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Effects of Ti-based catalysts on hydrogen desorption kinetics of nanostructured magnesium hydride
, Article International Journal of Hydrogen Energy ; Volume 39, Issue 36 , December , 2014 , Pages 21007–21014 ; ISSN: 03603199 ; Simchi, A ; Sadati, M ; Hosseini, H. M ; Targholizadeh, H ; Khakbiz, M ; Sharif University of Technology
Abstract
In the present work, the synergetic effect of Ti-based catalysts (TiH2 and TiO2 particles) on hydrogen desorption kinetics of nanostructured magnesium hydride was investigated. Nanostructured 84mol% MgH2-10%mol TiH2-6%mol TiO2 nanocomposite powder was prepared by high-energy ball milling and subjected to thermal analyses. Evaluation of the absorption/desorption properties revealed that the addition of the Ti-based catalysts significantly improved the hydrogen storage performance of MgH2. A decrease in the decomposition temperature (as high as 100°C) was attained after co-milling of MgH2 with the Ti-based catalysts. Meanwhile, solid-state chemical reactions between MgH2 and TiO2 nanoparticles...
Production of net-shaped dense metal-carbide-based composites through an infiltration process at intermediate temperature
, Article International Journal of Refractory Metals and Hard Materials ; Volume 38 , 2013 , Pages 35-39 ; 02634368 (ISSN) ; Sani, M. A. F ; Shabani, K ; Bodaghi, M ; Sharif University of Technology
2013
Abstract
Tungsten composites are interesting materials for high temperature applications. These composites are conventionally produced by solid state reaction, where elevated temperatures and long sintering processes are inevitable, and generally produce volatile components that increase defects and impair the properties of the composites for high temperature applications. In the present paper, synthesis of dense near net-shaped transition metal-metal carbide by reaction casting is studied, which creates a potential application for the composite at 2000 C. Since the pores of the ceramic preform are filled with reaction products, this technique is referred to as displacive compensation porosity (DCP)....
Effect of Y2O3 and Er2O3 co-dopants on phase stabilization of bismuth oxide
, Article Ceramics International ; Volume 37, Issue 8 , 2011 , Pages 3451-3455 ; 02728842 (ISSN) ; Maghsoudipour, A ; Alizadeh, M ; Nemati, A ; Sharif University of Technology
2011
Abstract
Bi2O3 compositions were prepared to investigate the effect of rare earth metal oxides as co-dopants on phase stability of bismuth oxide. Compositions containing 9-14 mol% of Y2O3 and Er2O3 were synthesized by solid state reaction. The structural characterization was carried out using X-ray powder diffraction. The XRD results show that the samples containing 12 and 14 mol% total dopants had cubic structure, whereas the samples with lower dopant concentrations were tetragonal. Comparing the lattice parameters of the cubic phases of (Bi 2O3)0.88(Y2O3) 0.06(Er2O3)0.06 and (Bi 2O3)0.86(Y2O3) 0.07(Er2O3)0.07 revealed that lattice parameter decreases by increasing the dopant concentration. The XRD...
Structural and electrical transport properties of hexagonal 4H BaRu 1-xMnxO3 perovskite
, Article Physica B: Condensed Matter ; Volume 406, Issue 18 , September , 2011 , Pages 3363-3366 ; 09214526 (ISSN) ; Fallahi, S ; Akhavan, M ; Sharif University of Technology
2011
Abstract
In this paper, structural and electrical transport properties of hexagonal, 4H-type, BaRu1-xMnxO3 (x=0-0.3), synthesized by the solid-state reaction method at ambient pressure, have been presented. Electrical transport properties are measured over a temperature range of 10300 K in the magnetic field up to 15 kOe. The low temperature resistivity (10K
Fe 50Co 50 nanoparticles via self-propagating high-temperature synthesis during milling
, Article Powder Technology ; Volume 208, Issue 3 , 2011 , Pages 623-627 ; 00325910 (ISSN) ; Yourdkhani, A ; Koohestani, H ; Sadrnezhaad, S. K ; Asmatulu, R ; Sharif University of Technology
Abstract
Self-propagating exothermic reactions during mechanical milling of FeCl 3/CoCl 2 mixture together with sodium seeds resulted in formation of Fe 50Co 50 nanoparticles. Highly exothermic reactions resulted in temperature raise and formation of Fe 50Co 50 phase within the first 5min; however Fe 50Co 50 single-phase was obtained after 30min of milling. The products were characterized by XRD, SEM, EDS, TEM and VSM. Obtained results showed that both milling time and NaCl salt matrix affected the size, morphology, microstructure and magnetic properties of the produced particles
Friction stir processing of an aluminum-magnesium alloy with pre-placing elemental titanium powder: In-situ formation of an Al3 Ti-reinforced nanocomposite and materials characterization
,
Article
Materials Characterization
;
Volume 108
,
October
,
2015
,
Pages 102-114
;
10445803 (ISSN)
; Simchi, A
; Kokabi, A. H
; Gerlich, A. P
;
Sharif University of Technology
Elsevier Inc
2015
Abstract
A fine-grained Al-Mg/Al3 Ti nanocomposite was fabricated by friction stir processing (FSP) of an aluminum-magnesium (AA5052) alloy with pre-placed titanium powder in the stirred zone. Microstructural evolutions and formation of intermetallic phases were analyzed by optical and electron microscopic techniques across the thickness section of the processed sheets. The microstructure of the nanocomposite consisted of a fine-grained aluminum matrix (1.5 μm), un-reacted titanium particles (<40 μm) and reinforcement particles of Al3 Ti (<100 nm) and Mg2 Si (<100 nm). Detailed microstructural analysis indicated solid-state interfacial reactions between the aluminum...
Effects of nanometric inclusions on the microstructural characteristics and strengthening of a friction-stir processed aluminum-magnesium alloy
, Article Materials Science and Engineering A ; Volume 642 , August , 2015 , Pages 215-229 ; 09215093 (ISSN) ; Simchi, A ; Kokabi, A. H ; Švec, P ; Simančík, F ; Gerlich, A. P ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
An aluminum-magnesium alloy was friction-stir processed in the presence of TiO2 nanoparticles which were pre-placed in a groove on the surface to produce a composite. Field emission-scanning and transmission electron microscopy studies show that solid state chemical reactions occur between the Al-Mg matrix and the ceramic particles upon the severe plastic deformation process. The microstructure of the aluminum alloy consists of a coarse grain structure, large complex (Fe,Mn,Cr)3 SiAl12 particles, and small Mg2 Si precipitates. After friction stir processing, a deformed grain structure containing rod-like Al-Fe-Mn-Si precipitates is attained, along...
Reactive friction stir processing of AA 5052-TiO2 nanocomposite: Process-microstructure-mechanical characteristics
, Article Materials Science and Technology (United Kingdom) ; Volume 31, Issue 4 , 2015 , Pages 426-435 ; 02670836 (ISSN) ; Simchi, A ; Kokabi, A. H ; Sadeghahmadi, M ; Gerlich, A. P ; Sharif University of Technology
Maney Publishing
2015
Abstract
Friction stir processing (FSP) is a solid state route with a capacity of preparing fine grained nanocomposites from metal sheets. In this work, we employed this process to finely distribute TiO2 nanoparticles throughout an Al-Mg alloy, aiming to enhance mechanical properties. Titanium dioxide particles (30 nm) were preplaced into grooves machined in the middle of the aluminium alloy sheet and multipass FSP was afforded. This process refined the grain structure of the aluminium alloy, distributed the hard nanoparticles in the matrix and promoted solid state chemical reactions at the interfaces of the metal/ceramic particles. Detailed optical and electron microscopic studies showed that the...
Effects of annealing on phase evolution, microstructure and magnetic properties of mechanically synthesized nickel-ferrite
, Article Ceramics International ; Volume 36, Issue 7 , 2010 , Pages 2241-2245 ; 02728842 (ISSN) ; Sadrnezhaad, S. K ; Sharif University of Technology
2010
Abstract
The influence of milling and subsequent annealing on nickel-ferrite phase formation was investigated by X-ray diffraction (XRD). Microstructure and magnetic properties of NiFe 2O 4 were determined by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and vibration sample magnetometry (VSM). Single phase nanosized nickel-ferrite was obtained by 30 h mechanical alloying (MA) and subsequent annealing at 600 °C for 1 h. Magnetic properties of the milled powder were extensively affected by the annealing temperature. Considerable growth of the particles and necking by sintering resulted from annealing at 1000 °C
Effect of samarium oxide on the electrical conductivity of plasma-sprayed SOFC anodes
, Article JOM ; Volume 68, Issue 10 , 2016 , Pages 2569-2573 ; 10474838 (ISSN) ; Samadi, H ; Nemati, A ; Sharif University of Technology
Minerals, Metals and Materials Society
Abstract
Solid oxide fuel cells (SOFCs) are rapidly becoming recognized as a new alternative to traditional energy conversion systems because of their high energy efficiency. From an ecological perspective, this environmentally friendly technology, which produces clean energy, is likely to be implemented more frequently in the future. However, the current SOFC technology still cannot meet the demands of commercial applications due to temperature constraints and high cost. To develop a marketable SOFC, suppliers have tended to reduce the operating temperatures by a few hundred degrees. The overall trend for SOFC materials is to reduce their service temperature of electrolyte. Meanwhile, it is...
Microstructure, Strength, and Wear Behavior Relationship in Al-Fe3O4 Nanocomposite Produced by Multi-pass Friction Stir Processing
, Article Journal of Materials Engineering and Performance ; Volume 26, Issue 7 , 2017 , Pages 3516-3530 ; 10599495 (ISSN) ; Movahedi, M ; Kokabi, A. H ; Sharif University of Technology
Springer New York LLC
2017
Abstract
Aluminum matrix in situ nanocomposite was produced by one to six passes friction stir processing (FSP) with pre-placed Fe3O4 nanoparticles (15-20 nm). Microstructure studies showed that solid-state reactions between the aluminum matrix and Fe3O4 particles during the process led to in situ formation of Al3Fe and Al5Fe2 in the stir zone. Initial Fe3O4 as well as Al-Fe intermetallic compounds (IMCs) particles were homogeneously dispersed in a fine grain matrix after six passes of FSP. Hardness and ultimate tensile strength of the composites were increased 64 and 27%, respectively, compared to the base metal. The reasons were studied in the light of reinforcing particles distribution, formation...
Surface modifications of an aluminum-magnesium alloy through reactive stir friction processing with titanium oxide nanoparticles for enhanced sliding wear resistance
, Article Surface and Coatings Technology ; Volume 309 , 2017 , Pages 114-123 ; 02578972 (ISSN) ; Simchi, A ; Kokabi, A. H ; Sharif University of Technology
Elsevier B.V
2017
Abstract
Reactive friction stir processing (RFSP) has been employed to modify the surface properties of AA5052 Al-Mg alloy through grain refinement and the distribution of ultrafine hard nanoparticles (2 to 6% volume fractions of 50 nm titanium dioxide). The heat generated induced solid state reactions between the metal matrix and the reinforcement to form Al3Ti/MgO inclusions. The role of grain refinement and distributed hard nanoparticles on the tribological behavior of the alloy under dry sliding wear condition was evaluated. The wear rates and friction coefficient as well as macro- and micro-features of the worn surfaces indicate that the wear mechanism (at 3–7 kgf and 0.5 m/s) is abrasive. The...
Effect of interlayers on softening of aluminum friction stir welds
, Article Materials Science and Engineering A ; Volume 727 , 2018 , Pages 1-10 ; 09215093 (ISSN) ; Movahedi, M ; Kokabi, A. H ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Effects of the zinc, copper and brass interlayers were studied on the microstructure evolution and mechanical properties of the wrought aluminum friction stir welds. Optical and scanning electron microscopes (SEM) as well as X-ray diffraction (XRD) analysis were used for investigation of the distribution, dissolution and reactions of the interlayers, grain structure in the stir zone and fracture surfaces. Longitudinal and transverse tensile and microhardness tests were also carried out in order to evaluate the mechanical properties of the welds. The results showed that without insertion of the interlayer, the joint efficiency (ratio of the weld strength to the aluminum base metal strength)...
A new Y-based HTSC with Tc above 100 K
, Article Physica C: Superconductivity and its Applications ; Volume 469, Issue 22 , 2009 , Pages 2012-2014 ; 09214534 (ISSN) ; Akhavan Farshchi, Y ; Akhavan, M ; Sharif University of Technology
2009
Abstract
In search of finding the dominant mechanism in high temperature superconductivity phenomena, the Y3Ba5Cu8O18 compound was synthesized through the standard solid-state reaction technique. Characteristic XRD experiment was performed on the samples and was analyzed by the MAUD software refinement program. The analysis results indicate a 358 phase structure with the initial nominal stoichiometry. The electrical resistivity and its behavior under different magnetic field were measured. The electrical resistivity indicates the transition temperature Tc onset = 102 K with transition width ΔTc = 2.4 K. This is the first observation of such a high transition temperature in the Y-based compound....
Preparation and Characterization of LaOFeAs Iron based Superconductor by Solid State Reaction
, M.Sc. Thesis Sharif University of Technology ; Khosrovabady, Hossein (Supervisor) ; Akhavan, Mohammad (Co-Advisor)
Abstract
The discovery of superconductivity in compounds containing magnetic elements such as Iron, Cobalt and Nickel has attracted the attention of many researchers in last few years. Before the discovery of superconductivity in LaOFeP it was believed that the superconductivity and magnetic properties are in conflict to each other. Untill now, variety of researches in Iran has been done on preparation and characterization of Copper oxide superconductors without any attention to the Iron based superconductors. Accordingly, the main purpose of this thesis is preparation and optimization of LaOFeAs as the basis compound of 1111 Iron based superconductors using the solid state reaction method. This...
Properties–microstructure relationship in Al–Fe in situ composite produced by friction stir processing
, Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 233, Issue 10 , 2019 , Pages 1955-1965 ; 14644207 (ISSN) ; Movahedi, M ; Sadoughi Yarandi, A ; Sharif University of Technology
SAGE Publications Ltd
2019
Abstract
Effects of Fe particle volume percent (from 0 to 5%) and changing the tool rotation direction in each pass were studied on the microstructure evolution and mechanical properties of the in situ Al/intermetallic composites produced by three passes friction stir processing (FSP) with ∼10 µm Fe particles. Optical and scanning electron microscopes were used for the investigation of the composite homogeneity, formation of Al–Fe intermetallic compounds, and fracture surfaces. Tensile and microhardness tests were also carried out to evaluate the mechanical properties of the composites. Solid-state reactions between the aluminum matrix and Fe particles led to in situ formation of Al3Fe and Al5Fe2...
Microstructural evaluation and mechanical properties of Al1050/TiO 2 -Graphite hybrid nanocomposite produced Via friction stir processing
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 50, Issue 5 , 2019 , Pages 2443-2461 ; 10735623 (ISSN) ; Movahedi, M ; Kokabi, A. H ; Sharif University of Technology
Springer Boston
2019
Abstract
Production of Al1050/TiO 2 -graphite hybrid nanocomposite via friction stir processing (FSP) was studied. The effect of graphite-to-TiO 2 volume fraction ratio (Gr/TiO 2 ), at a constant rotational speed (ω) and three levels of tool traverse speed (ν), on the microstructural evolution and mechanical properties of the nanocomposites was investigated. While TiO 2 is supposed to enhance the strength and hardness, graphite is believed to improve the tribological behavior. Furthermore, formation of intermetallic compounds (IMCs) through the solid-state reactions between the reinforcements and aluminum matrix may also promote the mechanical properties. To assess these assumptions, longitudinal and...
Microstructural and mechanical characteristics of AA1050/mischmetal oxide in-situ hybrid surface nanocomposite by multi-pass friction stir processing
, Article Surface and Coatings Technology ; Volume 388 , 2020 ; Ebadi, M ; Alishavandi, S ; Kokabi, A. H ; Sharif University of Technology
Elsevier B.V
2020
Abstract
Surface hybrid in-situ aluminum matrix nanocomposite (AMNC) was fabricated by multi-pass friction stir processing (FSP) and a tool traversing speed of 100 mm/min and rotating speed of 1600 rpm with an objective to enhance mechanical properties. Mischmetal oxide (MMO) powder with an initial size of 50 nm, at a concentration of 8.5 vol% was used as the reinforcing particles. EDS particle analyses revealed in-situ solid-state chemical reactions between the Al matrix and the MMO particles. The reaction products, MM3Al and MM3Al11, were distributed uniformly in the discontinuously dynamic recrystallized nano and UFG microstructure. Increasing pass number improved the particle distribution and...
Microstructural Evaluation during dissimilar transient liquid phase bonding of TiAl/Ni-based superalloy
, Article Journal of Alloys and Compounds ; Volume 825 , June , 2020 ; Kaflou, A ; Gholamipour, R ; Pouranvari, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
The paper aims at understanding solidification phenomena and solid state precipitations during dissimilar transient liquid phase bonding of γ-TiAl intermetallic compound to IN718 Ni-based superalloy using a quinary Ni–7Cr–3Fe–4.5Si–3.2B (wt%) filler metal. The mechanisms of intermetallic formation via solidification and solid state reactions are discussed. The joint is featured by the formation of Ni-rich solid solution in an isothermal solidification zone near to IN718, Ni-rich solid solution and isostructural binary phases solid solution designated as Al1-xNi3Six in an isothermal solidification zone near to TiAl, boride/silicide and boro-silicide formation during binary and ternary...
Two-dimensional mechanism of electrical conductivity in Gd1-xCexBa2Cu3O7-δ
, Article Journal of Physics Condensed Matter ; Volume 20, Issue 34 , 2008 ; 09538984 (ISSN) ; Mazaheri, M ; Akhavan, M ; Sharif University of Technology
2008
Abstract
Partial substitutions of Pr and Ce are known to suppress the superconducting state in REBa2Cu3O7-δ systems. We have substituted Ce for Gd in Gd1-xCexBa 2Cu3O7-δ compounds with x = 0.0-0.6 by the standard solid-state reaction technique. X-ray diffraction (XRD) experiments are performed and their results are refined by the Rietveld method. XRD analysis shows a predominantly single-phase perovskite structure with few impurity phases. Our resistivity results show that, by increasing the Ce content, Tc decreases, the transition temperature width increases, and in the normal state a metal-insulator transition (MIT) occurs at x c = 0.12. The normal state resistivity of the samples and their slopes...