Sharif Digital Repository

In this study, some stabilized magnetite based ferrofluids were synthesized using Dextran as a stabilizing agent. In order to achieve optimum experimental conditions for synthesizing ferrofluids as MRI contrast agents, the Taguchi method was used. This approach was employed to design and minimize the number of required experiments. By using the Taguchi orthogonal (L16) array, four parameters including solution temperature and alkalinity, reaction temperature and stirring rate were selected at four predetermined levels for 16 experiments. Synthesizing processes established based on this set of experimental conditions were carried out and the obtained ferrofluids were characterized using PCS,... 

FeNiCo base powder alloy with nominal composition Fe-27Ni-17Co-4Ti (wt%) was prepared from elemental powders by mechanical alloying. The structure of milled powders was characterized by XRD and SEM. The effect of nanosize structure on magnetic properties and shape memory behavior was studied using VSM and DSC. After milling for 240 minutes by high energy vibrational ball mill under argon atmosphere, supersaturated solid solution formed with mean crystallite size of ∼20 nm. Results of VSM examinations showed that by milling for 240 minutes saturation magnetization and intrinsic coercivity reached 304 emu/gr and 21 Oe, respectively. XRD analyses made it clear that transformation from BCC to... 

In this work, a new approach is described for the calculation of the relaxation time and magnetic anisotropy energy of magnetic nanoparticles. Ferrofluids containing monodispersed magnetite nanoparticles were synthesized via hydrothermal method and then heated using the 10 kA/m external AC magnetic fields in three different frequencies: 10, 50 and 100 kHz. By measuring the temperature variations during the application of the magnetic field, the total magnetic time constant including both Brownian and Neel relaxation times can be calculated. By measuring the magnetic core size and hydrodynamic size of particles, the magnetic anisotropy can be calculated too. Synthesized ferrofluids were... 

In this research, the possibility that nanostructured aluminium titanate (tialite) powder can be used as a chemical source for producing Al2O3 and Al3Ti precipitates in aluminium matrix composites has been investigated. Optical microscopy, FE-SEM, XRD, DSC and TGA examinations were used to characterize the synthesized specimens. The results showed that a porous structure and inferior mechanical properties were obtained in as-sintered samples. The further thermomechanical treatments i.e. cyclic rolling and hot extrusion improved the mechanical properties and led to a dense microstructure with a homogeneous distribution of Al2O3 and... 

Finemet soft magnetic alloy has been in the focus of interest in the last years due to its high saturation magnetization, high permeability and low core loss. The great quantity of papers has been devoted to the study of its structural and magnetic properties, confirms this claim. This paper reviews the different researches performed on Finemet up to now. The criteria that should be satisfied in order to have the high glass forming ability in an alloy and also the techniques applied for production of Finemet ribbons, powders and bulk samples have been explained. In addition, the mechanism of devitrification, nanocrystallization and magnetic softness in this applicable magnetic alloy has been... 

A heterogeneous catalyst for epoxidation of alkenes has been synthesized by introducing polyoxomolybdate into a natural zeolite as a solid and green support. The prepared catalyst was characterized by FT-IR, inductively coupled plasma optical emission spectrometry (ICP-OES), powder X-ray diffraction (XRD), N2 absorption–desorption, field emission scanning electron micrograph (FE-SEM) and transmission electron microscopy (TEM). The catalytic investigations disclosed that nanocluster polyoxomolybdate supported on the surface is an active and recyclable catalyst in liquid phase alkene epoxidation in dichloroethane at 80 °C. © 2017 Informa UK Limited, trading as Taylor & Francis Group  

An Al-5 wt% Ti composite was fabricated via powder metallurgy and hot extrusion from initial pure Al and Ti powders. The effect of subsequent heat treatment at 600 °C for different time intervals on microstructure and mechanical properties was investigated. XRD and EDS analyses showed the in-situ formation of Al3Ti intermetallic. SEM micrographs demonstrated the formation of core-shell structured particles in Al matrix for composites heat treated up to moderate heating times (4 h). Generation of voids and pores in the heat treated composites was considered as a result of the Kirkendall effect. Mechanical properties of composites were studied by hardness and tensile testing methods at room... 

The design of 3-dimensional (3-D) nanostructured materials on the novel current collectors has recently considered as a promising strategy for developing high-performance supercapacitors. Herein, in the first step, a novel 3-D nickel nanocone arrays (NCAs) are synthesized on the surface of nickel plate (NP) by a one-step electrodeposition method without using any template (NCAs-NP). Then, a simple and efficient method is developed for fabricating ternary metal sulfides electrodes based on the electrodeposition of nickel cobalt iron sulfide (Ni-Co-Fe-S) ultrathin nanosheets on the surface of NCAs-NP. Taking advantages of the unique flower like structure of Ni-Co-Fe-S ultrathin nanosheets and... 

Nanocrystallization kinetics of amorphous Finemet alloy was studied using Vyazovkin advanced isoconversional method under non-isothermal condition. Well known Kissinger model-fitting method and four isoconversional methods of Kissinger-Akahira-Sunose (KSA), Flynn-Wall-Ozawa (FWO), Tang, and Starink were also used for the determination of activation energy. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) patterns were used for thermal and structural analyses, respectively. According to Vyazovkin and other isoconversional methods, the mean value of variable activation energy, as a function of conversion, was obtained as 350 kJ mol-1. While, according to Kissinger method,... 

A high performance asymmetric supercapacitor (ASC)has been fabricated by using nickel oxide-cobalt oxide nanosheets (NiO–CoO NSs), which were directly grown on carbon nanotubes (CNTs)and hydrothermal carbon spheres (HTCs)as positive and negative electrodes, respectively. Both electrode materials are binder-free prepared by using a catalytic chemical vapour deposition (CVD)approach followed by a facile hydrothermal method for cathode and a one-step environmental-friendly route called hydrothermal carbonization for anode. Using NiO–CoO NSs@CNTs and HTCs, which were directly grown on Ni foam, not only leads to a very small equivalent series resistance, but also provides an impressive capacitive... 

Developing advanced electrode materials with metal–organic frameworks (MOFs) has increasingly attracted attentions as an effective method for improving supercapacitors performances. However, their poor conductivity has limited their use in energy applications. In this paper, an effective strategy is presented to reduce the electric resistance of MOFs by the in situ synthesis of Ni-based MOFs with graphene (Ni-MOF/graphene). The fabricated Ni-MOF/graphene composite was characterized by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), Raman spectra, Brunauer–Emmett–Teller (BET) and... 

Zeolite-based micromotors were developed to eliminate the biological and chemical contamination of water in a fast and efficient way. The motors consist of a silver-exchanged zeolite core and a partial catalytic coating. These porous engines showed rapid killing of Pseudomonas aeruginosa bacteria cells in a very short time, less than 7.5 minutes. The heavy metal uptake of the zeolitic motors during the first 20 minutes of contact was considerably higher than that of zeolite particles by 23% for Pb2+, 19% for Co2+, and 16% for Ni2+. Also, the maximum removal efficiency of the motors (at room temperature and for 6 hours) for Pb2+, Co2+, and Ni2+ was 93%, 87%, and 78%, respectively, higher than... 

Palladium nanoparticles supported on polyoxometalate as a solid carrier were successfully prepared and evaluated as a heterogeneous nanocatalyst for the Mizoroki-Heck cross-coupling reactions. This supported catalyst was characterized by a set of techniques, including XRD, chemical analysis (ICP-OES), IR spectroscopy, TEM and FE-SEM analyses. Poly (ethylene glycol) was employed as an environmentally friendly solvent for coupling reactions. The various fundamental reaction parameters that influence the efficiency of the reaction and yield of the desired reaction products were optimized. This catalytic system showed good activities and evolve a strategy for achieving five times catalyst and... 

In the present study, a rational two-step strategy is employed for the green, fast, very simple, and highly controllable synthesis of the bimetallic nickel-cobalt-based metal-organic frameworks (MOFs) on glassy carbon substrates by in situ transformation of nickel-cobalt-layered double hydroxide nanosheet (NiCo-LDHs NSs) intermediates into nickel-cobalt-benzene tricarboxylic acid MOFs (E-NiCo-BTC MOFs). The structural characteristics of the electrode materials in each step were investigated via Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, elemental mapping, field emission scanning electron microscopy, and transmittance electron microscopy.... 

An Al-5 wt% Ti composite was fabricated via powder metallurgy technique and hot extrusion. The produced composite samples were heat-treated subsequently at 600 °C for various time durations of 0, 4 and 10 h to achieve different volume fractions of the intermetallic Al3Ti phase. Pure aluminum sample was produced as a benchmark specimen to be compared to the composite samples. SEM studies were used to investigate the microstructure of the composite samples, and it was revealed that core-shell structured particles were formed in the composite heat-treated for 4 h. Triple point bending test was performed on the single edge notched beam specimens of the heat-treated Al-5 wt% Ti composite and the... 

In this study, for the first time, we reported a fast and facile three-step in situ strategy for direct controllable growth of the Co3(BTC)2 MOFs thin films on the GCE, through the rapid conversion of the electrodeposited Co(OH)2 nano-flakes on rGO/GCE, to crystalline rectangular bar-shape structures of MOFs. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and elemental mapping analysis used to the structural and morphological characterization of the well-synthesized MOFs. The as-prepared Co3(BTC)2 MOFs were used to construct a non-enzymatic sensing platform for determining the glucose... 

This paper presents a modified particle swarm optimization (MPSO) algorithm for solving the optimal power flow (OPF) problems. The main distinction of this approach is in using particle's worth experience in stead of the best previous experience. The proposed approach is evaluated on the IEEE 30-bus test system which minimizes the total fuel cost considering operational constraints such as power flow equations, transmission flow limits, bus voltages and reactive power of generators. The results obtained using the proposed approach are compared with results of other optimization methods  

A kinetic model for growth of ZnO nanorods via vapor-liquid-solid (VLS) mechanism based on the bulk diffusion of Zn atoms through the Au-Zn droplet is presented. The dependences of the growth rate on size are given quantitatively. A general expression for the growth rate of nanorods during VLS process is derived. The derived formula shows the dependences of growth rate on lateral size of nanorods, concentration and supersaturation of Zn atoms in the liquid droplet. Based on the presented kinetic model the smaller nanorods have faster growth rate. Au-catalyzed ZnO nanorods are grown by chemical vapor transport and condensation (CVTC) process experimentally. Theoretical and experimental... 

In this research, a facile, two-step synthesis of Fe3O4–LCysteine–graphene quantum dots (GQDs) nanocomposite is reported. This synthesis method comprises the preparation of GQDs via hydrothermal route, which should be conjugated to the LCysteine functionalized core–shell magnetic structure with the core of about 7.5-nm iron oxide nanoparticle and 3.5-nm LCysteine shell. LCysteine, as a biocompatible natural amino acid, was used to link magnetite nanoparticles (MNPs) with GQDs. X-ray powder diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray were used to investigate the presence and formation of MNPs, L Cysteine functionalized MNPs,... 

In this research, a facile, two-step synthesis of Fe3O4–LCysteine–graphene quantum dots (GQDs) nanocomposite is reported. This synthesis method comprises the preparation of GQDs via hydrothermal route, which should be conjugated to the LCysteine functionalized core–shell magnetic structure with the core of about 7.5-nm iron oxide nanoparticle and 3.5-nm LCysteine shell. LCysteine, as a biocompatible natural amino acid, was used to link magnetite nanoparticles (MNPs) with GQDs. X-ray powder diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray were used to investigate the presence and formation of MNPs, L Cysteine functionalized MNPs,...