فهرست مطالب

  • Volume:9 Issue:2, 2013
  • تاریخ انتشار: 1392/08/12
  • تعداد عناوین: 7
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  • Sh. Sohrabnezhad, D. Rezaei Ochbelgh, N. Morsali Golboos Pages 61-70
    In this research, cobalt and nickel sulfide nanoparticles (NPs) were grown on AlMCM-41 matrix by using ion exchange method. The prepared samples were irradiated by thermalized neutron that emitted from Am-Be source up to fluencies (7.9+E9n/cm2). After that, X-ray diffraction (XRD), UV-Vis spectroscopy, Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for irradiated and non-irradiated samples characterization. The results show nanoparticles aggregation in NiS/AlMCM-41 is more than CoS/AlMCM-41 sample. The TEM images show average size of CoS NPs before and after neutron radiation about 20 and 50 nm, respectively. In this way, average size of NiS anoparticles before and after neutron radiation 130 and 70 nm respectively. The DRS results show that Co2+ and Ni2+ ions produced after neutron radiation, located in tetrahedral sites in AlMCM-41. The results indicate host materials have important role in decrease of radiation defects (RDs).
    Keywords: Nanocomposite, Neutron Irradiation, Diffuse Reflectance Spectroscopy, Aggregation, Radiation Defects
  • H. Tamaddon, A. Maghsoudipour Pages 71-76
    The fuel cells are distinguished as generating of green allocable energy and are electrochemical devices of low environmental impact. Porous nanocrystalline strontium-doped lanthanum manganite La0.8Sr0.2MnO3 (LSM) cathode materials were prepared by mechanochemical route in various grinding times. Carbon black was employed to produce pores. The formation of LSM single phase was studied by X-ray diffraction patterns. Porosity and density amounts were measured by means of Archimedes method, furthermore,contraction of sintered samples was comparably evaluated. Scanning electron microscopy (SEM) images were used for morphological study. It is shown that the open and total porosity generally decrease with sintering temperature, however the milling time increase these factors. Relying on open porosity amount and distribution, relative density and microstructural scrutiny the proper sintering temperature was determined. The microstructural investigation indicates that the grains grow as the sintering temperature increases which leads to decrease the number of the open pores.
    Keywords: SOFC, LSM, Mechanochemical Synthesis, Cathode, Sintering Trend
  • A. H. Meghdadi Isfahani, M. M. Heyhat Pages 77-84
    For better understanding the effect of nanofluid flow in a porous medium, a set of experiments were conducted on a horizontal glass micromodel for Al2O3-water nanofluids. To characterize the flow of nanofluids the same experiment was done by pure water. The glass micromodel was constructed by a photolithography technique. The Al2O3-water nanofluids were produced by a two-step method and no surfactant or PH changes were used. The nanofluids were made in different volume fractions of 0.1%, 0.5%, and 1%. The experimental results show that the pressure drop of nanofluids through the micromodel increases up to 43% at volume concentration of 0.01. Moreover, the Al2O3-water nanofluids behave like a Newtonian fluid and follow Darcy’s law at low Reynolds numbers. The permeability of the porous medium has been evaluated in different volume fraction of nanofluids and pure water. The results reveal that the assessed permeability doesn’t change significantly in various volume concentrations of nanoparticles in the constructed micromodel. A semi analytical correlation was proposed for calculating the permeability of such porous medium.
    Keywords: Nanofluid, Micromodel, Porous Medium, Permeability, Experiment
  • M. Noroozifar, M. Khorasani-Motlagh, Z. Yavari Pages 85-94
    Nanosized TiO2 particles were prepared by sol–gel method. The TiO2 particles were co-deposited with chromium using electrodeposition technique. In investigating of coating surfaces by scanning electron microscope (SEM), the results showed that the morphology of the coating surface was changed by adding TiO2 nanoparticles to the chromium coating. The corrosion behavior of the coatings was assessed by polarization technique in four media such as seawater, pipeline water, distilled water and 3.5% NaCl solution. The results showed that adding the TiO2 nanoparticles into chromium coating, caused a decrease in current and rate of corrosion, and so increased the period of conservation from cupric undercoat.
    Keywords: TiO2 Nanoparticles, Corrosion, Composite Coating, Chromium Electroplating, Tafel Curve
  • P. Boroojerdian Pages 95-100
    SnO nanoparticles were synthesized using microwave–assisted hydrothermal method. It was noticed that at 300 and 600 watt microwave power, SnO formed and remained in the tetragonal phase. At 900 watt, SnO2 started appearing and a mixture of SnO and SnO2 phases coexisted. The particle size varied from ~2 to ~13 nm at 300 to 900 watt radiation power. The UV-V absorption spectra showed the excitonic peaks of ~288, ~300 and ~315 nm corresponding to crystal sizes of ~2, ~6 and ~10 nm, respectively. For particles larger than 10 nm, no excitonic peak was observed. The appearance of these excitonic peaks could be attributed to the conversion of indirect band gap in bulk SnO to direct band gap in SnO nanoparticles. To verify this assumption, photoluminescence spectroscopy was carried out. The results showed a strong emission of 677 nm upon excitation at 336 nm wavelength, confirmed the assumption.
    Keywords: SnO, Nanoparticles, Microwave–Assisted Synthesis, Semiconducting Material
  • M. Zahedifar, M. Farangi, M. H. Pakzamir Pages 101-108
    Silicon nanowire (SiNW) arrays were produced by electroless method on polycrystalline Si substrate, in HF/ AgNO3 solution. Although the monocrystalline silicon wafer is commonly utilized as a perfect substrate, polycrystalline silicon as a low cost substrate was used in this work for photovoltaic applications. In order to study the influence of etching time (which affects the SiNWs length) on different elements in AC equivalent circuit of the fabricated solar cells, impedance spectroscopy was accomplished for the first time in forward bias direction and under illumination. Measurements indicated a growth of recombination with increase in etching time that may be attributed to enhancement in the number of defects on nanowires surfaces as a result of increase in the length of SiNWs. This trend reduces recombination resistance in device equivalent AC circuit and reduces the efficiency of solar cells. Impedance spectra and fitting curves also showed that the effective carrier lifetime decreases with increase in etching time.
    Keywords: Silicon, Nanowire length, Electroless Method, Impedance Spectroscopy, Effective Carrier lifetime
  • Z. Khayat Sarkar, F. Khayat Sarkar Pages 109-114
    This study investigated the applicability of polyethylene glycol (PEG-4000) coated Fe3O4 magnetic nanoparticles for the selective removal of toxic pb (II) ion from wastewater. The Fe3O4 magnetic nanoparticles of 24 nm were synthesized using a coprecipitation method and characterized by Scanning electron microscopy (SEM), vibratingsample magnetometer (VSM), and X-ray diffraction (XRD). SEM images show that the dimension of particles is about 24 nm. VSM patterns indicate superparamagnetic properties of Fe3O4 magnetic nanoadsorbent. XRD indicated the sole existence of inverse cubic spinel phase of Fe3O4 magnetic nanoadsorbent. The influence of different parameters, such as pH, contact time and type of eluent on the amount of Pb2+ removed were investigated. The adsorption process was found to be highly pH dependent, which made the nanoparticles selectively adsorb this metal from wastewater. The optimum pH required for maximum adsorption was found to be 6 for lead. The maximum contact time for the equilibrium condition is 10 min. The modified Fe3O4 magnetic nanoparticles thus regenerated could be used again to remove the Pb+2 ions.
    Keywords: Polyethylene Glycol (PEG, 4000), Coated Fe3O4 Magnetic Nanoparticles, Pb (II) Ion, Superparamagnetic, Co, precipitation, Wastewater