Synthesis and Characterization of Tungsten Oxide Nanostructures PDF Download
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Author: Rong Hu
Publisher:
ISBN: 9781374678644
Category :
Languages : en
Pages :
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Author: Rong Hu
Publisher:
ISBN: 9781374678644
Category :
Languages : en
Pages :
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Book Description
Author: Rong Hu (Ph. D.)
Publisher:
ISBN:
Category : Nanostructures
Languages : en
Pages : 166
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Book Description
Author: Pavan K. Dasari
Publisher:
ISBN:
Category : Nanostructures
Languages : en
Pages : 162
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Book Description
Electrochromic tungsten trioxide (WO3) solutions were synthesized utilizing a sol-gel processing technique. These solutions by their very nature are unstable and readily precipitate without stabilization. Both polymer based stabilization using polyethylene oxide (PEO) and electrostatic stabilization by pH modification methods were utilized to stabilize and isolate WO3 colloids. Tungsten colloidal nanoparticles in the size range of 10 to 50 nm were observed. The primary goal of this work was to explore and control the sizes of nano particles of WO3 under various conditions. Data obtained from atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic light scattering measurements (DLS) gave convincing results about the different growth rates of tungsten colloids. We also obtained information regarding the shapes of WO3 particles. Long needle-like dendrites are seen at low concentrations of PEO and flower like crystallized structures are obtained at higher concentrations. All these results provided substantial evidence about different growth rates of WO3 colloids.
Author: 洪昆權
Publisher:
ISBN: 9781374667396
Category :
Languages : en
Pages :
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This dissertation, "Synthesis of One-dimensional Tungsten Oxide Nanostructures" by 洪昆權, Kunquan, Hong, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled SYNTHESIS OF ONE-DIMENSIONAL TUNGSTEN OXIDE NANOSTRUCTURES Submitted by Hong Kunquan for the degree of Doctor of Philosophy at The University of Hong Kong in January 2008 Tungsten oxide has been used for various optical devices, sensors and so forth for its outstanding electrochromic, optochromic, gaschromic and electronic properties. One-dimensional (1D) tungsten oxide nanostructures are expected to improve the performance of those devices as well as to open up new applications. o Generally, high temperature (1200-2000 C) and special equipments are required in the synthesis of these tungsten oxide nanostructures, which can be obstacles for a wider application. In this thesis, some new methods have been developed to synthesize 1D tungsten oxide nanostructures. The relevant growth mechanisms were also investigated. Firstly, a simple method was devised to grow tungsten oxide nanostructures by thermal evaporation at low temperature and yet without using catalyst. By o heating tungsten powder at 650 C, and tungsten plate or tungsten powder covered o silicon substrates at 400 C, tungsten oxide (W O ) nanowires with diameter of 18 49 10-50 nm were obtained with high quantity. It was further shown that the presence of a pre-oxide layer on tungsten substrate is essential for high yield W O 18 49 nanowire growth. Under optimal conditions, the diameter of the nanowires can be decreased down to 4-7 nm. Second, when potassium iodide (KI) was introduced in the synthesis, various types of nanostructures or micro-structures, such as tungsten oxide and potassium tungstates (K W O ) micro-walls were obtained, depending 2 3 10 on the temperature of substrate, the gas flow and the pressure in the reactor. It was o found that tungsten oxide nanowires can be synthesized at 400 C in the presence of KI, and the addition of source materials will enhance the growth. Finally, by thermally evaporating tungsten trioxide powder source, tungsten oxide W O nanowires were also synthesized with high yield and on a large 18 49 scale. Depending on the temperature of the source (in the range of 900-1000 C), the diameter of the tungsten oxide nanowires varies from 10 nm to 100 nm, following an exponential relation. Nanowires with controllable diameter are therefore obtainable by this method. Under other conditions, nanowires, nanoplates, nanocrystals and comb-like nanostructures were obtained on silicon substrate. The growth mechanisms of these nanostructures, especially the dependence of nanowire size on source temperature, were further investigated. It is found that the diameter of nanowires increases with growth time but a maximum diameter seems to exist as determined by the source temperature. A theoretical model was used to analyze the growth mechanism for the diameter control where zero-dimensional (0D) and two-dimensional (2D) nucleation contribute to the growth of length and the diameter of the nanowire respectively. DOI: 10.5353/th_b3955855 Subjects: Tungsten oxides - Synthesis Nanostructures
Author: Thokozani Mpanza
Publisher:
ISBN:
Category : Gas sensing mechanism
Languages : en
Pages : 81
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Author: Daniela Nunes
Publisher: Elsevier
ISBN: 012811505X
Category : Technology & Engineering
Languages : en
Pages : 331
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Book Description
Metal Oxide Nanostructures: Synthesis, Properties and Applications covers the theoretical and experimental aspects related to design, synthesis, fabrication, processing, structural, morphological, optical and electronic properties on the topic. In addition, it reviews surface functionalization and hybrid materials, focusing on the advantages of these oxide nanostructures. The book concludes with the current and future prospective applications of these materials. Users will find a complete overview of all the important topics related to oxide nanostructures, from the physics of the materials, to its application. - Delves into hybrid structured metal oxides and their promising use in the next generation of electronic devices - Includes fundamental chapters on synthesis design and the properties of metal oxide nanostructures - Provides an in-depth overview of novel applications, including chromogenics, electronics and energy
Author: Kunquan Hong
Publisher:
ISBN:
Category : Nanostructures
Languages : en
Pages : 232
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Book Description
Author: Wing-Ching James Yiu
Publisher:
ISBN: 9781361102794
Category :
Languages : en
Pages :
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Book Description
This dissertation, "Synthesis of One-dimensional Tungsten Oxide Nano-structures by Thermal Evaporation" by Wing-ching, James, Yiu, 姚穎貞, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled SYNTHESIS OF ONE-DIMENSIONAL TUNGSTEN OXIDE NANO-STRUCTURES BY THERMAL EVAPORATION Submitted by Yiu Wing Ching James for the degree of Master of Philosophy at The University of Hong Kong in October 2005 Synthesis of one-dimensional nanomaterials (1D NM) is the essence of nanotechnology development. Thermal Evaporation by a tube furnace is commonly used to produce a wide range of 1D NM for studies on physical properties and corresponding applications. Presently, the studies on producing Tungsten Oxide (WO, X=1-3) NM is rare due to the high synthesis temperature required. For decades, the eutectic alloying technique has been used by materials engineers to obtain desirable alloys at a low temperature. Therefore, Thermal Evaporation may work with the eutectic alloying technique to synthesis WO NMs at a low temperature. It is known that by using potassium iodide (KI) as catalysts, tungsten (W) and potassium (K) form a eutectic alloy upon thermal evaporation; the alloys then act as seeds for 1D NMs growth. However, many important synthesis parameters of this technique are still unclear. It is not clear how air pressure, catalysts distribution methods, and humidity would affect the morphologies and quality of products. It is also not clear whether other halide salt can as well work as catalysts for WO NM growth. The lack of such information makes product quality, including diameter, length, and phase purity difficult. In order to improve the control growth of 1D WO NMs produced by thermal evaporation, a number of experiments were carried out as part of the study. The significance of air pressure on products quality was investigated by comparing specimens generated in atmospheric and in super-low pressures. The effect of catalysts distribution methods on products morphologies was shown by using a solution method to distribute catalysts, and by directly placing the catalyst powder on sample substrate. In addition, sodium chloride (NaCl) was used to test if other halide salt, apart from KI, work as the catalysts for WO NMs growth. The influence of humidity was examined by introducing a large amount of moisture during the thermal evaporation process. The final part of this project involved the fabrication method of Anodized Aluminum Membrane (AAM), which consists of many nanochannels that can be the template for WO 1D NMs growth. In these experiments, it is found that low pressures are critical for the monodispersity of nanoproducts. When KI catalysts are distributed by solution method, grown products have a finer diameter and the synthesis temperature is lower than those directly using KI powder as a catalyst. It is found that NaCl could not act as a catalyst for low temperature growth, therefore KI is essential for WO NMs synthesis. When moisture was introduced during thermal evaporation, large amount of nanoribbons was produced. Finally, high quality AAM could be fabricated by applying the optimum anodization voltage, which favors self-ordering of nanopores. An empirical equation was established to find the optimum anodization voltage for a particular electrolyte. DOI: 10.5353/th_b3204777 Subjects: Tungsten oxides - Synthesis Nanostructured materials - Synthesis Nanostructures Nanotechnology
Author: Y. Djaoued
Publisher:
ISBN:
Category :
Languages : en
Pages : 10
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Author: Hilmi Ünlü
Publisher: Springer
ISBN: 3319253409
Category : Science
Languages : en
Pages : 688
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Book Description
This book focuses on the fundamental phenomena at nanoscale. It covers synthesis, properties, characterization and computer modelling of nanomaterials, nanotechnologies, bionanotechnology, involving nanodevices. Further topics are imaging, measuring, modeling and manipulating of low dimensional matter at nanoscale. The topics covered in the book are of vital importance in a wide range of modern and emerging technologies employed or to be employed in most industries, communication, healthcare, energy, conservation , biology, medical science, food, environment, and education, and consequently have great impact on our society.
