1,721,017 research outputs found
Room temperature fabrication of graphene flake structured thin film directly from graphite particles using dry spray deposition and its molecular dynamics simulation
No full textCarbon based materials such as graphite, graphene, carbon nanotube (CNT), carbon fiber (CF) etc. have significant role in today’s science and technology and the discovery of graphene is the extreme of a long chain of continuous improvement in the science of carbon. Since the isolation of graphene, the number of proposed application is continuing to increase to reach graphene out of the lab for suitable industrial applications, which solely depends on structure of graphene. Recently graphene flake structures have attracted enormous attention to researchers for diverse applications. This dissertation demonstrates the formation of graphene flake structures directly from graphite particles at room temperature. A nano-particle deposition system (NPDS), which is a dry spray deposition method generally used for deposition of metals and ceramics, has been introduced to deposit graphite particles. In this research, at first graphite powder was deposited on a glass substrate without using binders and the deposited thin film was characterized.
The deposited thin film contained small and few-layer graphene flake structures as observed using field effect scanning electron microscopy (FE-SEM) and confirmed using X-ray diffraction (XRD) and Raman spectroscopy. We also suggest a mechanism of small and few-layer graphene flake structures formation during thin film preparation. The suggested mechanism was interlayer separation of micron-sized graphite particles and cracking of particles into small pieces during deposition due to the high impact velocity experienced by the graphite particles.
And the effect of substrate to deposition of micron sized graphite particles was studied under the same process conditions by utilizing wide ranged hardness value containing various substrates and the numbers of molecular dynamics simulations were carried out to extract some valuable information of deposition mechanism which may provide a guideline for graphene flake structured thin film preparation in future.Maste
FABRICATION OF SUPERHYDROPHOBIC METALLIC SURFACES WITH FAST WETTABILITY TRANSITION USING NANOSECOND LASER ABLATION AND HEAT TREATMENT
No full textRecently, the fabrication of superhydrophobic metallic surfaces by means of pulsed laser ablating has been developed. After laser ablating, samples are typically aged in ambient air for a relatively long time of several weeks/months or chemically coated to achieve superhydrophobicity. To accelerate the wettability transition from hydrophilicity to superhydrophobicity without the use of additional chemical treatment, a simple heat treatment post process has been developed. In the present work, grid patterns were first fabricated on various metal by a nanosecond pulsed laser, then an additional heat treatment was applied. The proposed post process reduced the wettability transition time from several weeks/months to within several hours. Additionally, effect of step size, effect of different heat treating temperature, and effect of water during wettability change were investigated. The mechanism of wettability change was also explained. Several potential applications such as self-cleaning, transport of water droplet, water storage/positioning, drag reduction, and anti-corrosion were proposed.Docto
Deposition of 2D Materials by Vacuum Kinetic Spray Method and Its Application in Supercapacitors
No full textThe developments in mobile/portable electronics and alternative energy vehicles prompted engineers and researchers to develop electrochemical energy storage devices called supercapacitors, as the third-generation type capacitors. Most of the research and development on supercapacitors focus on electrode materials, electrolytes, and hybridization. Some attempts have been directed towards increasing the energy density by employing electroactive materials, such as metal oxides and conducting polymers. However, the high cost and toxicity of applicable metal oxides and poor long-term stability of the conducting polymers paved the way for alternative electrode materials. The electroactive materials with carbon particles in composites have been used substantially to improve the stability of supercapacitors. Furthermore, the use of carbon particles and metal oxides could significantly increase the energy density of supercapacitor electrodes compared to metal oxides. Recent developments in carbon materials, such as carbon nanotubes (CNTs), activated carbon, reduced graphene oxide, and graphene, have found applications in supercapacitors because of their enhanced double-layer capacitance due to the large surface area, electrochemical stability, and excellent mechanical and thermal properties.
Several approaches have been used to develop binder-free supercapacitor hybrid electrode materials, such as electrochemical deposition, chemical bath deposition, chemical vapor deposition, and the sol-gel method. These approaches have been shown some drawbacks, such as complicated processes, long processes time, expensive equipment, high vacuum, volatile precursors and toxic chemicals. On the contrary, the nanoparticle deposition system (NPDS) offers low vacuum, room temperature, eco-friendly, and binder-free deposition method.
The main objective of this thesis is to study the deposition of some electroactive materials using the NPDS technique. Promising electroactive materials, such as few-layer graphene nano-flakes, molybdenum disulfide, nickel hydroxide, and graphene-based composites have been selected to be deposited by the NPDS. The deposition was carried out with different deposition parameters, and different contents of the electroactive materials. By studying the structural and electrochemical performance of these materials, we have established a complete set of deep understandings on the concepts, structures at varying lengthy scales and electrochemical performance.
The research carried out in this thesis are briefly summarized as follows:
(1) The effect of the deposition parameters on the formation of few-layer graphene nano-flakes and their related electrochemical performance are examined by changing the scan speed of the deposition. The faster scan speed of deposition shows higher degree of fragmentation and better electrochemical performance. The electrochemical performance of the few-layer graphene nano-flakes symmetric supercapacitor was further improved by increasing the different electrolytes concentration.
(2) The influence of MoS2 content on the electrochemical performance of MoS2-graphite hybrid electrode is studied. The MoS2-graphite hybrid electrode deposited with 5, 10, 15, 20, 25 and 30% wt. of MoS2 by the NPDS on stainless-steel substrates. The capacitance of the MoS2-graphite hybrid electrodes based symmetric supercapacitor demonstrates maximum areal capacitance at 15% of MoS2 content used in the deposition (5.1 mF cm-2 @ 2 mV s-1).
(3) Ni(OH)2 deposited by the NPDS on nickel sheets and nickel foam. The structural and electrochemical performance of the Ni(OH)2 deposited with different parameters on nickel sheets are compared. The deposited Ni(OH)2 on nickel sheets with 5 mm SoD and 0.3 MPa carrier gas pressure demonstrates better electrochemical performance. The Ni(OH)2 deposition on nickel foam with 5 mm SoD and 0.3 MPa showed superior specific capacitance (2092 F g-1 @ 1 A g-1) and good cyclic stability.
(4) The effect of Ni(OH)2 content in Ni(OH)2-graphene hybrid electrodes on the electrochemical performance is examined. Ni(OH)2 and graphite powders is mixed with 20, 40, 60, and 80% wt. of Ni(OH)2 and deposited on nickel foam substrate. The structural and electrochemical performance of the Ni(OH)2-graphene hybrids is investigated. The Ni(OH)2-graphene hybrids demonstrates a maximum specific capacitance at 10% the content of the Ni(OH)2 in the hybrid electrode. An asymmetric supercapacitor is fabricated based on 10% Ni(OH)2-graphene hybrid electrodes as a positive electrode and rGO as a negative electrode. The Ni(OH)2-Gr//rGO ASC displays an energy density of 64 W h kg-1 and a high power density of 8230 W kg-1.Docto
Development of one-step and fast manufacturing process for stable superhydrophobic surface using laser beam machining under silicone oil on metals and ceramics
No full textRecently, a number of publications using laser fabrication superhydrophobic surfaces have increased. After laser fabrication, the surface exhibits hydrophilicity, so it is necessary to combine with other methods to create a superhydrophobic surface. As a result, laser combined with heat treatment was chosen to fabricate the superhydrophobic surface because this post-process doesn’t need chemical treatment or complex equipment. With this post-process, two kinds of materials as titanium, soda-lime glass were chosen for the fabrication of superhydrophobic surfaces. And the effect of laser power, step size, and pattern design on wettability were investigated. However, taking a long time for heat treatment as for 6 hours for titanium, 48 hours for soda-lime glass is one of the most disadvantages. Therefore, developing a new, simple, and fast process for the fabrication of superhydrophobic surfaces is essential. This new process used laser beam machining under silicone oil for fabricating superhydrophobic on various materials. In detail, with the new process, the study also reported the influence of changing laser parameters such as laser power, scan speed, step size, pattern design (grid, line-patterned), and silicone oil height during the fabrication process. Besides, the stability and robustness of the surface fabrication in the two processes (new process and post-process) to be used for evaluating the quality of the surface were also investigated. The stability of the superhydrophobic surface was tested by an aging test – put in the ambient air for a long time. Meanwhile, the robustness of the superhydrophobic surface was checked by scotch tape test. Finally, some potential applications were reported as water bouncing, water adhesion, self-cleaning, water position, controlling of water moving with different shapes (maze, circle, zigzag).Docto
Facile One-Step Deposition of Nanosized Ni(OH)2-MoS2 Heterostructure Electrodes for Efficient Oxygen Evolution Reaction
No full textThe growing demand for clean and sustainable energy sources relies on efficient and cost-effective electrocatalysts for the OER, a key energy conversion and storage device process. Using a vacuum kinetic spray technique nano-sized Ni (OH)2-MoS2 nanocomposites (NCs) electrocatalysts on nickel foam are fabricated from the corresponding micron powder. The modified working electrodes by Ni (OH)2-MoS2 NCs were utilized for oxygen evolution reaction (OER) at different weight ratios of MoS2 (25, 50, and 75 wt.%). The surface state of the electrode is examined using sensitive techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). SEM images showed that the microparticles were fragmented into smaller nanoscale particles. XPS spectra revealed the synergy enhancement in the Ni (OH)2-MoS2 NCs that resulted in a strong improvement in the OER activity, which hybrid NCs with 75 wt.% MoS2 exhibits the lowest overpotential of 282 mV@10 mA·cm-2 and the lowest Tafel slope of 54 mV·dec-1. Besides, the long-term OER durability is verified up to 50 h.Maste
Mechanical Exfoliation of 2D-Materials and Formation of Nanocomposites with Transition Metal Compounds by Vacuum Kinetic Spray Process for Energy Conversion and Sensing Applications
No full textThe wide spreading of using two dimensional (2D) materials (i.e., graphene, MoS2, and Boron nitride) and their hybrid nanocomposites (NCs) with functional semiconductor compounds in electrochemical applications related to energy conversion, energy storage, and non-enzymatic sensing applications require a cost-effective technique that is amenable to large size production. This goal cannot be simply achieved because there is no single system for the fabrication of 2D materials and their hybrid NCs in one process. The top-down approaches based on the mechanical exfoliation of layered materials are commonly used for the mass production of pure 2D materials. The conventional methods for layered materials exfoliations through the mechanical approach are ball milling (wet or dry) and sonochemical techniques. In these techniques, the pure 2D materials were prepared in successive steps for a very long time. Also, these techniques require solvents with suitable surface energy that match with the type of the layered material to facilitate the stacked layers' exfoliation. The use of chemicals and solvents require further cleaning from waste product and the product only in the powder form. This requires hard labor work and increases the fabrication cost. Furthermore, the fabrication of 2D-materials hybrid NCs with a functional nanosized semiconductor cannot be achieved in one process, in which the pure 2D materials and the nanosized semiconductor materials are prepared individually. Then, both materials were mixed by chemical approach to form interfacial bonding between them. This would further increase the fabrication time consumption and reduce the overall cost efficiency.
The dry spray coating based on the vacuum kinetic spray process was utilized for the direct deposition of nanosized thin films in one step from the corresponding micron powder at room temperature without any chemical treatment. There is various low-temperature dry manufacturing process such as cold spray, aerosol deposition (AD), as well as the nanoparticle deposition system (NPDS). The main difference between these techniques is the optimized pressure range for micron powder feeding as well as deposition pressure. The cold spray and AD techniques have similar system configurations of particle deposition but have some limitations on particle size range and type, which strongly affect the ability of deposition. As an example, the cold spray technique is mostly used for the deposition of metallic powder whereas the AD technique is frequently used for ceramic films. This indicated the limitation of deposition of metal/ceramics composites by these techniques. In contrast, the NPDS system has the optimum pressure range for deposition of either nano-sized ceramics or metallic as well as their hybrid NCs thin films at room temperature in one step. Furthermore, the graphene thin films were successfully deposited by the NPDS in one step on various substrate types. The kinetic induced transformation of graphite-staked layers to graphene nanosheets in one step by the NPDS at room temperature was explained in terms of the mechanical exfoliation of graphite stacked layers at impact velocity higher than a critical value. This would provide a new route for layered materials mechanical exfoliation based on the vacuum kinetic spray process that differs from the conventional technique that follows either sonochemical or ball milling approaches
The ability of graphite stacked layers separation by the NPDS in one step motivated us to examine the ability of mechanical exfoliation of other graphene-like materials (i.e., layered materials) with a similar hexagonal structure such as molybdenum disulfide (MoS2) and boron nitride (BN) by the NPDS without the need of any chemical assistance. Hence, we could use the NPDS as a single system for the mechanical exfoliation for various layered materials. Moreover, the NPDS was used to fabricate graphene-based hybrid NCs with various functional nanosized semiconductors. So, we investigated the ability of hybrid NCs formation with another graphene-like material especially MoS2 to demonstrate the benefit of using the NPDS system as a single system for layered materials exfoliation and formation of hybrid NCs with other functional materials, which reduce the fabrication time and consequently enhance the fabrication cost efficiency.
To improve the charge transfer kinetics at the electrode/electrolyte interface in the electrochemical energy applications the 2D-nanomaterials (NMs) like graphene and MoS2 nanosheets are commonly used. The hybridization between the 2D-NMs and the other functional nano-sized semiconductor would result in the improvement of overall activity toward various electrochemical applications. Optimization of modified electrode performance is strongly dependent on the composition constituent at the heterostructure interfaces. This indicates the need to study the effect of the composition ratio between the 2D NMs and the other functional materials on the electrochemical performance of the fabricated electrodes.
The main objectives of this study are classified into three main parts:
First, we want to provide a new mechanical approach for pure layered materials exfoliation using the NPDS according to the vacuum kinetic spray process. This was achieved by studying the mechanical exfoliation of various layered materials with a similar hexagonal phase such as graphite, MoS2, and BN using the same deposition condition by the NPDS. This indicated the applicability of NPDS as a single and solvent-free system for layered materials exfoliation.
Second, we fabricated various graphene-based hybrid NCs with various transition metals (TMs) compounds (i.e., Ni(OH)2, Co3O4, Mn3O4, and ZnO) by the NPDS at room temperature in a one-step process on various substrate type (i.e., porous nickel foam and flat titanium sheet). All fabricated electrodes revealed the successful exfoliation of graphite stacked layers to graphene nanosheets in one step as well as the strong synergy improvement between the formed graphene nanosheets and the TMs species. The observed synergy improvement resulted in the activity enhancement toward water splitting-based energy conversion and non-enzymatic H2O2 detection applications. The catalytic activity of TMs-graphene hybrid NCs towards the water splitting through various routes including electrocatalytic, photocatalytic, and photo-electrocatalytic as well as and non-enzymatic H2O2 sensing was found to be strongly dependent on the initial ratio of TMs: graphite mixture, in which the optimum combination was estimated for each application.
Third, we fabricated various MoS2-based hybrid NCs with spinel transition metals (TMs) compounds (i.e., Co3O4 and Mn3O4) by the NPDS at room temperature in a one-step process on various substrate type (i.e., porous nickel foam and flat titanium sheet). All fabricated electrodes revealed the successful exfoliation of MoS2 stacked layers to small MoS2 nanosheets and strong synergy improvement between the formed MoS2 nanosheets and the spinel TMs species. The observed synergy improvement resulted in the activity enhancement toward water splitting-based energy conversion and non-enzymatic H2O2 sensing applications. The catalytic activity of TMs-MoS2 hybrid NCs towards the electrocatalytic water splitting and non-enzymatic H2O2 sensing was found to be strongly dependent on the initial ratio of TMs: MoS2 mixture, in which the optimum combination was estimated for each application.
The obtained results indicated that the NPDS technique is an efficient and eco-friendly technique for layered materials exfoliation and fabrication of hybrid NCs with high efficiency in various energy and sensing applications in one deposition step at room temperature in a short fabrication time. This indicated the improvement of fabrication cost efficiency compared with other conventional processes.Docto
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effect of polypropylene on the mechanical properties and water absorption of carbon-fiber-reinforeced-polyamide-6/polypropylene composite
No full textLightweight materials are becoming important in many industries, such as automotive, portable electronics, and so on. Polymer blends containing polyamide-6 (PA6) and polypropylene (PP) have been widely applied for weight reduction and low water absorption. It is well known that PA6 has a high affinity for water, and its mechanical properties and dimensional stability are often significantly affected by the absorption of water, whereas PP is characterized by its moisture resistance, low density and cost. The aim of our research was to investigate the effect of PP on the weight reduction, water absorption, dimensional stability and mechanical properties of carbon-fiber-reinforced PA6 composite in order to find a proper way to improve carbon-fiber-reinforced PA6 widely used in industry especially for high humidity or underwater applications. We assessed the mechanical properties by a tensile test and the microstructure by scanning electron microscopy for composites with and without water saturation. After being saturated with water, the composites with PP showed better ultimate tensile strength, elastic modulus, elongation, density for weight reduction and dimensional stability than the composite without PP.Maste
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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