Search

Forced convective jet applied onto carbon arc plasma has significant effects on the formation of carbon nanoparticles (CNPs) containing multiwalled carbon nanotubes mixed with multishelled nanoparticles produced by the “arc in water” method. There is an optimized flow rate of the convective jet that leads to the highest production yield, largest hydrodynamic diameter of the products, and the reduced crystalline defects. With the convective flow rate of 1.36 dm3/min, the highest yield and production rate of CNPs could be obtained at 48.5% and 9.32 g/h, respectively. These effects of the forced convective jet originate from the enhanced quenching of carbon clusters vaporized from graphite anode. Analysis of convective flow field subjected to the arc plasma zone is conducted to indicate that synthesis of CNPs by the arc in water method can be elaborately controlled. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The article discusses a study of the influence of the origin of zinc oxide (ZnO) on the photoluminescence and thermal stability of polyimide (PI) films with dispersed ZnO nanoparticles. The study synthesized a fluorinated polyimide. The presence of ZnO crystallites in the film was said to be indicated in the characteristics of X-ray diffraction (XRD) peaks. Results show that the preparation of films under nitrogen has resulted to higher fluorescent intensity.

Abstract: Hydroxyapatite (HAp) has been synthesized by various methods, such as co-precipitation, sol–gel, and microemulsion. However, particle size, particle size distribution and cost were drawbacks of those techniques. In this study, HAp nanoparticles were prepared by means of emulsion liquid membrane system (ELM) or water-in-oil-in-water system (W/O/W). The aim of the work was to evaluate the preparation of HAp nanoparticles using ELM consisting of Span 20 and Tween 80 as a mixture of biodegradable surfactant and caproic acid as an extractant. The effect of Ca/P ratio, reaction temperature, and calcination temperature on the characteristics of synthesized particles was investigated. The synthesized HAp particles were amorphous calcium deficient apatites. Ca/P molar ratio of the synthesized particle (Ca/Pp) increased with increasing initial Ca/P molar ratio (Ca/Pi) and reach maximum at Ca/Pp of 1.65. We found significant amount of β-TCP in the particles prepared with high initial Ca/Pi molar ratio of 2.00 at which the undesired reactions at high Ca2+ concentration occurred. Increasing of reaction and calcinations temperature resulted in the reduction of surface area. After thermal treatment at temperatures ranged from 450 to 750°C, the specific surface area reduced from 227 to 58m2/g. At temperature of 750°C, we found that the morphology of microsized particles instead of nanosized ones. [Copyright &y& Elsevier]

Abstract: The electret filter is composed of permanently charged electret fibers highly capable of collecting charged and uncharged nanosize particles. Compared to the ordinary non-electret fiber, the aerosol collection efficiency η of the electret fiber can initially be significantly higher. In our previous study, η of the electret fiber under dust loading is found to be approximated as the sum of the electrical and mechanical collection efficiencies. It is also shown that the former efficiency can be approximated as a logarithmic function of the dust load. Since the expensive electret filter cannot practically be cleaned and re-used, it is crucial to lengthen its service life without compromising its collection efficiency. In the present study, the time-dependent dust-loaded collection efficiencies of four electret filters with the same average packing density of 0.04 but different linear spatial distributions of the packing density along the filter thickness (0.04 throughout, front 0.03–back 0.05, front 0.02–back 0.06, front 0.01–back 0.07) are simulated and compared. The maximum penetrations and clogging points of the four filters are different. At the maximum 4% penetration through filter D (front 0.01–back 0.07) is two times higher than filter A (0.04 throughout), but the dust load at clogging point of filter D is about 4 times higher than filter A. The results show a significant difference in the distributions of the mass deposited particles along the filter thickness as time passes. As a result, it is possible to quadruple the filter service life by packing the filter loosely on the inlet side and progressively more densely towards the outlet side, while maintaining a sufficiently high aerosol collection efficiency at all times. [Copyright &y& Elsevier]

Abstract: ZnS nanoparticles with different morphology; spherical, ellipsoidal particles'' nanotubes and nanorods, could be successfully synthesized from quaternary W/O microemulsion system. The morphology of the final products could be clearly confirmed by the scanning electron microscopy (SEM) and the transmission electron microscopy (TEM). The effect of cosurfactant on size and morphology of the obtained products have been explored in this work. The key controlling parameters such as the molar ratio of water to surfactant (w o) and the reactant concentration, which affect the product characteristics, have also been investigated. [Copyright &y& Elsevier]

Abstract: Carbon-coated silica gel beads could be prepared by immersing porous silica gel beads in a resorcinol–formaldehyde (RF) aqueous solution and then following by drying and pyrolysis in nitrogen atmosphere. With the proposed method, deposition of colloidal nanoparticles formed during the sol–gel polycondensation of the RF solution was successfully prepared on the mesopores of the silica gel beads. Both size and concentration of the colloidal particles could be controlled by the gelation time and the mixing ratio (V EtOH /V RF ) of the RF solution to ethanol. The porous characteristics of the prepared carbon-coated silica gel beads and the amounts of deposited carbon could be controlled by changing V EtOH /V RF. Without any significant decrease in mesoporosity, the maximal carbon contents of carbon-coated silica gel beads could be increased up to 18wt% in the inner part and 53wt% on the outer surface, respectively. [Copyright &y& Elsevier]

Abstract: A new strategy for single-step synthesis of copper and carbon nanoparticle composite by arc discharge in liquid nitrogen was proposed. The synthesized products consist of carbon nanoparticles (CNPs) which include multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanohorns (SWCNHs) and multi-shelled carbon nanocapsules (MSCNCs) containing Cu clusters inside. Evidence of transmission electron microscopic analyses reveal that under with arc current of 180A arc discharge between copper and graphite electrodes in liquid nitrogen could provide MSCNCs with narrow size distribution in a range of 70–150nm. Meanwhile, MWCNTs with diameter of 20–40nm and length of 150–350nm became selectively synthesized under the condition of discharge in liquid nitrogen with arc current of 100A. Spectroscopic analyses confirm that copper nanoparticles are cuprite while BET analyses also reveal that the synthesized nanocomposite possess acceptably high specific surface area. [Copyright &y& Elsevier]

Abstract: Effect of monoolein surfactant which promotes n-hexane to dissolve in water was investigated to enhance the carbon nanoparticle (CNP) synthesis by arc discharge in liquid. The production rate of CNPs consisting of multi-shelled fullerenes and multi-walled carbon nanotubes was increased by the addition of the n-hexane to water with support of monoolein surfactant. An optimal amount of monoolein led to the maximal production rate of CNPs which was ca. two-fold higher than that obtained from a pure water system. This effect is ascribed to the role of n-hexane and monoolein to provide carbon clusters to the arc reactive zone. The hydrodynamic particle sizes of CNPs and their crystallinity were also enhanced by the addition of these organic compounds. As the vapor pressure of the organic component is significantly suppressed, the proposed method is much safer than that using pure organic liquid. [Copyright &y& Elsevier]