| 1. |
- Dong, Lin, et al.
(författare)
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Measurement of radiative lifetime in CdSe/CdS core/shell structured quantum dots
- 2009
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Ingår i: 2009 Asia Communications and Photonics Conference and Exhibition, ACP 2009. - Washington, D.C. : OSA. - 9781557528773 ; , s. 5377385-
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Konferensbidrag (refereegranskat)abstract
- Radiative lifetime of chemically synthesized colloidal CdSe/CdS core/shell quantum dots is measured. Influence of the core size on the electron-hole pair separation is analyzed. A long radiative lifetime and the existence of electron-hole pair separation suggest high potential of these dots as gain material to achieve lasing under continuous-wave excitation.
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| 2. |
- Dong, Lin, et al.
(författare)
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Photoluminescence from quasi-type-II spherical CdSe-CdS core-shell quantum dots
- 2013
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 52:1, s. 105-109
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Tidskriftsartikel (refereegranskat)abstract
- Spherical CdSe-CdS core-shell quantum dots (QDs) are found to be flexible in the transition between the type-I regime and the type-II regime with different core/shell dimensions. The quasi-type-II feature of the colloidal dots is confirmed with time-resolved photoluminescence (PL) measurements. Two recombination paths of the excitons with significantly different decay rates are observed and analyzed. The spherical CdSe-CdS core-shell QDs are numerically simulated to investigate the carrier separation. A relatively long radiative lifetime and high degree of spatial carrier separation provide good potential to achieve lasing under continuous-wave excitation. Amplified spontaneous emission at room temperature is detected from the QDs embedded in the polymer matrix. It is shown that a larger shell thickness results in a lower pumping threshold, while a smaller shell thickness leads to higher PL efficiency.
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| 3. |
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| 4. |
- Furberg, Richard, et al.
(författare)
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Dendritically ordered nano-particles in a micro-porous structure for enhanced boiling
- 2006
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Ingår i: Proceedings of 13th International Heat Transfer Conference, NAN-07. - 1567002250
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Konferensbidrag (refereegranskat)abstract
- Presented research is an experimental study of the pool boiling performance of copper surfaces enhanced with a newly developed structure. The enhanced surfaces were fabricated with an electrodeposition method where metallic nano-particles are formed and dendritically connected into an ordered micro-porous structure. To further alter the grain size of the dendritic branches, some surfaces underwent an annealing treatment. The tests were conducted with the test objects horizontally oriented and submerged in a refrigerant: R134A, at saturated conditions and at an absolute pressure of 4 bar. The heat flux varied between 0.1 and 10 W/cm2. The boiling performance of the enhanced surfaces was found to be dependent on controllable surface characteristics such as thickness of the structure and the interconnectivity of the grains in the dendritic branches. Temperature differences less than 0.3 °C and 1.5 °C at heat fluxes of 1 and 10 W/cm2 respectively have been recorded, corresponding to heat transfer coefficients up to 7.6 Wcm-2K-1. The micro-porous structure has been shown to facilitate high performance boiling, which is attributed to its high porosity (∼94%), a dendritically formed and exceptionally large surface area, and to a high density of well suited vapor escape channels (50 – 470 per mm2).
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| 5. |
- Furberg, Richard, et al.
(författare)
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Experimental investigation of an evaporator enhanced with a micro-porous structure in a two-phase thermosyphon loop
- 2009
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Ingår i: HT2008. - NEW YORK : AMER SOC MECHANICAL ENGINEERS. - 9780791848487 ; , s. 327-334
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Konferensbidrag (refereegranskat)abstract
- Following is an experimental study of six different evaporators in a closed two-phase thermosyphon loop system, where the influence of various evaporator dimensions and surfaces was investigated. The evaporators featured a 30 mm long rectangular channel with hydraulic diameters ranging from 1.2-2.7 mm. The heat transfer surface of one of the tested evaporators was enhanced with copper nano-particles, dendritically connected into an ordered micro-porous three dimensional network structure. To facilitate high speed video visualization of the two-phase flow in the evaporator channel, a transparent polycarbonate window was attached to the front of the evaporators. Refrigerant 134A was used as a working fluid and the tests were conducted at 6.5 bar. The tests showed that increasing channel diameters generally performed better. The three largest evaporator channels exhibited comparable performance, with a maximum heat transfer coefficient of about 2.2 W/(cm(2)K) at a heat flux of 30-35 W/cm(2) and a critical heat flux of around 50 W/cm(2). Isolated bubbles characterized the flow regime at peak performance for the large diameter channels, while confined bubbles and chaotic churn flow typified the evaporators with small diameters. In line with previous pool boiling experiments, the nucleate boiling mechanism was significantly enhanced, tip to 4 times, by the nano- and micro-porous enhancement structure.
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| 6. |
- Furberg, Richard, et al.
(författare)
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Porous layer
- 2006
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Patent (populärvet., debatt m.m.)
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| 7. |
- Furberg, Richard, et al.
(författare)
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The Use of a Nano- and Microporous Surface Layer to Enhance Boiling in a Plate Heat Exchanger
- 2009
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Ingår i: Journal of heat transfer. - : ASME International. - 0022-1481 .- 1528-8943. ; 131:10
-
Tidskriftsartikel (refereegranskat)abstract
- Presented research is an experimental study of the performance of a standard plate heat exchanger evaporator, both with and without a novel nano- and microporous copper structure, used to enhance the boiling heat transfer mechanism in the refrigerant channel. Various distance frames in the refrigerant channel were also employed to study the influence of the refrigerant mass flux on two-phase flow heat transfer. The tests were conducted at heat fluxes ranging between 4.5 kW/m(2) and 17 kW/m(2) with 134a as refrigerant. Pool boiling tests of the enhancement structure, under similar conditions and at various surface inclination angles, were also performed for reasons of comparison. The plate heat exchanger with the enhancement structure displayed up to ten times enhanced heat transfer coefficient in the refrigerant channel, resulting in an improvement in the overall heat transfer coefficient with over 100%. This significant boiling enhancement is in agreement with previous pool boiling experiments and confirms that the enhancement structure may be used to enhance the performance of plate heat exchangers. A simple superposition model was used to evaluate the results, and it was found that, primarily, the convective boiling mechanism was affected by the distance frames in the standard heat exchanger. On the other hand, with the enhanced boiling structure, variations in hydraulic diameter in the refrigerant channel caused a significant change in the nucleate boiling mechanism, which accounted for the largest effect on the heat transfer performance.
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| 8. |
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| 9. |
- He, Zeming, et al.
(författare)
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Effect of ceramic dispersion on thermoelectric properties of nano ZrO2/CoSb3 composites
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:4, s. 043707-
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, nano- ZrO2 CoSb3 composites were fabricated by milling ZrO2 and CoSb3 powders and hot pressing at different sintering temperatures. For the prepared compacts, the phase purity, microstructure, and temperature-dependent thermoelectric properties were characterized. The effect of nano- ZrO2 dispersion on composite electrical conductivity and thermal conductivity is strictly clarified by comparing the transport properties of the nondispersed and dispersed CoSb3 at identical porosity, so that the effect of porosity on thermoelectric parameters could be eliminated. The effect of the insulating inclusion itself on transport properties is also considered and eliminated using effective media theories. It is clearly verified that charge carrier scattering and phonon scattering occur simultaneously to lower the electrical conductivity and the thermal conductivity of CoSb3 due to the introduction of nano- ZrO2 inclusions. The investigated composites show higher electrical conductivity due to existence of metallic Sb and lower thermal conductivity because of nanodispersion. At the ranges of high measuring temperature (673-723 K) and low porosity (6%-9%), the ratio of electrical conductivity to thermal conductivity of the dispersed CoSb3 is higher than that of nondispersed CoSb3, and the dimensionless figure of merit (ZT) of the composite could probably be improved at these ranges with the enhanced ratio of electrical conductivity to thermal conductivity and Seebeck coefficient, which is assumed to be increased by a potential barrier scattering.
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| 10. |
- He, Zeming, et al.
(författare)
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Nano ZrO2/CoSb3 composites with improved thermoelectric figure of merit
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:23, s. 235602-
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Tidskriftsartikel (refereegranskat)abstract
- Nano ZrO2/CoSb3 composites with different ZrO 2 contents were prepared using hot pressing. The phase purity, the microstructure and the temperature-dependent transport parameters of the composites were investigated. The dimensionless figure of merit (ZT) of 0.18 of the non-dispersed CoSb3 preponderates the maximal value (0.17) of pure CoSb3 reported in the literature, which is attributed to the prepared sample having higher electrical conductivity due to the existence of a small amount of metallic Sb and lower thermal conductivity due to the fine-grained structure. Compared to non-dispersed CoSb3, a further improvement of 11% on ZT (0.20) was achieved in the composite with 0.05ZrO 2 inclusions, which resulted from the enhanced ratio of electrical conductivity to thermal conductivity and the Seebeck coefficient. The nanodispersion method provides an effective approach to improving a material's thermoelectric properties and performance.
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| 11. |
- He, Zeming, et al.
(författare)
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Thermoelectric properties of hot-pressed skutterudite CoSb3
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:5, s. 053713-
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, skutterudite CoSb3 were fabricated by hot pressing at different sintering temperatures under vacuum and argon. For the prepared compacts, the phase, the microstructure, and the temperature dependent thermoelectric properties were characterized. The correlation of the materials factors: density, grain size, Sb content, with the thermoelectric variables: Seebeck coefficient, electrical conductivity, thermal conductivity, and dimensionless figure of merit (ZT), is presented. The achieved ZT values are also compared with those reported in the literature. The investigated samples show larger electrical conductivity due to existence of metallic Sb and smaller thermal conductivity because of fine-grained structure. A maximal ZT of 0.11 was achieved for the samples sintered at 853 K under vacuum and at 773 K under argon. A moderate improvement on ZT for pure CoSb3 is shown in the present work.
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| 12. |
- Kodash, V. Y., et al.
(författare)
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Field-activated sintering of skutterudites
- 2007
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 57:6, s. 509-511
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Tidskriftsartikel (refereegranskat)abstract
- Skutterudite (Co0.92Ni0.08)4Sb11.88Te0.12 powder has been consolidated under an applied electrical field using a field-assisted sintering technique (FAST). The low FAST sintering temperature and relatively high heating rate considerably reduce grain growth during sintering.
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| 13. |
- Li, Shanghua, et al.
(författare)
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Bulk synthesis of transparent and homogeneous polymeric hybrid materials with ZnO quantum dots and PMMA
- 2007
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 19:24, s. 4347-
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Tidskriftsartikel (refereegranskat)abstract
- [GRAPHICS] In situ sol-gel polymerization is demonstrated for fabricating transparent poly(methyl methacrylate) (PMMA)-ZnO quantum dot (QD)-hybrid materials in bulk dimension. ne transparent PMMA-ZnO QD hybrid materials exhibit enhanced UV-shielding effects in the entire UV range, even at concentrations as low as 0.02 wt %.
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| 14. |
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| 15. |
- Li, Shanghua, et al.
(författare)
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Effects of annealing and doping on nanostructured bismuth telluride thick films
- 2008
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 20:13, s. 4403-4410
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth telluride is the state-of-the-art thermoelectric (TE) material for cooling applications with a figure of merit of ∼1 at 300 K. There is a need for the development of TE materials based on the concept of thick films for miniaturized devices due to mechanical and manufacturing constraints for the thermoelement dimensions. We reported earlier a method for the fabrication of high-quality nanostructured bismuth telluride thick films with thickness from 100 to 350 μm based on electrochemical deposition techniques. In this paper, annealing is performed to further improve the TE performance of the nanostructured bismuth telluride thick films and n/p-type solid solutions are successfully fabricated by doping Se and Sb, respectively. The conditions for both annealing and doping for the thick films are investigated, and the effects of annealing and doping on morphology, crystalline phase, grain size, Seebeck coefficient, homogeneity, electrical conductivity, and power factor of the bismuth telluride thick films have been studied.
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| 16. |
- Li, Shanghua, 1981-
(författare)
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Engineering nanomaterials with enhanced functionality
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the engineering of novel nanomaterials, particularly nanocomposites and nanostructured surfaces with enhanced functionalities. The study includes two parts; in the first part, an in situ sol-gel polymerization approach is used for the synthesis of polymer-inorganic hybrid material and its exceptional transparent UV-shielding effect has been investigated. In the second part, electrodeposition process has been adapted to engineer surfaces and the boiling performance of the fabricated nanostructured surfaces is evaluated. In the first part of the work, polymer-inorganic hybrid materials composed of poly(methylmethacrylate) (PMMA) and zinc compounds were prepared by in situ sol-gel transition polymerization of zinc complex in PMMA matrix. The immiscibility of heterophase of solid organic and inorganic constituents was significantly resolved by an in situ sol-gel transition polymerization of ZnO nanofillers within PMMA in the presence of dual functional agent, monoethanolamine, which provided strong secondary interfacial interactions for both complexing and crosslinking of constituents. In the second part of the work, nanoengineering on the surface of copper plates has been performed in order to enhance the boiling heat transfer coefficient. Micro-porous surfaces with dendritic network of copper nanoparticles have been obtained by electrodeposition with dynamic templates. To further alter the grain size of the dendritic branches, the nanostructured surfaces underwent a high temperature annealing treatment. Comprehensive characterization methods of the polymer-inorganic hybrid materials and nanoengineered surfaces have been undertaken. XRD, 1H NMR, FT-IR, TGA, DSC, UV-Vis, ED, SEM, TEM and HRTEM have been used for basic physical properties. Pool boiling tests were performed to evaluate the boiling performance of the electrodeposited nanostructured micro-porous structures. The homogeneous PZHM exhibited enhanced UV-shielding effects in the entire UV range even at very low ZnO content of 0.02 wt%. Moreover, the relationship between band gap and particle size of incorporated ZnO by sol-gel process was in good agreement with the results calculated from the effective mass model between bandgap and particle size. The fabricated enhanced surface has shown an excellent performance in nucleate boiling. At heat flux of 1 W/cm2, the heat transfer coefficient is enhanced over 15 times compared to a plain reference surface. A model has been presented to explain the enhancement based on the structure characteristics.
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| 17. |
- Li, Shanghua, 1981-
(författare)
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Fabrication of Nanostructured Materials for Energy Applications
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- World energy crisis has triggered more attention to energy saving and energy conversion systems with high efficiency. There is a growing awareness that nanoscience and nanotechnology can have a profound impact on energy generation, conversion, and recovery. Nanotechnology-based solutions are being developed for a wide range of energy problems such as, solar electricity, hydrogen generation and storage, batteries, fuel cells, heat pumps and thermoelectrics. This thesis deals with the design and fabrication of novel functional materials/architectures for energy-related applications. The study includes two parts: Nanostructured thermoelectric (TE) materials for energy conversion and nanostructured metallic surfaces for energy heat transfer. In the first part, the focus is given to the fabrication of novel nanostructured TE materials and architectures. TE materials are very important functional materials that can convert heat to electrical energy and vice versa. Recently, nanostructuring TE materials showed very promising potential to improve their TE figure of merit which opens a new venue for the TE world. As a result, some advanced nanostructured TE architectures are proposed as the state-of-the-art TE materials/structures. Among these advanced TE architectures, bismuth telluride nanowires/thick films and skutterudite nanocomposites with nanoinclusions have been successfully fabricated and some of their advantageous TE performance has been demonstrated. For example, an improvement of 11% on the figure of merit, ZT, was achieved in the CoSb3 nanocomposite with 5 mole% ZrO2 as nanoinclusion. Comprehensive physico-chemical characterization techniques have been used for the synthesized TE materials. The potential-Seebeck microprobe, 4-point probe and laser flash apparatus have been used for the measurement of TE parameters on the TE materials. In the second part of the thesis, we developed a nanostructured macro-porous (NMp) surface for enhancing heat transfer in boiling process. Enhanced surfaces for boiling improve the energy efficiency of heat pumping equipment such as air conditioners, refrigerators, etc. Conventional techniques currently used for fabricating enhanced surfaces are often based on the use of complicated mechanical machine tools and require a large consumption of materials and give only limited enhancement of the boiling heat transfer. In this thesis, we present a new approach to fabricate enhanced surfaces by using electrodeposition under specific conditions forming in-situ dynamic gas bubble templates. As a result, the NMp metallic surface layer comprising of dendritically ordered copper branches is obtained. Since the structure is formed during the evolution of the dynamic bubbles, it is ideal for the bubble generation applications such as boiling. The efficiency of the NMp surfaces for boiling heat transfer was evaluated in pool boiling experiments. At the heat flux of 1 W/cm2, the heat transfer coefficient for the NMp surface is found to be more than 17 times higher than the reference surface. It's estimated that such an effective boiling surface would improve the energy efficiency of many heat pumping machines with 10 - 30 %. The extraordinary enhancement of boiling performance is explained by the structure characteristics, which assist in enhancing nucleation of the gas bubbles, subsequent coalescence, and facilitated departure from the surfaces.
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| 18. |
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| 19. |
- Li, Shanghua, et al.
(författare)
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Fabrication of nanostructured thermoelectric bismuth telluride thick films by electrochemical deposition
- 2006
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 18:16, s. 3627-3633
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth telluride ( Bi2Te3)-based solid solutions are state-of-the-art thermoelectric (TE) materials for cooling applications at room temperature with a high figure of merit ZT. Nanostructured TE bismuth telluride thick films have been fabricated by electrodeposition from a solution containing bismuth nitrate and tellurium dioxide in 1 M nitric acid onto gold-sputtered aluminum substrates. A conventional three-electrode cell was used with a platinum sheet as the counter electrode and a saturated calomel electrode (SCE) as the reference electrode. Ethylene glycol (EG) was added to the electrolyte in order to increase the thickness of the deposited films, and its effect on the structure, morphology, and compositional stoichiometry of the deposited film was investigated. SEM and XRD were used for structural and compositional characterization. Bismuth telluride films with thicknesses of ca. 350 mu m, a stoichiometric composition of Bi2Te3, and a hexagonal crystal structure were obtained. A microprobe technique was used to measure the lateral Seebeck coefficient in several samples. The free-standing films were shown to be of high homogeneity, where the abundance distribution of the Seebeck coefficient showed a half width of less than 1 mu V K-1 and a high electrical conductivity of around 450 S cm(-1) at room temperature.
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| 20. |
- Li, Shanghua, et al.
(författare)
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Fabrication of transparent polymer-inorganic hybrid material
- 2005
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Ingår i: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 9781558998308 ; , s. 190-194
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Konferensbidrag (refereegranskat)abstract
- Polymer-inorganic hybrid materials composed of polymethyl methacrylate (PMMA) and zinc compounds were prepared by sol-gel in-situ transition polymerization of zinc complex in PMMA matrix. Zinc acetate dihydrate dissolved in ethanol was used as the inorganic precursor. Monoethanolamine (MEA) acted as a complexing agent to control the hydrolysis of zinc acetate to produce a zinc compound network, and then PMMA, formed in-situ through a radical polymerization, were chemically bonded to the forming zinc compound network to realize a hybrid material. Transparent homogenous hybrid materials with slight colours from pink to yellow were fabricated by varying the composition. TEM, FT-IR were employed to investigate structural and physical properties. The UV-shielding effect was evaluated by UV-VIS. The low content of zinc (around 0.02 wt%) and the fine particle size rendered it visibly transparent and capable of greatly attenuating UV radiation in the full UV range.
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| 21. |
- Li, Shanghua, 1980-, et al.
(författare)
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Nanocomposites of polymer and inorganic nanoparticles for optical and magnetic applications
- 2010
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Ingår i: Nano reviews. - : CoAction Publishing. - 2000-5121. ; 1, s. 5214-
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Tidskriftsartikel (refereegranskat)abstract
- This article provides an up-to-date review on nanocomposites composed of inorganic nanoparticles and the polymer matrix for optical and magnetic applications. Optical or magnetic characteristics can change upon the decrease of particle sizes to very small dimensions, which are, in general, of major interest in the area of nanocomposite materials. The use of inorganic nanoparticles into the polymer matrix can provide high-performance novel materials that find applications in many industrial fields. With this respect, frequently considered features are optical properties such as light absorption (UV and color), and the extent of light scattering or, in the case of metal particles, photoluminescence, dichroism, and so on, and magnetic properties such as superparamagnetism, electromagnetic wave absorption, and electromagnetic interference shielding. A general introduction, definition, and historical development of polymer-inorganic nanocomposites as well as a comprehensive review of synthetic techniques for polymer-inorganic nanocomposites will be given. Future possibilities for the development of nanocomposites for optical and magnetic applications are also introduced. It is expected that the use of new functional inorganic nano-fillers will lead to new polymer-inorganic nanocomposites with unique combinations of material properties. By careful selection of synthetic techniques and understanding/exploiting the unique physics of the polymeric nanocomposites in such materials, novel functional polymer-inorganic nanocomposites can be designed and fabricated for new interesting applications such as optoelectronic and magneto-optic applications.
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| 22. |
- Li, Shanghua, et al.
(författare)
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Nature-inspired boiling enhancement by novel nanostructured macroporous surfaces
- 2008
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 18:15, s. 2215-2220
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Tidskriftsartikel (refereegranskat)abstract
- World energy crisis has triggered more attention to energy saving and energy conversion systems. Enhanced surfaces for boiling are among the applications of great interest since they can improve the energy efficiency of heat pumping equipment (i.e., air conditioners, heat pumps, refrigeration machines). Methods that are used to make the state-of-the-art enhanced Surfaces are often based on complicated mechanical machine tools, are quite material-consuming and give limited enhancement of the boiling heat transfer. Here, we present a new approach to fabricate enhanced surfaces by using a simple electrodeposition method with in-situ grown dynamic gas bubble templates. As a result, a well-ordered 3D macro-porous metallic surface layer with nanostructured porosity is obtained. Since the structure is built based on the dynamic bubbles, it is perfect for the bubble generation applications Such as nucleate boiling. At heat flux of 1W cm(-2), the heat transfer coefficient is enhanced over 17 times compared to a plain reference Surface. It's estimated that such ail effective boiling surface Would improve the energy efficiency of many heat Pumping machines with 10-30%. The extraordinary boiling performance is explained based on the structure characteristics.
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| 23. |
- Li, Shanghua, et al.
(författare)
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Novel Solution Route Synthesis of Low Thermal Conductivity Nanocrystalline Bismuth Telluride
- 2010
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 10:11, s. 7658-7662
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Tidskriftsartikel (refereegranskat)abstract
- A novel synthesis approach based on a solution route has been developed for the fabrication of nanocrystalline bismuth telluride. The method consists of dissolving both bismuth and tellurium into the same organic solvent with the assistance of complexing agents and one-step coprecipitation of bismuth telluride. The synthesized nanocrystalline bismuth telluride powders possess rhombohedral crystal structure and are nanosheet/nanorod-like with an average size of between 30 and 40 nm. The thermal conductivity of the hot-pressed compact consolidated from the as-synthesized nanopowders is 0.39-0.45 Wm(-1)K(-1) in the temperature range of 323 to 523 K, which is at most one third of that of bulk bismuth telluride-based materials reported in the literature. Such low thermal conductivity of the investigated bismuth telluride is mainly attributed to substantially high concentration of grain boundaries provided by nanostructuring to scatter phonons intensively.
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| 24. |
- Li, Shanghua, et al.
(författare)
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Synthesis and magnetic properties of bulk transparent PMMA/Fe-oxide nanocomposites
- 2009
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 20:18
-
Tidskriftsartikel (refereegranskat)abstract
- PMMA/Fe-oxide nanocomposites are fabricated by a chemical method. Monodispersed Fe-oxide nanoparticles are well dispersed in the PMMA matrix by in situ polymerization, resulting in a bulk transparent polymeric nanocomposite. The magnetic behavior of the PMMA/Fe-oxide nanocomposites is investigated. The transparent PMMA/Fe-oxide nanocomposite has potentially interesting magneto-optic applications without compromising the advantages of a lightweight, noncorrosive polymeric material with very high transparency even for bulk samples.
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| 25. |
- Li, Shanghua, et al.
(författare)
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Template electrodeposition of ordered bismuth telluride nanowire arrays
- 2009
-
Ingår i: Journal of Nanoscience and Nanotechnology. - 1533-4880 .- 1533-4899. ; 9:2, s. 1543-1547
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Tidskriftsartikel (refereegranskat)abstract
- Thermoelectric bismuth telluride nanowire arrays have been synthesized by direct-current electrodeposition into porous anodic alumina membranes both galvanostatically and potentiostatically. The as-synthesized Bi2Te3 nanowire arrays are highly ordered in large area, stoichiometric, uniform, with high aspect ratio (above 100) and high filling ratio (>90%) of the membrane. The effects of different electrochemical deposition parameters on crystal structures, morphology and composition have been investigated. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) have been used to characterize the physical and chemical properties of the nanowires.
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| 26. |
- Li, Shanghua, et al.
(författare)
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The effect of ceria nanoparticles on the breakdown strength of transformer oil
- 2015
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Ingår i: 2015 IEEE 11th International Conference on the Properties and Applications of Dielectric Materials (ICPADM). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781479989034 ; , s. 289-292
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Konferensbidrag (refereegranskat)abstract
- Nanotechnologies have potential to be used in transformer industry in enhancing material properties which may lead to a compact design of transformer and reduced manufacturing cost. Effect of adding different nanoparticles such as titania, silica, nano-diamond, etc. has been studied in literatures. In this paper, nano-ceria particles have been successfully added into transformer mineral oil with different content. The suspension is very stable and no segmentation can be observed over several months. The ceria nanoparticles are commercially available, which have a quite narrow size distribution. UV-Vis, TGA and FT-IR are used to characterize the ceria nanofluids. The water content of the ceria nanofluids has been measured by Karl Fisher titration, which is important for the breakdown strength of transformer oil. AC voltage breakdown and lightning impulse voltage breakdown measurements have been performed on the ceria nanofluids. An enhancement of 15% on AC breakdown voltage has been observed on ceria nanofluids with some content compared to reference transformer oil. On the other hand, no clear difference on the lightning impulse breakdown voltage is observed between the ceria nanofluids and reference transformer oil.
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| 27. |
- Li, Shanghua, et al.
(författare)
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Thermoelectric properties of CoSb3 with maize-like structure
- 2007
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Ingår i: Physica Status Solidi-Rapid Research Letter. - : Wiley. - 1862-6254 .- 1862-6270. ; 1:6, s. 259-261
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Tidskriftsartikel (refereegranskat)abstract
- Maize-like CoSb3 powders were obtained via the chemical alloying method. After the consolidation of the nanopowder using hot press, the CoSb3 compact shows a higher Seebeck coefficient and lower thermal conductivity. For the investigated CoSb3, a ZT of 0.15 at 673 K is shown. Though the achieved ZT does not reach the optimal value (0. 17 to 0. 18) for pure CoSb3, due to its lower electrical conductivity, the novel structure fabrication provides an interesting and promising approach to enhancing the thermoelectric performance.
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| 28. |
- Lin, Meng Meng, et al.
(författare)
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Complete separation of magnetic nanoparticles via chemical cleavage of dextran by ethylenediamine for intracellular uptake
- 2010
-
Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 20:3, s. 444-447
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Tidskriftsartikel (refereegranskat)abstract
- Completely water dispersible and highly monodispersed superparamagnetic iron oxide nanoparticles (SPIONs) were prepared. The surface of SPIONs was modified with dual-crosslinked amine activated dextran (AMD) and chemical cleavage of AMD on SPIONs was carried out by ethylenediamine hydrochloride (EDA). Transmission electron microscopy (TEM) revealed that individual SPIONs were completely separated in water and the average diameter of resulting nanoparticles was 4.4 nm.
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| 29. |
- Ma, Ying, et al.
(författare)
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Samarium-doped ceria nanowires : Novel synthesis and application in low-temperature solid oxide fuel cells
- 2010
-
Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 22:14, s. 1640-1644
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Tidskriftsartikel (refereegranskat)abstract
- Samarium-doped ceria (SDC) nanowires are synthesized by a novel, template-, surfactant-free and cost-effective method, using citric acid as precipitating/complexing agent for formation of citrate precursor nanowires. The single SOFC based on SDC nanowires/Na2CO3 nanocomposites as electrolyte is fabricated and the maximum power densities of 417 and 522 mW cm-2 at 550 and 600°C are achieved, showing great potential for low-temperature SOFCs.
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| 30. |
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| 31. |
- Saleemi, Mohsin, et al.
(författare)
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Fabrication and Spark Plasma Sintering of Nanostructured Bismuth Telluride (Bi2Te3)
- 2012
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Ingår i: 9Th European Conference On Thermoelectrics (ECT2011). - : American Institute of Physics (AIP). - 9780735410480 ; , s. 115-118
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Konferensbidrag (refereegranskat)abstract
- Thermoelectric (TE) devices can harvest residual low-grade waste heat energy. Bismuth telluride (Bi2Te3) and its alloys are mostly used TE materials in the bulk form for making TE modules. We report a simple, fast and very high yield synthetic process for the bulk Bi2Te3 nanopowders with hexagonal plate like morphology. Spark plasma sintering (SPS) process has been optimized in order to preserve nanostructure while achieving a high compaction density of the pellets. Electron microscopy analysis was used to determine the effect of SPS parameters during compaction on the grain growth. Optimal conditions for the fabricated nanopowder was determined as 673 K, 70 MPa pressure with no holding time, which resulted in average lateral grain size in the range of 165-190 nm for a compact density of 98%. About 50% reduction of thermal conductivity was observed as compared to its bulk counterparts, revealing the feasibility of suggested route in the preservation of nanostructure and enhanced phonon scattering.
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| 32. |
- Saleemi, Mohsin, et al.
(författare)
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Synthesis, processing, and thermoelectric properties of bulk nanostructured bismuth telluride (Bi2Te3)
- 2012
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 22:2, s. 725-730
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth telluride (Bi2Te3) is the best-known commercially used thermoelectric material in the bulk form for cooling and power generation applications at ambient temperature. However, its dimensionless figure-of-merit-ZT around 1 limits the large-scale industrial applications. Recent studies indicate that nanostructuring can enhance ZT while keeping the material form of bulk by employing an advanced synthetic process accompanied with novel consolidation techniques. Here, we report on bulk nanostructured (NS) undoped Bi2Te3 prepared via a promising chemical synthetic route. Spark plasma sintering has been employed for compaction and sintering of Bi2Te3 nanopowders, resulting in very high densification (>97%) while preserving the nanostructure. The average grain size of the final compacts was obtained as 90 +/- 5 nm as calculated from electron micrographs. Evaluation of transport properties showed enhanced Seebeck coefficient (-120 mu V K-1) and electrical conductivity compared to the literature state-of-the-art (30% enhanced power factor), especially in the low temperature range. An improved ZT for NS bulk undoped Bi2Te3 is achieved with a peak value of similar to 1.1 at 340 K.
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| 33. |
- Sugunan, Abhilash, et al.
(författare)
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Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots
- 2011
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 22:42, s. 425202-
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.
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| 34. |
- Wang, Xiaodi, et al.
(författare)
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Ceria-based nanocomposite with simultaneous proton and oxygen ion conductivity for low-temperature solid oxide fuel cells
- 2011
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 196:5, s. 2754-2758
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Tidskriftsartikel (refereegranskat)abstract
- The samarium doped ceria-carbonate (SDC/Na2CO3) nanocomposite systems have shown to be excellent electrolyte materials for low-temperature SOFCs, yet, the conduction mechanism is not well understood. In this study, a four-probe d.c. technique has been successfully employed to study the conduction behavior of proton and oxygen ion in SDC/Na2CO3 nanocomposite electrolyte. The results demonstrated that the SDC/Na2CO3 nanocomposite electrolyte possesses unique simultaneous proton and oxygen ion conduction property, with the proton conductivity 1-2 orders of magnitude higher than the oxygen ion conductivity in the temperature range of 200-600 degrees C, indicating the proton conduction in the nanocomposite mainly accounts for the enhanced total ionic conductivity. It is suggested that the interface in composite electrolyte supplies high conductive path for proton, while oxygen ions are probably transported by the SDC grain interiors. An empirical "Swing Model" has been proposed as a possible mechanism of superior proton conduction. (C) 2010 Elsevier B.V. All rights reserved.
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| 35. |
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| 36. |
- Wang, Xiaodi, 1981-, et al.
(författare)
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SDC/Na2CO3 nanocomposite : New freeze drying based synthesis and application as electrolyte in low-temperature solid oxide fuel cells
- 2012
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 37:24, s. 19380-19387
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Tidskriftsartikel (refereegranskat)abstract
- A key issue to develop low-temperature solid oxide fuel cells (LTSOFCs) is to develop new electrolyte materials with enhanced ionic conductivity. Recently, SDC/Na2CO3 nanocomposite, as a proton and oxide co-ion conductor, has been developed as promising electrolyte candidates for LTSOFCs, where Na2CO3 as the secondary phase performs several crucial functions. However, it's difficult to control the homogeneity of Na 2CO3 phase in the composite by the current methods for composite fabrication. In this study, we report a new freeze drying technique to fabricate SDC/Na2CO3 nanocomposites with different content of Na2CO3. Structural and morphological study confirmed that the homogeneity of both SDC and Na2CO3 phases in the nanocomposite is well controlled by the freeze drying technique. The effect of Na2CO3 content on proton and oxygen ion conductivities of SDC-carbonate samples were investigated by the four-probe d.c. measurement. Proton conductivity transformation around 350 °C has been observed for all the SDC/Na2CO3 nanocomposites due to the glass transition of amorphous Na2CO3 phase, and the proton conductivity is dependent on Na2CO3 content. While oxygen ion conductivity deceases with the increasing of Na2CO3 volume fraction in the nanocomposite. Finally, SOFCs were fabricated using SDC/Na2CO3 nanocomposite samples and tested for electrochemical performances. The excellent performance of SOFCs using SDC/Na2CO3 nanocomposite electrolyte verifies that nanocomposite approach is an effective way to fabricate electrolyte with enhanced ionic conductivity for LTSOFCs.
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| 37. |
- Zhou, Jian, et al.
(författare)
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Synthesis and Seebeck coefficient of nanostructured phosphorus-alloyed bismuth telluride thick films
- 2008
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Ingår i: Physica Status Solidi. C, Current topics in solid state physics. - : Wiley. - 1610-1634 .- 1610-1642. ; 5:11, s. 3453-3457
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorous-alloyed Bi2Te3 thick films have been prepared by electrochemical deposition. The average grain size of the films was calculated to be 14-26 nm based on Scherrer's equation. The effect of P on the Seebeck coefficient of thermoelectric P-alloyed Bi2Te3 thick film was investigated. The results show that P-alloyed thick film has n-type conductivity with the Seebeck coefficient of -35 mu V/K. The correlation between P site occupancy in the crystal and the Seebeck coefficient was discussed.
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