Papers by Keyword: Core-Shell

Abstract: Spherical submicron SiO2 particles have been coated with luminescent Lu2O3: Eu3+ layers by a Pechini sol-gel process, resulting in the formation of SiO2@Lu2O3: Eu3+ core-shell particles(300, 500 nm). The obtained core–shell phosphors have perfect spherical shape with narrow size distribution, smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (50 nm for four deposition cycles). Under the excitation of ultraviolet, the Eu3+ ion mainly shows its characteristic emissions in the core-shell particles from Lu2O3: Eu3+) shells. The PL intensity of Eu3+ increases with the number of coating cycles.

Abstract: Spherical submicron SiO₂ particles have been coated with luminescent Y₂O₃: Tb³⁺ layers by a Pechini sol-gel process, resulting in the formation of SiO₂@Y₂O₃: Tb³⁺ core-shell particles. The obtained core–shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 450 nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (35 nm for two deposition cycles). Under the excitation of ultraviolet, the Tb³⁺ ion mainly shows its characteristic emissions in the core-shell particles from Y₂O₃: Tb³⁺) shells. The emission intensity of Tb³⁺ can be tuned by the annealing temperature and the number of coating cycles.

Abstract: Core-shell nanoparticle has created great interest among researchers due to their various unique properties. The new properties created are combination of both the core and the shell. In this work, pre-prepared Nickel (Ni) nanoparticles were coated with Gold (Au) to produce core-shell structure. Formation mechanism of the core-shell structure is investigated via UV-Vis spectrum of the as-synthesized particles and its supernatants. Ni nanoparticles were synthesized using polyol method with hydrazine as the reducing agent. Coating of Au was conducted using sodium citrate as the reducing agent and acid citric to control the pH of the mixture. UV-Vis absorption spectra analysis of as-synthesized nanoparticles and the supernatant results revealed that the coating happened via redox-transmetallation process with a very broad peak at about 540 nm and size range of 26 - 40 nm. XPS results suggest that the coating consists of Au compound.

Abstract: The microscopic morphologies of Bi₃₀Ga₇₀ immiscible alloy particles were investigated. Monosized microparticles with similar core-shell structures were fabricated for the first time by one step using the Pulsated Orifice Ejection Method. The EDS revels that the core and the shell consist of a Ga-rich phase (＞90 at. %) and a Bi-rich phase (＞80 at. %), respectively. The DSC testing at different temperatures is performed. Core-shell microstructures as well as endothermic peaks and exothermic peaks are observed after heating-cooling cycles when the working temperature is below the temperature of spinodal line, indicating good thermal stability after phase transformation. The thermal energy storage was preliminary tested, which is a good attempt for thermal energy storage. It is likely to use core-shell structures as microencapsulated phase change materials.

Abstract: A core-shell structure of Cu@SiO₂, namely, silica-coated Cu nanoparticles, was synthesized by a simple liquid phase reaction. The reaction bath was optimized by evaluating the balance between the dissolution behavior of Cu nanoparticles and the deposition rate of SiO₂ shells for coating. The Cu nanoparticles were fabricated by an electroless deposition method. The deposition and dissolution behaviors of Cu were quantitatively evaluated by quartz crystal microbalance (QCM) measurements, combined with the reducing ability evaluated by the mixed potential measurements. SiO₂ shells were synthesized by a sol-gel process of tetraethyl orthosilicate (TEOS). The optimal responsiveness bath condition was also elucidated by the QCM measurement to evaluate the deposition rate of SiO₂ shells, which was much faster than the dissolution rate of Cu nanoparticles, indicating that the SiO₂ shells sufficiently coated the Cu nanoparticles. The stability of annealed Cu@SiO₂ nanoparticles was considerably increased and by using them, the red color glaze is achieved in easy and safe way.

Abstract: Core-shell Ag@ZnO heterostructures are designed and fabricated by a facile two-step chemical method. The heterostructures are composed of Ag microspheres as the core, on which plenty of small ZnO nanorods grow as the shell. The morphological, structural and Raman properties of the composites were investigated by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman scattering spectra. A strong surface-enhanced Raman scattering (SERS) and Raman red shift of ZnO nanorods were observed in Ag@ZnO core-shell nanocomposites due to the effect of Ag microspheres.

Abstract: Carboxylic waterborne polyurethane was synthesized with isophorone diisocyanate (IPDI), polyether glycol (PPG) and 2,2-bis (hydroxymethyl) propionic acid (DMPA) as major materials, and terminated with C=C by using β-hydroxyethyl ethacrylate (HEMA). And then 2, 2-azobis (isobutyronitrile) (AIBN) and cumene hydroperoxide (CHPO)/tetraethylenepentamine (TEPA), as a representative of different kinds of initiators, were employed to prepare SiO₂/polymer composites via double in situ miniemulsion polymerization, in which the prepared waterborne polyurethane was used as a reactive surfactant. The morphology of SiO₂/polymer, the microstructure and thermal properties were characterized and discussed. The results indicated that the morphologies of SiO₂/polymer composites initiated by AIBN with waterborne polyurethane as surfactant, which showed core-shell microcapsulated structure with SiO₂ microsphere fabricated inside the shells of polymer, were different from the products prepared by conventional surfactant. Morphological evolution of the particles with polymerization and their dependence on types of initiator played key roles in achieving the microencapsulated shapes.

Abstract: In this work, surface effects including surface elasticity and residual surface stress on the buckling of nanowires are theoretically investigated. Based on modified core-shell (MC-S) model, the effective elasticity incorporating surface elasticity effect of the nanowire is derived, and by using the generalized Young-Laplace equation the residual surface stress is accounted for. The ratio of critical load with and without surface effects are obtained for a nanowire loaded in uniaxial compression. Taking silver (Ag) nanowires as an example, the analyzed results demonstrate that the influence of surface effects on the critical load of buckling becomes more and more significant as the nanowire diameter decreases. Moreover, it is shown that the influence of residual surface stress on the critical load is more prominent than that of surface elasticity.

Abstract: Monodispersed silica spheres with particles size of ca. 450 nm were successfully synthesized using modified Stöber method. The synthesized monodispersed silica spheres were successfully coated with copper through modified sol-gel method employing nonsurfactant template and catalyst. A renewable nonsurfactant template, decyl-alcohol (C10) and catalyst were used to modify the silica surfaces prior to coating with copper. In order to study the effect of catalyst on copper deposition onto silica surfaces, ammonia was used as catalyst in various amounts. The X-ray diffraction patterns of Si-Cu core-shell exhibited a broad peak corresponding to amorphous silica networks and exhibited monoclinic CuO phase. It was found that samples modified in the presence of 1 ml catalyst exhibited relatively homogeneous deposition. The surface area of uncoated core (SiO₂) was at ca. 7.04 m²/g and coated samples 1 ml catalyst was at ca. 8.21m²/g.

Abstract: Two different BaTiO₃ (160nm) nanopowders coated with Y and with Dy were fabricated by an aqueous chemical coating method, and their dielectric properties and microstructures were investigated with X-ray diffraction, Impedance analyzer, SEM and TEM. Y and Dy were coated on the BaTiO₃ powder using nitrates. Coated BaTiO₃ powders were pressed in a disk shape and sintered at 1150~1200°C for 2 hours in reduced atmosphere of 10%H₂ - 90%N₂. Coating layer of the BaTiO₃ particle was thin with a thickness of 3 ~ 5nm. Coated BaTiO₃ sintered sample exhibited a larger lattice parameter (a, c) and smaller tetragonality (c/a) than pure BaTiO₃ one. Y coated BaTiO₃ sample sintered at 1200°C showed good dielectric properties with a high dielectric constant of around 2000 and a stable temperature coefficient of capacitance (TCC).