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Sample records for ge-doped amorphous silica

  1. Ultraviolet radiation (UVR) dosimetry system and the use of Ge-doped silica optical fibres

    NASA Astrophysics Data System (ADS)

    Abdul Rahman, Ahmad Taufek; Abu Bakar, Noor Khairunnisa; Chandra Paul, Mukul; Bradley, D. A.

    2014-11-01

    Previous studies have shown that over exposure to ultraviolet radiation (UVR), either from sunlight or artificial sources, can cause severe biological effects including cataracts, photokeratitis and skin cancer. In this respect, there exists the need to introduce a sensitive UV dosimetric material capable of measuring radiation dose to high accuracy in order to deliver UVR safely and efficiently. Present study has focussed on the investigation of the potential thermoluminescent (TL) sensitivity of commercially available germanium (Ge)-doped silica (SiO2) optical fibres subjected to UVR. The main interest of this study is to find out whether these doped SiO2 optical fibres can be used as a sensible integrator of environmental UV exposures. In the present study, commercially available Ge-doped SiO2 optical fibres have been used with a core diameter of 11 μm (CorActive, Canada), 23 μm (Central Glass and Ceramic Research Institute Kolkata, India) and 50 μm (Central Glass and Ceramic Research Institute Kolkata, India) and a cladding diameter of 125±0.1 μm, irradiated over a wide range of UV dose. Results have shown that these fibres exhibit a linear dose response (with correlation coefficient better than 0.9852). The 50 μm fibre produces greater TL response than that obtained for 11- and 23 μm fibres. The TL results are compared with that of the well-established TL dosimeter material lithium fluoride.

  2. Influence of dose history on thermoluminescence response of Ge-doped silica optical fibre dosimeters

    NASA Astrophysics Data System (ADS)

    Moradi, F.; Mahdiraji, G. A.; Dermosesian, E.; Khandaker, M. U.; Ung, N. M.; Mahamd Adikan, F. R.; Amin, Y. M.

    2017-05-01

    Nowadays, silica based optical fibres show enough potential to be used as TL dosimeters in different applications. Reuse of optical fibre as a practical dosimeter demands to complete removal of accumulated doses via previous irradiations. This work investigates the existence and/or effect of remnant doses in fibre dosimeter from the previous irradiations, and proposes a method to control this artifact. A single mode Ge-doped optical fibre is used as TL radiation sensor, while a well calibrated Gammacell with 60Co source is used for irradiations. The effect of irradiation history on the TL response of optical fibres is surveyed extensively for doses ranged from 1 to 1000 Gy. The results show that the absorbed dose history in a fibre affects its response in the next irradiation cycles. It is shown that a dose history of around 100 Gy can increase the response of optical fibre by a factor of 1.72. The effect of annealing at higher temperatures on stabilizing the fibre response is also examined and results revealed that another alteration in the structure of trapping states occurs in glass medium which can change the sensitivity of fibres. Preservation of the sensitivity during successive irradiation cycles can be achieved by a proper annealing procedure accompanied by a pre-dose treatment.

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. Amorphous silica-like carbon dioxide

    NASA Astrophysics Data System (ADS)

    Santoro, Mario; Gorelli, Federico A.; Bini, Roberto; Ruocco, Giancarlo; Scandolo, Sandro; Crichton, Wilson A.

    2006-06-01

    Among the group IV elements, only carbon forms stable double bonds with oxygen at ambient conditions. At variance with silica and germania, the non-molecular single-bonded crystalline form of carbon dioxide, phase V, only exists at high pressure. The amorphous forms of silica (a-SiO2) and germania (a-GeO2) are well known at ambient conditions; however, the amorphous, non-molecular form of CO2 has so far been described only as a result of first-principles simulations. Here we report the synthesis of an amorphous, silica-like form of carbon dioxide, a-CO2, which we call `a-carbonia'. The compression of the molecular phase III of CO2 between 40 and 48GPa at room temperature initiated the transformation to the non-molecular amorphous phase. Infrared spectra measured at temperatures up to 680K show the progressive formation of C-O single bonds and the simultaneous disappearance of all molecular signatures. Furthermore, state-of-the-art Raman and synchrotron X-ray diffraction measurements on temperature-quenched samples confirm the amorphous character of the material. Comparison with vibrational and diffraction data for a-SiO2 and a-GeO2, as well as with the structure factor calculated for the a-CO2 sample obtained by first-principles molecular dynamics, shows that a-CO2 is structurally homologous to the other group IV dioxide glasses. We therefore conclude that the class of archetypal network-forming disordered systems, including a-SiO2, a-GeO2 and water, must be extended to include a-CO2.

  8. Thermal resistance between amorphous silica nanoparticles

    NASA Astrophysics Data System (ADS)

    Meng, Fanhe; Elsahati, Muftah; Liu, Jin; Richards, Robert F.

    2017-05-01

    Nanoparticle-based materials have been used as thermal insulation in a variety of macroscale and microscale applications. In this work, we investigate the heat transfer between nanoparticles using non-equilibrium molecular dynamics simulations. We calculate the total thermal resistance and thermal boundary resistance between adjacent amorphous silica nanoparticles. Numerical results are compared to interparticle resistances determined from experimental measurements of heat transfer across packed silica nanoparticle beds. The thermal resistance between nanoparticles is shown to increase rapidly as the particle contact radius decreases. More significantly, the interparticle resistance depends strongly on the forces between particles, in particular, the presence or absence of chemical bonds between nanoparticles. In addition, the effect of interfacial force strength on thermal resistance increases as the nanoparticle diameter decreases. The simulations results are shown to be in good agreement with experimental results for 20 nm silica nanoparticles.

  9. Deposition of Ge-doped silica thin films for an integrated optic application using a matrix distributed electron cyclotron resonance PECVD reactor

    NASA Astrophysics Data System (ADS)

    Botha, Roelene; Bulkin, Pavel V.; Swart, Pieter L.

    2007-10-01

    Optical quality Ge-doped SiO2 thin films, suitable for an integrated optic version of a gain equalizer for erbium-doped fibre amplifiers (EDFAs), have been deposited using a matrix distributed electron cyclotron resonance plasma-enhanced chemical vapour deposition (MDECR-PECVD) system. Using spectroscopic ellipsometry and infrared transmission spectroscopy, the optical constants and hydroxyl content of the films were calculated. Losses due to the hydroxyl overtone at 1.37 μm are found to be approximately 0.251 dB/cm. An RBS analysis determined the germanium content of the films to be in the vicinity of 4 at.%. A comparison of the atomic percentage of germanium in the films and their corresponding refractive indices with values obtained using other deposition methods is also discussed.

  10. 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

  11. Molecular dynamics simulation of wetting on modified amorphous silica surface

    NASA Astrophysics Data System (ADS)

    Chai, Jingchun; Liu, Shuyan; Yang, Xiaoning

    2009-08-01

    The microscopic wetting of water on amorphous silica surfaces has been investigated by molecular dynamics simulation. Different degrees of surface hydroxylation/silanization were considered. It was observed that the hydrophobicity becomes enhanced with an increase in the degree of surface silanization. A continuous transformation from hydrophilicity to hydrophobicity can be attained for the amorphous silica surfaces through surface modification. From the simulation result, the contact angle can exceed 90° when surface silanization percentage is above 50%, showing a hydrophobic character. It is also found that when the percentage of surface silanization is above 70% on the amorphous silica surface, the water contact angle almost remains unchanged (110-120°). This phenomenon is a little different from the wetting behavior on smooth quartz plates in previous experimental report. This change in the wettability on modified amorphous silica surfaces can be interpreted in terms of the interaction between water molecules and the silica surfaces.

  12. 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.

  13. 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.

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

    PubMed

    Rarivomanantsoa, Michaël; Jund, Philippe; Jullien, Rémi

    2004-03-08

    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.

  15. 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.

  16. 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.

  17. Face-specific Replacement of Calcite by Amorphous Silica Nanoparticles

    NASA Astrophysics Data System (ADS)

    Liesegang, M.; Milke, R.; Neusser, G.; Mizaikoff, B.

    2016-12-01

    Amorphous silica, composed of nanoscale spheres, is an important biomineral, alteration product of silicate rocks on the Earth's surface, and precursor material for stable silicate minerals. Despite constant progress in silica sphere synthesis, fundamental knowledge of natural silica particle interaction and ordering processes leading to colloidal crystals is absent so far. To understand the formation pathways of silica spheres in a geologic environment, we investigated silicified Cretaceous mollusk shell pseudomorphs from Coober Pedy (South Australia) using focused ion beam (FIB)-SEM tomography, petrographic microscopy, µ-XRD, and EMPA. The shells consist of replaced calcite crystals (<2 mm) composed of ordered arrays of uniform, close-packed silica spheres 300 ± 10 nm in size. Concentric layered spheres composed of 40 nm-sized subparticles provide evidence that, at least in the final stage, particle aggregation was the major sphere growth mechanism. Silica sphere arrays in periodically changing orientations perfectly replicate polysynthetic twinning planes of calcite. FIB-SEM tomography shows that cubic closed-packed sphere arrangements preserve the twin lamellae, while the twin plane consists of a submicrometer layer of randomly ordered spheres and vacancies. To transfer crystallographic information from parent to product, the advancement of synchronized dissolution and precipitation fronts along lattice planes is essential. We assume that the volume-preserving replacement process proceeds via a face-specific dissolution-precipitation mechanism with intermediate subparticle aggregation and subsequent layer-by-layer deposition of spheres along a planar surface. Porosity created during the replacement reaction allows permanent fluid access to the propagating reaction interface. Fluid pH and ionic strength remain constant throughout the replacement process, permitting continuous silica nanoparticle formation and diffusion-limited colloid aggregation. Our study

  18. Nucleation, evolution, and growth dynamics of amorphous silica nanosprings

    NASA Astrophysics Data System (ADS)

    Wojcik, Peter M.; Bakharev, Pavel V.; Corti, Giancarlo; McIlroy, D. N.

    2017-01-01

    The initial phases of amorphous silica nanospring formation via a vapor-liquid-solid mechanism are reported. The low temperature eutectic of Au-Si results in the formation of an asymmetrical shaped catalyst at the early stages of nanospring formation. As solid silica is formed below the Au-Si catalyst the system lowers its surface free energy and forms multiple amorphous silica nanowires beneath a common catalyst, as opposed to a single nanowire. The diameter of one of the nanowires forming the nanospring ranges between 10-20 nm. The difference in growth rates of the individual nanowires creates an asymmetry in the interfacial surface tension on the boundaries of the Au-Si catalyst/nanowires interface. Using Stokes’ theorem it is shown that there is a variable work of adhesion on the outer boundary of the Au-Si catalyst/nanowire interface of a nanospring, which is defined as an effective contact angle anisotropy. The anisotropic growth on the catalyst/nanowire boundary results in the nanowires coherently coiling into to a single, larger, helical structure with an overall diameter of 70-500 nm.

  19. Glacial Meltwater as a Source of Amorphous Silica on Early Mars

    NASA Astrophysics Data System (ADS)

    Rutledge, A. M.; Horgan, B.; Havig, J. R.; Rampe, E. B.; Scudder, N. A.; Hamilton, T. L.

    2017-10-01

    Cold-climate silica cycling on mafic volcanics due to glacial meltwater alteration is a significant terrestrial weathering process. Amorphous silica deposits on Mars could be interpreted as mineralogical evidence for past ice sheet melt.

  20. Barrier Heights and Anharmonicities in a Model of Amorphous Silica

    NASA Astrophysics Data System (ADS)

    Laird, Brian

    1998-03-01

    The low-temperature dynamics of glasses and amorphous materials are believed to be dominated by low-energy localized excitations, which are generally described as either two-level states or low-frequency localized vibrations. Recently, the existence and nature of such localized excitations in simple (fragile) model glass formers have been the subject of several simulation studies. In this work, we use a variety of techniques to analyze computer simulations of the low-temperature dynamics and structure of amorphous silica (SiO_2) using the force model of van Beest, Kramer and van Santen (BKS)[Phys. Rev. Lett. 64, 1955 (1990)]. This system is the archetypical example of a strong glass former. In particular we examine the relationship between the types of motion that lead to barrier crossing and the directions on the potential surface that are locally highly anharmonic.

  1. Amorphous Silica-Promoted Lysine Dimerization: a Thermodynamic Prediction

    NASA Astrophysics Data System (ADS)

    Kitadai, Norio; Nishiuchi, Kumiko; Nishii, Akari; Fukushi, Keisuke

    2017-08-01

    It has long been suggested that mineral surfaces played a crucial role in the abiotic polymerization of amino acids that preceded the origin of life. Nevertheless, it remains unclear where the prebiotic process took place on the primitive Earth, because the amino acid-mineral interaction and its dependence on environmental conditions have yet to be understood adequately. Here we examined experimentally the adsorption of L-lysine (Lys) and its dimer (LysLys) on amorphous silica over a wide range of pH, ionic strength, adsorbate concentration, and the solid/water ratio, and determined the reaction stoichiometries and the equilibrium constants based on the extended triple-layer model (ETLM). The retrieved ETLM parameters were then used, in combination with the equilibrium constant for the peptide bond formation in bulk water, to calculate the Lys-LysLys equilibrium in the presence of amorphous silica under various aqueous conditions. Results showed that the silica surface favors Lys dimerization, and the influence varies greatly with changing environmental parameters. At slightly alkaline pH (pH 9) in the presence of a dilute NaCl (1 mM), the thermodynamically attainable LysLys from 0.1 mM Lys reached a concentration around 50 times larger than that calculated without silica. Because of the versatility of the ETLM, which has been applied to describe a wide variety of biomolecule-mineral interactions, future experiments with the reported methodology are expected to provide a significant constraint on the plausible geological settings for the condensation of monomers to polymers, and the subsequent chemical evolution of life.

  2. Amorphous Silica-Promoted Lysine Dimerization: a Thermodynamic Prediction.

    PubMed

    Kitadai, Norio; Nishiuchi, Kumiko; Nishii, Akari; Fukushi, Keisuke

    2017-08-15

    It has long been suggested that mineral surfaces played a crucial role in the abiotic polymerization of amino acids that preceded the origin of life. Nevertheless, it remains unclear where the prebiotic process took place on the primitive Earth, because the amino acid-mineral interaction and its dependence on environmental conditions have yet to be understood adequately. Here we examined experimentally the adsorption of L-lysine (Lys) and its dimer (LysLys) on amorphous silica over a wide range of pH, ionic strength, adsorbate concentration, and the solid/water ratio, and determined the reaction stoichiometries and the equilibrium constants based on the extended triple-layer model (ETLM). The retrieved ETLM parameters were then used, in combination with the equilibrium constant for the peptide bond formation in bulk water, to calculate the Lys-LysLys equilibrium in the presence of amorphous silica under various aqueous conditions. Results showed that the silica surface favors Lys dimerization, and the influence varies greatly with changing environmental parameters. At slightly alkaline pH (pH 9) in the presence of a dilute NaCl (1 mM), the thermodynamically attainable LysLys from 0.1 mM Lys reached a concentration around 50 times larger than that calculated without silica. Because of the versatility of the ETLM, which has been applied to describe a wide variety of biomolecule-mineral interactions, future experiments with the reported methodology are expected to provide a significant constraint on the plausible geological settings for the condensation of monomers to polymers, and the subsequent chemical evolution of life.

  3. 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

  4. Stabilizing Unstable Amorphous Menthol through Inclusion in Mesoporous Silica Hosts.

    PubMed

    Cordeiro, Teresa; Castiñeira, Carmem; Mendes, Davide; Danède, Florence; Sotomayor, João; Fonseca, Isabel M; Gomes da Silva, Marco; Paiva, Alexandre; Barreiros, Susana; Cardoso, M Margarida; Viciosa, Maria T; Correia, Natália T; Dionisio, Madalena

    2017-09-05

    The amorphization of the readily crystallizable therapeutic ingredient and food additive, menthol, was successfully achieved by inclusion of neat menthol in mesoporous silica matrixes of 3.2 and 5.9 nm size pores. Menthol amorphization was confirmed by the calorimetric detection of a glass transition. The respective glass transition temperature, Tg = -54.3 °C, is in good agreement with the one predicted by the composition dependence of the Tg values determined for menthol:flurbiprofen therapeutic deep eutectic solvents (THEDESs). Nonisothermal crystallization was never observed for neat menthol loaded into silica hosts, which can indicate that menthol rests as a full amorphous/supercooled material inside the pores of the silica matrixes. Menthol mobility was probed by dielectric relaxation spectroscopy, which allowed to identify two relaxation processes in both pore sizes: a faster one associated with mobility of neat-like menthol molecules (α-process), and a slower, dominant one due to the hindered mobility of menthol molecules adsorbed at the inner pore walls (S-process). The fraction of molecular population governing the α-process is greater in the higher (5.9 nm) pore size matrix, although in both cases the S-process is more intense than the α-process. A dielectric glass transition temperature was estimated for each α (Tg,dielc(α)) and S (Tg,dielc(S)) molecular population from the temperature dependence of the relaxation times to 100 s. While Tg,dielc(α) agrees better with the value obtained from the linearization of the Fox equation assuming ideal behavior of the menthol:flurbiprofen THEDES, Tg,dielc(S) is close to the value determined by calorimetry for the silica composites due to a dominance of the adsorbed population inside the pores. Nevertheless, the greater fraction of more mobile bulk-like molecules in the 5.9 nm pore size matrix seems to determine the faster drug release at initial times relative to the 3.2 nm composite. However, the latter

  5. 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.

  6. Preparation and photoluminescence properties of amorphous silica nanowires

    NASA Astrophysics Data System (ADS)

    Wu, X. C.; Song, W. H.; Wang, K. Y.; Hu, T.; Zhao, B.; Sun, Y. P.; Du, J. J.

    2001-03-01

    Bulk-quantity amorphous silica nanowires (SiONWs) have been synthesized by carbothermal reduction reaction between silicon dioxide and active carbons. Transmission electron microscopy (TEM) image shows the formation of the nanowires at a diameter of 60-110 nm and a length up to hundreds micrometers. Besides most smooth-surface polyp-shaped nanowires, two other forms of nanowires, named amoeba-shaped and frog-egg-shaped nanowires, have also been observed. The nanowires can emit stable and high brightness blue light at 435 nm (2.85 eV) under excitation at 260 nm (4.77 eV). The formation of the nanowires into different shapes may be explained by the vapor-liquid-solid (VLS) mechanism.

  7. Temperature stability of high Ge-doped fibre Bragg grating

    NASA Astrophysics Data System (ADS)

    Guo, Jiangtao; Tu, Feng; Wei, Huifeng; Deng, Tao; Tong, Weijun

    2010-12-01

    Temperature stability based on high Ge-doped fibre Bragg grating (FBG) is presented. A high Ge-doped photosensitive fibre (PSF) used for writing FBG was manufactured. Temperature characteristic of the FBG from 20 to 300°C had been researched. The transmission efficiency is about 75% at 300°C.

  8. 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.

  9. 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.

  10. 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

  11. Silica glass structure generation for ab initio calculations using small samples of amorphous silica

    NASA Astrophysics Data System (ADS)

    van Ginhoven, Renée M.; Jónsson, Hannes; Corrales, L. René

    2005-01-01

    Multiple small samples of amorphous silica have been generated and optimized using classical dynamics and the van Beest-Kramer-van Santen (BKS) empirical potential function. The samples were subsequently optimized and annealed using density functional theory (DFT) with both the local density and the generalized gradient approximations. A thorough analysis of the local and medium-range structure of the optimized samples obtained from the different methods was carried out. The structural characteristics obtained for the average of small systems each containing ca. 100 ions are compared for each of the different methods, and to the BKS simulation of a larger system. The differences found between the DFT and BKS simulations and the effects of volume relaxation on the structures are discussed. Fixed-volume samples are compared to neutron scattering data, with good agreement to 5Å , the length limit of the sample sizes used here. It is shown that by creating multiple small samples, it is possible to achieve a good statistical sampling of structural features consistent with larger simulated glass systems. This study also shows that multiple small samples are necessary to capture the structural distribution of silica glass, and therefore to study more complex processes in glass, such as reactions.

  12. Removal of free carbon and crystal structure change of amorphous silica fume by calcination

    NASA Astrophysics Data System (ADS)

    Tie, Shengnian; Zhang, Shaohong

    2017-07-01

    The calcination process was used to remove free carbon and to change the structure of amorphous microsilica powder. The results show that the carbon content in amorphous silica powder strongly depends on the calcination temperature. When the calcination temperature is higher than 900∘C, the free carbon content, SiO2 content and weight loss of microsilica powder tend to be stable, with values of 0.05%, 83.8% and 4.8%, respectively. The crystalline structure, particle size and morphology start changing at a calcination temperature of 850∘C. When the calcination temperature is higher than 900∘C, the amorphous microsilica powder is fully crystallized. The morphology of the silica fume kept its original spherical shape under 850∘C, while above 850∘C the microsilica powder recrystallizes. These results provide a basis for chemical removal of metal impurities in the preparation of high-purity silica powder.

  13. Optimization of large amorphous silicon and silica structures for molecular dynamics simulations of energetic impacts

    NASA Astrophysics Data System (ADS)

    Samela, Juha; Norris, Scott A.; Nordlund, Kai; Aziz, Michael J.

    2011-07-01

    A practical method to create optimized amorphous silicon and silica structures for molecular dynamics simulations is developed and tested. The method is based on the Wooten, Winer, and Weaire algorithm and combination of small optimized blocks to larger structures. The method makes possible to perform simulations of either very large cluster hypervelocity impacts on amorphous targets or small displacements induced by low energy ion impacts in silicon.

  14. A Thermodynamic Consideration on the Mechanism of Ultrasensitive Moisture Sensing by Amorphous Silica

    NASA Astrophysics Data System (ADS)

    Tsukahara, Y.; Tsuji, T.; Oizumi, T.; Akao, S.; Takeda, N.; Yamanaka, K.

    2017-07-01

    We detected the change in the phase velocity of surface acoustic waves propagating along the amorphous silica layer on a spherical single-crystal quartz due to the very small amount of moisture at less than 1 μmol{\\cdot } mol^{-1} in the ambient N2 gas. This was made possible for the first time because this system, called a ball SAW moisture sensor, was extremely sensitive. The measured phase velocity changed as a function of moisture density and temperature and was fitted strikingly well with a thermodynamic model assuming that dissociated H+ and OH- dissolved into the amorphous silica layer at room temperature.

  15. 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%.

  16. 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%.

  17. Pressure-induced silica quartz amorphization studied by iterative stochastic surface walking reaction sampling.

    PubMed

    Zhang, Xiao-Jie; Shang, Cheng; Liu, Zhi-Pan

    2017-02-08

    The crystal to amorphous transformation is a common phenomenon in Nature and has important impacts on material properties. Our current knowledge on such complex solid transformation processes is, however, limited because of their slow kinetics and the lack of long-range ordering in amorphous structures. To reveal the kinetics in the amorphization of solids, this work, by developing iterative reaction sampling based on the stochastic surface walking global optimization method, investigates the well-known crystal to amorphous transformation of silica (SiO2) under external pressures, the mechanism of which has long been debated for its non-equilibrium, pressure-sensitive kinetics and complex product components. Here we report for the first time the global potential energy surface (PES) and the lowest energy pathways for α-quartz amorphization from first principles. We show that the pressurization at 15 GPa, the reaction condition, can lift the quartz phase energetically close to the amorphous zone, which thermodynamically initializes the amorphization. More importantly, the large flexibility of Si cation coordination (including four, five and six coordination) results in many kinetically competing routes to more stable dense forms, including the known MI, stishovite, newly-identified MII and TI phases. All these pathways have high barriers due to the local Si-O bond breaking and are mediated by amorphous structures with five-fold Si. This causes simultaneous crystal-to-crystal and crystal-to-amorphous transitions. The high barrier and the reconstructive nature of the phase transition are the key kinetics origin for silica amorphization under pressures.

  18. Predicting catalyst-support interactions between metal nanoparticles and amorphous silica supports

    NASA Astrophysics Data System (ADS)

    Ewing, Christopher S.; Veser, Götz; McCarthy, Joseph J.; Lambrecht, Daniel S.; Johnson, J. Karl

    2016-10-01

    Metal-support interactions significantly affect the stability and activity of supported catalytic nanoparticles (NPs), yet there is no simple and reliable method for estimating NP-support interactions, especially for amorphous supports. We present an approach for rapid prediction of catalyst-support interactions between Pt NPs and amorphous silica supports for NPs of various sizes and shapes. We use density functional theory calculations of 13 atom Pt clusters on model amorphous silica supports to determine linear correlations relating catalyst properties to NP-support interactions. We show that these correlations can be combined with fast discrete element method simulations to predict adhesion energy and NP net charge for NPs of larger sizes and different shapes. Furthermore, we demonstrate that this approach can be successfully transferred to Pd, Au, Ni, and Fe NPs. This approach can be used to quickly screen stability and net charge transfer and leads to a better fundamental understanding of catalyst-support interactions.

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  1. 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

  2. Pressure-induced amorphization in crystalline silica: Soft phonon modes and shear instabilities in coesite

    SciTech Connect

    Dean, David W.; Wentzcovitch, Renata M.; Keskar, N.; Chelikowsky, James R.; Binggeli, N.

    2000-02-01

    Quartz and closely related materials will transform under pressure from crystalline states to amorphous forms. Here we examine coesite, a high-pressure form of silica which also undergoes pressure induced amorphization. We find that coesite, like quartz, possesses a shear instability closely coupled to a zone-edge phonon softening at pressures comparable to the amorphization transformation. The commonality of these features strongly suggests that a coupling between a shear and a phonon soft mode plays an important role in pressure induced amorphization. This mechanism is similar to that observed in martensitic transformations. The densities for the phases produced at high pressures, as calculated from variable cell shape molecular dynamics, follow the experimental glassy region joining coesite to stishovite. (c) 2000 The American Physical Society.

  3. Diffusion and aggregation of oxygen vacancies in amorphous silica

    NASA Astrophysics Data System (ADS)

    Munde, Manveer S.; Gao, David Z.; Shluger, Alexander L.

    2017-06-01

    Using density functional theory (DFT) calculations, we investigated oxygen vacancy diffusion and aggregation in relation to dielectric breakdown in amorphous silicon dioxide (a-SiO2). Our calculations indicate the existence of favourable sites for the formation of vacancy dimers and trimers in the amorphous network with maximum binding energies of approximately 0.13 eV and 0.18 eV, respectively. However, an average energy barrier height for neutral vacancy diffusion is found to be about 4.6 eV, rendering this process unfeasible. At Fermi level positions above 6.4 eV with respect to the top of the valence band, oxygen vacancies can trap up to two extra electrons. Average barriers for the diffusion of negative and double negatively charged vacancies are found to be 2.7 eV and 2.0 eV, respectively. These barriers are higher than or comparable to thermal ionization energies of extra electrons from oxygen vacancies into the conduction band of a-SiO2. In addition, we discuss the competing pathways for electron trapping in oxygen deficient a-SiO2 caused by the existence of intrinsic electron traps and oxygen vacancies. These results provide new insights into the role of oxygen vacancies in degradation and dielectric breakdown in amorphous silicon oxides.

  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.

  6. Transformations induced in bulk amorphous silica by ultrafast laser direct writing.

    PubMed

    Oliveira, Vitor; Sharma, Sahendra P; Herrero, Pilar; Vilar, Rui

    2013-12-01

    A transmission electron microscopy study of nanogratings formed in bulk amorphous silica by direct writing with an ultrafast pulsed laser with a radiation wavelength of 1030 nm and pulse duration of 560 fs is presented. The results achieved show that the nanogratings are composed of planar nanostructures with an average periodicity of 250 nm and typical thickness of about 30 nm, consisting of alternating layers of heavily damaged material and layers of material where a dense precipitation of nanocrystals occurred. The crystallization of silica to form these nanocrystals can be explained by the large pressures and temperatures reached in these regions as a result of nanoplasma formation and recombination.

  7. 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.

  8. An enormous amorphous silica stock in boreal wetlands

    NASA Astrophysics Data System (ADS)

    Struyf, Eric; MöRth, Carl-Magnus; Humborg, Christoph; Conley, Daniel J.

    2010-12-01

    We investigated amorphous Si (ASi) in a boreal wetland in northern Sweden. We found enormous stocks of ASi in the upper soil layers (up to 11% of dry weight), in the form of diatom frustules and plant ASi. A consistent exponential decrease in ASi concentrations was observed with increasing depth in the soil profile. An inverse modeling approach shows that vegetation takes up a substantial part of weathered dissolved Si (DSi). Concurrent analysis of N and C indicates a faster turnover in and a higher leakage from the ASi pool. The magnitude of the biological buffering we observed is unprecedented and supports the emerging paradigm of the importance of biological uptake of DSi governing the export of DSi from terrestrial ecosystems. Our results complicate current models of silicate transport, highlighting the necessity to incorporate ecosystem biological buffering in our concept of Si biogeochemistry.

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

    PubMed Central

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

    2016-01-01

    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 65ZnO or silica-coated 65ZnO NPs in male Wistar Han rats. Groups of IV-injected rats were sequentially euthanized, and 18 tissues were collected and analyzed for 65Zn 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 65ZnO were shorter (initial - <1 minute; terminal - 2.5 minutes) than uncoated 65ZnO (initial - 1.9 minutes; terminal - 38 minutes). Interestingly, the silica-coated 65ZnO group had higher 65Zn associated with red blood cells and higher initial uptake in the liver. The 65Zn 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 nanoparticles. PMID:26581431

  10. 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.

  11. Origin of the second peak in the mechanical loss function of amorphous silica

    NASA Astrophysics Data System (ADS)

    Billman, Chris R.; Trinastic, Jonathan P.; Davis, Dustin J.; Hamdan, Rashid; Cheng, Hai-Ping

    2017-01-01

    The thermal noise in amorphous oxides is the limiting factor for gravitational wave detectors and other high-precision optical devices. Through the fluctuation-dissipation theorem, the thermal noise is directly connected to the internal friction (Q-1). Computational calculations of Q-1 that use a two-level system (TLS) model have previously been performed for several coating materials, facilitating the search for coatings with lower thermal noise. However, they are based on a historical approximation made within the TLS model that treats the TLS distribution as uncorrelated, which has limited the predictive power of the model. In this paper, we demonstrate that this approximation limits the physical description of amorphous oxides using the TLS model and a fully correlated distribution must be used to calculate high-temperature behavior. Not only does using a correlated distribution improve the theoretical standing of the TLS model, calculations of Q-1 using a fully correlated distribution reproduce and uncover the physical mechanisms of a second peak observed in measurements of ion-beam sputtered amorphous silica. We also explore the details of the thermal activation of TLSs and analyze the atomic transitions that contribute to Q-1 in amorphous silica.

  12. 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

  13. Laser-driven formation of a high-pressure phase in amorphous silica.

    PubMed

    Salleo, Alberto; Taylor, Seth T; Martin, Michael C; Panero, Wendy R; Jeanloz, Raymond; Sands, Timothy; Génin, François Y

    2003-12-01

    Because of its simple composition, vast availability in pure form and ease of processing, vitreous silica is often used as a model to study the physics of amorphous solids. Research in amorphous silica is also motivated by its ubiquity in modern technology, a prominent example being as bulk material in transmissive and diffractive optics for high-power laser applications such as inertial confinement fusion (ICF). In these applications, stability under high-fluence laser irradiation is a key requirement, with optical breakdown occurring when the fluence of the beam is higher than the laser-induced damage threshold (LIDT) of the material. The optical strength of polished fused silica transmissive optics is limited by their surface LIDT. Surface optical breakdown is accompanied by densification, formation of point defects, cratering, material ejection, melting and cracking. Through a combination of electron diffraction and infrared reflectance measurements we show here that synthetic vitreous silica transforms partially into a defective form of the high-pressure stishovite phase under high-intensity (GW cm(-2)) laser irradiation. This phase transformation offers one suitable mechanism by which laser-induced damage grows catastrophically once initiated, thereby dramatically shortening the service lifetime of optics used for high-power photonics.

  14. Ultrahigh Vacuum Studies of the Fundamental Interactions of Chemical Warfare Agents and Their Simulants with Amorphous Silica

    DTIC Science & Technology

    2015-07-14

    CWAs, GD, VX, and HD , on a metal oxide surface. Adapted from references 41-43. 16 1.2.2 Heterogeneous Catalysts The metal oxides mentioned...Heterogeneous Catalysts ...........................................................................................16 1.3 Silica...96 Chapter 4. Adsorption and Desorption of HD Simulants from Amorphous Silica

  15. 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

  16. 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.

  17. 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

  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.

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

    SciTech Connect

    Vries, Wilke de; Doerenkamp, Carsten; Zeng, Zhaoyang; Niehaus, Oliver; Pöttgen, Rainer; Eckert, Hellmut

    2016-05-15

    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, N{sub 2} 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. - Graphical abstract: The amphiphilic radical CAT-16 is used as a template for the synthesis of amorphous mesoporous silica. The resulting paramagnetic hybrid materials are characterized by BET, FTIR, NMR, EPR and magnetic susceptibility studies. - Highlights: • Amphiphilic CAT-16 as a template for mesoporous silica. • Comprehensive structural characterization by BET, FTIR; EPR and NMR. • Strength of radical-radical interactions tuable within CAT-16/CTAB mixtures.

  20. 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

  1. 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.

  2. Silica nanoparticles on front glass for efficiency enhancement in superstrate-type amorphous silicon solar cells

    NASA Astrophysics Data System (ADS)

    Das, Sonali; Banerjee, Chandan; Kundu, Avra; Dey, Prasenjit; Saha, Hiranmay; Datta, Swapan K.

    2013-10-01

    Antireflective coating on front glass of superstrate-type single junction amorphous silicon solar cells (SCs) has been applied using highly monodispersed and stable silica nanoparticles (NPs). The silica NPs having 300 nm diameter were synthesized by Stober technique where the size of the NPs was controlled by varying the alcohol medium. The synthesized silica NPs were analysed by dynamic light scattering technique and Fourier transform infrared spectroscopy. The NPs were spin coated on glass side of fluorinated tin oxide (SnO2: F) coated glass superstrate and optimization of the concentration of the colloidal solution, spin speed and number of coated layers was done to achieve minimum reflection characteristics. An estimation of the distribution of the NPs for different optimization parameters has been done using field-emission scanning electron microscopy. Subsequently, the transparent conducting oxide coated glass with the layer having the minimum reflectance is used for fabrication of amorphous silicon SC. Electrical analysis of the fabricated cell indicates an improvement of 6.5% in short-circuit current density from a reference of 12.40 mA cm-2 while the open circuit voltage and the fill factor remains unaltered. A realistic optical model has also been proposed to gain an insight into the system.

  3. Differential toxicity of amorphous silica nanoparticles toward phagocytic and epithelial cells

    NASA Astrophysics Data System (ADS)

    Malugin, Alexander; Herd, Heather; Ghandehari, Hamidreza

    2011-10-01

    The objective of this study was to evaluate the influence of size and surface functionality of amorphous silica nanoparticles (SNPs) on their interaction with cultured cells. The intracellular uptake, phagocytic activity, and possible mechanisms of toxicity induced by SNPs were studied on murine alveolar macrophages and two epithelial cancer cell lines. It was found that phagocytic cells are more susceptible to amorphous SNPs than epithelial cells. SNPs with functionalized surfaces were capable to induce the formation of apoptotic cells to a higher extent than plain particles. Plain SNPs induced plasma membrane damage in phagocytic cells to a higher extent and caused cell death in a shorter period of time than surface-functionalized SNPs. The prevalence of necrotic mode of cell death was observed after treatment with plain SNPs. In the range studied surface functionality played an important role in SNPs toxicity.

  4. COHESION OF AMORPHOUS SILICA SPHERES: TOWARD A BETTER UNDERSTANDING OF THE COAGULATION GROWTH OF SILICATE DUST AGGREGATES

    SciTech Connect

    Kimura, Hiroshi; Kobayashi, Hiroshi

    2015-10-10

    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.

  5. 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.

  6. Microstructure of a granular amorphous silica ceramic synthesized by spark plasma sintering.

    PubMed

    Röding, M; Del Castillo, L A; Nydén, M; Follink, B

    2016-12-01

    We study the microstructure of a granular amorphous silica ceramic material synthesized by spark plasma sintering. Using monodisperse spherical silica particles as precursor, spark plasma sintering yields a dense granular material with distinct granule boundaries. We use selective etching to obtain nanoscopic pores along the granule borders. We interrogate this highly interesting material structure by combining scanning electron microscopy, X-ray computed nanotomography and simulations based on random close packed spherical particles. We determine the degree of anisotropy caused by the uni-axial force applied during sintering, and our analysis shows that our synthesis method provides a means to avoid significant granule growth and to fabricate a material with well-controlled microstructure.

  7. Investigation of the micro-mechanical properties of femtosecond laser-induced phases in amorphous silica

    NASA Astrophysics Data System (ADS)

    Athanasiou, Christos-Edward; Bellouard, Yves

    2016-03-01

    Femtosecond pulses used in the regime where self-organized patterns are found have two noticeable effects in amorphous silica's (a-SiO2) optical and chemical properties: The decrease of the material's refractive index as well as an enhanced etching selectivity. However, the effect on the material mechanical properties is unexplored. In this paper, we present elastic modulus measurements of fused silica exposed to femtosecond laser pulses in the regime where nanogratings are found. The measurement principle is based on the use of femtosecond laser fabricated displacement amplification mechanism combined with a discrete stiffness model. In this laser exposure regime, a significant decrease of the elastic modulus is observed. Our findings are consistent with the existence of a porous structure found within nanogratings lamellas.

  8. 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.

  9. Realistic models of amorphous silica: A comparative study of different potentials

    NASA Astrophysics Data System (ADS)

    von Alfthan, S.; Kuronen, A.; Kaski, K.

    2003-08-01

    The creation of realistic models of amorphous silica has been studied using the Monte Carlo based method of Wooten, Winer, and Weaire, where the bond-topology is optimized with respect to an interatomic potential model. The commonly used Keating potentials are compared and their strengths and weaknesses are assessed. The mean oxygen bond-angle obtained using these potentials turned out to be too small. A modification of the potential parameters is shown to correct this feature and thus produce better results when used with the Wooten-Winer-Weaire method.

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

    PubMed

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

    2014-09-01

    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 (Q8 M8 (H) ) and hydrogen silsesquioxane (T8 H8 ), 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/m(2) ) were typically obtained in this work. The propanol-bonded phase was characterized by spectroscopic (infrared (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. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. 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.

  12. Steps toward interstellar silicate mineralogy. V. Thermal Evolution of Amorphous Magnesium Silicates and Silica

    NASA Astrophysics Data System (ADS)

    Fabian, D.; Jäger, C.; Henning, Th.; Dorschner, J.; Mutschke, H.

    2000-12-01

    The thermally induced amorphous-to-crystalline transition has been studied for bulk sheets and micrometre-sized particles of magnesium silicate glass (MgSiO3), nanometre-sized amorphous magnesium silicate (MgSiO3 and Mg2SiO4 smokes) and amorphous silica particles (SiO2). Silicate glass was produced by the shock-quenching of melts. Samples of nanometre-sized smoke particles have been obtained by the laser ablation technique. Both the MgSiO3 and the Mg2SiO4 smokes have been found to consist of two particle species; particles of smaller size ranging in diametre from 10 nm to about 100 nm and bigger size ranging from a few 100 nm to almost 3 micrometres in diametre. Nanometre-sized particles have been shown to be depleted in magnesium whereas the micrometre-sized particles were found to be enriched in Mg. Generally, the particles are composed of nonstoichiometric magnesium silicates with compositions varying even inside of the particles. Frequently, the particles contained internal voids that are assumed to have been formed by thermal shrinkage or outgassing of the particles' interior during cooling. Annealing at 1000 K transformed the magnesium silicate smokes into crystalline forsterite (c-Mg2SiO4), tridymite (a crystalline modification of SiO2) and amorphous silica (a-SiO2) according to the initial Mg/Si-ratio of the smoke. Crystallization took place within a few hours for the Mg2SiO4 smoke and within one day for the MgSiO3 smoke. The MgSiO3 glass evolved more slowly because crystallization started at the sample surface. It has been annealed at temperatures ranging from 1000 to 1165 K. In contrast to the smoke samples, MgSiO3 glass crystallized as orthoenstatite (MgSiO3). Only after 50 hours of annealing at 1000 K, weak indications of forsterite and tridymite formation have been found in the X-ray diffraction spectra. At a temperature of 1000 K, amorphous silica nanoparticles showed distinctly lower rates of thermal evolution compared with the magnesium silicates

  13. 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.

  14. Studying the loading effect of acidic type antioxidant on amorphous silica nanoparticle carriers

    NASA Astrophysics Data System (ADS)

    Ravinayagam, Vijaya; Rabindran Jermy, B.

    2017-06-01

    The study investigates the suitable nanosilica carriers to transport acidic type cargo molecules for potential targeted drug delivery application. Using phenolic acidic type antioxidant gallic acid (GA) as model compound, the present study investigates the loading effect of GA (0.3-15.9 mmol GA g-1 support) on textural characteristics of amorphous silica nanoparticles such as Q10 silica (1D), structured two-dimensional Si-MCM-41 (2D), and three-dimensional Si-SBA-16 (3D). The variation in the nature of textures after GA loading was analyzed using X-ray diffraction, N2 adsorption, FT-IR, scanning electron microscopy with energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy. Among the nanocarriers, high adsorption of GA was found in the following order: Si-SBA-16 (3D)˜Si-KIT-6 (3D) > Si-MCM-41 (2D) > ultralarge pore FDU-12 (ULPFDU-12; 3D) > Q10 (1D)˜mesostructured cellular silica foam (MSU-F). 3D-type silicas Si-SBA-16 and KIT-6 were shown to maintain structural integrity at acidic condition (pH ˜3) and accommodate GA in non-crystalline form. In the case of ULPFDU-12 and MSU-F cellular foam, only crystalline deposition of GA occurs with a significant variation in the surface area and pore volume. [Figure not available: see fulltext.

  15. 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.

  16. Elevated transition temperature in Ge doped VO2 thin films

    NASA Astrophysics Data System (ADS)

    Krammer, Anna; Magrez, Arnaud; Vitale, Wolfgang A.; Mocny, Piotr; Jeanneret, Patrick; Guibert, Edouard; Whitlow, Harry J.; Ionescu, Adrian M.; Schüler, Andreas

    2017-07-01

    Thermochromic GexV1-xO2+y thin films have been deposited on Si (100) substrates by means of reactive magnetron sputtering. The films were then characterized by Rutherford backscattering spectrometry (RBS), four-point probe electrical resistivity measurements, X-ray diffraction, and atomic force microscopy. From the temperature dependent resistivity measurements, the effect of Ge doping on the semiconductor-to-metal phase transition in vanadium oxide thin films was investigated. The transition temperature was shown to increase significantly upon Ge doping (˜95 °C), while the hysteresis width and resistivity contrast gradually decreased. The precise Ge concentration and the film thickness have been determined by RBS. The crystallinity of phase-pure VO2 monoclinic films was confirmed by XRD. These findings make the use of vanadium dioxide thin films in solar and electronic device applications—where higher critical temperatures than 68 °C of pristine VO2 are needed—a viable and promising solution.

  17. 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

  18. 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

    2015-08-20

    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.

  19. 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

  20. Activation of the inflammasome by amorphous silica and TiO2 nanoparticles in murine dendritic cells.

    PubMed

    Winter, Meike; Beer, Hans-Dietmar; Hornung, Veit; Krämer, Ursula; Schins, Roel P F; Förster, Irmgard

    2011-09-01

    Nanomaterials are increasingly used in various food applications. In particular, nanoparticulate amorphous SiO2 is already contained, e.g., in spices. Since intestinal dendritic cells (DC) could be critical targets for ingested particles, we compared the in vitro effects of amorphous silica nanoparticles with fine crystalline silica, and micron-sized with nano-sized TiO2 particles on DC. TiO2- and SiO2-nanoparticles, as well as crystalline silica led to an upregulation of MHC-II, CD80, and CD86 on DC. Furthermore, these particles activated the inflammasome, leading to significant IL-1β-secretion in wild-type (WT) but not Caspase-1- or NLRP3-deficient mice. Silica nanoparticles and crystalline silica induced apoptosis, while TiO2 nanoparticles led to enhanced production of reactive oxygen species (ROS). Since amorphous silica and TiO2 nanoparticles had strong effects on the activation-status of DC, we suggest that nanoparticles, used as food additives, should be intensively studied in vitro and in vivo, to ensure their safety for the consumer.

  1. Effect of Alkali Ions on the Amorphous to Crystalline Phase Transition of Silica

    NASA Astrophysics Data System (ADS)

    Venezia, A. M.; La Parola, V.; Longo, A.; Martorana, A.

    2001-11-01

    The effect of the addition of alkali ions to commercial amorphous silica, generally used as support for heterogeneous catalysts, has been investigated from the point of view of morphological and structural changes. Samples of alkali-doped silica were prepared by impregnation and subsequent calcination at various temperatures. The structural effect of Li, Na, K, and Cs was determined by use of techniques such as wide-angle (WAXS) and small-angle X-ray scattering (SAXS). The WAXS diffractograms, analyzed with the Rietveld method using the GSAS program, allowed qualitative and quantitative identification of the fraction of the different silica polymorphs like quartz, tridymite, and cristobalite. SAXS measurements, using the classical method based on Porod's law, yielded the total surface area of the systems. The calculated areas were compared with the surface areas determined by the nitrogen adsorption technique using the analytical method of Brunauer-Emmett-Teller. The results are explained in terms of sizes of the alkali ions and cell volume of the different crystalline phases.

  2. Effect of amorphous silica nanoparticles on in vitro RANKL-induced osteoclast differentiation in murine macrophages

    PubMed Central

    2011-01-01

    Amorphous silica nanoparticles (nSP) have been used as a polishing agent and/or as a remineralization promoter for teeth in the oral care field. The present study investigates the effects of nSP on osteoclast differentiation and the relationship between particle size and these effects. Our results revealed that nSP exerted higher cytotoxicity in macrophage cells compared with submicron-sized silica particles. However, tartrate-resistant acid phosphatase (TRAP) activity and the number of osteoclast cells (TRAP-positive multinucleated cells) were not changed by nSP treatment in the presence of receptor activator of nuclear factor κB ligand (RANKL) at doses that did not induce cytotoxicity by silica particles. These results indicated that nSP did not cause differentiation of osteoclasts. Collectively, the results suggested that nanosilica exerts no effect on RANKL-induced osteoclast differentiation of RAW264.7 cells, although a detailed mechanistic examination of the nSP70-mediated cytotoxic effect is needed. PMID:21777482

  3. 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

  4. 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

  5. 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.

  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

    2016-06-02

    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.

  7. Growth mechanism of Ge-doped CZTSSe thin film by sputtering method and solar cells.

    PubMed

    Li, Jinze; Shen, Honglie; Chen, Jieyi; Li, Yufang; Yang, Jiale

    2016-10-19

    Ge-doped CZTSSe thin films were obtained by covering a thin Ge layer on CZTS precursors, followed by a selenization process. The effect of the Ge layer thickness on the morphologies and structural properties of Ge-doped CZTSSe thin films were studied. It was found that Ge doping could promote grain growth to form a compact thin film. The lattice shrank in the top-half of the film due to the smaller atomic radius of Ge, leading to the formation of tensile stress. According to thermodynamic analysis, Sn was easier to be selenized than Ge. Thus, Ge preferred to remain on the surface and increased the surface roughness when the Ge layer was thin. CZTSe was easier to form than Ge-doped CZTSe, which caused difficulty in Ge doping. These results offered a theoretical and experimental guide for preparing Ge-doped CZTSSe thin films for the potential applications in low-cost solar cells. With a 10 nm Ge layer on the top of the precursor, the conversion efficiency of the solar cell improved to 5.38% with an open-circuit voltage of 403 mV, a short-circuit current density of 28.51 mA cm(-2) and a fill factor of 46.83% after Ge doping.

  8. Solid dispersion particles of amorphous indomethacin with fine porous silica particles by using spray-drying method.

    PubMed

    Takeuchi, Hirofumi; Nagira, Shinsuke; Yamamoto, Hiromitsu; Kawashima, Yoshiaki

    2005-04-11

    The solid dispersion particles of indomethacin (IMC) were prepared with different types of silica, non-porous (Aerosil 200) or porous silica (Sylysia 350) by using spray-drying method. Powder X-ray diffraction analysis showed that IMC in solid dispersion particles is in amorphous state irrespective of the type of silica formulated. In DSC analysis, the melting peak of IMC in solid dispersion particles with Sylysia 350 shifted to lower temperature than that in solid dispersion particles with Aerosil 200 although the peak of each solid dispersion particles was much smaller than that of original IMC crystals. Dissolution property of IMC was remarkably improved by formulating the silica particles to the solid dispersion particles. In comparing the effect of the type of the silica particles, the dissolution rate of solid dispersion particles with Sylysia 350 was faster than that with Aerosil 200. The formulation amount of IMC did not affect on the amorphous state of IMC in the resultant solid dispersion particles in powder X-ray diffraction patterns. However, the area of the melting peak of IMC in the solid dispersion particles increased and an exothermic peak owing to recrystallization was observed with increasing the IMC content in the DSC patterns. The dissolution rate of IMC from the solid dispersion particles with Sylysia 350 was faster than that of Aerosil 200 irrespective of IMC content. In stability test, amorphous IMC in the solid dispersion particles with each silica particles did not crystallize under storing at severe storage conditions (40 degrees C, 75% RH) for 2 months, while amorphous IMC without silica easily crystallized under same conditions.

  9. 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. © The

  10. 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.

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

    PubMed

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

    2008-01-18

    Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25 degrees 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 beta-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 beta-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 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 concentrations for the development of a robust

  12. 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

  13. 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

  14. Classical molecular dynamics and ab initio simulations of chemical-mechanical polishing of amorphous silica

    NASA Astrophysics Data System (ADS)

    Chagarov, Evgueni Anatolievich

    Chemical-mechanical polishing (CMP) is a widely accepted process in the semiconductor industry. Despite intense theoretical and experimental research on CMP, there is a serious lack of fundamental understanding of the physical-chemical processes of polishing. The present work is intended to investigate these fundamental processes on an atomistic level. To model CMP on the atomic scale, a model of the amorphous silica is prepared by applying Design of Experiments (DOE) techniques to systematically investigate molecular dynamics preparation. These simulations yield high-quality models of amorphous silica, which are in excellent agreement with experimental results and are defect-free. Molecular dynamics simulations are performed to investigate the mechanical deformation during CMP of silica for different geometries and relative velocities. The simulations clarify asperity shape evolution during the process of shear and reveal temperature distributions as a function of time. It is found that the ratio of radii of a particle and asperity strongly affects the amount of the material removed whereas the relative velocity has a weaker affect on it. During shear, a significant local temperature increase occurs. This temperature increase lasts for a short time (picoseconds), but it can have a major impact on the amount of material removed. It is found that there could be significant deposition of the material from the particle to the slab, which can fill surface trenches and thereby make the surface smoother. An analytic model is developed for describing the amount of material removed as a function of asperity and particle radii and relative velocity. Density-functional calculations of different surfaces of two silica polymorphs, alpha-quartz and beta-cristobalite, are performed. The surface energies are calculated as a function of oxygen partial pressure for several different surface reconstructions and terminations. The case of hydrogen passivation is investigated to

  15. 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.

  16. Strong photoluminescence emission from GaN grown on amorphous silica substrates by gas source MBE

    NASA Astrophysics Data System (ADS)

    Iwata, K.; Asahi, H.; Asami, K.; Kuroiwa, R.; Gonda, S.

    1998-06-01

    GaN layers are grown on amorphous fused silica glass substrates by gas source MBE using an ion removed electron cyclotron resonance (ECR) radical cell. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction measurements reveal that they are polycrystalline. However, they show a strong photoluminescence emission peak without deep level emission. The emission peak is red-shifted by about 150 meV from that of the excitonic emission peak of GaN grown on a sapphire substrate and has wide spectral half-width (˜250 meV at 77 K). The peak is not corresponding to the donor-acceptor pair (DAP) emission but is excitonic from the excitation power and temperature dependence of PL spectrum. These optical properties indicate that GaN layers grown on a glass substrate are promising for fabrication of large area and low cost light emitting devices and solar cells.

  17. 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.

  18. 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.

  19. Classical and ab-initio molecular dynamic simulation of an amorphous silica surface

    NASA Astrophysics Data System (ADS)

    Mischler, C.; Kob, W.; Binder, K.

    2002-08-01

    We present the results of a classical molecular dynamic simulation as well as of an ab-initio molecular dynamic simulation of an amorphous silica surface. In the case of the classical simulation we use the potential proposed by van Beest et al. (BKS) whereas the ab-initio simulation is done with a Car-Parrinello method (CPMD). We find that the surfaces generated by BKS have a higher concentration of defects (e.g., concentration of two-membered rings) than those generated with CPMD. In addition also the distribution functions of the angles and of the distances are different for the short rings. Hence we conclude that whereas the BKS potential is able to correctly reproduce the surface on the length scale beyond ≈5 Å, it is necessary to use an ab-initio method to reliably predict the structure at small scales.

  20. 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.

  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. A computational study of x-ray emission from laser-irradiated Ge-doped foams

    SciTech Connect

    Colvin, Jeffrey D.; Fournier, Kevin B.; May, Mark J.; Scott, Howard A.

    2010-07-15

    New advances in fabrication of low-density high-Z-doped foams have opened new windows on understanding how materials that are not in local thermodynamic equilibrium (LTE) are heated and radiate. Simulations are discussed in this paper of the x-ray spectral emissions from laser-irradiated very low-density Ge-doped silica aerogel targets using a two-dimensional radiation-hydrodynamics code incorporating a modern non-LTE superconfiguration atomic model. Details of the computational model are presented, and it is shown that, for the long-scale-length, subcritical-density, approx2-3 keV electron temperature plasmas created in experiments at the Omega laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], the simulations provide a close match to both the measured Ge L-shell emission (approx1-1.5 keV) and the measured Ge K-shell emission (approx10-11 keV), but only by accounting properly for nonlocal thermal conduction. The older average-atom atomic model is shown to be inadequate for these non-LTE plasmas.

  3. Improved stability of a phase change memory device using Ge-doped SbTe at varying ambient temperature

    NASA Astrophysics Data System (ADS)

    Wu, Zhe; Lee, Suyoun; Park, Young-Wook; Ahn, Hyung-Woo; Jeong, Doo Seok; Jeong, Jeung-hyun; No, Kwangsoo; Cheong, Byung-ki

    2010-03-01

    Ge-doped SbTe (Ge-ST) was compared with Ge2Sb2Te5 (GST) for its potential use in the phase-change memory with improved stability at varying ambient temperature (TA). Device characteristics such as RESET current, RESET resistance, and SET resistance of Ge-ST devices were found to vary significantly less with TA than those of GST devices. From measured carrier density, mobility, and optical band gaps, these findings are interpreted to derive from a metallic nature of the crystalline Ge-ST in contrast with a semiconducting nature of the crystalline GST as well as a relatively weaker covalent bonding in amorphous Ge-ST.

  4. Oxidative stress induced by pure and iron-doped amorphous silica nanoparticles in subtoxic conditions.

    PubMed

    Napierska, Dorota; Rabolli, Virginie; Thomassen, Leen C J; Dinsdale, David; Princen, Catherine; Gonzalez, Laetitia; Poels, Katrien L C; Kirsch-Volders, Micheline; Lison, Dominique; Martens, Johan A; Hoet, Peter H

    2012-04-16

    Amorphous silica nanoparticles (SiO₂-NPs) have found broad applications in industry and are currently intensively studied for potential uses in medical and biomedical fields. Several studies have reported cytotoxic and inflammatory responses induced by SiO₂-NPs in different cell types. The present study was designed to examine the association of oxidative stress markers with SiO₂-NP induced cytotoxicity in human endothelial cells. We used pure monodisperse amorphous silica nanoparticles of two sizes (16 and 60 nm; S16 and S60) and a positive control, iron-doped nanosilica (16 nm; SFe), to study the generation of hydroxyl radicals (HO·) in cellular-free conditions and oxidative stress in cellular systems. We investigated whether SiO₂-NPs could influence intracellular reduced glutathione (GSH) and oxidized glutathione (GSSG) levels, increase lipid peroxidation (malondialdehyde (MDA) and 4-hydroxyalkenal (HAE) concentrations), and up-regulate heme oxygenase-1 (HO-1) mRNA expression in the studied cells. None of the particles, except SFe, produced ROS in cell-free systems. We found significant modifications for all parameters in cells treated with SFe nanoparticles. At cytotoxic doses of S16 (40-50 μg/mL), we detected weak alterations of intracellular glutathione (4 h) and a marked induction of HO-1 mRNA (6 h). Cytotoxic doses of S60 elicited similar responses. Preincubation of cells being exposed to SiO₂-NPs with an antioxidant (5 mM N-acetylcysteine, NAC) significantly reduced the cytotoxic activity of S16 and SFe (when exposed up to 25 and 50 μg/mL, respectively) but did not protect cells treated with S60. Preincubation with NAC significantly reduced HO-1 mRNA expression in cells treated with SFe but did not have any effect on HO-1 mRNA level in cell exposed to S16 and S60. Our study demonstrates that the chemical composition of the silica nanoparticles is a dominant factor in inducing oxidative stress.

  5. A lucrative chemical processing of bamboo leaf biomass to synthesize biocompatible amorphous silica nanoparticles of biomedical importance

    NASA Astrophysics Data System (ADS)

    Rangaraj, Suriyaprabha; Venkatachalam, Rajendran

    2017-06-01

    Synthesis of silica nanoparticles from natural resources/waste via cost effective route is presently one of the anticipating strategies for extensive applications. This study reports the low-cost indigenous production of silica nanoparticles from the leftover of bamboo (leaf biomass) through thermal combustion and alkaline extraction, and examination of physico-chemical properties and yield percentage using comprehensive characterization tools. The outcome of primed silica powder exhibits amorphous particles (average size: 25 nm) with high surface area (428 m2 g-1) and spherical morphology. Despite the yield percentage of silica nanoparticles from bamboo leave ash is 50.2%, which is less than rice husk ask resources (62.1%), the bamboo waste is only an inexpensive resource yielding high purity (99%). Synthesis of silica nanoparticles from natural resources/waste with the help of lucrative route is at present times one of the anticipating strategies for extensive applications. In vitro study on animal cell lines (MG-63) shows non-toxic nature of silica nanoparticles up to 125 µg mL-1. Hence, this study highlights the feasibility for the mass production of silica nanoparticles from bamboo leave waste rather using chemical precursor of silica for drug delivery and other medical applications.

  6. Timescales and mechanisms of formation of amorphous silica coatings on fresh basalts at Kīlauea Volcano, Hawai'i

    NASA Astrophysics Data System (ADS)

    Chemtob, Steven M.; Rossman, George R.

    2014-10-01

    Young basalts from Kīlauea Volcano, Hawai'i, frequently feature opaque surface coatings, 1-80 μm thick, composed of amorphous silica and Fe-Ti oxides. These coatings are the product of interaction of the basaltic surface with volcanically-derived acidic fluids. Previous workers have identified these coatings in a variety of contexts on Hawai'i, but the timescales of coating development, coating growth rates, and factors controlling lateral coating heterogeneity were largely unconstrained. We sampled and analyzed young lava flows (of varying ages, from hours to ~ 40 years) along Kīlauea's southwest and east rift zones to characterize variation in silica coating properties across the landscape. Coating thickness varies as a function of flow age, flow surface type, and proximity to acid sources like local fissure vents and regional plumes emitted from Kīlauea Caldera and Pu'u Ō'ō. Silica coatings that form in immediate proximity to acid sources are more chemically pure than those forming in higher pH environments, which contain significant Al and Fe. Incipient siliceous alteration was observed on basalt surfaces as young as 8 days old, but periods of a year or more are required to develop contiguous coatings with obvious opaque coloration. Inferred coating growth rates vary with environmental conditions but were typically 1-5 μm/year. Coatings form preferentially on flow surfaces with glassy outer layers, such as spatter ramparts, volcanic bombs, and dense pahoehoe breakouts, due to glass strain weakening during cooling. Microtextural evidence suggests that the silica coatings form both by in situ dissolution-reprecipitation and by deposition of silica mobilized in solution. Thin films of water, acidified by contact with volcanic vapors, dissolved near-surface basalt, then precipitated amorphous silica in place, mobilizing more soluble cations. Additional silica was transported to and deposited on the surface by silica-bearing altering fluids derived from the

  7. Size distributions of coastal ocean suspended particulate inorganic matter: Amorphous silica and clay minerals and their dynamics

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaodong; Stavn, Robert H.; Falster, Alexander U.; Rick, Johannes J.; Gray, Deric; Gould, Richard W.

    2017-04-01

    Particulate inorganic matter (PIM) is a key component in estuarine and coastal systems and plays a critical role in trace metal cycling. Better understanding of coastal dynamics and biogeochemistry requires improved quantification of PIM in terms of its concentration, size distribution, and mineral species composition. The angular pattern of light scattering contains detailed information about the size and composition of particles. These volume scattering functions (VSFs) were measured in Mobile Bay, Alabama, USA, a dynamic, PIM dominated coastal environment. From measured VSFs, we determined through inversion the particle size distributions (PSDs) of major components of PIM, amorphous silica and clay minerals. An innovation here is the extension of our reported PSDs significantly into the submicron range. The PSDs of autochthonous amorphous silica exhibit two unique features: a peak centered at about 0.8 μm between 0.2 and 4 μm and a very broad shoulder essentially extending from 4 μm to >100 μm. With an active and steady particle source from blooming diatoms, the shapes of amorphous silica PSDs for sizes <10 μm varied little across the study area, but showed more particles of sizes >10 μm inside the bay, likely due to wind-induced resuspension of larger frustules that have settled. Compared to autochthonous amorphous silica, the allochthonous clay minerals are denser and exhibit relatively narrower PSDs with peaks located between 1 and 4 μm. Preferential settling of larger mineral particles as well as the smaller but denser illite component further narrowed the size distributions of clay minerals as they were being transported outside the bay. The derived PSDs also indicated a very dynamic situation in Mobile Bay when a cold weather front passed through during the experiment. With northerly winds of speeds up to 15 m s-1, both amorphous silica and clay minerals showed a dramatic increase in concentration and broadening in size distribution outside the exit

  8. Differences in gene expression and cytokine production by crystalline vs. amorphous silica in human lung epithelial cells

    PubMed Central

    2012-01-01

    Background Exposure to respirable crystalline silica particles, as opposed to amorphous silica, is associated with lung inflammation, pulmonary fibrosis (silicosis), and potentially with lung cancer. We used Affymetrix/GeneSifter microarray analysis to determine whether gene expression profiles differed in a human bronchial epithelial cell line (BEAS 2B) exposed to cristobalite vs. amorphous silica particles at non-toxic and equal surface areas (75 and 150 × 106μm2/cm2). Bio-Plex analysis was also used to determine profiles of secreted cytokines and chemokines in response to both particles. Finally, primary human bronchial epithelial cells (NHBE) were used to comparatively assess silica particle-induced alterations in gene expression. Results Microarray analysis at 24 hours in BEAS 2B revealed 333 and 631 significant alterations in gene expression induced by cristobalite at low (75) and high (150 × 106μm2/cm2) amounts, respectively (p < 0.05/cut off ≥ 2.0-fold change). Exposure to amorphous silica micro-particles at high amounts (150 × 106μm2/cm2) induced 108 significant gene changes. Bio-Plex analysis of 27 human cytokines and chemokines revealed 9 secreted mediators (p < 0.05) induced by crystalline silica, but none were induced by amorphous silica. QRT-PCR revealed that cristobalite selectively up-regulated stress-related genes and cytokines (FOS, ATF3, IL6 and IL8) early and over time (2, 4, 8, and 24 h). Patterns of gene expression in NHBE cells were similar overall to BEAS 2B cells. At 75 × 106μm2/cm2, there were 339 significant alterations in gene expression induced by cristobalite and 42 by amorphous silica. Comparison of genes in response to cristobalite (75 × 106μm2/cm2) revealed 60 common, significant gene alterations in NHBE and BEAS 2B cells. Conclusions Cristobalite silica, as compared to synthetic amorphous silica particles at equal surface area concentrations, had comparable effects on the viability of human bronchial epithelial cells

  9. Oral hesperidin-Amorphization and improved dissolution properties by controlled loading onto porous silica.

    PubMed

    Wei, Qionghua; Keck, Cornelia M; Müller, Rainer H

    2017-02-25

    The oral bioavailability of poorly soluble drugs can be improved by amorphization generated by loading into the pores of mesoporous particles (pore size 2-50nm). The main mechanisms are increased kinetic saturation solubility and dissolution velocity due to the amorphous drug state and the nano-size of the drug (=increased dissolution pressure). In this study, the maximum achievable drug loading compared to the theoretical drug loading, and the effect of drug loading degree on the dissolution properties (solubility, dissolution velocity) were investigated. Hesperidin was used as the model active (having also practical relevance for e.g. nutraceutical products), loading was performed onto AEROPERL(®) 300 Pharma. Degree of successful drug loading could be easily followed by simple light microscopy (=useful tool for formulation optimization), and was in agreement with scanning electron microscopy. Amorphous versus crystalline state was followed by X-ray diffraction and differential scanning calorimetry. Loadings prepared were 28.6wt.%, 54.5wt.% and 60.0wt.%, the maximum theoretical loading was 72.5wt.%. Obviously the maximum drug loading is not achievable, the 54.5wt.% drug loading was the practical maximum with already some minor crystalline hesperidin on the surface. Interestingly, the maximum kinetic saturation solubility was obtained for the 54.5wt.% drug loading (941.74μg/ml in pH 6.8 PBS), versus 408.80μg/ml for the 60.0wt.% drug loading (=overloaded system). The raw drug powder had a thermodynamic solubility of only 18.40μg/ml. The fastest in vitro release was obtained with the 28.6wt.% loaded system, followed by the 54.5wt.% and 60.0wt.% loadings. The dissolution properties (solubility, dissolution velocity) can obviously be influenced by a "controlled loading". This is a simple, cost-effective technological alternative to modulating this property by chemical modification of silica, requiring a new costly regulatory approval of these chemically modified

  10. The safety of nanostructured synthetic amorphous silica (SAS) as a food additive (E 551).

    PubMed

    Fruijtier-Pölloth, Claudia

    2016-12-01

    Particle sizes of E 551 products are in the micrometre range. The typical external diameters of the constituent particles (aggregates) are greater than 100 nm. E 551 does not break down under acidic conditions such as in the stomach, but may release dissolved silica in environments with higher pH such as the intestinal tract. E 551 is one of the toxicologically most intensively studied substances and has not shown any relevant systemic or local toxicity after oral exposure. Synthetic amorphous silica (SAS) meeting the specifications for use as a food additive (E 551) is and has always been produced by the same two production methods: the thermal and the wet processes, resulting in E 551 products consisting of particles typically in the micrometre size range. The constituent particles (aggregates) are typically larger than 100 nm and do not contain discernible primary particles. Particle sizes above 100 nm are necessary for E 551 to fulfil its technical function as spacer between food particles, thus avoiding the caking of food particles. Based on an in-depth review of the available toxicological information and intake data, it is concluded that the SAS products specified for use as food additive E 551 do not cause adverse effects in oral repeated-dose studies including doses that exceed current OECD guideline recommendations. In particular, there is no evidence for liver toxicity after oral intake. No adverse effects have been found in oral fertility and developmental toxicity studies, nor are there any indications from in vivo studies for an immunotoxic or neurotoxic effect. SAS is neither mutagenic nor genotoxic in vivo. In intact cells, a direct interaction of unlabelled and unmodified SAS with DNA was never found. Differences in the magnitude of biological responses between pyrogenic and precipitated silica described in some in vitro studies with murine macrophages at exaggerated exposure levels seem to be related to interactions with cell culture proteins

  11. 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.

  12. 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.

  13. Acute Toxicity of Amorphous Silica Nanoparticles in Intravenously Exposed ICR Mice

    PubMed Central

    Wang, Wen; Jin, Minghua; Du, Zhongjun; Li, Yanbo; Duan, Junchao; Yu, Yongbo; Sun, Zhiwei

    2013-01-01

    This study aimed to evaluate the acute toxicity of intravenously administrated amorphous silica nanoparticles (SNPs) in mice. The lethal dose, 50 (LD50), of intravenously administrated SNPs was calculated in mice using Dixon's up-and-down method (262.45±33.78 mg/kg). The acute toxicity was evaluated at 14 d after intravenous injection of SNPs at 29.5, 103.5 and 177.5 mg/kg in mice. A silicon content analysis using ICP-OES found that SNPs mainly distributed in the resident macrophages of the liver (10.24%ID/g), spleen (34.78%ID/g) and lung (1.96%ID/g). TEM imaging showed only a small amount in the hepatocytes of the liver and in the capillary endothelial cells of the lung and kidney. The levels of serum LDH, AST and ALT were all elevated in the SNP treated groups. A histological examination showed lymphocytic infiltration, granuloma formation, and hydropic degeneration in liver hepatocytes; megakaryocyte hyperplasia in the spleen; and pneumonemia and pulmonary interstitial thickening in the lung of the SNP treated groups. A CD68 immunohistochemistry stain indicated SNPs induced macrophage proliferation in the liver and spleen. The results suggest injuries induced by the SNPs in the liver, spleen and lungs. Mononuclear phagocytic cells played an important role in the injury process. PMID:23593469

  14. Chemical Warfare Agent Surface Adsorption: Hydrogen Bonding of Sarin and Soman to Amorphous Silica.

    PubMed

    Davis, Erin Durke; Gordon, Wesley O; Wilmsmeyer, Amanda R; Troya, Diego; Morris, John R

    2014-04-17

    Sarin and soman are warfare nerve agents that represent some of the most toxic compounds ever synthesized. The extreme risk in handling such molecules has, until now, precluded detailed research into the surface chemistry of agents. We have developed a surface science approach to explore the fundamental nature of hydrogen bonding forces between these agents and a hydroxylated surface. Infrared spectroscopy revealed that both agents adsorb to amorphous silica through the formation of surprisingly strong hydrogen-bonding interactions with primarily isolated silanol groups (SiOH). Comparisons with previous theoretical results reveal that this bonding occurs almost exclusively through the phosphoryl oxygen (P═O) of the agent. Temperature-programmed desorption experiments determined that the activation energy for hydrogen bond rupture and desorption of sarin and soman was 50 ± 2 and 52 ± 2 kJ/mol, respectively. Together with results from previous studies involving other phosphoryl-containing molecules, we have constructed a detailed understanding of the structure-function relationship for nerve agent hydrogen bonding at the gas-surface interface.

  15. 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.

  16. Highly selective PdCu/amorphous silica-alumina (ASA) catalysts for groundwater denitration.

    PubMed

    Xie, Yongbing; Cao, Hongbin; Li, Yuping; Zhang, Yi; Crittenden, John C

    2011-05-01

    Catalytic nitrate reduction is a promising technology in groundwater purification. In this study, PdCu bimetallic catalysts supported on an industrial amorphous silica-alumina (ASA) were synthesized and used to simulate catalytic removal of nitrate in groundwater. The catalysts exhibited very high activity and the highest catalytic selectivity toward N₂O and N₂ was 90.2%. The optimal Pd/Cu weight ratio was four. Relatively low reduction temperature was found benefit the catalytic stability and 300 °C was the appropriate reduction temperature during catalyst preparation. With an average particle size 5.4 nm, the metal particles were very uniformly distributed on the catalyst surface prepared with the codeposition method. This kept the catalyst more stable than the PdCu/Al₂O₂ catalyst with larger metal particles. According to XRD, TEM, and XPS results, the metals maintained zero-valence but aggregated by about 2 nm during the denitration reaction, which caused gradual deactivation of the catalysts. Little leaching of Cu and Pd from the catalyst might also have a slightly negative impact to the stability of the catalysts. A simple treatment was found to redistribute the particles on the deactivated catalysts, and high catalytic activity was recovered after this process.

  17. 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

  18. Highly conductive Ge-doped GaN epitaxial layers prepared by pulsed sputtering

    NASA Astrophysics Data System (ADS)

    Ueno, Kohei; Arakawa, Yasuaki; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

    2017-10-01

    Highly conductive Ge-doped GaN epitaxial layers were grown by low-temperature pulsed sputtering, and their fundamental structural and electrical properties were investigated. The room-temperature (RT) electron concentration was increased to 5.1 × 1020 cm‑3 by the Ge doping, and the atomically flat stepped and terraced surface and the crystalline quality of the layers were maintained. Consequently, the RT resistivity was reduced to 0.20 mΩ·cm, which is comparable to that for typical transparent conductive oxides such as indium tin oxide. The contact resistance of Ge-doped GaN with a Ti/Al/Ti/Au metal stack prepared without annealing was as low as 0.087 Ω·mm. Furthermore, the selective formation of a Ge-doped region using an SiO2 mask was demonstrated. The results clearly indicate the strong potential of pulsed sputtering Ge-doped GaN growth for forming low-parasitic-resistance contact layers of various electrical and optical devices.

  19. 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.

  20. Cellular internalization and stress response of ingested amorphous silica nanoparticles in the midgut of Drosophila melanogaster.

    PubMed

    Pandey, Ashutosh; Chandra, Swati; Chauhan, Lalit Kumar Singh; Narayan, Gopeshwar; Chowdhuri, Debapratim Kar

    2013-01-01

    Amorphous silica nanoparticles (aSNPs) are used for various applications including food industry. However, limited in vivo studies are available on absorption/internalization of ingested aSNPs in the midgut cells of an organism. The study aims to examine cellular uptake of aSNPs (<30nm) in the midgut of Drosophila melanogaster (Oregon R(+)) owing to similarities between the midgut tissue of this organism and human and subsequently cellular stress response generated by these nanoparticles. Third instar larvae of D. melanogaster were exposed orally to 1-100μg/mL of aSNPs for 12-36h and oxidative stress (OS), heat shock genes (hsgs), membrane destabilization (Acridine orange/Ethidium Bromide staining), cellular internalization (TEM) and apoptosis endpoints. A significant increase was observed in OS endpoints in the midgut cells of exposed Drosophila in a concentration- and time-dependent manner. Significantly increased expression of hsp70 and hsp22 along with caspases activation, membrane destabilization and mitochondrial membrane potential loss was also observed. TEM analysis showed aSNPs-uptake in the midgut cells of exposed Drosophila via endocytic vesicles and by direct membrane penetration. aSNPs after their internalization in the midgut cells of exposed Drosophila larvae show membrane destabilization along with increased cellular stress and cell death. Ingested aSNPs show adverse effects on the cells of GI tract of the exposed organism thus their industrial use as a food-additive may raise concern to human health. Copyright © 2012 Elsevier B.V. All rights reserved.

  1. 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.

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

    PubMed

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

    2014-01-01

    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.

  3. 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

  4. Atomic structure and dehydration mechanism of amorphous silica: Insights from 29Si and 1H solid-state MAS NMR study of SiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Kim, Hyun Na; Lee, Sung Keun

    2013-11-01

    Detailed knowledge of the atomic structure of hydrous species on surface of amorphous silica and the effect of temperature and particle size on their atomic configurations are essential to understand the nature of fluids-amorphous silicates interactions and the dehydration processes in the amorphous oxides. Here, we report the 29Si, 1H MAS, and 1H-29Si heteronuclear correlation (HetCor) NMR spectra of 7 nm and 14 nm amorphous silica nanoparticles—a model system for natural amorphous silica—where previously unknown details of changes in their atomic structures with varying dehydration temperature and particle size are revealed. Diverse hydroxyl groups with varying atomic configurations and molecular water apparently show distinct dehydration trends. The dehydration (i.e., removal of water) of amorphous silica nanoparticles mostly results in the increase of isolated silanol by removing water molecules from hydrogen-bonded silanols associated water molecules. With further increase in dehydration temperature, the intensity of isolated silanol peak decreases above ˜873 K, suggesting that the condensation of isolated silanol may occur mainly above ˜873 K. The entire dehydration (and dehydroxylation) process completes at ˜1473 K. Both the water (i.e., physisorbed water and hydrogen-bonded water) and hydrogen-bonded silanol species show a dramatic change in the slope of intensity variation at ˜873 K, indicating that most of silanols is hydrogen-bonded to water rather than to other silanols. The fraction of hydrogen-bonded proton species is also much smaller in 14 nm amorphous silica nanoparticles than in 7 nm amorphous silica nanoparticles mainly due to the presences of larger fractions of water and hydrogen-bonded silanol species. 29Si NMR results show that with increasing dehydration temperature, the fraction of Q4 species apparently increases at the expense of Q2 and Q3 species. The fractions of Q2 and Q3 structures in 7 nm amorphous silica nanoparticles are

  5. Very strong photoluminescence emission from GaN grown on amorphous silica substrate by gas source MBE

    NASA Astrophysics Data System (ADS)

    Asahi, H.; Iwata, K.; Tampo, H.; Kuroiwa, R.; Hiroki, M.; Asami, K.; Nakamura, S.; Gonda, S.

    1999-05-01

    Polycrystalline GaN layers showing very strong photoluminescence (PL) intensities are successfully grown on amorphous fused silica (SiO 2) substrates by gas source molecular beam epitaxy (MBE) using an ion removed electron cyclotron resonance radical cell. The PL intensity is larger than that of undoped single crystalline GaN grown on sapphire by gas source MBE and is comparable to that of Si-doped single crystalline GaN grown on sapphire by metalorganic vapor-phase epitaxy at Nichia Chemical. The PL peak emission is considered to be excitonic. Undoped GaN layers grown on silica substrates exhibit n-type conduction and both n- and p-type conductions are achieved by impurity doping. These results open up the area of "Polycrystalline Semiconductor Photonics".

  6. 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

  7. 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

  8. Cytokine production by co-cultures exposed to monodisperse amorphous silica nanoparticles: the role of size and surface area.

    PubMed

    Napierska, Dorota; Thomassen, Leen C J; Vanaudenaerde, Bart; Luyts, Katrien; Lison, Dominique; Martens, Johan A; Nemery, Benoit; Hoet, Peter H M

    2012-06-01

    The aim of this study was to test the influence of nanoparticle size and surface area (SA) on cytokine secretion by co-cultures of pulmonary epithelial cells (A549), macrophages (differentiated THP-1 cells) and endothelium cells (EA.hy926) in a two-compartment system. We used monodisperse amorphous silica nanoparticles (2, 16, 60 and 104 nm) at concentrations of 5 μg/cm² cell culture SA or 10 cm² particle SA/cm². A549 and THP-1 cells were exposed to nanoparticles for 24h, in the presence of EA.hy926 cells cultured in an insert introduced above the bi-culture after 12h. Supernatants from both compartments were recovered and TNF-α, IL-6, IL-8 and MIP-1α were measured. Significant secretion of all cytokines was observed for the 2 nm particles at both concentrations and in both compartments. Larger particles of 60 nm induced significant cytokine secretion at the dose of 10 cm² particle SA/cm². The use of multiple cellular types showed that cytokine secretion in single cell cultures is amplified or mitigated in co-cultures. The release of pro-inflammatory mediators by endothelial cells not directly exposed to nanoparticles indicates a possible endothelium activation after inhalation of silica particles. This work shows the role of size and SA in cellular response to amorphous nanosilica. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  9. Chrysotile asbestos detoxification with a combined treatment of oxalic acid and silicates producing amorphous silica and biomaterial.

    PubMed

    Valouma, Aikaterini; Verganelaki, Anastasia; Maravelaki-Kalaitzaki, Pagona; Gidarakos, Evangelos

    2016-03-15

    This study was primarily imposed by the ever increasing need for detoxification of asbestos and asbestos containing materials (ACM), with potential application onsite. The present work investigates potential detoxification of pure chrysotile (Chr) asbestos via a combined treatment of oxalic acid dihydrate (Oxac) (Η2C2Ο4·2Η2Ο) with silicates, such as tetraethoxysilane (TEOS) (SiH20C8O4) and pure water glass (WG) (potassium silicate) (K2SiO3). These reagents used in the experimental procedure, do not cause adverse effects on the environment and are cost effective. The results of FTIR, XRD, optical and scanning microscopy coupled with EDS analyses indicated that all of the applied treatments destructed the Chr structure and yielded silica of amorphous phase and the biomaterial glushinskite from the Oxac reacted with brucite [Mg(OH)2] layer. Each of the proposed formulations can be applied for the detoxification of asbestos, according to priorities related to the specific products of the recovery treatment. Therefore, Oxac acid leaching followed by the TEOS addition is preferred in cases of glushinskite recovery; TEOS treatment of asbestos with subsequent Oxac addition produced amorphous silica production; finally Oxac acid leaching followed by WG encapsulated the asbestos fibers and can be used in cases of onsite asbestos and ACM detoxification. Copyright © 2015 Elsevier B.V. All rights reserved.

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

    SciTech Connect

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

    2016-03-07

    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

  11. 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)

  12. 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.

  13. 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

  14. S and O adsorption on pure and Ge doped Ag(1 1 1)

    NASA Astrophysics Data System (ADS)

    Blomqvist, J.; Salo, P.; Alatalo, M.

    2004-09-01

    We have studied the possibility of preventing the sulphur poisoning of silver surfaces by doping them with Ge. Our first principles calculations show that the presence of Ge at the topmost surface layer does not affect the adsorption characteristics of S much, yet Ge helps to bind oxygen much more strongly. We thus predict that Ge doping induces a protective O layer which helps to prevent the poisoning caused by sulphur.

  15. 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.

  16. Synthesis of uniformly dispersed anatase nanoparticles inside mesoporous silica thin films via controlled breakup and crystallization of amorphous TiO2 deposited using atomic layer deposition.

    PubMed

    Sree, Sreeprasanth Pulinthanathu; Dendooven, Jolien; Masschaele, Kasper; Hamed, Heidari M; Deng, Shaoren; Bals, Sara; Detavernier, Christophe; Martens, Johan A

    2013-06-07

    Amorphous titanium dioxide was introduced into the pores of mesoporous silica thin films with 75% porosity and 12 nm average pore diameter via Atomic Layer Deposition (ALD) using alternating pulses of tetrakis(dimethylamino)titanium and water. Calcination provoked fragmentation of the deposited amorphous TiO2 phase and its crystallization into anatase nanoparticles inside the nanoporous film. The narrow particle size distribution of 4 ± 2 nm and the uniform dispersion of the particles over the mesoporous silica support were uniquely revealed using electron tomography. These anatase nanoparticle bearing films showed photocatalytic activity in methylene blue degradation. This new synthesis procedure of the anatase nanophase in mesoporous silica films using ALD is a convenient fabrication method of photocatalytic coatings amenable to application on very small as well as very large surfaces.

  17. Synthesis of uniformly dispersed anatase nanoparticles inside mesoporous silica thin films via controlled breakup and crystallization of amorphous TiO2 deposited using atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Sree, Sreeprasanth Pulinthanathu; Dendooven, Jolien; Masschaele, Kasper; Hamed, Heidari M.; Deng, Shaoren; Bals, Sara; Detavernier, Christophe; Martens, Johan A.

    2013-05-01

    Amorphous titanium dioxide was introduced into the pores of mesoporous silica thin films with 75% porosity and 12 nm average pore diameter via Atomic Layer Deposition (ALD) using alternating pulses of tetrakis(dimethylamino)titanium and water. Calcination provoked fragmentation of the deposited amorphous TiO2 phase and its crystallization into anatase nanoparticles inside the nanoporous film. The narrow particle size distribution of 4 +/- 2 nm and the uniform dispersion of the particles over the mesoporous silica support were uniquely revealed using electron tomography. These anatase nanoparticle bearing films showed photocatalytic activity in methylene blue degradation. This new synthesis procedure of the anatase nanophase in mesoporous silica films using ALD is a convenient fabrication method of photocatalytic coatings amenable to application on very small as well as very large surfaces.

  18. Changing the dose metric for inhalation toxicity studies: short-term study in rats with engineered aerosolized amorphous silica nanoparticles.

    PubMed

    Sayes, Christie M; Reed, Kenneth L; Glover, Kyle P; Swain, Keith A; Ostraat, Michele L; Donner, E Maria; Warheit, David B

    2010-03-01

    Inhalation toxicity and exposure assessment studies for nonfibrous particulates have traditionally been conducted using particle mass measurements as the preferred dose metric (i.e., mg or microg/m(3)). However, currently there is a debate regarding the appropriate dose metric for nanoparticle exposure assessment studies in the workplace. The objectives of this study were to characterize aerosol exposures and toxicity in rats of freshly generated amorphous silica (AS) nanoparticles using particle number dose metrics (3.7 x 10(7) or 1.8 x 10(8) particles/cm(3)) for 1- or 3-day exposures. In addition, the role of particle size (d(50) = 37 or 83 nm) on pulmonary toxicity and genotoxicity endpoints was assessed at several postexposure time points. A nanoparticle reactor capable of producing, de novo synthesized, aerosolized amorphous silica nanoparticles for inhalation toxicity studies was developed for this study. SiO(2) aerosol nanoparticle synthesis occurred via thermal decomposition of tetraethylorthosilicate (TEOS). The reactor was designed to produce aerosolized nanoparticles at two different particle size ranges, namely d(50) = approximately 30 nm and d(50) = approximately 80 nm; at particle concentrations ranging from 10(7) to 10(8) particles/cm(3). AS particle aerosol concentrations were consistently generated by the reactor. One- or 3-day aerosol exposures produced no significant pulmonary inflammatory, genotoxic, or adverse lung histopathological effects in rats exposed to very high particle numbers corresponding to a range of mass concentrations (1.8 or 86 mg/m(3)). Although the present study was a short-term effort, the methodology described herein can be utilized for longer-term inhalation toxicity studies in rats such as 28-day or 90-day studies. The expansion of the concept to subchronic studies is practical, due, in part, to the consistency of the nanoparticle generation method.

  19. 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.

  20. Chemical Warfare Agent Surface Adsorption: Hydrogen Bonding of Sarin and Soman to Amorphous Silica

    DTIC Science & Technology

    2014-03-17

    This conclusion is supported by the IR data of Figure 2, which shows spectroscopic evidence for molecular adsorption . Determination of the desorption... liquids and vapors and the ability to perform surface-sensitive IR spectroscopy and XPS as well as mass spectrometry (MS). The instrument is built around a...Kinetics in Amorphous Solid Water. J. Chem. Phys. 2007, 127, 184707. (12) Quenneville, J.; Taylor, R. S.; van Duin, A. C. T. Reactive Molecular Dynamics

  1. Laser-driven formation of a high-pressure phase in amorphous silica

    SciTech Connect

    Salleo, Alberto; Taylor, Seth T.; Martin, Michael C.; Panero, Wendy R.; Jeanloz, Raymond; Genin, Francois Y.; Sands, Timothy

    2002-05-31

    A combination of electron diffraction and infrared reflectance measurements shows that synthetic silica transforms partially into stishovite under high-intensity (GW/cm2) laser irradiation, probably by the formation of a dense ionized plasma above the silica surface. During the transformation the silicon coordination changes from four-fold to six-fold and the silicon-oxygen bond changes from mostly covalent to mostly ionic, such that optical properties of the transformed material differ significantly from those of the original glass. This phase transformation offers one suitable mechanism by which laser-induced damage grows catastrophically once initiated, thereby dramatically shortening the service lifetime of optics used for high-power photonics applications such as inertial confinement fusion.

  2. 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

  3. Preparation and tableting of long-term stable amorphous rutin using porous silica.

    PubMed

    Wei, Qionghua; Keck, Cornelia M; Müller, Rainer H

    2017-04-01

    Amorphous state of drugs increases the oral bioavailability, but typically faces physical stability problems. Amorphous rutin was generated and physically stabilized by encapsulating inside mesopores of porous AEROPERL® 300 Pharma and named as rutin CapsMorph® in this study. AEROPERL® 300 Pharma was loaded with rutin dissolved in DMSO containing Tween 80, and subsequently the solvent evaporated (wetness impregnation method). The loading process was monitored by light microscopy and scanning electron microscopy (SEM). X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to confirm the amorphous state in AEROPERL® 300 Pharma. A loading of 20% of the rutin-AEROPERL® 300 Pharma mixture was obtained. The amorphous state proved to be stable over 2years of storage at room temperature. Due to the amorphous state and the nanosize of the rutin in the mesopores, the kinetic saturation solubility increased to about 4mg/ml (water, 0.1MHCl, pH 6.8PBS) compared to the maximum observed thermodynamic equilibrium solubility of rutin raw drug powder of only 74.48±1.42μg/ml in pH 6.8PBS (=increase by factor about 54). The dissolution velocity also increased distinctly, e.g. about 96.1% of rutin dissolution from CapsMorph® powder in water within 5min compared to less than 40% of raw drug powder after 3h. Tablets were produced with rutin CapsMorph®, raw drug powder and their dissolution velocity compared to a marketed product. About 83.0-95.6% were released from the rutin CapsMorph® tablet within 5min, compared to 42.7-52.5% from the marketed tablet after 3h (water, 0.1MHCl, pH 6.8PBS). After dissolution the supersaturation level of rutin CapsMorph® remained over about 2h, then solubility slowly reduced, but remained after 48h still multifold above the thermodynamic rutin solubility. This should be sufficient for many poorly soluble drugs to achieve a sufficient bioavailability. For optimal exploitation of the supersaturation, a multiple step release

  4. Interactions and Binding Energies of Dimethyl Methylphosphonate and Dimethyl Chlorophosphate with Amorphous Silica

    DTIC Science & Technology

    2012-07-10

    INTRODUCTION Developing a complete understanding of the uptake , bonding, and chemistry of chemical warfare agents (CWAs) on surfaces is critical to the...composition affect interfacial binding on the high-surface-area sorbent, silica. The uptake and binding of organophosphates (the general class of CWA simulants...affected by adsorption. Through these observations, we have begun to learn about the key functional groups involved in the uptake of the molecules on a

  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. Properties of amorphous silica nanoparticles colloid drug delivery system synthesized using the micelle formation method

    NASA Astrophysics Data System (ADS)

    Ab Wab, Hajarul Azwana; Abdul Razak, Khairunisak; Zakaria, Nor Dyana

    2014-02-01

    This study describes the formation and properties of a silica nanocolloid drug delivery system synthesized using micelle formation method. Previously, we have reported feasibility of using the same approach to entrap colorless water soluble drug (isoniazid). However, the entrapment of the drug inside nanoparticles (NPs) could not be observed due to its colorless nature. In this study, poor water soluble Rifampicin (RIF) was used as a drug model. Orange color of RIF enables observation and measurement using UV-Vis spectrophotometer. Several parameters were systematically studied: reaction temperature (25-70 °C) produced 28-97 nm, amount of surfactant (4-9 g) produced 44-66 nm, butanol volume (6-18 ml) produced 50-157 nm, and drug concentration. Particle size could be tuned from 28 to 157 nm by varying synthesis parameters. NP size was highly influenced by reaction temperature and butanol. Silica nanocolloid-entrapped RIF (50 and 70 nm SiRif) were synthesized and further analyzed for biological application. The stability of SiRif in biological media, such as in 0.1, 0.5, and 1.0 M NaCl solution and 5, 10, and 25 % mouse serum, was examined. RIF was successfully entrapped inside silica nanocolloids. Moreover, 50 and 70 nm SiRif exhibited almost similar stability in NaCl and mouse serum. The drug release profiles in 0.1 and 1.0 mM phosphate buffer solutions and different pH at 37 °C were examined for several days. Results indicate that 70 nm SiRif had higher drug loading and slower release profile than 50 nm SiRif. 70 nm SiRif was optimally released at pH 6.8.

  8. Release behavior of trans,trans-farnesol entrapped in amorphous silica capsules

    PubMed Central

    Sousa, Filipa L.; Horta, Sara; Santos, Magda; Rocha, Sĺlvia M.; Trindade, Tito

    2012-01-01

    Farnesol, a compound widely found in several agro-food by-products, is an important bioactive agent that can be exploited in cosmetics and pharmaceutics but the direct bioapplication of this compound is limited by its volatility. Here the entrapment of farnesol in silica capsules was investigated to control the release of this bioactive compound in the vapor phase and in ethanol solutions. The preparation of silica capsules with oil cores was obtained by employing a sol–gel method using O/W/O multiple emulsions. Two distinct chemical vehicles for farnesol have been investigated, retinol and oleic acid, that afterwards have been emulsified as internal oil phases. The volatile release of farnesol from the as-prepared SiO2 capsules was investigated by headspace solid phase microextraction (HS-SPME) followed by gas chromatographic analysis (GC), and the release to ethanol was carried out by direct injection of the ethanolic fraction into the GC system. It is demonstrated that these capsules are efficient for the long controlled release of farnesol and that the respective profiles depend on the chemical parameters employed in the synthesis of the capsules. PMID:25755994

  9. 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

  10. 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.

  11. Macrophages participate in local and systemic inflammation induced by amorphous silica nanoparticles through intratracheal instillation

    PubMed Central

    Yang, Man; Jing, Li; Wang, Ji; Yu, Yang; Cao, Lige; Zhang, Lianshuang; Zhou, Xianqing; Sun, Zhiwei

    2016-01-01

    Silica nanoparticles (SiNPs) are amongst the most commonly used materials in the field of nanomedicine and, therefore, their influence on organisms has drawn increasing attention in recent years. Most reports have focused on the single tissue reactions induced by SiNPs. Herein, the reaction of primary organs to SiNPs following intratracheal instillation in mice was analyzed by histopathology and ultrastructure observation. Following elucidation of the role of macrophages in local and systemic inflammation, the underlying mechanisms were explored using a macrophage cell line in vitro. The results suggest that macrophages swallow the SiNPs and secrete inflammatory factors by activating the NLRP3 inflammasome, thus participating in local and systemic inflammation. PMID:27920528

  12. Electrical property and structural analysis of amphoteric impurity Ge doped GaSe crystal grown by liquid phase growth

    NASA Astrophysics Data System (ADS)

    Sato, Y.; Zhao, S.; Maeda, K.; Tanabe, T.; Oyama, Y.

    2017-06-01

    In order to improve conversion efficiency of THz wave generation, Germanium (Ge)-doped gallium selenide (GaSe) single crystals have been grown by Temperature Difference Method under Controlled Vapor Pressure (TDM-CVP). In this article, electrical property and lattice constant of Ge doped GaSe (GaSe:Ge) crystal are compared with that of not-intentionally doped GaSe crystal. Compared with non-doped GaSe crystal, carrier concentration p was decreased by Ge-doping (not-intentionally doped GaSe p = 3.2 ×1015 cm-3 at 255 K, GaSe:Ge p = 4.9 ×1014 cm-3 at 255 K). In addition, it has been confirmed that lattice constant of GaSe crystal increased with doping Ge concentration increased.

  13. Genotoxicity evaluation of nanosized titanium dioxide, synthetic amorphous silica and multi-walled carbon nanotubes in human lymphocytes.

    PubMed

    Tavares, Ana M; Louro, Henriqueta; Antunes, Susana; Quarré, Stephanie; Simar, Sophie; De Temmerman, Pieter-Jan; Verleysen, Eveline; Mast, Jan; Jensen, Keld A; Norppa, Hannu; Nesslany, Fabrice; Silva, Maria João

    2014-02-01

    Toxicological characterization of manufactured nanomaterials (NMs) is essential for safety assessment, while keeping pace with innovation from their development and application in consumer products. The specific physicochemical properties of NMs, including size and morphology, might influence their toxicity and have impact on human health. The present work aimed to evaluate the genotoxicity of nanosized titanium dioxide (TiO2), synthetic amorphous silica (SAS) and multiwalled carbon nanotubes (MWCNTs), in human lymphocytes. The morphology and size of those NMs were characterized by transmission electron microscopy, while the hydrodynamic particle size-distributions were determined by dynamic light scattering. Using a standardized procedure to ensure the dispersion of the NMs and the cytokinesis-block micronucleus assay (without metabolic activation), we observed significant increases in the frequencies of micronucleated binucleated cells (MNBCs) for some TiO2 NMs and for two MWCNTs, although no clear dose-response relationships could be disclosed. In contrast, all forms of SAS analyzed in this study were unable to induce micronuclei. The present findings increase the weight of evidence towards a genotoxic effect of some forms of TiO2 and some MWCNTs. Regarding safety assessment, the differential genotoxicity observed for closely related NMs highlights the importance of investigating the toxic potential of each NM individually, instead of assuming a common mechanism and equal genotoxic effects for a set of similar NMs. Copyright © 2013 Elsevier Ltd. All rights reserved.

  14. Neutron Compton scattering investigation of sodium hydride: From bulk material to encapsulated nanoparticulates in amorphous silica gel

    NASA Astrophysics Data System (ADS)

    Seel, A. G.; Sartbaeva, A.; Mayers, J.; Ramirez-Cuesta, A. J.; Edwards, P. P.

    2011-03-01

    In this study we utilize neutron Compton scattering (NCS) to determine differences in nuclear momentum distributions in NaH, both as bulk material and encapsulated as nanoscale particles (from 20 to 50 nm in diameter) within an amorphous silica-gel matrix (SiGNaH). In addition, elemental Na dispersed in such a matrix is also studied (SiGNa). Data treatment and fitting of experimental spectra yields comparison of the nuclear Compton profiles and radial momentum distributions for the proton in both bulk NaH and nanoscale SiGNaH, with resultant proton kinetic energies being in agreement with previous inelastic neutron studies of bulk NaH. Slight differences in proton radial momentum distributions for bulk and nanoscale systems are witnessed and discussed. The technique of stoichiometric-fixing is applied to the backscattering spectra of each system in order to examine changes in the Na profile width, and NCS is shown to be sensitive to the chemical environment change of this heavier nucleus. Examination of the Si and O profile widths in the gel samples also supports this method.

  15. Neutron Compton scattering investigation of sodium hydride: from bulk material to encapsulated nanoparticulates in amorphous silica gel.

    PubMed

    Seel, A G; Sartbaeva, A; Mayers, J; Ramirez-Cuesta, A J; Edwards, P P

    2011-03-21

    In this study we utilize neutron Compton scattering (NCS) to determine differences in nuclear momentum distributions in NaH, both as bulk material and encapsulated as nanoscale particles (from 20 to 50 nm in diameter) within an amorphous silica-gel matrix (SiGNaH). In addition, elemental Na dispersed in such a matrix is also studied (SiGNa). Data treatment and fitting of experimental spectra yields comparison of the nuclear Compton profiles and radial momentum distributions for the proton in both bulk NaH and nanoscale SiGNaH, with resultant proton kinetic energies being in agreement with previous inelastic neutron studies of bulk NaH. Slight differences in proton radial momentum distributions for bulk and nanoscale systems are witnessed and discussed. The technique of stoichiometric-fixing is applied to the backscattering spectra of each system in order to examine changes in the Na profile width, and NCS is shown to be sensitive to the chemical environment change of this heavier nucleus. Examination of the Si and O profile widths in the gel samples also supports this method.

  16. 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.

  17. 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.

  18. Amorphous silica modeled with truncated and screened Coulomb interactions: A molecular dynamics simulation study

    NASA Astrophysics Data System (ADS)

    Carré, Antoine; Berthier, Ludovic; Horbach, Jürgen; Ispas, Simona; Kob, Walter

    2007-09-01

    We show that finite-range alternatives to the standard long-range pair potential for silica by van Beest et al. [Phys. Rev. Lett. 64, 1955 (1990)] might be used in molecular dynamics simulations. We study two such models that can be efficiently simulated since no Ewald summation is required. We first consider the Wolf method, where the Coulomb interactions are truncated at a cutoff distance rc such that the requirement of charge neutrality holds. Various static and dynamic quantities are computed and compared to results from simulations using Ewald summations. We find very good agreement for rc≈10Å. For lower values of rc, the long-range structure is affected which is accompanied by a slight acceleration of dynamic properties. In a second approach, the Coulomb interaction is replaced by an effective Yukawa interaction with two new parameters determined by a force fitting procedure. The same trend as for the Wolf method is seen. However, slightly larger cutoffs have to be used in order to obtain the same accuracy with respect to static and dynamic quantities as for the Wolf method.

  19. In vitro toxicity of amorphous silica nanoparticles in human colon carcinoma cells.

    PubMed

    Gehrke, Helge; Frühmesser, Anne; Pelka, Joanna; Esselen, Melanie; Hecht, Lena L; Blank, Holger; Schuchmann, Heike P; Gerthsen, Dagmar; Marquardt, Clarissa; Diabaté, Silvia; Weiss, Carsten; Marko, Doris

    2013-05-01

    The use of nanostructured silica (SiO2) particles is no longer restricted to biomedical and (bio-) technological fields but rather finding applications in products of the food industry. Thus, our studies on the toxicological relevance of SiO2 nanoparticles focused on cytotoxic effects, the modulation of the cellular redox status and the impact on DNA integrity in human colon carcinoma cells (HT29). The results indicate that these SiO2 nanoparticles stimulate the proliferation of HT29 cells, depending on the incubation time and the particle size. The cytotoxicity of the investigated SiO2 nanoparticles was found to depend on the concentration, size and on the FCS content of the culture medium. Furthermore, SiO2 seem to interfere with glutathione biosynthesis. The results indicate further that effects of SiO2 NPs are not mediated by oxidative stress but by interference with the MAPK/ERK1/2 as well as the Nrf2/ARE signalling pathways. Additionally, investigations regarding DNA integrity revealed no substantial (oxidative) DNA damage.

  20. Optical properties of uniform, porous, amorphous Ta2O5 coatings on silica: temperature effects

    NASA Astrophysics Data System (ADS)

    Anghinolfi, L.; Prato, M.; Chtanov, A.; Gross, M.; Chincarini, A.; Neri, M.; Gemme, G.; Canepa, M.

    2013-11-01

    We present spectroscopic ellipsometry (SE) results, in the 0.75-5 eV spectral range, obtained on highly uniform Ta2O5 coatings deposited on high-quality silica substrates by ion sputtering. The study was motivated mainly by issues related to the exploitation of Ta2O5-SiO2 λ/4 multilayers in detectors of gravitational waves. Two sets of samples with nominal thicknesses of 40 and 500 nm were considered. A sub-set of samples was treated with post-growth annealing in air for several hours at temperatures Tann up to 600 °C. The SE data were complemented with photothermal common-path interferometry measurements at 1064 nm providing data about absorption losses in the 1-4 ppm range. SE data, taken at room temperature, were analysed by exploiting three different three-phase (substrate/film/surface) models (Cody-Lorentz, Tauc-Lorentz and Herzinger-Johs) of the fundamental absorption edge. Following the literature (Stenzel 2009 J. Phys. D: Appl. Phys. 42 055312) the simulations exploited a graded nano-porosity inside the coating, testing both the shape and composition of the pores. The best simulation of data was obtained using the Cody-Lorentz approach and a quasi-uniform density (6-7.5%) of empty spherical pores, slowly degrading from the substrate/film interface towards the film/ambient interface. A comparison with the literature indicated a high stoichiometric quality of the coatings. The analysis of samples annealed to increasingly higher Tann showed (i) a slight blue-shift of the energy gap (ii) an increase in the pore volume fraction, (iii) an increase (1-2%) in the coating thickness, (iv) a small (less than 1%) reduction in the index of refraction in the transparency region and (v) a limited increase in absorption losses. These findings were interpreted in terms of a release of the compressive strain inherent to the deposition process.

  1. 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

  2. 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. Published by Elsevier Inc.

  3. 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

  4. 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.

  5. 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.

  6. Irradiation temperature effects on the induced point defects in Ge-doped optical fibers.

    NASA Astrophysics Data System (ADS)

    Alessi, A.; Reghioua, I.; Girard, S.; Agnello, S.; Di Francesca, D.; Martin-Samos, L.; Marcandella, C.; Richard, N.; Cannas, M.; Boukenter, A.; Ouerdane, Y.

    2017-02-01

    We present an experimental investigation on the combined effects of temperature and irradiation on Ge-doped optical fibers. Our samples were X-ray (10 keV) irradiated up to 5 kGy with a dose rate of 50 Gy(SiO2)/s changing the irradiation temperature in the range 233-573 K. After irradiation we performed electron paramagnetic resonance (EPR) and confocal microscopy luminescence (CML) measurements. The recorded data prove the generation of different Ge related paramagnetic point defects and of a red emission, different from that of the Ge/Si Non-Bridging Oxygen Hole center. Furthermore, by comparing the behaviour of the EPR signal of the Ge(1) as a function of the irradiation temperature with the one of the red emission we can exclude that this emission is originated by the Ge(1).

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  9. Assessing the amorphousness and periodicity of common domain boundaries in silica bilayers on Ru(0 0 0 1)

    NASA Astrophysics Data System (ADS)

    Burson, Kristen M.; Büchner, Christin; Heyde, Markus; Freund, Hans-Joachim

    2017-01-01

    Domain boundaries are hypothesized to play a role in the crystalline to amorphous transition. Here we examine domain boundary structures in comparison to crystalline and amorphous structures in bilayer silica grown on Ru(0 0 0 1). Atomically resolved scanning probe microscopy data of boundaries in crystalline bilayer films are analyzed to determine structural motifs. A rich variety of boundary structures including rotational, closed-loop, antiphase, and complex boundaries are identified. Repeating units with ring sizes of 558 and 57 form the two most common domain boundary types. Quantitative metrics are utilized to assess the structural composition and degree of order for the chemically equivalent crystalline, domain boundary, and amorphous structures. It is found that domain boundaries in the crystalline phase show similarities to the amorphous phase in their ring statistics and, in some cases, in terms of the observed ring neighborhoods. However, by assessing order and periodicity, domain boundaries are shown to be distinct from the glassy state. The role of the Ru(0 0 0 1) substrate in influencing grain boundary structure is also discussed.

  10. Direct stimulation of human fibroblasts by nCeO2 in vitro is attenuated with an amorphous silica coating.

    PubMed

    Davidson, Donna C; Derk, Raymond; He, Xiaoqing; Stueckle, Todd A; Cohen, Joel; Pirela, Sandra V; Demokritou, Philip; Rojanasakul, Yon; Wang, Liying

    2016-05-04

    Nano-scaled cerium oxide (nCeO2) is used in a variety of applications, including use as a fuel additive, catalyst, and polishing agent, yet potential adverse health effects associated with nCeO2 exposure remain incompletely understood. Given the increasing utility and demand for engineered nanomaterials (ENMs) such as nCeO2, "safety-by-design" approaches are currently being sought, meaning that the physicochemical properties (e.g., size and surface chemistry) of the ENMs are altered in an effort to maximize functionality while minimizing potential toxicity. In vivo studies have shown in a rat model that inhaled nCeO2 deposited deep in the lung and induced fibrosis. However, little is known about how the physicochemical properties of nCeO2, or the coating of the particles with a material such as amorphous silica (aSiO2), may affect the bio-activity of these particles. Thus, we hypothesized that the physicochemical properties of nCeO2 may explain its potential to induce fibrogenesis, and that a nano-thin aSiO2 coating on nCeO2 may counteract that effect. Primary normal human lung fibroblasts were treated at occupationally relevant doses with nCeO2 that was either left uncoated or was coated with aSiO2 (amsCeO2). Subsequently, fibroblasts were analyzed for known hallmarks of fibrogenesis, including cell proliferation and collagen production, as well as the formation of fibroblastic nodules. The results of this study are consistent with this hypothesis, as we found that nCeO2 directly induced significant production of collagen I and increased cell proliferation in vitro, while amsCeO2 did not. Furthermore, treatment of fibroblasts with nCeO2, but not amsCeO2, significantly induced the formation of fibroblastic nodules, a clear indicator of fibrogenicity. Such in vitro data is consistent with recent in vivo observations using the same nCeO2 nanoparticles and relevant doses. This effect appeared to be mediated through TGFβ signaling since chemical inhibition of the TGF

  11. Photocatalytic performance of highly amorphous titania-silica aerogels with mesopores: The adverse effect of the in situ adsorption of some organic substrates during photodegradation

    NASA Astrophysics Data System (ADS)

    Lázár, István; Kalmár, József; Peter, Anca; Szilágyi, Anett; Győri, Enikő; Ditrói, Tamás; Fábián, István

    2015-11-01

    Titania-silica composite aerogels with 16-29% Ti-content by the mass were synthesized by the sol-gel method from different Ti-precursors, and calcined at 500 °C. These aerogels are highly amorphous as no crystalline TiO2 phase can be detected in them by X-ray diffraction methods, and show the dominating presence of either mesopores or macropores. The incorporation of Ti into the silica structure is shown by the appearance of characteristic IR transitions of Sisbnd Osbnd Ti vibrations. The characteristic band-gap energies of the different aerogels are estimated to be between 3.6 and 3.9 eV from UV reflection spectra. Band-gap energy decreases with decreasing pore-size. When suspended in solution, even these highly amorphous aerogels accelerate the photodegradation of salicylic acid and methylene blue compared to simple photolysis. Kinetic experiments were conducted under illumination, and also in the dark to study the adsorption of the substrates onto the suspended aerogels. We assume that the fast in situ adsorption of the organic substrates mask the suspended aerogel particles from UV photons, which reduces the rate of photocatalysis. We managed to mathematically separate the parallel processes of photocatalysis and adsorption, and develop a simple kinetic model to describe the reaction system.

  12. Structural, phononic and electronic properties of Ge-doped γ-graphynes: A first-principles study

    NASA Astrophysics Data System (ADS)

    Liu, Junxian; Xin, Zihua; Yan, Xiao; Li, Hui; Yu, M.

    2017-05-01

    Three stable Ge-doped γ-graphyne-like structures have been systematically studied by first principles calculations based on density functional theory (DFT). These analogues were derived by substituting carbon atoms alternately with Ge atoms in the hexatomic ring of γ-graphyne family and referred to as GeC-graphyne, GeC-graphdiyne and GeC-graphyne-3. These novel systems were found to have planar structures with Ge atoms staying at hexagons with sp2-hybridization. Their dynamical stabilities were confirmed from calculated phonon dispersion spectrums, and their electronic band structures show direct band gap semiconducting behaviors with the band gaps of 1.186 eV, 0.967 eV and 0.828 eV, respectively, indicating that Ge-doping can effectively increase the band gap of pristine γ-graphyne family materials.

  13. 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.

  14. Effect of doping on the intersubband absorption in Si- and Ge-doped GaN/AlN heterostructures.

    PubMed

    Ajay, A; Lim, C B; Browne, D A; Polaczyński, J; Bellet-Amalric, E; Bleuse, J; den Hertog, M I; Monroy, E

    2017-10-06

    In this paper, we study band-to-band and intersubband (ISB) characteristics of Si- and Ge-doped GaN/AlN heterostructures (planar and nanowires) structurally designed to absorb in the short-wavelength infrared region, particularly at 1.55 μm. Regarding the band-to-band properties, we discuss the variation of the screening of the internal electric field by free carriers, as a function of the doping density and well/nanodisk size. We observe that nanowire heterostructures consistently present longer photoluminescence decay times than their planar counterparts, which supports the existence of an in-plane piezoelectric field associated to the shear component of the strain tensor in the nanowire geometry. Regarding the ISB characteristics, we report absorption covering 1.45-1.75 μm using Ge-doped quantum wells, with comparable performance to Si-doped planar heterostructures. We also report similar ISB absorption in Si- and Ge-doped nanowire heterostructures indicating that the choice of dopant is not an intrinsic barrier for observing ISB phenomena. The spectral shift of the ISB absorption as a function of the doping concentration due to many body effects confirms that Si and Ge efficiently dope GaN/AlN nanowire heterostructures.

  15. Effect of doping on the intersubband absorption in Si- and Ge-doped GaN/AlN heterostructures

    NASA Astrophysics Data System (ADS)

    Ajay, A.; Lim, C. B.; Browne, D. A.; Polaczyński, J.; Bellet-Amalric, E.; Bleuse, J.; den Hertog, M. I.; Monroy, E.

    2017-10-01

    In this paper, we study band-to-band and intersubband (ISB) characteristics of Si- and Ge-doped GaN/AlN heterostructures (planar and nanowires) structurally designed to absorb in the short-wavelength infrared region, particularly at 1.55 μm. Regarding the band-to-band properties, we discuss the variation of the screening of the internal electric field by free carriers, as a function of the doping density and well/nanodisk size. We observe that nanowire heterostructures consistently present longer photoluminescence decay times than their planar counterparts, which supports the existence of an in-plane piezoelectric field associated to the shear component of the strain tensor in the nanowire geometry. Regarding the ISB characteristics, we report absorption covering 1.45–1.75 μm using Ge-doped quantum wells, with comparable performance to Si-doped planar heterostructures. We also report similar ISB absorption in Si- and Ge-doped nanowire heterostructures indicating that the choice of dopant is not an intrinsic barrier for observing ISB phenomena. The spectral shift of the ISB absorption as a function of the doping concentration due to many body effects confirms that Si and Ge efficiently dope GaN/AlN nanowire heterostructures.

  16. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. 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.

  18. 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.

  19. Exploring the aneugenic and clastogenic potential in the nanosize range: A549 human lung carcinoma cells and amorphous monodisperse silica nanoparticles as models.

    PubMed

    Gonzalez, Laetitia; Thomassen, Leen C J; Plas, Gina; Rabolli, Virginie; Napierska, Dorota; Decordier, Ilse; Roelants, Mathieu; Hoet, Peter H; Kirschhock, Christine E A; Martens, Johan A; Lison, Dominique; Kirsch-Volders, Micheline

    2010-12-01

    We explored how to assess the genotoxic potential of nanosize particles with a well validated assay, the in vitro cytochalasin-B micronucleus assay, detecting both clastogens and aneugens. Monodisperse Stöber amorphous silica nanoparticles (SNPs) of three different sizes (16, 60 and 104 nm) and A549 lung carcinoma cells were selected as models. Cellular uptake of silica was monitored by ICP-MS. At non-cytotoxic doses the smallest particles showed a slightly higher fold induction of micronuclei (MNBN). When considering the three SNPs together, particle number and total surface area appeared to account for MNBN induction as they both correlated significantly with the amplitude of the effect. Using nominal or cellular dose did not show statistically significant differences. Likewise, alkaline comet assay and FISH-centromeric probing of MNBN indicated a weak and not statistically significant induction of oxidative DNA damage, chromosome breakage and chromosome loss. This line of investigation will contribute to adequately design and interpret nanogenotoxicity assays.

  20. 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.

  1. Quantifying Silica Reactivity in Subsurface Environments: An Integrated Experimental Study of Quartz and Amorphous Silica to Establish a Baseline for Glass Durability

    SciTech Connect

    Dove, Patricia

    2003-06-10

    An immediate EM science need is a reliable kinetic model that predicts long-term waste glass performance. A framework for which the kinetics of mineral-solution reactions can be used to interpret complex silicate glass properties is required to accurately describe the current and future behavior of glasses as synthetic monoliths or natural analogs. Reaction rates and mechanisms are essential elements in deciphering mineral/material reactivity trends within a compositional series or across a matrix of complex solution compositions. An essential place to start, and the goal of this research, is to quantify the reactivity of crystalline and amorphous SiO2 phases in the complex fluids of natural systems.

  2. Quantifying Silica Reactivity in Subsurface Environments: An Integrated Experimental Study of Quartz and Amorphous Silica to Establish a Baseline for Glass Durability

    SciTech Connect

    Dove, Patricia M.

    2001-06-15

    An immediate EM science need is a reliable kinetic model that predicts long-term waste glass performance. A framework for which the kinetics of mineral-solution reactions can be used to interpret complex silicate glass properties is required to accurately describe the current and future behavior of glasses as synthetic monoliths or natural analogs. Reaction rates and mechanisms are essential elements in deciphering mineral/material reactivity trends within a compositional series or across a matrix of complex solution compositions. An essential place to start, and the goal of this research, is to quantify the reactivity of crystalline and amorphous SiO2 phases in the complex fluids of natural systems.

  3. Amorphous Silica Particles Relevant in Food Industry Influence Cellular Growth and Associated Signaling Pathways in Human Gastric Carcinoma Cells.

    PubMed

    Wittig, Anja; Gehrke, Helge; Del Favero, Giorgia; Fritz, Eva-Maria; Al-Rawi, Marco; Diabaté, Silvia; Weiss, Carsten; Sami, Haider; Ogris, Manfred; Marko, Doris

    2017-01-13

    Nanostructured silica particles are commonly used in biomedical and biotechnical fields, as well as, in cosmetics and food industry. Thus, their environmental and health impacts are of great interest and effects after oral uptake are only rarely investigated. In the present study, the toxicological effects of commercially available nano-scaled silica with a nominal primary diameter of 12 nm were investigated on the human gastric carcinoma cell line GXF251L. Besides the analysis of cytotoxic and proliferative effects and the comparison with effects of particles with a nominal primary diameter of 200 nm, emphasis was also given to their influence on the cellular epidermal growth factor receptor (EGFR) and mitogen-activated protein kinases (MAPK) signaling pathways-both of them deeply involved in the regulation of cellular processes like cell cycle progression, differentiation or proliferation. The investigated silica nanoparticles (NPs) were found to stimulate cell proliferation as measured by microscopy and the sulforhodamine B assay. In accordance, the nuclear level of the proliferation marker Ki-67 was enhanced in a concentration-dependent manner. At high particle concentrations also necrosis was induced. Finally, silica NPs affected the EGFR and MAPK pathways at various levels dependent on concentration and time. However, classical activation of the EGFR, to be reflected by enhanced levels of phosphorylation, could be excluded as major trigger of the proliferative stimulus. After 45 min of incubation the level of phosphorylated EGFR did not increase, whereas enhanced levels of total EGFR protein were observed. These results indicate interference with the complex homeostasis of the EGFR protein, whereby up to 24 h no impact on the transcription level was detected. In addition, downstream on the level of the MAP kinases ERK1/2 short term incubation appeared to affect total protein levels without clear increase in phosphorylation. Depending on the concentration

  4. Amorphous Silica Particles Relevant in Food Industry Influence Cellular Growth and Associated Signaling Pathways in Human Gastric Carcinoma Cells

    PubMed Central

    Wittig, Anja; Gehrke, Helge; Del Favero, Giorgia; Fritz, Eva-Maria; Al-Rawi, Marco; Diabaté, Silvia; Weiss, Carsten; Sami, Haider; Ogris, Manfred; Marko, Doris

    2017-01-01

    Nanostructured silica particles are commonly used in biomedical and biotechnical fields, as well as, in cosmetics and food industry. Thus, their environmental and health impacts are of great interest and effects after oral uptake are only rarely investigated. In the present study, the toxicological effects of commercially available nano-scaled silica with a nominal primary diameter of 12 nm were investigated on the human gastric carcinoma cell line GXF251L. Besides the analysis of cytotoxic and proliferative effects and the comparison with effects of particles with a nominal primary diameter of 200 nm, emphasis was also given to their influence on the cellular epidermal growth factor receptor (EGFR) and mitogen-activated protein kinases (MAPK) signaling pathways—both of them deeply involved in the regulation of cellular processes like cell cycle progression, differentiation or proliferation. The investigated silica nanoparticles (NPs) were found to stimulate cell proliferation as measured by microscopy and the sulforhodamine B assay. In accordance, the nuclear level of the proliferation marker Ki-67 was enhanced in a concentration-dependent manner. At high particle concentrations also necrosis was induced. Finally, silica NPs affected the EGFR and MAPK pathways at various levels dependent on concentration and time. However, classical activation of the EGFR, to be reflected by enhanced levels of phosphorylation, could be excluded as major trigger of the proliferative stimulus. After 45 min of incubation the level of phosphorylated EGFR did not increase, whereas enhanced levels of total EGFR protein were observed. These results indicate interference with the complex homeostasis of the EGFR protein, whereby up to 24 h no impact on the transcription level was detected. In addition, downstream on the level of the MAP kinases ERK1/2 short term incubation appeared to affect total protein levels without clear increase in phosphorylation. Depending on the concentration

  5. 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.

  6. The role of Al in the formation of secondary Ni precipitates on pyrophyllite, gibbsite, talc, and amorphous silica: a DRS study

    NASA Astrophysics Data System (ADS)

    Scheinost, Andreas C.; Ford, Robert G.; Sparks, Donald L.

    1999-10-01

    Formation of secondary Ni precipitates is an important mechanism of Ni retention in neutral and alkaline clay/water systems. However, the structure and composition of these secondary phases, and their stability is still disputable. Using existing structure refinement data and new ab-initio FEFF 7 calculations we show that Ni-edge X-ray absorption fine structure spectroscopy alone may not be able to unequivocally discriminate four possible candidate compounds: α-Ni(OH)2, the isostructural but Al-substituted layered double hydroxide (Ni-Al LDH), and 1:1 and 2:1 Ni-containing phyllosilicates. Hence, we investigated the potential of diffuse reflectance spectroscopy (DRS) in determining in situ the Ni phase forming in the presence of four sorbents, pyrophyllite, talc, gibbsite, and amorphous silica. The 3A2g → 3T1g(F) band (ν2) of octahedrally coordinated Ni2+ could be reliably extracted from the reflectance spectra of wet pastes. In the presence of the Al-free talc and amorphous silica, the ν2 band was at ≈14,900 cm-1, but shifted to 15,300 cm-1 in the presence of Al-containing pyrophyllite and gibbsite. This shift suggests that Al is dissolved from the sorbent and substitutes for Ni in brucite-like hydroxide layers of the newly forming precipitate phase, causing a decrease of the Ni-O distances and, in turn, an increase of the crystal-field splitting energy. Comparison with Ni model compounds showed that the band at 14,900 cm-1 is a unique fingerprint of α-Ni(OH)2, and the band at 15,300 cm-1 of Ni-Al LDH. Although the complete transformation of α-Ni(OH)2 into a Ni phyllosilicate causes a significant contraction of the Ni hydroxide sheet as indicated by band positions intermediate to those of α-Ni(OH)2 and Ni-Al LDH, incipient states of silication do not influence Ni-O distances and cannot be detected by DRS. The first evidence for the formation of a precipitate was obtained after 5 min (pyrophyllite), 7 hr (talc), 24 hr (gibbsite), and 3 days (amorphous

  7. 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

  8. 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.

  9. Direct formation of thermally stabilized amorphous mesoporous Fe2O3/SiO2 nanocomposites by hydrolysis of aqueous iron III nitrate in sols of spherical silica particles.

    PubMed

    Khalil, Kamal M S; Mahmoud, Hatem A; Ali, Tarek T

    2008-02-05

    Nanocomposite materials containing 10% and 20% iron oxide/silica, Fe2O3/SiO2 (w/w), were prepared by direct hydrolysis of aqueous iron III nitrate solution in sols of freshly prepared spherical silica particles (Stöber particles) present in their mother liquors. This was followed by aging, drying, calcination up to 600 degrees C through two different ramp rates, and then isothermal calcinations at 600 degrees C for 3 h. The calcined and the uncalcined (dried at 120 degrees C) composites were characterized by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), N2 adsorption/desorption techniques, and scanning electron microscopy as required. XRD patterns of the calcined composites showed no line broadening at any d-spacing positions of iron oxide phases, thereby reflecting the amorphous nature of Fe2O3 in the composite. The calcined composites showed nitrogen adsorption isotherms characterizing type IV isotherms with high surface area. Moreover, surface area increased with the increasing of the iron oxide ratio and lowering of the calcination ramp rate. Results indicated that iron oxide particles were dispersed on the exterior of silica particles as isolated and/or aggregated nanoparticles. The formation of the title composite was discussed in terms of the hydrolysis and condensation mechanisms of the inorganic FeIII precursor in the silica sols. Thereby, fast nucleation and limited growth of hydrous iron oxide led to the formation of nanoparticles that spread interactively on the hydroxylated surface of spherical silica particles. Therefore, a nanostructured composite of amorphous nanoparticles of iron oxide (as a shell) spreading on the surface of silica particles (as a core) was formed. This morphology limited the aggregation of Fe2O3 nanoparticles, prevented silica particle coalescence at high temperatures, and enhanced thermal stability.

  10. Advanced treatment technique for swine wastewater using two agents: Thermally polymerized amorphous silica and hydrated lime for color and phosphorus removal and sulfur for nitrogen removal.

    PubMed

    Hasegawa, Teruaki; Kurose, Yohei; Tanaka, Yasuo

    2017-04-12

    The efficacy of advanced treatment of swine wastewater using thermally polymerized, modified amorphous silica and hydrated lime (M-CSH-lime) for color and phosphorus removal and sulfur for nitrogen removal was examined with a demonstration-scale treatment plant. The color removal rate was approximately 78% at M-CSH-lime addition rates of > 0.055 wt/v%. The PO43--P removal rate exceeded 99.9% with > 0.023 wt/v%. pH of the effluent from the M-CSH-lime reactor increased with the addition rate till a maximum value of 12.7, which was effective in disinfection. The recovered M-CSH-lime would be suitable as a phosphorus fertilizer because the total P2 O5 content was approximately 10%. The nitrogen oxide (NOx-N) removal rate by sulfur denitrification increased to approximately 80% when the NOx-N loading rate was around 0.1 kg-N/ton-S/day. It was suggested that the combination of the two processes would be effective in the advanced treatment of swine wastewater.

  11. Importance of agglomeration state and exposure conditions for uptake and pro-inflammatory responses to amorphous silica nanoparticles in bronchial epithelial cells.

    PubMed

    Gualtieri, Maurizio; Skuland, Tonje; Iversen, Tore-Geir; Låg, Marit; Schwarze, Per; Bilaničová, Dagmar; Pojana, Giulio; Refsnes, Magne

    2012-11-01

    Amorphous silica nanoparticles (SiNPs, 30 and 50 nm) and rhodamine-coated SiNPs (50 nm) were examined for their ability to induce pro-inflammatory responses and cytotoxicity in BEAS-2B cells under different experimental conditions. The SiNPs formed micrometre-sized agglomerates in the absence of bovine serum albumin (BSA) in the culture medium, whereas with BSA (0.1%) they were much less agglomerated. All the SiNPs induced IL-6 and IL-8 responses, as measured by ELISA and real-time PCR. The responses were more marked without BSA and higher for the rhodamine SiNPs than the plain ones. Rhodamine SiNPs were not taken up by cells during a 3-h exposure, even though cytokine mRNAs were up-regulated. In conclusion, agglomerated SiNPs induced more potent cytokine responses than the non-agglomerated ones; either due to the agglomeration state per se or more conceivably to a change in surface reactivity against cellular targets due to BSA. Furthermore, cytokine expression was up-regulated independently of SiNP uptake.

  12. Co-assessment of cell cycle and micronucleus frequencies demonstrates the influence of serum on the in vitro genotoxic response to amorphous monodisperse silica nanoparticles of varying sizes.

    PubMed

    Gonzalez, Laetitia; Lukamowicz-Rajska, Magdalena; Thomassen, Leen C J; Kirschhock, Christine E A; Leyns, Luc; Lison, Dominique; Martens, Johan A; Elhajouji, Azeddine; Kirsch-Volders, Micheline

    2014-12-01

    Serum proteins have been shown to modulate the cytotoxic and genotoxic responses to nanomaterials. The aim was to investigate the influence of serum on the induction of micronuclei (MN) by nanoparticles (NPs) of different sizes. Therefore, A549 human lung carcinoma cells and amorphous monodisperse silica nanoparticles (SNPs) were used as models. Assessment of the cell viability, cell cycle changes and induction of MN by SNPs ranging from 12 to 174 nm was performed in presence or absence of serum, applying the in vitro flow cytometry-based MN assay. Here, it has been demonstrated that serum has an influence on these end points, with a lower cell viability in absence of serum compared with the presence of serum. Further, cell cycle changes, specifically, G1 and S-phase arrest, were observed in absence of serum for four out of six SNPs tested. A size-dependent MN induction was observed: larger SNPs being more active in absence of serum. In addition, the serum influence was characterised by a size-dependency for cytotoxic and genotoxic effects, with a higher influence of serum for smaller particles. The data indicate that the in vitro micronucleus assay in presence and absence of serum could be advised for hazard assessment because it demonstrates a higher sensitivity in serum-free conditions than in conditions with serum. However, this recommendation applies only if the cell line used is able to proliferate under serum-free conditions because cell division is a prerequisite for MN expression.

  13. 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.

  14. Ge doping of β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ahmadi, Elaheh; Koksaldi, Onur S.; Kaun, Stephen W.; Oshima, Yuichi; Short, Dane B.; Mishra, Umesh K.; Speck, James S.

    2017-04-01

    The Ge doping of β-Ga2O3(010) films was investigated using plasma-assisted molecular beam epitaxy as the growth method. The dependences of the amount of Ge incorporated on the substrate temperature, Ge-cell temperature, and growth regime were studied by secondary ion mass spectrometry. The electron concentration and mobility were investigated using Van der Pauw Hall patterns. Hall measurement confirmed that Ge acts as an n-dopant in β-Ga2O3(010) films. These results were compared with similar films doped by Sn. The Hall data showed an improved electron mobility for the same electron concentration when Ge is used instead of Sn as the dopant.

  15. Mass extinction spectra and size distribution measurements of quartz and amorphous silica aerosol at 0.33-19 μm compared to modelled extinction using Mie, CDE, and T-matrix theories

    NASA Astrophysics Data System (ADS)

    Reed, Benjamin E.; Peters, Daniel M.; McPheat, Robert; Smith, Andrew J. A.; Grainger, R. G.

    2017-09-01

    Simultaneous measurements were made of the spectral extinction (from 0.33-19 μm) and particle size distribution of silica aerosol dispersed in nitrogen gas. Two optical systems were used to measure the extinction spectra over a wide spectral range: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter. The measurements were applied to one amorphous and two crsystalline silica (quartz) samples. In the infrared peak values of the mass extinction coefficient (MEC) of the crystalline samples were 1.63 ± 0.23 m2g-1 at 9.06 μm and 1.53 ± 0.26 m2g-1 at 9.14 μm with corresponding effective radii of 0.267 and 0.331 μm, respectively. For the amorphous sample the peak MEC value was 1.37 ± 0.18 m2g-1 at 8.98 μm and the effective radius of the particles was 0.374 μm. Using the measured size distribution and literature values of the complex refractive index as inputs, three scattering models were evaluated for modelling the extinction: Mie theory, the Rayleigh continuous distribution of ellipsoids (CDE) model, and T-matrix modelling of a distribution of spheroids. Mie theory provided poor fits to the infrared extinction of quartz (R2 < 0.19), although the discrepancies were significantly lower for Mie theory and the amorphous silica sample (R2 = 0.86). The CDE model provided improved fits in the infrared compared to Mie theory, with R2 > 0.82 for crsytalline sillica and R2 = 0.98 for amorphous silica. The T-matrix approach was able to fit the amorphous infrared extinction data with an R2 value of 0.995. Allowing for the possibility of reduced crystallinity in the milled crystal samples, using a mixture of amorphous and crystalline T-matrix cross-sections provided fits with R2 values greater than 0.97 for the infrared extinction of the crystalline samples.

  16. 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

  17. Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces

    NASA Astrophysics Data System (ADS)

    Nelson, Joey; Wasylenki, Laura; Bargar, John R.; Brown, Gordon E.; Maher, Kate

    2017-10-01

    Metal ion-mineral surface interactions and the attendant isotopic fractionation depend on the properties of the mineral surface and the local atomic-level chemical environment. However, these factors have not been systematically examined for phases of the same composition with different levels of surface disorder. We present pH-dependent adsorption edges, X-ray absorption spectra, and isotopic measurements to illustrate the effects of surface structural disorder and surface coverage on zinc(II) (Zn(II)) surface complexation and isotope fractionation. Our results demonstrate that Zn(II) surface complexes on quartz and amorphous silica (SiO2(am)) transition from octahedral to tetrahedral coordination by oxygen as surface coverage increases. In low ionic strength solutions (I = 0.004 M) and at low surface loadings (Γ < 0.6 μmol m-2), Zn(II) adsorbs to the quartz surface predominantly as outer-sphere octahedral complexes (RZn-O = 2.05 Å) with no significant isotopic fractionation (Δ66/64Znaqueous-sorbed = -0.01 ± 0.06‰) from aqueous Zn(II). In contrast, under similar chemical conditions and surface loading, outer-sphere Zn(II) adsorption complexes are not observed on SiO2(am) surfaces. At high ionic strength (I = 0.1 M) and low surface loading (Γ < 0.2 μmol m-2), inner-sphere, monodentate octahedral Zn(II) complexes (RZn-O = 2.05-2.07 Å) are observed on both quartz and SiO2(am) surfaces. At the same ionic strength (I = 0.1 M) and higher surface loading (Γ = 0.6-1.4 μmol m-2), Zn(II) forms inner-sphere, monodentate tetrahedral complexes (RZn-O = 1.98 Å) at the quartz surface. On the SiO2(am) surface under similar chemical conditions and surface loading, Zn(II) forms dominantly inner-sphere, monodentate tetrahedral complexes with shorter Znsbnd O bond distances (RZn-O = 1.94 Å). Despite different coordination numbers, the measured equilibrium isotope fractionation factors for inner-sphere octahedral and tetrahedral complexes versus dissolved Zn, under the

  18. 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.

  19. 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.

  20. Study of point defects in as-drawn and irradiated Ge-doped optical fibers using cathodoluminescence

    NASA Astrophysics Data System (ADS)

    Reghioua, I.; Girard, S.; Alessi, A.; Di Francesca, D.; Marin, E.; Morana, A.; Fanetti, M.; Martin-Samos, L.; Richard, N.; Raine, M.; Valant, M.; Boukenter, A.; Ouerdane, Y.

    2017-02-01

    In the present paper, we report an experimental investigation of Ge-doped Optical Fibers (OFs) which were investigated by Cathodoluminescence (CL) measurements. We followed the evolution, under 10 keV electron exposure, of the emissions present in three different samples: the first one was the as-drawn fiber (pristine), the second one was irradiated with a CW UV laser at 244 nm and the last one was irradiated at the dose of 9 MGy (SiO2) by γ-rays. Moreover, taking advantage of the employed experimental set-up, which allows to perform spatially-resolved (<1μm) CL measures, we were able to investigate the emission evolution in two differently doped zones of the fiber. Our data indicate that (i) the CL spectra of our three samples are dominated by the 400 nm emission band related to the Germanium Lone Pair Center (GLPC), (ii) the spatial distribution of this defect differs in the three fibers and (iii) the electron exposure decreases the GLPC concentration in all samples (pristine, UV and γ irradiated). A comparison between the CL and photoluminescence (PL) measurements shows comparable results.

  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. Microstructure and conduction behavior of BiFeO3 thin film deposited on Ge-doped ZnO

    NASA Astrophysics Data System (ADS)

    Raghavan, Chinnambedu Murugesan; Choi, Ji Ya; Kim, Sang Su

    2017-02-01

    BiFeO3 (BFO) thin films were deposited on a Ge-doped ZnO (GZO)/Si(100) and a Pt(111)/Ti/SiO2/Si(100) using a pulsed laser deposition technique. An improved crystal growth property was observed for the BFO thin film deposited on the GZO/Si(100). The BFO thin film, which was deposited on the (00 l) textured GZO/Si(100), exhibited preferred ( l00) orientated grains, while randomly orientated grains were observed for the thin film deposited on the Pt(111)/Ti/SiO2/Si(100). When compared with the Pt/BFO/Pt capacitor, the GZO/BFO/GZO capacitor exhibited improved conduction behaviors, such as a low leakage current density and high stability against electrical breakdown. From the J-E curves, conduction of the GZO/BFO/GZO and the Pt/BFO/Pt capacitors was found to be dominated by Ohmic and space charge limited conductions at low and high electric field, respectively.

  3. A density functional theory investigation on amantadine drug interaction with pristine and B, Al, Si, Ga, Ge doped C60 fullerenes

    NASA Astrophysics Data System (ADS)

    Parlak, Cemal; Alver, Özgür

    2017-06-01

    Amantadine is a well-known drug for its treatment effect on Parkinson's disease and influenza infection or hepatitis. Heteroatom doped fullerenes have been extensively examined for their possible usage in sensor technology and medical applications as drug delivery vehicles. In this research, pristine and B, Al, Si, Ga, Ge doped C60 fullerenes and their interaction with amantadine drug molecule were investigated based on the density functional theory calculations. Findings suggest that doped C60 fullerenes might be used to detect the presence of amantadine and they might be used as drug delivery vehicles because of their moderately high adsorption energies with amantadine.

  4. 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.

  5. A study of the alumina-silica gel adsorbent for the removal of silicic acid from geothermal water: increase in adsorption capacity of the adsorbent due to formation of amorphous aluminosilicate by adsorption of silicic acid.

    PubMed

    Yokoyama, Takushi; Ueda, Akira; Kato, Koichi; Mogi, Katsumi; Matsuo, Shorin

    2002-08-01

    Two kinds of adsorbents (Si adsorbent and Al adsorbent) for the removal of silicic acid from geothermal water to retard the formation of silica scales were prepared using silicic acid contained in geothermal water. The Si adsorbent was prepared by evaporating geothermal water, and the Al adsorbent was prepared by evaporating geothermal water after the addition of aluminum chloride. The specific surface area of the Si adsorbent was small and it's adsorption capacity of silicic acid was low. Although the specific surface area of the Al adsorbent was also small, it was significantly increased by the adsorption of silicic acid and it's adsorption capacity was high. Based on the change in the local structure of aluminum ion by the adsorption of silicic acid, the Al adsorbent was considered to be silica particles covered with crystalline aluminum hydroxide. Moreover, it was concluded that the increase in the specific surface area of the Al adsorbent and the decrease in the zeta potential were due to the formation of an amorphous aluminosilicate with a large surface area and a negative charge (one 4-coordinated Al) by the reaction between aluminum ions and silicic acids.

  6. 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.

  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.

  8. IR studies of the impact of Ge doping on the successive conversion of VO{sub n} defects in Czochralski-Si containing carbon

    SciTech Connect

    Londos, C. A.; Andrianakis, A.; Sgourou, E. N.; Emtsev, V. V.; Ohyama, H.

    2011-02-01

    We report infrared absorption studies of oxygen-related defects in electron-irradiated Ge-doped Czochralski-Si. Our investigation was mainly focused on the reaction channel leading to the formation of VO{sub n} (1{<=}n{<=}6) defects. The VO{sub n} defects form mainly upon annealing, as a result of the successive aggregation of oxygen atoms in the initial VO defect produced by the irradiation: (VO+O{sub i}{yields}VO{sub 2}+O{sub i}{yields}VO{sub 3}+O{sub i}{yields}VO{sub 4},...). It was found that the ratio of the conversion of VO{sub n} to VO{sub n+1} defects is sensitive to the Ge content of the material. In particular, the ratio of the conversion of the VO to the VO{sub 2} defects was found to decrease with the increase in Ge concentration of the samples, although the opposite trend was observed for the VO{sub 3} to VO{sub 4} conversion. However, the VO{sub 2} to VO{sub 3} conversion changes only slightly with Ge content, being practically unaffected for Ge concentrations up to 2x10{sup 20} cm{sup -3}. In the case of VO{sub 2} formation, the phenomenon was attributed to the elastic strains induced in the lattice due to the Ge presence which affects the balance between the reactions VO+O{sub i}{yields}VO{sub 2}, VO+Si{sub I}{yields}O{sub i}, mainly involved in the decay of the VO and the growth of the VO{sub 2} defects. In the case of VO{sub 4} formation, the phenomenon was discussed by taking into account the enhancement of the diffusivity of the O{sub i} atoms in the Ge-doped Si, which could lead to an enhancement of the rate of the reaction VO{sub 3}+O{sub i}{yields}VO{sub 4}. For the VO{sub 3} formation this effect is practically negligible due to the fact that at the temperatures of VO{sub 2} to VO{sub 3} conversion oxygen diffusivity is quite small. The exhibited behavior in the conversion of the VO{sub n} to VO{sub n+1} defects (n=1,2,3) was similar in Ge-doped samples with low carbon content ([C{sub s}]<2x10{sup 16} cm{sup -3}) and in Ge-doped samples with

  9. New approach for the determination of aerosol refractive indices - Part II: Experimental set-up and application to amorphous silica particles

    NASA Astrophysics Data System (ADS)

    Hubert, P.; Herbin, H.; Visez, N.; Pujol, O.; Petitprez, D.

    2017-10-01

    This article is the Part II of a work aimed at proposing a new method for determining the optical constants of aerosols. The Part I detailed the theoretical and numerical basis of an algorithm devoted to retrieve the imaginary and the real part of complex refractive indices from extinction spectra of aerosols. This algorithm associates the Mie theory, the single subtractive Kramers-Kronig relation, and an optimal estimation method in an iterative process. This Part II presents the experimental set-up developed to record simultaneously high spectral resolution extinction spectra and size distributions of airborne silica particles. Extinction spectra are measured with a high spectral resolution on a broad spectral range, including both infrared (650 - 2 , 500cm-1) and UV-visible (9 , 000 - 32 , 500cm-1) spectral regions. Experimental data were used to retrieve the complex refractive indices of aerosol particles. By associating the numerical procedure presented in the first paper and this experimental set-up, complex refractive indices of silica spherical aerosol particles have been determined under controlled experimental conditions. Additional comparison between experimental and simulated extinction spectra from retrieved complex refractive indices shows that this new methodology provides optical properties representative of the material.

  10. FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Design and Fabrication of an Er-Doped Silica Optical Fiber with Six Photosensitive Subcores

    NASA Astrophysics Data System (ADS)

    Li, Jian; Wang, Jing; Liu, Peng; Lu, Shao-Hua; Mao, Xiang-Qiao; Jiang, Wei-Wei; Ning, Ti-Gang; Jian, Shui-Sheng

    2009-07-01

    A type of multi-core Er-doped photosensitive silica optical fiber (MC-EDPF) is proposed and fabricated, in which a high consistency Er-doped core is surrounded by six high consistency Ge-doped cores. The multi-core design can overcome the difficulties encountered in the design and fabrication of single-core EDPFs through a modified chemical vapor deposition method combined with solution doping technology, and there is a conflict between high consistency Er doping and high consistency Ge doping. The absorption of MC-EDPFs achieved 15.876 dB/m at 1550nm and 10 dB/m at 980nm. The reflectivity of the fiber Bragg gratings (FBGs) written directly on the MC-EDPFs is as much as 96.84%.

  11. Difference in the behavior of oxygen deficient defects in Ge-doped silica optical fiber preforms under ArF and KrF excimer laser irradiation

    NASA Astrophysics Data System (ADS)

    Essid, M.; Brebner, J. L.; Albert, J.; Awazu, K.

    1998-10-01

    Photobleaching of optical absorption bands in the 5 eV region and the creation of others at higher and lower energy have been examined in the case of ArF (6.4 eV) and KrF (5 eV) excimer laser irradiation of 3GeO2:97SiO2 glasses. We report a difference in the transformation process of the neutral oxygen monovacancy and also of the germanium lone pair center (GLPC) into electron trap centers associated with fourfold coordinated Ge ions and Ge-E' centers when we use one or the other laser. Correlations between absorption bands and electron spin resonance signals were made after different steps of laser irradiation. It was found that the KrF laser generates twice as many Ge-E' centers as the ArF laser for the same dose of energy delivered. The main reason for this difference is found to be the more efficient bleaching of the GLPC (5.14 eV) by the KrF laser compared to that by the ArF laser.

  12. 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.

  13. The investigations of nanoclusters and micron-sized periodic structures created at the surface of the crystal and amorphous silica by resonant CO2 laser irradiation

    NASA Astrophysics Data System (ADS)

    Mukhamedgalieva, A. F.; Bondar, A. M.; Svedov, I. M.; Kononov, M. A.; Laptev, V. B.; Novikova, N. N.

    2016-12-01

    The creation of nanoclasters and micrometer sized periodical structures at the surface of silica (crystal quartz and fused quartz) by action of pulsed CO2 laser radiation (pulse energy of 1 J, pulse time of 70 ns) have been investigated. The laser action on the surface of samples lead to appearance of two kind of structures - periodical micron-sized structures with the period length close to wave length of CO2 laser irradiation and nanoclusters with size close to 50-100 nanometers. This creation connects with the intensive ablation of matter at the maxima of standing waves which are a results of the interference of falling and surfaces waves. This connects with the resonant absorption of infrared laser radiation by silicate minerals.

  14. Co-exposure to amorphous silica nanoparticles and benzo[a]pyrene at low level in human bronchial epithelial BEAS-2B cells.

    PubMed

    Wu, Jing; Shi, Yanfeng; Asweto, Collins Otieno; Feng, Lin; Yang, Xiaozhe; Zhang, Yannan; Hu, Hejing; Duan, Junchao; Sun, Zhiwei

    2016-11-01

    Both ultrafine particles (UFP) and polycyclic aromatic hydrocarbons (PAHs) are widely present in the environment, thus increasing their chances of exposure to human in the daily life. However, the study on the combined toxicity of UFP and PAHs on respiratory system is still limited. In this study, we examined the potential interactive effects of silica nanoparticles (SiNPs) and benzo[a]pyrene (B[a]P) in bronchial epithelial cells (BEAS-2B). Cells were exposed to SiNPs and B[a]P alone or in combination for 24 h. Co-exposure to SiNPs and B[a]P enhanced the malondialdehyde (MDA) contents and reduced superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities significantly, while the reactive oxygen species (ROS) generation had a slight increase in the exposed groups compared to the control but not statistically significant. Cell cycle arrest induced by the co-exposure showed a significant percentage increase in G2/M phase cells and a decrease in G0/G1 phase cells. In addition, there was a significant increase in BEAS-2B cells multinucleation as well as DNA damage. Cellular apoptosis was markedly increased even at the low-level co-exposure. Our results suggest that co-exposure to SiNPs and B[a]P exerts synergistic and additive cytotoxic and genotoxic effects.

  15. 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.

  16. Temperature-induced amorphization of SiO[sub 2] stishovite

    SciTech Connect

    Grimsditch, M. ); Popova, S. Institute of High Pressure Physics, 142092 Troick Moscow Region ); Brazhkin, V.V.; Voloshin, R.N. )

    1994-11-01

    A Raman-scattering investigation of stishovite, a high-pressure crystalline polymorph of SiO[sub 2], shows that at around 650 [degree]C it becomes amorphous. The amorphous material produced during the initial stages of amorphization is not identical to ordinary silica since it exhibits features of the high-pressure amorphous polymorph. Above 800 [degree]C there is little remaining evidence of stishovite but the amorphous material has transformed to a state indistinguishable from that of silica. Annealing effects in densified silica are also presented and compared with the stishovite results.

  17. Ultrafast crystallization and thermal stability of In-Ge doped eutectic Sb{sub 70}Te{sub 30} phase change material

    SciTech Connect

    Lee Meiling; Miao Xiangshui; Ting Leehou; Shi Luping

    2008-02-15

    Effect of In and Ge doping in the form of In{sub 2}Ge{sub 8}Sb{sub 85}Te{sub 5} on optical and thermal properties of eutectic Sb{sub 70}Te{sub 30} alloys was investigated. Crystalline structure of In{sub 2}Ge{sub 8}Sb{sub 85}Te{sub 5} phase change material consists of a mixture of phases. Thermal analysis shows higher crystallization temperature and activation energy for crystallization. Isothermal reflectivity-time measurement shows a growth-dominated crystallization mechanism. Ultrafast crystallization speed of 30 ns is realized upon irradiation by blue laser beam. The use of ultrafast and thermally stable In{sub 2}Ge{sub 8}Sb{sub 85}Te{sub 5} phase change material as mask layer in aperture-type super-resolution near-field phase change disk is realized to increase the carrier-to-noise ratio and thermal stability.

  18. P-doped carbon nanotube and Ge-doped boron nitride nanotube as a real catalysts for N2O + SiO reaction: DFT examination

    NASA Astrophysics Data System (ADS)

    Najafi, Meysam

    2017-10-01

    The mechanisms of N2O reduction via SiO on surfaces of P-doped carbon nanotube (CNT) and Si-doped boron nitride nanotube (BNNT) by density functional theory were investigated. The P and Si adsorption energies on surfaces of CNT and BNNT were calculated to be -314.6 and -347.2 kcal/mol, respectively. The decomposition of CNT-P-N2O and BNNT-Ge-N2O and reduction of CNT-P-O* and BNNT-Ge-O* by SiO molecule were investigated. The BNNT-Ge-O* has lower activation energy and more negative ΔGad rather than CNT-P-O* and therefore the process of BNNT-Ge-O* + SiO → BNNT-Ge + SiO2 was spontaneous more than CNT-P-O* + SiO → CNT-P + SiO2 from thermodynamic view point. Results show that activation energy for BNNT-Ge-O* + N2O → BNNT-Ge-O2 + N2 and CNT-P-O* + N2O → CNT-P-O2 + N2 reactions were 27.89 and 31.56 kcal/mol, respectively. The results show that P-doped CNT and Ge-doped BNNT can be observed as a real catalyst for the reduction of N2O.

  19. Wavelength tunable long period gratings based on silica waveguide geometric modulation

    NASA Astrophysics Data System (ADS)

    Jiang, Jia; Callender, Claire L.; Ledderhof, Christopher J.; Ding, Jianfu

    2011-03-01

    This paper presents planar long period grating (LPG) devices based on a periodic thickness variation in the waveguide core, fabricated by etching into the lower cladding layer prior to definition of the waveguide layer. This periodic geometric change results in a stable grating structure and a permanent refractive index modulation of 10-4 or higher, which is comparable to the index modulation in Ge-doped silica material induced by photo irradiation techniques widely used in fiber grating fabrication. This grating produces a strong resonance at a particular wavelength in the transmission spectrum, enabling a range of applications from wavelength filtering to signal distribution in communication networks. In this work, a polymer and silica hybrid architecture has been implemented in order to achieve wavelength tunability. Using a thermally oxidized silicon layer as a lower cladding, a Ge-doped silica ridge is patterned using conventional photolithography and reactive ion etching to form the waveguide core, which is then covered with a low index fluorinated polymer cladding. While the silica waveguides offer a lower propagation loss and an easy processability, the top polymer allows the device to be thermally tuned over a wide wavelength range by exploiting the opposite thermo-optic coefficient between fluorinated polymer and silica, and the high sensitivity of the underlying LPG to the refractive index of the cladding layer. Strong rejection bands have been demonstrated in the C+L band, in good agreement with theoretical calculations. Corrugated structures have been defined across an extended area under multiple waveguides resulting in coupling of light from the fundamental mode into cladding modes and back into the neighboring waveguides located far from the evanescent coupling distance. This kind of coupler can facilitate devices that require extraction and control of a particular waveguide mode for applications such as multiple channel signal distribution and

  20. 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.

  1. Ice sheets as a missing source of silica to the polar oceans

    NASA Astrophysics Data System (ADS)

    Hawkings, Jon R.; Wadham, Jemma L.; Benning, Liane G.; Hendry, Katharine R.; Tranter, Martyn; Tedstone, Andrew; Nienow, Peter; Raiswell, Rob

    2017-01-01

    Ice sheets play a more important role in the global silicon cycle than previously appreciated. Input of dissolved and amorphous particulate silica into natural waters stimulates the growth of diatoms. Here we measure dissolved and amorphous silica in Greenland Ice Sheet meltwaters and icebergs, demonstrating the potential for high ice sheet export. Our dissolved and amorphous silica flux is 0.20 (0.06-0.79) Tmol year-1, ~50% of the input from Arctic rivers. Amorphous silica comprises >95% of this flux and is highly soluble in sea water, as indicated by a significant increase in dissolved silica across a fjord salinity gradient. Retreating palaeo ice sheets were therefore likely responsible for high dissolved and amorphous silica fluxes into the ocean during the last deglaciation, reaching values of ~5.5 Tmol year-1, similar to the estimated export from palaeo rivers. These elevated silica fluxes may explain high diatom productivity observed during the last glacial-interglacial period.

  2. The world ocean silica cycle.

    PubMed

    Tréguer, Paul J; De La Rocha, Christina L

    2013-01-01

    Over the past few decades, we have realized that the silica cycle is strongly intertwined with other major biogeochemical cycles, like those of carbon and nitrogen, and as such is intimately related to marine primary production, the efficiency of carbon export to the deep sea, and the inventory of carbon dioxide in the atmosphere. For nearly 20 years, the marine silica budget compiled by Tréguer et al. (1995) , with its exploration of reservoirs, processes, sources, and sinks in the silica cycle, has provided context and information fundamental to study of the silica cycle. Today, the budget needs revisiting to incorporate advances that have notably changed estimates of river and groundwater inputs to the ocean of dissolved silicon and easily dissolvable amorphous silica, inputs from the dissolution of terrestrial lithogenic silica in ocean margin sediments, reverse weathering removal fluxes, and outputs of biogenic silica (especially on ocean margins and in the form of nondiatomaceous biogenic silica). The resulting budget recognizes significantly higher input and output fluxes and notes that the recycling of silicon occurs mostly at the sediment-water interface and not during the sinking of silica particles through deep waters.

  3. 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

  4. Photoluminescence decay dynamics of transparent silica glass prepared from nanometer-sized silica particles

    SciTech Connect

    Yamada, Tomoko; Uchino, Takashi

    2005-08-22

    The time-resolved photoluminescence (PL) decays are measured for transparent amorphous silica prepared from solid-phase sintering of nanometer-sized silica particles, which has recently been shown to exhibit a unique white PL emission under ultraviolet excitation [T. Uchino and T. Yamada, Appl. Phys. Lett. 85, 1164 (2004)]. Unlike usual PL processes observed in normal silica glass, it is shown that the present PL results from trapping-controlled migration of photoexcited carriers and their radiative recombination.

  5. Photoluminescence decay dynamics of transparent silica glass prepared from nanometer-sized silica particles

    NASA Astrophysics Data System (ADS)

    Yamada, Tomoko; Uchino, Takashi

    2005-08-01

    The time-resolved photoluminescence (PL) decays are measured for transparent amorphous silica prepared from solid-phase sintering of nanometer-sized silica particles, which has recently been shown to exhibit a unique white PL emission under ultraviolet excitation [T. Uchino and T. Yamada, Appl. Phys. Lett. 85, 1164 (2004)]. Unlike usual PL processes observed in normal silica glass, it is shown that the present PL results from trapping-controlled migration of photoexcited carriers and their radiative recombination.

  6. Potential of silica bodies (phytoliths) for nanotechnology.

    PubMed

    Neethirajan, Suresh; Gordon, Richard; Wang, Lijun

    2009-08-01

    Many plant systems accumulate silica in solid form, creating intracellular or extracellular silica bodies (phytoliths) that are essential for growth, mechanical strength, rigidity, predator and fungal defence, stiffness and cooling. Silica is an inorganic amorphous oxide formed by polymerization processes within plants. There has been much research to gain new insights into its biochemistry and to mimic biosilicification. We review the background on plant silica bodies, silica uptake mechanisms and applications, and suggest possible ways of producing plant silica bodies with new functions. Silica bodies offer complementary properties to diatoms for nanotechnology, including large-scale availability from crop wastes, lack of organic impurities (in some), microencapsulation and microcrystalline quartz with possibly unique optical properties.

  7. 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.

  8. 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(P5+, As5+)/ri(Ge4+)<1 and ri(Sb5+, Bi5+)/ri(Ge4+)>1, respectively. In passing from P to As impurity atoms the activation energy ΔEe 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, Δr‧s=r‧s(As)-r‧s(P)≈0.029 a.u. On the contrary, in passing from Sb to Bi impurity atoms, ΔEe value is decreased by (-0.028 eV) whereas the electron density parameter rises by Δr‧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 As5+ and Ge4+ 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 studied.

  9. Differences in both matrix metalloproteinase 9 concentration and zymographic profile between plasma and serum with clot activators are due to the presence of amorphous silica or silicate salts in blood collection devices.

    PubMed

    Mannello, Ferdinando; Tanus-Santos, Jose E; Meschiari, Cesar A; Tonti, Gaetana A

    2008-03-01

    Matrix metalloproteinases (MMPs) are promising diagnostic tools, and blood sampling/handling alters MMP concentrations between plasma and serum and between serum with and without clot activators. To explain the higher MMP-9 expression in serum collected with clot accelerators relative to serum with no additives and to plasma, we analyzed the effects of increasing amounts of silica and silicates (components of clot activators) in citrate plasma, serum, and buffy coats collected in both plastic and glass tubes from 50 healthy donors, and we analyzed the effects of silica and silicate on cultured leukemia cells. The levels of MMP-2 did not show significant changes between glass and plastic tubes, between serum and plasma, between serum with and without clot accelerators, or between silica and silicate treatments. No modification of MMP-9 expression was obtained by the addition of silica or silicate to previously separated plasma and serum. Increasing the amounts of nonsoluble silica and soluble silicate added to citrate and empty tubes prior to blood collection resulted in increasing levels of MMP-9 relative to citrate plasma and serum. Silica and silicate added to buffy coats and leukemia cells significantly induced MMP-9 release/secretion, demonstrating that both silica and silicate induce the release of pro- and complexed MMP-9 forms. We recommend limiting the misuse of serum and avoiding the interfering effects of clot activators.

  10. Evolution of the structure of amorphous ice: from low-density amorphous through high-density amorphous to very high-density amorphous ice.

    PubMed

    Martonák, R; Donadio, D; Parrinello, M

    2005-04-01

    We report results of molecular dynamics simulations of amorphous ice for pressures up to 22.5 kbar. The high-density amorphous ice (HDA) as prepared by pressure-induced amorphization of I(h) ice at T=80 K is annealed to T=170 K at various pressures to allow for relaxation. Upon increase of pressure, relaxed amorphous ice undergoes a pronounced change of structure, ranging from the low-density amorphous ice at p=0, through a continuum of HDA states to the limiting very high-density amorphous ice (VHDA) regime above 10 kbar. The main part of the overall structural change takes place within the HDA megabasin, which includes a variety of structures with quite different local and medium-range order as well as network topology and spans a broad range of densities. The VHDA represents the limit to densification by adapting the hydrogen-bonded network topology, without creating interpenetrating networks. The connection between structure and metastability of various forms upon decompression and heating is studied and discussed. We also discuss the analogy with amorphous and crystalline silica. Finally, some conclusions concerning the relation between amorphous ice and supercooled water are drawn.

  11. 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

  12. Silica Lubrication in Faults (Invited)

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Silica-rich rocks are common in the crust, so silica lubrication may be important for causing fault weakening during earthquakes if the phenomenon occurs in nature. In laboratory friction experiments on chert, dramatic shear weakening has been attributed to amorphization and attraction of water from atmospheric humidity to form a 'silica gel'. Few observations of the slip surfaces have been reported, and the details of weakening mechanism(s) remain enigmatic. Therefore, no criteria exist on which to make comparisons of experimental materials to natural faults. We performed a series of friction experiments, characterized the materials formed on the sliding surface, and compared these to a geological fault in the same rock type. Experiments were performed in the presence of room humidity at 2.5 MPa normal stress with 3 and 30 m total displacement for a variety of slip rates (10-4 - 10-1 m/s). The friction coefficient (μ) reduced from >0.6 to ~0.2 at 10-1 m/s, but only fell to ~0.4 at 10-2 - 10-4 m/s. The slip surfaces and wear material were observed using laser confocal Raman microscopy, electron microprobe, X-ray diffraction, and transmission electron microscopy. Experiments at 10-1 m/s formed wear material consisting of ≤1 μm powder that is aggregated into irregular 5-20 μm clumps. Some material disaggregated during analysis with electron beams and lasers, suggesting hydrous and unstable components. Compressed powder forms smooth pavements on the surface in which grains are not visible (if present, they are <100 nm). Powder contains amorphous material and as yet unidentified crystalline and non-crystalline forms of silica (not quartz), while the worn chert surface underneath shows Raman spectra consistent with a mixture of quartz and amorphous material. If silica amorphization facilitates shear weakening in natural faults, similar wear materials should be formed, and we may be able to identify them through microstructural studies. However, the sub

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

    PubMed

    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

    2014-10-09

    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.

  14. 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

  15. Precipitated silica as flow regulator.

    PubMed

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

    2008-08-07

    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.

  16. Developments in production of silica-based thermoluminescence dosimeters

    NASA Astrophysics Data System (ADS)

    Bradley, D. A.; Siti Shafiqah, A. S.; Siti Rozaila, Z.; Sabtu, Siti Norbaini; Abdul Sani, S. F.; Alanazi, Abdulaziz H.; Jafari, S. M.; Amouzad Mahdiraji, G.; Mahamd Adikan, F. R.; Maah, M. J.; Nisbet, A. N.; Tamchek, N.; Abdul Rashid, H. A.; Alkhorayef, M.; Alzimami, K.

    2017-08-01

    This work addresses purpose-made thermoluminescence dosimeters (TLD) based on doped silica fibres and sol-gel nanoparticles, produced via Modified Chemical Vapour Deposition (MCVD) and wet chemistry techniques respectively. These seek to improve upon the versatility offered by conventional phosphor-based TLD forms such as that of doped LiF. Fabrication and irradiation-dependent factors are seen to produce defects of differing origin, influencing the luminescence of the media. In coming to a close, we illustrate the utility of Ge-doped silica media for ionizing radiation dosimetry, first showing results from gamma-irradiated Ag-decorated nanoparticles, in the particular instance pointing to an extended dynamic range of dose. For the fibres, at radiotherapy dose levels, we show high spatial resolution (0.1 mm) depth-dose results for proton irradiations. For novel microstructured fibres (photonic crystal fibres, PCFs) we show first results from a study of undisturbed and technologically modified naturally occurring radioactivity environments, measuring doses of some 10 s of μGy over a period of several months.

  17. 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

  18. 78 FR 14540 - Cyromazine, Silica Silicates (Silica Dioxide and Silica Gel), Glufosinate Ammonium, Dioctyl...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-06

    ... AGENCY Cyromazine, Silica Silicates (Silica Dioxide and Silica Gel), Glufosinate Ammonium, Dioctyl Sodium... the registration review of cyromazine, silica silicates (silica dioxide and silica gel), glufosinate...). Silica silicates, silicon dioxide and silica gel, are insecticides and acaracides used in...

  19. 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.

  20. 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.

  1. Pressure Drops Due to Silica Scaling

    SciTech Connect

    Brown, K.L.; Freeston, D.H.; Dimas, Z.O.; Slatter, A.

    1995-01-01

    Experience with reinjection returns in many geothermal fields has prompted a move towards injecting waste fluids at some distance from the production field. This means that often, reinjection pipelines cover very long distances. If the waste water in the pipelines is supersaturated with respect to amorphous silica, then the deposition of silica in these pipelines is almost certain. Although the deposit may be of negligible thickness, the inner surface characteristics of the pipe will be different to those of clean mild steel. During a silica scaling experiment. geothermal brine was passed through a series of pipes of different sizes and over a period of three weeks, silica scale formed on the inner surface. The pressure drop along a distance of approximately 5m was measured by a water manometer in all test pipe sections. Significant pressure drop was observed during this time and can be correlated with the increase in the friction factor of the pipe walls due to silica scaling.

  2. Transport in Thermally Grown Silica on Silicon.

    DTIC Science & Technology

    1980-01-01

    catalyze the crvstallization of amorphous silica to cristobalite . 4 "" rhc activation ener- 4ies for oxidation when cristobalite forms increase but...categories. These are 65 kcal (due to formation of cristobalite ); " 40 kcal (in dry oxygen); and 30 kcal or less (in moist oxygen). S TU’ARY Based on

  3. 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.

  4. 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.

  5. The formation and deposition of primary silica granules - A new model of early Archean silica deposition

    NASA Astrophysics Data System (ADS)

    Stefurak, E. J.; Lowe, D. R.; Zentner, D.; Fischer, W. W.

    2013-12-01

    In the modern silica cycle, biologically-mediated silica precipitation provides the dominant sink for dissolved silica in seawater, with additional smaller sinks in the form of authigenic phyllosilicates and silica cements. Fundamental questions remain about the mechanics of the processes responsible for removing silica from seawater prior to the evolution of silica biomineralization in late Proterozoic time, with important implications for the chemistry of seawater on the early Earth, including alkalinity budgets and the efficiency of the silicate weathering feedback. The degree to which dissolved silica leaves seawater as authigenic phyllosilicates instead of amorphous silica is important because these 'reverse weathering' reactions do not consume CO2. The abundant presence of siliceous sedimentary rocks in Archean sequences, mainly in the form of chert, reinforces the inference that abiotic silica precipitation played a more significant role during Archean time. Previous authors hypothesized that these cherts formed as primary marine precipitates, but were unable to identify a specific mode of sedimentation. Here we present sedimentologic, petrographic, and geochemical evidence that some and perhaps many Archean cherts were deposited exclusively or in large part as primary, sub-spherical, structureless, sand-sized silica grains, here termed silica granules, which precipitated within marine waters. This mode of silica deposition appears to be unique to Archean time and provides evidence that primary abiotic silica precipitation indeed occurred in Archean oceans. Furthermore, the apparent early cementation of some granules indicates that the rate of silica precipitation was rapid under certain environmental conditions, which could provide insight into microfossil preservation via early silicification.

  6. Production and Application of Olivine Nano-Silica in Concrete

    NASA Astrophysics Data System (ADS)

    Mardiana, Oesman; Haryadi

    2017-05-01

    The aim of this research was to produce nano silica by synthesis of nano silica through extraction and dissolution of ground olivine rock, and applied the nano silica in the design concrete mix. The producing process of amorphous silica used sulfuric acid as the dissolution reagent. The separation of ground olivine rock occurred when the rock was heated in a batch reactor containing sulfuric acid. The results showed that the optimum mole ratio of olivine- acid was 1: 8 wherein the weight ratio of the highest nano silica generated. The heating temperature and acid concentration influenced the mass of silica produced, that was at temperature of 90 °C and 3 M acid giving the highest yield of 44.90%. Characterization using Fourier Transform Infrared (FTIR ) concluded that amorphous silica at a wavenumber of 1089 cm-1 indicated the presence of siloxane, Si-O-Si, stretching bond. Characterization using Scanning Electron Microscope - Energy Dispersive Spectroscopy (SEM-EDS) showed the surface and the size of the silica particles. The average size of silica particles was between 1-10 μm due to the rapid aggregation of the growing particles of nano silica into microparticles, caused of the pH control was not fully achieved.

  7. Picosecond amorphization of SiO2 stishovite under tension

    PubMed Central

    Misawa, Masaaki; Ryuo, Emina; Yoshida, Kimiko; Kalia, Rajiv K.; Nakano, Aiichiro; Nishiyama, Norimasa; Shimojo, Fuyuki; Vashishta, Priya; Wakai, Fumihiro

    2017-01-01

    It is extremely difficult to realize two conflicting properties—high hardness and toughness—in one material. Nano-polycrystalline stishovite, recently synthesized from Earth-abundant silica glass, proved to be a super-hard, ultra-tough material, which could provide sustainable supply of high-performance ceramics. Our quantum molecular dynamics simulations show that stishovite amorphizes rapidly on the order of picosecond under tension in front of a crack tip. We find a displacive amorphization mechanism that only involves short-distance collective motions of atoms, thereby facilitating the rapid transformation. The two-step amorphization pathway involves an intermediate state akin to experimentally suggested “high-density glass polymorphs” before eventually transforming to normal glass. The rapid amorphization can catch up with, screen, and self-heal a fast-moving crack. This new concept of fast amorphization toughening likely operates in other pressure-synthesized hard solids. PMID:28508056

  8. Picosecond amorphization of SiO2 stishovite under tension.

    PubMed

    Misawa, Masaaki; Ryuo, Emina; Yoshida, Kimiko; Kalia, Rajiv K; Nakano, Aiichiro; Nishiyama, Norimasa; Shimojo, Fuyuki; Vashishta, Priya; Wakai, Fumihiro

    2017-05-01

    It is extremely difficult to realize two conflicting properties-high hardness and toughness-in one material. Nano-polycrystalline stishovite, recently synthesized from Earth-abundant silica glass, proved to be a super-hard, ultra-tough material, which could provide sustainable supply of high-performance ceramics. Our quantum molecular dynamics simulations show that stishovite amorphizes rapidly on the order of picosecond under tension in front of a crack tip. We find a displacive amorphization mechanism that only involves short-distance collective motions of atoms, thereby facilitating the rapid transformation. The two-step amorphization pathway involves an intermediate state akin to experimentally suggested "high-density glass polymorphs" before eventually transforming to normal glass. The rapid amorphization can catch up with, screen, and self-heal a fast-moving crack. This new concept of fast amorphization toughening likely operates in other pressure-synthesized hard solids.

  9. 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.

  10. 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

  11. Theory of amorphous ices

    PubMed Central

    Limmer, David T.; Chandler, David

    2014-01-01

    We derive a phase diagram for amorphous solids and liquid supercooled water and explain why the amorphous solids of water exist in several different forms. Application of large-deviation theory allows us to prepare such phases in computer simulations. Along with nonequilibrium transitions between the ergodic liquid and two distinct amorphous solids, we establish coexistence between these two amorphous solids. The phase diagram we predict includes a nonequilibrium triple point where two amorphous phases and the liquid coexist. Whereas the amorphous solids are long-lived and slowly aging glasses, their melting can lead quickly to the formation of crystalline ice. Further, melting of the higher density amorphous solid at low pressures takes place in steps, transitioning to the lower-density glass before accessing a nonequilibrium liquid from which ice coarsens. PMID:24858957

  12. NiO gate GaN-based enhancement-mode hetrojunction field-effect transistor with extremely low on-resistance using metal organic chemical vapor deposition regrown Ge-doped layer

    NASA Astrophysics Data System (ADS)

    Suzuki, Asamira; Choe, Songbeak; Yamada, Yasuhiro; Otsuka, Nobuyuki; Ueda, Daisuke

    2016-12-01

    In this paper, we present a normally-off GaN-based transistor with an extremely low on-resistance (R on) fabricated by using a Ge-doped n++-GaN layer for ohmic contacts. We developed a novel GaN regrowth technique using Ge as a dopant, which achieved an extremely high doping concentration of 1 × 1020 cm-3, and thereby the lowest specific contact resistance of 1.5 × 10-6 Ω·cm2. The NiO gate fabricated using an atomic layer deposition technique reduced the spacing between the source and drain electrodes. The fabricated device showed the record-breaking R on of 0.95 Ω·mm with the maximum drain current and transconductance of 1.1 A/mm and 490 mS/mm, respectively. Note that the obtained threshold voltage was 0.55 V. This extremely low R on characteristic indicates the great potential of NiO-gate GaN-based heterojunction field-effect transistors.

  13. 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.

  14. Tritium in amorphous silicon

    SciTech Connect

    Sidhu, L.S.; Kosteski, T.; O`Leary, S.K.; Gaspari, F.; Zukotynski, S.; Kherani, N.P.; Shmadya, W.

    1996-12-31

    Preliminary results on infrared and luminescence measurements of tritium incorporated amorphous silicon are reported. Tritium is an unstable isotope that readily substitutes hydrogen in the amorphous silicon network. Due to its greater mass, bonded tritium is found to introduce new stretching modes in the infrared spectrum. Inelastic collisions between the beta particles, produced as a result of tritium decay, and the amorphous silicon network, results in the generation of excess electron-hole pairs. Radiative recombination of these carriers is observed.

  15. 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.

  16. Generation of crystalline silica from sugarcane burning.

    PubMed

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

    2010-07-08

    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

  17. Amorphous silica nanoparticles trigger vascular endothelial cell injury through apoptosis and autophagy via reactive oxygen species-mediated MAPK/Bcl-2 and PI3K/Akt/mTOR signaling

    PubMed Central

    Guo, Caixia; Yang, Man; Jing, Li; Wang, Ji; Yu, Yang; Li, Yang; Duan, Junchao; Zhou, Xianqing; Li, Yanbo; Sun, Zhiwei

    2016-01-01

    Environmental exposure to silica nanoparticles (SiNPs) is inevitable due to their widespread application in industrial, commercial, and biomedical fields. In recent years, most investigators focus on the evaluation of cardiovascular effects of SiNPs in vivo and in vitro. Endothelial injury and dysfunction is now hypothesized to be a dominant mechanism in the development of cardiovascular diseases. This study aimed to explore interaction of SiNPs with endothelial cells, and extensively investigate the exact effects of reactive oxygen species (ROS) on the signaling molecules and cytotoxicity involved in SiNPs-induced endothelial injury. Significant induction of cytotoxicity as well as oxidative stress, apoptosis, and autophagy was observed in human umbilical vein endothelial cells following the SiNPs exposure (P<0.05). The oxidative stress was induced by ROS generation, leading to redox imbalance and lipid peroxidation. SiNPs induced mitochondrial dysfunction, characterized by membrane potential collapse, and elevated Bax and declined bcl-2 expression, ultimately leading to apoptosis, and also increased number of autophagosomes and autophagy marker proteins, such as LC3 and p62. Phosphorylated ERK, PI3K, Akt, and mTOR were significantly decreased, but phosphorylated JNK and p38 MAPK were increased in SiNPs-exposed endothelial cells. In contrast, all of these stimulation phenomena were effectively inhibited by N-acetylcysteine. The N-acetylcysteine supplement attenuated SiNPs-induced endothelial toxicity through inhibition of apoptosis and autophagy via MAPK/Bcl-2 and PI3K/Akt/mTOR signaling, as well as suppression of intracellular ROS property via activating antioxidant enzyme and Nrf2 signaling. In summary, the results demonstrated that SiNPs triggered autophagy and apoptosis via ROS-mediated MAPK/Bcl-2 and PI3K/Akt/mTOR signaling in endothelial cells, and subsequently disturbed the endothelial homeostasis and impaired endothelium. Our findings may provide

  18. Ice sheets as a missing source of silica to the polar oceans

    PubMed Central

    Hawkings, Jon R.; Wadham, Jemma L.; Benning, Liane G.; Hendry, Katharine R.; Tranter, Martyn; Tedstone, Andrew; Nienow, Peter; Raiswell, Rob

    2017-01-01

    Ice sheets play a more important role in the global silicon cycle than previously appreciated. Input of dissolved and amorphous particulate silica into natural waters stimulates the growth of diatoms. Here we measure dissolved and amorphous silica in Greenland Ice Sheet meltwaters and icebergs, demonstrating the potential for high ice sheet export. Our dissolved and amorphous silica flux is 0.20 (0.06–0.79) Tmol year−1, ∼50% of the input from Arctic rivers. Amorphous silica comprises >95% of this flux and is highly soluble in sea water, as indicated by a significant increase in dissolved silica across a fjord salinity gradient. Retreating palaeo ice sheets were therefore likely responsible for high dissolved and amorphous silica fluxes into the ocean during the last deglaciation, reaching values of ∼5.5 Tmol year−1, similar to the estimated export from palaeo rivers. These elevated silica fluxes may explain high diatom productivity observed during the last glacial–interglacial period. PMID:28120824

  19. Ice sheets as a missing source of silica to the polar oceans.

    PubMed

    Hawkings, Jon R; Wadham, Jemma L; Benning, Liane G; Hendry, Katharine R; Tranter, Martyn; Tedstone, Andrew; Nienow, Peter; Raiswell, Rob

    2017-01-25

    Ice sheets play a more important role in the global silicon cycle than previously appreciated. Input of dissolved and amorphous particulate silica into natural waters stimulates the growth of diatoms. Here we measure dissolved and amorphous silica in Greenland Ice Sheet meltwaters and icebergs, demonstrating the potential for high ice sheet export. Our dissolved and amorphous silica flux is 0.20 (0.06-0.79) Tmol year(-1), ∼50% of the input from Arctic rivers. Amorphous silica comprises >95% of this flux and is highly soluble in sea water, as indicated by a significant increase in dissolved silica across a fjord salinity gradient. Retreating palaeo ice sheets were therefore likely responsible for high dissolved and amorphous silica fluxes into the ocean during the last deglaciation, reaching values of ∼5.5 Tmol year(-1), similar to the estimated export from palaeo rivers. These elevated silica fluxes may explain high diatom productivity observed during the last glacial-interglacial period.

  20. 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.

  1. Using Nucleation Theory to Understand the Dissolution Kinetics of Vitreous and Biogenic Silica: The Paradox of the Silica Polymorphs

    NASA Astrophysics Data System (ADS)

    Han, N.; de Yoreo, J. J.; Wallace, A. F.; Dove, P. M.

    2006-12-01

    Recent studies of the global biogeochemistry are refocusing on the demineralization kinetics of biogenic silicas—amorphous silicas produced by marine phytoplankton, sponges and terrestrial plants. Amorphous silica lacks the crystalline order that can be studied with classical terrace, ledge, and kink-based models of crystal growth and dissolution. Despite variations in Si-O-Si bond lengths and angles, all of these materials share the same fundamental chemical unit, silica tetrahedron. Silica tetrahedra on quartz surfaces have distinct hydration chemistries with two predominant types of sites available for reaction with water: gamma species have a higher degree of connectivity with the mineral surface via binding to three bridging oxygens while beta groups are bonded to two bridging oxygens. Surface groups of amorphous silica have the same coordinations as gamma and beta species in quartz. Support for the idea that crystalline and amorphous SiO2 exhibit similar dissolution and growth reaction pathways are found in rate data reported for the synthetic and biogenic amorphous silicas and quartz. Previous studies show that the `bulk' rate of silica production by quartz and amorphous silica is enhanced 50- 100 fold when alkaline or alkaline earth cations are introduced to otherwise pure solutions. Our recent study of quartz dissolution found this `salt effect' arises by a transition from dissolution at preexisting step edges and dislocation defects (detachment of beta species) to the homogeneous nucleation of vacancy islands across the entire surface (plucking of gamma species) in CaCl2 and NaCl solutions. This transition to homogeneous nucleation results in an exponential dependence of quartz dissolution rate on increasing chemical driving force (undersaturation) that is explained by the classical nucleation theory that was developed for crystal growth. We pose the question of why amorphous silica should also be enhanced 100-fold by electrolytes. From a mechanistic

  2. Diffusion and Mechanical Properties of Polyether-Polyurethanes Reinforced with Silica

    DTIC Science & Technology

    2016-05-01

    compare filled and unfilled urethane composites ...........7 Fig. 5 Influence of silica loading on the urethane carbonyl .............................8...purity, amorphous silica powder available from Fiber Optic Center (New Bedford, MA). The particle size was 500 nm. Polyurethane composites ...2,000 composite . The unfilled urethane shows typical elastomer behavior with a low modulus and high elongation at break, at approximately 2,400%. As

  3. Irradiation-induced amorphization of AlPO 4

    NASA Astrophysics Data System (ADS)

    Sreeram, A. N.; Hobbs, L. W.; Bordes, N.; Ewing, R. C.

    1996-08-01

    AlPO 4, in the mineral form berlinite, is isostructural with α-quartz. We have investigated the irradiation-induced amorphization of hydrothermally-grown berlinite and found that — like quartz and other silicas but unlike most other phosphates — it undergoes solid-state radiolyis, with an efficiency fifty times that of quartz at room temperature, and amorphizes at an absorbed ionization dose of about 1 GGy. High-resolution TEM revealed that — unlike quartz in which small amorphous inclusions nucleate — electron-irradiated AlPO 4 proceeds uniformly to an aperiodic state, much as do cristobalite and tridymite, and 20 times faster. It was found also to amorphize under 1.5 MeV Kr + ion irradiation at a collisional energy density (10 eV/atom) similar to that for quartz and in keeping with the degree of structural freedom afforded by its tetrahedral network structure. The critical ion fluence for amorphization was found to increase by a factor of 5 between 300 and 600 K. Radial distribution functions derived from energy-filtered electron diffraction patterns from regions amorphized by electrons resemble those of electron-amorphized quartz with some additional features.

  4. Fabrication of arc-induced long-period gratings in different silica fibers

    NASA Astrophysics Data System (ADS)

    Ranjan, Rajeev; Esposito, Flavio; Campopiano, Stefania; Iadicicco, Agostino

    2017-05-01

    In this work, we report on recent results about the fabrication of Long Period Gratings (LPGs) in different single mode optical fibers, by means of Electric Arc Discharge (EAD) technique. In particular, the results are related to three optical fibers with different doping elements, i.e.: standard telecommunication Ge-doped SMF28, highly photosensitive B/Gecodoped PS1250/1500, and P-doped P-SM-5 fibers. EAD leads to a point-by-point LPG inscription, due to localized tapering of the transversal size of the core and cladding regions along the fiber, and to changes of the silica refractive index due to the stress relaxation induced by local hot spots. Here, we take into consideration both standard and unconventional silica fibers and the aim of the work is to identify an appropriate "recipe" for each fiber, for manufacturing LPGs with strong and narrow attenuation bands (depth higher than 25 dB) and trivial power losses (<0.5 dB). Indeed, a proper combination of arc power and duration, as well as fiber tension, allows for the appropriate core and cladding modulation and thus for the desired LPGs spectral features. The sensitivity characteristics towards surrounding refractive index (SRI) and temperature changes of these LPGs are also investigated, highlighting the effects of different kind of doping.

  5. Trehalose amorphization and recrystallization.

    PubMed

    Sussich, Fabiana; Cesàro, Attilio

    2008-10-13

    The stability of the amorphous trehalose prepared by using several procedures is presented and discussed. Amorphization is shown to occur by melting (T(m)=215 degrees C) or milling (room temperature) the crystalline anhydrous form TRE-beta. Fast dehydration of the di-hydrate crystalline polymorph, TRE-h, also produces an amorphous phase. Other dehydration procedures of TRE-h, such as microwave treatment, supercritical extraction or gentle heating at low scan rates, give variable fractions of the polymorph TRE-alpha, that undergo amorphization upon melting (at lower temperature, T(m)=130 degrees C). Additional procedures for amorphization, such as freeze-drying, spray-drying or evaporation of trehalose solutions, are discussed. All these procedures are classified depending on the capability of the undercooled liquid phase to undergo cold crystallization upon heating the glassy state at temperatures above the glass transition temperature (T(g)=120 degrees C). The recrystallizable amorphous phase is invariably obtained by the melt of the polymorph TRE-alpha, while other procedures always give an amorphous phase that is unable to crystallize above T(g). The existence of two different categories is analyzed in terms of the transformation paths and the hypothesis that the systems may exhibit different molecular mobilities.

  6. 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.

  7. 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.

  8. Atomistic Modeling of Mechanical Loss in Amorphous Oxides

    NASA Astrophysics Data System (ADS)

    Hamdan, Rashid; Trinastic, Jonathan; Cheng, Hai-Ping

    2013-03-01

    The mechanical and optical loss in amorphous solids, described by the internal friction and light scattering susceptibility are investigated using classical, atomistic molecular dynamics simulation. We implemented the trajectory bisection method and the non-local ridge method in DL-POLY molecular dynamics simulation software. These methods were used to locate the different local potential energy minima that a system visits through an MD trajectory and the transition state between any two consecutive minima. From the distributions of the barrier height and asymmetry, and the relaxation time of the different transition states we calculated the internal friction of pure amorphous silica and mixed oxides. Acknowledgment: NSF/PHYS

  9. 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.

  10. Synthesis of stable ACC using mesoporous silica gel as a support.

    PubMed

    Fu, Fen; Tian, Liang Guang; Xu, Sheng; Xu, Xian Gang; Hu, Xiao Bo

    2014-01-01

    Stable amorphous calcium carbonate supported by mesoporous silica gel was successfully synthesized. The silica gel support is prepared through the hydrolytic polycondensation of ethyl silicate under suitable conditions. Laser scanning confocal microscopy (LSCM) observations reveal that the morphology of the products is branched with cruciform-like and flower-like structure. Raman spectroscopic analysis and scanning electron microscopy (SEM) observation of the products confirm the combination of stable amorphous calcium carbonate (ACC) nanoparticles and mesoporous silica gel. A possible growth mechanism for the branched structure has been proposed. Results indicate potential application of this work to ACC storage, crystal engineering, biomimetic synthesis, etc.

  11. Synthesis of stable ACC using mesoporous silica gel as a support

    NASA Astrophysics Data System (ADS)

    Fu, Fen; Tian, Liang Guang; Xu, Sheng; Xu, Xian Gang; Hu, Xiao Bo

    2014-08-01

    Stable amorphous calcium carbonate supported by mesoporous silica gel was successfully synthesized. The silica gel support is prepared through the hydrolytic polycondensation of ethyl silicate under suitable conditions. Laser scanning confocal microscopy (LSCM) observations reveal that the morphology of the products is branched with cruciform-like and flower-like structure. Raman spectroscopic analysis and scanning electron microscopy (SEM) observation of the products confirm the combination of stable amorphous calcium carbonate (ACC) nanoparticles and mesoporous silica gel. A possible growth mechanism for the branched structure has been proposed. Results indicate potential application of this work to ACC storage, crystal engineering, biomimetic synthesis, etc.

  12. Synthesis of stable ACC using mesoporous silica gel as a support

    PubMed Central

    2014-01-01

    Stable amorphous calcium carbonate supported by mesoporous silica gel was successfully synthesized. The silica gel support is prepared through the hydrolytic polycondensation of ethyl silicate under suitable conditions. Laser scanning confocal microscopy (LSCM) observations reveal that the morphology of the products is branched with cruciform-like and flower-like structure. Raman spectroscopic analysis and scanning electron microscopy (SEM) observation of the products confirm the combination of stable amorphous calcium carbonate (ACC) nanoparticles and mesoporous silica gel. A possible growth mechanism for the branched structure has been proposed. Results indicate potential application of this work to ACC storage, crystal engineering, biomimetic synthesis, etc. PMID:25246865

  13. Amorphous pharmaceutical solids.

    PubMed

    Vranić, Edina

    2004-07-01

    Amorphous forms are, by definition, non-crystalline materials which possess no long-range order. Their structure can be thought of as being similar to that of a frozen liquid with the thermal fluctuations present in a liquid frozen out, leaving only "static" structural disorder. The amorphous solids have always been an essential part of pharmaceutical research, but the current interest has been raised by two developments: a growing attention to pharmaceutical solids in general, especially polymorphs and solvates and a revived interest in the science of glasses and the glass transition. Amorphous substances may be formed both intentionally and unintentionally during normal pharmaceutical manufacturing operations. The properties of amorphous materials can be exploited to improve the performance of pharmaceutical dosage forms, but these properties can also give rise to unwanted effects that need to be understood and managed in order for the systems to perform as required.

  14. 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.

  15. Postsynthetic processing of copper hydroxide-silica tubes.

    PubMed

    Roszol, Laszlo; Makki, Rabih; Steinbock, Oliver

    2013-06-28

    Using reaction conditions far from equilibrium, we produce hollow tubes of silica-supported Cu(OH)2. The samples are then processed postsynthetically without compromising the macroscopic tubular structure. We specifically induce an amorphous-crystalline transition and demonstrate the sequential conversion of Cu(OH)2 to CuO, Cu2O, and metallic copper using thermal treatment and wet chemistry.

  16. 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.

  17. Inexpensive approach for production of high-surface-area silica nanoparticles from rice hulls biomass.

    PubMed

    Palanivelu, Rajagounder; Padmanaban, Periasamy; Sutha, Sadhasivam; Rajendran, Venkatachalam

    2014-12-01

    In this study, we prepared amorphous and crystalline silica nanoparticles from rice hulls biomass using pyrolysis technique at different processing temperatures such as 923, 973, 1023, 1073, 1123 and 1173 K. X-ray fluorescence studies show that the purity of all the synthesised silica nanoparticles is in the range of 98-99.7%. X-ray diffraction studies reveal that amorphous silica nanoparticles are formed at 923-1023 K, whereas crystalline particles at 1073-1173 K. Morphology and microstructure of silica nanoparticles are studied by scanning electron and transmission electron microscopes. Silica nanoparticles obtained at different processing temperatures yield particle size in the range of 6-100 nm. Chemical composition and surface functionalities of the particles are examined by energy-dispersive X-ray diffraction and Fourier transform infrared spectroscopic studies. The developed method effectively uses rice hulls biomass as a green natural source in the synthesis of amorphous and crystalline silica nanoparticles with high-specific surface area. The optimised processing temperature (1023 K) enables amorphous silica nanoparticles to have high-specific surface area of 538 m(2)g(-1).

  18. Origin of organism-dependent biogenic silica quartz formation.

    PubMed

    Sato, Kiminori

    2011-12-15

    Organism-dependent biogenic quartz formation in the steady-state environment is a phenomenon that can address the global environmental issues such as diagenetic evolution, biogeochemical cycling, and reservoir formation, but detailed studies have not been performed so far. Here, steady-state quartz formation is studied for amorphous silica of different biogenic origin on the basis of the recently established mechanistic model [Sato et al., J. Phys. Chem. C 2011, 115, 18131]. Amorphous silica originated from rice husks possesses angstrom-scale pores larger by 1.3 Å than those originated from diatom algae. The slight difference of pore size dramatically reduces activation energies of water diffusion by 78% and reactions of water molecules at pore surfaces by 47%, resulting in the reduction of activation energy of biogenic quartz formation by 64%. The present findings evidence that angstrom-scale pores intrinsically residing in the amorphous matrix are the organism-dependent origin of steady-state biogenic quartz formation.

  19. 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

  20. 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. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

  1. Molecular imprinting of bulk, microporous silica

    NASA Astrophysics Data System (ADS)

    Katz, Alexander; Davis, Mark E.

    2000-01-01

    Molecular imprinting aims to create solid materials containing chemical functionalities that are spatially organized by covalent or non-covalent interactions with imprint (or template) molecules during the synthesis process. Subsequent removal of the imprint molecules leaves behind designed sites for the recognition of small molecules, making the material ideally suited for applications such as separations, chemical sensing and catalysis. Until now, the molecular imprinting of bulk polymers and polymer and silica surfaces has been reported, but the extension of these methods to a wider range of materials remains problematic. For example, the formation of substrate-specific cavities within bulk silica, while conceptually straightforward, has been difficult to accomplish experimentally. Here we describe the imprinting of bulk amorphous silicas with single aromatic rings carrying up to three 3-aminopropyltriethoxysilane side groups; this generates and occupies microporosity and attaches functional organic groups to the pore walls in a controlled fashion. The triethoxysilane part of the molecules' side groups is incorporated into the silica framework during sol-gel synthesis, and subsequent removal of the aromatic core creates a cavity with spatially organized aminopropyl groups covalently anchored to the pore walls. We find that the imprinted silicas act as shape-selective base catalysts. Our strategy can be extended to imprint other functional groups, which should give access to a wide range of functionalized materials.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. Chemistry of Silica in Cerro Prieto Brines

    SciTech Connect

    Weres, Oleh; Iglesias, Eduardo; Tsao, Leon

    1980-04-01

    The precipitation of amorphous silica from synthetic geothermal, brines which resemble the flashed brine at Cerro Prieto has been studied. It was found that part of the dissolved silica quickly polymerizes to form suspended colloidal silica. The colloidal silica flocculates and settles slowly at unmodified brine pH values near 7.35. Raising the pH of the brine to about 7.8 by adding base and stirring for a few minutes causes rapid and complete flocculation and settling. these results have been confirmed in the field using actual Cerro Prieto brine. Both in the laboratory and in the field quaternary amines were found to be effective with some brine compositions but not with others. Polyacrylamides do not work at all. These results suggest the following simple preinjection brine treatment process: age the brine for 10-20 minutes in a covered holding tank, add 20-30 ppm lime (CaO), stir for 5 minutes, and separate the flocculated silica from the brine using a conventional clarifier. The brine coming out of such a process will be almost completely free of suspended solids. The pilot plant tests needed to reduce this conceptual process to practice are discussed. The rate of deposition of silica scale from synthetic brines was separately studied. It was found that a modest decrease in pH could significantly reduce the scaling rate at a reasonable cost. The equilibrium chemistry of Cerro Prieto brine was studied theoretically. These calculations indicate that increasing the brine pH to remove silica might cause some precipitation of carbonate minerals, but also that this problem could easily be eliminated at a reasonable cost if it did arise.

  7. 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

  8. Diagenetic silica enrichment and late-stage groundwater activity in Gale crater, Mars

    NASA Astrophysics Data System (ADS)

    Frydenvang, J.; Gasda, P. J.; Hurowitz, J. A.; Grotzinger, J. P.; Wiens, R. C.; Newsom, H. E.; Edgett, K. S.; Watkins, J.; Bridges, J. C.; Maurice, S.; Fisk, M. R.; Johnson, J. R.; Rapin, W.; Stein, N. T.; Clegg, S. M.; Schwenzer, S. P.; Bedford, C. C.; Edwards, P.; Mangold, N.; Cousin, A.; Anderson, R. B.; Payré, V.; Vaniman, D.; Blake, D. F.; Lanza, N. L.; Gupta, S.; Van Beek, J.; Sautter, V.; Meslin, P.-Y.; Rice, M.; Milliken, R.; Gellert, R.; Thompson, L.; Clark, B. C.; Sumner, D. Y.; Fraeman, A. A.; Kinch, K. M.; Madsen, M. B.; Mitrofanov, I. G.; Jun, I.; Calef, F.; Vasavada, A. R.

    2017-05-01

    Diagenetic silica enrichment in fracture-associated halos that crosscut lacustrine and unconformably overlying aeolian sedimentary bedrock is observed on the lower north slope of Aeolis Mons in Gale crater, Mars. The diagenetic silica enrichment is colocated with detrital silica enrichment observed in the lacustrine bedrock yet extends into a considerably younger, unconformably draping aeolian sandstone, implying that diagenetic silica enrichment postdates the detrital silica enrichment. A causal connection between the detrital and diagenetic silica enrichment implies that water was present in the subsurface of Gale crater long after deposition of the lacustrine sediments and that it mobilized detrital amorphous silica and precipitated it along fractures in the overlying bedrock. Although absolute timing is uncertain, the observed diagenesis likely represents some of the most recent groundwater activity in Gale crater and suggests that the timescale of potential habitability extended considerably beyond the time that the lacustrine sediments of Aeolis Mons were deposited.

  9. Presence of nano-sized silica during in vitro digestion of foods containing silica as a food additive.

    PubMed

    Peters, Ruud; Kramer, Evelien; Oomen, Agnes G; Rivera, Zahira E Herrera; Oegema, Gerlof; Tromp, Peter C; Fokkink, Remco; Rietveld, Anton; Marvin, Hans J P; Weigel, Stefan; Peijnenburg, Ad A C M; Bouwmeester, Hans

    2012-03-27

    The presence, dissolution, agglomeration state, and release of materials in the nano-size range from food containing engineered nanoparticles during human digestion is a key question for the safety assessment of these materials. We used an in vitro model to mimic the human digestion. Food products subjected to in vitro digestion included (i) hot water, (ii) coffee with powdered creamer, (iii) instant soup, and (iv) pancake which either contained silica as the food additive E551, or to which a form of synthetic amorphous silica or 32 nm SiO(2) particles were added. The results showed that, in the mouth stage of the digestion, nano-sized silica particles with a size range of 5-50 and 50-500 nm were present in food products containing E551 or added synthetic amorphous silica. However, during the successive gastric digestion stage, this nano-sized silica was no longer present for the food matrices coffee and instant soup, while low amounts were found for pancakes. Additional experiments showed that the absence of nano-sized silica in the gastric stage can be contributed to an effect of low pH combined with high electrolyte concentrations in the gastric digestion stage. Large silica agglomerates are formed under these conditions as determined by DLS and SEM experiments and explained theoretically by the extended DLVO theory. Importantly, in the subsequent intestinal digestion stage, the nano-sized silica particles reappeared again, even in amounts higher than in the saliva (mouth) digestion stage. These findings suggest that, upon consumption of foods containing E551, the gut epithelium is most likely exposed to nano-sized silica.

  10. 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.

  11. Mesoporous silica coated silica-titania spherical particles: from impregnation to core-shell formation.

    PubMed

    Shiba, Kota; Takei, Toshiaki; Ogawa, Makoto

    2016-11-22

    The coating of solid surfaces with inorganic materials is a promising approach not only to impart various functionalities but also to modify physicochemical properties that are affected by the geometry/structure of the coating. In this study, a silica-hexadecyltrimethylammonium (silica-CTA) hybrid layer was deposited on monodispersed spherical particles composed of titania and octadecylamine (titania-ODA) by a sol-gel reaction of tetraethoxysilane in aqueous CTA/ammonia/methanol solution. The formation of the coating was confirmed by SEM and TEM observations. The coating thickness varied from a few nm to 100 nm depending on the Si/Ti ratio. We found that Si/Ti = 0.68 resulted in the formation of microporous silica-titania particles with the pore size of 0.7 nm as revealed by nitrogen adsorption/desorption measurements. Because the titania-ODA particles can be converted to mesoporous titania particles after removing ODA by acid/base treatment, the silica species can be impregnated into the titania particles and replace ODA under basic conditions. By increasing the Si/Ti molar ratio up to 1.4, silica-titania particles with non-porous structures were obtained. An amorphous to anatase transition occurred at around 800 °C, indicating the complete impregnation of silica inside the titania particles. Further increases of the Si/Ti molar ratio (to 3.4 and 6.8) led to the formation of the silica-CTA shell on the core particles, and the shell was converted to mesoporous silica layers with a pore size of 2 nm after calcination at 550 °C for 5 h. Non-linear control of the pore size/structure is presented for the first time; this will be useful for the precise design of diverse hybrid materials for optical, catalytic and biomedical applications.

  12. Amorphous silicon photovoltaic devices

    DOEpatents

    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.

  13. 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.

  14. 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.

  15. Silica extraction from geothermal water

    DOEpatents

    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.

  16. The Effect of Bacterial Surfaces on Silica Precipitation

    NASA Astrophysics Data System (ADS)

    Yee, N.; Phoenix, V. R.; Konhauser, K. O.; Benning, L. G.

    2001-12-01

    Bacterial silicification is an important geological process in modern geothermal environments (e.g., New Zealand, Iceland, Japan). The precipitation of silica onto bacterial surfaces can affect microbial fossilization, chemical sediment formation, the porosity and permeability of crustal rocks, and silica transport in geothermal hot springs. Previous studies have suggested that active deposition of silica onto bacterial cells begins with the precipitation of heterogeneously nucleated aggregates of amorphous silica. However, the effect of bacteria on silica precipitation is poorly understood, and it is unclear if bacterial surfaces enhance the kinetics of silica precipitation or if the bacteria act as passive precipitation surfaces. In this study, we performed silica precipitation experiments with the filamentous cyanobacteria Calothrix sp. (strain KC97) to elucidate the rates and mechanisms of silicate biomineralization. Batch experiments were conducted as a function of time, Si saturation states, temperature, pH and Fe concentrations. Experiments at both undersaturated and supersaturated conditions indicate that Si-bacteria interactions are weak, and that minimal bacterial silica sorption/precipitation occurs. In supersaturated solutions, abotic polymerization rates are rapid and at the times scales of our experiments (1-300 hours) the presence of bacteria does not enhance silica nucleation or monomeric silica polymerization. However, the presence of Fe-coated bacteria significantly increases silica sorption/precipitation rates, and the extent of Si sorption/precipitation increases with increasing Fe concentrations. Fe precipitation experiments performed without Si indicate that iron precipitation onto bacterial surfaces occurs very rapidly and significantly faster than abotic controls. The experimental data suggest that in the presence of Fe, bacterial silicification occurs as a two step process: 1) Fe precipitates onto bacterial cells via heterogeneous surface

  17. Single-layer honeycomb like structure of silica

    NASA Astrophysics Data System (ADS)

    Cahangirov, Seymur; Ozcelik, V. Ongun; Ciraci, Salim

    2014-03-01

    Silica or SiO2, the main constituent of earth's rocks has several 3D complex crystalline and amorphous phases, but it does not have a graphite like layered structure in 3D. Our theoretical analysis and numerical calculations from the first-principles predict that silica can have stable, suspended, single-layer honeycomb like allotrope, h α-silica (silicatene), which can be viewed to be derived from the oxidation of silicene and it has intriguing atomic structure with re-entrant angles in hexagons. It is a wide band gap semiconductor, which attains remarkable electromechanical properties showing geometrical changes under external electric field. In particular, it is an auxetic nanomaterial with negative Poisson's ratio and has high piezoelectric coefficient. Coverage of foreign adatoms can attribute new functionalities to h α-silica such that by oxidation it turns into to a wide band gap insulator like the parent quartz.

  18. Incorporation of terbium(III) ion into mesoporous silica particles

    NASA Astrophysics Data System (ADS)

    Kataoka, Takuya; Wang, Liyin; Kobayashi, Kouhei; Nishikawa, Masami; Tagaya, Motohiro

    2016-10-01

    Terbium(III)-doped mesoporous silicas were synthesized, and the states of terbium ions in the silica frameworks were investigated. The mesopores were preserved upon doping at terbium ion molar concentrations relative to (Si+Tb) up to 15 mol %, indicating the interaction of terbium ions with Si-O bonds. Significant morphological changes of the particles were observed with increasing the doping concentration. The shapes of the photoluminescence spectra due to the transitions of 5D4 → 7F6 and 5D4 → 7F5 were indicative of the presence of terbium ions in the silica matrix, and the quantum efficiency (2.1-2.8%) and lifetime (1.6-1.9 ms) decreased with increasing the doping concentration up to 15 mol %. Therefore, the terbium ions are considered to be located inside the amorphous silica frameworks, where they electrostatically interact with the O atoms of silanol and siloxane groups.

  19. Amorphous material in high strain experimental fault gouges

    SciTech Connect

    Yund, R.A.; Blanpied, M.L.; Tullis, T.E.; Weeks, J.D. )

    1990-09-10

    The microstructures of gouges produced in room temperature, rotary shear sliding experiments were examined by transmission electron microscopy. Gouges were produced by sliding on ground surfaces of granite, quartzite, or marble except for one experiment in which a 1-mm-thick simulated gouge layer was used. Water was added to the sliding surfaces of all but one sample. Crystal plastic processes play no role in the granite and quartzite gouges and a minor role in the marbles. All of the gouges consist of mostly submicron crystalline fragments; in addition, the granite gouges contain 5-60% amorphous material, and the quartzite gouge contains {approximately}50% amorphous material. In the granite samples the composition of the amorphous material commonly lies between K-rich and Na, Ca-rich feldspars, although portions may be silica-rich. The microstructural relations suggest that the amorphous material forms by comminution of fragments rather than by melting. The amount of amorphous material increases, and the size of the largest crystalline fragments decreases, with an increase in average shear strain, although the microstructure is nearly uniform throughout each granite gouge layer. These observations suggest that after slip becomes localized on Y shear surfaces and/or R{sub 1} Riedel shears the entire gouge layer must continue to undergo deformation. It is suggested that cyclic deformation in the gouge must occur to accommodate the passage of geometric irregularities on the active slip surfaces.

  20. 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.

  1. Preparation of Potassium-Posphate-embedded Amorphous Silicate Material from Rice Straw Waste

    NASA Astrophysics Data System (ADS)

    Nandiyanto, A. B. D.; Permatasari, N.; Sucahya, T. N.; Purwanti, S. T.; Munawaroh, H. S. H.; Abdullah, A. G.; Hasanah, L.

    2017-03-01

    Rice straw is one of the agricultural wastes that increased every year. Since rice straw ash contains 74.6% of silica, this material is potentially used to produce silica. Thus, the purpose of this study was to investigate the possibility process for generating potassium-phosphate-embedded amorphous silica material. To extract silica from rice straw waste, we used potassium hydroxide solution followed by an acid precipitation treatment. Based on the experimental results, the proposed method is potential to be used as an alternative technique for getting silica material. In addition, the method has a positive impact on the environment because this is potential for reducing the amount of rice straw waste, whereas at the same time this provides an added value to the rice straw waste itself.

  2. 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.

  3. Microbial silica deposition in geothermal hot waters.

    PubMed

    Inagaki, F; Motomura, Y; Ogata, S

    2003-02-01

    A combined use of molecular ecological techniques and geochemical surveys revealed that thermophilic or hyperthermophilic microorganisms living in geothermal environments are likely to be implicated in the formation of biogenic siliceous deposits. Electron microscopic observations indicated that numerous microorganism-like fabrics were preserved in naturally occurring siliceous deposits such as siliceous sinter, geyserite, and silica scale, which suggests microbial contribution to silica precipitation. Molecular phylogenetic analyses suggested that extreme thermophilic bacteria within the genera Thermus and Hydrogenobacter are predominant components among the indigenous microbial community in siliceous deposits formed in pipes and equipment of Japanese geothermal power plants. These bacteria seem to actively contribute to the rapid formation of huge siliceous deposits. Additionally, in vitro examination suggested that Thermus cells induced the precipitation of supersaturated amorphous silica during the exponential growth phase, concomitant with the production of a specific cell envelope protein. Dissolved silica in geothermal hot water may be a significant component in the maintenance of position and survival of microorganisms in limited niches.

  4. Amorphous metallic foam

    NASA Astrophysics Data System (ADS)

    Schroers, Jan; Veazey, Chris; Johnson, William L.

    2003-01-01

    The bulk glass forming alloy Pd43Ni10Cu27P20 is processed into a low-density amorphous metallic foam. Pd43Ni10Cu27P20 is mixed with hydrated B2O3, which releases gas at elevated temperature and/or low pressure. Very homogeneous foams are achieved due to the high viscosity of the alloy even at its liquidus temperature. By processing at the liquidus temperature and decreasing the pressure to 10-2 mbar, well-distributed bubbles expand to foam the material. Foam densities as low as 1.4×103 kg/m3 were obtained, corresponding to a bubble volume fraction of 84%. The bubble diameter ranges between 2×10-4 and 1×10-3 m. Thermal analysis by differential scanning calorimetry confirms the amorphous nature of the foam. Furthermore, it reveals that the foam's thermal stability is comparable to the bulk material.

  5. 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.

  6. 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.

  7. Defects in Amorphous Metals.

    DTIC Science & Technology

    1982-07-01

    this map with a similar plot of the experimental data. An experimental deformation data map for Pd-based amorphous al- loys is shown in fig. 10. In the...Masumoto. I Mat. Sci. 12 (1977) 1927, [IgI T M Ha.es. J. W Allen. J. Tauc . B. C. Giessen and J. J. Hauser. Phys. Re. Lett. 41 i197s) 1282 [191 J

  8. High-harmonic generation in amorphous solids

    DOE PAGES

    You, Yong Sing; Yin, Yanchun; Wu, Yi; ...

    2017-09-28

    High-harmonic generation in isolated atoms and molecules has been widely utilized in extreme ultraviolet photonics and attosecond pulse metrology. Recently, high-harmonic generation has been observed in solids, which could lead to important applications such as all-optical methods to image valance charge density and reconstruct electronic band structures, as well as compact extreme ultraviolet light sources. So far these studies are confined to crystalline solids; therefore, decoupling the respective roles of long-range periodicity and high density has been challenging. Here we report the observation of high-harmonic generation from amorphous fused silica. We also decouple the role of long-range periodicity by comparingmore » harmonics generated from fused silica and crystalline quartz, which contain the same atomic constituents but differ in long-range periodicity. These results advance current understanding of the strong-field processes leading to high-harmonic generation in solids with implications for the development of robust and compact extreme ultraviolet light sources.« less

  9. 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.

  10. Fabrication of monodisperse hollow silica spheres and effect on water vapor permeability of polyacrylate membrane.

    PubMed

    Bao, Yan; Yang, Yongqiang; Ma, Jianzhong

    2013-10-01

    Polystyrene/silica core-shell spheres were fabricated using polystyrene as templates by hydrolysis and condensation of tetraethyl orthosilicate through a sol-gel process, in which polystyrene was synthesized by emulsion polymerization. Then, hollow silica spheres were obtained after selective removal of the organic polystyrene core from the polystyrene/silica core-shell spheres by tetrahydrofuran etching. The effect of hollow silica spheres on water vapor permeability, mechanical property, and water uptake of polyacrylate membrane were investigated. The microstructure analysis shows that the mean size and wall thickness of hollow silica spheres are 170 nm and 20 nm, respectively. The silica shells consist of amorphous silica seed assembly with a broad size distribution, which roughen the surfaces of hollow silica spheres greatly. The specific surface area of hollow silica spheres is bigger than that of polystyrene/silica core-shell spheres. Hollow silica spheres can significantly improve water vapor permeability of polyacrylate membrane, but lead to the reduction in mechanical property.

  11. 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

  12. The Stabilization of Amorphous Zopiclone in an Amorphous Solid Dispersion.

    PubMed

    Milne, Marnus; Liebenberg, Wilna; Aucamp, Marique

    2015-10-01

    Zopiclone is a poorly soluble psychotherapeutic agent. The aim of this study was to prepare and characterize an amorphous form of zopiclone as well as the characterization and performance of a stable amorphous solid dispersion. The amorphous form was prepared by the well-known method of quench-cooling of the melt. The solid dispersion was prepared by a solvent evaporation method of zopiclone, polyvinylpyrrolidone-25 (PVP-25), and methanol, followed by freeze-drying. The physico-chemical properties and stability of amorphous zopiclone and the solid dispersion was studied using differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), hot-stage microscopy (HSM), X-ray diffractometry (XRD), solubility, and dissolution studies. The zopiclone amorphous solid-state form was determined to be a fragile glass; it was concluded that the stability of the amorphous form is influenced by both temperature and water. Exposure of amorphous zopiclone to moisture results in rapid transformation of the amorphous form to the crystalline dihydrated form. In comparison, the amorphous solid dispersion proved to be more stable with increased aqueous solubility.

  13. 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.

  14. Synthesis of quenchable amorphous diamond

    DOE PAGES

    Zeng, Zhidan; Yang, Liuxiang; Zeng, Qiaoshi; ...

    2017-08-22

    Diamond owes its unique mechanical, thermal, optical, electrical, chemical, and biocompatible materials properties to its complete sp3-carbon network bonding. Crystallinity is another major controlling factor for materials properties. Although other Group-14 elements silicon and germanium have complementary crystalline and amorphous forms consisting of purely sp3 bonds, purely sp3-bonded tetrahedral amorphous carbon has not yet been obtained. In this letter, we combine high pressure and in situ laser heating techniques to convert glassy carbon into “quenchable amorphous diamond”, and recover it to ambient conditions. Our X-ray diffraction, high-resolution transmission electron microscopy and electron energy-loss spectroscopy experiments on the recovered sample andmore » computer simulations confirm its tetrahedral amorphous structure and complete sp3 bonding. This transparent quenchable amorphous diamond has, to our knowledge, the highest density among amorphous carbon materials, and shows incompressibility comparable to crystalline diamond.« less

  15. Spherical ordered mesoporous silicas and silica monoliths as stationary phases for liquid chromatography.

    PubMed

    Galarneau, Anne; Iapichella, Julien; Brunel, Daniel; Fajula, François; Bayram-Hahn, Zöfre; Unger, Klaus; Puy, Guillaume; Demesmay, Claire; Rocca, Jean-Louis

    2006-04-01

    Ordered mesoporous silicas such as micelle-templated silicas (MTS) feature unique textural properties in addition to their high surface area (approximately 1000 m2/g): narrow mesopore size distributions and controlled pore connectivity. These characteristics are highly relevant to chromatographic applications for resistance to mass transfer, which has never been studied in chromatography because of the absence of model materials such as MTS. Their synthesis is based on unique self-assembly processes between surfactants and silica. In order to take advantage of the perfectly adjustable texture of MTS in chromatographic applications, their particle morphology has to be tailored at the micrometer scale. We developed a synthesis strategy to control the particle morphology of MTS using the concept of pseudomorphic transformation. Pseudomorphism was recognized in the mineral world to gain a mineral that presents a morphology not related to its crystallographic symmetry group. Pseudomorphic transformations have been applied to amorphous spherical silica particles usually used in chromatography as stationary phases to produce MTS with the same morphology, using alkaline solution to dissolve progressively and locally silica and reprecipitate it around surfactant micelles into ordered MTS structures. Spherical beads of MTS with hexagonal and cubic symmetries have been synthesized and successfully used in HPLC in fast separation processes. MTS with a highly connected structure (cubic symmetry), uniform pores with a diameter larger than 6 nm in the form of particles of 5 microm could compete with monolithic silica columns. Monolithic columns are receiving strong interest and represent a milestone in the area of fast separation. Their synthesis is a sol-gel process based on phase separation between silica and water, which is assisted by the presence of polymers. The control of the synthesis of monolithic silica has been systematically explored. Because of unresolved yet

  16. 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.

  17. Silica, silicosis, and cancer

    SciTech Connect

    Goldsmith, D.F.; Winn, D.M.; Shy, C.M.

    1986-01-01

    These proceedings collect papers on occupational exposure. Topics include: measurement of silica dust, mortality in granite workers, effects of quartz in coal mine dust, pneumoconiosis, and lung cancer.

  18. Hydrogenated Amorphous Silicon

    NASA Astrophysics Data System (ADS)

    Street, R. A.

    1991-08-01

    Divided roughly into two parts, the book describes the physical properties and device applications of hydrogenated amorphous silicon. The first section is concerned with the atomic and electronic structure, and covers growth defects and doping and defect reactions. The emphasis is on the optical and electronic properties that result from the disordered structure. The second part of the book describes electronic conduction, recombination, interfaces, and multilayers. The special attribute of a-Si:H which makes it useful is the ability to deposit the material inexpensively over large areas, while retaining good semiconducting properties, and the final chapter discusses various applications and devices.

  19. Sonochemical synthesis of silica and silica sulfuric acid nanoparticles from rice husk ash: a new and recyclable catalyst for the acetylation of alcohols and phenols under heterogeneous conditions.

    PubMed

    Salavati-Niasari, Masoud; Javidi, Jaber

    2012-11-01

    Silica nanoparticles were synthesized from rice husk ash at room temperature by sonochemical method. The feeding rate of percipiteting agent and time of sonication were investigated. The nanostructure of the synthesized powder was realized by the FE-SEM photomicrograph, FT-IR spectroscopy, XRD and XRF analyses. These analytical observations have revealed that the nano-sized amorphous silica particles are formed and they are spheroidal in shape. The average particle size of the silica powders is found to be around 50 nm. The as-synthesized silica nanoparticles were subsequently modified with chlorosulfonic acid and prepared silica sulfuric acid nanoparticles, which were employed as an efficient catalyst for the acylation of alcohols and phenols with acetic anhydride in excellent yields under solvent-free conditions at room temperature. This reported method is simple, mild, and environmentally viable and catalyst can be simply recovered and reused over 9 times without any significant loss of its catalytic activity.

  20. Modeling and Simulation of Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Pandey, Anup

    The general and practical inversion of diffraction data - producing a computer model correctly representing the material explored - is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this dissertation, we introduce a robust method, Force-Enhanced Atomic Refinement (FEAR), which jointly exploits the power of ab initio atomistic simulation along with the information carried by diffraction data. As a preliminary trial, the method has been implemented using empirical potentials for amorphous silicon (a-Si) and silica ( SiO2). The models obtained are comparable to the ones prepared by the conventional approaches as well as the experiments. Using ab initio interactions, the method is applied to two very different systems: amorphous silicon (a-Si) and two compositions of a solid electrolyte memory material silver-doped GeSe3. It is shown that the method works well for both the materials. Besides that, the technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. It offers a means to add a priori information in first principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information. Moreover, the method has also been used to create a computer model of a-Si, using highly precise X-ray diffraction data. The model predicts properties that are close to the continuous random network models but with no a priori assumptions. In addition, using the ab initio molecular dynamics simulations (AIMD) we explored the doping and transport in hydrogenated amorphous silicon a-Si:H with the most popular impurities: boron and phosphorous. We investigated doping for these impurities and the role of H in the doping process. We revealed the network motion and H hopping induced by

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

    PubMed

    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.

  2. 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.

  3. Physical processes of quartz amorphization due to friction

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Muto, J.; Nagahama, H.; Miura, T.; Arakawa, I.; Shimizu, I.

    2011-12-01

    Solid state amorphization of minerals occurs in indentations, in shock experiments, and in high pressure metamorphic quartz rock. A production of amorphous material is also reported in experimentally created silicate gouges (Yund et al., 1990), and in San Andreas Fault core samples (Janssen et al., 2010). Rotary-shear friction experiments of quartz rocks imply dynamic weakening at seismic rates (Di Toro et al., 2004). These experiments have suggested that weakening is caused by formation and thixotropic behavior of a silica gel layer which comprises of very fine particles of hydrated amorphous silica on fault gouges (Goldsby & Tullis, 2002; Hayashi & Tsutsumi, 2010). Therefore, physical processes of amorphization are important to better understand weakening of quartz bearing rocks. In this study, we conducted a pin-on-disk friction experiment to investigate details of quartz amorphization (Muto et al, 2007). Disks were made of single crystals of synthetic and Brazilian quartz. The normal load F and sliding velocity V were ranged from 0.01 N to 1 N and from 0.01 m/s to 2.6 m/s, respectively. The friction was conducted using quartz and diamond pins (curvature radii of 0.2 ~ 3 mm) to large displacements (> 1000 m) under controlled atmosphere. We analyzed experiment samples by Raman spectroscopy and FT-IR. Raman spectroscopy (excitation wavelength 532.1 nm) provides lattice vibration modes, and was used to investigate the degree of amorphization of samples. Raman spectra of friction tracks on the disk show clear bands at wavenumbers of 126, 204, 356, 394, and 464 cm-1, characteristic of intact α-quartz. Remarkably, in experiments using diamond pins (F = 0.8 N, normal stress σr calculated by contact area = 293 ~ 440 MPa, V = 0.12 ~ 0.23 m/s), the bands at 204 and 464 cm-1 gradually broaden to reveal shoulders on the higher-wavenumber sides of these peaks. Especially, two distinguished peaks at 490 and 515 cm-1 and a weak broad peak at 606 cm-1 appear sporadically on

  4. Review of development of a silica-based thermoluminescence dosimeter

    NASA Astrophysics Data System (ADS)

    Yusoff, A. L.; Hugtenburg, R. P.; Bradley, D. A.

    2005-12-01

    Development of a silica-based material suitable for thermoluminescence dosimetry (TLD) is described. Doped silica samples were prepared in-house using the sol-gel technique. Results from a micro-X-ray fluorescence (μ-XRF) study of Zn-doped silica have confirmed the capability of the sol-gel processing steps in producing homogeneously doped samples. The ability of sol-gel processing in producing doped samples with different dopant charge states has been illustrated in the case of copper (I)- and copper (II)-doped silica samples. The charge states of the dopants have been verified using the technique of X-ray absorption near-edge structure (XANES). X-ray diffraction (XRD) investigations have shown the structure of samples doped with erbium, copper (I) and copper (II) (listed in order of decreasing effect) to be altered by the dopants, albeit with the samples remaining in an amorphous state. Local structure studies, carried out using the method of extended X-ray absorption fine structure (EXAFS), reveal that in most cases the local environment of the dopant is similar to the respective native structure of the respective metal oxides. Conversely, in a number of cases, the dopant atoms occupy the silicon sites in the silica tetragonal geometry. Thermoluminescence (TL) studies were carried out on aluminium, copper (I), germanium, manganese, tin, and zinc-doped silica samples. Weight for weight, the most sensitive thermoluminescent material was found to be 4.0 mol% aluminium-doped silica, providing ˜3.5 times the TL yield of TLD100 and ˜5.4 times that of germanium-doped silica. The photon dose response of aluminium-doped silica was observed to be linear over the range of investigated dose, 0.5-10.0 Gy.

  5. 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.

  6. 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.

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

    SciTech Connect

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

    2016-05-16

    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.

  8. Bulk acoustic wave resonators made of amorphous materials

    NASA Astrophysics Data System (ADS)

    Breuzet, Michel

    1990-08-01

    The investigation of plates vibrating at radio frequency and made of amorphous conductive or insulating materials is carried out. Capacitive excitation was employed for this type of resonator made of non piezoelectric material. The advantage of using contour vibration modes is demonstrated, with particular reference to the Lame mode. The optimization of mountings designed to minimize resonator/mounting coupling is investigated. The finite element computing method was applied. The results obtained on resonators made of AU4G and vitreous silica (SiO2) are discussed.

  9. Compensated amorphous silicon solar cell

    DOEpatents

    Carlson, David E.

    1980-01-01

    An amorphous silicon solar cell incorporates a region of intrinsic hydrogenated amorphous silicon fabricated by a glow discharge wherein said intrinsic region is compensated by P-type dopants in an amount sufficient to reduce the space charge density of said region under illumination to about zero.

  10. 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.

  11. 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.

  12. Synthesis and characterization of biocomposites based on chitosan and geothermal silica

    NASA Astrophysics Data System (ADS)

    Kusumastuti, Yuni; Petrus, Himawan Tri Bayu Murti; Yohana, Fiska; Buwono, Agung Tri; Zaqina, Radinda Bian

    2017-03-01

    With the amount of about 3000 ton per year of precipitate silica, Dieng's geothermal power plant possesses potential to utilize the precipitate silica. This material is a result of silica scaling mitigation that reduces the geothermal power plant productivity to the point of 40% within a year. In this study, the precipitated silica which is mostly in the amorphous state has potential uses for biomaterial such as bone graft composite. In order to obtain best of geothermal quality, purification was conducted using dry washing method to reach 95.65% of SiO2 purity. The silica was mixed in gel phase with 17.11% of water content. The geothermal silica was mixed with composition of chitosan/gelatin/geothermal silica (C/G/GS) and chitosan/pectin/geothermal silica (C/P/GS) biocomposites with certain ratio. Those two biocomposites were characterized and compared in order to determine the effect of geothermal silica addition into the matrix. From the observation, in general, it was obtained that the swelling ratio of C/P/GS is higher than C/G/GS. However, in comparison to the sample without geothermal silica addition, the swelling ratio of silica added biocomposites at various composition is lower. In term of Young's modulus at 1:1:1 ratio, silica addition into C/P biocomposite decreased the value while addition of silica into C/G biocomposite increased Young's modulus value. In general, no interaction was observed significantly between Young's modulus and swelling ratio. The interaction between the functional group of chitosan, pectin or gelatin and geothermal silica in the composite was also revealed by FTIR spectra analysis.

  13. 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.

  14. Ammonia hardening of porous silica antireflective coatings

    NASA Astrophysics Data System (ADS)

    Belleville, Philippe F.; Floch, Herve G.

    1994-10-01

    The adhesion of sol-gel antireflective porous silica coatings on vitreous optical substrates has been dramatically improved by exposure to ammonia vapors or a dip in basic solutions. The approximately 70 to 270-nm thick coatings consisted of monolayers of spherical, 20-nm diameter amorphous silica particles deposited from ethanolic colloidal suspensions by conventional liquid coating techniques. Although, the as-deposited coatings had only low adhesion and were easily damaged when cleaned by standard drag-wiping procedures, coatings exposed over 5 hours to ammonia vapors passed both adhesive-tape and moderate abrasive- resistance tests. The increase in strength was accompanied by a roughly 20% shrinkage of the original coating thickness but the antireflective properties were retained. Our explanation of this chemical effect is a base-catalyzed phenomenon leading to surface silanol condensation and hydrogen-bonding of neighbor silica particles. In addition, since this basic treatment enhanced the laser damage resistance, such strengthened antireflective coatings have been successfully evaluated on flashlamps used on Phebus, Europe's most powerful laser. This allows an increase of the laser-disk pumping efficiency.

  15. 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.

  16. Silica problem in the design of geothermal power plants

    NASA Astrophysics Data System (ADS)

    Dipippo, R.

    1985-02-01

    The silica problem is examined from the perspective of the power plant designer to develop a procedure to enable a quick estimate to be made of the potential seriousness of the silica deposition problem for a wide variety of resources and for selected types of power plant. The method employs correlations for the equilibrium solubilities of quartz and amorphous silica and for the saturated liquid enthalpy and the latent heat of water substance. Single- and double-flash plants optimized for highest thermodynamic efficiency are considered. Binary-type plants are included generically without mention of cycle specifics. The results are presented both graphically and in tabular form, and the governing equations will be given in an easily-programmable form.

  17. 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.

  18. Mesoporous silicas with tunable morphology for the immobilization of laccase.

    PubMed

    Gascón, Victoria; Díaz, Isabel; Márquez-Álvarez, Carlos; Blanco, Rosa M

    2014-05-30

    Siliceous ordered mesoporous materials (OMM) are gaining interest as supports for enzyme immobilization due to their uniform pore size, large surface area, tunable pore network and the introduction of organic components to mesoporous structure. We used SBA-15 type silica materials, which exhibit a regular 2D hexagonal packing of cylindrical mesopores of uniform size, for non-covalent immobilization of laccase. Synthesis conditions were adjusted in order to obtain supports with different particle shape, where those with shorter channels had higher loading capacity. Despite the similar isoelectric points of silica and laccase and the close match between the size of laccase and the pore dimensions of these SBA-15 materials, immobilization was achieved with very low leaching. Surface modification of macro-/mesoporous amorphous silica by grafting of amine moieties was proved to significantly increase the isoelectric point of this support and improve the immobilization yield.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. Silica deposits on Mars with features resembling hot spring biosignatures at El Tatio in Chile

    NASA Astrophysics Data System (ADS)

    Ruff, Steven W.; Farmer, Jack D.

    2016-11-01

    The Mars rover Spirit encountered outcrops and regolith composed of opaline silica (amorphous SiO2.nH2O) in an ancient volcanic hydrothermal setting in Gusev crater. An origin via either fumarole-related acid-sulfate leaching or precipitation from hot spring fluids was suggested previously. However, the potential significance of the characteristic nodular and mm-scale digitate opaline silica structures was not recognized. Here we report remarkably similar features within active hot spring/geyser discharge channels at El Tatio in northern Chile, where halite-encrusted silica yields infrared spectra that are the best match yet to spectra from Spirit. Furthermore, we show that the nodular and digitate silica structures at El Tatio that most closely resemble those on Mars include complex sedimentary structures produced by a combination of biotic and abiotic processes. Although fully abiotic processes are not ruled out for the Martian silica structures, they satisfy an a priori definition of potential biosignatures.

  4. Ball milling synthesis of silica nanoparticle from rice husk ash for drug delivery application.

    PubMed

    Salavati-Niasari, Masoud; Javidi, Jaber; Dadkhah, Mahnaz

    2013-07-01

    Silica nanoparticles were synthesized from rice husk ash at room temperature by using high energy planetary ball mill. The milling time and mill rotational speed were varied in four levels. The morphology of the synthesized powders was investigated by the FE-SEM and TEM image as well as XRD patterns. The results have revealed that the nano-sized amorphous silica particles are formed after about 6 h ball milling and they are spherical in shape. The average particle size of the silica powders is found to be around 70 nm which decreases with increasing ball milling time or mill rotational speed. The as-synthesized silica nanoparticles were subsequently employed as drug carrier to investigate in vitro release behavior of Penicillin-G in simulated body fluid. UV-Vis spectroscopy was used to determine the amount of Penicillin-G released from the carrier. Penicillin-G release profile from silica nanoparticles exhibited a delayed release effect.

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

    SciTech Connect

    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 good 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.

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

    DOE PAGES

    McCoy, C. A.; Gregor, M. C.; Polsin, D. N.; ...

    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

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

    SciTech Connect

    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 good 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.

  8. 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.

  9. 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.

  10. 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.

  11. Production of Nano Amorphous SiO2 from Malatya Pyrophyllite

    NASA Astrophysics Data System (ADS)

    Sarikaya, Musa; Depci, Tolga; Aydogmus, Ramazan; Yucel, Aysegul; Kizilkaya, Nilgun

    2016-10-01

    Pyrophyllite (Al4Si8O20(OH)4) is an important industrial clay mineral. In this paper, highly pure nano silica powder was synthesized by alkaline treatment method from the local pyrophyllite deposit which is in Malatya, Turkey. The morphologies, structures and properties of the raw pyrophyllite and the obtained nano amorphous SiO2 were determined by XRF, XRD, ATR, SEM and EDX. The results showed that the nano silica can be produced with a high purity (98%) and nano size (< 50 nm).

  12. 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.

  13. 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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. 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.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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 SiO2. 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.

  17. 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.

  18. Class H cement hydration at 180 °C and high pressure in the presence of added silica

    SciTech Connect

    Jupe, Andrew C.; Wilkinson, Angus P.; Luke, Karen; Funkhouser, Gary P.

    2008-10-06

    Under deep oil-well conditions of elevated temperature and pressure, crystalline calcium silicate hydrates are formed during Portland cement hydration. The use of silica rich mineral additives leads to the formation of crystalline hydrates with better mechanical properties than those formed without the additive. The effects of silica flour, silica fume (amorphous silica), and a natural zeolite mixture on the hydration of Class H cement slurries at 180 C under externally applied pressures of 7 and 52 MPa are examined in real time using in-situ synchrotron X-ray diffraction. For some compositions examined, but not all, pressure was found to have a large effect on the kinetics of crystalline hydrate formation. The use of silica fume delayed both C{sub 3}S hydration and the formation of crystalline silicate hydrates compared to what was seen with other silica sources.

  19. Class H cement hydration at 180 deg. C and high pressure in the presence of added silica

    SciTech Connect

    Jupe, Andrew C.; Wilkinson, Angus P. Luke, Karen; Funkhouser, Gary P.

    2008-05-15

    Under deep oil-well conditions of elevated temperature and pressure, crystalline calcium silicate hydrates are formed during Portland cement hydration. The use of silica rich mineral additives leads to the formation of crystalline hydrates with better mechanical properties than those formed without the additive. The effects of silica flour, silica fume (amorphous silica), and a natural zeolite mixture on the hydration of Class H cement slurries at 180 deg. C under externally applied pressures of 7 and 52 MPa are examined in real time using in-situ synchrotron X-ray diffraction. For some compositions examined, but not all, pressure was found to have a large effect on the kinetics of crystalline hydrate formation. The use of silica fume delayed both C{sub 3}S hydration and the formation of crystalline silicate hydrates compared to what was seen with other silica sources.

  20. 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.

  1. Amorphous and Ultradisperse Crystalline Materials,

    DTIC Science & Technology

    The book sums up experimental and theoretical findings on amorphous and ultradisperse crystalline materials , massive and film types. Present-day... crystalline materials of metallic systems are presented. Emphasis is placed on inorganic film materials.

  2. Crystalline Silica Primer

    USGS Publications Warehouse

    ,

    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.

  3. Characterization Techniques for Amorphous Alloys

    NASA Astrophysics Data System (ADS)

    Carow-Watamura, U.; Louzguine, D. V.; Takeuchi, A.

    This document is part of Part 2 http://dx.doi.org/10.1007/9getType="URL"/> 'Systems from B-Be-Fe to Co-W-Zr' of Subvolume B 'Physical Properties of Ternary Amorphous Alloys' of Volume 37 'Phase Diagrams and Physical Properties of Nonequilibrium Alloys' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains the Chapter '2 Characterization Techniques for Amorphous Alloys' with the content:

  4. 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.

  5. Evolution of Morphology and Crystallinity of Silica Minerals Under Hydrothermal Conditions

    NASA Astrophysics Data System (ADS)

    Isobe, H.

    2011-12-01

    Silica minerals are quite common mineral species in surface environment of the terrestrial planets. They are good indicator of terrestrial processes including hydrothermal alteration, diagenesis and soil formation. Hydrothermal quartz, metastable low temperature cristobalite and amorphous silica show characteristic morphology and crystallinity depending on their formation processes and kinetics under wide range of temperature, pressure, acidity and thermal history. In this study, silica minerals produced by acidic hydrothermal alteration related to volcanic activities and hydrothermal crystallization experiments from diatom sediment are examined with crystallographic analysis and morphologic observations. Low temperature form of cistobalite is a metastable phase and a common alteration product occured in highly acidic hydrothermal environment around fumaroles in geothermal / volcanic areas. XRD analysis revealed that the alteration degree of whole rock is represented by abundance of cristobalite. Detailed powder XRD analysis show that the primary diffraction peak of cristobalite composed with two or three phases with different d-spacing and FWHM by peak profile fitting analysis. Shorter d-spacing and narrower FWHM cristobalite crystallize from precursor materials with less-crystallized, longer d-spacing and wider FWHM cristobalite. Textures of hydrothermal cristobalite in altered rock shows remnant of porphylitic texture of the host rock, pyroxene-amphibole andesite. Diatom has amorphous silica shell and makes diatomite sediment. Diatomite found in less diagenetic Quarternary formation keeps amorphous silica diatom shells. Hydrothermal alteration experiments of amorphous silica diatomite sediment are carried out from 300 °C to 550 °C. Mineral composition of run products shows crystallization of cristobalite and quartz progress depending on temperature and run durations. Initial crystallization product, cristobalite grains occur as characteristic lepispheres and

  6. 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. © Crown copyright 2014.

  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. 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.

  9. 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.

  10. 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

  11. Hydrogenated amorphous silicon photonics

    NASA Astrophysics Data System (ADS)

    Narayanan, Karthik

    2011-12-01

    Silicon Photonics is quickly proving to be a suitable interconnect technology for meeting the future goals of on-chip bandwidth and low power requirements. However, it is not clear how silicon photonics will be integrated into CMOS chips, particularly microprocessors. The issue of integrating photonic circuits into electronic IC fabrication processes to achieve maximum flexibility and minimum complexity and cost is an important one. In order to minimize usage of chip real estate, it will be advantageous to integrate in three-dimensions. Hydrogenated amorphous silicon (a-Si:H) is emerging as a promising material for the 3-D integration of silicon photonics for on-chip optical interconnects. In addition, a-Si:H film can be deposited using CMOS compatible low temperature plasma-enhanced chemical vapor deposition (PECVD) process at any point in the fabrication process allowing maximum flexibility and minimal complexity. In this thesis, we demonstrate a-Si:H as a high performance alternate platform to crystalline silicon, enabling backend integration of optical interconnects in a hybrid photonic-electronic network-on-chip architecture. High quality passive devices are fabricated on a low-loss a-Si:H platform enabling wavelength division multiplexing schemes. We demonstrate a broadband all-optical modulation scheme based on free-carrier absorption effect, which can enable compact electro-optic modulators in a-Si:H. Furthermore, we comprehensively characterize the optical nonlinearities in a-Si:H and observe that a-Si:H exhibits enhanced nonlinearities as compared to crystalline silicon. Based on the enhanced nonlinearities, we demonstrate low-power four-wave mixing in a-Si:H waveguides enabling high speed all-optical devices in an a-Si:H platform. Finally, we demonstrate a novel data encoding scheme using thermal and all-optical tuning of silicon waveguides, increasing the spectral efficiency in an interconnect link.

  12. 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.

  13. 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.

  14. Heat of immersion of silica gel in normal alkanes and alcohols

    SciTech Connect

    Dubinin, M.M.; Isirikyan, A.A.; Nikolaev, K.M.; Polyakov, N.S.; Tatarinova, L.I.

    1986-12-20

    In order to differentiate phenomena on a smooth surface from those related to surface curvature, they must, strictly speaking, study these phenomena separately on completely nonporous and porous adsorbents of the same chemical nature. However, it is virtually impossible to obtain a completely nonporous adsorbent with a sufficiently developed surface. Thus, a permissible compromise for solving this problem lies in the selection of a porous adsorbent such that, on one hand, the effect of surface curvature is excluded due to wide pores and, on the other hand, reliable quantitative data for the properties of this surface with virtually zero curvature are obtained due to the development of the surface. For these purposes, they used a modification of their previous method and obtained silica gel (SG) with a developed surface s = 218 m/sup 2//g and broad pores D/sub max/ = 20 nm. They found that mesoporous silica gel with 20 nm pore diameter may be taken as a practical model of nonporous amorphous silica, according to the liquid immersion heats. The heats of wetting of the hydrated amorphous silica surface by normal aliphatic alcohols and hydrocarbons are independent of the number of carbon atoms in the molecules and are 220 and 65 mJ/m/sup 2/, respectively. The interphase (liquid-solid) surface layer or normal alcohol molecules on silica gel is a Langmuir palisade with the OH alcohol groups directed toward the silica surface.

  15. In-situ grown silica sinters in Icelandic geothermal areas.

    PubMed

    Tobler, Dominique J; Stefánsson, Andri; Benning, Liane G

    2008-12-01

    Field in-situ sinter growth studies have been carried out in five geochemically very different Icelandic geothermal areas with the aim to quantify the effects of water chemistry, (e.g. silica content (250 to 695 p.p.m. SiO(2)), salinity (meteoric to seawater), pH (7.5 to 10)), temperature (42-96 degrees C) and microbial abundance (prevalence, density) on the growth rates, textures and structures of sinters forming within and around geothermal waters. At each location, sinter growth was monitored over time periods between 30 min and 25 months using glass slides that acted as precipitation substrates from which sinter growth rates were derived. In geothermal areas like Svartsengi and Reykjanes, subaqueous sinters developed rapidly with growth rates of 10 and 304 kg year(-1 )m(-2), respectively, and this was attributed primarily to the near neutral pH, high salinity and medium to high silica content within these geothermal waters. The porous and homogeneous precipitates that formed at these sites were dominated by aggregates of amorphous silica and they contained few if any microorganisms. At Hveragerdi and Geysir, the geothermal waters were characterized by slightly alkaline pH, low salinity and moderate silica contents, resulting in substantially lower rates of sinter growth (0.2-1.4 kg year(-1 )m(-2)). At these sites sinter formation was restricted to the vicinity of the air-water interface (AWI) where evaporation and condensation processes predominated, with sinter textures being governed by the formation of dense and heterogeneous crusts with well-defined spicules and silica terraces. In contrast, the subaqueous sinters at these sites were characterized by extensive biofilms, which, with time, became fully silicified and thus well preserved within the sinter edifices. Finally, at Krafla, the geothermal waters exhibited high sinter growth rates (19.5 kg year(-1 )m(-2)) despite being considerably undersaturated with respect to amorphous silica. However, the bulk of

  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. Allotropic composition of amorphous carbon

    SciTech Connect

    Yastrebov, S. G. Ivanov-Omskii, V. I.

    2007-08-15

    Using the concept of an inhomogeneous broadening of spectral lines of the basic oscillators responsible for forming the spectrum, the experimental dependences of the dispersion of the imaginary part of permittivity are analyzed for amorphous carbon. It turned out that four types of oscillators contribute to this dependence. The first three types represent the electron transitions from the energy-spectrum ground state for {pi} and {sigma} electrons of amorphous carbon to an excited state. The fourth type is related to the absorption of electromagnetic radiation by free charge carriers. The absolute values of squared plasma frequencies of oscillators are estimated, and, using them, the relative fraction of sp{sup 2}-bonded atoms forming the amorphous-carbon skeleton is calculated. This estimate agrees closely with the theoretical predictions for amorphous carbon of the same density as the material under study. The dependence of the relative fraction of sp{sup 2}-bonded atoms contained in amorphous hydrogenised carbon on annealing temperature is determined. The developed method is also applied to the analysis of the normalized curve for the light extinction in the interstellar medium. The contribution to the extinction of two varieties of interstellar matter is detected.

  18. Rayleigh scattering by aqueous colloidal silica as a cause for the blue color of hydrothermal water

    NASA Astrophysics Data System (ADS)

    Ohsawa, Shinji; Kawamura, Takao; Takamatsu, Nobuki; Yusa, Yuki

    2002-03-01

    Thermal waters in hydrothermal ponds, bathing pools and the brines of geothermal electric power plants commonly have a characteristic blue color. Although many researchers have assumed that the blue color is due to a colloidal suspension and/or absorption by dissolved ferrous iron or by water itself, there has been no specific effort to identify the physical nature of this phenomenon. We have tested, in synthetic and natural solutions, whether aqueous colloidal silica is responsible for the blue color. Aqueous colloidal silica is formed by silica polymerization in thermal waters of the neutral-chloride type which contain initially monomeric silica in concentrations up to three times above the solubilities of amorphous silica. The hue of the blue thermal waters in the pools tested agrees with that of a synthesized colloidal silica solution. Grain-size analyses of aqueous colloidal silica in the blue-colored thermal waters demonstrate that the color is caused by Rayleigh scattering from aqueous colloidal silica particles with diameters (0.1-0.45 μm) smaller than the wavelengths of visible radiation.

  19. 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 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 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.

  20. Dissolution-rate enhancement of fenofibrate by adsorption onto silica using supercritical carbon dioxide.

    PubMed

    Sanganwar, Ganesh P; Gupta, Ram B

    2008-08-06

    Dissolution rate of a poorly water-soluble drug, fenofibrate, is increased by adsorbing the drug onto silica. The adsorption is achieved by first dissolving the drug in supercritical carbon dioxide and then depressurizing the solution onto silica. Loadings of up to 27.5 wt.% drug onto silica are obtained. Since solvents are not used in the loading process, the fenofibrate/silica formulation is free of any residual solvent, and carbon dioxide is freely removed upon depressurization. The formulation is characterized using infrared spectroscopy, ultraviolet spectroscopy, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. Based on in vitro dissolution study, a significant increase in the dissolution rate (approximately 80% drug release in 20 min) of drug-silica formulation is observed as compared to micronized fenofibrate (approximately 20% drug release in 20 min), which can be attributed to increase in the surface area and decrease in the crystallinity of drug after adsorption onto silica. Two different formulations are compared: (A) amorphous fenofibrate/silica and (B) slightly crystalline fenofibrate/silica. The second formulation is found to be more stable on storage.

  1. Silica-based systems for oral delivery of drugs, macromolecules and cells.

    PubMed

    Diab, Roudayna; Canilho, Nadia; Pavel, Ileana A; Haffner, Fernanda B; Girardon, Maxime; Pasc, Andreea

    2017-04-20

    According to the US Food and Drug Administration and the European Food Safety Authority, amorphous forms of silica and silicates are generally recognized to be safe as oral delivery ingredients in amounts up to 1500mg per day. Silica is used in the formulation of solid dosage forms, e.g. tablets, as glidant or lubricant. The synthesis of silica-based materials depends on the payload nature, drug, macromolecule or cell, and on the target release (active or passive). In the literature, most of the examples deal with the encapsulation of drugs in mesoporous silica nanoparticles. Still to date limited reports concerning the delivery of encapsulated macromolecules and cells have been reported in the field of oral delivery, despite the multiple promising examples demonstrating the compatibility of the sol-gel route with biological entities, likewise the interest of silica as an oral carrier. Silica diatoms appear as an elegant, cost-effective and promising alternative to synthetic sol-gel-based materials. This review reports the latest advances silica-based systems and discusses the potential benefits and drawbacks of using silica for oral delivery of drugs, macromolecules or cells. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. 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.

  3. Effect of Silica-Particle Characteristics on Impact/Usual Fatigue Properties and Evaluation of Mechanical Characteristics of Silica-Particle Epoxy Resins

    NASA Astrophysics Data System (ADS)

    Yamamoto, Isamu; Higashihara, Takashi; Kobayashi, Toshiro

    The structure (crystalline or amorphous) and shape (globular or irregular) of silica fillers were varied and their effects on the impact fatigue and usual fatigue properties in the particle-filled epoxy resins were investigated. The fatigue crack extension process was discussed in terms of initiation and propagation processes. Furthermore, the mechanical characteristics of the material were evaluated by considering the tensile properties, fatigue resistance and the fracture behavior. It has been found that the epoxy resin filled with irregular crystalline silica-particles possessed the best combination of mechanical properties.

  4. Synthesis and adsorption of silica gel modified 3-aminopropyltriethoxysilane (APTS) from corn cobs against Cu(II) in water

    NASA Astrophysics Data System (ADS)

    Purwanto, Agung; Yusmaniar, Ferdiani, Fatmawati; Damayanti, Rachma

    2017-03-01

    Silica gel modified APTS was synthesized from silica gel which was obtained from corn cobs via sol-gel process. Silica gel was synthesized from corn cobs and then chemically modified with silane coupling agent which has an amine group (NH2). This process resulting modified silica gel 3-aminopropyltriethoxysilane (APTS). Characterization of silica gel modified APTS by SEM-EDX showed that the size of the particles of silica gel modified APTS was 20µm with mass percentage of individual elements were nitrogen (N) 15.56%, silicon (Si) 50.69% and oxygen (O) 33.75%. In addition, silica gel modified APTS also showed absorption bands of functional groups silanol (Si-OH), siloxane (Si-O-Si), and an aliphatic chain (-CH2-), as well as amine (NH2) from FTIR spectra. Based on the characterization of XRD, silica gel 2θ of 21.094° and 21.32° respectively. It indicated that both material were amorphous. Determination of optimum pH and contact time on adsorption of silica gel 3-aminopropyltriethoxysilane (APTS) against Cu(II). The optimum pH and contact time was measured by using AAS. Optimum pH of adsorption silica gel modified APTS against metal Cu(II) could be obtained at pH 6 while optimum contact time was at 30 minutes, with the process of adsorption metal Cu(II) occured based on the model Freundlich isotherm.

  5. The bouncing threshold in silica nanograin collisions.

    PubMed

    Nietiadi, Maureen L; Umstätter, Philipp; Tjong, Tiffany; Rosandi, Yudi; Millán, Emmanuel N; Bringa, Eduardo M; Urbassek, Herbert M

    2017-06-28

    Using molecular dynamics simulations, we study collisions between amorphous silica nanoparticles. Our silica model contains uncontaminated surfaces, that is, the effect of surface hydroxylation or of adsorbed water layers is excluded. For central collisions, we characterize the boundary between sticking and bouncing collisions as a function of impact velocity and particle size and quantify the coefficient of restitution. We show that the traditional Johnson-Kendall-Roberts (JKR) model provides a valid description of the ingoing trajectory of two grains up to the moment of maximum compression. The distance of closest approach is slightly underestimated by the JKR model, due to the appearance of plasticity in the grains, which shows up in the form of localized shear transformation zones. The JKR model strongly underestimates the contact radius and the collision duration during the outgoing trajectory, evidencing that the breaking of covalent bonds during grain separation is not well described by this model. The adhesive neck formed between the two grains finally collapses while creating narrow filaments joining the grains, which eventually tear.

  6. 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.

  7. Nanostructures having crystalline and amorphous phases

    DOEpatents

    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.

  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. Universal features of amorphous plasticity

    NASA Astrophysics Data System (ADS)

    Budrikis, Zoe; Castellanos, David Fernandez; Sandfeld, Stefan; Zaiser, Michael; Zapperi, Stefano

    2017-07-01

    Plastic yielding of amorphous solids occurs by power-law distributed deformation avalanches whose universality is still debated. Experiments and molecular dynamics simulations are hampered by limited statistical samples, and although existing stochastic models give precise exponents, they require strong assumptions about fixed deformation directions, at odds with the statistical isotropy of amorphous materials. Here, we introduce a fully tensorial, stochastic mesoscale model for amorphous plasticity that links the statistical physics of plastic yielding to engineering mechanics. It captures the complex shear patterning observed for a wide variety of deformation modes, as well as the avalanche dynamics of plastic flow. Avalanches are described by universal size exponents and scaling functions, avalanche shapes, and local stability distributions, independent of system dimensionality, boundary and loading conditions, and stress state. Our predictions consistently differ from those of mean-field depinning models, providing evidence that plastic yielding is a distinct type of critical phenomenon.

  10. 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.

  11. 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.

  12. Universal features of amorphous plasticity

    PubMed Central

    Budrikis, Zoe; Castellanos, David Fernandez; Sandfeld, Stefan; Zaiser, Michael; Zapperi, Stefano

    2017-01-01

    Plastic yielding of amorphous solids occurs by power-law distributed deformation avalanches whose universality is still debated. Experiments and molecular dynamics simulations are hampered by limited statistical samples, and although existing stochastic models give precise exponents, they require strong assumptions about fixed deformation directions, at odds with the statistical isotropy of amorphous materials. Here, we introduce a fully tensorial, stochastic mesoscale model for amorphous plasticity that links the statistical physics of plastic yielding to engineering mechanics. It captures the complex shear patterning observed for a wide variety of deformation modes, as well as the avalanche dynamics of plastic flow. Avalanches are described by universal size exponents and scaling functions, avalanche shapes, and local stability distributions, independent of system dimensionality, boundary and loading conditions, and stress state. Our predictions consistently differ from those of mean-field depinning models, providing evidence that plastic yielding is a distinct type of critical phenomenon. PMID:28671191

  13. Universal features of amorphous plasticity.

    PubMed

    Budrikis, Zoe; Castellanos, David Fernandez; Sandfeld, Stefan; Zaiser, Michael; Zapperi, Stefano

    2017-07-03

    Plastic yielding of amorphous solids occurs by power-law distributed deformation avalanches whose universality is still debated. Experiments and molecular dynamics simulations are hampered by limited statistical samples, and although existing stochastic models give precise exponents, they require strong assumptions about fixed deformation directions, at odds with the statistical isotropy of amorphous materials. Here, we introduce a fully tensorial, stochastic mesoscale model for amorphous plasticity that links the statistical physics of plastic yielding to engineering mechanics. It captures the complex shear patterning observed for a wide variety of deformation modes, as well as the avalanche dynamics of plastic flow. Avalanches are described by universal size exponents and scaling functions, avalanche shapes, and local stability distributions, independent of system dimensionality, boundary and loading conditions, and stress state. Our predictions consistently differ from those of mean-field depinning models, providing evidence that plastic yielding is a distinct type of critical phenomenon.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Enhanced antimicrobial activity of essential oil components immobilized on silica particles.

    PubMed

    Ruiz-Rico, María; Pérez-Esteve, Édgar; Bernardos, Andrea; Sancenón, Félix; Martínez-Máñez, Ramón; Marcos, María D; Barat, José M

    2017-10-15

    The antimicrobial activity of essential oils components (EOCs) is well-known. However, their high volatility and powerful aroma limit their application in the formulation of a wide range of food products. In this context, the antimicrobial activity of carvacrol, eugenol, thymol and vanillin grafted onto the surface of three silica supports with different morphologies, textural properties and chemical reactivities (fumed silica, amorphous silica and MCM-41) was evaluated herein. Materials characterization revealed a good immobilization yield and all the devices showed a micro-scale particle size. Sensory evaluation revealed that sensory perception of EOCs decreases after covalent immobilization. Moreover, immobilization greatly enhanced the antimicrobial activity of the essential oil components against Listeria innocua and Escherichia coli compared to free components. The incorporation of EOCs immobilized on silica particles into pasteurized milk inoculated with L. innocua demonstrated their effectiveness not only for in vitro conditions, but also in a real food system. Copyright © 2017 Elsevier Ltd. All rights reserved.

  19. 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.

  20. Ultrastable Amorphous Sb2Se3 Film.

    PubMed

    Zhang, Kai; Li, Yang; Huang, Quan; Wang, Bihan; Zheng, Xuerong; Ren, Yang; Yang, Wenge

    2017-08-31

    Increasing the thermostability of amorphous materials has been a long journey to improve their properties. The metastable nature of chalcogenide glasses limits their practical applications as an amorphous semiconductor in photovoltaic performance. Here, we report the formation and physical properties of ultrastable amorphous Sb2Se3 with an enhanced thermal stability compared to ordinary amorphous Sb2Se3 (ΔTx= 17 K). By in situ high temperature-high energy synchrotron X-ray diffraction, the difference in structure relaxation between ordinary and ultrastable amorphous Sb2Se3 was manifested by local structure evolution. Ultrastable amorphous Sb2Se3 showed the smallest surface roughness and highest refractive index, the mechanism behind was further discussed in terms of fast molecular mobility and molecular orientation during vapor deposition. Formation of ultrastable amorphous Sb2Se3 demonstrated a promising avenue to obtain novel functional amorphous semiconductor with modulated structure and property.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. Silica - Boronate affinity material for quick enrichment of intracellular nucleosides.

    PubMed

    Wang, Shuxia; Li, Huihui; Guan, Xiujuan; Cheng, Ting; Zhang, Haixia

    2017-05-01

    Boronic acid modified materials have been widely used to adsorb nucleosides, but their adsorption capacities require further improvement. Most cis-diol containing biomolecules are in very low abundance along with interfering components in real samples, and need to be enriched specially. In this study, we synthesize a kind of silica absorbent modified with boronic acid derivative, using amorphous silica as raw material and obtaining high adsorption capacity for adenosine. In addition, the adsorption equilibrium can be completed within 10s and 1min for the desorption. Finally, the material was successfully applied to enrich nucleosides from cells and the spiked recoveries were found between 82.21% and 118.9%. The results showed that the prepared adsorbent has potential to effectively enrich cis-diol substances from cell samples. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. 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.

  7. 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

  8. Spheroidization of silica powders by radio frequency inductively coupled plasma with Ar-H2 and Ar-N2 as the sheath gases at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Li, Lin; Ni, Guo-hua; Guo, Qi-jia; Lin, Qi-fu; Zhao, Peng; Cheng, Jun-li

    2017-09-01

    Amorphous spherical silica powders were prepared by inductively coupled thermal plasma treatment at a radio frequency of 36.2 MHz. The effects of the added content of hydrogen and nitrogen into argon (serving as the sheath gas), as well as the carrier gas flow rate, on the spheroidization rate of silica powders, were investigated. The prepared silica powders before and after plasma treatment were examined by scanning electron microscopy, X-ray diffraction, and laser granulometric analysis. Results indicated that the average size of the silica particles increased, and the transformation of crystals into the amorphous state occurred after plasma treatment. Discharge image processing was employed to analyze the effect of the plasma temperature field on the spheroidization rate. The spheroidization rate of the silica powder increased with the increase of the hydrogen content in the sheath gas. On the other hand, the spheroidization rate of the silica power first increased and then decreased with the increase of the nitrogen content in the sheath gas. Moreover, the amorphous content increased with the increase of the spheroidization rate of the silica powder.

  9. 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.

  10. Amorphous titanium-oxide supercapacitors

    NASA Astrophysics Data System (ADS)

    Fukuhara, Mikio; Kuroda, Tomoyuki; Hasegawa, Fumihiko

    2016-10-01

    The electric capacitance of an amorphous TiO2-x surface increases proportionally to the negative sixth power of the convex diameter d. This occurs because of the van der Waals attraction on the amorphous surface of up to 7 mF/cm2, accompanied by extreme enhanced electron trapping resulting from both the quantum-size effect and an offset effect from positive charges at oxygen-vacancy sites. Here we show that a supercapacitor, constructed with a distributed constant-equipment circuit of large resistance and small capacitance on the amorphous TiO2-x surface, illuminated a red LED for 37 ms after it was charged with 1 mA at 10 V. The fabricated device showed no dielectric breakdown up to 1,100 V. Based on this approach, further advances in the development of amorphous titanium-dioxide supercapacitors might be attained by integrating oxide ribbons with a micro-electro mechanical system.

  11. 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.

  12. Optical absorption in amorphous silicon

    SciTech Connect

    O`Leary, S.K.; Zukotynski, S.; Perz, J.M.; Sidhu, L.S.

    1996-12-31

    The role that disorder plays in shaping the form of the optical absorption spectrum of hydrogenated amorphous silicon is investigated. Disorder leads to a redistribution of states, which both reduces the Tauc gap and broadens the absorption tail. The observed relationship between the Tauc gap and the breadth of the absorption tail is thus explained.

  13. Amorphous titanium-oxide supercapacitors

    PubMed Central

    Fukuhara, Mikio; Kuroda, Tomoyuki; Hasegawa, Fumihiko

    2016-01-01

    The electric capacitance of an amorphous TiO2-x surface increases proportionally to the negative sixth power of the convex diameter d. This occurs because of the van der Waals attraction on the amorphous surface of up to 7 mF/cm2, accompanied by extreme enhanced electron trapping resulting from both the quantum-size effect and an offset effect from positive charges at oxygen-vacancy sites. Here we show that a supercapacitor, constructed with a distributed constant-equipment circuit of large resistance and small capacitance on the amorphous TiO2-x surface, illuminated a red LED for 37 ms after it was charged with 1 mA at 10 V. The fabricated device showed no dielectric breakdown up to 1,100 V. Based on this approach, further advances in the development of amorphous titanium-dioxide supercapacitors might be attained by integrating oxide ribbons with a micro-electro mechanical system. PMID:27767103

  14. 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

  15. Simultaneous utilization of soju industrial waste for silica production and its residue ash as effective cationic dye adsorbent

    USDA-ARS?s Scientific Manuscript database

    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 ...

  16. 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.

  17. 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.

  18. Study of interaction in silica glass via model potential approach

    SciTech Connect

    Mann, Sarita; Rani, Pooja

    2016-05-06

    Silica is one of the most commonly encountered substances in daily life and in electronics industry. Crystalline SiO{sub 2} (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 SiO{sub 2} 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.

  19. 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.

  20. 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.

  1. In vitro efficacies of oils, silicas and plant preparations against the poultry red mite Dermanyssus gallinae.

    PubMed

    Maurer, Veronika; Perler, Erika; Heckendorn, Felix

    2009-06-01

    The aim of this study was to test the effectiveness of physically acting substances (oils and silicas) and plant preparations for the control of the poultry red mite Dermanyssus gallinae (De Geer 1778). Reproduction and survival of fed D. gallinae females were evaluated in vitro for a total of 168 h using the "area under the survival curve" (AUC) to compare survival of the mites between treatments. Four oils (two plant oils, one petroleum spray oil and diesel), one soap, three silicas (one synthetic amorphous silica, one diatomaceous earth (DE) and one DE with 2% pyrethrum extract) and seven plant preparations (derived from Chrysanthemum cineariaefolium, Allium sativum, Tanacetum vulgare, Yucca schidigera, Quillaja saponaria, Dryopteris filix-mas, and Thuja occidentalis) were tested at various concentrations. All the oils, diesel and soap significantly reduced D. gallinae survival. All silicas tested inhibited reproduction. DE significantly reduced mite survival, but amorphous silica was less effective in vitro. Except for pure A. sativum juice and the highest concentration of C. cineariaefolium extract, the plant preparations tested resulted in statistically insignificant control of D. gallinae.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Structure and Properties of Silica Glass Densified in Cold Compression and Hot Compression

    NASA Astrophysics Data System (ADS)

    Guerette, Michael; Ackerson, Michael R.; Thomas, Jay; Yuan, Fenglin; Bruce Watson, E.; Walker, David; Huang, Liping

    2015-10-01

    Silica glass has been shown in numerous studies to possess significant capacity for permanent densification under pressure at different temperatures to form high density amorphous (HDA) silica. However, it is unknown to what extent the processes leading to irreversible densification of silica glass in cold-compression at room temperature and in hot-compression (e.g., near glass transition temperature) are common in nature. In this work, a hot-compression technique was used to quench silica glass from high temperature (1100 °C) and high pressure (up to 8 GPa) conditions, which leads to density increase of ~25% and Young’s modulus increase of ~71% relative to that of pristine silica glass at ambient conditions. Our experiments and molecular dynamics (MD) simulations provide solid evidences that the intermediate-range order of the hot-compressed HDA silica is distinct from that of the counterpart cold-compressed at room temperature. This explains the much higher thermal and mechanical stability of the former than the latter upon heating and compression as revealed in our in-situ Brillouin light scattering (BLS) experiments. Our studies demonstrate the limitation of the resulting density as a structural indicator of polyamorphism, and point out the importance of temperature during compression in order to fundamentally understand HDA silica.

  7. Nanoporous silica-based protocells at multiple scales for designs of life and nanomedicine

    DOE PAGES

    Sun, Jie; Jakobsson, Eric; Wang, Yingxiao; ...

    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

  8. 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.

  9. In vitro effects of cisplatin-functionalized silica nanoparticles on chondrocytes

    NASA Astrophysics Data System (ADS)

    Bhowmick, Tridib Kumar; Yoon, Diana; Patel, Minal; Fisher, John; Ehrman, Sheryl

    2010-10-01

    In this study, we evaluated the combined effect of a known toxic molecule, cisplatin, in combination with relatively nontoxic nanoparticles, amorphous fumed silica, on chondrocyte cells. Cisplatin was attached to silica nanoparticles using aminopropyltriethoxy silane as a linker molecule, and characterized in terms of size, shape, specific surface area, as well as the dissolution of cisplatin from the silica surface. The primary particle diameter of the as-received silica nanoparticles ranged from 7.1 to 61 nm, estimated from measurements of specific surface area, and the primary particles were aggregated. The effects of cisplatin-functionalized silica particles with different specific surface areas (41, 85, 202, 237, and 297 m2/g) were compared in vitro on chondrocytes, the parenchymal cell of hyaline cartilage. The results show that adverse effects on cell function, as evidenced by reduced metabolic activity measured by the MTT assay and increased membrane permeability observed using the Live/Dead stain, can be correlated with specific surface area of the silica. Cisplatin-functionalized silica nanoparticles with the highest specific surface area incited the greatest response, which was almost equivalent to that induced by free cisplatin. This result suggests the importance of particle specific surface area in interactions between cells and surface-functionalized nanomaterials.

  10. 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.

  11. Structure and Properties of Silica Glass Densified in Cold Compression and Hot Compression.

    PubMed

    Guerette, Michael; Ackerson, Michael R; Thomas, Jay; Yuan, Fenglin; Bruce Watson, E; Walker, David; Huang, Liping

    2015-10-15

    Silica glass has been shown in numerous studies to possess significant capacity for permanent densification under pressure at different temperatures to form high density amorphous (HDA) silica. However, it is unknown to what extent the processes leading to irreversible densification of silica glass in cold-compression at room temperature and in hot-compression (e.g., near glass transition temperature) are common in nature. In this work, a hot-compression technique was used to quench silica glass from high temperature (1100 °C) and high pressure (up to 8 GPa) conditions, which leads to density increase of ~25% and Young's modulus increase of ~71% relative to that of pristine silica glass at ambient conditions. Our experiments and molecular dynamics (MD) simulations provide solid evidences that the intermediate-range order of the hot-compressed HDA silica is distinct from that of the counterpart cold-compressed at room temperature. This explains the much higher thermal and mechanical stability of the former than the latter upon heating and compression as revealed in our in-situ Brillouin light scattering (BLS) experiments. Our studies demonstrate the limitation of the resulting density as a structural indicator of polyamorphism, and point out the importance of temperature during compression in order to fundamentally understand HDA silica.

  12. Amorphous Semiconductors: From Photocatalyst to Computer Memory

    NASA Astrophysics Data System (ADS)

    Sundararajan, Mayur

    Amorphous semiconductors are useful in many applications like solar cells, thin film displays, sensors, electrophotography, etc. The dissertation contains four projects. In the first three projects, semiconductor glasses which are a subset of amorphous semiconductors were studied. The last project is about exploring the strengths and constraints of two analysis programs which calculate the particle size information from experimental Small Angle X-ray Scattering data. By definition, glasses have a random atomic arrangement with no order beyond the nearest neighbor, but strangely there exists an Intermediate Range Order (IRO). The origin of IRO is still not clearly understood, but various models have been proposed. The signature of IRO is the First Sharp Diffraction Peak(FSDP) observed in x-ray and neutron scattering data. The FSDP of TiO 2 SiO2 glass photocatalyst with different Ti:Si ratio from SAXS data was measured to test the theoretical models. The experimental results along with its computer simulation results strongly supported one of two leading models. It was also found that the effect of doping IRO on TiO2 SiO2 is severe in mesoporous form than the bulk form. Glass semiconductors in mesoporous form are very useful photocatalysts due to their large specific surface area. Solar energy conversion of photocatalysts greatly depends on their bandgap, but very few photocatalysts have the optical bandgap covering the whole visible region of solar spectrum leading to poor efficiency. A physical method was developed to manipulate the bandgap of mesoporous photocatalysts, by using the anisotropic thermal expansion and stressed glass network properties of mesoporous glasses. The anisotropic thermal expansion was established by S/WAXS characterization of mesoporous silica (MCM-41). The residual stress in the glass network of mesoporous glasses was already known for an earlier work. The new method was initially applied on mesoporous TiPO4, and the results were

  13. Flexible amorphous metal films with high stability

    NASA Astrophysics Data System (ADS)

    Liu, M.; Cao, C. R.; Lu, Y. M.; Wang, W. H.; Bai, H. Y.

    2017-01-01

    We report the formation of amorphous Cu50Zr50 films with a large-area of more than 100 cm2. The films were fabricated by ion beam assisted deposition with a slow deposition rate at moderate temperature. The amorphous films have markedly enhanced thermal stability, excellent flexibility, and high reflectivity with atomic level smoothness. The multifunctional properties of the amorphous films are favorites in the promising applications of smart skin or wearable devices. The method of preparing highly stable amorphous metal films by tuning the deposition rate instead of deposition temperature could pave a way for exploring amorphous metal films with unique properties.

  14. 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.

  15. 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.

  16. A hydrothermal peroxo method for preparation of highly crystalline silica-titania photocatalysts.

    PubMed

    Krivtsov, Igor; Ilkaeva, Marina; Avdin, Viacheslav; Khainakov, Sergei; Garcìa, Jose R; Ordòñez, Salvador; Dìaz, Eva; Faba, Laura

    2015-04-15

    A new completely inorganic method of preparation of silica-titania photocatalyst has been described. It has been established that the addition of silica promotes crystallinity of TiO2 anatase phase. Relative crystallinity and TiO2 crystal size in the silica-titania particles increase with the silica content until SiO2/TiO2 molar ratio of 0.9, but at higher molar ratios they start to decrease. The single-source precursor containing peroxo titanic (PTA) and silicic acids has been proved to be responsible for high crystallinity of TiO2 encapsulated into amorphous silica. It has been proposed that peroxo groups enhance rapid formation of crystalline titania seeds, while silica controls their growth. It has been concluded from the TEM that the most morphologically uniform anatase crystallites covered with SiO2 particles are prepared at SiO2/TiO2 molar ratio of 0.4. This sample, according to (29)Si NMR, also shows the high content of hydroxylated silica Q(3) and Q(2) groups, and it is the most photocatalytically active in UV-assisted decomposition of methylene blue among the tested materials. It has been determined that the increase in the amount of the condensed Q(4) silica in the mixed oxides leads to the decrease in photocatalytic performance of the material, despite its better crystallinity. High crystallinity, low degree of incorporation of Ti atoms in SiO2 in the mixed oxide and adsorption of methylene blue in the vicinity of photoactive sites on the hydroxylated silica have been considered as the main factors determining the high degradation degree of methylene blue in the presence of silica-titania. Copyright © 2014 Elsevier Inc. All rights reserved.

  17. Topological Insulators in Amorphous Systems

    NASA Astrophysics Data System (ADS)

    Agarwala, Adhip; Shenoy, Vijay B.

    2017-06-01

    Much of the current understanding of topological insulators, which informs the experimental search for topological materials and systems, is based on crystalline band theory, where local electronic degrees of freedom at different crystal sites hybridize with each other in ways that produce nontrivial topology. Here we provide a novel theoretical demonstration of realizing topological phases in amorphous systems, as exemplified by a set of sites randomly located in space. We show this by constructing hopping models on such random lattices whose gapped ground states are shown to possess nontrivial topological nature (characterized by Bott indices) that manifests as quantized conductances in systems with a boundary. Our study adds a new dimension, beyond crystalline solids, to the search for topological systems by pointing to the promising possibilities in amorphous solids and other engineered random systems.

  18. Topological Insulators in Amorphous Systems.

    PubMed

    Agarwala, Adhip; Shenoy, Vijay B

    2017-06-09

    Much of the current understanding of topological insulators, which informs the experimental search for topological materials and systems, is based on crystalline band theory, where local electronic degrees of freedom at different crystal sites hybridize with each other in ways that produce nontrivial topology. Here we provide a novel theoretical demonstration of realizing topological phases in amorphous systems, as exemplified by a set of sites randomly located in space. We show this by constructing hopping models on such random lattices whose gapped ground states are shown to possess nontrivial topological nature (characterized by Bott indices) that manifests as quantized conductances in systems with a boundary. Our study adds a new dimension, beyond crystalline solids, to the search for topological systems by pointing to the promising possibilities in amorphous solids and other engineered random systems.

  19. Multifractal and mechanical analysis of amorphous solid dispersions.

    PubMed

    Adler, Camille; Teleki, Alexandra; Kuentz, Martin

    2017-05-15

    The formulation of lipophilic and hydrophobic compounds is a challenge for the pharmaceutical industry and it requires the development of complex formulations. Our first aim was to investigate hot-melt extrudate microstructures by means of multifractal analysis using scanning electron microscopy imaging. Since the microstructure can affect solid dosage form performance such as mechanical properties, a second objective was to study the influence of the type of adsorbent and of the presence of an amorphous compound on extrudate hardness. β-Carotene (BC) was chosen as poorly water-soluble model compound. Formulations containing a polymer, a lipid and two different silica based inorganic carriers were produced by hot-melt extrusion. Based on scanning electron microscopy/energy dispersive X-ray spectroscopy, the obtained images were analyzed using multifractal formalism. The breaking force of the strands was assessed by a three point bending test. Multifractal analysis and three point bending results showed that the nature of interparticle interactions in the inorganic carrier as well as the presence of amorphous BC had an influence on the microstructure and thus on the mechanical performance. The use of multifractal analysis and the study of the mechanical properties were complementary to better characterize and understand complex formulations obtained by hot-melt extrusion. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. Phonon interference in crystalline and amorphous confined nanoscopic films

    NASA Astrophysics Data System (ADS)

    Liang, Zhi; Wilson, Thomas E.; Keblinski, Pawel

    2017-02-01

    Using molecular dynamics phonon wave packet simulations, we study phonon transmission across hexagonal (h)-BN and amorphous silica (a-SiO2) nanoscopic thin films sandwiched by two crystalline leads. Due to the phonon interference effect, the frequency-dependent phonon transmission coefficient in the case of the crystalline film (Si|h-BN|Al heterostructure) exhibits a strongly oscillatory behavior. In the case of the amorphous film (Si|a-SiO2|Al and Si|a-SiO2|Si heterostructures), in spite of structural disorder, the phonon transmission coefficient also exhibits oscillatory behavior at low frequencies (up to ˜1.2 THz), with a period of oscillation consistent with the prediction from the two-beam interference equation. Above 1.2 THz, however, the phonon interference effect is greatly weakened by the diffuse scattering of higher-frequency phonons within an a-SiO2 thin film and at the two interfaces confining the a-SiO2 thin film.

  1. Low-temperature thermal expansion of amorphous solids

    SciTech Connect

    Ackerman, David Alan

    1982-01-01

    For most amorphous materials at temperatures below approx. = 1 K, the magnitudes and temperature dependences of specific heat, thermal conductivity and ultrasonic dispersion are qualitatively similar, independent of chemical composition. It has been suggested that thermal expansion also exhibits this universal behavior. The development of a dilatometer capable of resolving sample strains as small as 10/sup -12/ has permitted measurement of the linear thermal expansion of various glasses below 1 K. These investigations have demonstrated, however, that the low-temperature thermal expansion coefficient of glasses can be positive, negative, large or small. Analysis of measurements performed on two types of vitreous silica, two amorphous polymers, As/sub 2/S/sub 3/ and ZrO/sub 2/:Y/sub 2/O/sub 3/ is presented in the context of the phenomenological tunneling-states model. Consistency in explanation of thermal expansion and ultrasonic behavior is maintained by assuming a broad, weakly energy-dependent distribution of coupling strengths between phonons and the localized excitations thought to be characteristic of the glassy state.

  2. Rare earth modified silica-aluminas as supports for bifunctional catalysis

    SciTech Connect

    Soled, S.L.; McVicker, G.; Miseo, S.

    1996-12-31

    We have explored rare earth oxide-modified amorphous silica-aluminas as {open_quotes}permanent{close_quotes} intermediate strength acids used as supports for bifunctional catalysts. The addition of well dispersed weakly basic rare earth oxides {open_quotes}titrates{close_quotes} the stronger acid sites of amorphous silica-alumina and lowers the acid strength to the level shown by halided aluminas. Physical and chemical probes, as well as model olefin and paraffin isomerization reactions show that acid strength can be adjusted close to that of chlorided and fluorided aluminas. Metal activity is inhibited relative to halided alumina catalysts, which limits the direct metal-catalyzed dehydrocyclization reactions during paraffin reforming but does not interfere with hydroisomerization reactions.

  3. 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.

  4. 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

  5. Serpentinization processes: Influence of silica

    NASA Astrophysics Data System (ADS)

    Huang, R.; Sun, W.; Ding, X.; Song, M.; Zhan, W.

    2016-12-01

    Serpentinization systems are highly enriched in molecular hydrogen (H2) and hydrocarbons (e.g. methane, ethane and propane). The production of hydrocarbons results from reactions between H2 and oxidized carbon (carbon dioxide and carbon monoxide), which possibly contribute to climate changes during early history of the Earth. However, the influence of silica on the production of H2 and hydrocarbons was poorly constrained. We performed experiments at 311-500 °C and 3.0 kbar using mechanical mixtures of silica and olivine in ratios ranging from 0 to 40%. Molecular hydrogen (H2), methane, ethane and propane were formed, which were analyzed by gas chromatography. It was found that silica largely decreased H2 production. Without any silica, olivine serpentinization produced 94.5 mmol/kg H2 after 20 days of reaction time. By contrast, with the presence of 20% silica, H2 concentrations decreased largely, 8.5 mmol/kg. However, the influence of silica on the production of hydrocarbons is negligible. Moreover, with the addition of 20%-40% silica, the major hydrous minerals are talc, which was quantified according to an established standard curve calibrated by infrared spectroscopy analyses. It shows that silica greatly enhances olivine hydration, especially at 500 °C. Without any addition of silica, reaction extents were <5% at 17 days during olivine serpentinization at 500 °C and 3.0 kbar. By contrast, with the presence of 50% silica, olivine was completely transformed to talc within 9 days. This study indicates that silica impedes the oxidation of ferrous iron into ferric iron, and that rates of olivine hydration in natural geological settings are much faster with silica supply.

  6. 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

  7. 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

  8. Silica, Hybrid Silica, Hydride Silica and Non-Silica Stationary Phases for Liquid Chromatography. Part II: Chemical and Thermal Stability.

    PubMed

    Borges, Endler M; Volmer, Dietrich A

    2015-08-01

    In the first part of this review, stationary phases (silica, hybrid silica, hydride silica and non-silica stationary phases) were characterized and compared with respect to selectivity, efficiency, resolution, solvent consumption and analysis time. The present review focuses on the thermal and chemical stability of stationary phases. Stationary phases of high chemical and thermal stability are required for separations that are carried over a wide pH and/or temperature range. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  9. Silica activity in lunar lavas

    NASA Technical Reports Server (NTRS)

    Nash, W. P.; Haselton, J. D.

    1975-01-01

    Calculated values of log alpha SiO2 in lunar magmas range from approximately -0.8 to unity in the temperature range of 1100-1300 C. High-titanium mare basalts begin crystallizing at silica activities insufficient for orthopyroxene saturation; in contrast to terrestrial lavas, silica activities rise substantially with crystallization and cause silica saturation in the residuum. Igneous rocks of the highland regions have relatively higher initial silica activities than mare basalts. Thermodynamic calculations indicate that high-titanium mare basalts could be derived from a 90 to 240-km deep source region containing olivine and orthopyroxene in addition to other phases.

  10. Application of mesoporous silicon dioxide and silicate in oral amorphous drug delivery systems.

    PubMed

    Qian, Ken K; Bogner, Robin H

    2012-02-01

    Aqueous solubility of an active pharmaceutical ingredient is an important consideration to ensure successful drug development. Mesoporous materials have been investigated as an amorphous drug delivery system owing to their nanosized capillaries and large surface areas. The complex interactions of crystalline compounds with mesoporous media and their implication in drug delivery are not well understood. Molecules interacting with porous media behave very differently than those in bulk phase. Their altered dynamics and thermodynamics play an important role in the properties and product performance of the amorphous system. In this review, application of mesoporous silicon dioxide and silicates in drug amorphization is the main focus. First, as background, the nature of gas-porous media interactions is summarized. The synthesis of various types of mesoporous silica, which are used by many investigators in this field, is described. Second, the behavior of molecules confined in mesopores is compared with those in bulk, crystalline phase. The molecular dynamics of compounds due to confinement, analyzed using various techniques, and their consequences in drug delivery are discussed. Finally, the preparation and performance of drug delivery systems using mesoporous silica are examined.

  11. Transformations in the Medium-Range Order of Fused Silica under High Pressure

    NASA Astrophysics Data System (ADS)

    Dávila, Lílian P.; Caturla, Maria-José; Kubota, Alison; Sadigh, Babak; Díaz de La Rubia, Tomás; Shackelford, James F.; Risbud, Subhash H.; Garofalini, Stephen H.

    2003-11-01

    Molecular dynamics simulations of fused silica at shock pressures reproduce the experimental equation of state of this material and explain its characteristic shape. We demonstrate that shock waves modify the medium-range order of this amorphous system, producing changes that are only clearly revealed by its ring size distribution. The ring size distribution remains practically unchanged during elastic compression but varies continuously after the transition to the plastic regime.

  12. Formation and characterization of high surface area thermally stabilized titania/silica composite materials via hydrolysis of titanium(IV) tetra-isopropoxide in sols of spherical silica particles.

    PubMed

    Khalil, Kamal M S; Elsamahy, Ahmed A; Elanany, Mohamed S

    2002-05-15

    A direct synthetic route leading to titania particles dispersed on nonporous spherical silica particles has been investigated; 5, 10, and 20% (w/w) titania/silica sols mixtures were achieved via hydrolyzation of titanium tetra-isopropxide solution in the mother liquor of a freshly prepared sol of spherical silica particles (Stöber particles). Titania/silica materials were produced by subsequent drying and calcination of the xerogels so obtained for 3 h at 400 and 600 degrees C. The materials were investigated by means of thermal analyses (TGA and DSC), FT-IR, N(2) gas adsorption-desorption, powder X-ray diffraction (XRD), and transmission electron microscopy (TEM). In spite of the low surface area (13.1 m(2)/g) of the pure spherical silica particles calcined at 400 degrees C, high surface area and mesoporous texture titania/silica materials were obtained (e.g., S(BET) ca. 293 m(2)/g for the 10% titania/silica calcined at 400 degrees C). Moreover, the materials were shown to be amorphous toward XRD up to 600 degrees C, while reasonable surface areas were preserved. It has been concluded that dispersion of titania particles onto the surface of the nonporous spherical silica particles increase their roughness, therefore leading to composite materials of less firm packing and mesoporosity.

  13. 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.

  14. Alkoxy-Siloxide Metal Complexes: Precursors to Metal Silica, Metal Oxide Silica, and Metal Silicate Materials.

    NASA Astrophysics Data System (ADS)

    Terry, Karl William

    The alkoxy-siloxide complexes M (OSi(O ^{rm t}Bu)_3 ]_4 (M = Ti(1), Zr(2), Hf(3)), were prepared by reaction with their respective metal diethylamides. These compounds readily undergo low-temperature decomposition to their respective metal oxide silica materials rm(MO_2{cdot}4SiO_2). The volatile products of the thermolysis of 2 (ca. 200 ^circC) were isobutylene (11.7 equiv) and water (5.4 equiv). The rm ZrO _2{cdot}4SiO_2 material from the decomposition of 2 at 400^circ C was amorphous until ca. 1100^ circC where crystallization of t-ZrO _2 occurred. After thermolysis to 1500 ^circC, t-ZrO_2 and cristobalite were the major products with minor amounts of m-ZrO_2. The rm HfO_2{cdot}4SiO_2 material from the decomposition of 3 at 400^ circC was amorphous until ca. 1000 ^circC where crystallization of c/t -HfO_2 was observed. Thermolysis to 1460^circC yielded c/t -HfO_2, m-HfO_2, and minor amounts of cristobalite. The crystallization of anatase in the rm TiO_2{cdot }4SiO_2 material from decomposed 1 at 400^circC was apparent after thermolysis to 1000^circC. Thermolysis to 1400^circC gave a mixture of anatase, rutile, and cristobalite. Compound 2 was decomposed in xylenes and yielded a transparent gel which was isolated as a white powder upon drying in vacuuo. The compounds [ Me _2AlOSi(O^{t}Bu)_3] _2 (4) and [( ^{t}BuO)MeAlOSi(O^{t}Bu) _3]_2 (5) were structurally characterized and contain bent and planar rm Al_2O_2 four membered rings, respectively. Both 4 and 5 yield isobutylene upon thermolysis (ca. 200 ^circC) and the crystallization of mullite occurs at 1034^circC and 1017^circC, respectively (by DTA). The solution thermolysis of 4 in refluxing toluene yields an opaque white gel. The crystallization of mullite occurs at 1029^circC (by DTA). The compounds [ CuOSi(O ^{t}Bu)_3]_{n } (6) and [ CuOSi(O ^{t}Bu)_2Ph]_4 (7) were prepared by reaction with [ CuO^{t}Bu]_4. The thermolysis of 6 at 1000^circ C under argon gave Cu^circ and amorphous silica and thermolysis under

  15. 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.

  16. On Structure and Properties of Amorphous Materials

    PubMed Central

    Stachurski, Zbigniew H.

    2011-01-01

    Mechanical, optical, magnetic and electronic properties of amorphous materials hold great promise towards current and emergent technologies. We distinguish at least four categories of amorphous (glassy) materials: (i) metallic; (ii) thin films; (iii) organic and inorganic thermoplastics; and (iv) amorphous permanent networks. Some fundamental questions about the atomic arrangements remain unresolved. This paper focuses on the models of atomic arrangements in amorphous materials. The earliest ideas of Bernal on the structure of liquids were followed by experiments and computer models for the packing of spheres. Modern approach is to carry out computer simulations with prediction that can be tested by experiments. A geometrical concept of an ideal amorphous solid is presented as a novel contribution to the understanding of atomic arrangements in amorphous solids. PMID:28824158

  17. 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.

  18. 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.; 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.

  19. 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.

  20. Amorphous-Amorphous Phase Separation in API/Polymer Formulations.

    PubMed

    Luebbert, Christian; Huxoll, Fabian; Sadowski, Gabriele

    2017-02-15

    The long-term stability of pharmaceutical formulations of poorly-soluble drugs in polymers determines their bioavailability and therapeutic applicability. However, these formulations do not only often tend to crystallize during storage, but also tend to undergo unwanted amorphous-amorphous phase separations (APS). Whereas the crystallization behavior of APIs in polymers has been measured and modeled during the last years, the APS phenomenon is still poorly understood. In this study, the crystallization behavior, APS, and glass-transition temperatures formulations of ibuprofen and felodipine in polymeric PLGA excipients exhibiting different ratios of lactic acid and glycolic acid monomers in the PLGA chain were investigated by means of hot-stage microscopy and DSC. APS and recrystallization was observed in ibuprofen/PLGA formulations, while only recrystallization occurred in felodipine/PLGA formulations. Based on a successful modeling of the crystallization behavior using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), the occurrence of APS was predicted in agreement with experimental findings.

  1. 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.

  2. 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.

  3. The physics and applications of amorphous semiconductors

    SciTech Connect

    Madan, A.; Shaw, M.P.

    1988-01-01

    This is a treatise on the physics and applications of the new emerging technology of amorphous semiconductors. The authors focus upon research problems such as the optimization of device performance while also presenting the general physics of amorphous semiconductors. The first part of the book covers hydrogenated amorphous silicon type alloys, whose applications include inexpensive solar cells, thin film transistors, image scanners, electrophotography, optical recording, and gas sensors. The second part of the book discusses amorphous chalcogenides, whose applications include electrophotography, switching, and memory elements.

  4. Martian Hot Springs? Silica deposits in the Nili Patera Caldera.

    NASA Astrophysics Data System (ADS)

    Skok, J. R.; Mustard, J. F.; Ehlmann, B. L.; Murchie, S. L.

    2011-12-01

    The caldera of the Syrtis Major volcanic complex shows evidence of a late-stage, chemically evolved eruption that emplaced a volcanic cone and an evolved dacitic lava flow. This cone and flow contain several light-toned deposits, spectrally defined, with the CRISM instrument, by a broad asymmetrical absorption centered at 2.21 μm that is characteristic of a Si-OH bond. Additional weak 1.4 and 1.9 μm OH- and H2O related absorption features were detected that combined with the 2.21 μm feature confirms the detection of hydrated silica (SiO2 nH2O). The deposits are expressed morphologically as low mounds in stereo HiRISE data that superpose and post-date the volcanic flows. This mineral detection and volcanic context is consistent with several formation mechanisms, notably volcanic outgassing leading to fumarole surface alteration or silica deposition in volcanically driven hot springs. Since current orbital observations do not allow conclusive determination of precise mechanism, we here focus on the hot spring silica depositional hypothesis and investigate what the current observations tell us about such a system. These deposits would occur as post-eruption volcanic heat-driven hydrothermal convection of ground and possibly magmatic waters. Convecting, heated water would dissolve the igneous minerals in the basalt that forms the majority of the caldera mobilizing significant silica. Silica saturated fluids that reach the surface cool and deposit amorphous silica as the silica solubility in the fluids decreases. The large size and mound building nature of individual deposits require a significant and sustained fluid source for deposition. That amorphous silica deposits were detected in several distinct regions illustrates the prevalence of this process in this volcanic complex. The largest deposit is located on the southern flank of the cone and forms a fan-shaped morphology as the material is sourced from a vent and flows downslope. Another small deposit was

  5. 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).

  6. Amine Modification of Nonporous Silica Nanoparticles Reduces Inflammatory Response Following Intratracheal Instillation in Murine Lungs

    PubMed Central

    Morris, Angie S.; Adamcakova-Dodd, Andrea; Lehman, Sean E.; Wongrakpanich, Amaraporn; Thorne, Peter S.; Larsen, Sarah C.; Salem, Aliasger K.

    2015-01-01

    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 neither bare silica NPs nor amine-functionalized NPs using doses based on both mass concentration (below 200 μg/mL) and exposed total surface area (below 14 m2/L). To assess lung inflammation, C57/B16 mice were administered bare and amine-functionalized silica NPs via intra-tracheal instillation. Two doses (0.1 and 0.5 mg 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 (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

  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.

  8. Modulus-density scaling behaviour and framework architecture of nanoporous self-assembled silicas.

    PubMed

    Fan, Hongyou; Hartshorn, Christopher; Buchheit, Thomas; Tallant, David; Assink, Roger; Simpson, Regina; Kissel, Dave J; Lacks, Daniel J; Torquato, Salvatore; Brinker, C Jeffrey

    2007-06-01

    Natural porous materials such as bone, wood and pith evolved to maximize modulus for a given density. For these three-dimensional cellular solids, modulus scales quadratically with relative density. But can nanostructuring improve on Nature's designs? Here, we report modulus-density scaling relationships for cubic (C), hexagonal (H) and worm-like disordered (D) nanoporous silicas prepared by surfactant-directed self-assembly. Over the relative density range, 0.5 to 0.65, Young's modulus scales as (density)n where n(C)silicas exhibit a structure-specific hierarchy of modulus values Dsilica framework of self-assembled silica to contain a higher portion of small, stiff rings than found in other forms of amorphous silica. The nanostructure-specific hierarchy and systematic increase in framework modulus we observe, when decreasing the silica framework thickness below 2 nm, provides a new ability to maximize mechanical properties at a given density needed for nanoporous materials integration.

  9. Amorphous silicon based radiation detectors

    SciTech Connect

    Perez-Mendez, V.; Cho, G.; Drewery, J.; Jing, T.; Kaplan, S.N.; Qureshi, S.; Wildermuth, D. ); Fujieda, I.; Street, R.A. )

    1991-07-01

    We describe the characteristics of thin(1 {mu}m) and thick (>30{mu}m) hydrogenated amorphous silicon p-i-n diodes which are optimized for detecting and recording the spatial distribution of charged particles, x-rays and {gamma} rays. For x-ray, {gamma} ray, and charged particle detection we can use thin p-i-n photosensitive diode arrays coupled to evaporated layers of suitable scintillators. For direct detection of charged particles with high resistance to radiation damage, we use the thick p-i-n diode arrays. 13 refs., 7 figs.

  10. 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.

  11. Structural study of amorphous polyaniline

    NASA Astrophysics Data System (ADS)

    Laridjani, M.; Pouget, J. P.; MacDiarmid, A. G.; Epstein, A. J.

    1992-06-01

    Many materials, especially polymers, have a substantial volume fraction with no long range crystalline order. Through these regions are often termed amorphous, they frequently have a specific local order. We describe and use here a method, base on a non-energy dispersive X-ray diffraction technique, to obtain good quality interference functions and, by Fourier transform, radial distribution functions of the amorphous structure of polymers. We apply this approach to members of a family of electronic polymers of current interest : polyaniline emeraldine bases. We show that the local order exhibits significant differences in type I and type II materials, precipitated as salt and base respectively. These studies demonstrate the importance of sample preparation in evaluating the physical properties of polyaniline, and provide a structural origin for memory effects observed in the doping-dedoping processes. Beaucoup de matériaux, spécialement les polymères, ont une importante fraction de leur volume sans ordre cristallin à longue portée. Bien que ces régions soient souvent appelées amorphes, elles présentent fréquemment un ordre local caractéristique. Nous décrivons et utilisons dans ce papier une méthode, basée sur une technique de diffraction de rayons X non dispersive en énergie, pour obtenir des fonctions d'interférence de bonne qualité et, par transformée de Fourier, la fonction de distribution radiale des polymères amorphes. Nous appliquons cette technique à plusieurs éléments d'une même famille de polymères électroniques d'intérêt actuel : les polyanilines éméraldine bases. Nous montrons que l'ordre local présente d'appréciables différences dans les matériaux de type I et II, préparés respectivement sous forme de sel et de base. Cette étude démontre l'importance des conditions de préparation sur les propriétés physiques du polyaniline et donne une base structurale aux effets observés dans les processus de dopage-dédopage de

  12. Electrochemically Formed Porous Silica

    PubMed Central

    Chazalviel, Jean-Noël; Ozanam, François

    2011-01-01

    Controlled electrochemical formation of porous silica can be realized in dilute aqueous, neutral-pH, fluoride medium. Formation of a porous film is initiated by sweeping the potential applied to silicon to values higher than 20 V. Film formation, reaching a steady state, may be pursued in a wide range of potentials, including lower potentials. The origin of a threshold potential for porous film initiation has been explained quantitatively. All of the films appear mesoporous. Films grown at high potentials exhibit a variety of macrostructures superimposed on the mesoporosity. These macrostructures result from selective dissolution of silica induced by local pH lowering due to oxygen evolution. Films grown at potentials lower than 15 V appear uniform on the micrometer scale. However, all of the films also exhibit a stratified structure on the scale of a few tens of nanometres. This periodic structure can be traced back to the oscillatory behavior observed during the electrochemical dissolution of silicon in fluoride medium. It suggests that periodic breaking of the growing film may be responsible for this morphology. PMID:28879953

  13. Postshock temperatures in silica

    SciTech Connect

    Boslough, M.B.

    1988-06-10

    Experimental postshock temperatures for crystalline quartz released from shock states between 86 and 127 GPa and for fuset silica released from 59 to 73 GPa have been determined using previously measured spectral radiance data. The temperatures range from 3660 to 4150 K and are consistent with the interpretation based on shock temperature measurements, that the Hugoniot of SiO/sub 2/ crosses the phase boundary between stishovite and liquid. The new postshock temperatures were used to determine the Grueneisen parameter of liquid silica at high pressures and temperatures and the specific volume of the release state (..gamma../V = 3.5 Mg/m/sup 3/ and F/sub r/ = 0.266 m/sup 3//Mg, respectively), although there is some ambiguity as to whether this volume corresponds to a partial or total release state. To show the validity of these postshock temperatures, a radiative transport model was extended to times after free surface arrival of the shock wave. copyright American Geophysical Union 1988

  14. Peptide -- Silica Hybrid Networks

    NASA Astrophysics Data System (ADS)

    Altunbas, Aysegul; Sharma, Nikhil; Nagarkar, Radhika; Schneider, Joel; Pochan, Darrin

    2010-03-01

    In this study, a bio-inspired route was used to fabricate scaffolds that display hierarchical organization of an inorganic layer around an organic self-assembled peptide fibril template. The 20 amino acid peptide used in this study intramolecular folds into a beta-hairpin conformation on addition of a desired solution stimulus. This intramolecular folding is followed by intermolecular self-assembly of the peptides into a three dimensional network of entangled fibrils rich in beta-sheet with a high density of lysine groups exposed on the fibril-surfaces. The lysine-rich surface chemistry was utilized to create a silica shell around the fibrils. The mineralization process of the fibrils results in a rigid, porous silica network that retains the microscale and nanoscale structure of the peptide fibril network. Structural characterization via Transmission Electron Microscopy, cryogenic-Scanning Electron Microscopy, mechanical characterization via oscillatory rheology, Small Angle X-ray and Neutron Scattering of the silicified hydrogels will be presented.

  15. Probing the chemistry, structure, and dynamics of the water-silica interface

    NASA Astrophysics Data System (ADS)

    Lockwood, Glenn K.

    Despite its natural abundance and wide-ranging technological relevance, much remains unknown or unclear about water-silica interfaces. Computer simulation stands to bridge the gaps of knowledge left by experiment, and a recently developed Dissociative Water Potential has enabled the simulation of large amorphous silica surfaces in contact with water without having to impose a model of surface chemistry a priori. Earlier work with this model has revealed the existence of several protonated surface sites such as SiOH2 + and Si-(OH+)-Si that have yet to be extensively characterized. However, both experiment and quantum mechanical simulation have provided an increasing body of evidence that suggests these sites exist, and these sites may play key roles in some of the unexplained phenomena observed in water-silica systems. To this end, this Dissociative Water Potential has been applied to develop a comprehensive picture of the chemistry, structure, and dynamics of the water-silica interface that is unbiased by any expectation of what sites should form. The bridging OH site, Si-(OH+)-Si, does form and is characterized as a highly acidic site that occurs predominantly on strained Si-O-Si bridges near the interface. Similarly, the transient formation of SiOH2 + is observed, and this site is found to be more acidic than Si-(OH +)-Si. In addition to H3O+ that forms near the interface, all of these sites readily deprotonate and are expected to play a role in the enhanced proton conductivity experimentally observed in hydrated mesoporous silica. The reactions between water and silica are particularly relevant to the engineering of nuclear waste forms, and the role of water-silica interactions are also explored within the context of the degradation of silica-based waste forms exposed to radiation. Despite the significant simulation effort employed in glassy waste form research, no molecular models of radiation damage in silica include the effects of moisture. This deficiency is

  16. Hydrated silica exterior produced by biomimetic silicification confers viral vaccine heat-resistance.

    PubMed

    Wang, Guangchuan; Wang, Hong-Jiang; Zhou, Hangyu; Nian, Qing-Gong; Song, Zhiyong; Deng, Yong-Qiang; Wang, Xiaoyu; Zhu, Shun-Ya; Li, Xiao-Feng; Qin, Cheng-Feng; Tang, Ruikang

    2015-01-27

    Heat-lability is a key roadblock that strangles the widespread applications of many biological products. In nature, archaeal and extremophilic organisms utilize amorphous silica as a protective biomineral and exhibit considerable thermal tolerance. Here we present a bioinspired approach to generate thermostable virus by introducing an artificial hydrated silica exterior on individual virion. Similar to thermophiles, silicified viruses can survive longer at high temperature than their wild-type relatives. Virus inactivation assays showed that silica hydration exterior of the modified virus effectively prolonged infectivity of viruses by ∼ 10-fold at room temperature, achieving a similar result as that obtained by storing native ones at 4 °C. Mechanistic studies indicate that amorphous silica nanoclusters stabilize the inner virion structure by forming a layer that restricts molecular mobility, acting as physiochemical nanoanchors. Notably, we further evaluate the potential application of this biomimetic strategy in stabilizing clinically approved vaccine, and the silicified polio vaccine that can retain 90% potency after the storage at room temperature for 35 days was generated by this biosilicification approach and validated with in vivo experiments. This approach not only biomimetically connects inorganic material and living virus but also provides an innovative resolution to improve the thermal stability of biological agents using nanomaterials.

  17. 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.

  18. 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

  19. Size-dependent cytotoxicity of monodisperse silica nanoparticles in human endothelial cells.

    PubMed

    Napierska, Dorota; Thomassen, Leen C J; Rabolli, Virginie; Lison, Dominique; Gonzalez, Laetitia; Kirsch-Volders, Micheline; Martens, Johan A; Hoet, Peter H

    2009-04-01

    The effect that monodisperse amorphous spherical silica particles of different sizes have on the viability of endothelial cells (EAHY926 cell line) is investigated. The results indicate that exposure to silica nanoparticles causes cytotoxic damage (as indicated by lactate dehydrogenase (LDH) release) and a decrease in cell survival (as determined by the tetrazolium reduction, MTT, assay) in the EAHY926 cell line in a dose-related manner. Concentrations leading to a 50% reduction in cell viability (TC(50)) for the smallest particles tested (14-, 15-, and 16-nm diameter) ranging from 33 to 47 microg cm(-2) of cell culture differ significantly from values assessed for the bigger nanoparticles: 89 and 254 microg cm(-2) (diameter of 19 and 60 nm, respectively). Two fine silica particles with diameters of 104 and 335 nm show very low cytotoxic response compared to nanometer-sized particles with TC(50) values of 1095 and 1087 microg cm(-2), respectively. The smaller particles also appear to affect the exposed cells faster with cell death (by necrosis) being observed within just a few hours. The surface area of the tested particles is an important parameter in determining the toxicity of monodisperse amorphous silica nanoparticles.

  20. 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.

  1. Alkali-silica reaction products: Comparison between samples from concrete structures and laboratory test specimens

    SciTech Connect

    Sachlova, Sarka Prikryl, Richard; Pertold, Zdenek

    2010-12-15

    Alkali-silica gels (ASG) were investigated in concrete from bridge structures (constructed from the 1920s to 2000), as well as in experimental specimens; employing optical microscopy, petrographic image analysis, and scanning electron microscopy combined with energy dispersive spectroscopy (SEM/EDS). The main differences were found in the chemical composition and morphology of the ASGs. ASGs which had formed in older concrete samples (50-80 years old) show a partly crystalline structure and higher Ca{sup 2+} content, indicating their aging and maturation. Younger concrete samples and experimental test specimens exhibit the presence of amorphous ASG. The chemistry of ASG from experimental specimens reflects the chemical composition of accelerating solutions. - Research Highlights: {yields} Quantitative analysis of alkali-silica gels {yields} Comparison of ASR in experimental conditions with ASR in bridge structures {yields} Investigation of factors affecting alkali-silica reaction {yields} Investigation of ASR of different types of aggregates.

  2. Structure and stability of several high-pressure crystalline polymorphs of silica

    NASA Astrophysics Data System (ADS)

    Tse, John S.; Klug, Dennis D.; Allan, Douglas C.

    1995-06-01

    The structure and stability of several proposed high-pressure crystalline polymorphs of silica have been studied with a first-principles pseudopotential total-energy method within the local-density approximation. The monoclinic I2/a phase predicted recently from molecular-dynamics calculations on highly compressed amorphous silica or α quartz [J.S. Tse, D.D. Klug, and Y. LePage, Phys. Rev. Lett. 69, 3647 (1992)] is shown to be energetically competitive with the well-known stishovite structure and is substantially lower in energy than the cubic fluorite Pa3¯ structure up to 170 GPa. The results are in full accordance with previous molecular-dynamics calculations thus confirming that the empirical potential proposed by van Beest et al. is applicable to the study of the structure and dynamics of high-pressure phases of silica.

  3. Atomic Description of the Interface between Silica and Alumina in Aluminosilicates through Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy and First-Principles Calculations.

    PubMed

    Valla, Maxence; Rossini, Aaron J; Caillot, Maxime; Chizallet, Céline; Raybaud, Pascal; Digne, Mathieu; Chaumonnot, Alexandra; Lesage, Anne; Emsley, Lyndon; van Bokhoven, Jeroen A; Copéret, Christophe

    2015-08-26

    Despite the widespread use of amorphous aluminosilicates (ASA) in various industrial catalysts, the nature of the interface between silica and alumina and the atomic structure of the catalytically active sites are still subject to debate. Here, by the use of dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) and density functional theory (DFT) calculations, we show that on silica and alumina surfaces, molecular aluminum and silicon precursors are, respectively, preferentially grafted on sites that enable the formation of Al(IV) and Si(IV) interfacial sites. We also link the genesis of Brønsted acidity to the surface coverage of aluminum and silicon on silica and alumina, respectively.

  4. Diversity of iron and silica precipitation by microbial mats in hydrothermal waters, Iceland: Implications for Precambrian iron formations

    NASA Astrophysics Data System (ADS)

    Konhauser, K. O.; Ferris, F. G.

    1996-04-01

    Direct examination of microbial mats from Icelandic hot springs with transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed a consortium of bacterial cells in varying stages of mineralization. Differences in observed mineralogy largely reflect differences in the chemistry of the hydrothermal waters. Silica-rich spheroids formed epicellularly on cell walls and surrounding sheaths and capsules of microorganisms and, in some cases, intracellularly when presumably the cell(s) had lysed. Commonly, these precipitates were observed coalescing to form a matrix of amorphous silica that completely encapsulated the cells and/or replaced their cytoplasmic material. However, in other cells, the precipitates were composed of amorphous granules made exclusively of iron and silica in approximately equal proportions. At one locality, the bacteria formed several epicellular iron minerals, ranging from iron-mineralized capsules to fine-grained spheroids of amorphous ferric hydroxide and acicular aggregates of goethite. The complete encrustation of bacterial cells by silica, iron, or a combination of both may greatly enhance their preservation potential, such that these mineralized microorganisms may conceivably represent future microfossils. Thus, we may be witnessing contemporaneous biomineralization processes that are similar to those of the geologic past, particularly with regard to the origin of some Precambrian banded iron formations.

  5. 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.

  6. Silica-tin nanotubes prepared from rice husk ash by sol-gel method: Characterization and its photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Adam, Farook; Appaturi, Jimmy Nelson; Thankappan, Radhika; Nawi, Mohd Asri Mohd

    2010-11-01

    Silica-tin material has been synthesized by simple sol-gel method using rice husk ash as the source of silica and cetyltrimethylammonium bromide as the surfactant at room temperature. Calcination of the material at 500 °C for 5 h gave nanotubes with external diameter of 2-4 nm and an internal diameter of 1-2 nm. The BET specific surface area was found to be 607 m 2 g -1. Nitrogen sorption analysis exhibits a type IV isotherm with H3 hysteresis loop. The powder X-ray diffraction pattern showed that the material is amorphous. The photocatalytic activity of the prepared material was studied towards degradation of methylene blue under UV-irradiation. According to the experimental results the silica-tin nanotubes exhibit high photocatalytic activity compared to pure rice husk silica.

  7. Specific Interactions of Neutral Side Chains of an Adsorbed Protein with the Surface of α-Quartz and Silica Gel.

    PubMed

    Odinokov, Alexey V; Bagaturyants, Alexander A

    2015-07-16

    Many key features of the protein adsorption on the silica surfaces still remain unraveled. One of the open questions is the interaction of nonpolar side chains with siloxane cavities. Here, we use nonequilibrium molecular dynamics simulations for the detailed investigation of the binding of several hydrophobic and amphiphilic protein side chains with silica surface. These interactions were found to be a possible driving force for protein adsorption. The free energy gain was larger for the disordered surface of amorphous silica gel as compared to α-quartz, but the impact depended on the type of amino acid. The dependence was analyzed from the structural point of view. For every amino acid an enthalpy-entropy compensation behavior was observed. These results confirm a hypothesis of an essential role of hydrophobic interactions in protein unfolding and irreversible adsorption on the silica surface.

  8. In-vitro and in-vivo study of amorphous spironolactone prepared by adsorption method using supercritical CO2.

    PubMed

    Jiang, Qikun; Li, Yuanyuan; Fu, Qiang; Geng, Yajie; Zhao, Juanhang; Ma, Panqin; Zhang, Tianhong

    2015-02-01

    The aim of this study was to improve the oral bioavailability of spironolactone (SP). SP was adsorbed on the fumed silica using supercritical CO2 (scCO2) technology and further compressed into tablets. The morphology was observed by scanning electron microscopy (SEM), and the crystalline form was investigated by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). The dissolution test was performed in water, 0.1 M HCl solution, pH 4.5 acetate buffers and pH 6.8 phosphate buffers using the paddle method. The pharmacokinetics was undertaken in six dogs in a crossover fashion. SP was successfully prepared into tablets and presented in amorphous state. SP-silica scCO2 tablets displayed higher dissolution profiles than SP-silica physical mixtures tablets in different media. The AUC0-t and Cmax of SP-silica supercritical CO2 was 1.61- and 1.52-fold greater than those of SP-silica physical mixtures (p < 0.05), respectively. It is a promising method in improving dissolution and bioavailability by adsorbing SP, a poorly soluble drug, on the fumed silica using rapid expansion of supercritical solutions.

  9. 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.

  10. Mechanism of silica deposition in sorghum silica cells.

    PubMed

    Kumar, Santosh; Milstein, Yonat; Brami, Yaniv; Elbaum, Michael; Elbaum, Rivka

    2017-01-01

    Grasses take up silicic acid from soil and deposit it in their leaves as solid silica. This mineral, comprising 1-10% of the grass dry weight, improves plants' tolerance to various stresses. The mechanisms promoting stress tolerance are mostly unknown, and even the mineralization process is poorly understood. To study leaf mineralization in sorghum (Sorghum bicolor), we followed silica deposition in epidermal silica cells by in situ charring and air-scanning electron microscopy. Our findings were correlated to the viability of silica cells tested by fluorescein diacetate staining. We compared our results to a sorghum mutant defective in root uptake of silicic acid. We showed that the leaf silicification in these plants is intact by detecting normal mineralization in leaves exposed to silicic acid. Silica cells were viable while condensing silicic acid into silica. The controlled mineral deposition was independent of water evapotranspiration. Fluorescence recovery after photobleaching suggested that the forming mineral conformed to the cellulosic cell wall, leaving the cytoplasm well connected to neighboring cells. As the silicified wall thickened, the functional cytoplasm shrunk into a very small space. These results imply that leaf silica deposition is an active, physiologically regulated process as opposed to a simple precipitation. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

  11. 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

  12. Is Mg-stabilized amorphous calcium carbonate a homogeneous mixture of amorphous magnesium carbonate and amorphous calcium carbonate?

    PubMed

    Yang, Sheng-Yu; Chang, Hsun-Hui; Lin, Cang-Jie; Huang, Shing-Jong; Chan, Jerry C C

    2016-10-04

    We find two types of carbonate ions in Mg stabilized amorphous calcium carbonate (Mg-ACC), whose short-range orders are identical to those of ACC and amorphous magnesium carbonate (AMC). Mg-ACC comprises a homogeneous mixture of the nano-clusters of ACC and AMC. Their relative amount varies systematically at different pH.

  13. 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.

  14. 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.

  15. 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

  16. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. 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).

  18. Study on Au nanoparticles, TiO2 nanoclusters, and SiO2 nanoshells coated multi-wall carbon nanotubes/silica gel-glass

    NASA Astrophysics Data System (ADS)

    Zheng, Chan; Chen, Wenzhe; Ye, Xiaoyun

    2012-05-01

    Multi-wall carbon nanotubes (MWCNTs) coated with crystalline Au nanoparticles, TiO2 nanoclusters, and amorphous SiO2 nanoshells, to represent conductors, semiconductors, and insulators, respectively, were embedded in transparent silica gel-glass. The coated MWCNT/silica gel-glasses were prepared by the sol-gel technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD), UV/Vis spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy and pore structure measurements were used to investigate the morphology, structure, and texture properties of the coated MWCNT/silica gel-glasses. The hardness and elastic modulus of the silica gel-glasses were characterized using a Nanoindenter and found to depend on the coating materials. Coating the MWCNTs with crystalline Au nanoparticles, TiO2 nanoclusters, and amorphous SiO2 nanoshells leads to an increase in the hardness and elastic modulus, despite the higher specific surface area and pore volume of the coated MWCNT/silica gel-glasses. Consequently, we can conclude that the mechanical properties of coated MWCNT/silica gel-glass might be greatly dependent on the guest MWCNTs rather than the silica gel matrix.

  19. Physicochemical properties and in vitro intestinal permeability properties and intestinal cell toxicity of silica particles, performed in simulated gastrointestinal fluids.