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simchi--abdoreza
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Synthesis and Characterization of ATPEG-PMDA Hydrogels Conjugated with Thermo-Responsive Coated Magnetic Nanoparticles for Cartilage Tissue Engineering
, M.Sc. Thesis Sharif University of Technology ; Simchi, Abdoreza (Supervisor)
Abstract
A novel thermo responsive decorated system is designed by coating Fe3O4 magnetic nanoparticles with conjugated Pluronic-ATPEG copolymer incorporated into the PEG-PMDA Hydrogel for drug delivery to the cartilage tissue. Grafted copolymer was synthesized by reaction between carboxylated Pluronic and amino terminated Poly ethylene glycol (ATPEG) and confirmed by FTIR and NMR analysis. The magnetic nanoparticles were modified with the produced copolymer and characterized by TEM, HRTEM, XRD, DLS, and VSM. A typical product has 13 nm magnetic core and 105 nm hydrodynamic diameter with narrow size distribution. DLS results showed that there was an increase in size by increasing temperature from 25℃...
Damage Detection and Evaluation of Repair Materials and Techniques for Concrete Bridges
, M.Sc. Thesis Sharif University of Technology ; Joghataie, Abdoreza (Supervisor)
Abstract
Poor maintenance of concrete bridges in the past years in Iran, caused serious damages, so most of them need rehabilitation. The majority of repaired members are exposed to repeated damage because compatibility of repair material to substrate concrete not considered as well as weather and loading conditions. This study attempts to improve the repair achievement and durability of concrete bridges. This investigation contains two phases: preliminary study and experimental phase. Preliminary study attends to detect different types of damages of concrete bridges and their causes along with their propagation. The next part of this study discusses about various types of repair materials. In...
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...
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...
Structural characteristics and desorption properties of nanostructured MgH2 synthesised by high energy mechanical milling
, Article Powder Metallurgy ; Volume 54, Issue 4 , 2011 , Pages 480-483 ; 00325899 (ISSN) ; Kaflou, A ; Simchi, A ; Sharif University of Technology
2011
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...
Synergetic effect of Ni and Nb2O5 on dehydrogenation properties of nanostructured MgH2 synthesized by high-energy mechanical alloying
, Article International Journal of Hydrogen Energy ; Volume 34, Issue 18 , 2009 , Pages 7724-7730 ; 03603199 (ISSN) ; Kaflou, A ; Simchi, A ; Sharif University of Technology
2009
Abstract
Nanostructured MgH2-Ni/Nb2O5 nanocomposite was synthesized by high-energy mechanical alloying. The effect of MgH2 structure, i.e. crystallite size and lattice strain, and the presence of 0.5 mol% Ni and Nb2O5 on the hydrogen-desorption kinetics was investigated. It is shown that the dehydrogenation temperature of MgH2 decreases from 426 °C to 327 °C after 4 h mechanical alloying. Here, the average crystallite size and accumulated lattice strain are 20 nm and 0.9%, respectively. Further improvement in the hydrogen desorption is attained in the presence of Ni and Nb2O5, i.e. the dehydrogenation temperature of MgH2/Ni and MgH2/Nb2O5 is measured to be 230 °C and 220 °C, respectively. Meanwhile,...
Metal hydrides show potential under stress
, Article Metal Powder Report ; Volume 64, Issue 7 , 2009 , Pages 24-26,28 ; 00260657 (ISSN) ; Kaflou, A ; Simchi, A ; Sharif University of Technology
2009
Abstract
Work carried out in Iran seems to indicate that nanostructured materials may hold a key to fuel storage in a future hydrogen economy.... © 2009 Elsevier Ltd. All rights reserved
Sintering viscosity and sintering stress of nanostructured WC-Co parts prepared by powder injection moulding
, Article Powder Metallurgy ; Volume 54, Issue 1 , Nov , 2011 , Pages 84-88 ; 00325899 (ISSN) ; Sharif University of Technology
2011
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
Effect of C and Cu addition on the densification and microstructure of iron powder in direct laser sintering process
, Article Materials Letters ; Volume 62, Issue 17-18 , 2008 , Pages 2840-2843 ; 0167577X (ISSN) ; Sharif University of Technology
2008
Abstract
Laser sintering of Fe-C-Cu steel powder for rapid manufacturing of sintered components for functional testing was studied. The effects of C and Cu addition on the densification and the attendant microstructural features were investigated. The influence of iron particle size on the sintering kinetics was also examined. It is shown that the alloying elements significantly improve the densification rate when fine iron particles and high laser intensity are used. The mechanism of particle bonding and the effect of the alloying elements are presented. © 2008 Elsevier B.V. All rights reserved
Densification and microstructural evolution during co-sintering of Ni-base superalloy powders
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 37, Issue 8 , 2006 , Pages 2549-2557 ; 10735623 (ISSN) ; Sharif University of Technology
2006
Abstract
This work presents the effect of co-sintering on the densification and microstructural evolution in the two-layer stepwise graded composite of INCONEL 718 and INCONEL 625 superalloys. A pressureless co-sintering method in conjunction with a powder layering technique was used. The sintering was carried out in solid state and liquid phase in temperature ranging from 1260 °C through 1300 °C for 60 minutes in a low pressure of an argon atmosphere. Nonisothermal sintering behavior was also examined by dilatometric analysis. Similarly, the sintering response of the individual layers was characterized. The results reveal an enhanced densification rate during co-sintering of the composite layers....
Direct laser sintering of metal powders: Mechanism, kinetics and microstructural features
, Article Materials Science and Engineering A ; Volume 428, Issue 1-2 , 2006 , Pages 148-158 ; 09215093 (ISSN) ; Sharif University of Technology
2006
Abstract
In the present work, the densification and microstructural evolution during direct laser sintering of metal powders were studied. Various ferrous powders including Fe, Fe-C, Fe-Cu, Fe-C-Cu-P, 316L stainless steel, and M2 high-speed steel were used. The empirical sintering rate data was related to the energy input of the laser beam according to the first order kinetics equation to establish a simple sintering model. The equation calculates the densification of metal powders during direct laser sintering process as a function of operating parameters including laser power, scan rate, layer thickness and scan line spacing. It was found that when melting/solidification approach is the mechanism...
Effects of lubrication procedure on the consolidation, sintering and microstructural features of powder compacts
, Article Materials and Design ; Volume 24, Issue 8 , 2003 , Pages 585-594 ; 02641275 (ISSN) ; Sharif University of Technology
Elsevier Ltd
2003
Abstract
The role of lubrication procedure on the consolidation behavior of metallic powders and subsequent microstructural development during sintering was investigated. Iron powder and iron-0.8 w/o graphite powder mixture were used as model materials. The effects of die wall lubrication procedure were compared to the traditional admixed powder lubrication method. The influences of manufacturing parameters such as the compacting pressure in the range of 150-800 MPa and the sintering temperature from 400 to 1300 °C were studied. It was found that the lubrication procedure has a great influence on the consolidation and microstructural features of the materials investigated. Admixed lubricant aids the...
The role of particle size on the laser sintering of iron powder
, Article Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science ; Volume 35, Issue 5 , 2004 , Pages 937-948 ; 10735615 (ISSN) ; Sharif University of Technology
Minerals, Metals and Materials Society
2004
Abstract
The effects of powder particle size on the densification and microstructure of iron powder in the direct laser sintering process were investigated. Iron powders with particle sizes ranging from 10 to 200 μm were used. It was found that the sintered density increases as the laser energy input is increased. There is, however, a saturation level at which higher density cannot be obtained even at very intensive energy input. This saturation density increases as the size of the iron particles decreases. Meanwhile fine powders with narrow particle size distributions have a tendency toward agglomeration, and coarse powders with broad particle size distributions have a tendency toward segregation,...
Formation of carbon nanotubes in Iron-catalyzed arcing method: Effect of iron-ion charge in the aqueous medium [electronic resource]
, Article International Journal of Modern Physics B Condensed Matter Physics; Statistical Physics; Atomic, Molecular and Optical Physics ; 30 December 2011, Volume 25, Issue 32, PP. 4411-4417 ; Gheytani, S ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
Carbon nanotubes (CNTs) were synthesized via arc discharge in aqueous solutions containing ferrous and ferric irons to reveal the effect of iron-charge mole ratio, R = [Fe2+]/[Fe3+], on the purity of CNTs and the process yield. Raman spectroscopy and transmission electron microscopy were used to analyze the cathodic deposits. It is shown that the nucleation of multi-walled CNTs is catalyzed by ferric irons while their growth is affected by ferrous ions. Well-graphitized CNTs with a high-yield are obtained at R = 1 and total iron concentration of 0.05 M. The effect of iron charge is described based on the two-stage formation mechanism
Synthesis of a nanostructured MgH2–Ti alloy composite for hydrogen storage via combined vacuum arc remelting and mechanical alloying [electronic resource]
, Article Journal of Materials Letters ; 15 April 2011, Volume 65, Issue 7, Pages 1120–1122 ; Kaflou, A ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
To improve the hydrogen kinetics of magnesium hydride, TiCr1.2Fe0.6 alloy was prepared by vacuum arc remelting (VAR) and the alloy was co-milled with MgH2 to process nanostructured MgH2–5 at.% TiCr1.2Fe0.6 powder. The hydrogen desorption properties of the composite powder were studied and compared with pure magnesium hydride. X-ray diffraction (XRD) analysis showed that the composite powder prepared by VAR/mechanical alloying (MA) procedure consisted of β-MgH2, γ-MgH2, bcc Ti–Cr–Fe alloy, and small amount of MgO. The average size of particles and their grain structure after 4 h MA were determined by a laser particle size analyzer and XRD method and found to be 194 nm and 11 nm, respectively....
On the formation of SWCNTs and MWCNTs by Arc-discharge in aqueous solutions: the role of iron charge and counter ions [electronic resource]
, Article Journal of Fullerenes, Nanotubes and Carbon Nanostructures ; 2011, Volume 19, Issue 4, Pages 317-328 ; Shervin, Sh ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were synthesized in aqueous solutions containing FeCl2, FeCl3, FeSO4 and Fe2(SO4)3. The effects of iron charge and the counter ions on the formation of carbon nanotubes (CNTs) were investigated. Thermogravimetric (TG) analysis indicated that carbon multilayer structures including CNTs and multishell graphite particles were formed in deionized (DI) water without the iron precursor. SWCNTs were also synthesized in the presence of the iron ions. It was also found that the mole ratio of [Fe2+]/[Fe3+] in the solution has a significant influence on the purity of CNTs and the process yield. The highest yield was...
Characterization and antibacterial performance of electrodeposited chitosan–vancomycin composite coatings for prevention of implant-associated infections [electronic resource]
, Article Journal of Materials Science and Engineering: C ; 1 August 2014, Volume 41, Pages 240–248 ; Tamjid, E ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
Orthopaedic implant-associated infections are one of the most serious complications in orthopaedic surgery and a major cause of implant failure. In the present work, drug-eluting coatings based on chitosan containing various amounts of vancomycin were prepared by a cathodic electrophoretic deposition process on titanium foils. A three-step release mechanism of the antibiotic from the films in a phosphate-buffered saline solution was noticed. At the early stage, physical encapsulation of the drug in the hydrogel network controlled the release rate. At the late stage, however, in vitro degradation/deattachment of chitosan was responsible for the controlled release. Cytotoxicity evaluation of...
Flexible bactericidal graphene oxide–chitosan layers for stem cell proliferation [electronic resource]
, Article Journal of Applied Surface Science ; 15 May 2014, Volume 301, Pages 456–462 ; Akhavan, O ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
Graphene oxide (GO)–chitosan composite layers with stacked layer structures were synthesized using chemically exfoliated GO sheets (with lateral dimensions of ∼1 μm and thickness of ∼1 nm), and applied as antibacterial and flexible nanostructured templates for stem cell proliferation. By increasing the GO content from zero to 6 wt%, the strength and elastic modulus of the layers increased ∼80% and 45%, respectively. Similar to the chitosan layer, the GO–chitosan composite layers showed significant antibacterial activity (>77% inactivation after only 3 h) against Staphylococcus aureus bacteria. Surface density of the actin cytoskeleton fibers of human mesenchymal stem cells (hMSCs) cultured...
Densification and microstructural evolution during laser sintering of A356/SiC composite powders
, Article Journal of Materials Science ; Volume 46, Issue 5 , 2011 , Pages 1446-1454 ; 00222461 (ISSN) ; Godlinski, D ; Sharif University of Technology
2011
Abstract
This article reports experimental results on laser sintering of A356 aluminum alloy and A356/SiC composite powders. Effects of scan rate, sintering atmosphere, hatch spacing, and SiC volume fraction (up to 20%), and particle size (7 and 17 μm) on the densification were studied. The phase formation and microstructural development were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Laser sintering under argon atmosphere exhibited higher densification compared to nitrogen. A faster sintering kinetics was observed as the scan rate decreased. Except at a low SiC content (5 vol%), the composite powders exhibited...
Warm compaction of metallic powders
, Article Advances in Powder Metallurgy: Properties, Processing and Applications ; 2013 , Pages 86-108 ; 9780857094209 (ISBN) ; Nojoomi, A ; Sharif University of Technology
2013
Abstract
Warm compaction is a cost saving and effective method for obtaining high performance powder metallurgy (PM) parts. This chapter presents the principles of warm compaction and technical aspects of the process. The green and sintered properties of warm compacted parts are discussed and compared with conventionally (cold) produced compacts. The applications of the process for ferrous and non-ferrous PM parts are presented and future trends are outlined