Sharif Digital Repository

Roll bonding is the most important stage of the accumulative roll bonding process, which is used to produce high strength composites. The presence of a particle layer at the interface alters the bonding condition and increases the threshold reduction for the commencement of bonding. In this study, the bonding mechanism in presence of powder at the interface is analyzed and a theoretical model is proposed to predict the required threshold reduction in warm roll bonding of commercially pure aluminum sheets as a function of amount of alumina particles at the interface. The model considers the rolling parameters and the effect of amount and size of particles by defining some constants, which are... 

In the present study, the roll bonding behaviour of Al-3003/Al-4043 and Al-3003/Zn sheets were compared. The bi-layer sheets were produced by a roll bonding process at different reductions in thickness and rolling temperatures. The joint strengths of the sheets were evaluated by peel and bend testing before and after supplemental annealing treatment. The peeled surfaces were examined using a scanning electron microscope. The results indicated that the Al-3003/Al-4043 sheets were bonded with higher joint strength and lower threshold reductions in thickness with respect to the Al-3003/Zn sheets. In contrast to the Al-3003/Zn sheets, significant improvement was observed in the joint strength of... 

In recent years, the autoclaved aerated concrete (AAC) has been widely used in the building construction industry, especially for construction of infill walls. However, the AAC suffers from several drawbacks such as low compressive and tensile strength, high water absorption as well as insufficient resistance against impacts. To address such issues, this study evaluates the mechanical properties of the AAC blocks in which, the cement has been replaced with nano-graphene. For this purpose, various replacement ratios (0.2, 0.4, and 0.8) were selected and different tests such as compressive and tensile strength (cylindrical specimens with the size of 10 × 20 cm), impact resistance and water... 

A novel biopolymer-based hydrogel composite was synthesized through chemical crosslinking by graft copolymerization of partially neutralized acrylic acid onto the hydrolyzed collagen. The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis based on the swelling capacity of the hydrogels. This method was applied for the experiments and standard L16 orthogonal array with five factors and four levels. In the synthesis of the composite superabsorbent, N,N′-methylene bisacrylamide (MBA) as crosslinker, ammonium persulfate (APS) as initiator, acrylic acid (AA) as monomer, neutralization percent (NU), and collagen/kaolin weight ratio were used as... 

Industrial dehydrogenation of ethylbenzene to styrene is performed using potassium-promoted iron oxide catalyst. Many attempts have been made to understand the deactivation mechanism of the catalyst based on the chemical differences between the fresh and used catalysts. In the present work, in addition to the effect of chemical changes, the effect of structural changes of the internal areas on the catalyst activity was investigated. A fresh and used commercial catalyst from an industrial reactor which had been continuously used for two years under severe conditions (LHSV = 1 h-1, T = 610 °C, mass ratio of steam to ethylbenzene = 1.2, P = 1.2 atm) was studied. Nitrogen adsorption, Hg... 

The present study examined the sorption capacity and sorption kinetics of four-type perlite for oil spills clean up. These four types are different on their porous space, expansion ability and special surface area. The tests were done both in static and dynamic methods. Experiments showed that the perlite spread on oil spill rapidly and floated on the surface of oil spill because of its low density (80-180 kg/m3). Scanning Electron Micrograph (SEM) of a typical structure of expanded perlite showed that it of high porous space. Sorption kinetic of oil spill into porous expanded perlite was evaluated by weight increase of crude oil with sorption time. According to kinetic study sorption of oil... 

To investigate the Ta/Co/Cu/Co/NiO/Si(100) spin valve structure, fabrication and characterization of the Cu/Co/NiO/Si(100) system was studied for further understanding the structure. The system was grown by employing combinative DC sputtering-evaporation technique. Nickel oxide with a thickness of about 30 nm was deposited on Si(100) substrate using thermal evaporation technique.The cobalt film, then, with a thickness of about 3 nm was grown by DC sputtering under various applied negative bias voltages ranging from 0 to - 80 V. The optimum bias voltage (Vb = -60 V) for the growth of Co layer was determined by atomic force microscopy (AFM), four-point probe sheet measurement (Rs) and scanning... 

Investigation of BSCCO 2223 phase formation in superconducting thin films of Bi-based cuprates deposited on MgO substrate is reported. A series of films were made by in situ dc-magnetron sputtering method and another series were made by ex situ rf-magnetron sputtering technique. Same target have been used in both technique. In the case of the ex situ method, the films were annealed for different period of time at 800°C, and in the case of in situ method, the films were deposited at different temperature substrate. The influence of annealing time and the temperature of the substrate on the quality and the phase formation for ex situ and in situ method have studied, respectively. The results... 

In this paper, the effects of the multi-walled carbon nanotubes (MWCNTs) and nanographene (GP) on the mechanical performance of the cementitious mortars were investigated in different environments. Six mix designs were fabricated by considering the previous studies and exposed to potable water, acidic, and alkaline environments. The GP and MWCNTs partially replaced the cement with 0.25 %, 0.5 %, and 1 % of its weight. The standard mechanical tests, X-ray diffraction (XRD), and scanning electron microscope (SEM) analysis were performed on the specimens. The results indicated that including the MWCNTs and GP increases the compressive strength by 10 % and 20 % and similarly improves the tensile... 

A magnetic polyurethane (PU) nanocomposite was synthesized by an electrospinning technique and applied for isolation and preconcentration of fluoxetine from aquatic and biological samples. The nanocomposite was electrospun using a PU polymer solution containing the dispersed magnetic nanoparticles. The magnetic properties of iron nanoparticles, along with the use of an electrospinning technique, led to the formation of a suitable sorbent toward isolation of fluoxetine. The magnetic PU nanofibers could be subsequently removed from the sample solution by applying a permanent magnet. The scanning electron microscopy (SEM) image of the magnetic PU nanofibers confirms that their diameters are in... 

We present the preparation of polypropylene (PP)/fumed silica (FS) nanocomposites via in situ polymerization in this article. The approach includes preparation and utilization of a bisupported Ziegler-Natta catalytic system in which magnesium ethoxide and FS are used as conjugate supports of the catalyst. Catalyst preparation and polymerization processes are carried out in the slurry phase and under argon atmosphere. Scanning electron microscopy images show a good dispersion of the FS throughout the PP matrix. Results from differential scanning calorimetry reveal that the crystallization temperature of prepared nanocomposites increases by increasing FS loading. Also, crystal content of... 

In this study, we attempt to characterize the microstructural evolution during friction stir butt welding of Al-Cu-laminated composites and its effect on the fracture behavior of the joint. Emphasis is on the material flow and particle distribution in the stir zone. For this purpose, optical microscopy and scanning electron microscopy (SEM) images, energy-dispersive spectroscopy EDS and XRD analyses, hardness measurements, and tensile tests are carried out on the joints. It is shown that intermetallic compounds exist in lamellas of banding structure formed in the advancing side of the welds. In samples welded from the Cu side, the banding structure in the advancing side and the hook... 

Activated layered manganese oxides with deposited nano-sized gold or silver were synthesized and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectrometry, atomic absorption spectroscopy and energy-dispersive X-ray mapping. Here, we report that Au or Ag nanoparticles deposited on layered Mn oxides improve the catalytic activity of the Mn oxides toward the epoxidation of olefins in the presence of H2O2 and NaHCO3  

Nano-sized particles of manganese oxides have been prepared by a very simple and cheap process using a decomposing aqueous solution of manganese nitrate at 100 °C. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectrometry have been used to characterize the phase and the morphology of the manganese oxide. The nano-sized manganese oxide shows efficient catalytic activity toward water oxidation and the epoxidation of olefins in the presence of cerium(iv) ammonium nitrate and hydrogen peroxide, respectively  

The feasibility of fabricating relatively monodispersed polymeric nanoparticles by the electrospray method in a modified electrospray set-up is demonstrated in this study. The polymer solution is electrosprayed in the single cone-jet regime through a nozzle. After solvent evaporation, during which particles pave from the nozzle to collector, the fabricated nanoparticles can be collected in deionized water, which plays the role of surfactant for particles, not allowing them to aggregate. The results of scanning electron microscope and dynamic light scattering analysis clearly confirm the fabrication of monodispersed spherical polymeric nanoparticles with diameter range from 80 to 120nm with... 

The catalytic activity of Pt/Ni/TiO 2 nanotubes electrode toward glucose has been studied. Fabrication of Pt/Ni nanostructures was done in a single-bath solution through electrochemical pulse method by changing the deposition potential between -0.3 and -4 V vs. SCE, respectively. The resulting modified electrode represented high conductivity due to the effective presence of metallic components and uniform surface area caused by dispersion of Pt and Ni nanostructures. The scanning electron microscopy images also confirmed that a large amount of metals colonies were well-dispersed at the edge of the TiO 2 nanotubes. In addition, the Pt/Ni TiO 2 nanotubes modified electrode exhibited an... 

In this study, the failure analysis of a shaft of a unit, which had been failed during the service, was studied. This shaft was welded to the blades, and their chemical compositions were determined by spectroscopy method. In order to determine the root cause of failure and contribution factors, different investigation methods including visual examination, optical microscopy and scanning electron microscope analysis, and hardness test were carried out. It was concluded that the shaft was failed due to fatigue. The failure was caused by improper welding of blades to the shaft. At the end, in order to prevent or decelerate such failure, some recommended remedies were suggested  

A two-stage hydrogen-reduction/sintering procedure was used to synthesize W-15 wt%Cu nano-composite tablets. Hydrogen-reduction was carried out at 600, 650, 700 and 750 °C for 15-90 min and sintering was performed at 1100, 1150, 1200 and 1250 °C for 60 min. Morphology and grain size of the products were rigorously investigated by scanning electron microscope (SEM), X-ray diffractometer (XRD) and nano-particle Zeta-sizer. Maximum consolidation of the nano-composite product was achieved at 1200 °C. Hydrogen-reduction at 700 °C for 90 min showed an average particle size of ∼72.9 nm. Total reduction was achieved at higher temperatures and longer times. The mixture had a homogeneous structure... 

A series of reduced graphene oxide/ZnxCd1-xS (RGO/ZnxCd1-xS) nanocomposites (0 < x < 1) with different ratios of Zn/Cd were synthesized via a facile hydrothermal route under optimized experimental conditions and were carefully characterized by various techniques. Because very little is known about the morphology, specific surface area, and crystal phase effects of RGO/ZnxCd1-xS crystals on their photoresponsivity, field-emission scanning electron microscopy (FE-SEM), BET surface area analysis and X-ray diffraction (XRD) data were studied to investigate their effects on photoactivity. Based on the results, a crystal phase transition from a cubic phase in RGO/Zn0.9Cd0.1S to a hexagonal...