| 1. |
- Hilty, F. M., et al.
(författare)
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Development and optimization of iron- and zinc-containing nanostructured powders for nutritional applications
- 2009
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 20:47
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Tidskriftsartikel (refereegranskat)abstract
- Reducing the size of low-solubility iron (Fe)-containing compounds to nanoscale has the potential to improve their bioavailability. Because Fe and zinc (Zn) deficiencies often coexist in populations, combined Fe/Zn-containing nanostructured compounds may be useful for nutritional applications. Such compounds are developed here and their solubility in dilute acid, a reliable indicator of iron bioavailability in humans, and sensory qualities in sensitive food matrices are investigated. Phosphates and oxides of Fe and atomically mixed Fe/Zn-containing (primarily ZnFe(2)O(4))nanostructured powders were produced by flame spray pyrolysis (FSP). Chemical composition and surface area were systematically controlled by varying precursor concentration and feed rate during powder synthesis to increase solubility to the level of ferrous sulfate at maximum Fe and Zn content. Solubility of the nanostructured compounds was dependent on their particle size and crystallinity. The new nanostructured powders produced minimal color changes when added to dairy products containing chocolate or fruit compared to the changes produced when ferrous sulfate or ferrous fumarate were added to these foods. Flame-made Fe- and Fe/Zn-containing nanostructured powders have solubilities comparable to ferrous and Zn sulfate but may produce fewer color changes when added to difficult-to-fortify foods. Thus, these powders are promising for food fortification and other nutritional applications.
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| 2. |
- Teleki, A., et al.
(författare)
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Distinguishing between aggregates and agglomerates of flame-made TiO2 by high-pressure dispersion
- 2008
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 181:3, s. 292-300
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Tidskriftsartikel (refereegranskat)abstract
- The potential of high-pressure dispersion (HPD) and dynamic light scattering (DLS) is explored for rapid and quantitative estimation of the extent of particle aggregation and agglomeration by analyzing the entire particle size distribution. Commercially available and tailor-made TiO2 particles by flame spray pyrolysis (FSP) were characterized by X-ray diffraction, nitrogen adsorption and transmission electron microscopy (TEM). Volume distributions of these titania particles were obtained by DLS of their electrostatically stabilized (with Na4P2O7) aqueous suspensions. Dispersing these suspensions through a nozzle at 200 to 1400 bar reduced the size of agglomerates (particles bonded by weak physical forces) resulting in bimodal size distributions composed of their constituent primary particles and aggregates (particles bonded by strong chemical or sinter forces). Sintering FSP-made particles from 200 to 800 degrees C for 4 h progressively increased the minimum primary particle size (by grain growth) and aggregate size (by neck growth and phase transformation). (c) 2007 Elsevier B.V. All rights reserved.
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| 3. |
- Teleki, A, et al.
(författare)
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Flame-coating of titania particles with silica
- 2005
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Ingår i: Journal of Materials Research. - Swiss Fed Inst Technol, Particle Technol Lab, Inst Proc Engn, Dept Mech & Proc Engn, CH-8092 Zurich, Switzerland. Swiss Fed Inst Technol, Dept Chem & Appl Biosci, Inorgan Chem Lab, CH-8093 Zurich, Switzerland.. - 0884-2914 .- 2044-5326. ; 20:5, s. 1336-1347
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Tidskriftsartikel (refereegranskat)abstract
- Silica/titania composite particles were prepared by co-oxidation of titanium-tetra-isopropoxide and hexamethyldisiloxane in a co-flow diffusion flame reactor. The influence of precursor composition on product powder characteristics was studied by x-ray diffraction, nitrogen adsorption, electron microscopy, elemental mapping, and energy-dispersive x-ray analysis. The flame temperature was measured by Fourier transform infrared spectroscopy. The evolution of composite particle morphology from ramified agglomerates to spot- or fully coated particles was investigated by thermophoretic sampling and transmission/scanning electron microscopy. At 40-60 wt% TiO2, particles with segregated regions of silica and titania were formed, while at 80 wt% TiO2 rough silica coatings were obtained. Rapid flame-quenching with a critical flow nozzle at 5 cm above the burner nearly halved the product particle size, changed its crystallinity from pure anatase to mostly rutile and resulted in smooth silica coatings on particles containing 80 wt% TiO2.
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| 4. |
- Teleki, A., et al.
(författare)
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Sensing of organic vapors by flame-made TiO2 nanoparticles
- 2006
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Ingår i: Sensors and actuators. B, Chemical. - ETH, Inst Proc Engn, Dept Mech & Proc Engn, Particle Technol Lab, CH-8092 Zurich, Switzerland. SUNY Stony Brook, Dept Mat Sci & Engn, Stony Brook, NY 11794 USA. : Elsevier BV. - 0925-4005 .- 1873-3077. ; 119:2, s. 683-690
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured anatase TiO2 was produced by flame spray pyrolysis (FSP) and tested for sensing of volatile organic compounds and CO at 500 degrees C. The as-prepared powders were characterized by transmission/scanning electron microscopy, X-ray diffraction and nitrogen adsorption. Titania films about 30 mu m thick on alumina substrates interdigitated with gold electrodes were prepared by drop-coating a heptanol suspension of these powders. The films showed a high signal of n-type sensor to isoprene, acetone and ethanol at concentrations ranging from 1 to 75 ppm in dry N-2/O-2 at 500 degrees C. The response (within seconds) and recovery (within minutes) times were very fast. Heat-treatment at 900 degrees C caused a nearly complete anatase to rutile transformation and a transition to p-type sensing behavior. That resulted in a poor sensor signal to all hydrocarbons tested and considerably longer recovery times than that of the anatase sensor. That rutile sensor could detect CO that the original, anatase sensor could not. For ethanol the sensor response changed back to n-type. (c) 2006 Elsevier B.V. All rights reserved.
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| 5. |
- Teleki, A., et al.
(författare)
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The quality of SiO(2)-coatings on flame-made TiO(2)-based nanoparticles
- 2008
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 18:30, s. 3547-3555
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Tidskriftsartikel (refereegranskat)abstract
- Silica-coated titania nanoparticles are important in sunscreens, UV filters and optical nanocomposites. The surface characteristics (extent of coverage, texture and thickness) of in situ SiO(2)-coated, mostly rutile titania nanoparticles made in one step by flame spray pyrolysis (FSP) were compared to FSP-made mixed (co-oxidized) SiO(2)/TiO(2) ones by transmission electron microscopy (TEM), Raman, FT-IR spectroscopy, electrophoretic mobility and isopropanol chemisorption followed by mass spectroscopy. Increasing the silica content shifted the isoelectric point (IEP) toward that of pure silica for externally mixed SiO(2) and TiO(2), co-oxidized SiO(2)/TiO(2) and low SiO(2) content (< 10 wt%) silicacoated TiO(2) nanoparticles. At higher SiO(2) contents, SiO(2)-coated titania exhibited negative z potentials at all pH values (and thus no IEP) indicating hermetic or complete coverage of the TiO(2) surface by SiO(2) as was confirmed by isopropanol chemisorption. Co-oxidized particles containing segregated TiO(2) and SiO(2) domains exhibited Si-O-Ti and Si-O-Si bonds of higher IR intensity than hermetically-coated TiO(2). The latter exhibited a peak at 1225 cm(-1) attributed to Si-O-Si asymmetric vibrations in contrast to the former.
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| 6. |
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| 7. |
- Wengeler, R, et al.
(författare)
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High-pressure liquid dispersion and fragmentation of flame-made silica agglomerates
- 2006
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Ingår i: Langmuir. - Univ Karlsruhe, Inst Mech Proc Engn & Mech, D-76128 Karlsruhe, Germany. ETH, Particle Technol Lab, Dept Mech & Proc Engn, CH-8092 Zurich, Switzerland. : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 22:11, s. 4928-4935
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Tidskriftsartikel (refereegranskat)abstract
- The influence of primary particle diameter and the degree of agglomeration of flame-made silica agglomerate suspensions in aqueous solutions is studied by high-pressure dispersion (up to 1500 bar) through a nozzle with a 125 Am inner diameter. These particles were produced (4-15 g/h) by oxidation of hexamethyldisiloxane (HMDSO) in a coflow diffusion flame reactor. Their average primary particle size (10-50 nm) and degree of agglomeration were controlled by varying the oxygen and precursor flow rates. The particles were characterized by nitrogen adsorption, electron microscopy, and small-angle X-ray scattering. Hydrodynamic stresses break up soft agglomerates and yield hard agglomerate sizes in the range of 100-180 nm, as characterized by dynamic light scattering. Soft agglomerates exhibited decreasing light scattering diameters with increasing dispersion pressure, while hard agglomerates were insensitive.
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