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Shell Material (shell + material)

Distribution by Scientific Domains

Polymers and Materials Science	60%
Earth and Environmental Science	30%

Selected Abstracts

The Active-Core/Active-Shell Approach: A Strategy to Enhance the Upconversion Luminescence in Lanthanide-Doped Nanoparticles

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009
Fiorenzo Vetrone
Abstract Nanoparticles of NaGdF4 doped with trivalent erbium (Er3+) and ytterbium (Yb3+) are prepared by a modified thermal decomposition synthesis from trifluoroacetate precursors in 1-octadecene and oleic acid. The nanoparticles emit visible upconverted luminescence on excitation with near-infrared light. To minimize quenching of this luminescence by surface defects and surface-associated ligands, the nanoparticles are coated with a shell of NaGdF4. The intensity of the upconversion luminescence is compared for nanoparticles that were coated with an undoped shell (inert shell) and similar particles coated with a Yb3+ -doped shell (active shell). Luminescence is also measured for nanoparticles lacking the shell (core only), and doped with Yb3+ at levels corresponding to the doped and undoped core/shell materials respectively. Upconversion luminescence was more intense for the core/shell materials than for the uncoated nanoparticles, and is greatest for the materials having the "active" doped shell. Increasing the Yb3+ concentration in the "core-only" nanoparticles decreases the upconversion luminescence intensity. The processes responsible for the upconversion are presented and the potential advantages of "active-core"/"active-shell" nanoparticles are discussed. [source]

Synthesis and Optical Properties of KYF4/Yb, Er Nanocrystals, and their Surface Modification with Undoped KYF4,

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2008
Helmut Schäfer
Abstract KYF4/Yb3+, Er3+ nanocrystals with a mean diameter of approximately 13,nm were synthesized at 200,°C in the high boiling organic solvent N -(2-hydroxyethyl)ethylenediamine (HEEDA). The particles crystallize in the cubic phase known from , -NaYF4 and form transparent colloidal solutions in tetraethylene glycol (TEG) or propanol. Solutions containing 1,wt % of the nanocrystals in TEG display visible upconversion emission upon continuous wave (CW) excitation at 978,nm. Growing undoped KYF4 on the surface of the KYF4/Yb3+, Er3+ nanocrystals increases the upconversion efficiency by more than a factor of 20. The XRD data of these particles, display a slight increase in the mean particle size from 13 to 15.5,nm, indicating that only a part of the subsequently added KYF4 shell material is deposited onto the particle surface. Nevertheless the performed surface modification obviously leads to core/shell structured particles. [source]

Preparation and thermal properties of microencapsulated phase change material for enhancing fluid flow heat transfer

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2007
Yu Rao
Abstract Microencapsulated phase change material (MEPCM) is formed by packing PCM into a microcapsule with a solid but flexible shell. MEPCM can be used to enhance liquid cooling performance considerably. In this paper, experiments on the preparation of MEPCM with a double-layered shell have been conducted. An in-situ polymerization microencapsulation process was used to prepare the MEPCM with melamine resin as the shell material and n-Docosane (C22H46) as the core material. Interesting parameters like the size of the prepared MEPCM, the core mass fraction in the MEPCM, and the thermal storage capability of the prepared MEPCM have been measured and analyzed. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(1): 28,37, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20138 [source]

STRONTIUM ISOTOPE DATING OF SPICULITIC PERMIAN STRATA FROM SPITSBERGEN OUTCROPS AND BARENTS SEA WELL-CORES

JOURNAL OF PETROLEUM GEOLOGY, Issue 3 2010
S.N. Ehrenberg
Eight samples of brachiopod shell material have been analyzed for their strontium isotope composition in order to more accurately date Lower to Upper Permian siliceous biogenic strata of Spitsbergen (Kapp Starostin Formation) and the southern Barents Sea (Røye Formation). The results are interpreted as showing a mid-Artinskian age for the basal Vøringen Member of the Kapp Starostin Formation and a range of late Artinskian to Roadian for the overlying part of this unit. The upper part of the Røye Formation yields ages in the range Roadian to Wuchiapingian. These results are consistent with available biostratigraphic data and confirm the potential of strontium isotope stratigraphy for developing a more accurate chronology of the widespread spiculite deposits that characterize the northern margin of Pangea in late-Early Permian to Late Permian time and which constitute a potential target for petroleum exploration. [source]

Coaxial electrospinning of PC(shell)/PU(core) composite nanofibers for textile application

POLYMER COMPOSITES, Issue 5 2008
Xiao-Jian Han
To develop a novel functional composite material for textile application, a coaxial electrospinning technique was investigated to electrospin two different polymer solutions into core-shell structured nanofibers in which polyurethane and polycarbonate were used as core and shell materials, respectively. The resultant nanofibers were subsequently characterized by means of scanning electron microscope, transmission electron microscopy, fourier transform infrared spectroscopy, and tensile mechanical test. Furthermore, water vapour transmission rate and pliability of the resulting nonwoven mats were also measured. The preliminary results indicated that it is feasible to attach composite nanofibers, with possible fictionalization on the shell material, onto a substrate fabric. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source]

Quantifying sponge erosions in Western Australian pearl oyster shells

AQUACULTURE RESEARCH, Issue 9 2010
Sabine Daume
Abstract This paper describes several methods to estimate the amount of sponge erosion in pearl oyster shells (Pinctada maxima Jameson, 1901). Internal erosion can be calculated from non-destructive surface area estimates because a clear relationship was found between the eroded area on the surface of the shells and internal erosions. Grading shells into three different categories, according to the severity of erosion, also proved to be a suitable method to quickly assess the amount of sponge erosions. All methods were more accurate in shells with larger amounts of erosions. Using the described methods, the Lacepedes fishing ground was more diverse in bioeroding sponge species compared with sites at the 80-Mile fishing ground locations. Pione velans Hentschel, 1909 was the dominant bioeroding sponge species but Cliona dissimilis Ridley and Dendy, 1886 eroded more shell material than P. velans. Observed patterns suggest that P. velans had a more recent recruitment than C. dissimilis. We suggest that visual grading together with estimates from the shell surface will be sufficient to determine the general long-term trends in bioeroding sponge severity. However, results of monitoring programmes need to be supplemented by histological examination to confirm sponge activity and species identity. [source]

Late Quaternary history of the Kap Mackenzie area, northeast Greenland

BOREAS, Issue 3 2010
BERND WAGNER
Wagner, B., Bennike, O., Cremer, H. & Klug, M. 2010: Late Quaternary history of the Kap Mackenzie area, northeast Greenland. Boreas, Vol. 39, pp. 492,504. 10.1111/j.1502-3885.2010.00148.x. ISSN 0300-9483. The Kap Mackenzie area on the outer coast of northeast Greenland was glaciated during the last glacial stage, and pre-Holocene shell material was brought to the area. Dating of marine shells indicates that deglaciation occurred in the earliest Holocene, before 10 800 cal. a BP. The marine limit is around 53 m a.s.l. In the wake of the deglaciation, a glaciomarine fauna characterized the area, but after c. one millennium a more species-rich marine fauna took over. This fauna included Mytilus edulis and Mysella sovaliki, which do not live in the region at present; the latter is new to the Holocene fauna of northeast Greenland. The oldest M. edulis sample is dated to c. 9500 cal. a BP, which is the earliest date for the species from the region and indicates that the Holocene thermal maximum began earlier in the region than previously documented. This is supported by driftwood dated to c. 9650 cal. a BP, which is the earliest driftwood date so far from northeastern Greenland and implies that the coastal area was at least partly free of sea ice in summer. As indicated by former studies, the Storegga tsunami hit the Kap Mackenzie area at c. 8100 cal. a BP. Loon Lake, at 18 m a.s.l., was isolated from the sea at c. 6200 cal. a BP, which is distinctly later than expected from existing relative sea-level curves for the region. [source]

Base-Metal-Electroded BaTiO3 Capacitor Materials with Duplex Microstructures

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2004
I-Nan Lin
The effect of dopants and processing conditions on the dielectric properties of base-metal-electroded materials was investigated. BaTiO3 materials simultaneously doped with MgO and Y2O3 additives can achieve small capacitance variation (,C/C), which meets the X7R specification, when the proportion of additives is abundant enough and the materials are not over-fired. Presumably, small ,C/C values of thus obtained materials are the result of the formation of core,shell structure, which requires stringent control of material processing conditions. In contrast, X7R-type materials can be obtained in a much wider processing window, when prepared by mixing two BaTiO3 materials of suitable dielectric constant,temperature (K,T) characteristics. Duplexed materials prepared from these two end-point BaTiO3 materials with ratios ranging from 3:1 to 1:2 exhibit K,T behavior within the X7R specification, provided that one of the components possesses flat K,T behavior. Moreover, the dielectric properties of these materials were simulated using a simplified microstructural model. Simulation results indicate that the effective dielectric constant of core,shell materials, (Ke)CS, varies significantly not only with the dielectric properties of cores and shells, but also with the shell-to-core thickness ratio, whereas the effective dielectric constant of duplexed materials, (Ke)D, can be maintained at a very small ,C/C value for a wide range of end-point constituent ratios, which agrees very well with the measured K,T properties for the materials. [source]

Electron Backscatter Diffraction Study of Brachiopod Shell Calcite , Microscale Phase and Texture Analysis of a Polycrystalline Biomaterial

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5-6 2008
Wolfgang W. Schmahl
Abstract Electron backscatter diffraction (EBSD) is an easy to use and highly automated microdiffraction method suitable for the determination of crystallographic phase and crystallite orientation. The high level of hierarchical structural organization in the shells of marine organisms was studied. Calcite brachiopod shell materials were found to belong to three types of microstructure: nano- to microcrystalline layers of acicular crystals, fiber composites with calcite single crystal fibers with [uv0] morphological axes, and material formed by columnar crystals with [001] morphological axes selected by competitive growth. [source]