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Fabrication of Nanostructured Materials for Energy Applications
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , x, 72 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:12
Keyword [en]
Materials Chemistry
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4807ISBN: 978-91-7178-994-5 (print)OAI: oai:DiVA.org:kth-4807DiVA: diva2:14078
Public defence
2008-06-13, Sal N1, KTH-Electrum 3, Isafjordsgatan 28 A/D, Kista, 10:00
Opponent
Supervisors
Note
QC 20100924Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2010-09-24Bibliographically approved
List of papers
1. Template electrodeposition of ordered bismuth telluride nanowire arrays
Open this publication in new window or tab >>Template electrodeposition of ordered bismuth telluride nanowire arrays
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2009 (English)In: Journal of Nanoscience and Nanotechnology, ISSN 1533-4880, E-ISSN 1533-4899, Vol. 9, no 2, 1543-1547 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Bismuth Telluride, Nanowire, Thermoelectric, Anodic Alumina Membrane, Template Electrodeposition
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8682 (URN)10.1166/jnn.2009.C198 (DOI)000263653300198 ()2-s2.0-67649270914 (Scopus ID)
Note
QC 20100819. Uppdaterad från in press till published (20100819). 6th International Conference on Nanoscience and Technology, Beijing, PEOPLES R CHINA, JUN 04-06, 2007Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2017-12-14Bibliographically approved
2. Fabrication of nanostructured thermoelectric bismuth telluride thick films by electrochemical deposition
Open this publication in new window or tab >>Fabrication of nanostructured thermoelectric bismuth telluride thick films by electrochemical deposition
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2006 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 18, no 16, 3627-3633 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
bi2te3 films, electrodeposition, conductivity, thiourea, sulfate, sb2te3, copper
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-15879 (URN)10.1021/cm060171o (DOI)000239396900008 ()2-s2.0-33748281989 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Effects of annealing and doping on nanostructured bismuth telluride thick films
Open this publication in new window or tab >>Effects of annealing and doping on nanostructured bismuth telluride thick films
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2008 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 20, no 13, 4403-4410 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Bismuth, Electric conductivity, Electric power factor, Films, Microelectronics, Molecular beam epitaxy, Optical design, Reduction, Seebeck coefficient, Solid solutions, Thick films, Vapor deposition
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-8684 (URN)10.1021/cm800696h (DOI)000257279200034 ()2-s2.0-47749119959 (Scopus ID)
Note
QC 20100910. Uppdaterad från In press till Published (20100910)Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2017-12-14Bibliographically approved
4. Effect of ceramic dispersion on thermoelectric properties of nano ZrO2/CoSb3 composites
Open this publication in new window or tab >>Effect of ceramic dispersion on thermoelectric properties of nano ZrO2/CoSb3 composites
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2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 4, 043707- p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Dispersions, Hot pressing, Sintering, Thermal conductivity, Thermoelectricity, Zirconia
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-8685 (URN)10.1063/1.2561628 (DOI)000244530800049 ()2-s2.0-33847632045 (Scopus ID)
Note
QC 20100909Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2017-12-14Bibliographically approved
5. Nano ZrO2/CoSb3 composites with improved thermoelectric figure of merit
Open this publication in new window or tab >>Nano ZrO2/CoSb3 composites with improved thermoelectric figure of merit
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2007 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 18, no 23, 235602- p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Cobalt compounds, Electric conductivity, Hot pressing, Seebeck coefficient, Thermal conductivity, Zirconia
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-8686 (URN)10.1088/0957-4484/18/23/235602 (DOI)000246590700010 ()2-s2.0-34249097404 (Scopus ID)
Note
QC 20100923Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2017-12-14Bibliographically approved
6. Thermoelectric properties of hot-pressed skutterudite CoSb3
Open this publication in new window or tab >>Thermoelectric properties of hot-pressed skutterudite CoSb3
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2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 5, 053713- p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Electric conductivity, Hot pressing, Physical properties, Seebeck coefficient, Sintering, Thermal conductivity, Thermoelectricity, Vacuum applications, Fine grained structures, Skutterudites
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-8687 (URN)10.1063/1.2538036 (DOI)000244945400074 ()2-s2.0-33947411480 (Scopus ID)
Note
QC 20100924Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2017-12-14Bibliographically approved
7. Field-activated sintering of skutterudites
Open this publication in new window or tab >>Field-activated sintering of skutterudites
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2007 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 57, no 6, 509-511 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Field-assisted sintering technique, Grain growth, Skutterudite
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-8688 (URN)10.1016/j.scriptamat.2007.05.032 (DOI)000248638600016 ()2-s2.0-34447255673 (Scopus ID)
Note
QC 20100915Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2017-12-14Bibliographically approved
8. Thermoelectric properties of CoSb3 with maize-like structure
Open this publication in new window or tab >>Thermoelectric properties of CoSb3 with maize-like structure
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2007 (English)In: Physica Status Solidi-Rapid Research Letter, ISSN 1862-6254, Vol. 1, no 6, 259-261 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
skutterudites, transport
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-8689 (URN)10.1002/pssr.200701172 (DOI)000251314700019 ()2-s2.0-48249087611 (Scopus ID)
Note
QC 20100924Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2010-09-24Bibliographically approved
9. Nature-inspired boiling enhancement by novel nanostructured macroporous surfaces
Open this publication in new window or tab >>Nature-inspired boiling enhancement by novel nanostructured macroporous surfaces
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2008 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 18, no 15, 2215-2220 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
heat-transfer, saturated fc-72, silicon, walls
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-17788 (URN)10.1002/adfm.200701405 (DOI)000258795500009 ()2-s2.0-50249158588 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
10. Dendritically ordered nano-particles in a micro-porous structure for enhanced boiling
Open this publication in new window or tab >>Dendritically ordered nano-particles in a micro-porous structure for enhanced boiling
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2006 (English)In: Proceedings of 13th International Heat Transfer Conference, NAN-07, 2006, Vol. NAN-07Conference paper, Published paper (Refereed)
Abstract [en]

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).

National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-8691 (URN)1-56700-225-0 (ISBN)
Note
QC 20100924Available from: 2008-06-04 Created: 2008-06-04 Last updated: 2011-11-11Bibliographically approved

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