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Sintering viscosity and sintering stress of nanostructured WC–Co parts prepared by powder injection moulding [electronic resource]
, Article Journal of Powder Metallurgy ; Februrary 2011, Volume 54, Issue 1, P. 84-88 ; Sharif University of Technology
Abstract
The uniaxial viscosity and sintering stress of WC-10Co-0⊙ 9VC (wt-%) were obtained by a loading dilatometer as functions of fractional density (0⊙ 64< ρ< 0⊙ 93) and temperature (1084< T< 1297° C) according to a Newtonian constitutive law commonly used to simulate sintering. The viscosity is suggested to follow In η= a+ Q/RT+ bρ with the values of a= 52⊙ 3±4⊙ 5 and b= 16⊙ 8±0⊙ 2. Q reflects the temperature dependence of η and estimated to be 502±52 kJ mol-1. The sintering stress exhibited almost a constant value in the range of 0·05–0·4 MPa. It is shown that Rahaman's model best fits the experimental results. This paper describes experiments performed on nanostructured WC–Co feedstock to...
Transport Properties in Heterostructures of 2D Layers of Graphene with WS2 and hBN Quantum Dots
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Graphene based photodetectors which are modified with quantum dots, are the new generation of detectors. In these supplies an integration of graphene’s unique characteristics like high conductivity and mobility and the high light absorption of quantum dots, are used.In this research graphene by chemical vapor deposition in centimetric large scales, tungsten disulfide quantum dots, boron nitride and graphene quantum dots and 2D tungsten disulfide have been synthesized. In the next step each of them were characterized to modify the quality of used layers in heterostructure.Based on the characteristic tests, quantum dots aspect ratios were 1 to 5 nanometers. Also tungsten disulfide was obtained...
Investigation of Photoelectrochemical Properties of Porous W\WO3 Nanoplates Sensitized with Transition Metal Dichalcogenides Nanolayers for Water Splitting
, Ph.D. Dissertation Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Nowadays, storing solar renewable energy in hydrogen (as a clean fuel) is an attractive method for substitution of environmentally pollutant energy resources (fossil fuels) which is applicable through water splitting with the use of semiconductors. Among metal oxide photoanodes, WO3 as a moderate band gap semiconductor with high photo-stability, environmental compatibility, and low cost has attracted significant attention. However, photoelectron conversion efficiency of WO3 is still limited due to poor oxygen evolution reaction kinetics and charge carrier recombination. Herein, two strategies of nanostructuring and compositing with cocatalysts were applied to envisage with these limitations....
Synthesis and Characterization of Hybrids 3D Graphene/gold Nanostructures for Supercapacitors and Electrochemical Biosensors
, Ph.D. Dissertation Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Energy conversion and storage as well as life sciences are among the areas of our daily life. Interest in carbon nanomaterials for energy storage systems such as supercapacitors has enormously risen due to their attractive electrical conductivity, chemical inertness, and charge storage capacity. Producing these nanomaterials with a simple, scalable, and cost-effective method is the major problem for commercializing them. The reduction of graphitic oxide is a versatile procedure to prepare 3D graphene. Despite many green methods, the dynamics behind ultrafast thermal graphitization have remained elusive. Here, we demonstrate an effort to understand the graphitization mechanism of graphitic...
Structural characteristics and desorption properties of nanostructured MgH2 synthesised by high energy mechanical milling [electronic resource]
, Article Journal of Powder Metallurgy ; September 2011, Volume 54, Issue 4 , P.480-483 ; Kaflou, A ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
The effect of particle size, lattice strain and crystallite size on the hydrogen desorption properties of nanocrystalline magnesium hydride powder was investigated. Commercial MgH2 powder was milled in a Spex 8000M up to 16 h and its structural evolution and desorption characteristics at different time intervals were examined using various analytical techniques. At the early stage of milling, the formation of metastable γ-MgH2 phase was noticed. While the crystallite size gradually decreased to 12 nm with increasing the milling time, the accumulated lattice strain gained a maximum value of 0·9% after 4 h milling. The highest drop in the desorption temperature (∼100°C) was attained at the...
Study of Microstructure, Strengthening Mechanisms and Hot Deformation Behavior of Ultrafine-grained Al6063- Al203 Nanocomposites
, Ph.D. Dissertation Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
In this study, Al6063-Al203 nanocomposite powders were synthesized by reaction mechanical milling method. Nanometric reinforcement particles were formed via high- energy ball milling under a controlled oxygen containing atmosphere. Morphological and microstructural evolutions of nanocomposite powders were investigated by using X-ray diffraction (XRD), thermal analysis (DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods at different milling times. The results showed that mechanical milling stages were accelerated and the time for reaching steady- state condition was decreased by an increase in the oxygen content in the milling atmosphere. The in-situ...
Evaluation of Controlled Drug Release Chitosan-based Coatings on Titanium Implants: Microstructure, Bioactivity and Biocompatibility
, Ph.D. Dissertation Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Implant-associated infections are one of the most serious complications in orthopaedic and trauma surgery as it may result in poor functional outcome, implant failure, chronic osteomyelitis or even death. Great concerns have been taken to reduce implant-associated infections through progressing in operating standards, minimizing the possibility of contamination during surgery, reducing the establishment of infection by perioperative antibiotic prophylaxis, and confining of pathogenic strains by patient isolation. In spite of these preventions, the percentage of postoperative infections is still rising. Composite coatings with bone-bioactivity and drug-eluting capacity are considered as...
Investigation Physicochemical, Mechanical and Biological Properties of Chitosan-Graphene Oxide Electrospun Nanocomposite with Drug Release Capability as a Temporary Skin Graft
, Ph.D. Dissertation Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
In recent years, temporary skin grafts based on natural biopolymers modified with carbon nanostructures has received considerable for wound healing applications. In this study, Nanofibrous structures that mimic the native extracellular matrix and promote cell adhesion have attracted considerable interest for biomedical applications. Chitosan-polyvinylpyrrolidone (CS/PVP) films containing graphene oxide (GO) nanosheets (~1 nm thickness and micrometer length) were prepared by solvent casting methods. Experimental results showed that PVP concentration had a critical role on the water vapor permeability, transparency, hydrophilicity and thermal stability of the nanocomposite films. Antibacterial...
Synthesis and Characterization of Properties of Hybrid Nanoparticles of Gold-graphene
,
M.Sc. Thesis
Sharif University of Technology
;
Simchi, Abdolreza
(Supervisor)
Abstract
In recent years utilization of quantum dots for stem cells detection and clean energy production has received intensive attention. Graphene and its derivatives have been widely studied because of their effectiveness on electronical and optoelectronical devices, chemical sensors, nanocomposites, and energy storage. By use of metal nanoparticles, such as AuNPs, we can develop properties of graphene, and control them via shifting the absorption peak wavelength and increasing its biocompatibility. In this research, hybrid nanoparticles of gold-graphene as core-shell and conjugated by polymeric linkers containing amine or thiol functions are synthesized. Our purpose is stabilization the...
Chemical Vapor Processing of 2D MoS2 Nanolayers for Next Generation Inoptoelectronic Devices: Characterization and Properties
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Quite a few methods have been reported to synthesize monolayer MoS2, which has recently attracted scientist attentions. Fully controlled conditions, however, have not been achieved in these methods. In this research, two-dimensional MoS2 nanofilms have been synthesized by Chemical Vaper Deposition (CVD). Layer thickness of synthesized layer and effects of various parameters of used method have been investigated. Although every scientist synthesizes 2D MoS2 at 650°C in the CVD method by using seeds, in this research, it has been proved that MoS2 nanofilms can be produced at 575°C without using any seeds, which leads to lower consumption of time and price and increases the quality of...
Hybrid Lead sulfide-graphene Quantum Dots: Optoelectronic Properties and Cytotoxicity Evaluation
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
In recent years, quantum dots specially NIR QDs like lead sulfide have attracted a lot of attentions in various bioapplications such as bioimaging, stem cell tracking, etc. However, these materials are generally synthesized by using organic lagands like oleic acid which is not appropriate for bioapplications. Moreover, the cytotoxicity of these materials have severely restricted their applications. In this research, lead sulfide quantum dots were synthesized via a hot injection route. The nanocrystals had an average size of 3 nm passivated with oleic acid ligands and graphene nanosheets. Excitonic and photoluminescence peaks were observed in wavelengths of 950 and 1100 nm, respectively....
Synthesis of Boron Nitride Quantum Dots Using a Mechanical Milling- Solvothermal Process
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Boron Nitride Quantum Dots, as a new member of Heavy-metal-free Quantum dots has attracted many attention due to their unique properties. The hyroxylate functionalized BNQDs was synthesized with two steps fabrication approache which were contained mechanical milling and solvothermal process. It has been shown that 12 hours for mechanical milling and 24 hours for solvothermal process would be the most optimum time that produce well disperse functionalized BNQDs . The characterization results have proved that the as-prepared BNQDs have lateral size at around 5 nm with thickness in range of 4-6 layers. Also, it has been demonstrated that OH functional groups can attache into the surface of...
Manipulation of Electronic Structure in Boron Nitride Nanosheets to Improve Catalytic and Photocatalytic Properties
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
The variety of 2D materials and their wide range of properties, as well as numerous methods to manipulate them, have made this class of materials among prominent candidates for the future of the energy industry. Among the means available to tailor nanomaterials performance for such applications, introducing dopants and the creation of heteroatom-doped structures are of great interest. In this study, mixtures of urea, boric acid, and graphene oxide, as cheap and available precursors, were used to synthesize C-doped h-BN nanosheets. After the implementation of TGA/DSC to select a suitable calcination temperature of 950 C°, the samples were successfully synthesized with relatively precise...
Synthesis and Characterization of Hybrids 3D Graphene/gold Nanostructures for Supercapacitors and Electrochemical Biosensors
, Ph.D. Dissertation Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Energy conversion and storage as well as life sciences are among the areas of our daily life. Interest in carbon nanomaterials for energy storage systems such as supercapacitors has enormously risen due to their attractive electrical conductivity, chemical inertness, and charge storage capacity. Producing these nanomaterials with a simple, scalable, and cost-effective method is the major problem for commercializing them. The reduction of graphitic oxide is a versatile procedure to prepare 3D graphene. Despite many green methods, the dynamics behind ultrafast thermal graphitization have remained elusive. Here, we demonstrate an effort to understand the graphitization mechanism of graphitic...
Additive Manufacturing of Structured Stainless Steel Electrodes Functionalized with Transition Metal-Oorganic Frameworks for Water Splitting
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Water splitting reaction always faces challenges such as low efficiency, slow kinetics, and long-term instability of the catalyst. In this study, an electrode made of low-carbon 316 stainless steel fabricated by selective laser melting was initially used as the catalyst. The overpotential for hydrogen evolution reaction at a current density of 10 mA cm-2 using this electrode was calculated to be -0.505 V vs. RHE. This electrode had the capability of producing hydrogen gas at a rate of 3.6 mL min-1. Then, to reduce the overpotential, improve the efficiency, and stability of this electrode, its surface was modified by electrochemical methods, and metal-organic framework with cores of iron,...
Hot workability of ultrafine-grained aluminum alloy produced by severe plastic deformation of Al6063 powder and consolidation [electronic resource]
, Article Materials Science Forum ; Volume 667-669, 2011, Pages 979-984 ; Simchi, A. (Abdolreza) ; Seop Kim, Hyoung ; Sharif University of Technology
Abstract
Al6063 powder was subjected to severe plastic deformation via high-energy mechanical milling to prepare ultrafine-grained (UFG) aluminium alloy. Uniaxial compression test at various temperatures between 300 and 450 °C and strain rates between 0.01 and 1 s-1 was carried out to evaluate hot workability of the material. Microstructural studies were performed by EBSD and TEM. The average activation energy and strain rate sensitivity of the hot deformation process were determined to be 280 kJ mol-1 and 0.05, respectively. The deformation temperature and applied strain rate significantly affected the grain structure of UFG Al alloy. A finer grain structure was obtained at lower temperatures and...
Investigation of Mechanical Milling Effects on Al-Cu and Al-CuO Powder Mixture Morphological and Structural Characteristic and Mechanical Properties Changes Resultant from Age Hardening
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
In the present work, nanocrystalline Al-4wt%Cu alloy reinforced with nanometric Al2O3 particles was synthesized by in-situ reactive milling of Al and CuO powder mixture and hot extrusion. The effect of nanometric Al2O3 particles on the aging behavior and mechanical properties of this alloy was investigated. During mechanical milling, copper oxide were reduced and dissolved in the aluminum lattice. consequently, Al(Cu) solid solution matrix was produced. Also, nanometric Al2O3 particles were also distributed in the matrix uniformly. The powder blend was then pressed in an Al can at 100 MPa pressure and subsequently extruded at 450 0C at the extrusion ratio of 16:1. The density of the...
Fabrication and Chracatization of Novel Electrospun Chitosan Fibers Reinforced with Bacterial Cellulose and Nanodiamond for Wound Dressing Applications
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Chronic wounds are among the serious injuries which have called the attention of scientists to invest in an effort to fabricate temporary skin grafts and wound dressing materials. One of the widely acceptable solutions to this obstacle is to design a bioactive scaffold capable of regenerating tissue as well as delivering active agents to the site specific area. To this end, natural biopolymers are considered as suitable candidates to be employed in regenerative medicine due to their excellent biocompatibility. In addition, nanoparticles possess special properties such as the ability in sequestering the drug release which make them promising candidates in the fabrication of the...
Cosintering of powder injection molding parts made from ultrafine WC-Co and 316L stainless steel powders for fabrication of novel composite structures
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 41, Issue 1, January 2010, Pages 233-241 ; Petzoldt, F ; Sharif University of Technology
Abstract
Abstract Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (> 4 pct) is developed in the temperature range of 1080° C to 1350° C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the
Fabrication of Hybrid Graphene/Metal Electrodes for Biosensor Applications
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdolreza (Supervisor)
Abstract
Electrochemical sensing of glucose has received paramount attention in recent years, particularly, the non-enzymatic glucose sensing is one of the trends in the whole biosensing world. In this research, synthesis and evaluation of a hybrid structure of vertical oriented nickel nanorod-reduced graphene oxide sheets as a non-enzymatic glucose sensor were performed. The 3D array of nickel nanorods was synthesized by electrodeposition of nickel sulfate electrolyte in track-etched polycarbonate template with 100 nm pore size and 6-10 μm thickness. The electrodeposition performed in various conditions, and the best result was achieved by application of potential of 3 V for 60 minutes. The shiny...