Papers by Keyword: Hollow Sphere

Abstract: Carbon/TiO2 composites were prepared via the reaction under Autogenic Pressure at Elevated Temperature (RAPET) using alkoxides as precursor, and then porous TiO2 hollow spheres were derived after removing the carbon ingredient by calcination at 600°C. The influence of surfactant additives, including the addition ratio and the nature of the surfactants, on the morphology and the structures of the Carbon/TiO2 composites and the derived TiO2 were also studied with scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectrophotoscopy (DRS) and nitrogen adsorption-desorption measurements. The results revealed that the morphology of the products turned to spherical and then fusiform and the structures turned from hollow to solid with the increasing of surfactant additive. The BET surface area of the hollow TiO2 was modified from 12m2/g to 57m2/g after calcinations. The XRD investigation indicates that the phases of the TiO2 in both the carbon/TiO2 composites and the derived TiO2 hollow spheres are anatase.

Abstract: This paper presents the possibility of composite block production by using pressure infiltration technology. This method uses the pressure of an inert gas (usually argon or nitrogen) to force the melted matrix material to infiltrate the reinforcing elements. Three types of materials were considered: open cell metallic foam, metal matrix syntactic foam and carbon fiber reinforced metal matrix composite. Physical and mechanical investigations – such as SEM and compression tests – were performed. The results of measurements were summarized briefly.

Abstract: Bacterium have evolved a large variety of stunning morphologies controlled at the microor even nanoscopic level such as cocci, bacillus, vibrios and spirillum acting as templates can lead to the formation of corresponding hollow inorganic replicas. Here, cocci Streptococcus thermophilus has been used as a natural biotemplate to synthesize ZnO hollow spheres via a simple hydrothermal method, followed by calcination. The as-obtained products are characterized by techniques of TG, XRD, FESEM, TEM and N2 adsorption. A possible formation mechanism is proposed which has an effect on the bimodal pore structure of the products with pores in the mesoporous range. It has introduced a new concept to synthesize porous hollow spheres by using bacteria as a biotemplate and has opened up a new pathway to synthesize hollow nanospheres, nanotubes and other kinds of 3D hollow nanostructures with bacteria of different morphologies, dimensionalities and sizes as templates.

Abstract: Oxidation behavior of Cu nanoparticles in the formation process of hollow Cu2O spheres was investigated by TEM. The thickness of Cu2O layers on Cu nanoparticles oxidized at 323 K in air was measured as a function of oxidation time. At the initial stage of oxidation until the oxide film with 2.5 nm in thickness is formed, the thickness of oxide films on Cu nanoparticles with the diameter of 10, 20 and 35 nm shows a nearly equal value regardless of diameter of Cu. After the formation of 2.5 nm layer, however, the growth rate of the oxide films on smaller nanoparticles becomes slower than that on larger nanoparticles. This result suggests that the voids formed at the Cu/Cu2O interface prevent Cu atoms from diffusing outward across the interface because the volume ratio of voids to inner Cu in smaller nanoparticles is much larger than that in larger nanoparticles.

Abstract: A novel hollow sphere having rigid binaphthyl macrocycle as shell was prepared by means of sacrifice the silica core. The synthesis of hollow sphere from rigid colloidal silica particles occurs in three steps: a) modification of silica particles with vinyltriethoxysilane as coupling agent, b) immersion in the solution of monomer having rigid binaphthyl macrocycle and polymerization, and c) removal of silica particles. These macrocycles contained in the shell of hollow spheres belong to an important class of host-guest macrocyclic material in which the rigid backbone and C2 symmetry of the binaphthyl unit play an important role in complexing guest molecules. This will endow hollow sphere with new opportunities in molecular recognition and separation.The morphology of colloidal silica particles and hollow spheres was characterized by SEM and TEM.

Abstract: inno.zellmet is a large funded project which aims at the commercialisation of new, non-foam types of cellular metals. The project focuses on porous structures made from metallic short fibers and structures made from metallic hollow spheres, which are both chararacterised by multifunctionality and low specific weight. Six research institutes and 17 partners from industry constitute a local network that jointly develops solutions based on these "constructed materials". Target applications are situated in industrial sectors such as light-weight construction, decentralised energy generation, medical and biotechnology, as well as sound absorption and explosion protection for stationary machinery. inno.zellmet has started in March 2005 and will run for 3 years. During this time, it receives 3.9 Mio. EUR in funding from the German Federal Ministry of Education and Research under the "Unternehmen Region" initiative. This paper highlights some of the results obtained so far.

Abstract: New composite metal foams are processed using powder metallurgy (PM) and gravity casting techniques. The foam is comprised of steel hollow spheres, with the interstitial spaces occupied by a solid metal matrix (Al or steel alloys). The cyclic compression loading of the products of both techniques has shown that the composite metal foams have high cyclic stability at very high maximum stress levels up to 68 MPa. Under cyclic loading, unlike other metal foams, the composite metal foams do not experience rapid strain accumulation within collapse bands and instead, a uniform distribution of deformation happen through the entire sample until the densification strain is reached. This is a result of more uniform cell structure in composite metal foams compared to other metal foams. As a result, the features controlling the fatigue life of the composite metal foams have been considered as sphere wall thickness and diameter, sphere and matrix materials, and processing techniques as well as bonding strength between the spheres and matrix.

Abstract: Silica-doped poly(lactic acid) (PLA) composite hollow spheres containing calcium carbonates (Si-CCPC spheres) were prepared using aminopropyltriethoxysilane (APTES) for injectable bone fillers combined with a cell-delivery system. Si-CCPC spheres have a hollow spherical shape of ~1 mm in the external diameter and an open channel in the shell, which is selfformed. The channel size is about 500 *m in diameter. X-ray energy dispersive spectroscopy (EDS) analysis showed incorporation of silicon in Si-CCPC spheres. After soaking Si-CCPC spheres in simulated body fluid (SBF), hydroxycarbonate apatite formed on the Si-CCPC spheres. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) showed that the Si4+ ion is released from Si-CCPC spheres in SBF.

Abstract: Hollow hydroxyapatite microspheres (H-HAMs) with controlled characteristic mesoporous structure on the shell were successfully fabricated by using core template technology and sol-gel process. The fabrication of H-HAMs mainly included three distinct steps: the preparation of core template spheres of chitin by emulsifying chitin solution in oil, the formation of core-shell composite spheres of chitin-HA/chitin after a layer of chitin/HA solution coated on the surface of chitin core templates by means of a gelling process of chitin solution with the help of water in the cores, and the harvest of H-HAMs through a special sintering procedure to remove chitin. The size and shape of H-HAMs were chiefly determined by the size and morphology of core templates. The thickness of shells was easily controlled by altering water content of the starting template particles, and the characteristic mesoporous structure on the shell was related to the proportion of chitin in the chitin/HA composite solution and the sintering temperature. H-HAMs with characteristic mesoporous architecture on the shell have many potential applications such as used as a carrier for sustained release of drugs in the therapy of hard tissue system.

Abstract: Novel hollow spheres for bone fillers incorporating cells were prepared using composites consisting of poly(lactic acid) and calcium carbonates. An open channel of ~800 µm in diameter was easily formed using a chemical etching method to provide a pathway to the interior of the sphere. Cells could migrate through the open channel into the interior of the sphere. Bonelike apatite coating on the surface of the sphere was prepared by soaking in calcium chloride solution to supply excess Ca2+ ions on the surface and subsequently by soaking in simulated body fluid. The hollow spheres with an open channel may be one of the great potential candidates as novel bone fillers combined with a cell-delivery system.