural disorder and amorphization affect solid-state diffusion, and consider zirconolite as a currently important case study. By performing extensive molecular dynamics simulations, we disentangle the effects of amorphization and density, and show that a profound increase of solid-state diffusion takes place as a result of amorphization. Importantly, this can take place at the same density as in the crystal, representing an interesting general insight regarding solid-state diffusion. We find that decreasing the density in the amorphous system increases pre-factors of diffusion constants, but does not change the activation energy in the density range considered. We also find that atomic species in zirconolite are affected differently by amorphization and density change. Our microscopic insights are relevant for understanding how solid-state diffusion changes due to disorder and for building predictive models of operation of materials to be used to encapsulate nuclear waste.

  12. Neutron irradiation induced amorphization of silicon carbide

    SciTech Connect

    Snead, L.L.; Hay, J.C.

    1998-09-01

    This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 {times} 10{sup 25} n/m{sup 2}. Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density ({minus}10.8%), elastic modulus as measured using a nanoindentation technique ({minus}45%), hardness as measured by nanoindentation ({minus}45%), and standard Vickers hardness ({minus}24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C.

  13. Structure, thermodynamics, and crystallization of amorphous hafnia

    SciTech Connect

    Luo, Xuhui; Demkov, Alexander A.

    2015-09-28

    We investigate theoretically amorphous hafnia using the first principles melt and quench method. We identify two types of amorphous structures of hafnia. Type I and type II are related to tetragonal and monoclinic hafnia, respectively. We find type II structure to show stronger disorder than type I. Using the phonon density of states, we calculate the specific heat capacity for type II amorphous hafnia. Using the nudged elastic band method, we show that the averaged transition barrier between the type II amorphous hafnia and monoclinic phase is approximately 0.09 eV/HfO{sub 2}. The crystallization temperature is estimated to be 421 K. The calculations suggest an explanation for the low thermal stability of amorphous hafnia.

  14. Amorphization of Ti1- x Mn x

    NASA Astrophysics Data System (ADS)

    Chu, B.-L.; Chen, C.-C.; Perng, T.-P.

    1992-08-01

    Three amorphous Ti1- x Mn x alloy powders, with x = 0.4, 0.5, and 0.6, were prepared by mechanical alloying (MA) of the elemental powders in a high-energy ball mill. The amorphous powders were characterized by X-ray diffraction (XRD) and high-resolution transmission elec- tron microscopy (HRTEM). The crystallization temperatures for these alloys detected by dif- ferential scanning calorimetry (DSC) varied from 769 to 830 K. The calculated enthalpies of mixing in these amorphous phases are relatively small compared with those for other Ti-base binary alloys. The criteria for solid-state amorphization reaction are examined. It is suggested that the kinetics of nucleation and growth favors the formation of the amorphous phases and the supply of atoms for nucleation and growth is predominantly through the defective regions induced by MA.

  15. Repetitive Dosing of Fumed Silica Leads to Profibrogenic Effects through Unique Structure-Activity Relationships and Biopersistence in the Lung.

    PubMed

    Sun, Bingbing; Wang, Xiang; Liao, Yu-Pei; Ji, Zhaoxia; Chang, Chong Hyun; Pokhrel, Suman; Ku, Justine; Liu, Xiangsheng; Wang, Meiying; Dunphy, Darren R; Li, Ruibin; Meng, Huan; Mädler, Lutz; Brinker, C Jeffrey; Nel, André E; Xia, Tian

    2016-08-23

    Contrary to the notion that the use of fumed silica in consumer products can "generally (be) regarded as safe" (GRAS), the high surface reactivity of pyrogenic silica differs from other forms of synthetic amorphous silica (SAS), including the capacity to induce membrane damage and acute proinflammatory changes in the murine lung. In addition, the chain-like structure and reactive surface silanols also allow fumed silica to activate the NLRP3 inflammasome, leading to IL-1β production. This pathway is known to be associated with subchronic inflammation and profibrogenic effects in the lung by α-quartz and carbon nanotubes. However, different from the latter materials, bolus dose instillation of 21 mg/kg fumed silica did not induce sustained IL-1β production or subchronic pulmonary effects. In contrast, the NLRP3 inflammasome pathway was continuously activated by repetitive-dose administration of 3 × 7 mg/kg fumed silica, 1 week apart. We also found that while single-dose exposure failed to induce profibrotic effects in the lung, repetitive dosing can trigger increased collagen production, even at 3 × 3 mg/kg. The change between bolus and repetitive dosing was due to a change in lung clearance, with recurrent dosing leading to fumed silica biopersistence, sustained macrophage recruitment, and activation of the NLRP3 pathway. These subchronic proinflammatory effects disappeared when less surface-reactive titanium-doped fumed silica was used for recurrent administration. All considered, these data indicate that while fumed silica may be regarded as safe for some applications, we should reconsider the GRAS label during repetitive or chronic inhalation exposure conditions. PMID:27483033

  16. Admicellar polymerization of precipated silica

    SciTech Connect

    Reynolds, J.L.; Grady, B.P.; Harwell, J.H.

    1996-10-01

    The tendency of a surfactant molecule to adsorb at a solid-liquid interface is the basis for an in situ surface modification process, termed admicellar polymerization. The four-step admicellar polymerization process includes: (1) adsorption of surfactant at the solid-liquid interface, (2) adsolubilization of monomer into the surfactant bilayer, (3) polymerization using free-radical initiators and heat, (4) removal of excess surfactant to expose the polymer modified surface. The process is used to apply polymer to precipitated silica to enhance the compatibility of the silica when added to filled rubber. The adsorption isotherms were first determined for particular surfactant/silica combinations to find the surfactant concentration that would sufficiently adsolubilize the monomer, while remaining below the critical micelle concentration. A series of experiments were then devised for the polymerization reactions in which the surfactant and monomer amounts were varied over three levels to establish the optimal combination.

  17. Physisorbed Water on Silica at Mars Temperatures

    NASA Technical Reports Server (NTRS)

    Sutter, B.; Sriwatanapongse, W.; Quinn, R.; Klug, C.; Zent, A.

    2002-01-01

    The usefulness of nuclear magnetic resonance spectroscopy in probing water interactions on silica at Mars temperatures is discussed. Results indicate that two types of water occur with silica at Mars temperatures. Additional information is contained in the original extended abstract.

  18. Barite silica chimneys from the Sumisu Rift, Izu-Bonin Arc: possible analog to hematitic chert associated with Kuroko deposits

    NASA Astrophysics Data System (ADS)

    Urabe, Tetsuro; Kusakabe, Minoru

    1990-10-01

    Barite-bearing silica chimneys and crusts were found during ALVIN dives in a back-arc basin called the Sumisu Rift of the Izu-Bonin arc, northwest Pacific. These silica deposits mainly occur on the flank of a rhyolite lava dome of the bimodal volcanic suite along the rift axis. Analogous hydrothermal activity occurred around 15 Ma in the northeast Japan arc; the formation of Kuroko deposits at this time was closely related to submarine rhyolitic volcanism of bimodal suite in a back-arc rift. The chimneys are composed of filamentous amorphous silica and minor amount of barite and iron oxide amorphous to X-rays. The concentrations of minor elements Fe, Mn, Ba, Pb, Zn, Cu, As, and Sb are similar to those in the hematitic chert layers which constitute the uppermost part of Kuroko orebodies. Theδ 34S andδ 18O values of barite from the Sumisu Rift have ranges of 21.7-22.3 and 8.8-10.3‰, respectively. The oxygen isotopic values, which are about 2‰ higher than those of the Kuroko barite, indicate that the temperature of formation was less than 150°C. This is supported by the dominance of one phase (liquid) inclusions in the barite crystals and occurrence of amorphous silica. Such a low formation temperature has also been deduced for the hematitic chert of the Kuroko deposits. Therefore, it is suggested that the silica deposits in the Sumisu Rift are the present-day analog to the Kuroko chert. This hydrothermal activity appears to be responsible for the observed high contents of manganese in surface sediments of the Sumisu Rift basin. Equivalent regional zoning of distal bedded manganese deposits around Kuroko deposits is observed at the Hokuroku basin.

  19. Locomotion of Amorphous Surface Robots

    NASA Technical Reports Server (NTRS)

    Bradley, Arthur T. (Inventor)

    2016-01-01

    An amorphous robot includes a compartmented bladder containing fluid, a valve assembly, and an outer layer encapsulating the bladder and valve assembly. The valve assembly draws fluid from a compartment(s) and discharges the drawn fluid into a designated compartment to displace the designated compartment with respect to the surface. Another embodiment includes elements each having a variable property, an outer layer that encapsulates the elements, and a control unit. The control unit energizes a designated element to change its variable property, thereby moving the designated element. The elements may be electromagnetic spheres with a variable polarity or shape memory polymers with changing shape and/or size. Yet another embodiment includes an elongated flexible tube filled with ferrofluid, a moveable electromagnet, an actuator, and a control unit. The control unit energizes the electromagnet and moves the electromagnet via the actuator to magnetize the ferrofluid and lengthen the flexible tube.

  20. Locomotion of Amorphous Surface Robots

    NASA Technical Reports Server (NTRS)

    Bradley, Arthur T. (Inventor)

    2014-01-01

    An amorphous robot includes a compartmented bladder containing fluid, a valve assembly, and an outer layer encapsulating the bladder and valve assembly. The valve assembly draws fluid from a compartment(s) and discharges the drawn fluid into a designated compartment to displace the designated compartment with respect to the surface. Another embodiment includes elements each having a variable property, an outer layer that encapsulates the elements, and a control unit. The control unit energizes a designated element to change its variable property, thereby moving the designated element. The elements may be electromagnetic spheres with a variable polarity or shape memory polymers with changing shape and/or size. Yet another embodiment includes an elongated flexible tube filled with ferrofluid, a moveable electromagnet, an actuator, and a control unit. The control unit energizes the electromagnet and moves the electromagnet via the actuator to magnetize the ferrofluid and lengthen the flexible tube.

  1. Optothermal nonlinearity of silica aerogel

    NASA Astrophysics Data System (ADS)

    Braidotti, Maria Chiara; Gentilini, Silvia; Fleming, Adam; Samuels, Michiel C.; Di Falco, Andrea; Conti, Claudio

    2016-07-01

    We report on the characterization of silica aerogel thermal optical nonlinearity, obtained by z-scan technique. The results show that typical silica aerogels have nonlinear optical coefficient similar to that of glass (≃10-12 m2/W), with negligible optical nonlinear absorption. The nonlinear coefficient can be increased to values in the range of 10-10 m2/W by embedding an absorbing dye in the aerogel. This value is one order of magnitude higher than that observed in the pure dye and in typical highly nonlinear materials like liquid crystals.

  2. Silica Precursors Derived From TEOS

    NASA Technical Reports Server (NTRS)

    Philipp, Warren H.

    1993-01-01

    Two high-char-yield polysiloxane polymers developed. Designated as TEOS-A and TEOS-B with silica char yields of 55% and 22%, respectively. These free-flowing polymers are Newtonium liquids instead of thick gels. Easily synthesized by controlled hydrolysis of inexpensive tetraethoxysilane (TEOS). Adhesive properties of TEOS-A suggest its use as binder for fabrication of ceramic articles from oxide powders. Less-viscous and more-fluid lower-molecular-weight TEOS-B used to infiltrate already-formed porous ceramic compacts to increase densities without effecting shrinkage. Also used as paint to coat substrate with silica, and to make highly pure silicate powders.

  3. The properties of silica-gelatin composites

    NASA Astrophysics Data System (ADS)

    Stavinskaya, O. N.; Laguta, I. V.

    2010-06-01

    Silica-gelatin composites with various silica-to-gelatin ratios were obtained. The influence of high-dispersity silica on the swelling of composites in water and desorption of pyridoxine and thiamine vitamins incorporated into the material was studied. The addition of silica to gelatin was shown to increase the time of the dissolution of the materials in aqueous medium and decelerate the desorption of vitamins.

  4. Sub-chronic toxicity study in rats orally exposed to nanostructured silica

    PubMed Central

    2014-01-01

    Background Synthetic Amorphous Silica (SAS) is commonly used in food and drugs. Recently, a consumer intake of silica from food was estimated at 9.4 mg/kg bw/day, of which 1.8 mg/kg bw/day was estimated to be in the nano-size range. Food products containing SAS have been shown to contain silica in the nanometer size range (i.e. 5 – 200 nm) up to 43% of the total silica content. Concerns have been raised about the possible adverse effects of chronic exposure to nanostructured silica. Methods Rats were orally exposed to 100, 1000 or 2500 mg/kg bw/day of SAS, or to 100, 500 or 1000 mg/kg bw/day of NM-202 (a representative nanostructured silica for OECD testing) for 28 days, or to the highest dose of SAS or NM-202 for 84 days. Results SAS and NM-202 were extensively characterized as pristine materials, but also in the feed matrix and gut content of the animals, and after in vitro digestion. The latter indicated that the intestinal content of the mid/high-dose groups had stronger gel-like properties than the low-dose groups, implying low gelation and high bioaccessibility of silica in the human intestine at realistic consumer exposure levels. Exposure to SAS or NM-202 did not result in clearly elevated tissue silica levels after 28-days of exposure. However, after 84-days of exposure to SAS, but not to NM-202, silica accumulated in the spleen. Biochemical and immunological markers in blood and isolated cells did not indicate toxicity, but histopathological analysis, showed an increased incidence of liver fibrosis after 84-days of exposure, which only reached significance in the NM-202 treated animals. This observation was accompanied by a moderate, but significant increase in the expression of fibrosis-related genes in liver samples. Conclusions Although only few adverse effects were observed, additional studies are warranted to further evaluate the biological relevance of observed fibrosis in liver and possible accumulation of silica in the spleen in the NM-202

  5. Systematic characterization of polycrystalline silica-carbonate helices.

    PubMed

    Nakouzi, Elias; Knoll, Pamela; Hendrix, Kenzie B; Steinbock, Oliver

    2016-08-17

    Biomorphs are complex, life-like structures that emerge from the precipitation of barium carbonate and amorphous silica in alkaline media. Despite their inorganic nature, these microstructures have non-crystallographic morphologies such as helices and cardioid sheets. At the nanoscale, biomorphs arrange thousands of crystalline nanorods as hierarchical assemblies that resemble natural biominerals suggesting novel approaches towards the production of biomimetic materials. We report the synthesis of silica-carbonate biomorphs in single-phase, gradient-free solutions that differ markedly from the typical solution-gas or gel-solution setups. Our experimental approach significantly increases the duration of biomorph growth and hence assembles networks in which individual helices extend to several millimeters. These unusually long biomorphs allow the first quantitative measurements of mesoscopic parameters such as the helix wavelength, period, width, and linear as well as tangential growth velocities. We find that the latter quantities are system-specific and tightly conserved during many hours of growth. Moreover, the average double helix wavelength of (19 ± 3) μm and width of (9.6 ± 0.8) μm vary by less than 12% when the initial carbonate concentration is changed by three orders of magnitude. We also delineate the single helix growth mechanism and report the occurrence of ribbon-like structures and highly regular "superhelices". Our experiments clearly demonstrate the robustness and consistency of biomorph growth under stable chemical conditions. PMID:27492708

  6. High strain rate fracture behavior of fused silica

    NASA Astrophysics Data System (ADS)

    Ruggiero, Andrew; Iannitti, Gianluca; Testa, Gabriel; Limido, Jerome; Lacome, Jean; Olovsson, Lars; Ferraro, Mario; Bonora, Nicola

    2013-06-01

    Fused silica is a high purity synthetic amorphous silicon dioxide characterized by low thermal expansion coefficient, excellent optical qualities and exceptional transmittance over a wide spectral range. Because of its wide use in the military industry as window material, it may be subjected to high-energy ballistic impacts. Under such dynamic conditions, post-yield response of the ceramic as well as the strain rate related effects become significant and should be accounted for in the constitutive modeling. In this study, the procedure for constitutive model validation and model parameters identification, is presented. Taylor impact tests and drop weight tests were designed and performed at different impact velocities, from 1 to 100 m/s, and strain rates, from 102 up to 104 s-1. Numerical simulation of both tests was performed with IMPETUS-FEA, a general non-linear finite element software which offers NURBS finite element technology for the simulation of large deformation and fracture in materials. Model parameters were identified by optimization using multiple validation metrics. The validity of the parameters set determined with the proposed procedure was verified comparing numerical predictions and experimental results for an independent designed test consisting in a fused silica tile impacted at prescribed velocity by a steel sphere.

  7. [Preparation and infrared spectral analysis of nanoporous silica thin film].

    PubMed

    Wang, Juan; Zhang, Chang-rui; Feng, Jian; Yang, Da-xiang

    2005-07-01

    Crack-free homogeneous nanoporous silica films on silicon wafer have been synthesized via supercritical drying of wet gel films obtained by spin-coating the polymeric silica sol, which was prepared using sol-gel method with tetraethoxysilane (TEOS) as precursor. The film is amorphous and nanoporous, and three-dimensional network, cross-linked by the primary particles whose sizes distribute between 10-20 nm showed respectively by XRD and SEM micrograph. The structure of the nanoporous SiO2 thin film was studied by FTIR spectra. The SiO2 thin film was composed of Si-O-Si and Si-OR, and was hydrophobic. The film contained Si-OH and became hydrophilic after being heat-treated at 250 degrees C or above in air. The heat-treated SiO2 thin film becomes hydrophobic by reacting with trimethylchlorosilane(TMCS). The TMCS-modified SiO2 thin film remains hydrophobic and can keep its nanoporous structure at a temperature lower than 450 degrees C in nitrogen. PMID:16241051

  8. Comparison of silica-core optical fibers

    NASA Astrophysics Data System (ADS)

    McCann, Brian P.

    1991-07-01

    Silica-core optical fibers have become a standard vehicle to remotely deliver high-power laser energy from surgical lasers operating between 200 and 2400 nm. The three primary types of silica-core fibers: plastic-clad; hard-clad; and silica-clad; are discussed. The performance advantages of each are addressed and actual general-surgery medical applications are provided.

  9. Increased dissolution rate and oral bioavailability of hydrophobic drug glyburide tablets produced using supercritical CO₂ silica dispersion technology.

    PubMed

    Guan, Jibin; Han, Jihong; Zhang, Dong; Chu, Chunxia; Liu, Hongzhuo; Sun, Jin; He, Zhonggui; Zhang, Tianhong

    2014-04-01

    The aim of this study was to design a silica-supported solid dispersion of a water-insoluble drug, glyburide, to increase its dissolution rate and oral absorption using supercritical fluid (SCF) technology. DSC and PXRD results indicated that the encapsulated drug in the optimal solid dispersion was in an amorphous state and the product was stable for 6 months. Glyburide was adsorbed onto the porous silica, as confirmed by the SEM images and BET analysis. Furthermore, FT-IR spectroscopy confirmed that there was no change in the chemical structure of glyburide after the application of SCF. The glyburide silica-based dispersion could also be compressed into tablet form. In vitro drug release analysis of the silica solid dispersion tablets demonstrated faster release of glyburide compared with the commercial micronized tablet. In an in vivo test, the AUC of the tablets composed of the new glyburide silica-based solid dispersion was 2.01 times greater than that of the commercial micronized glyburide tablets. In conclusion, SCF technology presents a promising approach to prepare silica-based solid dispersions of hydrophobic drugs because of its ability to increase their release and oral bioavailability. PMID:24184803

  10. Quantification of surface amorphous content using dispersive surface energy: the concept of effective amorphous surface area.

    PubMed

    Brum, Jeffrey; Burnett, Daniel

    2011-09-01

    We investigate the use of dispersive surface energy in quantifying surface amorphous content, and the concept of effective amorphous surface area is introduced. An equation is introduced employing the linear combination of surface area normalized square root dispersive surface energy terms. This equation is effective in generating calibration curves when crystalline and amorphous references are used. Inverse gas chromatography is used to generate dispersive surface energy values. Two systems are investigated, and in both cases surface energy data collected for physical mixture samples comprised of amorphous and crystalline references fits the predicted response with good accuracy. Surface amorphous content of processed lactose samples is quantified using the calibration curve, and interpreted within the context of effective amorphous surface area. Data for bulk amorphous content is also utilized to generate a thorough picture of how disorder is distributed throughout the particle. An approach to quantifying surface amorphous content using dispersive surface energy is presented. Quantification is achieved by equating results to an effective amorphous surface area based on reference crystalline, and amorphous materials. PMID:21725707

  11. Amorphous metallic films in silicon metallization systems

    NASA Technical Reports Server (NTRS)

    Nicolet, M. A.; Kattelus, H.; So, F.

    1984-01-01

    The general objective was to determine the potential of amorphous metallic thin films as a means of improving the stability of metallic contacts to a silicon substrate. The specific objective pursued was to determine the role of nitrogen in the formation and the resulting properties of amorphous thin-film diffusion barriers. Amorphous metallic films are attractive as diffusion barriers because of the low atomic diffusivity in these materials. Previous investigations revealed that in meeting this condition alone, good diffusion barriers are not necessarily obtained, because amorphous films can react with an adjacent medium (e.g., Si, Al) before they recrystallize. In the case of a silicon single-crystalline substrate, correlation exists between the temperature at which an amorphous metallic binary thin film reacts and the temperatures at which the films made of the same two metallic elements react individually. Amorphous binary films made of Zr and W were investigated. Both react with Si individually only at elevated temperatures. It was confirmed that such films react with Si only above 700 C when annealed in vacuum for 30 min. Amorphous W-N films were also investigated. They are more stable as barriers between Al and Si than polycrystalline W. Nitrogen effectively prevents the W-Al reaction that sets in at 500 C with polycrystalline W.

  12. Crystalline to amorphous transformation in silicon

    SciTech Connect

    Cheruvu, S.M.

    1982-09-01

    In the present investigation, an attempt was made to understand the fundamental mechanism of crystalline-to-amorphous transformation in arsenic implanted silicon using high resolution electron microscopy. A comparison of the gradual disappearance of simulated lattice fringes with increasing Frenkel pair concentration with the experimental observation of sharp interfaces between crystalline and amorphous regions was carried out leading to the conclusion that when the defect concentration reaches a critical value, the crystal does relax to an amorphous state. Optical diffraction experiments using atomic models also supported this hypothesis. Both crystalline and amorphous zones were found to co-exist with sharp interfaces at the atomic level. Growth of the amorphous fraction depends on the temperature, dose rate and the mass of the implanted ion. Preliminary results of high energy electron irradiation experiments at 1.2 MeV also suggested that clustering of point defects occurs near room temperature. An observation in a high resolution image of a small amorphous zone centered at the core of a dislocation is presented as evidence that the nucleation of an amorphous phase is heterogeneous in nature involving clustering or segregation of point defects near existing defects.

  13. Constraints on abundance, composition, and nature of X-ray amorphous components of soils and rocks at Gale crater, Mars

    NASA Astrophysics Data System (ADS)

    Dehouck, Erwin; McLennan, Scott M.; Meslin, Pierre-Yves; Cousin, Agnès.

    2014-12-01

    X-ray diffraction patterns of the three samples analyzed by Curiosity's Chemistry and Mineralogy (CheMin) instrument during the first year of the Mars Science Laboratory mission—the Rocknest sand, and the John Klein and Cumberland drill fines, both extracted from the Sheepbed mudstone—show evidence for a significant amorphous component of unclear origin. We developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from CheMin data. In turn, the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions (all oxides ≥ 0 wt %): 21-22 wt % for Rocknest and 15-20 wt % for Cumberland, in good agreement with estimates derived from the diffraction patterns (~27 and ~31 wt %, respectively). Despite obvious differences between the Rocknest sand and the Sheepbed mudstone, the amorphous components of the two sites are chemically very similar, having comparable concentrations of SiO2, TiO2, Al2O3, Cr2O3, FeOT, CaO, Na2O, K2O, and P2O5. MgO tends to be lower in Rocknest, although it may also be comparable between the two samples depending on the exact composition of the smectite in Sheepbed. The only unambiguous difference is the SO3 content, which is always higher in Rocknest. The observed similarity suggests that the two amorphous components share a common origin or formation process. The individual phases possibly present within the amorphous components include: volcanic (or impact) glass, hisingerite (or silica + ferrihydrite), amorphous sulfates (or adsorbed SO42-), and nanophase ferric oxides.

  14. Theoretical models of hydrogen-induced defects in amorphous silicon dioxide

    NASA Astrophysics Data System (ADS)

    El-Sayed, Al-Moatasem; Wimmer, Yannick; Goes, Wolfgang; Grasser, Tibor; Afanas'ev, Valery V.; Shluger, Alexander L.

    2015-07-01

    We used density functional theory (DFT) calculations to model the interaction of hydrogen atoms and molecules with strained bonds and neutral oxygen vacancies in amorphous silica (a-SiO2). The results demonstrate that the interaction of atomic hydrogen with strained Si-O bonds in defect-free a-SiO2 networks results in the formation of two distinct defect structures, which are referred to as the [SiO4/H]0 and the hydroxyl E'center. To study the distribution of each defect's properties, up to 116 configurations of each center were calculated. We show that the hydroxyl E' center can be thermodynamically stable in the neutral charge state. In order to understand the origins and reactions of this defect, different mechanisms of formation, passivation, and depassivation have been investigated. The interaction of H with a single-oxygen vacancy in a-SiO2 was studied in 144 configurations, all resulting in the hydrogen bridge defect. The reaction of the hydrogen bridge defect with the second H atom is barrierless and fully passivates the O vacancy. The latter defect reacts with atomic H with a small barrier, restoring the hydrogen bridge defect. These results provide a better understanding of how atomic and molecular hydrogen can both passivate existing defects and create new electrically active defects in amorphous-silica matrices.

  15. High damage threshold anti-reflectors by physical vapor deposited amorphous fluoropolymer

    SciTech Connect

    Chow, R.; Spragge, M.K.; Loomis, G.E.; Thomas, I.M.; Rainer, F.; Ward, R.L.; Kozlowski, M.R.

    1993-11-01

    High laser-resistant anti-reflective coatings were made from an amorphous fluoropolymer (Teflon AF2400) material by physical vapor deposition. Single layers of Teflon AF2400 were thermally deposited in a vacuum chamber. Refractive index and adhesion of the coatings were determined as a function of deposition rate (2 to 20 {Angstrom}/s), substrate temperature (20 to 200C), and glow-discharge bias potential ({minus}1500 to 1500 V). An anti-reflective coating of an amorphous fluoropolymer (Teflon AF2400) had a laser resistance of > 47 J/cm{sup 2} (1.06 {mu}m, 3-ns pulselength) and is transparent from 200 nm to 1600 nm. The majority of the coatings had a 1.30 refractive index, similar to that of the bulk material. Scanning electron microscopy and preliminary nuclear magnetic resonance observations indicated that morphological changes caused the variations in the refractive index rather than compositional changes. The coatings adhered to fused silica and silicon wafers under normal laboratory handling conditions. Scotch tape with 12.6 gr/mm tension was sufficient to pull off every coating from fused silica substrates.

  16. Amorphous nanosilica induce endocytosis-dependent ROS generation and DNA damage in human keratinocytes

    PubMed Central

    2011-01-01

    Background Clarifying the physicochemical properties of nanomaterials is crucial for hazard assessment and the safe application of these substances. With this in mind, we analyzed the relationship between particle size and the in vitro effect of amorphous nanosilica (nSP). Specifically, we evaluated the relationship between particle size of nSP and the in vitro biological effects using human keratinocyte cells (HaCaT). Results Our results indicate that exposure to nSP of 70 nm diameter (nSP70) induced an elevated level of reactive oxygen species (ROS), leading to DNA damage. A markedly reduced response was observed using submicron-sized silica particles of 300 and 1000 nm diameter. In addition, cytochalasin D-treatment reduced nSP70-mediated ROS generation and DNA damage, suggesting that endocytosis is involved in nSP70-mediated cellular effects. Conclusions Thus, particle size affects amorphous silica-induced ROS generation and DNA damage of HaCaT cells. We believe clarification of the endocytosis pathway of nSP will provide useful information for hazard assessment as well as the design of safer forms of nSPs. PMID:21235812

  17. Silica-based materials as drug adsorbents: first principle investigation on the role of water microsolvation on Ibuprofen adsorption.

    PubMed

    Delle Piane, Massimo; Vaccari, Stefano; Corno, Marta; Ugliengo, Piero

    2014-08-01

    Silica-based materials find applications as excipients and, particularly for those of mesoporous nature, as drug delivery agents for pharmaceutical formulations. Their performance can be crucially affected by water moisture, as it can modify the behavior of these formulations, by limiting their shelf life. Here we describe the role of water microsolvation on the features of ibuprofen adsorbed on a model of amorphous silica surface by means of density functional theory (DFT) simulations. Starting from the results of the simulation of ibuprofen in interaction with a dry hydrophobic amorphous silica surface, a limited number of water molecules has been added to study the configurational landscape of the microsolvated system. Structural and energetics properties, as well as the role of dispersive forces, have been investigated. Our simulations have revealed that the silica surface exhibits a higher affinity for water than for ibuprofen, even if several structures coexist at room temperature, with an active competition of ibuprofen and water for the exposed surface silanols. Dispersive interactions play a key role in this system, as pure DFT fails to correctly describe its potential energy surface. Indeed, van der Waals forces are the leading contribution to adsorption, independently of whether the drug is hydrogen-bonded directly to the surface or via water molecules. PMID:24467179

  18. TCDD Adsorbed on Silica as a Model for TCDD Contaminated Soils: Evidence for Suppression of Humoral Immunity in Mice

    PubMed Central

    Kaplan, Barbara L. F.; Crawford, Robert B.; Kovalova, Natalia; Arencibia, Amaya; Kim, Seong Su; Pinnavaia, Thomas J.; Boyd, Stephen A.; Teppen, Brian J.; Kaminski, Norbert E.

    2011-01-01

    2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the prototypical aryl hydrocarbon receptor (AhR) ligand, exhibits immune suppression in vivo and in vitro. Suppression of primary humoral immune responses in particular has been well characterized as one of the most sensitive functional immune endpoints in animals treated with TCDD. Previous studies have used purified TCDD to elucidate the mechanisms by which TCDD and dioxin-like compounds (DLC) impair IgM production by B cells, but did not represent the route by which animals and humans are likely to be exposed environmentally. In the studies reported here, mice were treated with TCDD adsorbed onto a well-defined synthetic silica phase of known purity and physical properties, followed by sensitization with sheep erythrocytes to initiate a humoral immune. We found that surfactant-templated mesoporous forms of amorphous silica provided an ideal combination of purity, dispersibility and textural properties for immobilizing TCDD. TCDD-adsorbed silica distributed to the spleen and liver after oral administration as assessed by induction of cyp1a1 gene expression. Most notably, TCDD delivered in the adsorbed state on amorphous silica and as a solute in corn oil (CO) produced similar suppression of the anti-sheep red blood cell immunoglobulin M antibody forming cell response (sRBC IgM AFC) response at equivalent doses of TCDD. These results suggest that TCDD immobilized on silicate particles found in soils distributes to the spleen and suppresses humoral immunity. PMID:21272611

  19. Insights into the crystal and aggregate structure of Fe[superscript 3+] oxide/silica co-precipitates

    SciTech Connect

    Dyer, Laurence G.; Chapman, Karena W.; English, Phillip; Saunders, Martin; Richmond, William R.

    2012-03-15

    Structural characteristics of Fe{sup 3+} oxide/silica co-precipitates were investigated. The association between these materials is relevant to practically all natural aqueous systems due to the prevalence of iron and silicon in the Earth's crust. Crystallographic information is very difficult to obtain from these precipitates due to the nanocrystalline nature of ferrihydrite and the amorphous structure of precipitated silica. Several previously undetermined key insights were gained into the structure of iron oxide/silica co-precipitates through this examination. The distribution of iron and silicon throughout co-precipitate particles is illustrated along with the influence of their association. Evidence to the governing factor behind differences in apparent crystallinity is also presented. This information culminates in the formulation of a precipitation pathway, displaying the formation of the co-precipitates.

  20. Silica optical fibers: technology update

    NASA Astrophysics Data System (ADS)

    Krohn, David A.; McCann, Brian P.

    1995-05-01

    Silica-core optical fibers have long been the standard delivery medium for medical laser delivery systems. Their high strength, excellent flexibility, and low cost continue to make them the fiber of choice for systems operating from 300 to 2200 nm. An overview of the current fiber constructions available to the industry is reviewed. Silicone-clad fibers, hard- fluoropolymer clad fibers and silica-clad fibers are briefly compared in terms of mechanical and optical properties. The variety of fiber coatings available is also discussed. A significant product development of silica fiber delivery systems has been in side-firing laser delivery systems for Urology. These devices utilize silica-core fibers to project the laser energy at a substantial lateral angle to the conventional delivery system, typically 40 to 100 degrees off axis. Many unique distal tips have been designed to meet the needs of this potentially enormous application. There are three primary technologies employed in side-firing laser delivery systems: reflection off of an attached medium; reflection within an angle-polished fiber through total internal reflection; and reflection from both an angle-polished fiber and an outside medium. Each technology is presented and compared on the basis of operation modality, transmission efficiency, and power-handling performance.

  1. Latent ion tracks in amorphous silicon

    SciTech Connect

    Bierschenk, Thomas; Giulian, Raquel; Afra, Boshra; Rodriguez, Matias D; Schauries, D; Mudie, Stephen; Pakarinen, Olli H; Djurabekova, Flyura; Nordlund, Kai; Osmani, Orkhan; Medvedev, Nikita; Rethfield, Baerbel; Ridgway, Mark C; Kluth, Patrick

    2013-01-01

    We present experimental evidence for the formation of ion tracks in amorphous Si induced by swift heavy ion irradiation. An underlying core-shell structure consistent with remnants of a high density liquid structure was revealed by small-angle x-ray scattering and molecular dynamics simulations. Ion track dimensions dier for as-implanted and relaxed Si as attributed to dierent microstructures and melting temperatures. The identication and characterisation of ion tracks in amorphous Si yields new insight into mechanisms of damage formation due to swift heavy ion irradiation in amorphous semiconductors.

  2. Method of producing hydrogenated amorphous silicon film

    DOEpatents

    Wiesmann, Harold J.

    1980-01-01

    This invention relates to hydrogenated amorphous silicon produced by thermally decomposing silane (SiH.sub.4) or other gases comprising H and Si, from a tungsten or carbon foil heated to a temperature of about 1400.degree.-1600.degree. C., in a vacuum of about 10.sup.-6 to 19.sup.-4 torr, to form a gaseous mixture of atomic hydrogen and atomic silicon, and depositing said gaseos mixture onto a substrate independent of and outside said source of thermal decomposition, to form hydrogenated amorphous silicon. The presence of an ammonia atmosphere in the vacuum chamber enhances the photoconductivity of the hydrogenated amorphous silicon film.

  3. Peculiarities of Vibration Characteristics of Amorphous Ices

    NASA Astrophysics Data System (ADS)

    Gets, Kirill V.; Subbotin, Oleg S.; Belosludov, Vladimir R.

    2012-03-01

    Dynamic properties of low (LDA), high (HDA) and very high (VHDA) density amorphous ices were investigated within the approach based on Lattice Dynamics simulations. In this approach, we assume that the short-range molecular order mainly determines the dynamic and thermodynamic properties of amorphous ices. Simulation cell of 512 water molecules with periodical boundary conditions and disordering allows us to study dynamical properties and dispersion curves in the Brillouin zone of pseudo-crystal. Existence of collective phenomena in amorphous ices which is usual for crystals but anomalous for disordered phase was confirmed in our simulations. Molecule amplitudes of delocalized (collective) as well as localized vibrations have been considered.

  4. Structural relaxation of amorphous silicon carbide.

    PubMed

    Ishimaru, Manabu; Bae, In-Tae; Hirotsu, Yoshihiko; Matsumura, Syo; Sickafus, Kurt E

    2002-07-29

    We have examined amorphous structures of silicon carbide (SiC) using both transmission electron microscopy and a molecular-dynamics approach. Radial distribution functions revealed that amorphous SiC contains not only heteronuclear (Si-C) bonds but also homonuclear (Si-Si and C-C) bonds. The ratio of heteronuclear to homonuclear bonds was found to change upon annealing, suggesting that structural relaxation of the amorphous SiC occurred. Good agreement was obtained between the simulated and experimentally measured radial distribution functions. PMID:12144449

  5. Structural characterization of Ge nanocrystals in silica amorphised by ion irradiation

    NASA Astrophysics Data System (ADS)

    Araujo, L. L.; Giulian, R.; Johannessen, B.; Llewellyn, D. J.; Kluth, P.; Azevedo, G. de M.; Cookson, D. J.; Ridgway, M. C.

    2008-06-01

    Ge nanocrystals (NCs) grown by ion implantation in amorphous silica matrices were irradiated with 5 MeV Si ions over a different fluence range (2 × 1011-2 × 1013 cm-2) than previously reported. Size and depth distributions as well as structural disorder in the NCs were measured by RBS, TEM, SAXS and EXAFS. The EXAFS results show that the embedded Ge NCs are rendered amorphous at fluences ∼40 times lower than bulk crystalline Ge (c-Ge). No significant changes in the size or depth distribution of the NCs are observed for all irradiation fluences. Compared to c-Ge, the higher-energy structural state of the NCs prior to irradiation and the presence of the nanocrystal/matrix interface are considered the main causes for the peculiar amorphisation behavior of embedded Ge NCs.

  6. Characterizing structural and vibrational properties of nanoparticles embedded in silica with XAS, SAXS and auxiliary techniques

    NASA Astrophysics Data System (ADS)

    Araujo, Leandro L.; Kluth, Patrick; Giulian, Raquel; Sprouster, David J.; Johannessen, Bernt; Foran, Garry J.; Cookson, David J.; Ridgway, Mark C.

    2009-01-01

    Synchrotron-based techniques were combined with conventional analysis methods to probe in detail the structural and vibrational properties of nanoparticles grown in a silica matrix by ion implantation and thermal annealing, as well as the evolution of such properties as a function of nanoparticle size. This original approach was successfully applied for several elemental nanoparticles (Au, Co, Cu, Ge, Pt) and the outcomes for Ge are reported here, illustrating the power of this combined methodology. The thorough analysis of XANES, EXAFS, SAXS, TEM and Raman data for Ge nanoparticles with mean diameters between 4 and 9 nm revealed that the peculiar properties of embedded Ge nanoparticles, like the existence of amorphous Ge layers between the silica matrix and the crystalline nanoparticle core, are strongly dependent on particle size and mainly governed by the variation in the surface area-to-volume ratio. Such detailed information provides valuable input for the efficient planning of technological applications.

  7. Characterizing structural and vibrational properties of nanoparticles embedded in silica with XAS, SAXS and auxiliary techniques

    SciTech Connect

    Araujo, Leandro L.; Kluth, Patrick; Giulian, Raquel; Sprouster, David J.; Ridgway, Mark C.; Johannessen, Bernt; Foran, Garry J.; Cookson, David J.

    2009-01-29

    Synchrotron-based techniques were combined with conventional analysis methods to probe in detail the structural and vibrational properties of nanoparticles grown in a silica matrix by ion implantation and thermal annealing, as well as the evolution of such properties as a function of nanoparticle size. This original approach was successfully applied for several elemental nanoparticles (Au, Co, Cu, Ge, Pt) and the outcomes for Ge are reported here, illustrating the power of this combined methodology. The thorough analysis of XANES, EXAFS, SAXS, TEM and Raman data for Ge nanoparticles with mean diameters between 4 and 9 nm revealed that the peculiar properties of embedded Ge nanoparticles, like the existence of amorphous Ge layers between the silica matrix and the crystalline nanoparticle core, are strongly dependent on particle size and mainly governed by the variation in the surface area-to-volume ratio. Such detailed information provides valuable input for the efficient planning of technological applications.

  8. Confinement effects on collective water dynamics: Molecular dynamics study of optical Kerr response in silica nanopores

    NASA Astrophysics Data System (ADS)

    Milischuk, Anatoli; Ladanyi, Branka

    2014-03-01

    We report the results of the study of the effects of confinement on collective dynamical properties of water in model nanopores at ambient conditions. The main focus is on approximately cylindrical pores composed of amorphous silica, with diameters ranging from 20 to 40 Å, designed to represent MCM-41 materials. Results for hydrophilic and hydrophobic pores of similar dimensions, but with roughness reduced compared to silica nanopores, are also considered. The main quantity studied is the polarizability anisotropy time correlation function (TCF), which is related to the experimentally-observed optical Kerr effect (OKE) nuclear response. We investigate the effects on this TCF of the reduced molecular translational and rotational water mobility in the layers near the interface. We find that these effects lead to pore diameter dependent slowdown of polarizability anisotropy relaxation, in agreement with OKE experiments. Support from NSF grant number 1213682 is acknowledged.

  9. Defects in bilayer silica and graphene: common trends in diverse hexagonal two-dimensional systems

    PubMed Central

    Björkman, Torbjörn; Kurasch, Simon; Lehtinen, Ossi; Kotakoski, Jani; Yazyev, Oleg V.; Srivastava, Anchal; Skakalova, Viera; Smet, Jurgen H.; Kaiser, Ute; Krasheninnikov, Arkady V.

    2013-01-01

    By combining first-principles and classical force field calculations with aberration-corrected high-resolution transmission electron microscopy experiments, we study the morphology and energetics of point and extended defects in hexagonal bilayer silica and make comparison to graphene, another two-dimensional (2D) system with hexagonal symmetry. We show that the motifs of isolated point defects in these 2D structures with otherwise very different properties are similar, and include Stone-Wales-type defects formed by structural unit rotations, flower defects and reconstructed double vacancies. The morphology and energetics of extended defects, such as grain boundaries have much in common as well. As both sp2-hybridised carbon and bilayer silica can also form amorphous structures, our results indicate that the morphology of imperfect 2D honeycomb lattices is largely governed by the underlying symmetry of the lattice. PMID:24336488

  10. Rapid synthesis of a versatile organic/inorganic hybrid material based on pyrogenic silica.

    PubMed

    Becuwe, M; Cazier, F; Woisel, P; Landy, D; Delattre, F

    2010-10-01

    An efficient approach has been developed to synthesize a new versatile organo-silica material by non-conventional method (microwave irradiation and ultrasonic vibration) from amorphous pyrogenic silica and has been compared with thermic procedure. The samples were fully characterized by FTIR, solid-state (29)Si and (13)C CP/MAS NMR, thermogravimetric analysis (TGA), elemental analysis, scanning electron microscopy (SEM) and by N(2)-sorption isotherms measurements. The functionalization of silicon dioxide by 4-(chloromethylphenyl) trichlorosilane has been easily achieved by ultrasound irradiation in a very short time with high loading of organic fragments. Significant different sizes of pores were observed according to conventional or non-conventional synthesis procedure. In addition, new structural properties have been created with the emergence of a mesoporosity. PMID:20580377

  11. Self-induced growth of vertical GaN nanowires on silica

    NASA Astrophysics Data System (ADS)

    Kumaresan, V.; Largeau, L.; Oehler, F.; Zhang, H.; Mauguin, O.; Glas, F.; Gogneau, N.; Tchernycheva, M.; Harmand, J.-C.

    2016-04-01

    We study the self-induced growth of GaN nanowires on silica. Although the amorphous structure of this substrate offers no possibility of an epitaxial relationship, the nanowires are remarkably aligned with the substrate normal whereas, as expected, their in-plane orientation is random. Their structural and optical characteristics are compared to those of GaN nanowires grown on standard crystalline Si (111) substrates. The polarity inversion domains are much less frequent, if not totally absent, in the nanowires grown on silica, which we find to be N-polar. This work demonstrates that high-quality vertical GaN nanowires can be elaborated without resorting to bulk crystalline substrates.

  12. Self-induced growth of vertical GaN nanowires on silica.

    PubMed

    Kumaresan, V; Largeau, L; Oehler, F; Zhang, H; Mauguin, O; Glas, F; Gogneau, N; Tchernycheva, M; Harmand, J-C

    2016-04-01

    We study the self-induced growth of GaN nanowires on silica. Although the amorphous structure of this substrate offers no possibility of an epitaxial relationship, the nanowires are remarkably aligned with the substrate normal whereas, as expected, their in-plane orientation is random. Their structural and optical characteristics are compared to those of GaN nanowires grown on standard crystalline Si (111) substrates. The polarity inversion domains are much less frequent, if not totally absent, in the nanowires grown on silica, which we find to be N-polar. This work demonstrates that high-quality vertical GaN nanowires can be elaborated without resorting to bulk crystalline substrates. PMID:26895252

  13. Corrosion resistant amorphous metals and methods of forming corrosion resistant amorphous metals

    DOEpatents

    Farmer, Joseph C.; Wong, Frank M. G.; Haslam, Jeffery J.; Yang, Nancy; Lavernia, Enrique J.; Blue, Craig A.; Graeve, Olivia A.; Bayles, Robert; Perepezko, John H.; Kaufman, Larry; Schoenung, Julie; Ajdelsztajn, Leo

    2009-11-17

    A system for coating a surface comprises providing a source of amorphous metal, providing ceramic particles, and applying the amorphous metal and the ceramic particles to the surface by a spray. The coating comprises a composite material made of amorphous metal that contains one or more of the following elements in the specified range of composition: yttrium (.gtoreq.1 atomic %), chromium (14 to 18 atomic %), molybdenum (.gtoreq.7 atomic %), tungsten (.gtoreq.1 atomic %), boron (.ltoreq.5 atomic %), or carbon (.gtoreq.4 atomic %).

  14. Corrosion resistant amorphous metals and methods of forming corrosion resistant amorphous metals

    DOEpatents

    Farmer, Joseph C.; Wong, Frank M.G.; Haslam, Jeffery J.; Yang, Nancy; Lavernia, Enrique J.; Blue, Craig A.; Graeve, Olivia A.; Bayles, Robert; Perepezko, John H.; Kaufman, Larry; Schoenung, Julie; Ajdelsztajn, Leo

    2014-07-15

    A system for coating a surface comprises providing a source of amorphous metal, providing ceramic particles, and applying the amorphous metal and the ceramic particles to the surface by a spray. The coating comprises a composite material made of amorphous metal that contains one or more of the following elements in the specified range of composition: yttrium (.gtoreq.1 atomic %), chromium (14 to 18 atomic %), molybdenum (.gtoreq.7 atomic %), tungsten (.gtoreq.1 atomic %), boron (.ltoreq.5 atomic %), or carbon (.gtoreq.4 atomic %).

  15. Intracellularly Biodegradable Polyelectrolyte/Silica Composite Microcapsules as Carriers for Small Molecules.

    PubMed

    Gao, Hui; Goriacheva, Olga A; Tarakina, Nadezda V; Sukhorukov, Gleb B

    2016-04-20

    Microcapsules that can be efficiently loaded with small molecules and effectively released at the target area through the degradation of the capsule shells hold great potential for treating diseases. Traditional biodegradable polyelectrolyte (PE) capsules can be degraded by cells and eliminated from the body but fail to encapsulate drugs with small molecular weight. Here, we report a poly-l-arginine hydrochloride (PARG)/dextran sulfate sodium salt (DEXS)/silica (SiO2) composite capsule that can be destructed in cells and of which the in situ formed inorganic SiO2 enables loading of small model molecules, Rhodamine B (Rh-B). The composite capsules were fabricated based on the layer-by-layer (LbL) technique and the hydrolysis of tetraethoxysilane (TEOS). Capsules composed of nondegradable PEs and SiO2, polyllamine hydrochloride (PAH)/poly(sodium 4-styrenesulfonate) (PSS)/silica (the control sample), were prepared and briefly compared with the degradable composite capsules. An intracellular degradation study of both types of composite capsules revealed that PARG/DEXS/silica capsules were degraded into fragments and lead to the release of model molecules in a relatively short time (2 h), while the structure of PAH/PSS/silica capsules remained intact even after 3 days incubation with B50 cells. Such results indicated that the polymer components played a significant role in the degradability of the SiO2. Specifically, PAH/PSS scaffolds blocked the degradation of SiO2. For PARG/DEXS/silica capsules, we proposed the effects of both hydrolytic degradation of amorphous silica and enzymatic degradation of PARG/DEXS polymers as a cell degradation mechanism. All the results demonstrated a new type of functional composite microcapsule with low permeability, good biocompatibility, and biodegradability for potential medical applications. PMID:27008032

  16. Electron microscope analyses of the bio-silica basal spicule from the Monorhaphis chuni sponge.

    PubMed

    Werner, Peter; Blumtritt, Horst; Zlotnikov, Igor; Graff, Andreas; Dauphin, Yannicke; Fratzl, Peter

    2015-08-01

    We report on a structural analysis of several basal spicules of the deep-sea silica sponge Monorhaphis chuni by electron microscope techniques supported by a precise focused ion beam (FIB) target preparation. To get a deeper understanding of the spicules length growth, we concentrated our investigation onto the apical segments of two selected spicules with apparently different growth states and studied in detail permanent and temporary growth structures in the central compact silica axial cylinder (AC) as well as the structure of the organic axial filament (AF) in its center. The new findings concern the following morphology features: (i) at the tip we could identify thin silica layers, which overgrow as a tongue-like feature the front face of the AC and completely fuse during the subsequent growth state. This basically differs from the radial growth of the surrounding lamellar zone of the spicules made of alternating silica lamellae and organic interlayers. (ii) A newly detected disturbed cylindrical zone in the central region of the AC (diameter about 30 μm) contains vertical and horizontal cavities, channels and agglomerates, which can be interpreted as permanent leftover of a formerly open axial channel, later filled by silica. (iii) The AF consists of a three-dimensional crystal-like arrangement of organic molecules and amorphous silica surrounding these molecules. Similar to an inorganic crystal, this encased protein crystal is typified by crystallographic directions, lattice planes and surface steps. The 〈001〉 growth direction is especially favored, thereby scaffolding the axial cylinders growth and consequently the spicules' morphology. PMID:26094876

  17. The effect of impeller type on silica sol formation in laboratory scale agitated tank

    NASA Astrophysics Data System (ADS)

    Nurtono, Tantular; Suprana, Yayang Ade; Latif, Abdul; Dewa, Restu Mulya; Machmudah, Siti; Widiyastuti, Winardi, Sugeng

    2016-02-01

    The multiphase polymerization reaction of the silica sol formation produced from silicic acid and potassium hydroxide solutions in laboratory scale agitated tank was studied. The reactor is equipped with four segmental baffle and top entering impeller. The inside diameter of reactor is 9 cm, the baffle width is 0.9 cm, and the impeller position is 3 cm from tank bottom. The diameter of standard six blades Rushton and three blades marine propeller impellers are 5 cm. The silicic acid solution was made from 0.2 volume fraction of water glass (sodium silicate) solution in which the sodium ion was exchanged by hydrogen ion from cation resin. The reactor initially filled with 286 ml silicic acid solution was operated in semi batch mode and the temperature was kept constant in 60 °C. The 3 ml/minute of 1 M potassium hydroxide solution was added into stirred tank and the solution was stirred. The impeller rotational speed was varied from 100 until 700 rpm. This titration was stopped if the solution in stirred tank had reached the pH of 10-The morphology of the silica particles in the silica sol product was analyzed by Scanning Electron Microscope (SEM). The size of silica particles in silica sol was measured based on the SEM image. The silica particle obtained in this research was amorphous particle and the shape was roughly cylinder. The flow field generated by different impeller gave significant effect on particle size and shape. The smallest geometric mean of length and diameter of particle (4.92 µm and 2.42 µm, respectively) was generated in reactor with marine propeller at 600 rpm. The reactor with Rushton impeller produced particle which the geometric mean of length and diameter of particle was 4.85 µm and 2.36 µm, respectively, at 150 rpm.

  18. In vitro cytotoxicity and quantitative silica analysis of diatomaceous earth products.

    PubMed Central

    Bye, E; Davies, R; Griffiths, D M; Gylseth, B; Moncrieff, C B

    1984-01-01

    Mouse peritoneal macrophages were used to evaluate the relative cytotoxicity of a series of diatomaceous earth products in vitro. The amorphous and crystalline silica content of the products was determined by a combination of infrared spectroscopy and x ray powder diffraction techniques. The cytotoxicities of the high cristobalite content flux calcined materials were similar to that of the standard cristobalite ; both the natural and straight calcined materials had significantly greater activities than the flux calcined materials. Thus within the limitations of the macrophage cytotoxicity test the hypothesis that crystalline content is the only determinant of fibrogenicity of diatomaceous earth is not supported. Images PMID:6326795

  19. Properties of films prepared from low surface area/density alumina-silica

    SciTech Connect

    Hietala, S.L.; Smith, D.M. ); Hietala, V.M.; Frye, G.C.; Hurd, A.J.; Brinker, C.J. )

    1990-01-01

    A sol-gel method was use to prepare bulk, closed pore, amorphous alumina-silica. Films prepared from this 47wt% Al{sub 2}O{sub 3}- SiO{sub 2} composition were examined by SAW, elipsometry and electrical measurements. The films were found to have a surface area of 1.1 cm{sup 2}/cm{sup 2}, a refractive index of 1.44 at 633 nm, and a relative permittivity of 6.2 at 200 KHz. These properties indicate potential applications as hermetic seals, barrier coatings, dielectric layers for capacitors and passivation coatings for electronic circuits.

  20. Yb-doped silica glass and photonic crystal fiber based on laser sintering technology

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Wu, Jiale; Zhou, Guiyao; Xia, Changming; Liu, Jiantao; Tian, Hongchun; Liang, Wanting; Hou, Zhiyun

    2016-03-01

    We demonstrate the fabricating method for Yb3+-doped silica glass and double-cladding large mode area photonic crystal fiber (LMA PCF) based on laser sintering technology combined with a liquid phase doping method. The doped material prepared shows the amorphous property and the hydroxyl content is approximately 40 ppm. The attenuation of the fabricated LMA PCF is 14.2 dB m-1 at 976 nm, and the lowest value is 0.25 dB m-1 at 1200 nm. The laser slope efficiency is up to 70.2%.