• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 27
  • 9
  • 5
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 60
  • 42
  • 37
  • 13
  • 13
  • 12
  • 9
  • 9
  • 9
  • 8
  • 8
  • 7
  • 7
  • 7
  • 7
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

synthesis and characterization of nanostructured carbon supported Pt-based electrocatalysts

geng, xi 13 January 2012 (has links)
Fuel cell, as an alternative green power source for automobiles and portable electronics, has attracted worldwide attention due to its desirable properties such as high energy density and low greenhouse gas emission. Despite great progress in the past decades, several challenges still remain as obstacles for the large-scale commercialization. Among them, the high cost of Pt-based electrode material is considered as a major barrier, while the life span or stability of electrode catalysts is another concern since the electrocatalysts can be easily poisoned during the fuel cell operation. In order to overcome these issues, nanostructured carbon materials, especially carbon nanotubes (CNTs), are studied as catalyst support. In addition, recent research also suggests that the coupling of a second metal element with Pt can effectively protect the electrocatalysts from being poisoned and thus improve their long-term durability. The objective of the present work was to demonstrate an efficient synthetic method for the preparation of CNTs supported binary PtM (M=Ru, Sn) electrocatalysts. In this project, a polymer wrapping technique along with an in-situ polyol reduction strategy was adopted to decorate well-dispersed binary PtM nanoparticles on the surface of modified-CNTs. The unique nanostructures as well as the excellent catalytic activities of the as-prepared nanohybirds were investigated through a diversity of physiochemical and electrochemical characterization techniques. This fabrication method provided a simple and convenient route to assemble Pt-based catalyst on carbon substrates, which is useful for the further development of high-performance fuel cell catalysts.

Fabrication of Carbon Nanotubes by Using of Metal and Metal-free Chemical Vapor Deposition

Ma, Hui-ling 20 July 2007 (has links)

Feasibility of CNT Epoxy Thermoset Based Strain Sensors for Sensing in Structural Applications

Alexander, Jamel Hill 06 May 2017 (has links)
Since their development in the early 1930’s, strain gauges have become an integral part of our lives. The amount of strain measured using strain gauges are the basis for calculating the corresponding: car engine torque, train rail forces, detection of traffic flow and vehicle type, and monitoring bridge safety. As the design of structural parts become more complex in geometry, the need for highly sensitive strain sensors are becoming more essential to ensure the vitality of structural parts. This is especially true when it comes to additive manufactured (AM) parts made from metals, polymers and composites. If sensors can be miniaturized, or even in some cases, be incorporated as part of the host structure, this will provide a non-intrusive monitoring method during the manufacturing process and subsequent service life of the part. However prior to the actual use of embedded sensors, more information is needed regarding the sensitivity of the geometry to the fidelity of the signal. The objective of this research was to explore the feasibility of signal outputs from carbon nanotube (CNT)/epoxy strain sensors and their ability to sense strains on structural components. This research evaluated (1) how percolation within the sensors was affected based on sensor array geometry, (2) various weight percent (w/w%) loading of CNTs required for signal output, (3) how the various w/w% loading affected the mechanical and electrical resistance and conductivity of the sensors and (4) the ability of the sensors to give the same signal output under repeatable cyclic loading.

A Novel Paradigm of Sensing: Multi-signals Acquisition with one sensor

2014 June 1900 (has links)
Sensors with the capability of multi-signal acquisition at the “same” site and “same” time draw abundant attention throughout the academic society. However, designing of multi-signal sensors is a challenging process. The goal of the study is to explore the design theories and methodologies for multi-signal sensors with current device manufacturing technologies. To achieve this goal, this study strives to meet the following two objectives: (1) define general design principles for such sensors, and (2) develop demonstration prototypes to prove the effectiveness of the design principle. The study takes two signals acquisition as a vehicle without loss of generality. For Objective 1, this study proposes three general design principles for multi-signal sensors. The first design principle is to acquire multiple signals through a stem signal. The second principle is to design the structure so that one signal can be accurately inferred while another signal can be directly measured. The third principle is to design an integral structure that inherently acquires two signals. For objective 2, prototypes for the second and third principles were built to demonstrate the effectiveness of the design principles. Contributions of this study to the field of composite materials and sensor design include: (1) findings of the three design principles for multi-signal acquisition, (2) proof-of-concept construction/application of two prototype multi-signal devices (one for temperature and pressure, and the other for temperature and pH), and (3) discovery of the highly linear relationship between the temperature and electrical resistivity with a carbon nanotube and polymer composite within the temperature range from room temperature to approximately 70 Celsius degrees.

Growth of carbon nanotubes on electrospun cellulose fibres for high performance supercapacitors and carbon fibre composites

Li, Qiang January 2018 (has links)
The production of cellulose derived hybrid carbon nanofibre (CNF)/carbon nanotubes (CNTs) electrodes for the fabrication of supercapacitors and carbon fibre composites was investigated. The CNTs were grown via a floating catalyst chemical vapor deposition (CVD) method on the top surface of electrospun cellulose derived CNFs. These CNF and CNF/CNTs samples were then used as electrodes to produce liquid electrolyte-based supercapacitors. The growth of CNTs leads to an improvement of electrochemical performance compared to the plain CNFs. This improvement is due to the grown CNTs enlarging the reactive sites through enhanced surface area and porosity, and thereby increasing the conductivity of the system. CNTs have been also grown onto CNFs containing ferrocene and SiC particles. Composites were fabricated by combining the fibres and CNTs grown fibres with model polymers. The stress transfer properties of these materials have been estimated using an in situ Raman spectroscopic method by observing the shift of the Raman band during the tensile deformation of model polymer composites. Using this method, the elastic modulus of CNF/SiC/CNTs fibres has been estimated to be 208 ± 26 GPa. No shifts in the peak positions of bands relating to the carbon structure were obtained for in situ Raman spectroscopic studies of the CNF/CNTs fibres made from the ferrocene embedded fibres. This was thought to be due to the low yield of CNTs on the surface of the fibres. Furthermore, CNF/CNTs electrode-based structural supercapacitors, combining a solid electrolyte with the carbonized fibres, have been produced. These CNF/CNTs electrodes have a better capacitive performance than the plain CNF electrodes. There was a decrease in this performance with increased curing time of the resin, from 2 to 24 h, due to a lack of charge carrier mobility in the latter samples. A Raman spectroscopic study of the deformation of the carbon structures showed that the G-band shift towards a lower wavenumber position for the CNF and CNF/CNTs samples processed at a carbonization temperature of 2000 °C. Moduli of these fibres were estimated to be ~145 GPa and ~271 GPa, respectively, suggesting the growth of CNTs not only enhances the capacitive performance but also the mechanical properties of the structural supercapacitors. No Raman bend shift was found for the CNFs and CNF/CNTs samples processed below a carbonization temperature of 2000 °C, e.g. 900 °C and 1500 °C. This is because the graphitic structures are not well developed at carbonization temperatures below 1500 °C.

The correlation between the conductivity of the carbon nanotubes and its growth process

Chen, I-ting 28 July 2011 (has links)

Controlling the distribution of carbon nanotubes with colloidal masks: large-area patterning of carbon nanotube ring arrays.

Motavas, Saloome 29 April 2009 (has links)
Carbon nanotubes (CNTs) are nanometer-scale structures that have attracted broad interest due to their exceptional thermal, electronic, and mechanical properties. As a result, there has been a large effort to develop applications of these materials in various fields including nanoelectronics and nanophotonics, energy storage, and biomedical fields. However, controlled production and manufacturing of CNTs still remains a challenge. In this work we demonstrate a method for controlling the placement and distribution of carbon nanotubes on surfaces using colloidal lithography. CNTs in ring-like geometries display interesting properties due to their nanoscale curved structure. Although several methods have been introduced for the fabrication of these structures, large scale fabrication of CNT rings with controllable diameter in a practical manner has thus far been elusive. Here, we use colloidal lithography to assemble nanotubes from solution into rings with tunable diameter and controllable placement in large-area periodic arrays. Several parameters and conditions such as the mask size, concentration and type of solvent for the CNT solutions are tested, and nanotubes with different quality and purity are used. Characterization of the CNT ring arrays using scanning electron microscopy (SEM) and atomic force microscopy (AFM) are performed. These results demonstrate large periodic areas of rings with good uniformity throughout the arrays. The arrays consist of rings with diameters between 180–220 nm when using 780 nm diameter sphere colloidal masks. Analysis of ring thickness for these rings indicated their cross-sections are composed of approximately 10-15 individual tubes. Rings made with 450 nm spheres had diameters between 100-150 nm, showing the tunability of the ring diameter enabled by our method. In some cases, mesh-like structures in the form of periodic interconnected carbon nanotubes were also observed. Our results demonstrate an efficient and straightforward approach for patterning carbon nanotubes into well-defined surface distributions with controlled and tunable dimensions.

Low-Energy Electron Irradiation of Preheated and Gas-Exposed Single-Wall Carbon Nanotubes

Ecton, Philip 12 1900 (has links)
We investigate the conditions under which electron irradiation of single-walled carbon nanotube (SWCNT) bundles with 2 keV electrons produces an increase in the Raman D peak. We find that an increase in the D peak does not occur when SWCNTs are preheated in situ at 600 C for 1 h in ultrahigh vacuum (UHV) before irradiation is performed. Exposing SWCNTs to air or other gases after preheating in UHV and before irradiation results in an increase in the D peak. Small diameter SWCNTs that are not preheated or preheated and exposed to air show a significant increase in the D and G bands after irradiation. X-ray photoelectron spectroscopy shows no chemical shifts in the C1s peak of SWCNTs that have been irradiated versus SWCNTs that have not been irradiated, suggesting that the increase in the D peak is not due to chemisorption of adsorbates on the nanotubes.

Properties of 3D Printed Continuous Fiber-Reinforced CNTs and Graphene Filled Nylon 6 Nanocomposites

Liu, Zhihui January 2017 (has links)
No description available.

Immobilisation de biomolécules sur des monocouches auto-assemblées et élaboration de sondes AFM à nanotubes de carbonne fonctionnalisés pour des mesures d'interactions ligrand-récepteur / Immobilization of biomolecules on self-assembled monolayers and elaboration of carbon nanotube AFM probes functionalized for ligand-receptor interactions measures

Meillan, Matthieu 23 July 2014 (has links)
Lors de la mise au point de biocapteurs, le contrôle de l'état de surface sur laquelle sontimmobilisées les biomolécules est un paramètre crucial pour la fiabilité et la reproductibilité desmesures. Pour ce travail de Thèse, deux objectifs principaux ont été fixés :- obtenir de façon reproductible des films organiques fonctionnels capables de rendre lessurfaces inorganiques biocompatibles afin d'immobiliser des biomolécules sans les dénaturer.- se doter d'outils innovants afin d'analyser la distribution de biomolécules sur la surface etd'évaluer leur activité biologique à l'échelle de la molécule unique.L'immobilisation a été réalisée sur des SAMs terminées par une fonction acide carboxylique.Pour imager les surfaces nous avons choisi la Microscopie Atomique de Force (AFM) qui permetd'obtenir des informations à l'échelle nanométrique et de mesurer des interactions moléculaires del'ordre du piconewton (10-12 N).Des CNTs, générés par dépôt chimique en phase vapeur, sont fixés sur une pointe AFM. Puis Ilssont biofonctionnalisés selon un protocole de trempage original afin d'obtenir une modificationchimique sélective de leur apex. Les interactions entre un récepteur, immobilisé sur la surface, et sonligand, lié de façon covalente au CNT, sont mesurées à l'échelle de la molécule unique. / During the development of biosensors, control of the surface on which the biomolecules areimmobilized is a crucial parameter for the reliability and reproducibility of the measurements. For thisPhD work, two main objectives were set:- obtain in a reproducible way functional organic films able to make inorganic surfacebiocompatible for the immobilization of biomolecules without any denaturation.- develop innovative tools in order to analyze the distribution of biomolecules on the surface etevaluate their biological activity at single molecule scaleThe immobilization step was done on SAMs terminated by a carboxylic acid function.In order to image surfaces, Atomic Force Microscopy (AFM) was chosen. This technique permits toobtain information at nanometric scale and to measure molecular interactions in the range ofpiconewton forces (10-12 N).MWCNTs were linked to a commercial AFM tip by micro-welding under optical microscopy. CNTswere biofunctionalized at the nanotube apex by an original dipping procedure.The interactions between a ligand, immobilized on the surface, and a receptor covalently linked to aCNT have been characterized.

Page generated in 0.0299 seconds