Sharif Digital Repository

One-dimensional nanostructures of tin oxide nanotubes were fabricated by carbothermal evaporation at 900°C in air. The synthesized film was grown on Au-coated (100) Si substrate. Heterogeneous catalysis by Au/Sn droplets assisted the formation of the tin oxide nanotubes of less than 40 nm diameter at Sn vapor pressures around 1.4×10 -7 Pa. In order to reduce the nanotube diameter further, an increase in the Sn vapor pressure by changing the source materials' ratio seemed viable. © 2009 Springer-Verlag  

Alkoxides are the most common precursors used for the production of alumina nanopowders. These materials are, however, expensive and corrosive. This paper introduces a new method for the production of alumina nanopowders by rapid cooling of a synthetic caustic sodium aluminate solution (Bayer liquor), followed by calcination in the presence of a surface-stabilizing agent like 1,2-dihydroxy-3,5-benzene disulfonic acid disodium salt (Tiron). The powders produced are characterized by differential thermal analysis, XRD, transmission electron microscopy, scanning electron microscope, and Brunauer-Emmet-Teller. A nanopowder of α-alumina with an average crystallite size of 27.7 nm and an average... 

During recent years, many investigations have been carried out to determine how to select different materials for the making of Micro Electro Mechanical Systems (MEMS) and bio-MEMS. The NiTi shape memory alloy thin film has been much regarded as a promising candidate for MEMS due. to its unique shape memory effect and high energy output. In this research, NiTi thin film was fabricated using a sputtering technique from separate elemental Ni and Ti targets. The characterizations of the deposited films were, investigated using different analysis techniques, such as Field Emission SEM, DSC, XR.D, electrical resistivity measurement and nanoindentation. © Sharif University of Technology, June 2009... 

By making aligned and suspended copper nanowires, a high performance, transferable, and flexible transparent electrode is reported. Indium tin oxide is often used in devices such as displays, solar cells, and touchscreens that require transparent and conductive plates. Because of problems such as brittleness, high cost, and environmental effects, this material is facing rivals, the most serious of which are metallic nanowire meshes, especially copper. We developed a simple technique which uses a U-shaped collector in the electrospinning process with three advantages including the enhancement of the figure of merit (which is related to the surface resistance Rs and the transmittance T) by... 

Two-step sintering (TSS) was applied to suppress the accelerated grain growth of sub-micron (∼150 nm) alumina powder. The application of an optimum TSS regime led to a remarkable decrease of grain size down to ∼500 nm; while the grain size of the full-dense structures produced by conventional sintering ranged between 1 and 2 μm. To find how important the temperatures at sintering steps might be, several TSS regimes were conducted. The results showed that the temperatures at both sintering steps play vital roles in densification and grain growth of the alumina compacts. Based on the results, the optimum regime consisted of heating the green bodies up to 1250 °C (first step) and then holding... 

A new and effective hot milling system was designed and applied to the synthesis of PbZr0.95Ti0.05O3 (PZT) powder. PbO, ZrO2 and TiO2 powders were used as starting materials and hot milled at various temperatures ranging from 10 ̊°C to 800 ̊°C. The obtained powders were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Results indicated that pure, crystalline, and fine PZT powders with the average particle size of 170 nm can be successfully synthesized directly after a relatively short synthesis time of 12 h at lower temperature of 800 ̊°C by the hot milling technique. In contrast to this method, this study demonstrates that conventional solid-state... 

Water adsorption by bis-2-ethylhexyl phosphoric acid (D2EHPA) during the extraction of zinc, cobalt and nickel using a D2EHPA-kerosene/H2O mixture is investigated. Based on the experimental results, about 1 mol of water is adsorbed by 2 mol of D2EHPA (which exists in the form of a dimer), irrespective of the pH. Water adsorption decreases with presence of zinc, cobalt and nickel. The stoichiometric coefficients of D2EHPA in water adsorption reactions are determined with and without zinc, cobalt and nickel by applying the slope-analysis method. It is experimentally confirmed that 1.0, 1.8 and 1.2 mol of adsorbed water will be rejected from the organic phase when zinc, cobalt and nickel are... 

Nitinol shape memory alloy is a biocompatible material that is suitable for biomedical applications due to its superelasticity, shape memory effect, good corrosion and fatigue resistance, and sound damping properties. With the selective laser melting (SLM) additive manufacturing process, it is possible to produce customized NiTi implants in the form of porous metamaterials with complex geometries. This paper presents a review of modeling, production, and application of NiTi implants. First, the fundamentals of shape memory alloys and the SLM process are summarized. Then, the effects of the SLM process on the transformation temperatures and the impacts of Heat treatments on these temperatures... 

Fe-Ni nano-particles were synthesized by mechanical alloying and subsequent low-temperature hydrogen reduction of oxide mixtures. First, single-phase nickel ferrite was mechanically synthesized for 30 h with steel balls to powder weight ratio of 20 while the milling was operated at 300 rpm. The as-milled powder was then placed in contact with hydrogen at 600 °C for 1 h. Reduction reactions resulted in production of Fe-Ni nano-particles. Phase identification, morphological and microstructural studies, chemical analysis and magnetic property determination were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), energy dispersive... 

Stent implantation has been regarded as a major strategy to solve gastrointestinal diseases such as biliary obstruction during the last decade. The application of nitinol superelastic stents has been recently considered for minimising such problems as restenosis after stent implantation, the ability to low stent twist, unsuitable dynamic behaviour and inadequate strength radial of stent. In the present article, the effects of material properties on mechanical performance of Z shaped nitinol wire stent under crushing test for clinical applications are studied by finite element modelling. Nitinol stent shows better mechanical and clinical performance after applying 90% crushing, less chronic... 

For more than a decade, stent implantation has been strategically used for solving gastrointestinal dilemmas such as biliary stenosis. Predicaments like insufficient radial strength, low twisting ability, inappropriate dynamic behaviour and restenosis are expected to be solved by the introduction of new designs. Superelastic Nitinol stent is an interesting alternative for minimising these tight spots. The application of finite element method to predict metallurgical and geometric behaviour of superelastic Nitinol stents for biliary duct dilatation is supported by conventional crimp tests. Model calculations show that all stents encounter the highest stress in their intersegment curvature.... 

Nitinol stents are used to minimize improper dynamic behavior, low twistability, and inadequate radial mechanical strength of femoral artery stents. In this study, finite element method is used to investigate the effect of crimping and Austenite finish temperature (A f) of Nitinol on mechanical performance of Z-shaped open-cell femoral stent under crimping conditions. Results show that low A f Nitinol has better mechanical and clinical performance due to small chronic outward force, large radial resistive force, and appropriate superelastic behavior  

Optical fibers, in particular, glass fibers, are mostly used in the field of optical communication, however in recent years new optical sensors based on the optical fibers have been reported in literature and produced commercially. Extrinsic and intrinsic character of the fibers have been implemented in development of such sensing devices. Glass Optical Fibers (GOF) because of low attenuation are more suitable for the optical communication purposes while Plastic Optical Fibers are advantageous for the linking purpose and some sensing operations. Considering this point different (POF) optical fiber sensors have been developed by author to show potential applications of POFs in sensor... 

This article describes the synthesis and swelling properties of a superabsorbing hydrogel composite based on collagen. The composite have been prepared via graft copolymerization of acrylic acid (AA) in the presence of kaolin powder using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The certain variables of the graft copolymerization (i.e. the monomer, the initiator, and the crosslinker concentration as well as kaolin/collagen weight ratio) affected on the ultimate water-swelling capacity were optimized. Evidence of grafting and kaolin interaction was obtained by comparison of FTIR spectra of initial substrates and superabsorbent... 

Global warming persuades researchers to improve the effectiveness of renewable energy technologies, such as H2 production by methane steam reforming (MSR) an endothermic process. Herein, a nanocatalyst based on open-cell nickel foam 40 (pore per inch) with high thermal conductivity was prepared. The nanocatalyst was synthesized with a chemical stepwise synthesis approach, chemical pretreatment, pulsed electrocodeposition of Ni-Al2O3(γ) nanoparticles, and calcination. Measurements of thermal diffusivity(α) with flash xenon technique gained 4.41×10-6 m2s-1 and values of specific heat capacity, Cp, by differential scanning calorimetry (DSC) and thermal conductivity(λ) enhanced by 65% in... 

NiTiHf thin films with varying hafnium contents up to 28.7at% were fabricated using simultaneous sputter deposition from separate Ni, Ti, and Hf targets onto unheated substrates. The required film composition was achieved by adjusting the power ratio to the targets. The as-deposited films were amorphous; and post deposition annealing was performed at 550°C, slightly above their crystallization temperatures. The crystallization temperature of the films varied as a function of Hf concentration, and was as high as 520°C at a Hf content of 28.7at%. 2μm thick crystallized films with I0at% or greater Hf were martensitic at room temperature. DSC analysis demonstrated that above 10at%Hf additions... 

In the present study, the TiO2 nanotubes were grown on the surface of porous titanium foam by the anodization method. The surface of titanium foam before and after the coating of TiO2 nanotubes was structurally and morphologically characterized by X-ray diffraction (XRD), field emission electron microscope (FESEM) equipped with energy-dispersive X-ray (EDX). Additionally, the cytocompatibility of TiO2-coated porous titanium foam was evaluated by methyl thiazol tetrazolium (MTT) assay. The results have shown that the anatase crystalline phase was formed on the surface with a uniform thickness of 2.5 μm. Finally, TiO2-coated porous titanium foam was biocompatible and significantly enhanced the... 

Integrating implants with the surrounding bone tissue is a significant challenge in medical engineering. A promising option with appropriate biological and mechanical characteristics is porous titanium, which can be employed in mineralizing bones and ingrowth applications. In the present study, titanium foams were fabricated using titanium hydride powder and the following space holders: (1) needle-shaped urea, (2) spherical urea, and (3) cubic sodium chloride. All samples were characterized by means of scanning electron microscopy with an energy-dispersive X-ray spectrometer, X-ray diffraction, and mechanical compression testing. Our results revealed that powder metallurgy is suitable for...