فهرست مطالب

Ultrafine Grained and Nanostructured Materials - Volume:49 Issue: 1, 2016
  • Volume:49 Issue: 1, 2016
  • تاریخ انتشار: 1395/03/30
  • تعداد عناوین: 8
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  • Mahnaz Zakeri*, Omid Basiri Pages 1-10
    In this research, the influence of structure on the tensile properties of single- walled carbon nanotubes (CNTs) is evaluated using molecular mechanics technique and finite element method. The effects of diameter, length and chiral angle on elastic modulus and Poisson’s ratio of armchair, zigzag and chiral structures are investigated. To simulate the CNTs, a 3D FEM code is developed using the ANSYS commercial software. Considering the carbon-carbon covalent bonds as connecting load-carrying beam elements, and the atoms as joints of the elements, CNTs are simulated as space-frame structures. The atomic potentials are estimated using harmonic simple functions. The numerical results show that by increasing the diameter and length to a certain amount, the size effect on tensile behavior of modeled nanotubes is omitted. In fact, for nanotubes with diameter over 2 nm and length over 36.5 nm the chiral angle is the only effective factor on the tensile properties. Also, it is found that the structure has a little effect on the elasticity modulus, which is about 4%. However, Poisson’s ratio can be affected significantly with chiral angle. Asymmetric structures with angles θ
    Keywords: Chirality, Elasticity modulus, Equivalent continuum modeling, Poisson's ratio
  • Ali Khajezade, Mohammad Habibi Parsa*, Hamed Mirzadeh, Mehdi Montazeri, Pour Pages 11-16
    Severe plastic deformation is a technical method to produce functional material with special properties such as high strength and specific physical properties. Selection of an efficient severe plastic deformation for grain refinement is a challenging field of study and using a modeling technique to predict the refinement efficiency has gained a lot of attentions. A comparative study was carried out on the grain refinement ability of two severe plastic deformation techniques. Accordingly, beta-tin samples were processed for almost the same strain level by the equal channel angular extrusion (ECAE) and the newly developed multi-axial incremental forging and shearing (MAIFS). Optical microscope and tensile tests were used to investigate the microstructure and mechanical properties. It was found that the MAIFS process is more efficient in grain refinement than ECAE by help of crystal plasticity analysis and experimental observation. This was ascribed to the more activated slip systems in MAIFS than ECAE and activation of secondary modes of deformation in MAIFS. The conclusion was supported by the finer grains that was observed in the sample processed by MAIFS and compared with grain size of the sample processed by ECAE. Finally, these observations were related to materials flow for beta-Tin during tensile test.
    Keywords: Crystal Plasticity, Grain Refinement, Severe Plastic Deformation, Texture, VPSC
  • Mina Rabiee, Hamed Mirzadeh*, Abolghasem Ataie Pages 17-21
    Nanostructured Cu-20Fe alloy was synthesized by mechanical alloying process and the effects of process control agents (PCA) on the phase formation, crystallite refinement and morphology of powder particles were studied. The dissolution of Fe into Cu matrix and the morphology of powder particles were analyzed by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM), respectively. The mean crystallite size was approximated by the method developed by Williamson and Hall. It was found that in the absence of PCA (Toluene in the present work), the iron peaks vanish after 5 h of mechanical alloying process and the mean crystallite size of the matrix decreases to 35 nm and large agglomerated particles are formed during milling. In this regard, it was found that the addition of PCA decreases the rate of crystallite refinement and formation of solid solution but does not affect the final mean crystallite size. It was also found that the addition of PCA during milling decreases the powder particle size considerably and by preventing agglomeration can lead to a finer powder particle size compared with the initial unmilled powders. It was also revealed that the effect of PCA on particle size is much greater than the effect of milling time.
    Keywords: Crystallite Refinement, Mechanical Alloying, Nanomaterials, Process Control Agent
  • Mohammad Abdolahi Sereshki, Bahram Azad*, Ehsan Borhani Pages 22-28
    Accumulative roll bonding (ARB) imposes severe plastic strain on materials without changing the specimen dimensions. ARB process is mostly appropriate for practical applications because it can be performed readily by the conventional rolling process. An Al-2wt%Cu alloy was subjected to ARB process up to a strain of 4.8. Stacking of materials and conventional roll-bonding are repeated in the process. In this study, corrosion behavior of an Al-2wt%Cu alloy fabricated by ARB process was studied in 3.5%wtNaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The morphology of structures was analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Also, the electrochemical experiments showed that corrosion resistance of samples decreases with increasing the number of ARB cycles due to the formation of oxide layer on defects and energetic regions such as grain boundaries with low/high angle and high density dislocations accumulated in sub-grains. According to the nyquist curves, by continuing the process, the diameters of semicircles decreased and the corrosion resistance and the polarization resistance subsequently decreased. After 6-cycle ARB, link up of small pits and micro crack were seen. Also, with increasing the number of the ARB cycles, the mean grain size of specimens decreased and it reached to 650 nm after 6 cycles of ARB process.
    Keywords: Accumulative roll bonding (ARB), Al, 2wt%Cu Alloy, Electrochemical Impedance Spectroscopy (EIS), Pitting Corrosion, Polarization
  • Mohsen Reihanian*, Seyyed Mohammad Lari Baghal, Fateme Keshavarz Haddadian, Mohammad Hosein Paydar Pages 29-35
    In this study, the Al/Al2O3-SiC hybrid composite was produced by accumulative roll bonding (ARB). In the first and the second cycles, the particles were uniformly poured between the Al strips during each ARB cycle. In the subsequent cycles, ARB was repeated up to six cycles without adding the particles between the layers. After the total eight cycles, the particles were distributed uniformly without agglomeration in the Al matrix. The corrosion behavior of the hybrid composite was investigated and compared with that of the annealed and ARB processed Al. The corrosion tests were conducted by the potentiodynamic and electrochemical impedance spectroscopy tests in 3.5 wt-% NaCl solution. The anodic potential of the pure Al processed by ARB was more positive than that of the annealed Al while its corrosion current density was higher. The corrosion potential of the hybrid composite was somewhere between the annealed Al and ARB processed Al. The hybrid composite exhibited the lowest current density and the highest charge transfer resistance. The increased corrosion resistance of the hybrid composite was attributed to the inert character of the Al2O3 and SiC particles because these particles could decrease the active sites of the material surface and impeding the corrosive attacks.
    Keywords: Accumulative roll bonding (ARB), Corrosion, Metal, matrix composites (MMCs), Microstructure
  • Mansoor Anbia*, Faezeh Khosravi, Roghaye Dehghan Pages 36-42
    Hydrothermal and non-hydrothermal spherical TiO2 nanoporous with crystalline framework were prepared by sol-gel method. The Crystalline structures, morphologies and surface texturing of materials were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption-desorption isotherms. The Hydrothermal spherical TiO2 nanoporous was found to have a narrow and strong pore size distribution peaks with average of 37.8 Å and pore volume of 0.41 cm3/g and the (Brunauer–Emmett–Teller)BET specific surface area of 365 m2/g. Hydrothermal and non-hydrothermal spherical TiO2 nanoporous have been used as adsorbent to study of the adsorption behavior of Pb(II), Co(II) and Ni(II) ions from aqueous system in a batch system. Effect of equilibrium time on adsorption Pb(II), Co(II) and Ni(II) ions on these adsorbent was studied The results show that the shaking time 0.5 to 10h has no serious effect on the percentage of ions removal, and the adsorption is fast in all cases. The maximum uptake capacities of Hydrothermal and non-hydrothermal spherical TiO2 nanoporous was calculated. Both hydrothermal and non-hydrothermal TiO2 nanoporous materials were found to have very good potential as new adsorbents in removal of these ions. In batch systems the maximum uptake capacities of Pb(II), Ni(II) and Co(II) on the hydrothermal and non-hydrothermal TiO2 nanoporous materials was Co(II) > Pb(II) > Ni(II) and Co(II) > Ni(II) > Pb(II), respectively.
    Keywords: Adsorbent, Heavy metals, Nanoporous Materials, Titanium dioxide
  • Zahra Ostadmahmoodi Do, Tahereh Fanaei Sheikholeslami*, Hassan Azarkish Pages 43-47
    Nanowires (NWs) are recently used in several sensor or actuator devices to improve their ordered characteristics. Silicon nanowire (Si NW) is one of the most attractive one-dimensional nanostructures semiconductors because of its unique electrical and optical properties. In this paper, silicon nanowire (Si NW), is synthesized and characterized for application in photovoltaic device. Si NWs are prepared using wet chemical etching method which is commonly used as a simple and low cost method for producing nanowires of the same substrate material. The process conditions are adjusted to find the best quality of Si NWs. Morphology of Si NWs is studied using a field emission scanning electron microscopic technique. An energy dispersive X-Ray analyzer is also used to provide elemental identification and quantitative compositional information. Subsequently, Schottky type solar cell samples are fabricated on Si and Si NWs using ITO and Ag contacts. The junction properties are calculated using I-V curves in dark condition and the solar cell I-V characteristics are obtained under incident of the standardized light of AM1.5. The results for the two mentioned Schottky solar cell samples are compared and discussed. An improvement in short circuit current and efficiency of Schottky solar cell is found when Si nanowires are employed.
    Keywords: Fabrication, Nanowire, Silicon, Solar Cell
  • Ensieh Shahsavani, Nourollah Feizi, Aliakbar Dehno Khalaji* Pages 48-50
    In this paper, we have focused on the preparation and characterization of copper oxide nanoparticles by solid state thermal decomposition of copper(I) iodide in the presence of thiosemicarbazone ligands without the need for a catalyst, employing toxic solvent, template or surfactant and complicated equipment, which makes it efficient, one-step, simple and environment-friendly. CuO nanoparticles were achieved at 600 ˚C for 3 h as black products and characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The FT-IR spectra of black powders prepared show absorption maxima at ≈ 525 cm-1 which are due to Cu-O stretching mode. Also, all the X-ray diffraction peaks could be readily assigned to those of crystalline CuO. The absence of any residual ligand traces or other phases in the FT-IR spectra and XRD patterns confirmed the preparation of high purity and single phase copper oxide nanoparticles. The TEM images show that the synthesized copper oxide nanoparticles are of plate like shape with average diameters of 10 – 20 nm. On the basis of the above results, the use of thiosemicarbazone ligands at the presence of suitable transition metal ions is potentially capable of forming other transition metal oxide nanoparticles by solid state thermal decomposition.
    Keywords: Copper(I) Iodide, CuO nanoparticles, Thiosemicarbazone