Journal of Advanced Materials in Engineering (Esteghlal)

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Gold nanoshells are a new type of nanoparticles including dielectric cores with a continuous thin layer of gold. By varying the core diameter, shell thickness, and the ratio of these parameters, the optical properties of gold nanoshells can be tuned to have maximum absorption in the visible and near infrared spectrum range. The purpose of this research was to synthesize gold coated SiO2 nanoshells for biomedical applications particularly laser tissue soldering. Nanoshells were synthesized using Stober method. The nanoshells were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, UV-visible spectroscopy and atomic force microscopy. The Fourier transform infrared spectroscopy confirmed the functionalization of the surfaces of silica nanoparticles with NH2 terminal groups. A tunable absorption was observed between 470-600 nm with a maximum range of 530-560 nm. Based on the X-ray diffraction, three main peaks of Au (111), (200) and (220) were identified. Also, atomic force microscopy results showed that the diameter of silica core was about 100 nm and the thickness of gold shell about 10 nm. This result showed that it is possible to use these nanoshells with visible and infrared lasers for biomedical applications.

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In this study, magnetite (Fe3O4) nanoparticles were synthesized by chemical co-precipitation from the solution containing iron salts in alkaline medium under N2 gas and room temperature. Magnetite nanoparticles were characterized by X- ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), Brunauer-Emmet-Teller (BET), and vibrating-sample magnetometer (VSM). The rheological properties of magnetite ferrofluid were examined by rheology apparatus. The biocompatibility and cytotoxity of magnetite nanoparticles were evaluated by 3T3 and fibroblast cells. The results showed that the Fe3O4 magnetite nanoparticles coated by polyvinyl alcohol (PVA) could be an appropriate candidate for biomedical applications.

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Mechanical property of porous nickel-titanium alloy produced by volumetric combustion synthesis (VCS) for bone surgery applications is reported in this paper. Stress-strain behavior of the alloy is determined by uniaxial tension test. Superelastic diagram of the porous alloy is compared with that of the solid material cooled from austenite stability temperature. Due to movements of the dislocations, growth of the nucleation sites and thinning of the martensite plates during cooling, plastic deformation and necking behavior of these materials are principally different from that of the ordinary materials. Elastic modulus and yield stress of the material have nonlinear relationship with porosity percentage and obey the following correlations  and The stress-strain curves of the alloy show more than 6 percent elongation before rupture, even with 30 percent porosity. A comparison of the cleavage surfaces of the combustion synthesis samples with those of the powder metallurgical ones indicate great influence of production process on fracture mechanism.

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Hercynite, FeAl2O4, was synthesized via molten salt synthesis method in the coke bed at 800°C with 3h of holding time. It was synthesized by reacting stoichiometric compositions of Al2O3 and FeCl2.4H2O in eutectic compositions of alkaline chlorides NaCl-KCl-LiCl. The reactant to salt ratio was 1 to 3. The phase formation, and morphology of these synthesized powders after washing and filtration were characterized via X-ray diffraction (XRD), and scanning electron microscopy (SEM). Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were performed at temperatures up to 1000 °C at a heating rate of 10 °C/min in argon atmosphere, to elucidate the different reaction mechanisms in the synthesis of Hercynite by the molten-salt method. The effects of processing parameters including the temperature and holding time on the formation of FeAl2O4 were investigated. The results demonstrated that the formation of FeAl2O4 spinel could be initiated at 700°C. By increasing the temperature to 900 °C and holding time, the amounts of FeAl2O4 particles in the resulting powder increased at the expense of Hematite and Al2O3. Morphology of the synthesized powder was cubic and tetragonal, increased by increasing the holding time and temperature.

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In this research, ZrC nano particles were synthesized by self-propagating high temperature (SHS) using the mixed powder of ZrO2-C-Mg and NaF or NaCl diluent. The effect of different proportions of raw materials, milling time, composition of the diluent and also pickling on the synthesis of ZrC was investigated. Optimal amounts of magnesium and sodium fluoride for the synthesis of ZrC were 2.8 and 2 mol, respectively. Milling process of 120 minutes decreased the diffusion gap of raw material and increased the combustion reaction progress. XRD and SEM analysis showed that the NaF diluent more than NaCl caused a reduction in the size of the particles of ZrC and increased the progress of the combustion reaction. Synthesized samples were subjected to pickling in order to remove impurities of MgO by 37% HCl, and distilled water was used to wash off NaF and NaCl residues. ZrC particle size of different samples were in the range of 50-90 nm.

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In this study, the effect of Al₂O₃ addition as a diluent during mechanically activated self-propagating high temperature synthesis (MASHS) of Al₂O₃-ZrB₂ composite was investigated. For this purpose, the thermite mixture of Al, ZrO₂, H₃BO₃ and different amounts of Al₂O₃ (0, 3, 6, 9 wt.%) were used as the raw materials and mechanically activated for 5 h, then furnace sintering was performed at 650 °C. The results showed that by increasing the Al₂O₃ content up to 6 wt.%, the intensity of exothermic peak in the DSC curves increases, but for higher additive contents it decreases. In this case, more homogenous distribution of ZrB₂ particles with finer grain size was observed.

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In this research, TiAl/Al₂O₃ composite was synthesized from mechanically activated TiO₂-Al powder mixtures using microwave heating.The initial powder mixtures were mechanically activated and pressed into cylindrical tablets and then heated in a microwave oven. The effect of different amounts of excess Al and microwave susceptor material (SiC or graphite) on the ignition time and the resultant reaction products were evaluated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used for characterization of the synthesized samples. XRD patterns revealed that when there was no excess Al in the initial powder mixture, the main resulting intermetallic phase would be Ti₃Al with negligible amounts of TiAl, while with 10 wt% excess Al, TiAl phase could be formed in the composite product.The results also showed that microwave synthesis took place faster and more reproducible when samples were packed in the graphite powder than when placed between two SiC blocks.

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In this study, electrical wire explosion has been used to produce aluminum carbon nanotube (Al-CNT) nanocomposite particles in acetone medium. In order to synthesize Al-CNT nanocomposites, initially, CNTs were ultrasonically dispersed. Then, aluminum wire was exploded in this medium. Synthesized samples were characterized by Fourier Transform Infrared (FTIR) spectroscopy and Transmission Electron Microscopy (TEM) methods. The results exhibited formation of spherical nanoparticles in the medium. The average diameter of nanoparticles was 4 nm. Moreover, attained nanoparticles remained stable in acetone. Results revealed a good interaction between aluminum nanoparticles and CNTs in this medium. It is concluded that acetone is a suitable medium for synthesizing Al-CNT nanocomposite as appropriate dispersion of Al-CNT nanoparticles can be achieved in this medium.

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In this study, the parameters affecting the synthesis of silver nanoparticles were optimized by green chemical reduction method to make a conductive pattern. The raw materials used in this study, include silver nitrate as a source of
silver ions, polyvinylpyrrolidone as surface stabilizer, and glucose as the reducing agent. Effective parameters were investigated
by Taguchi statistical design, to determine the optimum conditions and achieve the smallest average particle size. Silver nanoparticles were characterized by X-ray diffraction and field emission scanning electron microscopy. The smallest particle size can be applied by solution adding rate of 0.1 ml/min, temperature 90 ^°C, weight ratio of glucose to silver nitrate 3 g/g and weight ratio of Polyvinylpyrrolidone to silver nitrate 3.2 g/g. According to.our expectation 20 nm silver nanoparticles were obtained in this condition. FE-SEM confirmed the above results and showed nanoparticles with a size of 25 nm. Finally, A conductive pattern was printed on a glass substrate with synthesized powder. The electrical resistance of the printed pattern was 0.088× 10 ^-4 Ω.cm.

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In this study, fabrication of an in-situ composite through aluminothermic combustion synthesis in An Al–V₂O₅-NiO system was investigated. Therefore, Al, V₂O₅ and NiO powders with stoichiometric ratio of 11:1:1, respectively, were milled for an  hour and finally the mixtures were compressed. In order to investigate the temperatures of phase transformations, Differential Thermal Analysis (DTA) was utilized. Heat treatment was applied on the raw samples according to their peak temperatures treated in DTA. X Ray Diffraction (XRD) analysis for the samples shows formation of phases such as Al₃V and Al₃Ni₂ at different sintering temperatures. Microstructure and phase analysis showed that during sintering of this sample, Al₃V phase was not formed below 700 °C, at 880 °C Al₃Ni₂ it was formed and after 950 °C, it was transformed to Al₄Ni₃ phase. In addition, after 950°C, Al₃V transformed into Al₂₃V₄ phase. Analysis of samples density and hardness showed that, due to increase of volume fraction percentages of reinforcing phase, these two parameters increase as well.

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