Advanced Materials Research Vols. 11-12

Abstract: Mesoporous carbon with high surface area and ordered structure was synthesized via a nanocasting process using mesoprous MCM-41 silica as a template and sucrose as a carbon precursor. Sample was characterized by XRD, SEM, TEM and nitrogen adsorption. The results show that the templated carbon has a BTE surface area ∼1200 m2/g, a pore volume ∼1.0 cm3/g, and a bimodal porosity centered at around 4 nm and 46 nm.

Abstract: Toward the tailored growth of carbon nanotubes (CNTs), CNT growth using hydrocarbon ion beams at the ion energy of 150 eV and the ion current densities of 10 ∼ 165 μA/cm2 was challenged at various growth temperatures. Fibrous protrusions with an amorphous nature grew at a low ion current density, whereas highly crystallized multi-wall CNTs were synthesized at high ion current densities. The higher the growth temperature and the ion current density, the smaller the CNT diameter. Similar to the conventional PECVD-grown CNTs, they grew via the so-called “tip-growth mode.”

Abstract: Submicrosized porous hollow silica spheres with a diameter of 350 nm and a shell thickness of approximately 10 nm were synthesized by a hydrothermal method using PMMA hollow particles as template. Through the hydrolysis of TEOS, a continuous and uniform coating of SiO2 was deposited over the surface of PMMA cores to form the core-shell structures. After calcining to remove the template, a pure hollow silica structure with holes in the shells was obtained. The as-prepared hollow products were characterized with TEM, SEM, EDS, BET and FT-IR. Its large surface area and hollow morphology will make this new material a promising agent for the applications of catalysts, controlled drug delivery and etc.

Abstract: The carbon nanotube/PMMA/PVAc composite film was prepared by solution casting. The carbon nanotube (CNT) and graphitized carbon nanotube (GCNT) were employed as conductive fillers in the composite films. The conductivity of the GCNT/PMMA/PVAc film is better than that of CNT/PMMA/PVAc film. The electrical percolation thresholds were at 5wt% and 2wt% respectively in the CNT/PMMA/PVAc film and GCNT/PMMA/PVAc film. The volume electric resistivities of CNT/PMMA/PVAc and GCNT/PMMA/PVAc composite film are at 0.044
⋅m and 0.007
⋅m respectively at 15wt% carbon nanotube. The significant difference of resistivity for the both types of composite film was due to different structure and crystallinity of CNT and GCNT.

Abstract: The microwave permittivity of multi-walled carbon nanotubes blended in paraffin wax has been studied in the frequency range from 2 to 18GHz. The dissipaton factors of the multi-walled carbon nanotubes are high at the microwave frequencies. The microwave permittivity of the multi-walled carbon nanotubes and paraffin wax (or other dielectric materials) composites can be tailored by the content of the carbon nanotubes. And ε′, ε″and tgδ of the composites increase with the volume filling factor (v) of the carbon nanotubes. The ε′ and ε″ of the multi-walled carbon nanotubes decrease with frequency in the frequency range from 2 to18 GHz. This property is very good for broadband radar absorbing materials. The classical effective medium functions can not effectively model the microwave permittivities of the composites containing multi-walled carbon nanotubes. The ε′ and ε″ can be effectively modeled using second-order polynomials (ε′, ε″=Av2+Bv+C). The high ε″ and dissipation factor tgδ (ε″/ε′) of multi-walled carbon nanotubes are due to the dielectric relaxation. The carbon nanotubes composites would be a good candidate for microwave absorbing material electromagnetic interface (EMI) shielding material.

Abstract: To prepare stable electrophoretic ink (E Ink) contains titanium dioxide particles, oil soluble red, dispersant and tetrachloroethylene (TCE), the modification of organic and inorganic material onto the particle surface was investigated. Modified particles were characterized by measurement of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) to confirm the composites and structures. The electrophoretic properties of sample in TCE were investigated by static sedimentation experiment and electrophoresis instrument. The type of inorganic and organic materials used for the surface modification influence dispersibility and charge property of particles. On the whole, organic modified particles especially modified by anionic surfactant show better properties. The process conditions were investigated in detail using SDBS as the modifier. The dispersibility and charge property have significantly improved in optimized modifying condition that the proportion of surfactant is 15%, pH is 6 and reaction time is 1 hour which means SDBS modified TiO2 is suitable for electrophoretic particles.

Abstract: Nanoparticles of metastable copper nitride(Cu3N) have been successfully fabricated from Cu mask using Ar ion ‘transcription method’ which is firstly invented by B.-S. Xu, C. Iwamoto and S.-I. Tanaka in 1996 [1]. The structural and morphological changes with irradiation time are studied by transmission electron microscopy (TEM). The thin film-like crystalline Cu3N which is covered with amorphous or polycrystalline cuprite (Cu2O) layer in the as-received Cu mask plays a role of target. Polycrystalline Cu3N nanoparticles nucleate and grow up to the average size of 15nm after 30 sec-irradiation. Coalesence of 50nm-sized grown Cu3N nanoparticles forms polycrystalline thin film after 2min-irradiation and its growth behavior follows Volmer-Weber mode. As irradiation time increases from 30 sec to 15 min, Cu3N nanoparticles are thought to be grown preferentially along the [111] and [100] directions. Cu2O still remain with Cu3N after 15 min.-irradiation.

Abstract: Nanoscale singularity at the reactive wetting front on the 6H-SiC (0006) surface with amorphous oxide layer was studied using video recorded in situ to clarify the dynamic atomistic behaviors of the brazing and the molten tip spreading on a high-temperature stage of a high-resolution transmission electron microscope. A 0.5-nm-thick precursor film spreading ahead of the main molten alloy on SiC (0006) at 1073 K and continuous spreading of the molten alloy were clearly observed on the SiC (0006) surface with a less than 1-nm-thick amorphous layer. Molten Ti and TiC nanolayers preceded the Ti5Si3 nanolayer at the tip and they traveled continuously at a velocity of 14 nm/sec on the plane perpendicular to SiC (0006). Since Ti atoms in the molten alloy diffuse sufficiently rapidly on the SiC surface to the tip, the formation of these layers may be the rate-determining step of spreading. Discontinuous spreading of the precursor tip on SiC (0006) with a thick amorphous film was observed in contrast to the continuous spreading on SiC with a thin film. This suggests that the spreading of the Ti molten alloy on SiC is also controlled by the dissolution of the amorphous layer.

Abstract: This paper aims at a simple preparation method of nanocrystalline copper powders through copper sulfate reduction by potassium borohydride in aqueous solution. The product powders obtained in various conditions were investigated by X-ray powder diffraction, transmission electron microscope and particle size distribution analyzer. The parameters that influence the preparation process of copper crystalline were researched, such as the effect of complexing agent, the molar ratio of copper sulfate to potassium borohydride and the quantity of protective polymer. Finally, the preferable reaction conditions were determined, and well-dispersed nanocrystalline copper powders with average diameter of 28.4nm were obtained.

Abstract: By overcoming less excitation efficiency of rare-earth ions due to small oscillator strength (∼10-6) of f-f transition, Eu3+ ions were intentionally introduced to nano-sized semiconductor of tin oxide (SnO2) in silica (SiO2)
matrix via a sol-gel route. As a consequence, the excitation energy was significantly absorbed by the nano-sized SnO2 with controlled band-gap energy owing to quantum size effect (QSE) and subsequently transferred from nano-sized SnO2 to the Eu3+ ions doped, resulting in the enhancement of Eu3+ red emission (external quantum efficiency : 75.6 %).